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THE ANIMAL
PARASITES OF MAN
BY
H. B. FANTHAM, M.A.Cantab., D.Sc.Lond.
_Lecturer on Parasitology, Liverpool School of Tropical Medicine_;
_Sectional Editor in Protozoology,
“Tropical Diseases Bulletin,” London_, _etc._
J. W. W. STEPHENS, M.D.Cantab., D.P.H.
_Sir Alfred Jones Professor of Tropical Medicine, Liverpool
University, etc._
AND
F. V. THEOBALD, M.A.Cantab., F.E.S., Hon. F.R.H.S.
_Professor of Agricultural Zoology, London University_; _Vice-
Principal and Zoologist of the South-eastern Agricultural College_;
_Mary Kingsley Medallist_; _Grande Médaille Geoffroy St. Hilaire_,
_Soc. Nat. d’Acclim. de France_, _etc._
PARTLY ADAPTED FROM
Dr. MAX BRAUN’S “Die Tierischen Parasiten des Menschen” (4th Edition,
1908) and an Appendix by Dr. OTTO SEIFERT.
NEW YORK
WILLIAM WOOD AND COMPANY
MCMXX.
PREFACE.
The English edition of Braun’s “Die Tierischen Parasiten des Menschen,”
produced in 1906, being out of print, the publishers decided to issue
another edition based on the translation of Braun’s fourth German
edition, which appeared in 1908, to which had been added an appendix,
by Dr. Otto Seifert on Treatment, etc.
When the work was considered with a view to a new edition, it was found
that a vast amount of new matter had to be incorporated, numerous
alterations essential for bringing it up to date were necessitated,
and many omissions were inevitable. The result is that parts of the
book have been rewritten, and, apart from early historical references,
the work of Braun has disappeared. This is more particularly the case
with the Protozoa section of the present work. The numerous additions,
due to the great output of scientific literature and other delays in
publication, have led to the book being somewhat less homogeneous
than we desired, and have necessitated the use of appendices to allow
of the presentation of new facts only recently ascertained. Many new
illustrations have been added or substituted for older, less detailed
ones. Some of these new figures were drawn specially for this book.
The first section, on the Protozoa, has been written by Dr.
Fantham, there being little of the original text left except parts
of the historical portions, and thus the section on Protozoa must
be considered as new. The second section, on Worms (except the
Acanthocephala, Gordiidæ and Hirudinea), has been remodelled by
Professor Stephens to such an extent that this, too, must not be looked
upon as a translation of Braun’s book. With regard to the Arthropoda,
much remains as in the last English edition, but some new matter added
by Braun in his fourth German edition is included, and much new matter
by Mr. Theobald has been incorporated. As regards the Appendix by Dr.
Seifert, the first section has been remodelled, but the sections on
the Helminthes and the Arthropoda are practically translations of the
original.
The authors desire to express their thanks to Miss A. Porter, D.Sc.,
J. P. Sharples, Esq., B.A., M.R.C.S., and H. F. Carter, Esq., F.E.S.,
for valuable help. They also wish to thank the authors, editors,
and publishers of several manuals and journals for their courtesy
in allowing the reproduction of certain of their illustrations. In
this connection mention must be made more particularly of Professor
Castellani, Dr. Chalmers, Professor Doflein, Dr. Leiper, the late
Professor Minchin, Professor Nuttall, Dr. Wenyon, Mr. Edw. Arnold,
Messrs. Baillière, Tindall and Cox, Messrs. Black, Messrs. Cassell,
Dr. Gustav Fischer, Messrs. Heinemann, the Cambridge University Press,
the Editors of the _Annals of Tropical Medicine and Parasitology_, the
Editors of the _Journal of Experimental Medicine_, and the Editor of
the _Tropical Diseases Bulletin_.
H. B. F.
J. W. W. S.
F. V. T.
_December, 1915._
CONTENTS.
PAGE
PREFACE iii
ERRATA xxxii
ON PARASITES IN GENERAL 1
Occasional and Permanent Parasitism 1
Entozoa, Endoparasites, Helminthes, Turbellaria 2
Hermaphroditism 4
Fertility of Parasites 5
Transmigrations 5
Commensals, Mutualists 6
Incidental and Pseudo-parasites 6
The Influence of Parasites on the Host 8
Origin of Parasites 10
Derivation of Parasites 19
Change of Host 20
Literature 22
THE ANIMAL PARASITES OF MAN 25
*A. Protozoa* 25
CLASSIFICATION OF THE PROTOZOA.
Class I. SARCODINA 27
Order. _Amœbina_ 27
_Foraminifera_ 27
_Heliozoa_ 27
_Radiolaria_ 28
Class II. MASTIGOPHORA 28
III. SPOROZOA 28
Sub-class 1. TELOSPORIDIA 28
Order. _Gregarinida_ 28
_Coccidiidea_ 28
_Hæmosporidia_ 28
Sub-class 2. NEOSPORIDIA 28
Order. _Myxosporidia_ 28
_Microsporidia_ 28
_Sarcosporidia_ 28
_Haplosporidia_ 29
Class IV. INFUSORIA 29
V. SUCTORIA 29
Class I. SARCODINA, Bütschli, 1882 29
Order. _Amœbina_, Ehrenberg 29
A. Human Intestinal Amœbæ 29
_Entamœba coli_, Lösch, 1875, emend. Schaudinn, 1903 32
_Entamœba histolytica_, Schaudinn, 1903 34
_Entamœba tetragena_, Viereck, 1907 38
Noc’s Entamœba, 1909 41
_Entamœba buccalis_, Prowazek, 1904 43
_Entamœba undulans_, Castellani, 1905 43
_Entamœba kartulisi_, Doflein, 1901 44
_Amœba gingivalis_, _A. buccalis_, _A. dentalis_ 44
Genus. _Paramœba_, Schaudinn, 1896 44
_Paramœba (Craigia) hominis_, Craig, 1906 45
B. Amœbæ from other Organs 45
_Entamœba pulmonalis_, Artault, 1898 45
_Amœba urogenitalis_, Baelz, 1883 45
_Amœba miurai_, Ijima, 1898 46
_Appendix_: “Rhizopods in Poliomyelitis Acuta” 46
Order. _Foraminifera_, d’Orbigny 47
Sub-order. _Monothalamia_ (Testaceous Amœbæ) 47
Genus. _Chlamydophrys_, Cienkowski, 1876 47
_Chlamydophrys enchelys_, Ehrenberg 47
_Leydenia gemmipara_, Schaudinn, 1896 49
Class II. MASTIGOPHORA, Diesing 50
Sub-class. FLAGELLATA, Cohn emend. Bütschli 50
Order. _Polymastigina_, Blochmann 52
Genus. _Trichomonas_, Donné, 1837 52
_Trichomonas vaginalis_, Donné 52
_Trichomonas intestinalis_, R. Leuckart, 1879 =
_Trichomonas hominis_, Davaine, 1854 54
Genus. _Tetramitus_, Perty, 1852 57
_Tetramitus mesnili_, Wenyon, 1910 57
Genus. _Lamblia_, R. Blanchard, 1888 57
_Lamblia intestinalis_, Lambl, 1859 57
Order. _Protomonadina_, Blochmann 60
Family. _Cercomonadidæ_, Kent emend. Bütschli 61
Genus. _Cercomonas_, Dujardin emend. Bütschli 61
_Cercomonas hominis_, Davaine, 1854 61
_Monas pyophila_, R. Blanchard, 1895 62
Family. _Bodonidæ_, Bütschli 63
Genus. _Prowazekia_, Hartmann and Chagas, 1910 63
_Prowazekia urinaria_, Hassall, 1859 63
_Prowazekia asiatica_, Castellani and Chalmers, 1910 65
_Prowazekia javanensis_, Flu, 1912 66
_Prowazekia cruzi_, Hartmann and Chagas, 1910 66
_Prowazekia weinbergi_, Mathis and Léger, 1910 66
_Prowazekia parva_, Nägler, 1910 66
Family. _Trypanosomidæ_, Doflein 66
Genus. _Trypanosoma_, Gruby, 1843 67
Historical 67
General 69
Morphology 70
_Trypanosoma gambiense_, Dutton, 1902 72
_Trypanosoma nigeriense_, Macfie, 1913 76
_Trypanosoma rhodesiense_, Stephens and Fantham, 1910 76
General Note on Trypanosomes with Posterior Nuclei 83
_Trypanosoma cruzi_, Chagas, 1909 83
_Trypanosoma lewisi_, Kent, 1881 88
_Trypanosoma brucei_, Plimmer and Bradford, 1899 93
_Trypanosoma evansi_, Steel, 1885 95
_Trypanosoma equinum_, Voges, 1901 96
_Trypanosoma equiperdum_, Doflein, 1901 97
_Trypanosoma theileri_, Bruce, 1902 98
_Trypanosoma hippicum_, Darling, 1910 98
_Endotrypanum schaudinni_, Mesnil and Brimont, 1908 99
_Trypanosoma boylei_, Lafont, 1912 99
Monomorphic Trypanosomes 99
_Trypanosoma vivax_, Ziemann, 1905 99
_Trypanosoma capræ_, Kleine, 1910 100
_Trypanosoma congolense_, Broden, 1904 100
_Trypanosoma simiæ_, Bruce, 1912 100
_Trypanosoma uniforme_, Bruce, 1910 101
General Note on Development of Trypanosomes in Glossina 101
Adaptation of Trypanosomes 101
Genus. _Herpetomonas_, Saville Kent, 1881 102
Genus. _Crithidia_, Léger, 1902, emend. Patton, 1908 104
Genus. _Leishmania_, Ross, 1903 104
_Leishmania donovani_, Laveran and Mesnil, 1903 105
_Leishmania tropica_, Wright, 1903 107
_Leishmania infantum_, Nicolle, 1908 109
Genus. _Histoplasma_, Darling, 1906 112
Genus. _Toxoplasma_, Nicolle and Manceaux, 1908 112
THE SPIROCHÆTES 114
The Spirochætes of the Blood 116
_Spirochæta duttoni_, Novy and Knapp, 1906 116
_Spirochæta gallinarum_, Stephens and Christophers, 1905
(= _Spirochæta marchouxi_, Nuttall, 1905) 119
_Spirochæta recurrentis_, Lebert, 1874 120
_Spirochæta rossii_, Nuttall, 1908 122
_Spirochæta novyi_, Schellack, 1907 122
_Spirochæta carteri_, Mackie and Manson, 1907 122
_Spirochæta berbera_, Sergent and Foley, 1910 122
Other Human Spirochætes 122
Some Animal Spirochætes 122
TREPONEMATA 124
_Treponema pallidum_, Schaudinn, 1905 124
_Treponema pertenue_, Castellani, 1905 127
Class III. SPOROZOA, Leuckart, 1879 128
Sub-class. TELOSPORIDIA, Schaudinn 129
Order. _Gregarinida_, Aimé Schneider emend. Doflein 129
Order. _Coccidiidea_ 135
Genus. _Eimeria_, Aimé Schneider, 1875 142
_Eimeria avium_, Silvestrini and Rivolta 142
_Eimeria stiedæ_, Lindemann, 1865 145
(_a_) Human Hepatic Coccidiosis 148
(_b_) Human Intestinal Coccidiosis 148
(_c_) Doubtful Cases 149
Genus. _Isospora_, Aimé Schneider, 1881 149
_Isospora bigemina_, Stiles, 1891 149
Doubtful Species 150
Order. _Hæmosporidia_, Danilewsky emend. Schaudinn 151
The Malarial Parasites of Man 155
Development of the Malarial Parasites of Man 159
The Species of the Malarial Parasites of Man 164
_Plasmodium vivax_, Grassi and Feletti, 1890 164
_Plasmodium malariæ_, Laveran 166
_Laverania malariæ_, Grassi and Feletti, 1890
(= _Plasmodium falciparum_, Welch, 1897) 167
_Plasmodium relictum_, Sergent, 1907 (in birds) 170
Cultivation of Malarial Parasites 170
Differential Characters of the Human Malarial Parasites 171
Family. _Piroplasmidæ_, França, 1909 172
Genus. _Babesia_, Starcovici, 1893 174
Genus. _Theileria_, Bettencourt, França and Borges, 1907 178
_Theileria parva_, Theiler, 1903 178
_Theileria mutans_, Theiler, 1907 180
Genus. _Anaplasma_, Theiler, 1910 180
Genus. _Paraplasm_a, Seidelin, 1911 180
Sub-class. NEOSPORIDIA, Schaudinn 181
Order. _Myxosporidia_, Bütschli 181
Order. _Microsporidia_, Balbiani 184
Order. _Actinomyxidia_, Stolč. 187
Order. _Sarcosporidia_, Balbiani 187
_Sarcosporidia_ observed in Man 193
Order. _Haplosporidi_a, Caullery and Mesnil, 1899 194
_Rhinosporidium kinealyi_, Minchin and Fantham, 1905 195
Class IV. INFUSORIA, Ledermüller, 1763 198
Genus. _Balantidium_, Claparède et Lachmann 200
_Balantidium coli_, Malmsten, 1857 200
_Balantidium minutum_, Schaudinn, 1899 204
Genus. _Nyctotherus_, Leidy, 1849 204
_Nyctotherus faba_, Schaudinn, 1899 205
_Nyctotherus giganteus_, P. Krause, 1906 205
_[Nyctotherus] africanus_, Castellani, 1905 206
THE CHLAMYDOZOA 207
PROTOZOA INCERTÆ SEDIS 210
_Sergentella hominis_, Brumpt, 1910 210
*B. Platyhelminthes (or Flat Worms)* 211
CLASSIFICATION OF THE PLATYHELMINTHES.
Class I. TURBELLARIA (or Eddy Worms) 212
Order 1. _Rhabdocœlida_ 212
2. _Tricladida_ 212
3. _Polycladida_ 212
Class II. TREMATODA (Sucking Worms) 212
III. CESTODA (Tapeworms) 212
Class II. TREMATODA, Rud. 212
Development of the Trematodes 222
Biology 229
CLASSIFICATION OF THE TREMATODES OF MAN.
Order. _Digenea_, v. Beneden, 1858 230
Sub-order. _Prostomata_, Odhner, 1905 230
Group. _Amphistomata_, Rudolphi, 1801, ep., Nitzsch, 1819 230
Family. _Paramphistomidæ_, Fischoeder, 1901 231
Sub-family. _Paramphistominæ_, Fischoeder, 1901 231
_Cladorchiinæ_, Fischoeder, 1901 231
Family. _Gastrodisciidæ_, Stiles and Goldberger, 1910 231
Group. _Distomata_, Retzius, 1782 231
Family. _Fasciolidæ_, Railliet, 1895 231
Sub-family. _Fasciolinæ_, Odhner, 1910 231
_Fasciolopsinæ_, Odhner, 1910 231
Family. _Opisthorchiidæ_, Braun, 1901, emend, auctor. 232
Sub-family. _Opisthorchiinæ_, Looss, 1899, emend, auctor. 232
_Metorchiinæ_, Lühe, 1909 232
Family. _Dicrocœliidæ_, Odhner, 1910 232
_Heterophyiidæ_, Odhner, 1914 232
_Troglotremidæ_, Odhner, 1914 232
_Echinostomidæ_, Looss, 1902 233
Sub-family. _Echinostominæ_, Looss, 1899 233
_Himasthlinæ_, Odhner, 1910 233
Family. _Schistosomidæ_, Looss, 1899 233
THE TREMATODES OBSERVED IN MAN 234
Family. _Paramphistomidæ_, Stiles and Goldberger,
emend. 1910 234
Sub-family. _Cladorchiinæ_, Fischoeder, 1901 234
Genus. _Watsonius_, Stiles and Goldberger, 1910 234
_Watsonius watsoni_, Stiles and Goldberger, 1910 234
Family. _Gastrodisciidæ_ 236
Genus. _Gastrodiscus_, Lkt., 1877 236
_Gastrodiscus hominis_, Lewis and McConnell, 1876 236
Family. _Fasciolidæ_, Railliet, 1895 237
Sub-family. _Fasciolinæ_, Odhner, 1910 237
Genus. _Fasciola_, L., 1758 237
_Fasciola hepatica_, L., 1758 237
Halzoun 242
_Fasciola gigantica_, Cobbold, 1856 244
Sub-family. _Fasciolopsinæ_, Odhner, 1910 245
Genus. _Fasciolopsis_, Looss, 1898 245
_Fasciolopsis buski_, Lank., 1857 245
_Fasciolopsis rathouisi_, Ward, 1903 246
_Fasciolopsis goddardi_, Ward, 1910 247
_Fasciolopsis fülleborni_, Rodenwaldt, 1909 247
Family. _Troglotremidæ_, Odhner, 1914 249
Genus. _Paragonimus_, Braun, 1899 249
_Paragonimus ringeri_, Cobb., 1880 249
Family. _Opisthorchiidæ_, Braun, 1901 252
Sub-family. _Opisthorchiinæ_, Looss, 1899 252
Genus. _Opisthorchis_, R. Blanch., 1845 252
_Opisthorchis felineus_, Riv., 1885 252
Genus. _Paropisthorchis_, Stephens, 1912 255
_Paropisthorchis caninus_, Barker, 1912 255
Genus. _Amphimerus_, Barker, 1912 (?) 257
_Amphimerus noverca_, Barker, 1912 (?) 258
Genus. _Clonorchis_, Looss, 1907 258
_Clonorchis sinensis_, Cobbold, 1875 258
_Clonorchis endemicus_, Baelz, 1883 259
Sub-family. _Metorchiinæ_, Lühe, 1909 261
Genus. _Metorchis_, Looss, 1899, emend. auctor. 261
_Metorchis truncatus_, Rud., 1819 261
Family. _Heterophyiidæ_, Odhner, 1914 262
Genus. _Heterophyes_, Cobbold, 1866 262
_Heterophyes heterophyes_, v. Sieb., 1852 262
_Metagonimus_, Katsurada, 1913; Yokogawa,
Leiper, 1913 264
_Metagonimus yokogawai_, Katsurada, 1913 264
Family. _Dicrocœliidæ_, Odhner, 1910 265
Genus. _Dicrocœlium_, Dujardin 265
_Dicrocœlium dendriticum_, Rud., 1819 266
Family. _Echinostomidæ_, Looss, 1902 267
Sub-family. _Echinostominæ_, Looss, 1899 267
Genus. _Echinostoma_, Rud., 1809; Dietz, 1910 267
_Echinostoma ilocanum_, Garrison, 1908 267
_Echinostoma malayanum_, Leiper, 1911 268
Sub-family. _Himasthlinæ_, Odhner, 1910 269
Genus. _Artyfechinostomum_, Clayton-Lane, 1915 269
_Artyfechinostomum sufrartyfex_, Clayton-Lane, 1915 269
Family. _Schistosomidæ_, Looss, 1899 269
Genus. _Schistosoma_, Weinl., 1858 269
_Schistosoma hæmatobium_, Bilharz, 1852 270
_Schistosoma mansoni_, Sambon, 1907 277
_Schistosoma japonicum_, Katsurada, 1904 277
Class III. CESTODA, Rud., 1808 282
Anatomy of the Cestoda 284
Development of the Tapeworms 297
Biology 306
CLASSIFICATION OF THE CESTODA OF MAN.
Order. _Pseudophyllidea_, Carus, 1863 308
Family. _Dibothriocephalidæ_, Lühe, 1902 308
Sub-family. _Dibothriocephalinæ_, Lühe, 1899 308
Order. _Cyclophyllidea_, v. Beneden 308
Family. _Dipylidiidæ_, Lühe, 1910 309
_Hymenolepididæ_, Railliet and Henry, 1909 309
_Davaineidæ_, Fuhrmann, 1907 309
Sub-family. _Davaineinæ_, Braun, 1900 309
Family. _Tæniidæ_, Ludwig, 1886 309
THE CESTODES OF MAN 309
Family. _Dibothriocephalidæ_ 309
Sub-family. _Dibothriocephalinæ_ 309
Genus. _Dibothriocephalus_, Lühe, 1899 309
_Dibothriocephalus latus_, L., 1748 310
_Dibothriocephalus cordatus_, R. Lkt., 1863 315
_Dibothriocephalus parvus_, Stephens, 1908 316
Genus. _Diplogonoporus_, Lönnbrg., 1892 316
_Diplogonoporus grandis_, R. Blanch., 1894 316
_Sparganum_, Diesing, 1854 317
_Sparganum mansoni_, Cobb., 1883 317
_Sparganum proliferum_, Ijima, 1905 318
Family. _Dipylidiidæ_, Lühe, 1910 320
Genus. _Dipylidium_, R. Lkt., 1863 320
_Dipylidium caninum_, L. 1758 320
Family. _Hymenolepididæ_, Railliet and Henry, 1909 323
Genus. _Hymenolepis_, Weinland, 1858 323
_Hymenolepis nana_, v. Sieb., 1852 323
_Hymenolepis diminuta_, Rud., 1819 326
_Hymenolepis lanceolata_, Bloch, 1782 328
Family. _Davaineidæ_, Fuhrmann, 1907 329
Sub-family. _Davaineinæ_, Braun, 1900 329
Genus. _Davainea_, R. Blanch., 1891 329
_Davainea madagascariensis_, Davaine, 1869 329
_Davainea_ (?) _asiatica_, v. Linst., 1901 330
Family. _Tæniidæ_, Ludwig, 1886 331
Genus. _Tænia_, L., 1758 331
_Tænia solium_, L., _p. p._, 1767 331
_Cysticercus acanthotrias_, Weinland, 1858 336
_Tænia bremneri_, Stephens, 1908 337
_Tænia marginata_, Batsch., 1786 338
_Tænia serrata_, Goeze, 1782 338
_Tænia crassicollis_, Rud., 1810 338
_Tænia saginata_, Goeze, 1782 338
_Tænia africana_, v. Linst., 1900 342
_Tænia confusa_, Ward, 1896 343
_Tænia echinococcus_, v. Sieb., 1853 344
Structure and Development of Echinococcus(Hydatid) 347
_Echinococcus multilocularis_ (Alveolar Colloid) 356
Serum Diagnosis of Echinococcus 359
*C. Nemathelminthes* 360
Class. NEMATODA 360
Anatomy of the Nematodes 360
Development of the Nematodes 371
CLASSIFICATION OF THE NEMATODA.
Family. _Anguillulidæ_, Gervais and van Beneden, 1859 374
_Angiostomidæ_, Braun, 1895 374
_Gnathostomidæ_ 374
_Dracunculidæ_, Leiper, 1912 374
_Filariidæ_, Claus, 1885 374
_Trichinellidæ_, Stiles and Crane, 1910 375
_Dioctophymidæ_ 375
_Strongylidæ_, Cobbold, 1864 375
_Physalopteridæ_ 375
_Ascaridæ_, Cobbold, 1864 375
_Oxyuridæ_ 375
THE NEMATODES OBSERVED IN MAN 376
Family. _Anguillulidæ_ 377
Genus. _Rhabditis_, Dujardin, 1845 377
_Rhabditis pellio_, Schneider, 1866 377
_Rhabditis niellyi_, Blanchard, 1885 378
_Rhabditis_, sp. 378
Genus. _Anguillula_, Ehrenberg, 1826 379
_Anguillula aceti_, Müller, 1783 379
Genus. _Anguillulina_, Gervais and Beneden, 1859 379
_Anguillulina putrefaciens_, Kühn, 1879 379
Family. _Angiostomidæ_, Braun, 1895 379
Genus. _Strongyloides_, Grassi, 1879 379
_Strongyloides stercoralis_, Bavay, 1877 380
Family. _Gnathostomidæ_ 384
Genus. _Gnathostoma_, Owen, 1836 384
_Gnathostoma siamense_, Levinson, 1889 384
_Gnathostoma spinigerum_, Owen, 1836 385
Family. _Dracunculidæ_, Leiper, 1912 385
Genus. _Dracunculus_, Kniphoff, 1759 385
_Dracunculus medinensis_, Velsch, 1674 386
Genus (of _Crustacea_). _Cyclops_, Müller, 1776 390
Family. _Filariidæ_ 390
Sub-family. _Filariinæ_ 390
Genus. _Filaria_, O. Fr. Müller, 1787 390
_Filaria bancrofti_, Cobbold, 1877 390
_Filaria demarquayi_, Manson, 1895 403
_Filaria taniguchi_, Penel, 1905 404
_Filaria_ (?) _conjunctivæ_, Addario, 1885 404
Group. _Agamofilaria_, Stiles, 1906 406
_Agamofilaria georgiana_ 406
_Agamofilaria palpebralis_, Pace, 1867
(_nec_ Wilson, 1844) 406
_Agamofilaria oculi humani_, v. Nordmann, 1832 406
_Agamofilaria labialis_, Pane, 1864 407
_Filaria (?) romanorum-orientalis_, Sarcani, 1888 407
_Filaria (?) kilimaræ_, Kolb, 1898 407
_Filaria_ (?) sp. ? 407
Genus. _Setaria_, Viborg, 1795 407
_Setaria equina_, Abildg., 1789 408
Genus. _Loa_, Stiles, 1905 409
_Loa loa_, Guyot, 1778 409
Genus. _Acanthocheilonema_, Cobbold, 1870 414
_Acanthocheilonema perstans_, Manson, 1891 414
Genus. _Dirofilaria_, Railliet and Henry, 1911 416
_Dirofilaria magalhãesi_, R. Blanchard, 1895 417
Sub-family. _Onchocercinæ_, Leiper, 1911 417
Genus. _Onchocerca_, Diesing, 1841 417
_Onchocerca volvulus_, R. Leuckart, 1893 417
Family. _Trichinellidæ_, Stiles and Crane, 1910 419
Sub-family. _Trichurinæ_, Ransom, 1911 419
Genus. _Trichuris_, Röderer and Wagler, 1761 419
_Trichuris trichiura_, Linnæus, 1761 419
Sub-family. _Trichinellinæ_, Ransom, 1911 421
Genus. _Trichinella_, Railliet, 1895 421
_Trichinella spiralis_, Owen, 1835 421
History of the Development of _Trichinella spiralis_ 423
Family. _Dioctophymidæ_ 431
Genus. _Dioctophyme_, Collet-Megret, 1802 431
_Dioctophyme gigas_, Rudolphi, 1802 431
Family. _Strongylidæ_ 432
Sub-family. _Metastrongylinæ_, Leiper, 1908 432
Genus. _Metastrongylus_, Molin, 1861 432
_Metastrongylus apri_, Gmelin, 1789 432
Sub-family. _Trichostrongylinæ_, Leiper, 1908 433
Genus. _Trichostrongylus_, Looss, 1905 434
_Trichostrongylus instabilis_, Railliet, 1893 434
_Trichostrongylus probolurus_, Railliet, 1896 435
_Trichostrongylus vitrinus_, _Looss_, 1905 435
Genus. _Hæmonchus_, Cobb., 1898 436
_Hæmonchus contortus_, Rudolphi, 1803; Cobb., 1898 436
Genus. _Nematodirus_, Ransom, 1907, emend. Railliet, 1912 438
Sub-genus. _Mecistocirrus_, Railliet, 1912 438
_Mecistocirrus fordi_, Daniels, 1908 438
Sub-family. _Ancylostominæ_, Railliet, 1909 438
Group. _Œsophagostomeæ_, Railliet and Henry, 1909 439
Genus. _Ternidens_, Railliet, 1909 439
_Ternidens deminutus_, Railliet and Henry, 1905 440
Genus. _Œsophagostomum_, Molin, 1861 441
_Œsophagostomum brumpti_, Railliet and Henry, 1905 441
_Œsophagostomum stephanostomum_ var. _thomasi_,
Railliet and Henry, 1909 443
_Œsophagostomum apiostomum_, Willach, 1891 444
Group. _Ancylostomeæ_, Railliet and Henry, 1909 445
Genus. _Ancylostoma_, Dubini, 1843, emend. Looss, 1905 445
_Ancylostoma duodenale_, Dubini, 1843 445
_Ancylostoma ceylanicum_, Looss, 1911 456
_Ancylostoma braziliense_, Gomez de Faria, 1910 456
Group. _Bunostomeæ_, Railliet and Henry, 1909 456
Genus. _Necator,_ Stiles, 1903 457
_Necator americanus_, Stiles, 1902 457
_Necator exilidens_, Cummins, 1912 459
Ancylostomiasis 459
Group. _Syngameæ_, Railliet and Henry, 1909 459
Genus. _Syngamus,_ von Siebold, 1836 459
_Syngamus kingi_, Leiper, 1913 459
Family. _Physalopteridæ_ 460
Genus. _Physaloptera_, Rudolphi, 1819 460
_Physaloptera caucasica_, v. Linstow, 1902 461
_Physaloptera mordens_, Leiper, 1907 461
Family. _Ascaridæ_, Cobbold, 1864 461
Sub-family. _Ascarinæ_ 461
Genus. _Ascaris_, L., 1758 461
_Ascaris lumbricoides_, L., 1758 463
_Ascaris_ sp. 465
_Ascaris texana_, Smith et Goeth, 1914 465
_Ascaris maritima_, Leuckart, 1876 465
Genus. _Toxascaris_, Leiper, 1907 465
_Toxascaris limbata_, Railliet and Henry, 1911 466
Genus. _Belascaris_, Leiper, 1907 466
_Belascaris cati_, Schrank, 1788 466
_Belascaris marginata_, Rudolphi, 1802 466
Genus. _Lagocheilascaris_, Leiper, 1909 466
_Lagocheilascaris minor_, Leiper, 1909 467
Family. _Oxyuridæ_ 467
Genus. _Oxyuris_, Rudolphi, 1803 467
_Oxyuris vermicularis_, Linnæus, 1767 467
Family. _Mermithidæ_ 469
Genus. _Mermis_, Dujardin, 1845 469
_Mermis hominis oris_, Leidy, 1850 469
_Agamomermis_, Stiles, 1903 470
_Agamomermis restiformis_, Leidy, 1880 470
TECHNIQUE 471
*D. Acanthocephala*, Rud 475
_Echinorhynchus gigas_, Goeze, 1782 477
_Echinorhynchus hominis_, Lambl, 1859 478
_Echinorhynchus moniliformis_, Bremser, 1819 478
*E. Gordiidæ* 479
*F. Hirudinea s. Discophora* (Leech) 480
Family. _Gnathobdellidæ_ (Leeches with Jaws) 481
Genus. _Hirudo_, L., 1758 481
_Hirudo medicinalis_, L., 1758 481
_Hirudo troctina,_ Johnston, 1816 482
Genus. _Limnatis_, Moq.-Tandon, 1826 482
_Limnatis nilotica_, Savigny, 1820 482
Genus. _Hæmadipsa_, Tennent, 1861 482
Family. _Rhynchobdellidæ_ (Leeches with Rostrum) 482
Genus. _Hæmentaria_, de Filippi, 1849 482
_Hæmentaria officinalis_, de Filippi 482
Genus. _Placobdella_, R. Blanchard 482
_Placobdella catenigera_, Moq.-Tandon 482
*G. Arthropoda* (Jointed-limbed Animals) 483
_A._ ARACHNOIDEA (Spiders, Mites, etc.) 483
Order. _Acarina_ (Mites) 484
Family. _Trombidiidæ_ (Running Mites) 485
Genus. _Trombidium_, Latreille (and Leptus) 485
_Leptus autumnalis,_ Shaw, 1790 485
_Trombidium tlalsahuate_, Lemaire, 1867 486
_Akamushi_ or _Kedani_ 487
Family. _Tetranychidæ_ (Spinning Mites) 488
Genus. _Tetranychus_, Dufour 488
_Tetranychus molestissimus_, Weyenbergh, 1886 488
_Tetranychus telarius_, L., 1758, var. russeolus, Koch 488
Family. _Tarsonemidæ_ 488
Genus. _Pediculoides_ 489
_Pediculoides ventricosus_, Newport, 1850 489
Genus. _Nephrophages_ 490
_Nephrophages sanguinarius_, Miyake and Scriba, 1893 490
Family. _Eupodidæ_ 491
Genus. _Tydeus,_ Koch 491
_Tydeus molestus_, Moniez, 1889 491
Family. _Gamasidæ_ (Coleopterous or Insect Mites) 491
Genus. _Dermanyssus_, Dugès 492
_Dermanyssus gallinæ_, de Geer, 1778 492
_Dermanyssus hirundinis_, Hermann, 1804 492
Genus. _Holothyrus_ 493
_Holothyrus coccinella_, Gervais, 1842 493
Family. _Ixodidæ_ (Ticks) 493
Classification of _Ixodidæ_ 496
Synopsis of Genera 496
Genus. _Ixodes_, Latreille 497
_Ixodes reduvius,_ L., 1758 497
_Ixodes holocyclus_, Neumann, 1899 499
_Ixodes hexagonus_, Leach, 1815 500
Genus. _Amblyomma_, Koch 500
_Amblyomma cayennense_, Koch, 1844 500
_Amblyomma americana_, Linnæus 501
_Amblyomma maculatum_, Koch 501
Genus. _Hyalomma_, Koch 501
_Hyalomma ægyptium_, L., 1758 501
Genus. _Hæmaphysalis_, Koch 502
_Hæmaphysalis punctata_, Canestrini and Fanzago,
1877–1878 502
Genus. _Dermacentor_, Koch 502
_Dermacentor reticulatus_, Fabricius, 1794 502
_Dermacentor venustus_, Banks 503
_Dermacentor occidentalis_, Neumann 504
_Dermacentor variabilis_, Say 505
Genus. _Margaropus_, Karsch 505
_Margaropus annulatus australis_, Fuller 505
_Margaropus microplus_, Canestrini 505
Genus. _Rhipicephalus_, Koch 505
_Rhipicephalus sanguineus_, Latreille, 1804 505
Neumann’s Table of Species of _Argas_ 505
Genus. _Argas_, Latreille 506
_Argas reflexus_, Fabricius, 1794 506
_Argas persicus_, Fischer de Waldheim, 1824 506
_Argas brumpti_, Neumann 507
_Argas chinche_, Gervais, 1844 508
Genus. _Ornithodorus_, Koch 508
_Ornithodorus moubata_, Murray, 1877 508
_Ornithodorus savignyi_, Audouin, 1827 509
_Ornithodorus coriaceus_, Koch 509
_Ornithodorus talaje_, Guerin, 1849 509
_Ornithodorus turicata_, Dugès, 1876 509
_Ornithodorus tholozani_, Laboulbène and Mégnin, 1882 510
_Ornithodorus mégnini, Dugès_, 1883 510
Family. _Tyroglyphidæ_ 511
Sub-family. _Tyroglyphinæ_ 511
Genus. _Aleurobius_, Canestrini 511
_Aleurobius (Tyroglyphus) farinæ_, de Geer (part), Koch 511
Genus. _Tyroglyphus_, Latreille 511
_Tyroglyphus siro_, L., 1756 511
_Tyroglyphus longior_, Gervais, 1844 512
_Tyroglyphus minor_ var. _castellani_, Hirst 513
Genus. _Glyciphagus_, Hering, 1838 513
_Glyciphagus prunorum_, Hering, and
_G. domesticus_, de Geer 513
_Glyciphagus cursor_, Gervais 513
_Glyciphagus buski_, Murray 513
Genus. _Rhizoglyphus_, Claparède, 1869 514
_Rhizoglyphus parasiticus_, Dalgetty, 1901 514
Genus. _Histiogaster_, Berlese, 1883 515
_Histiogaster_ (_entomophagus_ ?)
_spermaticus_, Trouessart, 1900 515
Genus. _Cheyletus_ 516
_Cheyletus mericourti_, Lab. 516
Family. _Sarcoptidæ_ (Itch Mites) 516
Sub-family. _Sarcoptinæ_ 518
Genus. _Sarcoptes_, Latreille 518
_Sarcoptes scabiei_, de Geer, 1778 518
_Sarcoptes minor_, Fürstenberg, 1861 520
Family. _Demodicidæ_ (Mites of the Hair-follicles) 522
Genus. _Demodex_, Owen 522
_Demodex folliculorum_, Simon, 1842 522
Order. _Pentastomida_ 523
Family. _Linguatulidæ_ 523
Genus. _Linguatula_, Fröhlich_ 524
_Linguatula rhinaria_, Pilger, 1802 524
Genus. _Porocephalus_ 526
_Porocephalus constrictus_, v. Siebold, 1852 526
_B._ INSECTA (_Hexapoda_) 529
CLASSIFICATION OF THE HEXAPODA.
(1) _Aptera_ 531
(2) _Neuroptera_ 531
(3) _Orthoptera_ 531
(4) _Thysanoptera_ 531
(5) _Hemiptera_ 531
(6) _Diptera_ 532
(7) _Lepidoptera_ 532
(8) _Hymenoptera_ 532
(9) _Coleoptera_ 532
Order. _Rhyncota_ 532
(_a_) _Rhyncota aptera parasitica_ 532
Family. _Pediculidæ_ (Lice) 532
Genus. _Pediculus_, Linnæus 532
_Pediculus capitis_, de Geer, 1778 532
_Pediculus vestimenti_, Nitzsch, 1818 533
Genus. _Phthirius_, Leach 534
_Phthirius inguinalis_, Redi, 1668 534
(_b_) _Rhyncota hemiptera_ 534
Family. _Acanthiadæ_ 534
Genus. _Cimex_ , Linnæus 534
_Cimex lectularius_ , Linnæus 534
_Cimex rotundatus_, Signoret, 1852 536
_Cimex columbarius_, Jenyns 536
_Cimex ciliatus_, Eversmann, 1841 537
Family. _Reduviidæ_ 537
Genus. _Conorhinus_, Lap. 537
_Conorhinus megistus_, Burm. 537
_Conorhinus sanguisuga_, Lec. (Blood-sucking Cone-nose) 537
_Conorhinus, sp. novum_ (Monster Bug) 538
_Conorhinus rubrofasciatus_, de Geer (Malay Bug) 538
_Conorhinus renggeri_, Herr-Schäff (Great Black Bug
of Pampas) 539
_Conorhinus variegatus_ (Variegated Cone-nose) 539
_Conorhinus nigrovarius_ 539
_Conorhinus protractus_ 539
Genus. _Reduvius_, etc. 539
_Reduvius personatus_, Linné 539
_Coriscus subcoleoptratus_, Kirby, 1837 540
_Rasahus biguttatus_, Say, 1831 540
_Melanolestes morio_, Erichson, 1848 (non-Walker) 540
_Melanolestes abdominalis_, Herrich-Schäffer, 1848 540
_Phonergates bicoloripes_ 541
Family. _Aradidæ_ 541
_Dysodius lunatus_, Fabr. (Pito Bug) 541
The Ochindundu 541
Family. _Lygæidæ_ 541
_Lyctocoris campestris_, Fabricius 541
_Rhodinus prolixus_, Stål, 1859 541
Order. _Orthoptera_ 542
Locusts Injurious to Man 542
Order. _Coleoptera_ 542
_Silvanus surinamensis_, Linnæus (Saw-toothed
Grain Beetle) 542
Order. _Diptera_ 543
_Aphaniptera_ or _Siphonaptera_ (Fleas) 543
Family. _Sarcopsyllidæ_ (Jiggers) 543
Genus. _Dermatophilus_, Guérin 544
_Dermatophilus cæcata_, Enderl. 544
_Dermatophilus penetrans_, L., 1758 (Jigger, Chigoe) 544
Genus. _Echidnophaga_, Olliff 544
_Echidnophaga gallinacea_, Westwood (Chigoe of Fowls) 544
Family. _Pulicidæ_ (True Fleas) 545
Genus. _Pulex_, Linn. 545
_Pulex irritans_, L., 1758 545
Genus. _Xenopsylla_, Glink 546
_Xenopsylla cheopis_, Rothschild 546
_Xenopsylla brasiliensis_, Baker 547
Genus. _Ctenocephalus_, Kolenati 547
Genus. _Hoplopsyllus_, Baker 547
_Hoplopsyllus anomalus_, Baker 547
Genus. _Ceratophyllus_, Centis 547
_Ceratophyllus fasciatus_, Bosc 547
Genus. _Ctenopsylla_, Kolenati 548
Genus. _Hystrichopsylla_, Taschenberg 548
_Pulex pallipes_ 548
SYSTEMATIC ANATOMICAL AND BIOLOGICAL REMARKS ON MOSQUITOES 548
CULICIDÆ OR MOSQUITOES 555
_The Classification of Culicidæ_ 561
_Notes on the Different Genera_ 566
Sub-family. _Anophelina_ 566
Genus. _Anopheles_, Meigen 566
Genus. _Myzomyia_, Blanchard; _Grassia_, Theobald 567
Genus. _Neomyzomyia_, Theobald 567
Genus. _Cycloleppteron_, Theobald 567
Genus. _Feltinella_, Theobald 567
Genus. _Stethomyia_, Theobald 567
Genus. _Pyretophorus_, Blanchard; _Howardia_,
Theobald 567
Genus. _Myzorhynchella_, Theobald 568
Genus. _Manguinhosia_, Cruz (in Peryassu) 568
Genus. _Chrystya_, Theobald 568
Genus. _Lophoscelomyia_, Theobald 568
Genus. _Arribalzagia_, Theobald 568
Genus. _Myzorhynchus_, Blanchard; _Rossia_, Theobald 568
Genus. _Nyssorhynchus_, Blanchard; _Laverania_, Theobald 569
Genus. _Cellia_, Theobald 569
Genus. _Neocellia_, Theobald 569
Genus. _Kertészia_, Theobald 569
Genus. _Manguinhosia_, Cruz 569
Genus. _Chagasia_, Cruz 570
Genus. _Calvertina_, Ludlow 570
Genus. _Birónella_, Theobald 570
Sub-family. _Megarhininæ_ 570
Genus. _Megarhinus_, Robineau Desvoidy 570
Genus. _Toxorhynchites_, Theobald 570
Sub-family. _Culicinæ_ 571
Genus. _Mucidus_, Theobald 571
Genus. _Psorophora_, Robineau Desvoidy 571
Genus. _Janthinosoma_, Arribalzaga 571
Genus. _Stegomyia_, Theobald 571
_Stegomyia fasciata_, Fabricius (Yellow Fever Mosquito) 574
_Stegomyia scutellaris_, Walker 575
Genus. _Theobaldia_, Neveu-Lemaire 575
_Theobaldinella_, Blanchard 575
_Theobaldia annulata_, Meigen 575
Genus. _Culex_, Linnæus 575
Genus. _Melanoconion_, Theobald 576
Genus. _Grabhamia_, Theobald 576
Genus. _Pseudotæniorhynchus_, Theobald; _Tæniorhynchus_,
Theobald, non-Arribalzaga 576
Genus. _Tæniorhynchus_, Arribalzaga; _Mansonia_,
Blanchard; _Panoplites_, Theobald 577
Genus. _Chrysoconops_, Goeldi 577
_Other Nematocera_ 577
Family. _Simulidæ_ 577
Family. _Chironomidæ_ (Midges) 579
Sub-family. _Ceratopogoninæ_ 580
Family. _Psychodidæ_ (Owl Midges) 581
_Brachycera_ (Flies) 582
Family. _Phoridæ_ 582
_Aphiochæta ferruginea_, Brun 583
_Phora rufipes_, Meig. 583
Family. _Sepsidæ_ 583
_Piophila casei_, L. 583
Family. _Syrphidæ_ (Hover and Drone Flies) 583
Family. _Drosophilidæ_ 584
_Drosophila melanogaster_, Br. 584
Family. _Muscidæ_ 584
_Teichomyza fusca_, Macq. 584
_Homalomyia canicularis_, L., etc. 584
_Homalomyia scalaris_, Fabr. 585
_Anthomyra desjardensii_, Macq. 585
_Hydrotæa meteorica_, L. 585
_Cyrtoneura stabulans_ 585
_Musca domestica_, Linn. (Common House-fly) 585
Genus. _Chrysomyia_, Rob. Desv. 587
_Chrysomyia_ (_Compsomyia_) _macellaria_, Fabr.; _Lucilia
macellaria_, Fabr. 587
_Chrysomyia viridula_, Rob. Desv. 588
Genus. _Lucilia_, Rob. Desv. 588
_Lucilia nobilis_, Meig. 588
Genus. _Pycnosoma_, Brauer and v. Bergenstamm 588
Genus. _Sarcophaga_, Mg. 589
_Sarcophaga carnaria_, L., 1758 589
_Sarcophaga magnifica_, Schiner, 1862 589
_Sarcophaga chrysotoma_, Wied 590
_Sarcophaga plinthopyga_, Wied 590
_Ochromyia anthropophaga_, E. Blanch.; _Cordylobia
arthrophaga_,Grünberg 590
_Auchmeromyia_ (_Bengalia_) _depressa_ (Walker) 591
Genus. _Cordylobia_, Grünberg, 1903 591
_Cordylobia grünbergi_, Dönitz 591
_Cordylobia anthropophaga_, Grünberg 592
_Lund’s Larva_ 593
_Auchmeromyia luteola_, Fabricius 593
Family. _Oestridæ_ 594
_Cutaneous Oestridæ_ 595
Genus. _Hypoderma_, Latreille 595
_Hypoderma bovis_, de Geer 595
_Hypoderma lineata_, de Villers 596
_Hypoderma diana_, Brauer 596
Genus. _Dermatobia_, Brauer 596
_Dermatobia cyaniventris_, Macq. 596
_Cavicolous Oestridæ_ 598
Genus. _Oestrus_, Linnæus 598
_Oestrus_ (_Cephalomyia_) _ovis_, L. 598
_Gastricolous Oestridæ_ 599
Genus. _Gastrophilus_, Leach 599
_Biting-mouthed and other Noxious Diptera which may be
Disease Carriers_ 600
Family. _Tabanidæ_ (Gad Flies) 600
Family. _Asilidæ_ (Wolf Flies) 602
Family. _Leptidæ_ 603
_Blood-sucking Muscidæ_ 603
Genus. _Glossina_, Westwood 603
_Glossina palpalis_, Rob. Desv. 607
_Glossina morsitans_, Westwood 608
Genus. _Stomoxys_, Geoffroy 609
Genus. _Lyperosia_, Rondani 610
_Pupipara_ or _Eproboscidæ_ 611
_Insects and Epidemic Poliomyelitis_ 612
ADDENDA 613
Akamushi or Kedani Sickness 613
Ticks.--African Tick Fever 613
Tick Paralysis 613
_Diptera._--_Psychodidæ_ 613
_Pulicidæ._--_Dermatophilus_ (_Sarcopsylla_) _penetrans_,
or the “Jigger” 613
_Brachycera._--_Leptidæ_ 613
Myiasis 615
Auricular Myiasis 615
Body, Head, and Clothes Lice 615
SUPPLEMENT: CLINICAL AND THERAPEUTICAL NOTES 617
*Protozoa* 617
Introduction 617
I.--AMŒBIC DYSENTERY 618
II.--TRYPANOSOMIASES 620
African Sleeping Sickness 620
South American Trypanosomiasis 623
III.--FLAGELLATE DIARRHŒA AND DYSENTERY 623
IV.--LEISHMANIASES 626
A. Kala-azar 626
Indian 626
Infantile 627
B. Oriental Sore, due to _Leishmania tropica_ 627
Naso-oral (Espundia) 628
V.--SPIROCHÆTOSES 629
A. Relapsing Fevers 629
B. Yaws or Frambœsia tropica 632
C. Syphilis 632
D. Bronchial Spirochætosis 632
VI.--MALARIA 633
VII.--BALANTIDIAN DYSENTERY 637
*Plathelminthes* (Flat Worms) 638
FASCIOLIASIS 638
_Fasciola hepatica_ 638
_Fasciolopsis buski_ 638
PARAGONIMIASIS 639
_Paragonimus ringeri_ 639
_Clonorchis sinensis_ 640
BILHARZIASIS 641
_Schistosoma hæmatobium_ 641
CESTODES 644
General 644
_Dibothriocephalus latus_ 658
_Sparganum mansoni_ 659
_Dipylidium caninum_ (_Tænia cucumerina_) 659
_Hymenolepis nana_ 661
_Tænia solium_ 662
_Tænia saginata_ 667
NEMATODES 674
_Strongyloides stercoralis_ 674
_Dracunculus medinensis_ (Dracontiasis) 675
_Filaria bancrofti_ 676
_Loa loa_ 678
_Trichuris trichiura_ 678
_Trichinella spiralis_ 680
_Eustrongylus gigas_ 681
_Ancylostoma duodenale_ (Ancylostomiasis) 682
_Ascaris lumbricoides_ (Ascariasis) 687
_Oxyuris vermicularis_ (Oxyuriasis) 694
*Hirudinea* (Leeches) 699
*Arthropoda* 702
ARACHNOIDEA 702
_Leptus autumnalis_ (Grass, Harvest, or Gooseberry Mite) 702
_Kedani, Akaneesch_ (The Japanese River or Inundation
Disease) 703
_Dermanyssus gallinæ_ (_avium_) 703
_Ixodes reduvius_ (_ricinus_ ) 704
_Sarcoptes scabiei_ (Scabies) 704
_Demodex folliculorum_ 708
_Demodex folliculorum canis_ 709
INSECTA 709
_Pediculus capitis_ (Head Louse) 709
_Pediculus vestimenti_ (Clothes Louse) 710
_Phthirius inguinalis_ (_Pediculus pubis_) (Crab Louse) 711
_Cimex_ (_Acanthia_) _lectularia_ (_Cimex lectularius_)
(Bed Bug) 713
_Pulex irritans_ (Human Flea) 714
_Dermatophilus_ (_Sarcopsylla_) _penetrans_ (Sand Flea) 714
_Myiasis_ 715
_Myiasis externa_ 715
_Gastricolous Oestridæ_ (Creeping Disease) 729
APPENDIX ON PROTOZOOLOGY 733
I.--NOTES ON RECENT RESEARCHES 733
Differences between _Entamœba histolytica_ and _E. coli_ 733
Phagedænic Amœbæ 733
_Endamœba gingivalis_ 733
_Entamœba kartulisi_ 734
_Craigia_ and Craigiasis 734
Human Trichomoniasis 734
_Chilomastix_ (_Tetramitus_) _mesnili_ 735
_Giardia_ (_Lamblia_) _intestinalis_ 736
_Cercomonas hominis_ 736
Transmissive Phase of Trypanosomes in Vertebrates 737
_Trypanosoma lewisi_ 737
Blepharoplastless Trypanosomes 737
The Experimental Introduction of certain Insect Flagellates
into various Vertebrates, and its bearing on the
Evolution of Leishmaniasis 737
The Transmission of _Spirochæta duttoni_ 739
_Spirochæta bronchialis_ 739
The Spirochætes of the Human Mouth 740
Coccidia in Cattle 741
The Hæmosporidia 742
The Leucocytozoa of Birds 742
II.--FORMULÆ OF SOME CULTURE MEDIA 742
Culture Media for growing Amœbæ 742
Culture Media for the growth of Protozoa parasitic
in the Blood 744
III.--BRIEF NOTES ON GENERAL PROTOZOOLOGICAL TECHNIQUE 745
Fresh Material 745
Stained Material 747
Fixatives 748
Stains 749
APPENDIX ON TREMATODA AND NEMATODA 753
TREMATODA 753
_Artyfechinostomum sufrartyfex_ 753
_Metagonimus_ (_Yokogawa_) _yokogawai_ 753
_Opisthorchis sp._ 753
_Schistosome cercariæ_ 753
_Distomata cercariæ_ 753
Group. _Ferrocercous cercariæ_ 753
Family. _Schistosomidæ_ 753
_Cercaria bilharzia_, Leiper, 1915 754
_Cercaria bilharziella_, Leiper, 1915 754
_Schistosoma mansoni_, Sambon, 1907 754
NEMATODA 754
Ancylostomiasis 754
Ground Itch 754
_Ascaris lumbricoides_ 754
Filariasis 755
_Onchocerca volvulus_ 755
_Strongyloides stercoralis_ 755
BIBLIOGRAPHY 756
INDEX 836
LIST OF ILLUSTRATIONS.
FIG. PAGE
1 _Amœba coli._ (After Loesch) 29
2 Encysted intestinal amœbæ. (After Grassi) 31
3 _Entamœba coli_, life-cycle. (After Castellani and Chalmers) 32
4 _Entamœba coli_, so-called autogamy. (From Minchin) 34
5 _Entamœba histolytica_ (_tetragena_ form). (After Hartmann) 35
6 _Entamœba histolytica_, ingestion of red blood corpuscles.
(After Hartmann) 35
7 _Entamœba histolytica_, section through infected intestinal
ulcer. (After Harris) 36
8 _Entamœba histolytica_ (_tetragena_), trophozoite and nuclei.
(After Hartmann) 38
9 _Entamœba histolytica_ (_tetragena_), cysts. (After Hartmann) 39
10 _Entamœba buccalis._ (After Leyden and Löwenthal) 43
11 _Entamœba kartulisi._ (After Kartulis) 44
12 _Amœba miurai._ (After Ijima) 46
13 _Chlamydophrys enchelys._ (After Cienkowski) 48
14 _Chlamydophrys enchelys_, encysted. (After Cienkowski) 49
15 _Leydenia gemmipara_, Schaudinn 50
16 _Trichomonas vaginalis._ (After Künstler) 53
17 _Trichomonas intestinalis._ (After Grassi) 54
18 _Trichomonas intestinalis._ (Original, Fantham) 55
19 _Lamblia intestinalis._ (After Wenyon, from Minchin) 58
20 _Lamblia intestinalis._ (After Grassi and Schewiakoff) 59
21 _Cercomonas hominis._ (After Davaine) 61
22 _Cercomonas hominis_, from an echinococcus cyst. (After Lambl) 61
23 _Monas pyophila._ (After Grimm) 62
24 _Prowazekia urinaria._ (After Sinton) 64
25 _Prowazekia urinaria_, excystation. (After Sinton) 65
26 _Trypanosoma brucei_ in division. (After Laveran and Mesnil) 70
27 _Trypanosoma lewisi_, rosettes. (After Laveran and Mesnil) 71
28 _Trypanosoma gambiense._ (After Dutton) 73
29 _Trypanosoma gambiense_, development in vertebrate host.
(Original, Fantham) 73
30 _Trypanosoma gambiense_, development in _Glossina palpalis_.
(After Robertson) 75
31 _Trypanosoma rhodesiense._ (After Stephens and Fantham) 77
32 Chart showing daily counts of number of Trypanosomes per cubic
millimetre of peripheral blood from a case of Rhodesian
sleeping sickness. (After Ross and Thomson) 79
33 _Trypanosoma cruzi_, schizogony. (After Chagas, from Castellani
and Chalmers) 84
34 _Trypanosoma cruzi_ in muscle. (After Vianna, from Castellani
and Chalmers) 85
35 _Trypanosoma cruzi_, development in _Triatoma megista_.
(After Chagas, from Castellani and Chalmers) 86
36 _Trypanosoma cruzi_, forms found in salivary glands of
_Triatoma_. (After Chagas, from Castellani and Chalmers) 87
37 _Trypanosoma lewisi_, from rat’s blood. (After Minchin) 89
38 _Trypanosoma lewisi_, from stomach of rat-flea. (After Minchin) 91
39 _Trypanosoma lewisi_, from rectum of rat-flea. (After Minchin) 92
40 _Trypanosoma brucei._ (After Laveran and Mesnil) 94
41 _Trypanosoma evansi._ (Original, Fantham) 96
42 _Trypanosoma equinum._ (After Laveran and Mesnil) 96
43 _Trypanosoma equiperdum._ (Original, Fantham) 97
44 _Trypanosoma theileri._ (After Laveran and Mesnil) 98
45 _Trypanosoma vivax._ (Original, Fantham) 100
46 _Trypanosoma congolense._ (Original, Fantham) 100
47 _Trypanosoma uniforme._ (Original, Fantham) 100
48 _Trypanosoma rotatorium._ (After Laveran and Mesnil) 101
49 _Herpetomonas_, _Crithidia_, _Trypanosoma_. (After Porter) 103
50 _Leishmania donovani._ (After Christophers, Patton, Leishman;
from Castellani and Chalmers) 106
51 _Toxoplasma gondii._ (After Laveran and Marullaz, from
_Trop. Dis. Bulletin_) 113
52 _Toxoplasma pyrogenes._ (After Castellani, from _Trop.
Dis. Bulletin_) 113
53 _Spirochæta balbianii._ (After Fantham and Porter) 114
54 _Spirochæta duttoni._ (After Fantham) 117
55 _Spirochæta duttoni_ and its coccoid bodies in the tick.
(After Fantham) 118
56 _Treponema pallidum._ (After Bell, from Castellani and
Chalmers) 124
57 _Treponema pallidum_, apparatus for cultivation of.
(After Noguchi) 125
58 _Treponema pertenue._ (After Castellani and Chalmers) 127
59 _Monocystis agilis._ (After Stein) 130
60 _Gregarina longa_, stages of growth of trophozoite 130
61 _Xyphorhynchus firmus._ (After Léger) 131
62 _Gregarina munieri._ (After Schewiakoff) 131
63 _Monocystis agilis_, spores. (After Bütschli) 132
64 Gregarines, conjugation and spore formation. (After Calkins
and Siedlecki, modified) 133
65 _Stylorhynchus oblongatus_, cyst and gametes. (After Léger) 133
66 Gregarines, various spores. (After Léger) 134
67 _Eimeria_ (_Coccidium_) _schubergi_, life-cycle diagram of.
(After Schaudinn) 139
68 _Eimeria avium_ in gut epithelium of grouse chick.
(After Fantham) 143
69 _Eimeria avium_, life-cycle, diagram of. (After Fantham) 144
70 _Eimeria stiedæ_ in section of rabbit’s intestine 145
71 _Eimeria stiedæ_, oöcysts from rabbit’s liver. (After Leuckart) 146
72 _Eimeria stiedæ_, spores. (After Balbiani) 146
73 _Eimeria stiedæ_, schizogony. (After R. Pfeiffer) 146
74 _Eimeria stiedæ_, section through infected nodule of liver 147
75 _Isospora bigemina._ (After Stiles) 150
76 _Hæmoproteus_ (_Halteridium_) _columbæ_, life-cycle.
(After Aragão, from Castellani and Chalmers) 152
77 _Leucocytozoön lovati._ (After Fantham) 153
78 Hæmogregarines from lizards. (After França) 154
79 _Leucocytogregarina canis_, life-cycle. (After Christophers,
from Castellani and Chalmers) 155
80 _Plasmodium vivax_, life-cycle. (After Schaudinn and Grassi) 160
81 Malignant tertian malarial parasite in intestine of
_Anopheles_. (After Grassi) 162
82 Oökinete of malignant tertian malaria in stomach of
_Anopheles_. (After Grassi) 162
83 Section of stomach of _Anopheles_ with malarial oöcysts.
(After Grassi) 163
84 Sporulation of malarial parasites in _Anopheles_.
(After Grassi) 163
85 Tertian malarial parasite in human red blood corpuscles.
(After Mannaberg) 165
86 Quartan malarial parasite in human red corpuscles.
(After Manson) 166
87 Malignant malarial parasite in human red corpuscles.
(After Manson) 168
88 Malarial crescents. (After Mannaberg) 168
89 Section through tubule of salivary gland of _Anopheles_
infected with malarial sporozoites. (After Grassi) 169
90 _Nuttallia equi_, life-cycle in red blood corpuscles.
(After Nuttall and Strickland) 173
91 _Babesia_ (_Piroplasma_) _canis_, life-cycle in blood of dog.
(After Nuttall and Graham-Smith) 175
92 _Theileria parva._ (After Nuttall and Fantham) 179
93 Myxosporidian spores and infected gill of fish.
(After J. Müller) 181
94 _Myxobolus mülleri_, spore. (After Bütschli) 181
95 _Myxobolus_, schema of spore. (After Doflein) 182
96 _Chloromyxum leydigi._ (After Thélohan) 182
97 _Myxobolus pfeifferi_, spore formation. (After Keysselitz,
from Minchin) 183
98 _Nosema apis._ (After Fantham and Porter) 185
99 _Nosema bombycis_ from silkworm. (After Balbiani) 186
100 _Nosema bombycis_, spores. (After Thélohan) 186
101 _Hexactinomyxon psammoryctis_, spore. (After Stolč) 187
102}
103} _Sarcocystis miescheriana_ in muscle of pig. (After Kühn) 188
104 _Sarcocystis miescheriana_, mature trophozoite 189
105 _Sarcocystis tenella_ in section, as seen in œsophagus
of sheep 190
106 _Sarcocystis tenella_, young trophozoite. (After Bertram) 190
107 _Sarcocystis miescheriana_, end portion of trophozoite.
(After Bertram) 190
108 _Sarcocystis blanchardi_ from ox. (From Wasielewski,
after van Eecke) 190
109 _Sarcocystis tenella._ (After Laveran and Mesnil) 191
110 _Haplosporidium heterocirri._ (After Caullery and Mesnil) 195
111 Haplosporidian spores. (After Caullery and Mesnil) 195
112 _Rhinosporidium kinealyi_, portion of ripe cyst.
(After Minchin and Fantham) 197
113 _Balantidium coli._ (After Leuckart) 200
114 _Balantidium coli_, free and encysted. (After Casagrandi
and Barbagallo) 200
115 _Balantidium minutum._ (After Schaudinn) 204
116 _Nyctotherus faba._ (After Schaudinn) 205
117 _Nyctotherus giganteus._ (After Krause) 206
118 _Nyctotherus africanus._ (After Castellani) 206
119 Trachoma bodies in conjunctival cells. (Original, Fantham) 209
120 Half of a transverse section through _Fasciola hepatica_, L. 214
121 _Harmostomum leptostomum_, Olss. 215
122 Median section through the anterior part of _Fasciola
hepatica_ 217
123 _Polystomum integerrimum._ (After Zeller) 218
124 _Allocreadium isoporum_, Looss. (After Looss) 218
125 Terminal flame cell of the excretory system. (Stephens) 219
126 Diagram of female genitalia. (Stephens) 220
127 Diagram of male and part of female genitalia. (Stephens) 220
128 Ovum of _Fasciola hepatica_, L. 223
129 Miracidium of _Fasciola hepatica_. (After Leuckart) 223
130 A group of cercariæ of _Echinostoma_ sp. 225
131 Development of _Fasciola hepatica_, L. (After Leuckart) 226
132 Young redia of _Fasciola hepatica_. (From Leuckart) 227
133 Older redia of _Distoma echinatum_ 227
134 Cercaria of _Fasciola hepatica_. (After Leuckart) 228
135 Encysted cercaria of _Fasciola hepatica_. (After Leuckart) 228
136 _Watsonius watsoni._ (After Shipley) 234
137 _Watsonius watsoni_: ventral projection composed from a
series of transverse sections. (After Stiles and
Goldberger) 235
138 _Gastrodiscus hominis._ (After Leuckart) 236
139 _Fasciola hepatica_, L. 238
140 _Fasciola hepatica_, showing the gut and its branches 239
141 _Fasciola hepatica_, L. (After Claus) 239
142 _Fasciola hepatica_: egg from liver of sheep. (After Thomas) 240
143 _Limnæus truncatulus_, Müll. (From Leuckart) 240
144 Young _Fasciola hepatica_. (From Leuckart) 242
145 _Fasciola gigantica._ (After Looss) 243
146 _Fasciolopsis buski_, Lank. (After Odhner) 245
147 _Fasciolopsis rathouisi_, Poir. (After Claus) 246
148 _Fasciolopsis fülleborni._ (After Fülleborn) 248
149 _Paragonimus ringeri_, Cobb. (After Katsurada) 250
150 _Paragonimus ringeri_, Cobb. (After Kubo) 250
150A _Paragonimus westermanii_, Kerb. (After Leuckart) 250
151 Egg of _Paragonimus ringeri_, Cobb. (After Katsurada) 251
152 Egg of _Opisthorchis felineus_ 253
153 _Opisthorchis felineus._ (After Stiles and Hassall) 253
154 _Opisthorchis pseudofelineus._ (After Stiles) 254
155 _Parapisthorchis caninus._ (After Stephens) 256
156 _Amphimerus noverca_, Braun. (After McConnell) 257
157 _Metorchis conjunctus._ (After Cobbold) 258
158 _Clonorchis sinensis._ (After Looss) 259
159 Ova of _Clonorchis sinensis_. (After Looss) 259
160 _Clonorchis endemicus._ (After Looss) 260
161 _Clonorchis endemicus_: eggs. (After Looss) 260
162 _Metorchis truncatus_ 262
163 _Heterophyes heterophyes._ (After Looss) 263
164 _Metagonimus yokogawai._ (After Leiper) 264
165 _Dicrocœlium dendriticum_ 265
166 Eggs of _Dicrocœlium dendriticum_ 266
167 Miracidia of _Dicrocœlium dendriticum_. (After Leuckart) 266
168 _Echinostoma ilocanum._ (After Brumpt) 268
169 _Echinostoma ilocanum._ (After Leiper) 268
170 _Echinostoma malayanum_, Leiper. (After Leiper) 269
171 _Schistosoma hæmatobium._ (After Looss) 270
172 Transverse section through a pair of _Schistosoma
hæmatobium_ in copulâ. (After Leuckart) 271
173 Anterior end of the male _Schistosoma hæmatobium_.
(After Looss) 271
174 _Schistosoma hæmatobium._ (After Leuckart) 276
175 _Schistosoma hæmatobium_, ovum of. (After Looss) 277
176 _Schistosoma japonicum._ (After Katsurada) 278
177 _Schistosoma japonicum._ (After Katsurada) 279
178 _Schistosoma japonicum._ (After Looss) 279
179}
180} _Schistosoma japonicum_ from dog. (After Katsurada) 280
181}
182 _Schistosoma japonicum._ (After Catto) 281
183 _Schistosoma japonicum._ (After Katsurada) 282
184 Schematic representation of a small part of a transverse
section of _Ligula_ sp. (After Blochmann) 287
185 Half of a transverse section through a proglottis of _Tænia
crassicollis_ 288
186 _Dipylidium caninum._ (After Benham) 289
187 Longitudinal section of the head and neck of _Tænia
crassicollis_ 290
188 _Tænia cœnurus._ (After Niemisec) 291
189 Young _Acanthobothrium coronatum_. (After Pintner) 292
190 Scolex of a cysticercoid from _Arion_ sp. (After Pintner) 292
191 Proglottis of _Tænia saginata_, Goeze, showing genitalia 293
192 _Dibothriocephalus latus._ (After Benham and Sommer
and Landois) 294
193 Diagram of genitalia of a Cestode. (Stephens) 295
194 Part of a transverse section through a proglottis of
_Dibothriocephalus latus_ 296
195 Egg of _Diplogonoporus grandis_. (After Kurimoto) 298
196 Uterine egg of _Tænia saginata_. (After Leuckart) 298
197 Oncosphere of _Tænia africana_ (after v. Linstow) and
oncosphere of _Dipylidium caninum_. (After Grassi
and Rovelli) 299
198 Diagram of a cysticercoid. (Stephens) 301
199 Diagram of a cysticercus. (Stephens) 301
200 Diagram of development of a cysticercus. (Stephens) 303
201 Section through a piece of a _Cœnurus cerebralis_ 304
202 Median section through a cysticercus. (After Leuckart) 304
203 _Cysticercus pisiformis_ in an evaginated condition 304
204 Various chains of segments of _Dibothriocephalus latus_ 311
205 Transverse section of the head of _Dibothriocephalus latus_ 311
206 Fairly mature proglottis of _Dibothriocephalus latus_ 311
207 _Dibothriocephalus latus._ (After Benham and Schauinsland) 312
208 Plerocercoid of _Dibothriocephalus latus_ 313
209 A piece of the body wall of the Burbot, _Lota vulgaris_ 313
210 Cephalic end of _Dibothriocephalus cordatus_. (After Leuckart) 315
211 _Diplogonoporus grandis_, Lühe, 1899. (After Ijima and
Kurimoto) 317
212 _Diplogonoporus grandis._ (After Ijima and Kurimoto) 317
213 Cephalic end of _Sparganum mansoni_, Cobb. (After Leuckart) 318
214 _Sparganum mansoni._ (After Ijima and Murata) 318
215 _Sparganum prolifer._ (After Ijima) 319
216 _Sparganum proliferum._ (After Stiles) 319
217 _Dipylidium caninum._ (After Diamare) 320
218 _Dipylidium caninum._ (After Benham and Moniez) 320
219 _Dipylidium caninum_: central portion of a proglottis.
(After Neumann and Railliet) 321
220 _Dipylidium caninum_: development of embryo. (After Benham,
Grassi, and Rovelli) 321
221 Larva (cysticercoid) of _Dipylidium caninum_. (After Grassi
and Rovelli) 322
222 _Hymenolepis nana_, v. Sieb. (After Leuckart) 324
223 _Hymenolepis nana_: head. (After Mertens) 324
224 _Hymenolepis nana_: an egg. (After Grassi) 324
225 Longitudinal section through the intestinal villus of a rat.
(After Grassi and Rovelli) 324
226 _Hymenolepis nana_ (_murina_): cross-section of proglottis
from a rat. (After v. Linstow) 325
227 _Hymenolepis nana_: longitudinal section of an embryo.
(After Grassi and Rovelli) 325
228 _Hymenolepis diminuta._ (After Zschokke) 326
229 _Hymenolepis diminuta._ (After Grassi) 326
230 _Hymenolepis diminuta._ (After Bizzozero) 326
231 _Hymenolepis diminuta._ (Stephens, after Nicoll and Minchin) 327
232 _Hymenolepis lanceolata._ (After Krabbe) 328
233 _Hymenolepis lanceolata._ (After Wolffhügel) 328
234 Scolex of _Davainea madagascariensis_. (After Blanchard) 330
235 Two fairly mature proglottids of _Tænia solium_ 332
236 Head of _Tænia solium_ 332
237 Large and small hooks of _Tænia solium_. (After Leuckart) 333
238 _Tænia solium._ (After Leuckart) 333
239 Two mature proglottids of _Tænia solium_ 333
240 Large and small hooklets of _Tænia marginata_. (After
Leuckart) 338
241 Mature segment of _Tænia saginata_ 339
242 Cephalic end of _Tænia saginata_ 339
243 _Tænia saginata._ (After Leuckart) 339
244 A piece of the muscle of the ox, with three specimens of
_Cysticercus bovis_. (After Ostertag) 340
245 Mature segment of _Tænia africana_. (After v. Linstow) 342
246 Proglottis of _Tænia africana_. (After v. Linstow) 343
247 Head of _Tænia africana_. (After v. Linstow) 343
248 _Tania confusa._ (After Guyer) 344
249 _Tania confusa._ (After Ward) 344
250 _Tania echinococcus_ 345
251 _Echinococcus veterinorum._ (After Leuckart) 347
252 }
252A} Diagrams of mode of formation of brood capsule and
scolices (Stephens) 348
253 Section through an invaginated echinococcus scolex.
(After Dévé) 350
254 A piece of the wall of an _Echinococcus veterinorum_
stretched out and seen from the internal surface 350
255 _Echinococcus hominis_ in the liver. (After Ostertag,
from Thomas) 351
256 Section through an echinococcus scolex in process of
vesicular metamorphosis. (After Dévé) 351
257 }
257A} Diagram of transformation of a scolex into a daughter
cyst. (Stephens) 352
258 Hooklets of echinococcus. (After Leuckart) 355
259 _Echinococcus multilocularis_ in the liver of the ox.
(After Ostertag) 357
260 Diagram of a transverse section of _Ascaris lumbricoides_.
(After Brandes) 362
261 Anterior end of an _Ascaris megalocephala_. (After Nassonow) 362
262 Transverse section through _Ascaris lumbricoides_ at the
level of the œsophagus behind the nerve ring.
(After Goldschmidt) 364
263 Schematic representation of the nervous system of a male
_Ascaris megalocephala_. (After Brandes) 365
264 Diagram of female genitalia 368
264A Diagram of male genitalia of a strongylid 368
265 Transverse section through the ovarian tube of _Belascaris
cati_ of the cat 369
266 Male of the rhabditic form of _Angiostomum nigrovenosum_ 370
267 Transverse section through the posterior extremity of the
body of _Ascaris lumbricoides_ (male) 370
268 Hind end of a male _Ascaris lumbricoides_ cut across at the
level of the dilator cells of the gut. (After Goldschmidt) 371
269 A piece of the trunk muscle of the pig with encapsuled
embryonic Trichinæ 373
270 _Strongyloides stercoralis_, female. (After Looss) 380
271 _Strongyloides stercoralis_, male. (After Looss) 380
272 _Strongyloides stercoralis_, female. (After Looss) 382
273 _Strongyloides stercoralis._ (After Looss) 382
274 _Strongyloides stercoralis._ (After Looss) 383
275 _Gnathostoma siamense._ (After Levinsen) 385
276 Guinea worm (_Dracunculus medinensis_). (After Leuckart) 387
277 Anterior extremity of Guinea worm. (After Leuckart) 387
278 _Dracunculus medinensis._ (After Claus) 387
279 Transverse section of female Guinea worm. (After Leuckart) 388
280 _Cyclops virescens_, female 389
281 _Filaria bancrofti._ (After Leiper) 391
282 _Mf. bancrofti_ in thick film, dried and stained with
hæmatoxylin. (After Fülleborn) 397
283 Schematic drawings of the anatomy of _Ml. loa_ and _Mf.
bancrofti_. (After Fülleborn) 399
284 _F. demarquayi._ (After Leiper) 403
285 _Mf. demarquayi_ in thick film, dried and stained with
hæmatoxylin. (After Fülleborn) 404
286 _Filaria_ (?) _conjunctivæ_. (After Addario) 405
287 _Filaria_ (?) _conjunctivæ_. (After Grassi) 405
288 _Setaria equina._ (After Railliet) 408
289 _Setaria equina_: anterior end. (After Railliet) 408
290 _Loa loa_: the anterior end of the male. (After R. Blanchard) 410
291 _Loa loa_: anterior portion of the female. (After Looss) 410
292 _Loa loa_ in situ. (After Fülleborn and Rodenwaldt) 410
293 _Loa loa_: male and female. (After Looss) 410
294 _Loa loa_: the hind end of a male and of a female.
(After Looss) 411
295 _Loa loa_: lateral view of tail of male showing papillæ.
(After Lane and Leiper) 411
296 _Loa loa._ (After Leiper) 411
297 _Mf. loa_: in thick film, dried and stained with hæmatoxylin.
(After Fülleborn) 413
298 _Acanthocheilonema perstans._ (After Leiper) 414
299 _Mf. perstans._ (After Fülleborn) 415
300 _Dirofilaria magalhãesi._ (After v. Linstow) 417
301 _Trichuris trichiura_ 420
302 _Trichinella spiralis._ (After Claus) 422
303 Isolated muscular fibre of a rat, invaded by Trichinella.
(After Hertwig-Graham) 425
304 Calcified Trichinella in the muscular system of a pig.
(After Ostertag) 426
305 Various phases of the calcification of Trichinella of
the muscles 426
306 _Dioctophyme gigas._ (After Railliet) 432
307 Eggs of _Dioctophyme gigas_. (After Railliet) 432
308 _Metastrongylus apri._ (Stephens) 433
309}
310} _Trichostrongylus instabilis._ (After Looss) 434
311}
312} _Trichostrongylus probolurus._ (After Looss) 435
313}
314} _Trichostrongylus vitrinus._ (After Looss) 436
315}
316} _Hæmonchus contortus._ (After Ransom) 437
316}
317 _Mecistocirrus fordi._ (After Stephens) 439
318 _Ternidens deminutus._ (After Railliet and Henry) 440
319}
320} _Œsophagostomum stephanostomum_ var. _thomasi_.
(After Thomas) 442
321}
322} _Œsophagostomum stephanostomum_ var. _thomasi_.
(After Thomas) 444
323}
324} _Ancylostoma duodenale_, male and female. (After Looss) 446
325 _Ancylostoma duodenale_, showing ventral teeth. (After Looss) 447
326 _Ancylostoma duodenale_: diagrammatic representation of
excretory system. (After a drawing by Looss) 448
327 _Ancylostoma duodenale._ (After Railliet) 449
328 _Ancylostoma duodenale_: bursa of male. (After Looss) 450
329 _Ancylostoma duodenale_: eggs in different stages of
development. (After Looss) 451
330 _Ancylostoma duodenale_: larva. (After Leichtenstern) 452
331 _Ancylostoma duodenale._ (After Looss) 453
332 _Ancylostoma ceylanicum._ (After Looss) 456
333 _Ancylostoma braziliense._ (After Gomez de Faria) 456
334 _Necator americanus._ (After Looss) 457
335 _Necator americanus_: lateral view. (After Looss) 458
336 _Necator americanus_: bursa of male. (After Looss) 458
337 _Syngamus kingi_: anterior end of male. (After Leiper) 460
338 _Syngamus kingi_: anterior end of female. (After Leiper) 460
339 Bursa of _Syngamus trachealis_. (Stephens) 461
340 _Physaloptera mordens_, Leiper, 1907. (After Leiper) 462
341 _Ascaris lumbricoides._ (From Claus) 463
342 Ovum of _Ascaris lumbricoides_ 463
343 Ovum of _Toxascaris limbata_ 466
344 Transverse section through the head part of _Belascaris
cati_ from the cat. (After Leuckart) 466
345}
346} Male female of _Oxyuris vermicularis_ 468
347 _Oxyuris vermicularis_: egg freshly deposited 468
348 _Oxyuris vermicularis_: egg twelve hours after deposition 468
348A The male of _Echinorhynchus augustatus_ 476
348B Anterior portion of the female apparatus of _Echinorhynchus
acus_. (After Wagener) 476
348C Egg of _Echinorhynchus gigas_. (After Leuckart) 477
348D The internal organs of the leech. (After Kennel) 480
348E _Hirudo medicinalis._ (After Claus) 481
349 _Leptus autumnalis._ (After Gudden) 485
350 _Leptus autumnalis._ (After Trouessart) 485
351 The kedani mite. (After Tanaka) 487
352 _Tetranychus telarius_ var. _russeolus_, Koch.
(After Artault) 488
353 _Pediculoides ventricosus._ (After Laboulbène and Mégnin) 489
354 _Nephrophages sanguinarius_: male, ventral surface.
(After Miyake and Scriba) 490
355 _Nephrophages sanguinarius_: female, dorsal aspect.
(After Miyake and Scriba) 490
356 _Tydeus molestus._ (After Moniez) 491
357 _Dermanyssus gallinæ._ (After Berlese) 492
358 _Dermanyssus hirundinis._ (After Delafond) 492
359 _Ixodes ricinus_, male. (After Pagenstecher) 498
360 Female of _Ixodes ricinus_. (After Pagenstecher) 498
361 _Argas reflexus._ (After Pagenstecher) 506
362 _Argas persicus._ (After Mégnin) 507
363 _Tyroglyphus farinæ_: male. (After Berlese) 512
364 _Tyroglyphus longior_, Gerv. (After Fum. and Robin) 512
365 _Rhizoglyphus parasiticus_: male and female. (After Dalgetty) 514
366 _Histiogaster_ (_entomophagus_ ?) _spermaticus_.
(After E. Trouessart) 515
367 _Sarcoptes scabiei._ (After Fürstenberg) 518
368 _Sarcoptes scabiei_: male, ventral aspect.
(After Fürstenberg) 519
369 _Sarcoptes minor_ var. _cati_. (After Railliet) 521
370 _Demodex folliculorum_ of the dog. (After Mégnin) 522
371 _Linguatula rhinaria_: female 524
372 Larva of _Linguatula rhinaria_ (_Pentastoma denticulatum_).
(After Leuckart) 524
373 _Linguatula rhinaria._ (After M. Koch) 525
374 Mouth-parts of _Pediculus vestimenti_. (After Denny) 533
375 Ovum of the head louse 533
376 Head louse, male 533
377 _Pediculus vestimenti_, Burm.: adult female 533
378 _Phthirius inguinalis_, Leach 534
379 Head of the bed bug from the ventral surface 535
380 _Dermatophilus penetrans_: young female. (After Moniez) 544
381 _Dermatophilus penetrans_: older female. (After Moniez) 544
382 _Pulex irritans_ 546
383 Larva of flea. (After Railliet) 546
384 _Pulex serraticeps_ 546
385 Head of a male and of a female Anopheles. (After Giles) 549
386 Head of a male and of a female Culex. (After Giles) 549
387 Mouth-parts of _Anopheles claviger_. (After Grassi) 550
388 _Anopheles maculipennis._ (After Nuttall and Shipley) 550
389 Longitudinal section of an Anopheles, showing alimentary
canal. (After Grassi) 551
390 _Anopheles maculipennis_, Meigen. (After Grassi) 552
391 Larva of _Anopheles maculipennis_, Fabr. (After Grassi) 553
392 Larva of Culex. (After Grassi) 553
393 Pupa of _Anopheles maculipennis_, Meig. (After Grassi) 554
394 Heads of Culex and Anopheles. (After Daniels) 556
395 Eggs of Culex, of Anopheles, of Stegomyia, of Tæniorhynchus,
and of Psorophora 557
396 Diagram showing the structure of a typical mosquito.
(Theobald) 558
397 Types of scales, head and scutellar ornamentation, forms of
clypeus. (Theobald, etc., etc.) 559
398 Neuration of wing. Explanation of wing veins and cells.
(Theobald) 560
399 Wing of _Anopheles maculipennis_, Meigen 566
400 Wing of a Culex 575
401 Wing of Simulium 579
402 Wing of Chironomus 579
403 A Ceratopogon, or midge 580
404 An owl midge, _Phlebotomus_ sp. (From Giles’s “Gnats or
Mosquitoes”) 581
405 Larva of _Homalomyia canicularis_ 585
406 Larvæ of _Calliphora vomitoria_ 585
407 Larva of _Chrysomyia macellaria_. (After Conil) 585
408 The screw-worm fly (_Chrysomyia macellaria_) 587
409 Ochromyia larva on the skin of man, South Africa.
(After Blanchard) 590
410 Head end of “larva of Natal.” (After Gedoelst) 591
411 Lund’s larva. (After Gedoelst) 593
412 _Dermatobia noxialis_, Goudot 597
413 Larva of _Dermatobia cyaniventris_. (After Blanchard) 597
414 Larva of _Dermatobia cyaniventris_. (After Blanchard) 597
415 The ox gad fly (_Tabanus bovinus_, Linn.) 601
416 The brimp (_Hæmatopota pluvialis_, Linn.) 602
417 Head of _Glossina longipalpis_. (After Grünberg) 604
418 Antenna of _Glossina pallidipes_, male. (After Austen) 604
419 _Glossina palpalis_ and puparium. (After Brumpt) 607
420 The tsetse-fly (_Glossina morsitans_, Westwood) 608
421 The stinging fly (_Stomoxys calcitrans_, Linn.) 609
422 _Trichomonas_ from cæcum and gut of rat. (Original, Fantham) 735
423 _Chilomastix_ (_Tetramitus_) _mesnili._ (Original, Fantham) 736
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ERRATA.
P. 31, line 6 from bottom: _delete_ “human,” as Leidy really worked
with _Endamœba blattæ_, parasitic in the gut of the cockroach.
P. 43, line 12 from bottom: _for_ “John’s” _read_ “Johns.”
P. 44, line 13 from bottom: _for_ “_Amœba buccalis_, Sternberg,” _read_
“_Amœba buccalis_, Steinberg.”
P. 46, line 13 from top: _for_ “breath” _read_ “breadth.”
P. 53, In footnote ^1, line 6 from bottom: _insert_ “see” before _Arch.
f. Protistenk_.
P. 75: To paragraph regarding development of the parasite in the fly’s
salivary glands, _add_ that the crithidial phase takes two to five
days.
P. 111, line 8 from top: the date of Sangiorgi should be 1911.
P. 142, line 7 from top: _insert_ “Genus.” before *Eimeria*.
P. 252, _Insert_ heading “Family. *Opisthorchiidæ*, Braun, 1901,”
_above_ “Sub-family. *Opisthorchiinæ*, Looss, 1899.”
P. 351, description of fig. 255, line 3: _for_ “Thoma” _read_ “Thomas.”
P. 471, line 15 from bottom: _for_ “alcohol 100 parts” _read_ “alcohol
100 c.c.”
P. 472, line 11 from bottom: _for_ “Or (2) 10 _per cent. formalin_,”
_read_ “Or (2) _fix in hot_ 10 _per cent. formalin_.”
P. 493, line 21 from top: _for_ “Conoy” _read_ “Couvy.”
P. 589, line 2 from top: _for_ “*carnosa*” _read_ “*carnaria*.”
P. 620, line 15 from top: _for_ “fo” _read_ “of.”
P. 622, line 12 from bottom: _delete_ comma after quantity.
P. 626, line 6 from bottom: _delete_ comma after Mackie (1915).
P. 638: _insert_ title “*TREMATODES*” above that of “Fascioliasis.”
P. 709, line 9 from bottom: _omit_ second Pediculus capitis.
P. 748, line 8 from top: _for_ “cytologica” _read_ “cytological.”
P. 753, line 4 from bottom: _for_ “*Fercocercous*” _read_
“*Furcocercous*.”
P. 755 line 7: _for_ “*Oncocerca*” _read_ “*Onchocerca*.”
ON PARASITES IN GENERAL.
By the term PARASITES is understood living organisms which, for
the purpose of procuring food, take up their abode, temporarily or
permanently, on or within other living organisms. There are both plants
and animals (Phytoparasites and Zoöparasites) which lead a parasitic
life in or upon other plants and other animals.
Phytoparasites are not included in the following descriptions of the
forms of parasitism, but a very large number of animal parasites
(zoöparasites) are described. The number of the latter, as a rule, is
very much underrated. How great a number of animal parasites exists
may be gathered from the fact that all classes of animals are subject
to them. Some of the larger groups, such as _Sporozoa_, _Cestoda_,
_Trematoda_ and _Acanthocephala_, consist entirely of parasitic
species, and parasitism even occurs among the vertebrates (_Myxine_).
It therefore follows that the characteristics of parasites lie, not in
their structure, but in the manner of their existence.
Parasitism itself occurs in various ways and degrees. According to
R. Leuckart, we should distinguish between OCCASIONAL (temporary)
and PERMANENT (stationary) PARASITISM. Occasional parasites, such as
the flea (_Pulex irritans_), the bed-bug (_Cimex lectularius_), the
leech (_Hirudo medicinalis_), and others, only seek their “host” to
obtain nourishment and find shelter while thus occupied. Without being
bound to the host, they usually abandon the latter soon after the
attainment of their object (_Cimex, Hirudo_), or they may remain on
the body of their host throughout their entire development from the
hatching of the egg (_Pediculus_). It follows from this mode of living
that the occasional parasites become sometimes distinguishable from
their free-living relatives, though only to a slight extent. It is,
therefore, seldom difficult to determine the systematic position of
temporary parasites from their structure.
In consequence of their mode of life, all these temporary parasites
live on the external surface of the body of their host, though more
rarely they take up their abode in cavities easily accessible from
the exterior, such as the mouth, nose and gills. They are therefore
frequently called EPIZOA or ECTOPARASITES; but these designations do
not cover only the temporary parasites, because numerous epizoa (as for
instance the louse) are parasitic during their entire life.
In contradistinction to these temporary parasites, the permanent
parasites obtain shelter as well as food from their host for a long
period, sometimes during the entire course of their life. They do not
seek their host only when requiring nourishment, but always remain with
it, thus acquiring substantial protection. The permanent parasites,
as a rule, live within the internal organs, preferably in those which
are easily accessible from the exterior, such as the intestine, with
its appendages. Nevertheless, permanent parasites are also found in
separate organs and systems, such as the muscular and vascular systems,
hollow bones and brain, while some live on the outer skin. Here again,
the terms ENTOZOA and ENDOPARASITES do not include all stationary
parasites; to the latter, for instance, the lice belong, which pass
all their life on the surface of the body of their host, where they
find shelter and food and go through their entire development. The
ectoparasitic trematodes, numerous insects, crustacea, and other
animals live in the same manner.
All “HELMINTHES,” however, belong to the group of permanent parasites.
This term is now applied to designate certain lowly worms which lead
a parasitic life (intestinal worms); but they are not all so termed.
For instance, the few parasitic TURBELLARIA are never classed with
the helminthes, although closely related to them. The turbellarians,
in fact, belong to a group of animals of which only a few members are
parasitic, whereas the helminthes comprise those groups of worms of
which all species (_Cestoda_, _Trematoda_, _Acanthocephala_), or at
least the majority of species (_Nematoda_), are parasitic. Formerly the
Linguatulidæ (_Pentastoma_) were classed with the helminthes because
their existence is also endoparasitic, and because the shape of their
body exhibits a great similarity to that of the true helminthes. Since
the study of the development of the Linguatulidæ (P. J. van Beneden,
1848, and R. Leuckart, 1858) has demonstrated that they are really
degenerate arachnoids, they have been separated from the helminthes.
It is hardly necessary to emphasize the fact that the helminthes or
intestinal worms do not represent a systematic group of animals, but
only a biological one, and that the helminthes can only be discussed
in the same sense as land and water animals are mentioned, _i.e._,
without conveying the idea of a classification in such a grouping. It
is true that formerly this was universally done, but very soon the
error of such a classification was recognized. Still, until the middle
of last century, the helminthes were regarded as a systematic group,
although C. E. v. Baer (1827) and F. S. Leuckart (1827) strenuously
opposed this view. Under the active leadership of J. A. E. Goeze,
J. G. H. Zeder, J. G. Bremser, K. A. Rudolphi and F. Dujardin, the
knowledge of the helminthes (helminthology) developed into a special
study, but unfortunately it lost all connection with zoology. It
required the intervention of Carl Vogt to disestablish the helminthes
as one class of animals, by uniting the various groups with those of
the free-living animals most closely related to them (_Platyhelminthes,
Nemathelminthes_).
PERMANENT PARASITISM in the course of time has caused animals adopting
this mode of life to undergo considerable, sometimes even striking,
bodily changes, permanent ectoparasites having as yet undergone least
alteration. The latter sometimes bear so unmistakably the likeness to
the group to which they belong, that even a superficial knowledge of
their structure and appearance often suffices for the recognition of
their systematic position. For instance, though the louse, like many
decidedly temporary parasites, has lost its wings--a characteristic of
insects--in consequence of parasitism, yet nobody would deny its insect
nature; such also occurs in other temporary parasites (_Cimex, Pulex_).
On the other hand, the changes in a number of permanent ectoparasites
(such as parasitic Crustacea) are far more considerable, and correspond
with those that have occurred in permanent endoparasites.
These alterations depend partly on retrogression and partly on the
acquisition of new peculiarities. In the former case, the change
consists in the loss of those organs which have become useless in a
permanent parasitic condition of existence, such as wings in the louse,
and the articulated extremities seen in the larval stage of parasitic
Crustacea. The loss of these organs goes hand in hand with the cohesion
of segments of the body that were originally separate, and alterations
in the muscular and nervous systems. In the same manner another means
of locomotion is lost--the ciliated coat--which is possessed by many
permanent parasites during their larval period. To all appearances,
this character is not secondary and recently acquired, but represents
a primary character inherited from free-living progenitors, and still
transmitted to the altered descendants, because of its use during
the larval stage (_e.g._, the larvæ of a great many Trematodes, the
oncospheres of some Cestodes). Amongst the retrogressions, the loss of
the organs of sense may be mentioned, particularly the eyes, which are
still present, not only in the nearest free-living forms but also in
the free-living larvæ of true parasites. It is only quite exceptionally
that the eyes are subsequently retained, as a rule they are lost.
Lastly, in a great many cases the digestive system also disappears,
as in parasitic Crustacea, in a few nematodes and trematodes, in all
cestodes and Acanthocephala. There remain at most the rudiments of the
muscles of the fore-gut, but these are adapted to entirely different
uses.
The new characters which permanent parasites may acquire are, first
of all, the remarkably manifold CLASPING and CLINGING ORGANS, which
are seldom (as in parasitic Crustacea) directly joined on to already
existing structures. In those instances in which organs for the
conveyance of food are retained, these likewise frequently undergo
transformation, in consequence of the altered food and manner of
feeding. Such alterations consist, for instance, in the transformation
of a masticating mouth apparatus into the piercing and sucking organs
of parasitic insects.
HERMAPHRODITISM (as in Trematodes, Cestodes, and a few Nematodes)
is a further peculiarity of many permanent parasites; moreover, the
association in couples that occurs, especially in trematodes, may
lead to complete cohesion and, exceptionally, also to re-separation
of the sexes. In many cases the females only are parasitic, while the
males live a free life, or there may be in addition the so-called
complementary males. Occasionally the male alone is parasitic, and in
that case lives within the female of the same species, which may live
free, like certain Gephyrea (_Bonellia_); or the female also may be
parasitic, as _Trichosoma crassicaudum_, which lives in the bladder of
the sewer rat (_Mus decumanus_).
We have numerous proofs that demonstrate how considerably the original
features of many parasites have become changed. We need only draw
attention to the aforementioned Linguatulidæ, also to many of the
parasitic Crustacea belonging to various orders. In all of these a
knowledge of the larval stages--in which there is no alteration, or
at most only a slight degree of change--serves to determine their
systematic position, _i.e._, the nearest conditions of relationship.
The most remarkable changes are observed in those groups that contain
only a few parasitic members, the majority leading a free life. A
striking instance is afforded by a snail, the well-known _Entoconcha
mirabilis_, Müller. This mollusc consists merely of an elongated sac
living in a Holothurian (_Synapta digitata_). It possesses none of
the characteristics of either the Gastropoda or any molluscs, and
in its interior there is nothing to be observed but the organs of
generation and the embryos. Nevertheless, the _Entoconcha_ is decidedly
a parasitic snail, as is clearly proved by its larvæ, but it is a snail
which, in consequence of parasitism, has lost all the characteristics
of molluscs in its mature condition, but still exhibits them in the
early stages of development.
Certain nematodes show very clearly to what devious courses parasitism
may lead. The _Atractonema gibbosum_, the life-history of which has
been described by R. Leuckart, and which lives in the larvæ and pupæ of
a dipterous insect (_Cecidomyia_), exhibits, in its early stage, the
ordinary characteristics of other threadworms. A few weeks later--the
males having died off immediately after copulation--the females are
transformed into spindle-shaped bodies, the mouth and anus of which are
closed. They carry with them an irregularly shaped appendage, in which
the segmenting ova are situated, and in which the further conditions of
life of the _Atractonema_ are accomplished. A minute examination has
demonstrated that this appendage is the prolapsed and enlarged vagina
of the animal which has become merely a supplementary attachment. The
conditions present in the _Sphærularia_, the nematoid nature of which
was long undiscovered, are still more remarkable. It was only when
Siebold proved that typical nematodes were hatched from their eggs that
their nature was recognized. The nematodes thus produced have not the
slightest resemblance to the parent.
The researches of Lubbock, A. Schneider, and more particularly of R.
Leuckart, have shown that what we call _Sphærularia bombi_ is not
an animal but merely an organ--the vagina--of a nematode worm. This
vagina at first grows, sac-like, from the body of the tiny nematode; it
gradually assumes enormous dimensions (2 cm. in length); it contains
the sexual organs and parts of the intestine. The remaining portion of
the actual animal then becomes small and shrivelled; it may be easily
overlooked, being but an appendage to the vagina with its independent
existence, and it finally disappears altogether.
The GREAT FERTILITY of parasites is another of their peculiarities,
though this may be also the case to a certain degree with some of the
free-living animals, the progeny of which are likewise exposed to
enormous destruction.
More remarkable, however, is the fact that the young of the
endoparasites only very exceptionally grow to maturity by the side
of their parents. Sooner or later they leave the organ inhabited by
the parents, frequently reach the open, and after a shorter or longer
period of free existence seek new hosts. During their free period,
moreover, a considerable growth may be attained, or metamorphosis
may take place, or even multiplication. In the exceptional cases in
which the young remain within the same host, they nevertheless usually
quit the organ inhabited by the parents. They likewise rarely attain
maturity within the host inhabited by the parents, but only, as in
other cases, after having gained access to fresh hosts.
These transmigrations play a very important _rôle_ in the natural
history of the internal parasites, but they frequently conceal the
cycle of development, for sometimes there are INTERMEDIATE GENERATIONS,
which themselves invade intermediate hosts. Even when there are
no intermediate generations, THE SYSTEM OF INTERMEDIATE HOSTS is
frequently maintained by the endoparasites.
According to the kind of food ingested by parasites, it has recently
become usual to separate the true parasites from those animals that
feed on the superfluity of the food of the host, or on products which
are no longer necessary to him, and to call the latter MESSMATES or
COMMENSALS. As examples, the Ricinidæ are thus designated, because,
like actual lice, they dwell among the fur of mammals or the plumage
of birds. They do not, however, suck blood, for which their mouth
apparatus is unsuited, but subsist on useless epidermic scales.
These epizoa, according to J. P. van Beneden, are, to a certain
extent, useful to their hosts by removing deciduous materials which
under certain circumstances might become harmful to them.[1] This
investigator, who has contributed so greatly to our knowledge of
parasites, assigns the Ricines to the MUTUALISTS, under which term
he comprises animals of various species which live in common, and
confer certain benefits on one another. The mutualists are usually
intimately connected in a mutually advantageous association known as
“symbiosis.”[2]
[1] According to Sambon, the Ricinidæ are by no means advantageous to
their hosts. These Hemipterous parasites give rise to an intolerable
itching which may cause loss of rest, emaciation, and sometimes even
death. Birds suffering from phthiriasis of the Ricines are usually in
bad health.
[2] For further information on these conditions, see “Die Schmarotzer
des Thierreichs,” by P. J. van Beneden, Leipzig, 1876; and “Die
Symbiose,” by O. Hertwig.
_Incidental and Pseudo Parasites._--In many cases the parasites
are confined to certain hosts, and may therefore be designated as
_specific_ to such hosts. Thus, hitherto, _Tænia solium_ and _Tænia
saginata_ in their adult condition have only been found in man; _Tænia
crassicollis_ only in the cat; _Brandesia_ (_Distoma_) _turgida_ and
_Halipegus_ (_Distoma_) _ovocaudatas_ only in _Rana esculenta_, and so
forth. In many other cases, however, certain species of parasites are
common to several, and sometimes many, species of hosts; _Dipylidium
caninum_ is found in the domestic cat as well as in the dog; _Fasciola
hepatica_ is found in a large number of herbivorous mammals (nineteen
species), _Diplodiscus_ (_Amphistomum_) _subclavatus_ in numerous
urodele and ecaudate amphibia, _Holostomum variabile_ in about
twenty-four species of birds, and so on. In these cases the hosts
are almost invariably closely related, belonging, as a rule, to the
same family or order, or at any rate to the same class. _Trichinella
spiralis_, which is found in man, and in the pig, bear, rat, mouse,
cat, fox, badger, polecat and marten, and is capable of being
artificially cultivated in the dog, rabbit, sheep, horse, in other
mammals, and even in birds, is one of the most striking exceptions.
Some parasites are so strictly confined to one species of host that,
even when artificially introduced into animals very closely related
to their normal host, they do not thrive, but sooner or later, often
very quickly, die off, and very rarely establish themselves. For
example, repeated attempts have been made to rear the adult _Tænia
solium_ in the dog, or to rear _Cysticercus cellulosæ_ in the ox,
or the _Cysticercus_ of _Tænia saginata_ in the pig, but they have
always proved unsuccessful. Only exceptionally has it been possible
to transfer _Cœnurus cerebralis_, the larval stage of a tapeworm
(_Tænia cœnurus_) of the dog from the brain of the sheep to that of
the domestic goat. On the other hand, in the case of the Trichinellæ
transference to a different host is easily accomplished.
Under natural conditions, it is not uncommon for certain kinds of
specific parasites to occur occasionally in unusual hosts. Their
relationship to the latter is that of INCIDENTAL PARASITES. Thus
_Echinorhynchus gigas_, a specific parasite of the pig, is only an
incidental parasite of man; _Fasciola hepatica_ and _Dicrocœlium
lanceatum_ are specific to numerous kinds of mammals, but may be found
incidentally in man. On the other hand, _Dibothriocephalus latus_, a
specific parasite of man, may occasionally take up its abode in the
dog, cat and fox. As a rule, all those parasites of man that are only
rarely met with, notwithstanding that human beings are constantly being
observed and examined by medical men, are termed INCIDENTAL PARASITES
OF MAN. In many cases we are acquainted with the normal or specific
host of these parasites. Thus we know the specific host of _Balantidium
coli_, _Eimeria stiedæ_, _Fasciola hepatica_, _Dipylidium caninum_,
etc.; in others the host is as yet unknown. In the latter case the
question partly relates to such forms as have been so deficiently
described that their recognition is impossible, partly to parasites
of man in various regions of the earth, the Helminthes and parasites
of which are totally unknown or only slightly known, or finally to
early developmental stages that are difficult to identify. Animals
that usually live free, and exceptionally become parasitic, may
likewise be called incidental parasites. In this category are included
a few _Anguillulidæ_ that have been observed in man; also _Leptodera
appendiculata_, which usually lives free, but may occasionally become
parasitic in black slugs (_Arion empiricorum_): when parasitic it
attains a larger size, and produces far more eggs than when living a
free life. In order to avoid errors, the term “incidental parasites”
should be confined to true parasites which, besides living in their
normal host, may also live in other hosts. Leuckart speaks of
FACULTATIVE PARASITISM in such forms as _Leptodera_. L. Oerley[3]
succeeded in artificially causing _Leptodera_ (_Rhabditis_) _pellio_
to assume facultative parasitism by introducing these worms into the
vagina of mice, where the parasites remained alive and multiplied.
_Leptodera pellio_ dies in the intestines of mammals and man; it
remains alive in frogs, but always escapes into the open with the fæces.
[3] Oerley, L., “Der Rhabditiden und ihre medizinische Bedeutung,”
Berlin, 1886, p. 65.
Recently the incidental parasites of man have also been called
“PSEUDO-PARASITES” or “PSEUDO-HELMINTHES.” Formerly, however, these
terms were applied not only to living organisms that do not and cannot
live parasitically, and that only exceptionally and incidentally get
into man, but also to any foreign bodies, portions of animals and
plants, or even pathological formations that left the human system
through the natural channels, and the true nature of which was
misunderstood. Frequently these bodies were described as living or
dead parasites and labelled with scientific names, as if they were
true parasites. A study of these errors, which formerly occurred very
frequently, would be as interesting as it would be instructive. It
is better not to use the expression pseudo-parasites for incidental
parasites, but to keep to the original meaning, for it is not at all
certain that pseudo-parasites are not described, even nowadays.
_The Influence of Parasites on the Host._--In a great many cases, we
are not in a position to state anything regarding any marked influence
exercised by the parasite on the organism, and on the conditions of
life, of the host. Most animals and many persons exhibit few signs of
such influence, an exception being infestation with helminthes and
certain other parasites which produce eosinophilia in the blood. As a
general rule, the parasite, which is always smaller and weaker than
its host, does not attempt to endanger the life of the latter, as
simultaneously its own existence would be threatened. The parasite,
of course, robs its host, but usually in a scanty and sparing manner,
and the injuries it inflicts can hardly be taken into account. There
are, however, numerous cases[4] in which the situation of the parasites
or the nature of their food, added to their number and movements, may
cause more or less injury, and even threaten the life of the host.
It stands to reason that a _Cysticercus cellulosæ_ situated in the
skin is of but slight importance, whereas one that has penetrated the
eye or the brain must give rise to serious disorders. A cuticular or
intestinal parasite is, as a rule, less harmful than a blood parasite.
A helminth, such as an _Ascaris lumbricoides_ or a tapeworm, that feeds
on the residues of foodstuffs within the intestine, will hardly affect
its host by depriving it of this material. The case is different when
the parasites are very numerous, especially when the heavily infested
host happens to be a young individual needing all it ingests for its
own requirements, and therefore unable to sustain the drain of numerous
intruders in the intestine. Disturbances also set in more rapidly when
the intestinal helminthes are blood-suckers, the injury to the host
resulting from the kind of food taken by the parasite.
[4] Lühe, M., “Ueber d. Fix. d. Helm. a. d. Darmwand ihrer Wirthe u.
die dadurch verursachten path-anat. Veränderungen d. Wirthsdarmes,”
_Trans. of IVth Intern. Zool. Cong._, Berlin, 1901; Mingazzini, P.,
“Ric. sul var. modo di fiss. delle tenie alla par. int. e sul loro
assorbimento,” _Ric. Lab. Anat. Roma e altri Lab. biol._, vol. x,
1904; Shipley, A. E., and E. G. Fearnsides, “The Effects of Metazoan
Parasites on their Hosts,” _Journ. Econ. Biol._, 1906, i, 2.
Generally, the disorders caused by loss of chyle are insignificant
when compared with those induced by the GROWTH and agglomeration of
the helminthes. The latter may cause chiefly obstructions of small
vessels or symptoms of pressure in affected or contiguous organs, with
all those complications which may arise secondarily, or they may even
lead to the complete obliteration of the organ invaded. Of course the
symptoms will vary according to the nature of the organ attacked.
In consequence also of the MOVEMENTS of the parasites, disorders are
set up that may tend to serious pathological changes of the affected
organs. The collective migrations, undertaken chiefly by the embryos
of certain parasites (as in trichinosis, acute cestode tuberculosis),
are still more harmful, as are also the unusual migrations of other
parasites, which, incidentally, may lead to the formation of so-called
worm abscesses or to abnormal communications (fistulæ) between organs
that are contiguous but possess no direct connection.
Recently, several authors have called attention to the fact that the
helminthes produce substances that are TOXIC to their host; and the
effects of such poisons explain the pathology of helminthiasis far more
satisfactorily than the theory of reflex action.
In a number of cases these toxic materials (leucomaines) have been
isolated and their effects on living organisms demonstrated by actual
experiments. It also appears that the absorption of materials formed by
the decomposition of dead helminthes may likewise cause toxic effects.
However, our knowledge of these conditions is as yet in its initial
stage.[5]
[5] Moursson et Schlagdenhauffen, “Nouv. rech. clin. et phys. sur
quelq. liquides organ.,” _C. R. Acad. Sci._, Paris, 1882, p. 791;
Debove, “De l’intox. hydat.,” _Bull. et Mém. Soc. méd. des Hôpit._,
1888; Linstow, v., “Ueb. d. Giftgehalt d. helm.,”_Internat. Monatsschr.
f. Anat. u. Phys._, xiii, 1896; Peiper, “Z. Symptomatol. der thier.
Paras.,” _Deutsche med. Wochenschr._, 1897, No. 40; Mingazzini, P.,
“Ric. sul veleno d. elm. int.,” _Rass. intern. d. med. modern. Ann._,
1901, ii, No. 6; Vaullegeard, A., “Etud. exp. et crit. sur l’action d.
helm.,” _Bull. Soc. Linn. de Normandie_, 1901, 5, Ser. T, vii, p. 84,
and others.
Nearly all the symptoms caused directly or indirectly by parasites are
of such a nature that the presence of the parasites cannot be diagnosed
with any certainty, or only very rarely. The most that can be done is
to deduce the presence of parasites by the exclusion of other causes.
Fortunately, however, there are sufficient means by which we may
confirm the diagnosis in a great many cases. Such means consist not
only in a minute examination of the patient by palpation, percussion
and local inspection, but also in the microscopical examination of
the natural secretions and excretions of the body, such as sputum,
nasal mucus, urine and fæces. Though such examinations may entail
loss of time, they are necessary in the interest of the patient. It
appears, moreover, that quackery, which has gained considerable ground
even in the treatment of the helminthic diseases of man, can thus be
considerably limited.
_Origin of Parasites._[6]--In former times, when the only correct views
that existed related to the origin of the higher animals, the mode
of multiplication of parasites as well as of other lowly animals was
ascribed to SPONTANEOUS GENERATION (_generatio æquivoca_), and this
opinion prevailed throughout the middle ages. The writers on natural
science merely devoted their time to the interpretation of the views
of the old authors, and perpetuated the opinions of the ancients
on questions, which, even in those days, could have been correctly
explained merely by observation.
[6] Die Geschichte der “Klinisch wichtigen Parasiten,” behandelt H.
Vierordt im “Handb. d. Gesch. d. Med. hrsg.” v. M. Neuburger u. J.
Pagel, Bd. ii, 1903.
It was only when observations were again recommenced, and the
microscope was invented, that the idea of spontaneous generation became
limited. Not only did the microscope reveal the organs of generation
or their products (eggs) in numerous animals, but Redi succeeded in
proving that the so-called _Helcophagi_ (flesh maggots) are only
the progeny of flies, and never appear in the flesh of slaughtered
animals when fully developed flies are prevented from approaching and
depositing their eggs on it. Swammerdam likewise knew that the “worms”
living in the caterpillars of butterflies were the larvæ of other
insects (ichneumon flies) which had laid their eggs in their bodies;
he also discovered the ova of lice. The two authors mentioned were,
however, unwilling to see that the experience they had gained regarding
insects applied to the helminthes. Leeuwenhoek also vehemently opposed
the theory of a spontaneous generation, maintaining that, on a basis
of common-sense, eggs, or at all events germs, must exist, even though
they could not be seen.
The use of the microscope also revealed a large number of very small
organisms in the water and moist soil, some of which undoubtedly
resembled helminthes. Considering the wide dissemination of these
minute organisms, it was natural to conjecture that after their almost
unavoidable introduction into the human system they should grow into
helminthes (Boerhave, Hoffmann). Linnæus went even further, for he
traced the descent of the liver-fluke of sheep from a free-living
planaria (_Dendrocœlum lacteum_), the _Oxyuris vermicularis_ from
free-living nematodes, and the _Tænia lata_ (_i.e._, _Dibothriocephalus
latus_) from a tapeworm (_Schistocephalus solidus_) found free in
the water. Linnæus’ statements met with general approval. However,
we must bear in mind that at that time the number of helminthes
known was very small, and many of the forms that we have long ago
learned to differentiate as specific were then regarded as belonging
to one species. Linnæus’ statements were partly supported by similar
discoveries by other investigators, such as Unzer, and partly also
by the discovery of eggs in many helminthes. It was believed that
the eggs hatched in the outside world gave rise to free-living
creatures, and that these, after their introduction into the
intestine, were transformed into helminthes. By means of these eggs
the old investigators tried to explain the HEREDITARY TRANSMISSION
of the intestinal worms, which was universally believed until the
commencement of the last century. Some authors went so far as to regard
the intestinal worms as congenital or inherited; they maintained the
possibility of direct transmission, as in suckling, and denied that
the eggs reaching the external world had anything to do with the
propagation of the parasites.
The more minute comparison between the supposed free-living stages of
the helminthes and their adult forms, and the impossibility of finding
corresponding free forms for the ever-increasing number of parasitic
species, revealed the improbability of Linnæus’ statements (O. Fr.
Müller). It was the latter author also who recognized the origin of the
tapeworms (_Schistocephalus, Ligula_) found free in the water. They
originate from fishes which they quit spontaneously.
However, in spite of the fact that van Doeveren and Pallas correctly
recognized the significance of the eggs in the transmission of
intestinal worms, these statements remained disregarded, as did
Abildgaard’s observation, experimentally confirmed, that the (immature)
cestodes from the abdominal cavity of sticklebacks became mature in the
intestines of aquatic birds. Moreover, at the end of the eighteenth and
the commencement of the nineteenth centuries, after helminthology had
been raised to a special branch of study by the successful results of
the investigations of numerous authors (Goeze, Bloch, Pallas, Müller,
Batsch, Rudolphi, Bremser), many of whom experienced a “divine joy”
in searching the intestines of animals for helminthes, some authors
reverted to _generatio æquivoca_, without, however, entirely denying
the existence of organs of generation and eggs. The fact that a few
nematodes bore living progeny--a fact of which Goeze was already
aware--had no influence on the erroneous opinion, as in such cases
it was considered that the young continued to develop beside the old
forms. There were also many helminthes known that never developed
sexual organs and never produced eggs, and which therefore were
referred to _generatio æquivoca_. People were convinced that the
intestinal mucous membrane or an intestinal villus could transform
itself into a worm, either in a general morbid condition of the body,
or in pathological changes of a more local character. The appearance of
helminthes was even regarded as useful and as a means for the expulsion
of injurious matter.
These views, firmly rooted and supported by such eminent authorities
as Rudolphi and Bremser, could not easily be overthrown. First, a
change took place in the knowledge of the trematodes. In 1773, O. Fr.
Müller discovered _Cercariæ_ living free in water. He regarded them as
independent creatures and gave them the name that is still used at the
present time. Nitzsch, who also minutely studied these organisms and
who recognized the resemblance of the anterior part of their bodies
to a _Fasciola_, did not, however, arrive at a correct conclusion.
He regarded the combination rather as that of a _Fasciola_ with a
_Vibrio_, for which he mistook the characteristic tail of the cercaria.
He also noticed the encystment (transformation into the “pupa”) on
foreign bodies of many species of these animals, but was of opinion
that this process signified only the termination of life.
Considerable attention was attracted to the matter when Bojanus first
published a paper entitled “A Short Note on Cercaria and their Place
of Origin.” He pointed out that the cercariæ creep out of the “royal
yellow worms,” which occur in freshwater snails (_Limnæa, Paludina_),
and are probably generated in these worms.
Oken, in whose journal, _Isis_ (1818, p. 729), Bojanus published his
discovery, remarks in an annotation, “One might lay a wager that these
Cercariæ are the embryos of Distomes.” Soon after (1827), C. E. v.
Baer was able to confirm Bojanus’ hypothesis that the cercariæ as a
“heterogeneous brood” originated from spores in parasitic tubes in
snails (germinating tubes). Moreover, Mehlis (_Isis_, 1831, p. 190)
not only discovered the opercula of the ova of _Distoma_, but likewise
saw the infusorian-like embryo emerge from the eggs of _Typhlocœlum_
(_Monostomum_) _flavum_ and _Cathæmasia_ (_Distoma_) _hians_. A few
years later (1835) v. Siebold observed the embryos (miracidia) of
the _Cyclocœlum_ (_Monostomum_) _mutabile_, and discovered in their
interior a cylindrical body that behaved like an independent being
(“necessary parasite”), and was so similar in appearance to the “royal
yellow worms” (Bojanus) that Siebold considered the origin of the
latter from the embryos of trematodes as, at all events, possible.
Meanwhile, v. Nordmann of Helsingfors had in 1832 seen the miracidia
of flukes provided with eyes swimming in water; v. Siebold (1835)
had observed the embryos, or oncospheres, of tapeworms furnished
with six hooklets in the so-called eggs of the Tænia; while Creplin
(1837) had discovered the “infusorial” young of the _Diphyllobothrium_
(_Bothriocephalus_) _ditremum_, and conjectured that similar embryos
were to be found in other cestodes with operculated eggs. At all
events, the fact was established that the progeny of the helminthes
appeared in various forms and was partly free living. The researches
of Eschricht (1841) were likewise of influence, as they elucidated
the structure of the Bothriocephali, and proved that the encysted and
sexless helminthes were merely immature stages.
J. I. Steenstrup (1842) was, however, the first to furnish explanations
for the numerous isolated and uncomprehended discoveries. Commencing
with the remarkable development of the Cœlenterata, he established the
fact that the Helminthes, especially the endoparasitic trematodes,
multiply by means of alternating and differently formed generations.
Just as the polyp originating from the egg of a medusa represents a
generation of medusæ, so does the germinal tube (“royal yellow worm”)
originating from the ciliated embryo of a Distoma, etc., represent
the cercaria. These were consequently regarded as the progeny of
trematodes, and Steenstrup, guided by his observations, conjectured
that the cercaria, whose entrance into the snails he had observed
accompanied by the simultaneous loss of the propelling tail, finally
penetrated into other animals, in which they became flukes.
Part of this hypothetical cycle of development was erroneous, and
in other particulars positive observation was lacking, but the path
pursued was in the right direction. Immediately after the appearance of
Steenstrup’s celebrated work, v. Siebold expressed his opinion that the
encapsuled flukes certainly had to travel, _i.e._, to be transmitted
with their bearers into other hosts, before becoming mature. This view
was experimentally confirmed by de Filippi, La Valette St. George
(1855), as well as by Pagenstecher (1857), while the metamorphosis of
the ciliated embryo of Distoma into a germinal tube was first seen by
G. Wagener (1857) in _Gorgodera_ (_Distoma_) _cygnoides_ of frogs.
All that we have subsequently learned from the works of numerous
investigators about the development of endoparasitic trematodes has
certainly increased our knowledge in various directions, and, apart
from the deviating development of the _Holostomidæ_ has, as a whole,
confirmed the briefly sketched cycle of development.
Steenstrup’s work on the cestodes did not attract the same attention
as his work on trematodes. Steenstrup always insisted on the “nurse”
nature of the cysticerci and other bladder-worms. Abildgaard (1790), as
well as Creplin (1829 and 1839), had already furnished the information
that certain sexless cestodes (_Schistocephalus_ and _Ligula_) from
the abdomen of fishes only become mature after their transference
to the intestine of aquatic birds. These passive migrations were
confirmed in an entire series of other cestodes, particularly by v.
Siebold (1844, 1848, 1850) and E. J. van Beneden (1849), not by actual
experiment, but by undoubted observation.
It was correctly believed that the ova or oncospheres penetrate into
certain intermediate hosts, in which they develop into unsegmented
larvæ. Here they remain until, with their host, they are swallowed by
some predacious animal. They then reach the intestine, being freed from
the surrounding membranes through the process of digestion, and settle
themselves there to form the adult chain of proglottides. Though some
few scientists, such as P. J. van Beneden and Em. Blanchard, deduced
from these observations that the bladder-worms (Cysticerci), which had
hitherto been regarded as a separate class of helminthes, were only
larval Tæniæ, this correct view was not at first universally accepted.
The foundation was too slight, and van Beneden was of opinion that the
Cysticerci were not necessary, but only appeared incidentally.
v. Siebold was a strenuous opponent to this theory, notwithstanding
his experiences on the change of hosts of the Tetrarhynchus. Together
with Dujardin (1850) he conjectured that the Tæniæ underwent a
deviating cycle of development. He was of opinion that the six-hooked
oncospheres left the intestine, in which the older generation lived,
and were scattered about with the fæces, and finally re-entered _per
os_ (_i.e._, with water and food) a host similar to the one they
had left, in the intestine of which they were directly transformed
into tapeworms. A change of host such as occurred in other cestodes
was not supposed to take place (the history of the cestodes was
at this time not entirely established). As the oncospheres of the
Tænia are enveloped in one calcareous or several softer coverings
which they cannot leave actively, and as, in consequence of this
condition, innumerable oncospheres cannot penetrate into an animal,
and others cannot reach the proper animal, v. Siebold conceded, at
least for the latter, the possibility of a further development. But
this was only supposed to occur because they had either invaded wrong
hosts, or, having reached the right hosts, had penetrated organs
unsuitable to their development, and had thus gone astray in their
travels, and had become hydropically degenerated tæniæ. This was v.
Siebold’s explanation of bladder-worms. Naturally, v. Siebold himself
conjectured that a recovery of the diseased tapeworm might occur, in a
few exceptional cases, after transmission into the correct host, as,
for instance, in the _Cysticercus fasciolaris_ of mice, the host of
which is the domestic cat, and in which there is a seemingly normally
developed piece of tapeworm situated between the caudal vesicle and the
cysticercus head.
Guided by correct views, F. Küchenmeister undertook in Zittau the
task of confirming the metamorphosis of _Cysticercus pisiformis_ of
hares and rabbits, into tapeworms in the intestine of the dog by means
of feeding experiments. The first reports on the subject, published
in 1851, were not likely to meet with universal approval, because
Küchenmeister first diagnosed the actual tapeworm he had been rearing
as _Tænia crassiceps_, afterwards as _Tænia serrata_, and finally as
_Tænia pisiformis_ n. sp. However, in any case, Küchenmeister, by means
of the reintroduction of experimental investigation, rendered a great
service to helminthology.
The publication of Küchenmeister’s works induced v. Siebold to
undertake similar experiments (1852 and 1853), which were partly
published by his pupil Lewald in 1852. But the positive results
obtained hardly changed Siebold’s opinion, for although he no longer
considered the bladder-worms as hydropically degenerated tapeworms, he
still regarded them as tæniæ that had strayed. The change of opinion
was partly due to an important work of the Prague zoologist, v. Stein
(1853). He was able to examine the development of a small bladder-worm
in the larvæ of the well-known meal-worm (_Tenebrio molitor_) and
to demonstrate that, as Goeze had already proved in the case of
_Cysticercus fasciolaris_ of mice, first the caudal vesicle is formed
and then the scolex, whereas Siebold believed that in bladder-worms the
posterior end of the scolex was formed first, and that this posterior
end underwent a secondary hydropic degeneration.
In opposition to v. Siebold, Küchenmeister successfully proved the
necessity of the bladder-worm stage by rearing tapeworms in dogs
from the _Cysticercus tenuicollis_ of domestic mammals and from the
_Cœnurus cerebralis_ of sheep. He, and simultaneously several other
investigators independently, succeeded, with material provided by
Küchenmeister, in rearing the _Cœnurus cerebralis_ in sheep from the
oncospheres of the _Tænia cœnurus_ of the dog (1854). R. Leuckart
obtained similar results in mice by feeding them with the mature
proglottides of the _Tænia crassicollis_ of cats (1854).
Küchenmeister also repeatedly reared the _Tænia solium_ of man from
the _Cysticercus cellulosæ_ of pigs (1855), and from the embryos
of this parasite P. J. van Beneden succeeded in obtaining the same
_Cysticercus_ in the pig (1854). As Küchenmeister distinguished the
_Tænia mediocanellata_, known to Goeze as _Tænia saginata_, amongst
the large tæniæ of man (1851), so it was not long before R. Leuckart
(1862) succeeded in rearing the cysticercus of the hookless tapeworm
in the ox. It is particularly to this last-named investigator that
helminthology is indebted more than to any other author. He followed
the gradual metamorphosis from oncospheres to cystic worms in all its
details.
In view of all the researches that were made, and which are too
numerous to mention individually, the idea that bladder-worms are
abnormal or only incidental forms had to be abandoned. Everything
pointed to the fact that in all cestodes the development is divided
between two kinds of animals; in one--the host, the adult tapeworm is
found; while in the other, the intermediate host, we find some form or
other of an intermediate stage (cysticercus in the broadest sense). The
practical application of this knowledge is self-evident. If no infected
pork or beef is ingested, no tapeworm can be acquired, and also the
rearing of cysticerci in the human body is prevented by avoiding the
introduction of the eggs of tapeworms.
Though these results were definitely proved by numerous researches,
yet they have been repeatedly challenged, notably by J. Knoch (1862)
in Petrograd, who, on the basis of experiments, sought to confirm a
direct development without an intermediate host and ciliated stage,
at all events as regards _Dibothriocephalus latus_. However, the
repeated communications of this author met with but little favour from
competent persons, partly because the experiments were conducted very
carelessly, and partly because their repetition on dog and man (R.
Leuckart) had no results (1863). It was only in 1883 that Braun was
able to prove that the developmental cycle of _Dibothriocephalus latus_
is similar to that of other Cestodes. The results obtained in other
places by Parona, Grassi, Ijima and Zschokke render any discussion of
Küchenmeister’s conclusions unnecessary.[7] Long after Knoch, a French
author, P. Mégnin, also pleaded for the direct development of some
cestodes, and especially some tæniæ. He (1879) also sought to prove a
genetic connection between the hookless and armed tapeworms of mammals,
but the arguments he adduced, so far as they rest on observations,
can be easily refuted or attributed to misinterpretation. Only one of
these arguments is correct, namely, that the number of the species
of tæniæ with which we are acquainted is far larger than that of the
corresponding cystic forms; but this disparity alone cannot be taken as
a proof of direct development. It can only be said that our knowledge
in this respect is deficient. As a matter of fact, we have during
recent years become acquainted with a large number of cystic forms,
hitherto unknown, belonging to tæniæ which have long been familiar. It
must also be borne in mind that no man in his lifetime can complete
an examination for bladder-worms of the large number of insects, for
instance, which may destroy an entire generation of an insectivorous
species of bird within a small district.
[7] Refer to the collected literature under _Dibothriocephalus latus_,
and the reply to Küchenmeister by Braun (“Ueber den Zwischenwirt des
breit. Bandw.” Würzb.: Stuber, 1886).
Naturally it does not follow that direct development in the cestodes
is altogether lacking. The researches of Grassi (1889) have furnished
an example in _Hymenolepis_ (_Tænia_) _murina_, which shows that
development may sometimes take place without an intermediate host,
notwithstanding the retention of the cystic stage. It was found that
the oncospheres of this species, introduced into rats of a certain age,
after a time grow into tapeworms without leaving the intestine, but not
directly, for they bore into the intestinal wall, where they pass the
cystic stage, the cysts afterwards falling into the intestinal lumen,
where they develop into tapeworms. The recent experiments of Nicoll
(1911) show that the larval stages of _Hymenolepis murina_ also occur
in the rat-flea, _Ceratophyllus fasciatus_.
Important observations were soon made on the remaining groups of
helminthes. The discussion on the origin of parasites soon became
confined to the helminthes. Amongst the Nematoda, it had long been
known that encapsuled forms existed that had at first been regarded as
independent species, but very soon they were pronounced to be immature
forms, in consequence of their lack of sexual organs. Though Dujardin
and also v. Siebold regarded them as “strayed” animals, v. Stein (1853)
very promptly demonstrated that the progeny of the nematodes were
destined to travel by discovering a perforating organ in the larval
nematodes of the mealworm. This was first experimentally confirmed
(1860) by R. Leuckart, R. Virchow and Zenker, all of whom succeeded not
only in bringing to maturity the muscle Trichinæ (known since 1830) in
the intestine of the animals experimented upon, but were likewise able
to follow the migrations of the progeny. Of course, the encapsulating
brood remained in the same organism, and in this respect deviated
from the broods of other helminthes which escape into the outer world
and find their way into other animals, but the encapsuled nematodes
could no longer be regarded as the result of straying. Subsequently,
R. Leuckart worked out, more or less completely, the history of the
development of numerous nematodes, or pointed out the way in which
further investigations should be made. It has been found that in
nematodes far more frequently than in other helminthes, the typical
course of development is subject partly to curtailment and partly to
complications, which sometimes considerably increase the difficulties
of investigation and have hitherto prevented the attainment of a
definite conclusion, though the way to it is now clear.
In a similar manner the works of R. Leuckart have cleared up the
development of the _Acanthocephala_ and _Linguatulida_. Of course,
much still remains to be done. So far, we do not even know all the
helminthes of man and of the domestic animals in all their phases
of life, and still less is known of those of other animals. We are
indebted to the discoveries of the last fifty years for the knowledge
arrived at, though comparatively few names are connected with it. The
gross framework is revealed, but the gaps have only been filled up here
and there. However, we may trustfully leave the completion of the whole
to the future, without fear that any essential alterations will take
place.
The deductions to be drawn are as follows: That the helminthes like
the ectoparasites multiply by sexual processes, that the entire course
of development of the helminthes is rarely or never gone through in
the same host as is the case with several ectoparasites, that the
progeny at an earlier or later stage of development, as eggs, embryos,
or larvæ, quit the host inhabited by the older generation, and
almost always attain the outer world: only in _Trichinella_ does the
development take place directly in the definite host. Where the eggs
have not yet developed they go through the embryonic evolution in the
outer world. The young larvæ are transmitted, either still enclosed
within the egg or embryonic covering, to the intermediate host or
more rarely they are transferred straight to the final host. In other
cases they may hatch out from their envelopes, and after a longer or
shorter period of free life, during which they may partake of food
and grow, they, as before, penetrate, usually in an active way, into
an intermediate host, or at once invade the final host. Exceptionally
(_e.g._, _Rhabdonema_), during the free life there may be a propagation
of the parasitic generation, and in this case only the succeeding
generation again becomes parasitic, and then at once reaches its final
host. The young forms which have invaded the final host become mature
in the latter, or after a longer or shorter period of parasitism again
wander forth (as the Œstridæ, Ichneumonidæ, etc.), and reach the adult
stage in the outer world. The young stages, during which the parasites
undergo metamorphoses or are even capable of producing one or several
intermediate generations, are passed in the intermediate hosts until,
as a rule, they are passively carried into the final host and there
complete their cycle of development by the formation of the organs
of generation. This mode of development, the spending of life in two
different kinds of animals (intermediate and final host), is typical of
the helminthes. This is manifested in the Acanthocephala, the Cestoda,
the majority of the endoparasitic Trematoda, a number of the Nematoda,
and the Linguatulidæ. There are now and then exceptions, however,
in which, for instance, the host and intermediate host change order
(_Trichinella_, _Hymenolepis murina_).
Parasites are hardly ever inherited amongst animals.[8] According to a
few statements, however, _Trichinella_ and _Cœnurus_ are supposed to
be transmissible from the infected mother to the fœtus. Otherwise most
animals acquire their parasites, especially the Entozoa, from without,
the parasites penetrating either actively, as in animals living in the
water, or passively with food and drink. A particular predisposition to
worms is not more likely than a spontaneous origin of parasites.
[8] However, in the Protozoa there are examples of hereditary
transmission of parasites, _e.g._, in the case of _Babesia_
(_Piroplasma_) _bovis_ and _Babesia canis_ in their invertebrate hosts
(ticks); in _Crithidia melophagia_ and _Crithidia hyalommæ_; and in the
case of _Spirochæta duttoni_ in its invertebrate host (a tick).
_Derivation of Parasites._--Doubt now no longer exists as to the
derivation of the temporary and of many of the stationary ectoparasites
from free-living forms. This conclusion is founded on the circumstance
that not only are there numerous intermediate degrees in the manner of
living and feeding between predacious and parasitic animals, but that
there is more or less uniformity in their structure. The differences
that exist are easily explained as consequences of altered conditions
of life. The case is more difficult in regard to groups that are
exclusively parasitic (_Cestoda_, _Trematoda_, _Acanthocephala_,
_Linguatulidæ_, and _Sporozoa_), or groups that are chiefly parasitic
(_Nematoda_), because in these cases the gulf that divides these
forms from free-living animals is wider. It is true that we know
that the nearest relatives of the _Linguatulidæ_ are found amongst
the _Arachnoidea_, and indeed in the _Acarina_; that, moreover,
the structure and development of the _Sporozoa_ refers them to the
_Protozoa_, and allows some of them to be regarded as the descendants
of the lowest _Rhizopoda_. We know that the _Trematoda_, and through
these the _Cestoda_, are closely related to the _Turbellaria_,
from which they may be traced. The _Nematoda_, and still more the
_Acanthocephala_, stand apart. This is less evident, however, in the
Nematoda, for there are numerous free-living members of these from
which it is possible that the parasitic species may be descended.
Indeed, this seems more than probable if such examples as _Leptodera_,
_Rhabdonema_ and _Strongyloides_ are taken into consideration, as well
as the conditions of life of free-living nematodes. These mostly, if
not exclusively, spend their lives in places where decomposing organic
substances are present in quantities; some species attain maturity
only in such localities, and there propagate very rapidly. Should the
favourable conditions for feeding be changed, the animals seek out
other localities, or they remain in the larval form for some time until
more favourable conditions set in. It is comprehensible that such forms
are very likely to adopt a parasitic manner of life which at first is
facultative (_Leptodera_, _Anguillula_), but may be regarded as the
transition to true parasitism. The great advantages attached to a
parasitic life consist not only in protection, but also in the supply
of suitable food, and consequently in the easier and greater production
of eggs, and thus fully account for the gradual passage of facultative
parasitism into true parasitism. In many forms the young stages live
free for some time (_Strongylidæ_), in others, as is the case in
_Rhabdonema_, parasitic and free-living generations alternate; in
others, again, the free period is limited to the egg stage or entirely
suppressed.
Though it is possible thus to connect the parasitic with the
free-living nematodes, by taking their manner of life into account,
this matter presents greater difficulties in regard to other
helminthes. It is true that the segmented Cestoda may be connected with
and traced from the less known and interesting single-jointed Cestoda
(_Amphilina_, _Archigetes_, _Caryophyllæus_, _Gyrocotyle_). Trematodes
are all parasites, with the exception of one group, _Temnocephalidæ_,
several genera and species of which live on the surface of the bodies
of Crustacea and turtles of tropical and sub-tropical freshwaters.
_Temnocephalidæ_ are, nevertheless, predacious. They feed on Infusoria,
the larvæ of small insects and Crustacea. So far as is known they do
not nourish themselves on part of the host. They belong to the group
of commensals, or more correctly, to that of the SPACE PARASITES,
which simply dwell with their host and do not even take a portion of
the superfluity of its food. However, space parasitism may still be
regarded as the first stage of commensalism, which is again to be
regarded as a sort of transition to true parasitism.
It is possible that parasitism came about in this way in the
trematodes, in which connection we must first consider the
turbellaria-like ancestors of the trematodes. Much can be said
in favour of such a genetic relationship between turbellaria and
trematodes, and hardly anything against it. It should also be
remembered that amongst the few parasitic turbellaria there are some
that possess clinging discs or suctorial pores, and these are only
differentiated from ectoparasitic trematodes by the possession of a
ciliated integument, which is found only in the larval stages of the
latter.
The Acanthocephala occupy an isolated position. Most authors certainly
regard them as related to the nematodes; in any case, the connection
is not a close one, and the far-reaching alterations which must have
occurred prevent a clear view. Perhaps the free original forms of
Acanthocephala are no longer in existence, but that such must have
existed is a foregone conclusion.
An explanation of the CHANGE OF HOST so frequent in parasites is more
difficult than that of their descent. R. Leuckart is of opinion that
the present intermediate hosts, which belong principally to the lower
animals, were the original hosts of the parasites, and fostered both
their larval and adult stages. It was only in course of time that the
original hosts sank to the position of intermediate hosts, the cause
for this alteration being that the development of parasites, especially
of the helminthes, through further development and differentiation
extended over a larger number of stages. The earlier stages remained
in their original hosts, but the later stages sought out other hosts
(higher animals). To prove this, Leuckart points out that the mature
stages of the helminthes, with but few exceptions, occur only in the
vertebrates which appeared later in the development of the animal
kingdom, while the great majority of intestinal worms of the lower
animals only represent young stages, which require transmission
into a vertebrate animal before they can become mature. The few
helminthes that attain maturity in the lower animals (_Aspidogaster_,
_Archigetes_) are therefore regarded by Leuckart as primitive forms,
and he compares them with the developmental stages of helminthes,
_Aspidogaster_ with rediæ, _Archigetes_ with cysticercoids. He
classes the nematodes that become mature in the invertebrates with
_Anguillulidæ_, _i.e._, with saprophagous nematodes from which the
parasitic species descend.
Leuckart therefore regards the change of hosts as secondary, so does
Sabatier. The latter, however, adduces other reasons for this (lack of
clinging organs and the necessity to develop them in an intermediary
stage); but in this connection he only considers the Cestoda. In
opposition to Leuckart, R. Moniez, however, is convinced that the
migrations of the helminthes, as well as the system of intermediate
hosts, represent the original order of things. Moniez traces all
Entozoa from saprophytes, but only a few of these were able to settle
directly in the intestine and there continue their development. These
are forms that at the present day still lack an intermediate host,
such as _Trichocephalus_, _Ascaris_, and _Oxyuris_. In most other
cases the embryos, however, consisted of such saprophytes as were, in
other respects, suitable to become parasites, but were incapable of
resisting the mechanical and chemical influences of the intestinal
contents. They were therefore obliged to leave the intestine at once,
and accomplished this by penetrating the intestinal walls and burrowing
in the tissues of their carriers. In this position, assisted by the
favourable conditions of nutrition, they could attain a relatively high
degree of development. Mechanical reasons prevented a return to the
intestines, where the eggs could be deposited. Most of them doubtless
died off as parasites, as also their young stages do at present when
they penetrate wrong hosts. Some of them, nevertheless, passively
reached the intestine of beasts of prey. Many were destroyed in the
process of mastication; for a small part, however, there was the
chance of reaching the intestine of a beast of prey undamaged, and
there, having become larger and more capable of resistance, maturity
was attained. By means of this incidental coincidence of various
favourable circumstances, these processes, according to Moniez, have
been established by heredity and have become normal.
This is not the place to express an opinion either for or against the
various hypotheses advanced, but the existence of these diametrically
opposed views alone will show the great difficulty of the question.
Independently, however, it appears more natural to come to the
conclusion that parasitism, as well as change of hosts, were gradual
transitions.
As a conclusion to this introductory chapter, a list of some of the
most important works on the parasitology of man and animals is appended.
LITERATURE.
GOEZE, J. A. E. Versuch einer Naturgeschichte der Eingeweidewürmer
thierischer Körper. Blankenburg, 1782. 4to, 471 pp., with 44 plates.
ZEDER, J. G. H. Erster Nachtrag zur Naturgeschichte der
Eingeweidewürmer. von J. A. E. Goeze. Leipzig, 1800. 4to, with 6
tables.
RUDOLPHI, C. A. Entozoorum sive vermium intestinalium historia
naturalis. I, Amstelod., 1808; ii, 1809. 8vo, with 18 plates.
RUDOLPHI, C. A. Entozoorum synopsis. Berol., 1819. 8vo, with 3 plates.
BREMSER, J. G. Ueber lebende Würmer im lebenden Menschen. Wien, 1819.
8vo, with 4 plates.
BREMSER, J. G. Icones helminthum, systema Rudolphii entozoologicum
illustrantes. Viennae, 1824. Fol. (Paris, 1837).
DUJARDIN, F. Histoire naturelle des helminthes ou vers intestinaux.
Paris, 1845. 8vo, with 12 plates.
DIESING, C. M. Systema helminthum. 2 vols. Vindobonnae, 1850, 1851.
8vo. Supplements by the same author: Revision der Myzhelminthen
(Report of the Session of the Imp. Acad. of Science. Wien,
xxxii, 1858); with addendum (ibid., xxxv, 1859); Revision der
Cephalocotyleen (ibid., xlix, 1864, and xlviii, 1864); Revision der
Nematoden (ibid., xlii, 1861); Supplements (ibid., xliii, 1862).
BENEDEN, P. J. VAN. Mémoire sur les Vers intestinaux. Paris, 1858.
4to, with 12 plates.
KÜCHENMEISTER, F. Die in und an dem Körper des lebenden Menschen
vorkommenden Parasiten. Leipzig, 1855. 8vo, with 14 plates.
LEUCKART, R. Die menschlichen Parasiten und die von ihnen
herrührenden Krankheiten. I, Leipzig, 1863; II, Leipzig, 1876. 8vo.
COBBOLD, T. Sp. Entozoa; an Introduction to the Study of
Helminthology. London, 1864. 8vo. Supplement, London, 1869.
DAVAINE, C. Traité des entozoaires et des maladies vermineuses de
l’homme et des animaux domestiques. 2nd edit. Paris, 1877. 8vo.
LINSTOW, O. V. Compendium der Helminthologie, ein Verzeichniss der
bekannten Helminthen, die frei oder in thierischen Körpern leben,
geordnet nach ihren Wohnthieren, unter Angabe der Organe, in denen
sie gefunden sind, und mit Beifügung der Litteraturquellen. Hanov.,
1878. 8vo. Supplement, including the years 1878–1888, Hanov., 1888.
COBBOLD, T. Sp. Parasites; a Treatise on the Entozoa of Man and
Animals, including some Account of the Entozoa. London, 1879. 8vo.
LEUCKART, R. Die Parasiten des Menschen und die von ihnen
herrührenden Krankheiten. 2nd edit. Leipzig, 1879–1886. The Protozoa,
Cestodes, Trematodes and Hirudinea have hitherto appeared (continued
by Brandes).
BÜTSCHLI, O. Protozoa in Bronn’s Klass. u. Ordn. d. Thierreichs.
Vol. i, Leipzig, 1880–1889. 8vo, with 79 plates.
BRAUN, M. Trematodes in Bronn’s Klass. u. Ordn. d. Thierreichs.
Vol. iv, 1, Leipzig, 1879–1893. 8vo, with 33 tables. (The first
thirteen sheets, comprising the history of the worms up to 1830, were
compiled by H. Pagenstecher.)
ZÜRN, F. A. Die thierischen Parasiten auf und in dem Körper unserer
Haussäugethiere, sowie die durch erstere veranlassten Krankheiten,
deren Behandlung und Verhütung. 2nd edit. Weimar, 1882. 8vo, with 4
plates.
COBBOLD, T. Sp. Human Parasites; a Manual of Reference to all the
Known Species of Entozoa and Ectozoa. London, 1882. 8vo.
KÜCHENMEISTER, F., and F. A. ZÜRN. Die Parasiten des Menschen. 2nd
edit. Leipzig, 1888., 8vo, with 15 plates.
BLANCHARD, R. Traité de zoologie médicale. I, Paris, 1889; II, 1890.
8vo.
NEUMANN, L. G. Traité des maladies parasitaires non microbiennes
des animaux domestiques. 2nd edit. Paris, 1892. 8vo. English edit.,
translated by G. Fleming. 2nd edit., revised by J. Macqueen. 1905.
London: Baillière, Tindall and Cox.
LOOSS, A. Schmarotzerthum in der Thierwelt. Leipzig, 1892. 8vo.
RAILLIET, A. Traité de zoologie médicale et agricole. 2nd edit. I,
Paris, 1895. 8vo.
PARONA, C. L’elmintologia italiana da’ suoi primi tempi all’ anno
1890. Genova, 1894. 8vo.
BRAUN, M. Cestoda in Bronn’s Klass. u. Ordn. d. Thierreichs. Vol. iv,
2, Leipzig, 1894–1900. 8vo, with 24 plates.
MOSLER, F., and E. PEIPER. Thier Parasit. (Spec. Path. u. Ther. v. H.
Nothnagel. Vol. vi.) Wien, 1894. 8vo, with 124 illustrations.
LAVERAN, A., et R. BLANCHARD. Les hématozoaires de l’homme et des
anim. Paris, 1895. 12mo, with 30 figs.
SLUITER, C. R. De dierl. paras. v. d. mensch en van onze huisdier.
Haag, 1895. 8vo.
BLANCHARD, R. Malad. parasit., paras. animaux, paras. végét. à
l’exclus. des bacter. (Traité de pathol. gén. de Ch. Bouchard,
vol. ii.) Paris, 1895. 8vo, with 70 figs.
HUBER, J. CH. Bibliographie der klin. Helminthol. München, 1895.
8vo. With Supplement, 1898, and continued as Bibl. d. klin. Entomol.
München, 1899–1900.
MONIEZ, R. Traité de parasitol. anim. et veget. appl. à la médecine.
Paris, 1896. 8vo, with 116 figs.
WEICHSELBAUM. Parasitologie (Weil’s Handb. d. Hyg.). Jena, 1898. 8vo,
with 78 illustrations.
KRAEMER, A. Die thierischen Schmarotzer des Auges (Gräfe and
Sämische’s Handb. d. ges Augenheilk.). Leipzig, 1899. 8vo, with 16
illustrations.
CHOLODKOWSKY, N. A. Icones helm. hominis. St. Petersburg, 1898–99.
Fol. (atlas with 15 plates).
PERRONCITO, E. I parassiti dell’ uomo e degli animali utili e le più
comuni malattie da essi prodotti. II_{a} ed. Milano 1902. 8^o. con
276 fig. e 25 tav.
STILES, Ch. W. and A. HASSALL. Index Catalogue of Medicine and
Veterinary Zoology. Washington, 1902 (U.S. Dept. of Agric., Bur. of
Anim. Ind., Bull. No. 39).
NEVEU-LEMAIRE, M. Précis de parasitologie humaine, parasites végétaux
et animaux. 4^e édit. Paris, 1911.
HOFER, B. Handbuch der Fischkrankheiten. München, 1904. 8^o. 18 Taf.
222 Abb.
GUIART, J., and L. GRIMBERT. Précis de Diagnostic chimique,
microscopique et parasitologique. Paris, 1906. With 500 figs.
OSTERTAG, R. Handbuch der Fleischbeschau. V. Aufl. mit 265 Abb.
Stuttgart, 1904.
STILES, Ch. W. The International Code of Zoological Nomenclature as
applied to Medicine (Hygienic Lab., Bull. No. 24, Washington, 1905).
STILES, C. W., and HASSALL, A. Trematoda and Trematode Diseases.
(Index Catalogue of Med. and Vet. Zoology.) Hygienic Lab., Bull. No.
37, Washington, 1908.
STILES, C. W., and HASSALL, A. Cestoda and Cestodaria. Hygienic Lab.,
Bull. No. 85, Washington, 1912.
LALOY, L. Parasitisme et mutualisme dans la nature. Paris, 1906. 8vo,
284 pp., 82 figs.
THEOBALD, F. V. A Monograph of the Culicidæ of the World. 5 vols. and
plates. 1901–1910. London: Brit. Museum, Nat. Hist.
JAMES, S. P., and LISTON, W. G. The Anopheline Mosquitoes of India.
2nd edit. 1911. Calcutta: Thacker, Spink and Co.
HOWARD, L. O., DYAR, H. G., and KNAB, F. The Mosquitoes of North
and Central America and the West Indies. 2 vols. 1912. Washington:
Carnegie Institution.
AUSTEN, E. E. African Blood-sucking Flies. 1909. London: Brit.
Museum, Nat. History.
AUSTEN, E. E. A Handbook of Tsetse-flies. 1911. London: Brit. Museum,
Nat. History.
CASTELLANI, A., and CHALMERS, A. J. Manual of Tropical Medicine. 2nd
edit. 1,747 pp. 1913. London: Baillière, Tindall and Cox.
KOLLE and WASSERMANN. Handbuch der pathogenen mikroorganismen. Jena:
Gustav Fischer.
MINCHIN, E. A. An Introduction to the Study of the Protozoa. 1912.
London: Arnold.
LAVERAN, A., et MESNIL, F. Trypanosomes et Trypanosomiases. 2nd edit.
1912. Paris: Masson and Co.
DOFLEIN, F. Lehrbuch der Protozoenkunde. 3rd edit. 1911. Jena: Gustav
Fischer.
NUTTALL, G. H. F., WARBURTON, C., COOPER, W. F., and ROBINSON, L. E.
Ticks--a Monograph of the Ixodoidea. Pt. I (1908). Pt. II. (1911).
University Press, Cambridge, England.
BRUMPT, E. Précis de Parasitologie. 2nd edit. 1913. Paris: Masson and
Co.
PATTON, W. S., and CRAGG, F. W. A Text-book of Medical Entomology.
1913. Christian Literature Society of India: London, Madras, and
Calcutta.
JOURNALS.
For current researches the following, among others, should be
consulted:--
_Annals of Tropical Medicine and Parasitology_, Liverpool.
_Annales de l’Institut Pasteur_, Paris.
_Archives de Parasitologie_, Paris.
_Archives de Zoologie Expérimentale et Générale_, Paris.
_Archiv für Protistenkunde_, Jena.
_Archiv für Schiffs- und Tropen-Hygiene_, Leipzig.
_Bulletin of Entomological Research_, London.
_Bulletin de l’Institut Pasteur_, Paris.
_Bulletin de la Société de Pathologie Exotique_, Paris.
_Bulletins of the Bureau of Animal Industry_, Washington.
_Centralblatt für Bakteriologie und Parasitenkunde_, Jena.
_Compt. Rend. Acad. Sci._, Paris.
_Compt. Rend. Soc. Biol._, Paris.
_Indian Journal of Medical Research_, Calcutta.
_Journal of Experimental Medicine_, New York.
_Journal of Medical Research_, Boston.
_Memorias do Instituto Oswaldo Cruz_, Rio de Janeiro.
_Parasitology_, Cambridge.
_Proceedings of the Royal Society_, London.
_Quarterly Journal of Microscopical Science_, London.
_Review of Applied Entomology_, London.
_Tropical Diseases Bulletin_ (London: Tropical Diseases Bureau).
_Zeitschrift für Infektionskrankheiten_, Berlin.
THE ANIMAL PARASITES OF MAN.
Man is one of those organisms in on on which a whole host of
parasites find conditions suitable for their existence: Protozoa,
Platyhelminthes, Nematoda, Acanthocephala, Hirudinea, and a large
number of Arthropoda (Arachnida as well as Insects) all include
members which are parasites of man. These animals either live on
the external surface of the body or within the intestine and its
appendages. Other organs and systems are not quite free from foreign
organisms--we are acquainted with parasites in the skeletal system,
in the circulatory system, in the brain, in the muscles, in the
excretory and genital organs, and even in the organs of sense.
It is possible, and perhaps might be advantageous, to arrange and
describe the parasites of man according to the situations in which
they are found (parasites of the skin, intestinal parasites, etc.).
Their description in the various stages of development would,
however, be disturbed when, as is generally the case, the different
stages are passed in different organs, and a work which treats more
fully of the natural history of the parasites than of the local
disorders to which they give rise would suffer thereby. It is,
therefore, preferable to describe the parasites of man in their
systematic order, and to mention their different situations in man in
describing each species.
A. *PROTOZOA*,
BY
H. B. FANTHAM, M.A., D.Sc.
All those animal organisms which throughout their entire life never
rise above the unicellular stage, or merely form simple, loose
colonies of similar unicellular animals, are grouped under the term
_Protozoa_ (Goldfuss, 1820), as the simplest types of animal life.
All the vital functions of these, the lowest forms of animals, are
carried out by their body substance, the protoplasm (sarcode). Often
particular parts possess special functions, but the limits of a cell
are never over-stepped thereby. These special parts of the cell are
called “cell-organs”; recently they have been termed “organellæ.”
The living protoplasm has the appearance of a finely granular, viscid
substance which, as a rule, when not surrounded by dense investing
membranes or skeletons, exhibits a distinct kind of movement, which
has been termed amœboid. According to the species, processes of
different forms and varying numbers called pseudopodia are protruded
and withdrawn, and with their assistance these tiny organisms glide
along--it might almost be said flow along--over the surface. In most
Protozoa two layers of cytoplasm may be recognised, and distinguished
by their appearance and structure, namely, the superficially
situated, viscid, and quite hyaline ectosarc or ectoplasm, and the
more fluid and always granular endosarc or endoplasm, which is
entirely enveloped by the ectoplasm. The two layers have different
functions; the movements originate from the ectoplasm, which also
undoubtedly fulfils the functions of breathing, introduction of food
and excretion. The endoplasm, which in some forms (Radiolaria) is
separated from the ectoplasm by a membrane, undertakes the digestion
of the food. To this distribution of functions between the various
layers of cytoplasm is due the development of particular cellular
organs, such as the appearance of cilia, flagella, suctorial tubules
(in the Suctoria) and the myophan striations, which are contractile
parts of the ectoplasm in Infusoria and Gregarines. In many cases
(Flagellata, Ciliata), an area is differentiated for the ingestion of
food (oral part, cytostome) to which there is often added a straight
or curved opening (cytopharynx), through which the food reaches the
endoplasm. The indigestible residue is either cast off through the
oral part or excreted by a special anal part (cytopyge). In rare
cases, structures sensitive to light, the so-called pigment or eye
spots are developed, _e.g._, _Euglena_. In the case of Infusoria
the endoplasm circulates slowly, and agglomerations of fluids (food
vacuoles) sometimes appear around each bolus of food; in these
vacuoles the food is digested under the action of certain materials
(ferments). Even in the lowliest Protozoa fluids to be excreted are,
as a rule, gathered into one, or, more rarely, several contractile
vacuoles, which regularly discharge their contents. This action,
however, is to a certain extent governed by the temperature of the
surrounding medium. In some Infusoria a tube-like channel in the
cytoplasm is joined to the contractile vacuole which usually occupies
a certain position; this forms a sort of excretory duct, and there
are also supply-canals leading to these organellæ.
Very frequently various substances are deposited in the endoplasm,
such as fatty granules, drops of oil, pigment granules, bubbles of
gas or crystals. More solid skeletal substances are secreted in or
on the ectoplasm. To the latter belong the cuticle of the Sporozoa
and Infusoria, the chalky shells containing one or several chambers
of the Foraminifera, the siliceous and very ornamental framework
of the Radiolaria, and the chitinous coat of many Flagellata,
Infusoria, etc. Some forms make use of foreign bodies found in their
surroundings, such as grains of sand, to construct their protective
coverings.
The food often consists of small animal or vegetable organisms and of
organic waste; it is usually introduced _in toto_ into the endoplasm.
On the other hand, the Suctoria extract nourishment from their prey
by means of their tentacles. Many parasitic species also ingest solid
food, others feed by endosmosis.
In all cases one nucleus at least is present. It is true that the
existence of non-nucleated Protozoa, the so-called _Monera_, is
still insisted upon, but some of these have already proved to be
nucleated, and the presence of nuclei in the others will no doubt be
established. Very often the number of nuclei increases considerably,
but these multinucleate stages are always preceded by uninucleate
stages. In the Infusoria, in addition to the larger or principal
nucleus (macronucleus) there is usually a smaller reproductive
nucleus (micronucleus). This dualism of the nuclear apparatus is
considered by some to be general, and usually to appear first at the
onset of reproduction.
The form and structure of the nucleus vary greatly in different
species. There are elongate, kidney-shaped, or even branched nuclei
as well as spherical or oval ones. In addition to vesicular nuclei
with a distinct karyosome and incidentally also with a nuclear
membrane, homogeneous and more solid formations are frequently
encountered. The nuclei are always differentiated from the protoplasm
by their reactions, particularly in regard to certain stains.
In many Protozoa an extra-nuclear mass, sometimes compact, sometimes
diffuse, arises from or near the nucleus. This mass, whose staining
reactions resemble those of the nucleus, is termed the chromidial
apparatus. On the dualistic hypothesis, two varieties of chromidia
occur, one originating from the vegetative nucleus (macronucleus),
being chromidia in the restricted sense, the other derived from the
reproductive or micronucleus being termed sporetia. Chromidia consist
of altered (? katabolic) nuclear material.
The nucleus plays the same part in the life of the single celled
organisms as it does in the cells of the Metazoa and Metaphyta. It
appears to influence in a certain manner all, or at least most,
of the processes of life, such as motility, regeneration, growth,
and generally also digestion. Its principal influence, however, is
exercised in the propagation of the cells, as this is always brought
about by the nucleus.
The PROPAGATION of the Protozoa is effected either by division or by
means of direct budding. In division, which is preceded by direct
or indirect (mitotic) division of the nucleus, the body separates
into two, several, or even a great many segments. In this process
the entire substance of the body is involved, or a small residual
fragment may be left, which does not undergo further division
and finally perishes. In the budding method of multiplication a
large number of buds are formed, either on the surface or in the
interior of the organism. Where divisions or buddings follow one
another rapidly, without the segments separating immediately after
their production, numerous forms develop, which are often unlike
the parental forms, and these are termed swarm spores or spores.
Divisions imperfectly accomplished lead to the formation of protozoal
colonies.
Sometimes encystment[9] takes place previous to division.
Frequently, also, sexual processes appear, such as the union of
two similar (isogamous) or dissimilar (anisogamous) individuals.
In the latter case sexual dimorphism occurs, with the formation of
males (microgametes) and of females (macrogametes). The union may
be permanent (copulation), the process being comparable with the
fertilisation of the ovum by a spermatozoon. On the other hand,
attachment may be transient (conjugation) when, after the exchange
of portions of the nucleus, the couple separate, to multiply
independently of each other. Sometimes there is an ALTERNATION OF
GENERATIONS, as there may be several methods of propagation combined
in the same species, either direct multiplication, conjugation, or
copulation being practised; the different generations may thus, in
certain cases, be unlike morphologically.
[9] Independently of propagation, many protozoa protect themselves from
death by encystment when the water in which they are living dries up;
in this condition the wind may carry them over wide tracts of land.
Protozoa inhabit salt water as well as fresh water; they are also
found on land in very damp places, and invade animals as parasites.
CLASSIFICATION OF THE PROTOZOA.
_Class I._--*Sarcodina* (_Rhizopoda_). Protozoa, the body substance
of which forms pseudopodia; many of them are capable of developing
chitinous, chalky, or siliceous coverings or skeletal structures,
which, however, permit the protrusion of the pseudopodia either over
the entire periphery or at certain points. They possess one nucleus
or several.
_Order 1._--_Amœbina_ (Lobosa) naked or with a simple shell,
sometimes formed of a foreign substance; the pseudopodia may be
lobose or finger-shaped; there may be a contractile vacuole;
generally only one nucleus. They live in fresh or salt water, in
the soil, and also parasitically.
_Order 2._--_Foraminifera_ (Reticularia). Mostly provided with
a calcareous shell, usually consisting of several chambers,
and allowing the protrusion of the pseudopodia either at the
periphery or only at the opening. The pseudopodia are filamentous
and frequently anastomosed; there is no contractile vacuole;
there are usually several nuclei. Mostly marine.
_Order 3._--_Heliozoa._ Naked, or with a chitinous or simple
radial siliceous skeleton; the pseudopodia are filamentous,
and are frequently supported by firmer axes, which exhibit no
tendency to anastomosis; there is a contractile vacuole; one or
several nuclei. Live in fresh water.
_Order 4._--_Radiolaria_. The body has radially-disposed
filamentous pseudopodia, and the nucleus is hidden in the central
capsule; there is almost always a siliceous framework, consisting
of pieces arranged radially, tangentially, or lattice-like; there
is no contractile vacuole, but fluid-containing hydrostatic
vacuoles are present in the peripheral protoplasm. Marine.
_Class II._--*Mastigophora* (_Flagellata_). Protozoa with one or
several long flagella used for locomotion and for acquiring food; in
stationary forms their only function is to take in food. Cytostome and
contractile vacuole may be present. May be either naked or provided
with protective coverings; one or more nuclei. They live either in
fresh or salt water, or may be parasitic.
This class is again divided into several sub-classes and orders, of
which only the Euflagellata, with the Protomonadina and Polymastigoda
are of interest here.
_Class III._--*Sporozoa.* Protozoa that only live parasitically in the
cells, tissues, or organs of other animals. They ingest liquid food
by osmosis; the surface of the body is covered with an ectoplasmic
layer, or cuticle; they have no cilia in the adult state, but may
form pseudopodia. Flagella occur, but only on the male propagating
individuals. There may be one or numerous nuclei, but no contractile
vacuole. Propagation by means of spores, mostly provided with
sporocysts, is characteristic.
_Sub-class_ 1.--*Telosporidia.* These are usually of constant form,
rarely amœboid; they are uninucleate in the mature state; they live
within host cells in the first stage. Spore-formation occurs at the
end of the life-cycle.
_Order 1._--_Gregarinida._ Body of a constant, usually elongate
form, surrounded by a cuticle. In the early stage they lead an
intracellular existence; in the mature stage they live within the
intestine or body cavity of invertebrate animals, especially the
Arthropoda, and, like intestinal parasites, are provided with
clinging organs. Copulation usually isogamous; the spores have
coats (chlamydospores) and usually contain several minute germs
(sporozoites).
_Order 2._--_Coccidiidea._ Body of uniform spherical or oval
shape: they lead an intracellular life, but are not freely motile
in cavities of the body. Fertilization is anisogamous; the spores
have coats or shells (sporocysts), and usually contain several
sporozoites. Exhibit alternation of generations.
_Order 3._--_Hæmosporidia._ Parasites of the blood corpuscles of
vertebrate animals; they exhibit amœboid movement; fertilization
is anisogamous; many present alternation of generations and hosts;
spores naked.
_Sub-class 2._--*Neosporidia.* They are multinucleate when adult,
and the form of the body varies exceedingly (often amœboid);
spore-formation commences before the completion of growth.
_Order 1._--_Myxosporidia._ The spores have valvular coats,
with or without caudal appendages, with two, rarely four, polar
capsules. They live free in such organs as the gall or urinary
bladder, but are chiefly found in connective tissue. They occur
especially in fishes.
_Order 2._--_Microsporidia._ Spores with coats or sporocysts; no
caudal appendage, with one polar capsule. They usually live in
the tissues of Arthropoda.
_Order 3._--_Sarcosporidia._ Elongate parasites of the muscular
fibres of amniotic vertebrates, on rare occasions they occur
also in the connective tissue; the spores, which are kidney or
sickle-shaped, are naked and apparently have no obvious polar
capsule.
_Order 4._--_Haplosporidia._ Simple organisms, forming simple
spores; they occur in Rotifers, Polychætes, Fish and Man.
_Class IV._--*Infusoria* (_Ciliata_). The body is generally uniform
in shape, with cilia and contractile vacuole, frequently also with
cytostome; usually has macro- and micro-nucleus; live free in water
and also parasitically.
The orders _Holotricha_, _Heterotricha_, _Oligotricha_, _Hypotricha_
and _Peritricha_ are classified according to the arrangement of the
cilia.
_Class V._--*Suctoria.* Bodies with suctorial tubes, contractile
vacuoles, macro- and micro-nucleus, no cytostome. They generally
invade aquatic animals as cavity parasites, yet also attack plants;
early stage ciliated. Live sometimes as parasites on Infusoria. [The
Suctoria are frequently regarded as a sub-class of the Infusoria.]
The Protozoa and Protophyta are sometimes united under the term
_Protista_ (Haeckel, 1866). The Spirochætes are Protists (see
pp. 114–128).
Class I. *SARCODINA*, Bütschli, 1882.
Order. *Amœbina*, Ehrenberg.
A. *Human Intestinal Amœbæ.*
The first record of the occurrence of amœba-like organisms in the
human intestine, that is, in intestinal evacuations, was that of
Lambl (1859); nevertheless, the case was not quite conclusive,
as the occurrence of testaceous amœbæ of fresh water (_Arcella_,
_Difflugia_) was also reported. In 1870 Lewis found amœbæ associated
with disorders of the large intestine in patients in Calcutta. A year
later Cunningham reported from the same locality that he had observed
on eighteen occasions, in one hundred examinations of dejecta from
cholera patients, colourless bodies with amœboid movements, which
became encysted and multiplied by fission. The daughter forms were
said to be capable of dividing again, but they might also remain
in contact. Contractile vacuoles were not noticed. The same bodies
were observed also in simple diarrhœa (twenty-eight cases out of one
hundred.)
[Illustration: FIG. 1.--_Amœba coli_, Lösch, in the intestinal mucus.
(After Lösch.)]
The case reported by Lösch in 1875 attracted more attention. It was
that of a peasant, aged 24, who came from the province of Archangel.
He was admitted into Eichwald’s clinic at Petrograd with symptoms
of dysentery. In the discharges containing blood and pus, Lösch
found amœbæ in large numbers. When at rest these amœbæ measured from
20 µ to 35 µ; in a state of movement their length might extend up
to 60 µ (fig. 1). The pseudopodia appeared only singly, and, since
they were hyaline (ectoplasmic), were thus distinguished from the
markedly granular endoplasm that enclosed a spherical nucleus of from
5 µ to 7 µ in diameter. One or more non-contractile vacuoles were
present. Quinine enemata had the effect of making the amœbæ disappear
from the fæces and thus causing the diarrhœa to abate. Four months
after admission the patient died from the results of intercurrent
pneumonia. At the autopsy ulceration of the large intestine was
found, especially in the lower parts. Lösch connected the amœbæ with
the ulcerations by experiments made on four dogs by injecting them
with recently passed stools (_per os et anum_). Eight days after the
last injection numerous amœbæ were found in the fæces of one of these
dogs; eighteen days after the injection the animal was killed. The
mucosa of the rectum was inflamed, covered with blood-stained mucus
and ulcerated in three places. Numbers of amœbæ were found both in
the pus of the ulcers and in the mucus. The three other dogs remained
healthy. From these observations Lösch concluded that the species of
amœba described by him as _Amœba coli_ could not be regarded as the
primary cause of the disease, but that it was certainly capable of
increasing a lesion of the large intestine already present, or at
least of preventing its healing.
B. Grassi (1879) found in the stools of healthy as well as in those
of diarrhœic patients from various localities in Northern Italy,
amœbæ similar to those discovered by Lösch. As this was of frequent
occurrence, the pathogenicity could not be definitely established.
Normand, formerly naval surgeon at Hong-Kong, observed numerous amœbæ
in the dejecta of two patients suffering from colitis.
Many further investigations, which cannot be quoted in detail, showed
not only that intestinal amœbæ were widely distributed in man, but
indicated with greater certainty their rôle as agents of dysentery.
The Commission sent out by the German Government in the year 1883
to investigate cholera in India and Egypt--whose members discovered
the cholera bacillus--also collected information with regard to
dysentery. In five cases of dysentery examined _post mortem_ at
Alexandria, with the exception of one case in which ulceration of the
colon had already cicatrized or was approaching cicatrization, R.
Koch found amœbæ as well as bacteria in sections from the base of the
ulcers, although such had previously escaped notice in examination of
the dejecta. Encouraged by these results, Kartulis (1885), who had
discovered amœba-like bodies in the stools of patients suffering from
intestinal complaints at Alexandria, continued his investigations.
The results, obtained from more than 500 cases, gave rise to the
theory that typical dysentery was caused by amœbæ as were also the
liver-abscesses that often accompany it. Kartulis supported his
theory not only by the regular occurrence of amœbæ in the stools
of dysenteric patients and their absence in other diseases, and by
the occurrence of the parasites in ulcers of the large intestine
and in the pus from liver-abscesses, but also by experiments which
he performed on cats. These were infected by injection _per anum_
of stool material rich in amœbæ from subjects of dysentery. The
infection took place also when amœba-containing, but bacteria-free,
pus from liver-abscesses was used. It has been objected that the
infection of man with _Amœba coli_, as the dysenteric amœbæ were then
generally designated, does not take place _per anum_ but _per os_.
This difficulty, however, diminished in proportion as the encysted
states of amœbæ (fig. 2), long known in the case of other Protozoa,
became understood. The infection of man (Calandruccio, 1890) and of
cats (Quincke and Roos) succeeded solely when material containing
such stages was used. Amœbæ introduced into the intestine multiply
there by fission (Harris, 1894). However, this theory, to which
various other authors gave support on the grounds of their own
observations, encountered opposition. Thus it was established that
amœbæ were not found in patients in every place where dysentery was
endemic, or else they were much rarer than was expected. Further,
amœbæ were present in the most varied kinds of intestinal diseases,
both of infective and non-infective characters. Also they were
present in quite healthy persons.
Moreover, for various reasons, infection experiments on animals
failed to supply proof, and finally a bacterium was discovered
(Shiga, 1898) to be the excitant of one form of dysentery.
Agglutination attested the specific part played by this organism,
as it was produced by the blood serum of a person suffering from
or recovered from dysentery, but not by the serum of one who was
uninfected. Bacillary dysentery consequently was a distinct entity.
The final step to be taken was to decide whether there was a specific
amœbic enteritis (amœbic dysentery or amœbiasis, according to
Musgrave).
[Illustration: FIG. 2.--Encysted intestinal amœbæ showing nuclear
multiplication. (After B. Grassi.)]
This question should decidedly be regarded from the positive point
of view. It is intimately connected with another, namely, whether
there are not several species of intestinal amœbæ. The possibility
of this had already been recognized. In addition to the _Amœba coli_
Lösch, R. Blanchard distinguished yet another, _Amœba intestinalis_,
and designated thereby the large amœbæ described in the first
communication made by Kartulis; later on he stated the distinction
between the species. Councilman and Lafleur[10] (1891) considered
the amœba of dysentery to be _Amœba coli_ Lösch and so re-named the
species _Amœba dysenteriæ_. Kruse and Pasquale (1893) employed the
same nomenclature, but retained the old name _Amœba coli_ Lösch for
the non-infectious species. Quincke and Roos (1893) set forth three
species: a smaller species (25 µ) finely granular, pathogenic for
men and cats (_Amœba coli_ Lösch); a larger species (40 µ) coarsely
granular, pathogenic for men but not for cats (_A. coli mitis_); and
a similar species non-pathogenic either for man or cat (_A. intestini
vulgaris_). Celli and Fiocca (1894–6) went still further, they
distinguished:
(1) _Amœba lobosa_ variety _guttula_ (= _A. guttula_ Duj), variety
_oblonga_ (= _A. oblonga_ Schm.) and variety _coli_ (= _A. coli_
Lösch).
(2) _Amœba spinosa_ n. sp. occurring in the vagina as well as in the
intestine of human patients suffering from diarrhœa and dysentery.
(3) _Amœba diaphana_ n. sp. found in the human intestine in cases of
dysentery.
(4) _Amœba vermicularis_ Weisse, present in the vagina and in
dysentery; and
(5) _Amœba reticularis_ n. sp. in dysentery.
[10] “Amœbic Dysentery,” _Johns Hopkins Hosp. Repts._, ii, pp. 395–548,
7 plates.
Shiga distinguished two species; a larger pathogenic species with
a somewhat active movement, and a small harmless species with a
somewhat sluggish movement. Bowman mentions two varieties, Strong
and Musgrave (1900) two species--the pathogenic _Amœba dysenteriæ_
and the non-pathogenic _Amœba coli_; Jäger (1902) and Jürgens (1902)
mention at least two species. In the following year (1903) a work
by Schaudinn was published which marked a real advance. This, in
conjunction with the establishing of a special genus (_Endamœba_ or
_Entamœba_) for human intestinal amœbæ first by Leidy[11] and then by
Casagrandi and Barbagallo,[12] for the time cleared up the confused
nomenclature, the old name _Amœba coli_ being retained for the
harmless intestinal amœbæ of man, whereas the pathogenic species was
designated _Entamœba histolytica_. The history of more recent work is
incorporated in the accounts of the entamœbæ given below.
[11] “On _Amœba blattae_,” _Proc. Acad. Nat. Sci._, Philadelphia
(1879), xxxi, p. 204.
[12] “_Entamœba hominis_ s. _Amœba coli_ (Lösch).” _Annali d’Igiene
speriment._ (1897), vii, p. 103. See also further remarks on p. 34.
*Entamœba coli*, Lösch, 1875, emend. Schaudinn, 1903.
Syn.: _Amœba coli_, Lösch, 1875. _Entamœba hominis_, Casagr. et Barbag.
1897.
The amœboid trophozoite, according to Lösch, measures 26 µ to 30 µ and
upwards; according to Grassi 8 µ to 22 µ; according to Schuberg 12 µ to
26 µ. A separation of the body substance into ectoplasm and endoplasm
is only perceived during movement. The pseudopodia, which are generally
only protruded singly, are broad and rounded at the end (lobopodia) and
are hyaline, while the remainder of the body is granular. The ectoplasm
is less refractile than the rest of the cytoplasm; it also stains less
intensely (fig. 1), and is best seen on protrusion of a pseudopodium.
Red blood corpuscles are rarely, if ever, found ingested in the
cytoplasm.
[Illustration: FIG. 3.--_Entamœba coli_: life-cycle, _a_-_e_, stages
in binary fission; _A_-_D_, schizogony, with formation of eight
merozoites; 2–10, cyst formation or sporogony, with formation of eight
nucleate cysts. (After Castellani and Chalmers)]
The nucleus is vesicular, and is spherical when inactive, measuring
5 µ to 7 µ, with a thick nuclear membrane. In the centre of the
nucleus is a chromatinic body or karyosome or sometimes several small
nuclear bodies formed of plastin and chromatin; the remaining chromatin
is arranged on the achromatic network in the form of fine granules,
especially thickly deposited on the nuclear membrane.
_Entamœba coli_ lives as a commensal in the upper portion of the
large intestine, where the fæces still possess a pulpy consistency.
With their concentration and change in reaction lower in the bowel,
the parasites either die or else if they are at a suitable stage of
development form resistant cysts. These cysts (fig. 2) can be found
in great abundance in normal fæces, as Grassi first observed. Slight
laxantia or intestinal diseases of any kind producing increased
peristalsis, however, show amœbæ even in the unencysted condition,
provided that the person harbours intestinal amœbæ generally. The
intensity of infection varies according to the locality; thus Schaudinn
found that 50 per cent. of the persons examined were infected with
harmless amœbæ in East Prussia, 20 per cent. in Berlin and about 66 per
cent. on the Austrian littoral.
The life-history (fig. 3) of the parasite exhibits two phases: (_a_)
asexual multiplication in the intestine, either by binary fission or
by schizogony with formation of eight merozoites, and (_b_) sporogony
leading to the production of eight-nucleate cysts. Infection results
from ingestion of cysts. Only cysts with eight nuclei are infective.
The diameter of such cysts is about 15 µ to 20 µ.
There are varying accounts of the details of the life-cycle of
_Entamœba coli_ in its different stages. Thus, regarding schizogony
or multiple fission it was formerly stated that the nucleus of the
parent amœba divided into eight portions, which after dissolution
of the nuclear membrane, passed outwards into the cytoplasm, which
segregated around each. Eight merozoites were thus produced. More
recently the process of schizogony has been considered to consist
in the repeated division of the nucleus into two, four, and finally
eight nuclei (fig. 3, A-D), and the formation of eight merozoites or
amœbulæ.
The process of encystment is initiated by the extrusion of all liquid
and foreign bodies from the protoplasm, which assumes a spherical
form (fig. 4, A). The rounded uninucleate amœba then secretes a soft
gelatinous coat, which finally differentiates into a double contoured
cyst wall in older cysts. According to Casagrandi and Barbagallo,
the size of the cyst varies from 8 µ to 30 µ, and averages about
15 µ. According to Schaudinn (1903) the cytological changes during
cyst formation are as follows. The nucleus of a rounded uninucleate
form divides into two (fig. 4, B). Each of these nuclei fragments
into chromidia (fig. 4, C), some of which are absorbed, while
others reunite so that the cell becomes binucleate again. Each of
these nuclei, by a twice repeated division, produces three nuclei
(fig. 4, D), the smaller two of which degenerate and were regarded as
reduction nuclei. There is a clear zone or vacuole in the middle of
the cyst during these maturation processes, dividing the cyst into
two halves. After the nuclear reduction the clear space disappears,
and each nucleus (termed by some a gamete nucleus) divides into
two pronuclei (fig. 4, E). The pronuclei of the pairs were said by
Schaudinn to differ slightly. Copulation occurs between pairs of
unlike pronuclei, and is an example of autogamy (fig. 4, F). When
complete, each of the fusion nuclei (synkarya) divides twice, giving
rise first to four and finally to eight nuclei. Eight amœbulæ are
thus formed within the cyst.
According to Hartmann and Whitmore (1911)[13], however, autogamy
does not occur within the cysts of _E. coli._ They consider that
eight small amœbulæ are formed (fig. 3, _2_-_10_) which escape from
the cyst and then conjugate in pairs (fig. 3, _10_-_12_), afterwards
growing into a new generation of trophozoites.
[13] _Archiv f. Protistenkunde_, xxiv, p. 182.
Only some 10 to 20 per cent. of the cysts evacuated with the
fæces undergo the full course of development, the majority perish
previously. In old dry fæces, only cysts with eight nuclei are found,
and it is these alone that cause the infection.
_Entamœba williamsi_, _E. bütschlii_, _E. hartmanni_ and _E. poleki_
(Prowazek) are probably only varieties of _E. coli_.
[Illustration: FIG. 4.--So-called autogamy of _Entamœba coli_. A,
rounded amœba; B, nucleus dividing; C, the two daughter-nuclei giving
off chromidia; D, each nucleus has formed two reduction nuclei; E,
cyst membrane formed, and gamete nuclei are dividing; F, cyst with two
synkarya.]
The principal feature distinguishing _Entamœba coli_ from _E.
histolytica_ is the formation of eight-nucleate cysts by the former as
contrasted with the tetra-nucleate cysts of the latter. The cyst-wall
of _E. coli_ is thicker than that of _E. histolytica_ (_tetragena_).
Further, _E. coli_ does not usually ingest red blood corpuscles, nor
are “chromidial blocks” present inside its cyst (see p. 40).
According to Chatton and Lalung-Bonnaire[14] (1912) the entamœbæ of
vertebrates should be placed in a separate genus _Löschia_, as they
differ in their life-history from _E. blattæ_, the type species of
_Entamœba_. Leidy (1879), however, named the genus _Endamœba_, but
further researches are necessary on biological variation among these
organisms.
[14] _Bull. Soc. Path. Exotique_, v, p. 135.
*Entamœba histolytica*, Schaudinn, 1903.
Syn.: _Amœba coli_, autt. p. p. _Amœba dysenteriæ_, autt. p. p.
The average size of the amœboid trophozoite is 25 µ to 30 µ. In fæces
diluted with salt solution the amœbæ swell to 40 µ and more. There is
sometimes separation of the body substance into a strongly refractile
vitreous ectoplasm and a corneous endoplasm, pronounced even in
repose, although the former is not equally thick at all parts of the
periphery. In the endoplasm generally there are numerous foreign bodies
(bacteria, epithelial cells, colourless and red blood corpuscles
(fig. 6), and occasionally living flagellates of the intestine). The
nucleus is 4 µ to 6 µ in diameter, and may be difficult to recognize
because it is sometimes weakly refractile and poor in chromatin. Its
shape is slightly variable; it is usually excentric, sometimes wholly
peripheral at the limit of the two parts of the body. Vacuoles are not
present in quite fresh specimens, but appear later. In the study of
_E. histolytica_, the morphological characters of the trophozoite or
vegetative stage of the organism formerly separated as _E. tetragena_
(figs. 5, 6, 8_a_) must be considered (see p. 38).
[Illustration: FIG. 5.--_Entamœba histolytica_ (_tetragena_ form),
showing three successive changes of form due to movement. × 1100.
(After Hartmann.)]
The history of the development of these species, which give rise
to amœbic enteritis as distinguished from bacillary dysentery,
was formerly not so well known as that of _E. coli_. Upon being
introduced into cats (_per anum_) dysenteric amœbæ provoke symptoms
similar to those in man. In the latter, besides metastatic liver
abscesses, abscesses of the lungs, and, according to Kartulis,
cerebral abscesses are occasionally produced. Marchoux (1899) states
that when the disease has lasted for some time liver abscesses are
produced in cats also.
[Illustration: FIG. 6.--_Entamœba histolytica_ which has ingested
many red blood corpuscles. × 1100. (After Hartmann.)]
[Illustration: FIG. 7.--Section through wall of large intestine (of a
man) close under an ulcer caused by _Entamœba histolytica_. A, amœbæ
that have penetrated partly in blood-vessels (Bv), partly in tissue
of submucosa to the muscularis. Magnified. (After Harris.)]
In the large intestine of infected cats the amœbæ creep over the
epithelium, and here and there they force the epithelial cells
apart, as well as removing them or pushing them in front of them;
the amœbæ thus insert themselves into the narrowest fissures. They
penetrate also into the glands through the epithelium, and thence
into the connective tissue of the mucosa. Intestinal and glandular
epithelia perish under the influence of these parasites: the cells
are pushed aside, fall to pieces or are absorbed by the amœbæ. In the
connective tissue of the mucosa the amœbæ migrate further, and often
accumulate above the muscles. Finally they rupture this and force
their way into the submucosa. In cats, apparently, the penetration
is not so great as in men, according to Kruse and Pasquale. During
their migration the parasites also gain access to the lymph-follicles
of the wall of the intestine, which become swollen and commence
to suppurate; follicular abscesses arise and after their rupture
follicular ulcers. The diseased patches in the mucosa are markedly
hyperæmic and numerous hæmorrhages are set up. Roos and Harris state
that the amœbæ also penetrate into the blood-vessels (fig. 7) and
this explains the occurrence of metastatic abscesses.[15] The whole
submucosa is severely swollen at the diseased spot and undergoes
small-celled infiltration in the neighbourhood of the colonies of
amœbæ. From these findings Jürgens (1902) draws the conclusion[16]
which is followed here, that the amœbæ are causative agents of the
enteritis of cats, which disease is well defined, both pathologically
and anatomically. Subsequent researches confirm the experience of
earlier authors; great precautions were taken to exclude errors,
hence, as with Gross and Harris, no exception can be taken to their
results. The inoculation material was derived from soldiers who
suffered from amœbic enteritis in China and who were admitted into
the garrison hospital at Berlin. In order to be independent of the
patients themselves, transmission experiments from cat to cat were
performed, after the first experiments on cats yielded positive
results. This was also effected by rectal feeding as employed by
earlier workers. Such appeared necessary in order to prevent the
evacuation of the inoculation material _per anum_, as well as to
avoid the employment of morphia and ether narcosis. Forty-six cats
were used for the experiments. Ten cats received tested stools
containing motile amœbæ from soldiers suffering from amœbic enteritis
contracted in China. Sixteen other cats received stools from cats
infected by inoculation. All the animals sickened and suffered from
the disease. Five cats received dejecta from human amœbic enteritis
in which, however, no _motile_ amœbæ were present. Thirteen cats
received stools from soldiers who suffered from bacillary dysentery.
None of the latter cats took the complaint and none showed changes
in the large intestine upon sectioning. The injection of various
bacteria, obtained from a stool of amœbic enteritis pathogenic
to cats, remained without result in both the cats employed for
this experiment. Lastly, two cats, which had been kept with those
artificially infected, were taken ill spontaneously and suffered from
the disease. In the opinion of Harris, who ascertained the harmless
nature of bacteria derived from the intestinal flora containing
dysenteric amœbæ, young dogs are capable of being infected.
[15] Lung abscesses generally arise by the bursting of a liver abscess
through the diaphragm into the right lower lobe of the lung, sometimes
also through conveyance of amœbæ by means of the blood-stream (Banting).
[16] These findings were confirmed by Schaudinn by means of
investigations on cats and men. _Cf._ also Alfred Gross, Marchoux,
P. G. Woolley, W. E. Musgrave, H. F. Harris and others.
Within the large intestine an active increase of _Entamœba
histolytica_ must occur. Nevertheless, Jürgens did not definitely
find changes that might be interpreted in this sense. Schaudinn
(1903) observed division and gemmation _in vivo_. Both processes, in
which the nucleus divides by amitosis, can only be distinguished by
the fact that the daughter individuals are similar in binary fission
but dissimilar in gemmation, whether they make their appearance
singly or in greater numbers. Schizogony, resulting in the formation
of eight individuals, which is so characteristic for _Entamœba coli_,
was not observed. (But schizogony, into four merozoites, is now known
to occur. Gemmation processes are apparently degenerative.)
Resistant stages, which serve for transmission to other hosts, are
according to Schaudinn[17] first formed when the diseased portions
commence to heal, or more accurately, the recovery commences when
the vegetative increase of the amœbæ in the intestine discontinues.
The so-called spores of _E. histolytica_ were distinguished very
definitely from those of _E. coli_; they were said to consist of
spheres of only 3 to 7 µ in diameter, which were surrounded by a
double membrane, at first colourless, but becoming a light brownish
yellow colour after a few hours, and possessing a protoplasmic
content containing chromidia. They were said to arise by fragments
of chromatin passing outwards from the nucleus of the amœba into
the surrounding cytoplasm (fig. 9, _a_) and undergoing so marked
an increase that finally the whole cytoplasm became filled with
chromidia. The remainder of the nucleus underwent degeneration and
became extruded. On the surface of the cytoplasm there then arose
small protuberances containing chromidia. These processes had
been observed in the living organisms. They gradually divided and
separated from membranes which later became yellow. The remainder of
the amœba perished. Craig[18] had also seen phases of this process
of development. It must be remarked that, according to recent
researches, these processes of exogenous sporulation are degenerative
in character (see p. 41). The small spores may be fungi. The
“sporulation” processes are only mentioned here as a warning. They
are now only of historic interest. By means of an experiment made on
a cat, Schaudinn ascertained that ingestion of permanent cysts, which
resist desiccation, is the cause of the infection. The animal took
food containing dry fæces with amœba cysts; these fæces came from a
patient suffering from amœbic enteritis in China. On the evening
of the third day the cat evacuated blood-stained mucous fæces which
contained large numbers of typical _Entamœba histolytica_. On the
fourth day after the infection the animal experimented upon died, and
the large intestine showed the changes previously stated.
[17] _Arb. a. d. kaiserl. Gesundheitsamte_, xix, pp, 547–576.
[18] “Life cycle of _Amœba coli_ in Human Body,” _American Medicine_,
1904, vii, p. 299; viii, p. 185.
_E. histolytica_ also is found in the large intestine. This was
originally shown to be the case by Kartulis, and the fact has
recently been confirmed from many quarters. It is also present in
the metastatic abscesses of which it is the cause (_cf._ among other
authors, Rogers, _Brit. Med. Journ._, 1902, ii, No. 2,177, p. 844;
and 1903, i, No. 2,214, p. 1315).
It should lastly be pointed out in this connection that mixed
infections also take place. For instance, in addition to _E.
histolytica_, _E. coli_, and, under certain circumstances,
flagellates may be found together. In the same way _E. coli_ may
come under observation even in bacillary dysentery. On the other
hand, Schaudinn stated that in cases of dysentery endemic in Istria,
_Entamœba coli_, if it had hitherto been present, disappeared, to
return again after recovery from the illness.
[Illustration: FIG. 8.--_Entamœba histolytica_. _a_, trophozoite
(_tetragena_ type) containing red blood corpuscles, × 1,300; _b_ and
_c_, two isolated nuclei showing different appearances of karyosome,
centriole and nuclear membrane, × 2,600. (After Hartmann.)]
(_Entamœba tetragena_, Viereck, 1907.)
This amœba must now be considered to be a part of the lifecycle of
_Entamœba histolytica_, in fact a very important part of that cycle,
especially in its tetranucleate cystic stages.
This organism, the so-called _Entamœba tetragena_, may occur in the
human intestine in cases of amœbic dysentery, especially in mild
or chronic cases. It was discovered by Viereck in 1907 in patients
suffering from dysentery contracted in Africa. Soon afterwards an
independent description was published by Hartmann, who called the amœba
_E. africana_. It was also studied by Bensen and Werner. Recently
(1912–13) much work has been published on this amœba by Darling and
others; in this way its relationship to Schaudinn’s _E. histolytica_
has been made known.
In general morphology it somewhat resembles _Entamœba coli_, and its
discoverer at first mistook it for a variety of that species. According
to Hartmann, a distinct ectoplasm is only clearly visible when a
pseudopodium is protruded (fig. 5). The granular endoplasm may contain
ingested red blood corpuscles (fig. 6). The large, round nucleus is
visible in the fresh state (fig. 8, _a_). So-called chromidial masses
(? crystalloidal substances) may occur in the cytoplasm.
[Illustration: FIG. 9.--_Entamœba histolytica_ (_tetragena_ form).
_a_, emission of chromatin from nucleus; _b_, nuclear division; _c_,
degenerating form with two nuclei; _d_, _e_, _f_, cysts containing
one, two and four nuclei respectively, and showing chromidial blocks.
× 2,000. (After Hartmann.)]
Some investigators, as Hartmann,[19] lay stress on the internal
structure of the nucleus (fig. 8, _b_, _c_), best seen in preparations
fixed wet and stained with iron-hæmatoxylin. The nucleus is limited
by a well-marked nuclear membrane, on the inside of which granules
or nodules of chromatin may occur. There is a karyosome, which, in
successfully stained specimens, shows, at times, a central dot called
a centriole. (The nucleus of _Entamœba coli_ does not contain such a
centriole.) However, the structure of the nucleus varies at different
periods during the life-cycle.
[19] _Arch. f. Protistenkunde_ (1911), xxiv, p. 163.
The diameter of the trophozoites or vegetative forms (fig. 8, _a_) is
variously given as from 20 µ to 40 µ. Multiplication proceeds by binary
fission and also by schizogony into four merozoites.[20]
[20] _See_ Darling, 1913, _Arch. Intern. Med._, vol. ii, pl. i, fig. 3.
Reproduction takes place by endogenous encystment (fig. 9, _d_-_f_),
which is preceded by nuclear division into two, reduction and then
autogamy. The interpretation of the latter phenomenon as autogamy is
disputed by some authors. The round cysts, which may measure 12 µ to
15 µ in diameter, contain four nuclei, together with darkly staining
masses of various shapes, the so-called “chromidial blocks” (fig. 9,
_f_). The cyst-wall of _E. histolytica_ (_tetragena_) is thinner than
that of _E. coli_, and the diameter of the cyst is rather less. _E.
histolytica_ has not yet been cultivated.
Infection in man occurs by way of the mouth by the ingestion of
cysts. A patient showing acute symptoms of dysentery is not usually
infective, for he is merely harbouring the large trophozoites, which,
by experiment, have been shown not to be infective to animals (kittens)
when administered by the mouth. The stools of recovered patients
may still contain cysts, and they may thus act as cyst-carriers or
reservoirs of disease by infecting water and soil. The stools of
such cyst-carriers are often solid, and so cysts of _E. histolytica_
(_tetragena_) are easily overlooked. Mathis (1913)[21] points out that
healthy carriers of _E. histolytica_ may be found; 8 per cent. of the
natives of Tonkin examined by him were healthy carriers of cysts.
[21] _Bull. Soc. Med. et Chirurg. Indo-Chine_, iv, p. 474.
In return cases, or prolonged untreated cases of entamœbic dysentery, a
generation of smaller trophozoites is associated with, or replaces the
larger ones. In stools they are frequently refractile and consequently
stain slowly _intra vitam_. These trophozoites are the “smaller,
senile, or pre-cyst generation” of Darling. This pre-cyst generation is
characterized by the presence of blocks of crystalloidal substance in
the cytoplasm, and by the possession of a prominent, densely stainable
karyosome. Darling believes this generation to be the same as that
described by Elmassian as _Entamœba minuta_.[22]
[22] _Centralbl. f. Bakter._, Orig., lii, p. 335.
Walker,[23] Darling,[24] Wenyon[25] and others believe that _Entamœba
histolytica_, which was only seen by Schaudinn in a single case, that
of a Chinaman, is really _E. tetragena_. Darling states that if the
published illustrations of _E. histolytica_ and of _E. tetragena_ are
collected from the literature and compared, it will be seen that the
writers have been calling _E. histolytica_ the large trophozoites seen
in dysenteric stools. These large trophozoites frequently display no
karyosome, but they can be demonstrated as _E. tetragena_ by animal
inoculation, or by the history of the case. On the other hand, the
illustrations of _E. tetragena_ show that the authors have been
dealing with the small generation or reduced forms (“_E. minuta_”),
which are the direct descendants of the large trophozoites. If kittens
are inoculated rectally with dysenteric material containing large
trophozoites, the strain may be carried in successive kittens for
four to six transfers. If, on the other hand, kittens are inoculated
rectally with small trophozoites of the pre-cyst generation, the
transmission cannot be carried through more than one or two kittens.
Wenyon has succeeded in maintaining _E. tetragena_ in kittens for
several generations.
[23] _Philip. Journ. Sc._ (1911), B, vi, p. 259.
[24] _Annals Trop. Med. and Parasitol._ (1913), vii, p. 321.
[25] _Brit. Med. Journ._, Nov. 15, 1913, p. 1287, and _Journ. Lond.
School Trop. Med._, ii, p. 27.
In some of the preparations from the last remove, pathological forms
of the trophozoites may be seen. These show abnormal forms of budding,
especially peripherally, such as have been described by Schaudinn and
by Craig as characteristic of _E. histolytica_. Schaudinn’s small
peripheral, exogenous buds and cysts are thus explained. Craig has
latterly changed his views.
Further, Darling states that _tetragena_ cysts fed by the mouth
to kittens produce bowel lesions in which trophozoites having the
characters of _E. tetragena_, _E. histolytica_ and _E. nipponica_
(Koidzumi) occur.
In view of the work of recent observers, the peculiar exogenous
encystment which Schaudinn made characteristic of _Entamœba
histolytica_ has been shown to be due to degenerative changes in senile
races of the amœba. _E. histolytica_ and _E. tetragena_ are one and the
same species, and its trophozoite is subject to variation. According
to some observers the _histolytica_ type of nucleus--described by
Schaudinn as being poor in chromatin and not easily seen in the
fresh state--occurs frequently in patients with severe symptoms of
dysentery; on the other hand, the _tetragena_ type of nucleus--round
and easily seen in the fresh state--may occur in cases presenting
slight dysenteric symptoms. Intermediate types of nuclei are seen. The
name of this species, the principal pathogenic amœba of man, must then
be _E. histolytica_ by priority. The cystic stages of _E. histolytica_
are those first recorded by Viereck and formerly described as _E.
tetragena_. The geographical distribution of _E. histolytica_ is wide.
*Noc’s Entamœba* (1909).
A species of Entamœba was cultivated by Noc[26] in 1909 from cysts
derived from liver abscesses, from dysenteric stools and from the
water supply of Saigon, Cochin China. He cultivated it in association
with bacteria. It is pathogenic. It has been considered allied to
_E. histolytica_, and shows internal segmentation or schizogony. It
exhibits polymorphism. This amœba has been found by Greig and Wells
(1911) in cases of dysentery in India. It is an important organism and
requires further investigation.
[26] Noc, F. (1909), _Ann. Inst. Pasteur_, xxiii, p. 177.
Certain other Entamœbæ[27] have been described at various times from
the intestinal tract of man. Probably most, if not all, of these are
not good species and in some cases much more information is needed.
[27] See Fantham, H. B. (1911), _Annals Trop. Med. and Parasitol._, v,
p. 111.
_Entamœba tropicalis_ (Lesage, 1908). This parasite is said to be
non-pathogenic, and to occur in the intestine of man in the tropics. It
has a general resemblance to _E. coli_, but forms small cysts (6 µ to
10 µ in diameter). The nucleus of the cyst is said to break up into a
variable number of daughter nuclei, from three to thirteen having been
noted. Lesage states that it is culturable in symbiosis with bacteria.
It is probably a variety of _E. coli_, if not a cultural amœba.
_Entamœba hominis_ (Walker, 1908) has a diameter of 6 µ to 15 µ. A
contractile vacuole is present. Encystment is total, and small cysts
are formed. It is culturable. The original strain, now lost, was
obtained from an autopsy in Boston Hospital. This organism is probably
a cultural amœba.
_Entamœba phagocytoides_ (Gauducheau, 1908). This parasite was
discovered in a case of dysentery at Hanoi, Indo-China. The amœba is
small, 2 µ to 15 µ in diameter. It is active. It ingests bacteria and
red blood corpuscles, while peculiar spirilla-like bodies are found in
its cytoplasm. It multiplies by binary and multiple fission. It can be
cultivated. More recently (1912) the author appears to consider the
amœba to be a stage of a _Trichomonas_, but abandons the view later
(1914). Further researches on this organism are needed.
_Entamœba minuta_ (Elmassian, 1909)[28] was found, in association with
_E. coli_, in a case of chronic dysentery in Paraguay. It resembles
_E. tetragena_ but is smaller, rarely exceeding 14 µ in diameter.
Schizogony occurs, four merozoites being produced. The encystment is
total and endogenous, giving rise to cysts containing four nuclei.
This amœba is considered by Darling and others to be the pre-cyst
trophozoite stage of _E. histolytica_ (_tetragena_).
[28] _Centralbl. f. Bakter._, Orig., lii, p. 335.
_Entamœba nipponica_ (Koidzumi, 1909) was found in the motions of
Japanese suffering from dysentery or from diarrhœa, in the former case
in company with _Entamœba histolytica_. Its diameter is 15 µ to 30 µ.
The endoplasm is phagocytic for red blood corpuscles. The nucleus is
well defined, resembling that of _E. coli_ and of _E. tetragena_.
Multiplication occurs by binary fission and by schizogony. Encystment
is total, but has not been completely followed. Darling and others
consider that this is an abnormal form of _E. histolytica_, while
Akashi (1913) doubts if it is an amœba at all, but rather is to be
regarded as shed epithelial cells.
GENERAL REMARK.--It is now considered by some workers that true
Entamœbæ cannot be cultivated on artificial media. Quite recently
Williams and Calkins (1913)[29] have somewhat doubted this opinion, and
state that certain cultural amœbæ, originally obtained from Musgrave in
Manila, exhibit the various morphological variations associated with
true entamœbæ of the human digestive tract.
[29] _Journ. of Med. Research_, xxix, p. 43.
*Entamœba buccalis*, Prowazek, 1904.
The size varies from 6 µ to 32 µ. Ectoplasm is always present; the
endoplasm contains numerous food-vacuoles. The nucleus is vesicular,
with a greenish tinted membrane which is poor in chromatin. The size
of the nucleus is from 1·5 µ to 4·5 µ. A contractile vacuole is not
visible. The pseudopodium is broad. It was discovered in the mouths of
persons with dental caries at Rovigno and also at Trieste, being most
easily found in dense masses of leucocytes, also among leptothrix and
spirochæte clusters. It can be easily distinguished from leucocytes
by more intense staining with neutral red. Multiplication proceeds by
fission. Transmission may take place through the small spherical cysts.
This species (fig. 10) has since been observed in Berlin, and is also
occasionally found in carcinoma of various regions of the oral cavity.
(Leyden and Löwenthal, 1905).
[Illustration: FIG. 10.--_Entamœba buccalis_, Prow. _a_-_d_, the same
specimen observed during five minutes. × 1,000. _e_, amœba fixed and
stained with iron-hæmatoxylin. × 1,500. (After Leyden and Löwenthal.)]
_Entamœba buccalis_, Prow., is said to be allied to a protozoön which
A. Tietze has found either encysted or free in the lumen of the
orifice of the parotid gland of an infant aged 4 months. The gland had
undergone pathological change, and had therefore been extirpated. The
organisms, which were roundish and three to four times the size of
the normal epithelial cells of the gland, were without a membrane and
possessed a nucleus in which the chromatic substance appeared to be
contained in a karyosome. Bass and John’s[30] (Feb. 1915) and Smith,
Middleton and Barrett (1914) state that _E. buccalis_ is the cause of
pyorrhœa alveolaris.
[30] _Journ. Amer. Med. Assoc._, lxiv, p. 553.
_Entamœba undulans_, Aldo Castellani, 1905.
Under this name a protozoön is described which A. Castellani found in
addition to _Entamœba histolytica_ and _Trichomonas intestinalis_ in
the fæces of an European planter living in Ceylon, who had suffered
from amœbic enteritis and liver abscess. The shape of the body was
roundish or oval, 25 µ to 30 µ in the greatest diameter. It was
without a flagellum, but with an undulating membrane, and capable
of protruding a long pseudopodium from different parts of its body
at short intervals. The nucleus could not always be recognized in
life; it was, however, always demonstrable by staining. One or
two contractile vacuoles were present. The protoplasm was finely
granular, showing no differentiation into ecto- and endo-plasm.
According to Braun, in spite of the author declaring himself
expressly against the flagellate nature of the parasite, such
a nature may be assumed to be tolerably certain in view of the
description and illustration.
It is now considered that _Entamœba undulans_ is a portion of a
flagellate, namely, _Trichomonas_.
*Entamœba kartulisi*, Doflein, 1901.
Doflein gave this name to amœbæ, from 30 µ to 38 µ in diameter, which
Kartulis (1893) found on examining the pus of an abscess in the right
lower jaw of an Arab, aged 43, and in a portion of bone that had been
extracted. The movements of the amœbæ (fig. 11) were more active
than those of “dysenteric amœbæ.” Their coarsely granular cytoplasm
contained blood and pus corpuscles, and a nucleus was generally only
recognizable after staining. Vacuoles were not seen with certainty.
Flexner reported upon a similar case, and Kartulis published five
additional cases. As in these cases dental caries was present the
infection is likely to have proceeded from the oral cavity as a result
of the carious teeth. Craig[31] (1911) considers that this parasite is
probably identical with _Entamœba histolytica_.
[31] “The Parasitic Amœbæ of Man,” Lippincott, Philadelphia.
[Illustration: FIG. 11.--_Entamœba kartulisi_, Dofl., from the pus of
an abscess in the lower jaw, showing different stages of movement.
(After Kartulis.)]
In the literature the following species have been reported as occurring
in the oral cavity of man:--
_Amœba gingivalis_, Gros, 1849. [? identical with _Entamœba buccalis_.]
_Amœba buccalis_, Sternberg, 1862. _Amœba dentalis_, Grassi, 1879.
Far too little, however, is known concerning these to regard them
as definite species, that is, independent organisms; Grassi thinks
it even possible there may have been a confusion in their case with
salivary corpuscles. If they really are amœbæ they are all of them
probably identical with _Entamœba buccalis_.
Genus *Paramœba*, Schaudinn, 1896.
Schaudinn established the genus _Paramœba_ for a marine rhizopod
which multiplied by division, became encysted at the end of its
vegetative life and then segmented into swarm bodies with two
flagella. These multiplied by longitudinal fission, and finally
passed into the condition of Amœbæ. Whether the human parasite
described by C. F. Craig (1906) as *Paramœba hominis.* belonged to
this genus was for a time uncertain. It is now placed in a new genus
Craigia, Calkins, 1912, since it possesses only one flagellum.[32]
[32] See Craig (1913), _Amer. Journ. Trop. Dis. and Prevent. Med._, i,
p. 351.
In the amœbic stage it is 15 µ to 25 µ in diameter; ecto- and
endo-plasm during rest are indistinguishable. The body substance
is granular, with a spherical, sharply contoured nucleus and an
accessory nuclear body. No vacuoles are present, but occasionally the
endoplasm contains red blood corpuscles. The pseudopodia are hyaline,
finger- or lobe-shaped, and are protruded either singly or in twos.
Multiplication is by binary fission and by the formation of spherical
cysts (15 µ to 20 µ in diameter) in which occurs successive division
of the nuclei, ultimately forming ten to twelve roundish bodies
each of which soon develops a flagellum. The flagellate stages have
similarly a spherical shape and attain a diameter of 10 µ to 15 µ.
They also occasionally contain red blood corpuscles and pass either
directly or after longitudinal division into the amœboid phase.
Craig found these Amœbæ and the flagellate stage belonging to them in
six patients in the military hospital at Manila (Philippine Islands),
five of whom were suffering from simple diarrhœa whilst the sixth
exhibited an amœbic enteritis and contained also _Paramœba hominis_,
with _Entamœba histolytica_, Schaudinn. In one of the other cases,
_Trichomonas intestinalis_ was present.
B. *Amœbæ from other Organs.*
*Entamœba pulmonalis*, Artault, 1898.
Artault[33] discovered a few amœboid forms with nucleus and vacuole
in the contents of a lung cavity. In the fresh condition they were
distinguishable from leucocytes by their remarkable capacity of light
refraction. They were also much slower than the latter in staining
with methylene blue or fuchsine. Their movements became more lively
in a strong light. Water and other reagents killed them, and then,
even when stained, they could not be distinguished from leucocytes.
They have also been seen by Brumpt. R. Blanchard found amœbæ which may
belong here in the lungs of sheep. _A. pulmonalis_ is perhaps the same
as _Entamœba buccalis_. Smith and Weidman[34] (1910, 1914) described
an entamœba, _E. mortinatalium_, from the lungs and other organs of
infants in America.
[33] _Arch. de Parasitologie_, i, p. 275.
[34] _Amer. Journ. Trop. Dis. and Prevent. Med._, ii, p. 256.
*Amœba urogenitalis*, Baelz, 1883.
This species was found in masses in the sanguineous urine as well
as in the vagina of a patient in Japan, aged 23. Shortly before the
death of the patient, which was caused by pulmonary tuberculosis,
hæmaturia with severe tenesmus of the bladder had set in. The amœba,
which showed great motility, and had a diameter of about 50 µ when
quiescent, exhibited a granular cytoplasm and a vesicular nucleus.
Baelz is of opinion that these parasites were introduced into the vulva
with the water used for washing the parts, and thence had penetrated
into the bladder and vagina. Doflein places the organism in the genus
_Entamœba_, and it is perhaps identical with _E. histolytica_.
Similar cases are also reported (1892–3) by other authors: Jürgens,
Kartulis, Posner, and Wijnhoff. Jürgens found small mucous cysts,
filled with amœboid bodies, in the bladder of an old woman suffering
from chronic cystitis; they were also found in the vagina. The
amœba observed by Kartulis in the sanguineous urine of a woman,
aged 58, suffering from a tumour of the bladder, measured 12 µ to
20 µ, and exhibited slow movements by protruding short pseudopodia.
The vacuoles and nucleus became visible only after staining with
methylene blue.
Posner’s case related to a man, aged 37, who had hitherto been quite
healthy and had never been out of Berlin. Suddenly, after a rigor,
he passed urine tinged with blood. This contained, besides red and
white blood corpuscles and hyaline and granular casts, large granular
bodies (about 50 µ in length and 28 µ in breadth), which slowly
altered their shape, and contained red blood corpuscles in addition
to other foreign matter. These bodies exhibited one or several nuclei
and some vacuoles. From the course of the disease, which extended
over a year, and during which similar attacks recurred, Posner came
to the conclusion that the amœbæ which had originally invaded the
bladder had penetrated into the pelvis of the kidney, where they
probably had settled in a cyst, and thence induced the repeated
attacks.
Wijnhoff observed four cases of amœburia in Utrecht.
*Amœba miurai*, Ijima, 1898.
[Illustration: FIG. 12.--_Amœba miurai_, Ij. × 500. _a_, fresh; _b_,
after treatment with dilute acetic acid. (After Ijima.)]
Under this term the author describes protoplasmic bodies which Miura,
in Tokyo, found in the serous fluid of a woman, aged 26, who had died
from pleuritis and peritonitis endotheliomatosa. Two days before
death these same forms had also appeared in the hæmorrhagic fæces
of the patient. The bodies were usually spherical or ellipsoidal,
and at one pole carried a small protuberance (fig. 12) beset with
filamentous short “pseudopodia” (really a pseudopodium covered with
cilia). Their size varied between 15 µ and 38 µ. The cytoplasm was
finely granular, and no difference was observable in the ecto- and
endo-plasm, only the villous appendage was clearer. The cytoplasm
contained vacuoles more or less numerous, none of which was
contractile. After the addition of acetic acid one to three nuclei
could be distinguished, 8 µ to 15 µ in size. Actual movements were
not observed. Taking everything into consideration, the independent
nature of these bodies is, to say the least, doubtful, although it
cannot be denied that they possess a certain similarity to the marine
_Amœba fluida_, Grüber or Greeff, and to a few other species. (It
is likely that cells present in serous exudation were mistaken for
amœbæ.)
APPENDIX.
“_Rhizopods in Poliomyelitis acuta._”
In three cases of poliomyelitis acuta which were investigated
by Ellermann, the spinal fluid obtained by puncture of the cord
contained bodies, from 10 µ to 15 µ in size, which had amœboid
movements and exhibited variously shaped pseudopodia in large
numbers. After staining, a usually excentric nucleus, about 1·5 µ in
size, was demonstrated in them.
Order. *Foraminifera*, d’Orbigny.
The order is divided by Max Schultze into Monothalamia and
Polythalamia. Only a few of the former can be considered here.
Sub-Order. *Monothalamia.* (Testaceous Amœbæ).
These forms occur frequently in fresh water, rarely in sea water.
They possess a shell which is either pseudo-chitinous in character,
or consists of foreign particles, or in a few cases is composed of
siliceous lamellæ. There is usually an orifice for the protrusion of
pseudopodia. The only representative of the order of interest here is:--
Genus. *Chlamydophrys*, Cienkowski, 1876.
The genus is based on a form which A. Schneider carefully
investigated and considered to be the _Difflugia enchelys_ of
Ehrenberg. L. Cienkowski rediscovered this same form and created
for it the genus _Chlamydophrys_. We agree with this view, but not
with the renaming of the organism (so common at the time). If the
parasite in dung, _Chlamydophrys stercorea_ Cienk. is identical with
_Difflugia enchelys_ of Ehrenberg, the old specific name should be
retained.
The genus is characterized by the possession of a hyaline,
structureless, slightly flexible shell which is ovoid or reniform.
At the more pointed pole there is an orifice situated terminally
or somewhat laterally, serving for the emergence of the filiform
pseudopodia (fig. 13, _a_). The protoplasm does not entirely fill the
interior of the shell. An equatorial zone bearing excretory granules
divides the shell internally into two almost equal portions. The
anterior portion is rich in vacuoles and serves for the reception
of nutriment and for digestion. The posterior part is vitreous, and
contains the nucleus. One to three contractile vacuoles are situated in
the equatorial zone.
*Chlamydophrys enchelys*, Ehrbg.
Syn.: _Chlamydophrys stercorea_, L. Cienkowski.
This species (fig. 13) is found in the fæces of various animals
(cattle, rabbits, mice, and lizards), and also in quite fresh human
fæces. According to Schaudinn, the parasite occurs so frequently in
the human fæces that it must be considered of wide distribution. The
species must traverse the intestine of man and animals during one stage
of its life cycle, as Schaudinn showed by experiments on himself and
on mice. He infected himself with cysts (fig. 14) by swallowing them,
and evacuated the first _Chlamydophrys_ as early as the following day.
After the evacuation of numerous specimens on one of the following days
the infection ceased.
The nucleus of a living specimen is surrounded by a hyaline, strongly
refractile chromidial mass, arranged in the form of a ring. Chromatin
stains colour it darkly.
_Asexual multiplication_ (fig. 13, _b_), which takes place in fæces,
follows a similar course to that of allied forms (_e.g._, _Euglypha_,
_Centropyxis_). It commences by the cytoplasm issuing from the
orifice of the shell and assuming the shape characteristic of the
mother organism, but in a reverse position. The nucleus then divides
by mitosis, when the daughter nuclei move apart from one another.
The chromidial ring also divides into two portions by a process of
dumb-bell like constriction. The one daughter nucleus remains in the
mother organism, the other moves towards the daughter individual, which
then separates from the parent.
[Illustration: FIG. 13.--_Chlamydophrys enchelys._ _a_, free, motile
form, showing nucleus, equatorial granules, vacuoles and pseudopodia;
_b_, dividing organism. × 760. (After Cienkowski.)]
In this species plasmogamic union of two or more individuals (up
to twenty) is frequently observed. Such colonies may similarly
divide, and in this way monstrosities frequently arise. When drying
of the fæces, or deficiency of food occurs, encystment takes place
apparently spontaneously. The whole body, as stated by Cienkowski,
issues from the shell, assumes a spherical shape (probably with
discharge of water) and becomes surrounded with a thick membrane
(fig. 14). After the addition of water and the escape of the encysted
_Chlamydophrys_, a new shell must be formed. Schaudinn, who has not
given a more detailed description of the process of encystment in
this species, but refers to Cienkowski and to similar observations
made on _Centropyxis_, states of the latter that the encystment takes
place within the shell.
The _sexual multiplication_ is accompanied by shedding of all the
foreign bodies and of the degenerating nucleus. The protoplasm, now
contracting into a sphere, remains behind in the shell with the
chromidial mass. From the latter several new nuclei arise (sexual
nuclei) often eight in number. The cytoplasmic sphere then segregates
into as many spherical portions as there are nuclei present. When
they have assumed an oval form, two flagella develop at one pole
and the flagellispores swarm out of the shell.[35] The biflagellate
swarm-spores, or gametes, copulate in pairs and apparently the
individuals of the pairs of gametes arise from different mother
organisms. The zygote secretes a thick covering which soon becomes
brown and rough. These zygote cysts or resistant spores must now pass
from the intestine of an animal in order to complete their development.
The escape of the cyst contents does not always take place in the
intestine; often it does not occur until after defæcation. These
shell-less individuals (amœbulæ) soon become invested with a shell. But
in the alkaline intestinal contents, shell formation may proceed even
while the organism is in the intestine, and multiplication may take
place.
[35] Schaudinn (1903), _Arb. a. d. Kaiserl. Gesundh._, xix, p. 547.
[Illustration: FIG. 14.--_Chlamydophrys enchelys_, encysted; on the
left the old capsule. × 760. (After Cienkowski.)]
Schaudinn’s further communication was of special interest; it was to
the effect that _Chlamydophrys_ was related to
*Leydenia gemmipara*, Schaudinn, 1896.
In the fluid removed by puncture from two patients suffering from
ascites in the first medical clinic in Berlin, cellular bodies with
spontaneous movement were found, which Leyden and Schaudinn regard as
distinct organisms. They remained alive without the use of the warm
stage for four or five hours, the external temperature being 24° to
25° C. In a quiescent condition they were of a spherical or irregular
polygonal form. Their surface was rarely smooth, being beset with
protuberances and excrescences (fig. 15). The substance of the body
was thickly permeated with light refractile granules with a yellowish
shimmer. The hyaline ectoplasm was rarely seen distinctly. All sizes
from 3 µ to 36 µ in diameter were observed. The movements were rather
sluggish, the ectoplasm in the meantime appearing in the form of one
or several lamellæ, in which also strings of the granular endoplasm
occurred, and frequently protruded over the border of the hyaline
pseudopodia. The tendency for the joining of several individuals by
means of their pseudopodia was so marked that associations ensued
similar to those known in free-living Rhizopoda.
The cytoplasm enclosed blood corpuscles as well as numerous vacuoles,
one of which pulsated slowly about every quarter of an hour. A
vesicular nucleus the diameter of which was about equal to one-fifth of
the body was present.
Multiplication took place by means of division and budding (fig. 15,
_c_), after previous direct division of the nucleus. The buds were
supposed to divide repeatedly soon after their appearance, thus giving
rise to minute forms of 3 µ.
There was a suspicion in both cases that the ascites was associated
with malignant neoplasms in the abdomen, and autopsy confirmed this
view in one case.
[Illustration: FIG. 15.--_Leydenia gemmipara_, Schaud. _a_, in a
quiescent condition, × 1000; _b_, in the act of moving, × 1000; _c_,
from a fixed preparation, showing a bud, × 1500.]
The parasite, which has seldom been observed, has been variously
interpreted; for example, it has been regarded merely as altered tissue
cells. It is now known, from Schaudinn’s researches, that _Leydenia
gemmipara_ is connected with abnormal conditions of _Chlamydophrys_,
occasionally occurring as a commensal in the ascitic fluid. The form is
produced when pathological conditions of the large intestine create an
alkaline reaction of its whole contents. The formation of shells then
often ceases, and these naked _Chlamydophrys_ are enabled to multiply
atypically by division and gemmation. Such stages, which are no longer
capable of a normal development, are the _Leydenia_, as Schaudinn has
demonstrated.
Class II. *MASTIGOPHORA*, Diesing.
Sub-Class. FLAGELLATA, Cohn emend. Bütschli.
During the motile part of their life the Flagellata possess one
or more flagella which serve for locomotion, and in many cases
also for the capture of food. A few groups (_Euglenoidinæ_,
_Choanoflagellata_) have only one flagellum, others two or several
of about equal length (_Isomastigoda_), or of various lengths
(_Monadina_, _Heteromastigoda_, _Dinoflagellata_). The long flagellum
is the principal one; the smaller ones on the same organism are
accessory flagella. The flagella directed backwards, which occur in
the Heteromastigoda and are used for clinging, are termed trailing
flagella or tractella. At the base of the flagellum, which is
almost always at the anterior end, a Choanoflagellate possesses a
cytoplasmic funnel-shaped neck or collar. In the parasitic forms an
undulating membrane is often present.
The body of the Flagellata is usually small, generally elongate and
of unchangeable form. It is frequently covered by a distinct cuticle,
and, in certain groups, by a hard envelope, or it may be more or
less loosely enveloped by a gelatinous or membranous covering. An
ectoplasmic layer is thin and not always obvious. The granular
cytoplasm contains a varying number of vacuoles, one of which may be
contractile, and is generally situated near the area from which the
flagella arise, that is, at the anterior extremity. The cytoplasm,
moreover, contains the nucleus, which is nearly always single; and in
many species there are also yellow, brown, or green chromatophores
of various shapes, such as occur in plants. Some species feed after
the manner of green plants (holophytic), or of plants devoid of
chlorophyll (saprophytic); others, again, ingest solid food, and
for this purpose usually possess a cytostome; the latter, however,
in a few forms is not used for its original function, but is
connected with the contractile vacuole. Many parasitic forms feed
by endosmosis. A few species possess eye-spots with or without
light-refracting bodies.
Variation in the form of the nuclear apparatus occurs. One nucleus
only, which may be compact or vesicular, is known in many species.
This nucleus is situated either centrally or sometimes near the
flagellar end of the body, but its position is subject to variation.
The flagella may arise near the nucleus. Other structures, such as
an axial filament and a rhizoplast, may be present. Some flagellates
are binucleate, the two nuclei--which often differ in size and
shape--being separated from each other. One of these nuclei is the
principal, vegetative or trophic nucleus; the other is an accessory
nucleus, frequently termed the blepharoplast, flagellar or kinetic
nucleus. One or more small basal granules are often present at or
very near the origin of the flagella.
Multiplication is by fission, usually longitudinal, which may occur
in either the free or encysted forms. Division is initiated by that
of the nucleus or nuclei (especially the kinetic nucleus). The
basal granule divides also. Collars and chromatophores, if present,
likewise separate into two. Variation in the method of doubling the
original number of flagella occurs. In most organisms, especially
uniflagellate forms, the flagellum splits lengthwise, after division
of the basal granule, blepharoplast and nucleus. The daughter
flagella may be of the same or different lengths and thicknesses.
Other flagellates at division are said to produce new flagella in the
neighbourhood of the original ones. The daughter organisms in such
cases are provided with one or more parental flagella in addition
to newly formed ones. It has been stated that in certain cases the
parent flagellate retains all its flagella, while new ones arise _ab
initio_ in the cytoplasm of the daughter forms.
Multiplication by longitudinal fission may be interrupted sooner or
later by the production of gametes, which form zygotes, from which
new generations of individuals arise. In many flagellates gamete
formation and sporogony are unknown, and asexual reproduction by
fission alone prevails.
Incomplete division results in the formation of colonies of
individuals. These colonies must not be confused with the aggregation
rosettes of flagellates found among the parasitic Mastigophora.
The individuals of aggregation rosettes are capable of immediate
separation from the rosette at will.
A number of parasitic Flagellata produce non-flagellate stages which
are very resistant to external conditions, the assumption of which
forms serves to protect the organisms during their transference
from one host to another. Such non-flagellate forms possess one
or more nuclei, are usually of an oval or rounded contour, and
are capable of developing into the full flagellate on the return
of more favourable conditions. These forms are often known as the
post-flagellate stage of the organism. When ingested by a new host,
the post-flagellate coat becomes more flexible, and the phase of the
organism which now recommences growth is known as the pre-flagellate
stage; it gradually develops into the typical flagellate organism.
Many Flagellata live free in fresh and salt water. They prefer
stagnant water, rich in organic products of decomposition, such as
puddles, swamps and pools. Those forms developing shells and colonies
are, as a rule, adherent. A number of species are parasitic in man
and animals, living mostly within the intestine or in the blood.
It is usual to classify the Flagellata in four orders:
_Euflagellata_, _Dinoflagellata_, _Choanoflagellata_, and
_Cystoflagellata_, of which only the _Euflagellata_ are of interest
to us. This is a group comprising numerous species, for the further
classification of which the number and position of the flagella are
utilised.
The Euflagellata observed in man belong to the Protomonadina as well
as to the Polymastigina. The former possess either only one or two
similar flagella, or one principal and one or two accessory flagella.
The Polymastigina possess at least three flagella of equal size,
or four to eight of unequal size, inserted at different points. An
undulating membrane may be present in members of both groups.
It must also be pointed out that unicellular organisms with one or
several flagella are not always classified with flagellates, for such
forms occur in Rhizopods as well as temporarily in the lower plants.
In addition, the examination of the flagellates, especially the
parasitic species, is very difficult on account of their diminutive
size and great activity; thus it happens that certain forms cannot
with certainty be included in the group because their description is
insufficient.
Order. *Polymastigina*, Blochmann.
The Polymastigina contains flagellates with three to eight flagella.
Some of the Flagellata parasitic in man belong to the Polymastigina,
and to two or three genera that are easily distinguishable.
Genus. *Trichomonas*, Donné, 1837.
The body is generally pyriform, the anterior part usually rounded,
the posterior part pointed. There are at the anterior extremity three
(? four) equally long flagella that are sometimes matted together.
A blepharoplast (kinetic nucleus) and basal granule are present,
together with a supporting structure known as an axial filament or
axostyle. In addition there is an undulating membrane, bordered by
a trailing flagellum, that commences at the anterior extremity and
proceeds obliquely backwards. The nucleus, which is vesicular, is
situated near the anterior extremity, and behind it are one or more
vacuoles, none of which seems to be contractile. These flagellates
are parasitic in vertebrate animals, and live chiefly in the
intestine.
*Trichomonas vaginalis*, Donné.
The form of the body is very variable, and is elongate, fusiform or
pear-shaped, also amœboid. The length varies between 15 µ and 25 µ,
and the breadth between 7 µ and 12 µ. The posterior extremity is drawn
out to a point and is about half the length of the remainder of the
body. The cuticle is very thin and the body substance finely granular.
At the anterior extremity there are three--some say four[36]--flagella
of equal length which are frequently united together, at least at the
base, and are easily detached.
[36] To explain this discrepancy it is stated that the border of the
undulating membrane can be detached in the form of an independent
flagellum. But Parisi (1910) places such quadriflagellate forms in the
sub-genus _Tetratrichomonas_, _Arch. f. Protistenk._, xix, p. 232.
There is an undulating membrane (fig. 16) which runs spirally across
the body, arising from the place of insertion of the flagella, and
terminating at the base of the caudal process. A cytostome seldom is
recognizable in fresh specimens, but is apparently present. The nucleus
is vesicular, elliptical and situated near the anterior extremity.[37]
[37] According to Marchand, the nucleus is connected with a line,
which becomes visible on addition of acetic acid, terminates at the
posterior extremity, and does not correspond to the line of insertion
of the undulating membrane. This formation probably is the same as the
axostyle in _Trichomonas batrachorum_, Perty. Blochmann (1884) also
mentions two longitudinal rows of granules, which commence at the same
place as the nucleus and converge posteriorly.
Multiplication takes place by division (Marchand). Encysted forms are
almost unknown.
_Trichomonas vaginalis_ lives in the vaginal mucus of women of
various ages, not in normal mucus, but in mucus of acid reaction.
It is found in menstruating females as well as in females who
have passed the menopause. It occurs in pregnant and non-pregnant
women, even in very young girls, provided always that they have a
vaginal catarrh with acid reaction of the secretion. Should the acid
reaction change, as, for instance, during menstruation, the parasites
disappear, as they do likewise on injection of any alkaline fluid
into the vagina. A low temperature (below +15° C.) is also fatal to
the parasites. These flagellates can pass from the vagina through the
urethra into the bladder, and produce severe catarrh, and are not
easily removed.
[Illustration: FIG. 16.--_Trichomonas vaginalis_, Donné. × 2,000
approx. (After Künstler.) Four flagella are represented, but usually
only three are present.]
_T. vaginalis_ appeared to be a parasite specific to the female organs
and not transmissible to man. However, several observations have since
been made that confirm the occurrence of this species in the urethra
of the male. The infection apparently takes place through coitus when
changes are present in the urethral mucous membrane. At any rate, three
cases observed point to this circumstance.
Attempts at experimental transmission to rabbits, guinea-pigs and dogs
failed (Blochmann, Dock). So far, the manner in which women become
infected is unknown.
*Trichomonas intestinalis*, R. Leuckart, 1879 = *Trichomonas hominis*,
Davaine, 1854.
Some authors believe that a second trichomonad inhabiting man,
_Trichomonas intestinalis_, R. Lkt., is identical with _Trichomonas
vaginalis_, Donné. Leuckart’s species was based on the discoveries
of Marchand (1875) and Zunker (1878), who stated that according to
all appearances, and in their opinion, it was the same as _Cercomonas
intestinalis_, Lambl, 1875 (_nec_ 1859), which they found in the fæces
of patients suffering from intestinal disorders. The organism is
described by them as being pear-shaped and 10 µ to 15 µ in length and
3 µ to 4 µ in breadth. The posterior extremity terminated in a point
(fig. 17).
[Illustration: FIG. 17.--_Trichomonas intestinalis_, Lkt. (After
Grassi.)]
A row of twelve or more cilia was said to commence at the anterior
end and extend over the body. Leuckart stated that this parasite,
placed by the two authors in the genus _Cercomonas_, was a
_Trichomonas_, and that they mistook the undulating membrane for
cilia, and overlooked the flagella. Notwithstanding its striking
similarity with _T. vaginalis_, it was said to be distinguishable
from that species by differences in the undulating membrane. Lambl’s
_C. intestinalis_[38] (of 1875) which corresponds with _C. hominis_,
Davaine[39] (1854), is regarded by Leuckart as a true Cercomonad
(characterized by a flagellum and the absence of an undulating
membrane, see p. 61), and is thus generically distinct from
_Trichomonas_.
[38] Under the term _Cercomonas intestinalis_, Lambl in different
years has described two entirely distinct Flagellata, namely, in 1859
(“Mikr. Unters. d. Darm- Excrete,” _Prag. Vierteljahrsschr. f. prakt.
Hlkde._, lxi, p. 51; and Lambl, _A. d. Franz-Josephs-Kinderspitale in
Prag_, Prag, 1860, i, p. 360), a form that at the present day is termed
_Lamblia intestinalis_; and in 1875 (in the _Russian Medical Report_,
No. 33), a species identical with _Cercomonas hominis_, Dav.
[39] Davaine, C., “Sur les anim. infus. trouv. dans les selles d.
malad. atteints du cholera et d’autr. malad.,” _C. R. Soc. Biol._,
1854, ii, p. 129.
The correctness of Leuckart’s judgment in regard to Marchand-Zunker’s
flagellate was demonstrated by Grassi’s researches, accounts of which
were published soon after. In about 100 cases of bowel complaints
in North Italy and Sicily, Grassi found Flagellata in the stools,
which he first named _Monocercomonas_ and _Cimænomonas_, but later
termed _Trichomonas_. However, in opposition to Leuckart, Grassi
has also classified Davaine’s _C. hominis_ (= _C. intestinalis_,
Lambl, 1875) as _Trichomonas_, and most authors have followed his
example. Hence arose the use of the name _Trichomonas hominis_. It
was through Janowski (1896) that the former view was again taken
up. After a review of the literature, the occurrence of Cercomonads
in the intestine of human beings in addition to Trichomonads was
considered by the author to have been proved, and he added a
description of the Trichomonads. According to this, all morphological
distinction between _T. vaginalis_, Donné, and _T. intestinalis_,
Leuckart, disappeared. On the other hand, it is worthy of note
that the smaller size, the more pear-shaped form, and the longer
flagella differentiate _T. intestinalis_ (= _T. hominis_) from _T.
vaginalis_.[40]
[40] For the present the following should be regarded as synonymous:
_Protoryxomyces coprinarius_, Cunningham (_Quart. Journ. Micr. Sci._
(2) 1880, xxi, p. 234), (_Zeitschr. f. Biol._, 1882, viii, p. 251).
_Monocercomonas hominis_, Grassi, 1882. _Cimænomonas hominis_,
Grassi, 1882. _Trichomonas hominis_, Grassi, 1888. _Cercomonas coli
hominis_, May (_Deutsches Archiv. f. klin. med._, 1891, xlix, p. 51).
_Monocercomonas hominis_, Epstein (_Prag. med. Wochenschr._ 1893,
Nos. 38–40). _Trichomonas confusa_, Stiles (_Zool. Anz._, 1902, xxv,
p. 689). _Trichomonas elongata_, _Trichomonas elliptica_, Cohnheim
(_Deutsche med. Wochenschr._, 1903, xxix, Nos. 12–14). _Trichomonas
elongata_, _Trichomonas caudata_, _Trichomonas flagellata_, Steinberg
(_Kiewer Zeitschr. f. neuere Medicin_, 1862). _Trichomonas pulmonalis_,
A. Schmidt, (_Münch. med. Wochenschr._, 1895, No. 51), and St. Artault
(_Arch. de parasit._ 1898, i, p. 279).
The easily deformed pear-shaped body has three free flagella
anteriorly, and an undulating membrane with its flagellar border
terminating in a short free flagellum posteriorly (figs. 17, 18).
The undulating membrane may coil itself spirally round the body. A
supporting rod or axostyle projects as a posterior spine. It appears
to begin near the nucleus and blepharoplast, which are situated near
the more rounded, anterior end of the body. There may be a chromatoid
basal supporting line along the body for the undulating membrane. Rows
of chromatoid granules are sometimes situated along one side of the
axostyle. A cytostome may sometimes be seen. In mice, Wenyon (1907)
found these parasites to vary in length from 3 µ to 20 µ. They occur
in the cæcum and intestine of mice, where their internal structure
seems more obvious than in man. The flagellates divide by longitudinal
fission.
[Illustration: FIG. 18.--_Trichomonas intestinalis_ from man, showing
anterior flagella, cytostomic depression anteriorly, undulating
membrane, nuclei, and axostyle. ×2,500. Original.]
_T. intestinalis_, R. Leuckart, appears to be capable of settling
in all parts of the human intestine in which the contents have an
alkaline reaction. Trichomonads have been cited as occurring in the
oral cavity by Steinberg, Zunker, Rappin and Prowazek; in the œsophagus
by Cohnheim, and in the stomach by Strube, Cohnheim, Zabel, Hensen
and Rosenfeld. The normal situation seems to be the small intestine.
The parasites then appear in the dejecta, especially in various
intestinal diseases the course of which is connected with an increased
peristalsis. They are also found in healthy persons, from whom they are
obtained after the administration of laxatives. They have been regarded
by some workers as commensals, which, however, have the power of
accelerating the onset of intestinal complaints, or at least of adding
to them. They have been found in cases of carcinoma of the stomach, and
in other diseases of that organ in which the acid reaction ceased.
Naturally, whether all the reports relate to the same species of
Trichomonas must remain undecided. Certain authors (Steinberg,
Cohnheim, van Emden) accept several species. Prowazek speaks of a
variety of _T. intestinalis_ inhabiting the oral cavity. This was
distinguished by a posterior process exceeding the length of the
body fourfold, and by a somewhat unusual course of the undulating
membrane. The food of this form, which was found in the whitish
deposit present, especially in the cavities of carious teeth,
consisted almost exclusively of micrococci. Schmidt and St. Artault
named the Trichomonads found in pathological products (_e.g._,
gangrene, putrid bronchitis, phthisis) of the lungs of man, as
_Trichomonas pulmonalis_. Trichomonads have also been found by
Wieting in lobular pneumonia in the lungs of pigs.
It is still uncertain in what way the infection takes place.
Experiments in the transmission of free trichomonads to mammals (_per
os_), in which the same or allied species occur (guinea-pigs, rats,
apes), have been without result. Probably encystment is necessary.
Such conditions are mentioned by May, Künstler, Roos, Schurmayer, van
Emden, Prowazek, Galli-Valerio and Schaudinn. According to Prowazek,
intestinal trichomonads of rats become encysted for conjugation. In
the cyst an accumulation of reserve food material occurs, causing
distension. The nuclei of the conjugants each give off a reduction
body and, after fusion, produce the nuclei for the daughter
individuals. According to Schaudinn the intestinal trichomonads lose
their flagella before conjugation, become amœboid and encyst in
twos, the formation of a large agglomeration of reserve substance
accompanying this. Galli-Valerio found double-contoured cysts in
the fæces of trichomonad-infected guinea-pigs, after the fæces had
been kept for a month in a damp chamber. When exposed to heat small
flagellates escaped from them. Administration of such material
containing cysts resulted in severe infection with trichomonads,
and death of the experimental guinea-pigs followed. The cyst wall
is clearly a protection against the deleterious acid reaction of
the stomach contents. Alexeieff (1911) and Brumpt (1912) think that
the trichomonad cysts of man are really fungi, while other workers
also doubt encystment among trichomonads. Wenyon (1907) states that
_T. intestinalis_ in mice produces spherical contracted forms which
escape from the body in the fæces.
Air, water, and under certain circumstances even food may be regarded
as vectors for the trichomonads. The occurrence of the organisms in
the oral cavity, and still more so in the lungs, is in favour of the
air being the transmitting agent. An observation made by Epstein
supports the idea of water transmission. Multiplication of the
trichomonads, once they have gained access to the body, is effected
by longitudinal division commencing at the anterior end (Künstler).
“Cercomonads” with several flagella and an undulating membrane, as
well as trichomonads, have been observed by Ross in some cases of
cutaneous ulcers.
Mello-Leitao (1913)[41] has described flagellate dysentery in children
in Rio de Janeiro. He states that it is due to _T. intestinalis_ and
_Lamblia intestinalis_ either separately or together. Flagellate
dysentery, he thinks, is benign and is the most frequent form of
dysentery in infants. The flagellates are pathogenic to infants under
three years of age. Escomel (1913)[42] found 152 cases of dysentery in
Peru due solely to Trichomonas. Such cases are probably widespread.
[41] _Brit. Journ. Children’s Diseases_, x, p. 60.
[42] _Bull. Soc. Path. Exot._, vi, p. 120.
Genus. *Tetramitus*, Perty, 1852.
*Tetramitus mesnili*, Wenyon, 1910.
Syn.: _Macrostoma mesnili_, _Chilomastix mesnili_, _Fanapapea
intestinalis_.
The genus _Tetramitus_ differs from _Trichomonas_ in possessing an
undulating membrane inserted in a deep groove or cytostome. There are
three anterior flagella. The pear-shaped organism measures 14 µ by 7 µ,
but smaller examples occur. _T. mesnili_ occurs in the human intestine,
having been described by Wenyon[43] (1910) from a man from the Bahamas
in the Seamen’s Hospital, London. Its occurrence is widespread.
Alexeieff considers that _Macrostoma_ and _Tetramitus_ are synonymous.
The parasite is the same as _Fanapapea intestinalis_, Prowazek, 1911,
from Samoa. Brumpt (1912) found _T. mesnili_ to be the causal agent of
colitis in a Frenchwoman. Nattan-Larrier (1912) considers it of little
pathological importance.
[43] _Parasitology_, iii, p. 210.
Gäbel[44] (1914) described an interesting case of seasonal diarrhœa
acquired in Tunis, in which a new Tetramitid was the causal agent. The
organism was pear-shaped, without an undulating membrane, and measured
6·5 µ to 8 µ by 5 µ to 6 µ. The cytostome was large, and there was
no skeletal support. Encystment occurred. Gäbel named the organism
_Difämus tunensis_ and considered that it was pathogenic.
[44] _Arch. f. Protistenk._, xxxiv, p. 1.
Genus. *Lamblia*, R. Blanchard, 1888.
Syn., _Dimorphus_, Grassi, 1879, _nec_ Haller, 1878; _Megastoma_,
Grassi, 1881, _nec_ de Blainville.
The body is pear-shaped, with a hollow on the under surface
anteriorly. It has four pairs of flagella directed backwards, of
which three pairs lie on the borders of the hollow disc, and the
fourth arises from the pointed posterior extremity.
*Lamblia intestinalis*, Lambl, 1859.
Syn.: _Cercomonas intestinalis_, Lambl, 1859 (_nec_ 1875); _Hexamitus
duodenalis_, Davaine, 1875; _Dimorphus muris_, Grassi, 1879;
_Megastoma entericum_, Grassi, 1881; _Megastoma intestinale_, R.
Blanch., 1886; _Lamblia duodenalis_, Stiles, 1902.
The organism is pear-shaped and bilaterally symmetrical. It is from
10 µ to 21 µ long and 5 µ to 12 µ broad and possesses a thin cuticle.
Anteriorly an oblique depression is present, which functions as a
sucking disc (fig. 19, _s_). Its edges are raised above the general
surface and are contractile. It corresponds to a peristome and acts as
an adhesive organ (fig. 20, _b_, _c_). No true cytostome is present.
A double longitudinal ridge, representing axostyles, extends from the
sucking disc to the tapering posterior extremity, which is prolonged as
two flagella from 9 µ to 14 µ long.
_Lamblia intestinalis_ possesses eight flagella (fig. 19). The first
pair of flagella, which cross one another, arise in a groove formed by
the anterior edge of the sucking disc. Two pairs of flagella (lateral
and median) are inserted on the posterior edge of the disc, while the
posterior flagella occur at the tapering posterior extremity of the
body. Basal granules are found at the bases of the flagella. The median
flagella are most active in movement, the anterior and lateral flagella
being less motile, as they are partially united to the body for part of
their length.
The nuclear apparatus is situated in the thin, anterior, hollowed
part of the body. It is at first dumb-bell shaped, the “handle” of
the dumb-bell being formed by a very slight connecting strand, which
eventually separates, so that the flagellate becomes binucleate, and
thus completes the general bisymmetry of the organism.
There is a karyosome in each nucleus. Other bodies of unknown function,
and possibly composed of chromatin, occur on or near the axostyles.
[Illustration: FIG. 19.--_Lamblia intestinalis_. A, ventral view; B,
side view; N, one of the two nuclei; _ax._, axostyles; _fl_^1, _fl_^2,
_fl_^3, _fl_^4, the four pairs of flagella; _s_, sucker-like depressed
area on the ventral surface; _x_, bodies of unknown function. (After
Wenyon.)]
Division has not been observed in the flagellate stages of the Lamblia,
but it occurs within the cysts. The resistant cysts (fig. 20, _e_) are
oval and are surrounded by a fairly thick, hyaline cyst wall. They
measure 10 µ to 15 µ by 7 µ to 9 µ, and may be tetranucleate. According
to Schaudinn, the cysts arise from the conjugation of two individuals,
and nuclear rearrangement occurs.
_L. intestinalis_ occurs in its flagellate stage in the duodenum and
jejunum, and rarely as such in the other parts of the intestine.
Normally it is found in the large intestine as cysts, which are voided
with the fæces. The hosts of Lamblia include _Mus musculus_, _M.
rattus_, _M. decumanus_, _M. silvestris_, _Arvicola arvensis_ and _A.
amphibius_, the dog and cat, rabbit, sheep and man. Cysts voided with
the fæces of infected animals reach plants or drinking water, and
thence are transferred to man.
The flagellate in these different hosts exhibits some variation in
size and in the problematic chromatic bodies. Bensen has suggested the
species _L. intestinalis_ from man, _L. muris_ from the mouse and _L.
cuniculi_ from the rabbit. It is not certain whether these different
species are necessary, as the variation may be due to differences of
environment.
[Illustration: FIG. 20.--_Lamblia intestinalis._ _a_, from the surface;
_b_, from the side; _c_, on intestinal epithelium cells; _d_, dead and
_e_, encysted. (After Grassi and Schewiakoff.)]
Like Trichomonas, Lamblia can multiply under inflammatory conditions
of the alimentary tract. Thus they are found in cases of diarrhœa,
carcinoma of the stomach, etc. The parasites attach themselves by
their sucking discs to the epithelial cells of the gut (fig. 20, _c_),
and though their numbers may be very great, their direct pathological
significance is not fully known. Their occurrence in cases of diarrhœa
has been explained as being due to the increased peristalsis, which
has detached the parasites from the epithelium. Free flagellate forms
perish in stools if kept, more especially if the temperature falls
below 0° C. or rises above 40° C. Lamblia has often been found in
dysenteric diseases, especially in the East, and is said to be the
causal agent of certain diarrhœas in India. Mathis (1914)[45] found
Lamblia in cases of diarrhœa with dysenteriform stools in Tonkin. He
also discovered healthy carriers of Lamblia cysts.
[45] _Bull. Soc. Med. Chirurg. Indo-Chine_, v, p. 55.
The parasite under discussion was first observed by Lambl (1859) in
the mucous evacuations of children. He regarded the parasite as a
Cercomonad and termed it _Cercomonas intestinalis_, which name as a
rule is applied to _Cercomonas hominis_, Davaine, although Stein had
already pointed out the difference between the two species. Grassi
(1879) observed this species first in mice (calling it _Dimorphus
muris_), and subsequently in human beings in Upper Italy and named
it _Megastoma entericum_. Bütschli and Blanchard then laid stress on
the identity of this species with Lambl’s _C. intestinalis_ (1859),
and consequently called it _Megastoma intestinale_. Later, Blanchard
drew attention to the circumstance that the generic name _Megastoma_
chosen by Grassi had already been used four times for various kinds
of animals, and established the genus _Lamblia_. Accordingly, _L.
intestinalis_ is the valid name, and should be generally adopted.
In Upper Italy the parasite in the encysted condition has also
been seen by Perroncito in man. At the same time, Grassi and
Schewiakoff began a new investigation of specimens from mice and
rats. In Germany, _L. intestinalis_ was found by Moritz and Hölzl,
Roos, Schuberg and Salomon. Moritz and Hölzl confirmed the relative
frequency of the species. In Königsberg, Prussia, a student found
encysted _Lamblia_ in his fæces. One case was reported from Finland
by Sievers, another case from Scandinavia by Müller. Frshezjesski and
Ucke reported cases from Russia. Jaksch announced the occurrence of
the parasite in Austria; Piccardi mentioned their presence again in
Italy. They were reported from Egypt by Kruse and Pasquale, and from
North America (Baltimore) by Stiles. Noc stated that 50 per cent. of
the population of Tonkin harboured _Lamblia_. Finally, the structure
of _L. intestinalis_ has been described by Metzner (1901), and by
Wenyon[46] (1907) in mice.
[46] _Arch. f. Protistenkunde_, Suppl. i, p. 169.
In all these cases _L. intestinalis_ has been observed in the small
intestine, or in the evacuations of patients with intestinal diseases.
It has also been found in the intestine of healthy subjects. Just
as _Trichomonas intestinalis_ may be found inhabiting the stomach
in diseases of that organ, in which an alkaline reaction is present
(carcinoma), so has _L. intestinalis_ been found to occur under
similar circumstances (Cohnheim, Zabel). However, in Schmidt’s case,
1 per cent. hydrochloric acid was certainly stated to be present.
Infection takes place by the ingestion of cysts (fig. 20, _e_), as was
established by Grassi, experimentally on himself. Cereal food-stuffs,
contaminated with Lamblia cysts from vermin of the locality, such as
rats and mice, serve to convey the infection to man. Such cysts may
probably be found in street-dust, etc. Stiles induced infection in
guinea-pigs, and Perroncito in mice and rabbits, by means of cysts of
Lamblia from human beings. Stiles suspected that flies could transport
Lamblia cysts. Mathis (1914) found that _L. intestinalis_ was not
amenable to emetine, at any rate in its cystic stage.
Order. *Protomonadina*, Blochmann.
The smallness of the Protomonadines and their less superficial
situation than the Polymastigines, may be the cause that so far as
the species occurring in man are concerned, they were formerly less
well known. As regards parasitic species, this group may be divided
as follows, according to the number of flagella and the presence or
absence of an undulating membrane:--
(1) _Cercomonadidæ_, with one flagellum at the anterior extremity,
without an undulating membrane.
(2) _Bodonidæ_, with two flagella, without an undulating membrane,
except in Trypanoplasma.
(3) _Trypanosomidæ_, with one flagellum, and an undulating membrane
along the length of the body in some genera.
Family. *Cercomonadidæ*, Kent emend. Bütschli.
Small uniflagellate forms, without cytostome.
Genus. *Cercomonas*, Dujardin emend. Bütschli.
Oval or rounded organisms, with the aflagellar end often drawn out into
a tail-like process.
*Cercomonas hominis*, Davaine, 1854.
Davaine found flagellates in the dejecta of cholera patients. They
had pear-shaped bodies, lengthening to a point posteriorly. Their
length was from 10 µ to 12 µ, and a flagellum about twice as long as
the body projected from one extremity (fig. 21). A nucleus was hardly
recognizable. Occasionally a somewhat long structure (cytostome?)
appeared at the anterior extremity. The animals moved with remarkable
activity. They also attached themselves by means of their posterior
extremities and swung about around the point of attachment. Davaine
found a smaller variety, only about 8 µ long, in the dejecta of a
typhoid patient (fig. 21, _b_).
[Illustration: FIG. 21.--_Cercomonas hominis_, Dav. _a_, larger,
_b_, smaller variety. Enlarged. (After Davaine.)]
[Illustration: FIG. 22.--_Cercomonas hominis_, Dav. From an
Echinococcus cyst. (After Lambl.)]
The Flagellata observed by Ekeckrantz (1869) in the intestine of
man belong to this form--at least to the larger variety--and Tham
(1870) reported fresh cases soon after. Lambl’s publication of 1875,
which was written in Russian, and became known through Leuckart’s
work on parasites, also alludes to apparently typical Cercomonads,
which, however, were discovered, not in the intestine, but in an
_Echinococcus_ cyst in the liver (fig. 22). The elliptical, fusiform,
rarely pear-shaped or cylindrical bodies of the parasites measured
5 µ to 14 µ in length, and were provided with a flagellum at one end,
while the other extremity usually terminated in a long point. An oral
aperture occurred at the base of the flagellum, and there were one or
two vacuoles near the posterior extremity. Longitudinal division was
also observed (fig. 22).
As already mentioned, this form, which Lambl termed _Cercomonas
intestinalis_, differs considerably from the form found by the same
author in 1859, which received the same designation (_cf. Lamblia
intestinalis_, p. 60), but it corresponds with _Cercomonas hominis_,
Davaine. The latter, as well as _C. intestinalis_, Lambl, 1875, is
usually classed with the Trichomonads, but, as has already been
remarked (_cf._ _Trichomonas intestinalis_, p. 54), this cannot be
considered correct, as only _one_ flagellum is present.
_Cercomonas vaginalis_ (Castellani and Chalmers, 1909) was found in the
vagina of native women in Ceylon.
Other species of _Cercomonas_ have, at various times, been recorded
from man. However, the parasitic species of the genus _Cercomonas_
require further investigation.
According to Janowski (1896–7), typical Cercomonads have also been
observed in the intestine of man by Escherich, also by Cahen,
Massiutin, Fenoglio, Councilman and Lafleur, Dock, Kruse and
Pasquale, Zunker, Quincke and Roos, and others. However, it is an
open question whether the Flagellata observed by Roos in one of his
cases belonged to Davaine’s species, the size showing some deviation
(14 µ to 16 µ). In his, as in many other cases, doubts have been
raised as to whether the flagellates found in the stools had actually
lived in the intestine, or had subsequently appeared in the fæces:
for this a surprisingly short time only is necessary. Salomon also
appears to have observed Cercomonads (_Berl. klin. Wochenschr._,
1899, No. 46).
As with _T. intestinalis_ so with _C. hominis_, it appears that
the parasite settles not only in the intestine but also in the
air-passages. This is demonstrated by the statements of Kannenberg
and Streng of the occurrence of Monads and Cercomonads in the
sputum and putrid expectoration in gangrene of the lungs, which no
doubt apply to _C. hominis_ (_cf._ also Artault). Possibly also the
Flagellata observed in the pleural exudation by Litten and Roos may
be included here; this is the more probable in Roos’s case as the
process ensued in the pleura after the breaking through of a vomica.
Perroncito and Piccardi have described encysted stages of Cercomonads.
*Monas pyophila*, R. Blanch., 1895.
[Illustration: FIG. 23.--_Monas pyophila_, R. Blanch. (After Grimm.)]
R. Blanchard thus designates a Flagellate that Grimm found in the
sputum, as well as in the pus of a pulmonary and hepatic abscess,
in the case of a Japanese woman living in Sapporo. The parasites
resemble large spermatozoa (fig. 23). The body, 30 µ to 60 µ, has
the shape of a heart or a myrtle leaf, and is surrounded by a thick
cuticle which is supposed to extend into the interior of the body,
dividing it into three parts. A long appendix at the rounded pole
is covered for the greater part of its length by the cuticle; the
extremity, however, is free and resembles a flagellum. The parasites
were very active, frequently changed their shape, and were able to
retract the long appendix within the body, which then assumed a round
form.
[This organism requires further investigation.]
Family. *Bodonidæ*, Bütschli.
_Protomonadina_ which are either free-living or parasitic, with two
dissimilar flagella, while the possession of an undulating membrane and
of a kinetic nucleus or blepharoplast is variable.
There are three genera:--
1. _Bodo_, Stein, 1878, without a kinetic nucleus and undulating
membrane.
2. _Prowazekia_, Hartmann and Chagas, 1910, with a kinetic
nucleus and without an undulating membrane.
3. _Trypanoplasma_, Laveran and Mesnil, 1901, with a kinetic
nucleus and undulating membrane.
Of these genera _Prowazekia_ must be discussed. _Bodo_ does not occur
in man. Species of _Trypanoplasma_ occur in the blood and in the gut
of various fishes, in the seminal receptacle of certain snails, in
the gut and genitalia of a flatworm (_Dendrocœlum lacteum_) and in
the vagina of a leech. Closely allied to _Trypanoplasma_ is the genus
_Trypanophis_, parasitic in the cœlenteric cavity of Siphonophores.
Genus. *Prowazekia*, Hartmann and Chagas, 1910.
The genus was founded for a flagellate parasite, _Prowazekia cruzi_,
discovered in a culture of human fæces in Brazil. Various other species
have been referred thereto. The genus is separated from _Bodo_ by
the possession of a second nucleus, the so-called kinetonucleus or
blepharoplast. It differs from _Trypanoplasma_ in the absence of an
undulating membrane. It is heteromastigote, that is, it possesses two
dissimilar flagella, one anteriorly directed and the other lateral and
trailing.
The principal species are:
*Prowazekia urinaria*, Hassall, 1859.
Syn.: _Bodo urinarius_, Hassall, 1859; _Trichomonas irregularis_,
Salisbury, 1868; _Cystomonas urinaria_, Blanchard, 1885; _Plagiomonas
urinaria_, Braun, 1895.
Hassall[47] in 1859 first found Bodo-like flagellates in human urine.
He examined fifty samples of urine from patients suffering from
albuminuria and from cholera. The reaction of the urine was alkaline
or sometimes only feebly acid. The flagellates were only seen after
the urine had been standing for several days. Hassall named the
organism _Bodo urinarius_, and gave a very good description of it
with illustrations. The flagellate, which was round or oval, measured
14 µ by 8 µ. The organism had “one, usually two, and sometimes three
lashes or cilia.” In 1868 Salisbury described a similar flagellate in
the urine under the name _Trichomonas irregularis_. Künstler in 1883
described the latter parasite under the name _B. urinarius_. In 1885
Blanchard, considering Künstler’s organism a different parasite from
Hassall’s, called it _Cystomonas urinaria_. Braun, in 1895, gave the
name _Plagiomonas urinaria_. Barrois (1894) considered Künstler’s and
Hassall’s organisms to be identical and not to be true parasites of
man. Sinton,[48] in 1912, found the flagellate in the deposit, after
centrifuging, of a 24-hour old specimen of alkaline urine from a
Mexican sailor in the Royal Southern Hospital, Liverpool. Sinton found
a kinetic nucleus or blepharoplast in the organism, and therefore
placed it in the genus _Prowazekia_.
[47] _Lancet_, 1859, ii, p. 503.
[48] _Annals Trop. Med. and Parasitology_, vi, p. 245.
[Illustration: FIG. 24.--Types of _Prowazekia urinaria_. (_a_)
sausage-shaped; (_b_) round; (_c_) carrot-shaped form. (After Sinton.)]
The flagellate stage (fig. 24) of the organism is polymorphic, and
may be either (_a_) sausage-shaped, 10 µ to 25 µ in length by 2·5 µ
to 6 µ in breadth; (_b_) round or oval, varying from 4 µ in diameter
to oval forms 15 µ by 10 µ; (_c_) a carrot-shaped form, of varying
size up to 25 µ by 4 µ. The kinetic nucleus is large and pear-shaped.
Near it are basal granules, closely applied to one another, from which
the flagella arise. There is a small cytostome near the roots of the
flagella. There is a well-marked karyosome in the nucleus. The movement
is jerky. The shorter, anterior flagellum may be used in food-capture.
In life, bacteria have been seen to be ingested. Food-vacuoles tend to
accumulate at the posterior (aflagellar) end. A contractile vacuole
may be present, near the base of the cytostome, and may really be the
dilated fundus of the latter. Division occurs by binary fission. The
organism can encyst (fig. 25, _a_), when the flagella are lost, and
round or oval cysts are found, 5 µ to 7 µ in diameter. After a time
flagella are formed inside the cyst, and the organism emerges therefrom
in its typical flagellate form (fig. 25, _b_-_f_).
Sinton’s case is interesting. He obtained the flagellate only twice
from the same patient, a Mexican then in hospital in Liverpool. The
flagellate was not found in the patient’s fæces, nor was it found in
the urine on later occasions when taken aseptically.
[Illustration: FIG. 25.--_Prowazekia urinaria_. Flagellate emerging
from cyst. (After Sinton.)]
In cultures _Prowazekia urinaria_ was always found in association with
bacteria. The cultures died at a temperature of 37° C., but grew well
at 20° C. Various media were useful at the lower temperature, such as
urine, salt agar, nutrient agar, serum agar, blood agar, peptone salt
solution, and diluted blood serum. The flagellate was, then, considered
to be an accidental contamination and not a true parasite of human
urine.
*Prowazekia asiatica*, Castellani and Chalmers, 1910.
The flagellate was found by the discoverers in the stools of patients
suffering from ankylostomiasis and diarrhœa in Ceylon. It was referred
by them to the genus _Bodo_, but in 1911 Whitmore[49] further studied
it and placed it in the genus _Prowazekia_. In the stools the
flagellate is found either as a long, slender form measuring 10 µ to
16 µ by 5 µ to 8 µ or as a rounded form 8 µ to 10 µ in diameter. Its
cytoplasm is alveolar. A rhizoplast connects the basal granules to the
kinetic nucleus. There is multiplication and cyst formation as before.
The organism is easily cultivated, especially in the condensation water
of nutrose agar and maltose agar. The pathogenicity is stated to be nil.
[49] _Arch. f. Protistenk._ xxii, p. 370.
*Prowazekia javanensis*, Flu, 1912.
Found in agar cultures from the motions of patients at Weltevreden,
Dutch East Indies.[50] The flagellates are 12 µ long and 5 µ broad. The
lateral flagellum is stated to be attached to the cell body for a short
distance. Regarding the karyosome in the nucleus, the author states
that the smaller the karyosome the more chromatin is deposited on the
nuclear membrane. Flu mentions that the specific name _javanensis_ is a
temporary one, as in the course of time it may be shown that there is
only one species of _Prowazekia_.
[50] _Geneesk. Tijdschr. v. Nederl. Ind._, lii, p. 659; _Med. v. d.
Burg. Geneesk. d. Nederl. Ind._, iii, p. 1.
*Prowazekia cruzi*, Hartmann and Chagas, 1910.
Found in a culture from human fæces on an agar plate in Brazil, and
considered to be a free-living form.[51] The organism is oval or
pear-shaped, 8 µ to 12 µ long and 5 µ to 6 µ broad. In human stools
at Tsingtau, China, a _Prowazekia_ has been found by Martini which he
thinks is the same as _Prowazekia cruzi_. He considers it to be a cause
of human diarrhœa and intestinal catarrh.
[51] _Mem. Inst. Osw. Cruz._, ii, p. 64.
*Prowazekia weinbergi*, Mathis and Léger, 1910.
This species was found in the fæces of men, both healthy and diarrhœic,
in Tonkin.[52] It is pear-shaped, 8 µ to 15 µ long by 4 µ to 6·5 µ
broad. The flagella occur at the broad end.
[52] _Bull. Soc. Med. Chir. Indo-Chine_, i, p. 471.
The discoverers think that _Prowazekia weinbergi_ is an intestinal
inhabitant, but non-pathogenic, since it was found to occur in the
fæces even when obtained with aseptic precautions.
*Prowazekia parva*, Nägler, 1910.
A free-living form found in the slime on the stones at the biological
station at Lunz. Another _Prowazekia_ was found in 1914 in tap-water in
Calcutta.
Family. *Trypanosomidæ*, Doflein.
The Trypanosomidæ, broadly considered, are uniflagellate organisms,
the flagellum being at the anterior end. The flagellum arises near the
blepharoplast (kinetic nucleus), which lies anterior, near or posterior
to the nucleus.
The following genera will be considered:--
_Trypanosoma_--with an undulating membrane along the length
of the body.
_Crithidia_--with a less well-developed undulating membrane
anteriorly (see fig. 49).
_Herpetomonas_--including the so-called _Leptomonas_, with anterior
free flagellum only, and no undulating membrane.
_Leishmania_--non-flagellate forms in mammalian blood, flagellate
herpetomonad stages in culture, probably occurring
naturally in Arthropods.
Genus. *Trypanosoma*, Gruby, 1843.
The members of the genus possess a single flagellum, which arises
posteriorly, adjacent to a blepharoplast or kinetic nucleus. The
flagellum forms a margin to an undulating membrane, and may or may not
be continued beyond the body as a free flagellum. Many species are
parasitic in vertebrate blood and in the digestive tracts of insects.
HISTORICAL.
The history of blood flagellates goes back to the year 1841, in which
Valentin discovered in the blood of a brook-trout (_Salmo fario_ L.)
minute bodies, from 7 µ to 13 µ in length, with active movements and
presenting marked changes in form. Valentin considered the parasite
a new species of the old genus _Proteus_ or _Amœba_, Ehrbg. This
announcement led Gluge (1842) to publish a similar discovery he had
made in frog’s blood. The latter forms were called by Mayer (1843)
_Amœba rotatoria_, _Paramœcium loricatum_ and _P. costatum_, while
Gruby (1843) called them _Trypanosoma sanguinis_.[53] Later it was
discovered that similar organisms occurred also in the blood of birds
(Wedl (1850), Danilewsky) and of mammals. Gros (1845) found them in
the mouse and mole, Chaussat (1850) in the house rat, Lewis (1879) in
the Indian rat, Wittich (1881) in the hamster. Danilewsky (1886–89)
and Chalachnikow (1888) investigated the structure and division of
trypanosomes.
[53] Gruby’s generic name is generally accepted. Still others have
been used, _e.g._, _Undulina_, Ray _Lankester_, _Globularia_ Wedl,
_Paramecioides_ Grassi, _Trypanomonas_ Danilewsky, _Hæmatomonas_
Mitrophanow.
In the case of all these forms, there was no discussion as to a
pathogenic influence on the host. Opinion, however, as to the action
of trypanosomes changed when, in 1880, Evans found flagellates in
the blood of horses in India that suffered from a disease endemic
there called “surra,” and associated the parasites with the disease.
Steel and Evans were successful in transmitting the parasites--first
known as _Spirochæta evansi_, Steel, then as _Trichomonas evansi_,
Crookshank, and finally as _Trypanosoma evansi_--to dogs, mules and
horses. They recognized that the above mentioned flagellates in the
blood of the experimental animals were the causal agents of the
disease.
From that time there was a considerable increase in the literature,
the contents of which have been summarized by Laveran and Blanchard.
In 1894 Rouget discovered trypanosomes in the blood of African horses
that suffer from “stallion’s disease” (dourine). In 1894 Bruce
found similar forms (_T. brucei_) in the blood of South African
mammals suffering from “nagana,” and in consequence attention was
drawn to the part which the much dreaded tsetse-fly played in the
transmission of “nagana.” In 1901 Elmassian discovered trypanosomes
in the blood of horses that were stricken with “mal de caderas,”
which is very common in the Argentine. The disease in cattle named
“galziekte” (gall-sickness), occurring in the Transvaal, was also at
one time attributed to a trypanosome remarkable for its great size,
and like some other species, bearing the name of its discoverer (_T.
theileri_).
The study of the species hitherto known has been carried on partly
by the above mentioned authors and in part by others, _e.g._,
Rabinowitsch and Kempner, Laveran and Mesnil, Wasiliewski, Senn.
It was greatly advanced by the method of double staining (with
alkaline methylene blue and eosin) introduced by Romanowsky (1891)
and elaborated by Ziemann, Leishman, Giemsa and others. By this means
the presence of a terminal flagellum and of an undulating membrane
at the side of the flattened and extended body was demonstrated.
Laveran and Mesnil (1901) discovered allied flagellates in the blood
of the fish, _Scardinius erythrophthalmus_. These flagellates, now
placed in the genus _Trypanoplasma_, had a second free flagellum in
addition to the one bordering the undulating membrane. Trypanoplasms
have since been found in both freshwater and marine fishes. The
transmission of trypanoplasms of freshwater fishes is effected by
leeches. _Trypanoplasma varium_ from _Cobitis_ is transmitted by
_Hemiclepsis marginata_ according to Léger, while the Trypanoplasmata
of _Cyprinus carpio_ and _Abramis brama_ reach new hosts by the
agency of _Piscicola_ according to Keysselitz.
Another ally of the Trypanosomidæ, _Trypanophis_, lives in the
cœlenteric cavity of Siphonophores. It has also an extra terminal
flagellum (Poche, Keysselitz). [_Trypanoplasma_ and _Trypanophis_
belong to the _Bodonidæ_, see p. 63].
Finally it was shown that Trypanosomes occurred in human beings.
Although Nepveu’s early report of trypanosomes in the blood of
malarial patients may be doubtful, subsequent researches by Forde
and Dutton demonstrated trypanosomes (fig. 28) in the blood of a
European, apparently suffering from malaria, living in the Gambia.
Dutton (1902) called the human trypanosome, _T. gambiense_. The
expedition despatched by the Liverpool School of Tropical Medicine
(1902) to Senegambia found trypanosome infections in six cases among
a thousand inhabitants examined.
About the same time attention was devoted to the disease of West
African negroes known for a century as “sleeping sickness.”
Castellani (1903) was the first to succeed in demonstrating the
presence of trypanosomes (at first called _T. ugandense_) in
centrifugalized cerebro-spinal fluid obtained by puncture from cases
of sleeping sickness in Uganda. Similar discoveries were made by
Bruce, who also found trypanosomes in the blood of those attacked
with sleeping sickness. Sambon regarded a species of _Glossina_ as
the transmitter. From consideration of the geographical distribution
of the disease Christy regarded _Glossina palpalis_ as the
transmitter. Brumpt first thought it was _G. morsitans_, but, later,
supported the view of _G. palpalis_. Bruce, Nabarro and Greig also
named the same insect as the transmitter, not only for geographical
reasons but also because healthy apes became infected by the bite
of certain _G. palpalis_. The inoculation of cerebro-spinal fluid
from subjects of sleeping sickness into the spinal canal of apes
(_Macacus_) had the same result.
Just as the discovery of the malarial parasites called forth a whole
flood of research memoirs which were followed by a second series on
the relation of the mosquitoes to malaria, so a similar outpouring
occurred after the discovery of the pathogenic trypanosomes of
mammals and men. In both cases the inquiry was not limited to the
stages in man and other vertebrate hosts, but the fate of the
parasites in the intermediate (invertebrate) hosts was investigated,
and allied species were obtained from many different hosts.
Novy and MacNeal (1903) were the first to cultivate trypanosomes in
artificial media (blood-agar).
In 1910 Stephens and Fantham recorded the presence of another human
trypanosome, _T. rhodesiense_, from a case of sleeping sickness
in Rhodesia, where _G. palpalis_ was absent. Kinghorn has since
demonstrated that _T. rhodesiense_ is transmitted by _G. morsitans_.
Kinghorn and Yorke believe that big game (_e.g._, antelope) is the
reservoir of _T. rhodesiense_.
The output of literature on trypanosomiasis in men and animals is
enormous. To cope with it the Sleeping _Sickness Bureau Bulletin_
was founded in 1908, and it is now (since November 1912) continued
as a section of the _Tropical Diseases Bulletin_, wherein current
literature is reviewed.
GENERAL.
Trypanosomes occur in the blood of representatives of all the
vertebrate classes. Often the trypanosomes occur so scantily in
the blood that they are overlooked on examination. A useful aid in
detecting the flagellates in such cases consists in the use of cultures
of the blood of the host on artificial media. Stimulated by the
medium multiplication occurs, and hence the parasites are more easily
detected. [For the composition of such culture media see Appendix.]
There is a periodicity in the appearance of the trypanosomes in
the peripheral blood of the host, due to alternating phases of
multiplication and of rest on the part of the parasites. Such
periodicity has been established both by biological and enumerative
methods. Again, a seasonal variation has been observed in the
occurrence of certain trypanosomes in the peripheral circulation of the
hosts; for example, some trypanosomes (_e.g._, _T. noctuæ_ in birds)
are found only in the summer in the blood, while in the winter they
occur in the internal organs.
Recent cultural researches have established that trypanosomes, _e.g._,
_T. americanum_, may be present in very small numbers in hosts,
such as cattle, which are quite unharmed by them, and in which the
presence of these flagellates formerly was never suspected (“cryptic
trypanosomiasis.”) However, the majority of the trypanosomes occurring
in domestic animals are usually deleterious or even lethal to their
hosts. Many wild animals, such as various species of antelope, harbour
trypanosomes without being injured thereby. In such cases it is
probable that the vertebrate hosts have been so long parasitized in the
past, that they have become tolerant and immune to the effects of the
flagellates. Should such trypanosomes of wild animals be transmitted to
domesticated stock or man, they may re-acquire their initial virulence
and become pathogenic to the new host. As a general statement, the
newer a parasite is to its host the greater is its virulence. For
example, _T. gambiense_, _T. rhodesiense_ and _T. brucei_ are innocuous
to big game in Africa, but are pathogenic to man and domestic animals
respectively. Pathogenic trypanosomes appear to have a wider range
of hosts, that is, to be less limited to one specific host than
non-pathogenic forms. Thus, _T. rhodesiense_ is pathogenic to man and
all laboratory animals, while it is non-pathogenic to antelopes and
their kind.
_Morphology._
[Illustration: FIG. 26.--_Trypanosoma brucei_ in division. _n_,
nucleus; _bl_, blepharoplast; _fl_, flagellum. × 2,000. (After Laveran
and Mesnil.)]
The general structure of the various trypanosomes shows much
uniformity, though variations in size and shape occur. Typically the
body is elongate and sinuous. The flagellar end tapers gradually to a
point, the aflagellar extremity usually being rounded or more blunt.
In some trypanosomes there is much diversity in size, the organisms
varying from long, slender forms to short, stumpy ones; in other
species relative constancy of size is maintained. The former are known
as polymorphic trypanosomes, the latter as monomorphic forms.
Two nuclei are present. The main or principal nucleus, sometimes termed
the trophic nucleus, is often situated towards the centre of the body;
it is frequently of the vesicular type, containing a karyosome. The
blepharoplast or kinetic nucleus is posterior to the nucleus, and
usually is rod-like. The flagellum arises close to the blepharoplast,
and forms an edge to the undulating membrane. It may or may not
extend beyond the limits of the undulating membrane. If it does so,
the unattached part is known as the free flagellum. Sometimes a small
granule is found at the origin of the flagellum. This is the basal
granule, and is considered by some to function as the centriole of the
kinetic nucleus.
The undulating membrane is a lateral extension of the ectoplasm or
periplast, and is the main agent in locomotion. It is edged by the
flagellum, which forms a deeply stainable border to it. Within the
membrane substance, often arranged parallel with its edge, are a number
of fine contractile elements, the myonemes. These contractile elements
may also occur on the body of the trypanosome. They are easily seen in
some large trypanosomes, but are difficult of demonstration in others,
owing to their great fineness.
[Illustration: FIG. 27.--_Trypanosoma lewisi_. Multiplication rosettes.
× 1,000. (After Laveran and Mesnil.)]
Multiplication of trypanosomes in the blood is brought about by binary
longitudinal fission (fig. 26). Division is initiated by that of the
blepharoplast and nucleus. The division may be equal or subequal,
whereby differences in size of individuals partly arise. Multiple
division by repeated binary fission, without complete separation of the
daughter forms, is known in some trypanosomes (_e.g._, _T. lewisi_),
and rosettes of parasites thereby are produced (fig. 27).
The classification of trypanosomes is very difficult. Laveran
(1911)[54] has suggested the examination of the relative length
of the flagellum as a diagnostic character, and so arranged these
flagellates in mammals in three groups. The first group included those
trypanosomes always having part of the flagellum free (_e.g._, _T.
evansi_, _T. vivax_); the second group comprised forms without a part
of the flagellum free (_e.g._, _T. congolense_), while the third group
included forms some members of which have free flagella, while others
have not (_e.g._, _T. gambiense_). Bruce[55] (1914) and Yorke and
Blacklock[56] (1914) have also devised classifications.
[54] _Ann. Inst. Pasteur_, xxv, p. 497.
[55] _Trans. Soc. Trop. Med. & Hyg._, viii, p. 1.
[56] _Annals Trop. Med. and Parasitol._, viii, p. 1.
Resting stages of some trypanosomes have been found in the internal
organs of their vertebrate hosts. The formation of these oval,
Leishmania-like bodies will be noted in individual cases later. Similar
small oval bodies form an important phase in the life-history of _T.
cruzi_, which multiplies normally by multiple fission or schizogony
into these oval, daughter elements, and not by binary longitudinal
fission in the circulating blood.
Polymorphism in trypanosomes (_e.g._, _T. gambiense_, _T. rhodesiense_)
is now interpreted as a phenomenon resulting from growth and
division.[57] Long, thin forms are those about to divide. Fully mature
forms are shorter and broader. Various intermediate types occur and
represent growth forms. Formerly, polymorphism was interpreted in terms
of sex, thin forms being regarded as males, broad forms as females,
while the intermediate types were termed indifferent. Conjugation
was not observed, and there is no evidence in support of the sexual
interpretation.
[57] Robertson (1912), _Proc. Roy. Soc._, B, lxxxv, p. 527.
The transmission of trypanosomes from one vertebrate host to another is
usually accomplished by the intermediation of some biting arthropod in
the case of terrestrial animals, while leeches are usually considered
to act as transmitters in the case of the trypanosomes occurring
in aquatic animals. Developmental phases of the life-histories of
trypanosomes occur in the invertebrate transmitters, and will be
considered in individual cases.
*Trypanosoma gambiense*, Dutton, 1902.
Syn.: _Trypanosoma hominis_, Manson, 1903. _Trypanosoma nepveui_,
Sambon, 1903. _Trypanosoma castellanii_, Kruse, 1903. _Trypanosoma
ugandense_, Castellani, 1903. _Trypanosoma fordii_, Maxwell Adams.
In vertebrate blood _Trypanosoma gambiense_ is polymorphic, for long,
thin forms may be seen in contrast with short, stumpy forms, as well
as intermediate forms (fig. 29, _a_--_c_). This polymorphism has been
interpreted in terms of sex, especially by German investigators,
following Schaudinn (see above). However, there is no evidence of
conjugation, and the polymorphic forms are more easily interpreted in
terms of growth and division, for the long thin forms are potential
dividing organisms, and the stumpy or short parasites, with little or
no free flagellum, are the adult individuals.
_Morphology of T. gambiense in the Circulating Blood._
_T. gambiense_ varies from 13 µ to 36 µ in length, its average length
being 24·8 µ, as was determined in 1913 by exact biometrical methods
by Stephens and Fantham.[58] Three forms of parasite occur. According
to Miss Robertson,[59] the relatively short forms from 13 µ to 21 µ
long may be regarded as the mature or “adult” type of parasite in
the blood. They carry on the cycle in the vertebrate. From them
intermediate forms, which are longer than the “adult” but at first have
the same breadth, arise by growth. They possess a free flagellum. The
intermediate forms grow into long individuals, which are those about to
divide. The products of division give rise, directly or indirectly, to
the adult forms.
[58] _Annals Trop. Med. and Parasitol._, vii, p. 27.
[59] _Phil. Trans._, B (1913), cciii, pp. 161–184.
[Illustration: FIG. 28.--_Trypanosoma gambiense_. × 1,700. (After
Dutton.)]
[Illustration: FIG. 29.--_Trypanosoma gambiense_. Development in
vertebrate host. _a_, long, slender, _b_, intermediate and _c_, short,
stumpy forms, found in the blood; _d_, _e_, _f_, non-flagellate, latent
forms from internal organs. × 2,000. (Original. From preparations by
Fantham.)]
The organism has an elongate body with an anterior or flagellar end
and a blunter posterior or non-flagellar end. The protoplasm is finely
granular, large inclusions being rare. The central nucleus is oval
and large, often containing most of its chromatin concentrated as a
karyosome, with small granules only scattered near or on the fine
nuclear membrane. The blepharoplast is either rounded or rod-shaped.
The undulating membrane is thrown into folds and is bordered by the
flagellum. A small basal granule may be present near, or at the actual
origin of the flagellum.
_Multiplication_ in the vertebrate is brought about by longitudinal
division. According to the recent account of division by Miss
Robertson, the blepharoplast doubles, then the flagellum splits for
the greater part of its length, and the daughter flagella separate,
one being shorter than the parent flagellum. The nucleus often shows
two well marked dark granules on the membrane at opposite poles, and
these appear to act as centrosomes. Nuclear constriction occurs and
the halves gradually separate. Finally the two daughter organisms
become free, the aflagellar end splitting last. The products of
division may be equal or unequal. Repeated division goes on in the
general circulation until the blood swarms with parasites. Then the
trypanosomes gradually disappear, and a period occurs when it is
practically impossible to demonstrate the parasite in the blood.
At such a period, trypanosomes can be obtained by puncture of the
enlarged lymphatic glands or of the spinal canal, or can be found in
the internal organs, more particularly in the spleen, lungs, liver and
bone-marrow. In the latter organs, latent bodies are produced (fig. 29,
_d_--_f_) which are capable of again becoming flagellates and entering
the general circulation. Their formation was described by Fantham
(1911).[60] The parasite contracts, the blepharoplast migrates towards
the nucleus, a very thin coat differentiates around the two nuclei
and a certain amount of cytoplasm, and the parts exterior to the coat
disintegrate, leaving a small, oval body behind. Fuller details are
given in connection with _T. rhodesiense_. Laveran (1911)[61] considers
that latent bodies are “involution” forms, but acknowledges that they
can flagellate and become infective in fresh blood.
[60] _Proc. Roy. Soc._, B, lxxxiii, p. 212.
[61] _C. R. Acad. Sci._, 153, p. 649.
No multiplication of the trypanosomes within the cells of the lung,
liver or spleen of infected monkeys was found by Miss Robertson in her
recent researches.
There appear to be negative periods in infected monkeys, since,
although trypanosomes may occur in their blood at such times, they are
not infective to _Glossina_.
_Development in Glossina palpalis._--The principal accounts are
those by Sir D. Bruce and his colleagues (1911),[62] and by Miss
Robertson[63] (1912), whose results will be followed. According to the
latter investigator _T. gambiense_ never enters the body cells of the
fly (_G. palpalis_), nor does it penetrate the gut wall into the body
cavity. Practically no crithidial stage occurs in the fly’s main gut,
but a trypanosome facies is retained therein.
[62] _Proc. Roy. Soc._, B, lxxxiii, p. 513.
[63] _Proc. Roy. Soc._, B, lxxxvi, p. 66.
After the trypanosomes are ingested by the fly during a meal of
infected blood, sooner or later multiplication occurs. This development
usually begins in the middle or posterior part of the mid gut, and
trypanosomes of varying sizes are produced. After the tenth or twelfth
day, many long, slender trypanosomes (fig. 30, _a_) are found, which
gradually move forwards into the proventriculus. Such long, slender
forms represent the limit of development in the lumen of the main gut.
The proventricular type, developed about the eighth to the eighteenth
or twentieth day, is not infective; it may occur in the crop, but is
not to be found permanently there. Between the tenth and the fifteenth
days multinucleate forms of trypanosomes are found, and may be styled
multiple forms (fig. 30, _b_). Some of these latter may be degenerative.
[Illustration: FIG. 30.--_Trypanosoma gambiense_. Development in the
fly, _Glossina palpalis_. _a_, slender, proventricular form; _b_,
multinucleate form; _c_, _d_, crithidial forms; _e_, infective type of
trypanosome found in salivary gland. × 2,500. (After Robertson.)]
_Invasion of the Salivary Glands of the Fly._--Long, slender
trypanosomes from the proventriculus pass forward into the hypopharynx.
They then pass back along the salivary ducts, about sixteen to thirty
days after the fly’s feed. The trypanosomes reach the salivary glands
as long, slender forms. In the glands they become shorter and broader,
attach themselves to the surrounding structures, and assume the
crithidial facies (fig. 30, _c_, _d_). As crithidial forms they remain
attached to the wall and multiply in the glands. These crithidial
stages differentiate into the short, broad trypanosome forms, capable
of swimming freely (fig. 30, _e_).
Miss Robertson considers the development in the main gut to be
indifferent multiplication, and that salivary fluid seems necessary to
stimulate trypanosomes to the apparently essential reversion to the
crithidial type. The second development in the salivary gland is the
essential feature. The short, stumpy forms of trypanosomes (fig. 30,
_e_) finally produced in the salivary glands are alone infective. No
conjugation of trypanosomes occurs in the fly. Only about 5 per cent.
of captive tsetse flies fed on trypanosome-infected blood become
infective, but they probably remain infective for the rest of their
lives.
J. G. Thomson and Sinton (1912)[64] have obtained in cultures the
various trypanosome forms of _T. gambiense_ seen in the fly’s main gut.
[64] _Annals Trop. Med. and Parasitol._, vi, p. 331.
Duke (1912)[65] found _T. gambiense_ in a species of antelope, the
situtunga (_Tragelaphus spekei_), on Damba Island in Victoria Nyanza.
Wild _G. palpalis_ could be infected therefrom. The antelope may then
act as a sleeping sickness reservoir in that district, but men are
apparently the chief reservoir.
[65] _Proc. Roy. Soc._, B, lxxxv, pp. 156, 483.
*Trypanosoma nigeriense*, Macfie, 1913.[66]
Macfie has recently (August, 1913) described a human trypanosome
from the Eket district of Southern Nigeria. It is common in young
people. The disease produced does not seem to be of a virulent type
in Nigeria, and does not occur in epidemic form. In the early stages
the glands of the neck are enlarged. In the later stages--cases of
which are rarer--lethargy appears. The parasite is a polymorphic
trypanosome, morphologically almost indistinguishable from _T.
gambiense_, though it may be slightly shorter. Macfie recorded the
occurrence in his preparations of a few trypanosomes appearing to have
a flagellum free during their whole length. Some of the parasites,
as seen in a sub-inoculated guinea-pig, are very small (8 µ long).
Other trypanosomes have their nuclei displaced somewhat anteriorly.
This parasite may only be a variety of _T. gambiense_. The parasite is
perhaps spread by _Glossina tachinoides_.
[66] _Annals Trop. Med. and Parasitol._, vii, p. 339; viii, p. 379.
*Trypanosoma rhodesiense*, Stephens and Fantham, 1910.
The parasite was found in the blood of a young Englishman who had
contracted sleeping sickness in the Luangwa Valley, North-eastern
Rhodesia, in the autumn of 1909. The patient had never been in an area
infested with _Glossina palpalis_.
(1) _Morphology._--The morphology of the parasite in man and
sub-inoculated rats was studied by Stephens and Fantham in 1910.[67]
They pointed out a morphological peculiarity in the presence of certain
trypanosomes with posterior nuclei in sub-inoculated animals, that is,
parasites in which the nucleus (trophonucleus) was situated towards
the posterior or aflagellar end, close up to or even beyond the
blepharoplast or kinetic nucleus (fig. 31, _4_, _5_). When the nucleus
was beside the blepharoplast, the former was seen to be kidney-shaped
(fig. 31, _4_). The posterior nuclear forms were of the stout and
stumpy variety, and about 6 per cent. of the stumpy forms were found to
have their nuclei displaced from the centre. The anterior or flagellar
end of these trypanosomes often contained chromatoid granules. _T.
rhodesiense_ varies in length from 12 µ to 39 µ[68]; short stumpy forms
vary from 13 µ to 21 µ, intermediate forms from 21 µ to 24 µ, and long,
slender forms from 25 µ onwards. The average length is 24·1 µ.
[67] _Proc. Roy. Soc._, B, lxxxiii, p. 28.
[68] Stephens and Fantham (1912–13), _Proc. Roy. Soc._, B, lxxxv,
p. 223, and _Annals Trop. Med. and Parasitol._, vii, p. 27.
[Illustration: FIG. 31.--_Trypanosoma rhodesiense._ 1, Long narrow
form; 2–4, nucleus passing to posterior (aflagellar) end; 5, nucleus
quite posterior. × 1,800. (After Stephens and Fantham.)]
Certain regular periods occur in the course of the trypanosomiasis when
few or no flagellate trypanosomes are found in the peripheral blood
of the patient or of the sub-inoculated animal. These periods can be
explained in terms of morphology, for the trypanosomes are capable of
assuming a non-flagellate form in the internal organs of the host,
particularly in the lungs and in the spleen. Such forms are known as
“latent” or “resting” forms. The term “latent body” was first used
by Moore and Breinl in 1907[69] in connection with _T. gambiense_.
Fantham[70] (1911) has described the process of formation of latent
from motile forms and the reconversion of the latent bodies into
active flagellates. Fresh preparations of splenic blood or lung blood
containing trypanosomes were made. A trypanosome gradually withdrew or
cast off its flagellum, concentrated its cytoplasm, and became more or
less elongate oval. Nucleus and blepharoplast approached one another
and came to lie more or less side by side. Then an opaque line often
made its appearance around the nuclear area and differentiated as a
slight envelope or covering, the cytoplasm external to this merely
degenerating. The small, oval, refractile body (fig. 29, _d_--_f_) thus
formed was a non-flagellate latent body, 2 µ to 4 µ in diameter, like
_Leishmania_ or the non-flagellate, multiplicative forms of _T. cruzi_
(fig. 34), and remains temporarily inactive in the internal organs of
the host. After this period of inactivity, the non-flagellate body,
recuperated by its rest, begins to elongate again. The nuclei separate.
From a small vacuole-like portion the flagellum differentiates and
forces out the ectoplasm, which assumes the form of the undulating
membrane with its flagellar border. Subsequent growth results in
the production of the typical trypanosome form, which re-enters the
circulating blood and multiplies by longitudinal binary fission.
Division of the parasite prior to the formation of a latent body may
occur and division of the latent forms themselves is known, though
less common. Consequently latent bodies, like the flagellate forms
themselves, show diversity in size. The blepharoplast of the latent
bodies is sometimes less well marked than in _Leishmania_ (see fig. 29,
_d_-_f_). Laveran’s views on these bodies have already been given on
p. 74.
[69] _Annals Trop. Med. and Parasitol._, i, p. 441.
[70] _Proc. Roy. Soc._, B, lxxxiii, p. 212.
(2) _Animal Reactions._--The posterior nuclear trypanosomes were found
in all sub-inoculated animals, such as rats, guinea-pigs, dogs, mice,
Macacus, rabbits and horses, but were not seen in the human patient,
as few trypanosomes occurred in his peripheral blood. R. Ross and D.
Thomson[71] found a periodic, cyclical variation in the number of the
parasites in the patient’s blood from day to day, the cyclical period
being about a week (fig. 32). Fantham and J. G. Thomson[72] (1911)
found a similar periodic, cyclical variation in the trypanosomes
in the blood of sub-inoculated rats, guinea-pigs and rabbits. On
counting the parasites in the blood of similar animals inoculated
with _T. gambiense_, they established, by enumerative methods, that
_T. rhodesiense_ was more virulent than _T. gambiense_, while Yorke
also showed this marked virulence of _T. rhodesiense_ in practically
all laboratory animals. In other words the duration of infection in
the case of _T. rhodesiense_ was shorter. It was also found that _T.
rhodesiense_ was resistant to atoxyl. The patient, from whom the
original strain was obtained, died about nine months after the probable
date of infection. Some patients infected with _T. rhodesiense_ have
died in an even shorter period, such as four or five months.
[71] _Proc. Roy. Soc._, B, lxxxii, p. 411.
[72] _Annals Trop. Med. and Parasitol._, iv, p. 417.
In sheep and goats _T. rhodesiense_ causes an acute disease, marked by
high fever, œdema of the face, and keratitis, as shown by Bevan and
others, death resulting after a relatively short period. _T. gambiense_
gives rise, in these animals, to no symptoms except fever, which may be
overlooked. _T. rhodesiense_ produces keratitis in dogs.
[Illustration: FIG. 32.--Chart showing daily counts of number of
trypanosomes per cubic millimetre of peripheral blood from a case of
Rhodesian sleeping sickness. (After R. Ross and D. Thomson.)]
Stannus and Yorke (1911) observed _T. rhodesiense_ in animals
inoculated from a case of sleeping sickness in Nyasaland. Sir D. Bruce
and his colleagues[73] have shown (1912) that _T. rhodesiense_ is the
parasite usually found in man and in animals sub-inoculated from cases
of sleeping sickness in Nyasaland. It has since been found in German
East Africa and Portuguese East Africa, while Ellacombe has described a
case from North-western Rhodesia.
[73] _Proc. Roy. Soc._, B, lxxxv, p. 423.
(3) _Serum Reactions._--Interesting experiments on this subject were
performed during 1911 and 1912 by various French investigators.
(_a_) _Action of Immune Serum_ (Mesnil and Ringenbach)[74]: (1) A
goat was infected with _T. rhodesiense_. Twenty-two days later its
serum mixed with _T. rhodesiense_ was injected into a mouse. Result:
Protection. (2) The serum mixed with _T. gambiense_ was injected into a
mouse. Result: Infection.
[74] _C.R. Soc. Biol._, lxxii, p. 58.
(_b_) _Action of Baboon Serum._--Contrary to _T. gambiense_, _T.
rhodesiense_ is very susceptible to human and baboon sera. Mesnil and
Ringenbach[75] showed that a dose of 1 c.c. of baboon (_Papio anubis_)
serum cured mice infected with _T. rhodesiense_. In the same dose it
acted very feebly on _T. gambiense_.
[75] _C.R. Acad. Sci._, 153, p. 1,097.
(_c_) _Action of Human Serum._--_1 c.c._ of human serum cured _T.
rhodesiense_ mice in three out of four cases; on _T. gambiense_ mice
there was no appreciable effect.
Laveran and Nattan-Larrier[76] have shown the same, namely, that human
sera act on _T. rhodesiense_, but are quite without action on _T.
gambiense_.
[76] _C.R. Acad. Sci._, 154, p. 18.
(_d_) _Trypanolytic Reactions._--Mesnil and Ringenbach[77] have also
shown that the sera of animals (man, monkey and guinea-pig) infected
with _T. gambiense_ are trypanolytic for the homologous trypanosome,
that is, _T. gambiense_, but have no action on the heterologous
trypanosome, that is, _T. rhodesiense_.
[77] _C.R. Soc. Biol._, lxxi, p. 609.
(4) _Cross Immunity Experiments._--(_a_) Mesnil and Ringenbach[78]
immunized a monkey (_Macacus rhesus_) against _T. gambiense_. It
was inoculated with _T. rhodesiense_ on June 7, 1911; on June 27
trypanosomes appeared, the infection being slight; on July 4 it died. A
control died in ten and a half days.
[78] _C.R. Soc. Biol._, lxxi, p. 271.
(_b_) Laveran[79] immunized a goat and mice against _T. gambiense_.
When they had acquired a solid immunity, they were inoculated with _T.
rhodesiense_. They became infected like the controls.
[79] _Bull. Soc. Path. Exot._, v, pp. 26, 241.
(_c_) Laveran and Nattan-Larrier[80] immunized a ram against _T.
brucei_, it subsequently became infected with _T. rhodesiense_.
[80] _C.R. Acad. Sci._, 154, p. 18.
(_d_) Laveran[81] immunized a ram and a sheep against different strains
of T_. brucei_. Inoculated with _T. rhodesiense_ they both acquired
acute infections and died. Conclusion: _T. rhodesiense_ is not _T.
brucei_.
[81] _Bull. Soc. Path. Exot._, v, p. 101.
When the converse set of experiments is tried, namely, immunizing
an animal against _T. rhodesiense_, and then inoculating with _T.
gambiense_, the difficulty immediately arises that it is impossible
to immunize an animal against _T. rhodesiense_, owing to its
virulence. But a partial and transitory immunity to _T. rhodesiense_
can be obtained by treating the infected animal with drugs, such as
arsenophenylglycin. The results, so far as they go, seem to show that
an animal immunized against _T. rhodesiense_ is immune not only to
_T. rhodesiense_, but also to _T. gambiense_, a fact which, according
to Mesnil and Léger, does not invalidate the specificity of _T.
rhodesiense_, but tends to show that the two trypanosomes are closely
related.
(5) _Mode of Transmission and Reservoir._--Kinghorn has shown that
_T. rhodesiense_ is transmitted by _Glossina morsitans_ in which it
undergoes development. Kinghorn and Yorke[82] found that about 16 per
cent. of the wild game examined in Northern Rhodesia was naturally
infected with _T. rhodesiense_. The wild game examined included
waterbuck, hartebeest, mpala, bushbuck and warthogs. One native dog
near the Nyasaland border was found infected, but not domestic stock.
Taute doubts whether _T. rhodesiense_ really occurs in wild game.
Approximately 3·5 per cent. of the tsetse flies fed on infected animals
may become permanently infected with _T. rhodesiense_, and capable of
infecting clean animals. Furthermore, a tsetse fly when once infective
probably remains infective for the rest of its life.
[82] _Annals Trop. Med. and Parasitol._, vii, p. 183.
Kinghorn and Yorke, however, have shown that climatic conditions,
namely, those of temperature, also affect the infectivity of the tsetse
fly, as the ratio of flies capable of transmitting _T. rhodesiense_
to those incapable of transmitting the virus is 1 : 534 in hot valley
districts (_e.g._, Nawalia, Luangwa Valley, temperature 75° to 85° F.),
while on elevated plateaux (_e.g._, Ngoa, on the Congo-Zambesi
watershed, temperature 60° to 70° F.) the ratio falls to 1 : 1312.
Mechanical transmission by the tsetse fly does not occur, if a period
of twenty-four hours has elapsed since the infecting meal.
_Developmental Cycle in the Fly._--The period which elapses between the
infecting feed of the flies and the date on which they become infective
varies from eleven to twenty-five days in the Luangwa Valley, according
to Kinghorn and Yorke. Attempts carried out at laboratory temperature
on the Congo-Zambesi plateau, during the cold season, to transmit _T.
rhodesiense_ by means of _G. morsitans_ were always unsuccessful. The
developmental cycle of the trypanosome in the fly is influenced by
the temperature to which the flies are subjected (as stated above).
The first portion of the developmental cycle proceeds at the lower
temperatures (60° to 70° F.), but higher temperatures are necessary
for the completion of the development of the trypanosome. Kinghorn
and Yorke found that the trypanosomes may persist in the fly, at an
incomplete stage of their development, for at least sixty days when the
climatic conditions were unfavourable.
The first portion of the developmental cycle of the trypanosome takes
place in the gut of the fly. Invasion of the salivary glands of the
tsetse is secondary to that of the intestine, but is necessary for
the infectivity of the fly. A relatively high mean temperature, 75°
to 85° F., is essential for the passage of the trypanosomes into the
salivary glands and the completion of their development therein.
Kinghorn and Yorke[83] state that the predominant type of trypanosome
in the intestine of infected _G. morsitans_ was a large broad form,
quite different from that which is most common in the salivary glands.
The trypanosome in the glands resembles the short form seen in the
blood of the vertebrate host. The authors quoted state that both the
intestinal and salivary gland forms of infective _G. morsitans_ are
virulent when inoculated into healthy animals.
[83] _Annals Trop. Med. and Parasitol._, vii, p. 281.
Bruce and colleagues[84] have quite recently (June, 1914) published
an account of their investigations of _T. rhodesiense_ in _G.
morsitans_ in Nyasaland. (Incidentally it may be remarked that Bruce
considers _T. rhodesiense_ to be identical with a polymorphic strain
of _T. brucei_--see pp. 83, 94). The development of _T. rhodesiense_
takes place in the alimentary canal and salivary glands, not in the
proboscis, of the tsetse fly. In feeding experiments with laboratory
bred flies, as well as with a few wild flies, fed on infected dogs
or monkeys, only 8 per cent. of the flies were found to be infected
on dissection. Of such infected flies, however, only some allow of
the complete development of the trypanosomes within them, in other
words only about 1 per cent of the flies become _infective_. The
length of time which elapses before a fly becomes infective varies
from fourteen to thirty-one days, averaging twenty-three days, when
kept at 84° F. (29° C.). The dominant intestinal type of flagellate
in the fly is that seen in the proventriculus, which contains many
long, slender trypanosomes. These proventricular forms find their
way to the salivary glands, wherein crithidial and encysted forms
are seen. They change into “blood forms,” which are short, stumpy
trypanosomes and are infective. “The infective type of trypanosome in
the salivary glands--corresponding to the final stage of the cycle of
development--is similar to the short and stumpy form found in the blood
of the vertebrate host.” The cycle is thus very similar to that of _T.
gambiense_ in _G. palpalis_ (fig. 30).
[84] _Proc. Roy. Soc._, B, lxxxvii, p. 516.
CULTURE.--J. G. Thomson (1912),[85] and subsequently Thomson and
Sinton, succeeded in cultivating _T. rhodesiense_ in a modified
Novy-MacNeal medium. The development obtained resembled that of the
trypanosome in the intestine of _Glossina_.
[85] _Annals Trop. Med. and Parasitol._, vi, pp. 103, 331.
GENERAL NOTE ON TRYPANOSOMES WITH POSTERIOR NUCLEI.
Posteriorly placed nuclei have been found to occur not only in _T.
rhodesiense_ by Stephens and Fantham (1910), but also in _T. pecaudi_
by Wenyon (1912), in _T. brucei_ by Blacklock (1912), and in _T.
equiperdum_ by Yorke and Blacklock (1912).
Recently Stephens and Blacklock (1913)[86] have shown that two
trypanosomes, different morphologically, have been confused under the
name _T. brucei_. One of these is polymorphic (_i.e._, it exhibits long
and slender as well as short and stumpy forms) and came from Uganda,
while the other is monomorphic and is the original Zululand strain
described by Bruce from cattle suffering from “nagana.” Bruce (1914)
considers that morphological change has occurred in _T. brucei_ in its
passage through laboratory animals, and thus explains the diversity of
views. The posterior nuclear forms described by Blacklock occurred in
the Uganda strain of _T. brucei_. (See p. 95.) Similarly, a posterior
nuclear form, _T. equi_, has been separated from _T. equiperdum_. (See
p. 98.)
[86] _Proc. Roy. Soc._, B, lxxxvi, p. 187.
Again, Bruce and his colleagues on the Royal Society Commission
investigating sleeping sickness in Nyasaland, have stated (April,
1913) that “evidence is accumulating that _T. rhodesiense_ and _T.
brucei_ (Plimmer and Bradford) are identical.” The exact identity of
trypanosomes showing posterior nuclei is, then, far from settled,
although Laveran by cross immunity tests has declared that _T. brucei_
is distinct from _T. rhodesiense_. No one has yet seen posterior nuclei
in _T. gambiense_.
*Trypanosoma cruzi*, Chagas, 1909.
Syn.: _Schizotrypanum cruzi_, Chagas, 1909.
The trypanosome was discovered by Chagas[87] in the intestine of the
bug, _Triatoma_ (_Conorhinus_) _megista_, in Brazil, and then in the
blood of a small monkey bitten by the bug. A little later it was found
in the blood of a child, aged two years, suffering from irregular
fever, extreme anæmia and enlarged glands in the State of Minas Geraes,
Brazil. Chagas found that he was able to infect many of the usual
laboratory animals with the trypanosome, by allowing the bug to bite
them. He was also able to culture the parasite on blood agar.
[87] _Mem. Inst. Oswaldo Cruz._, i, p. 159.
Chagas found the Reduviid bug, _Triatoma megista_, in the houses of the
poorer inhabitants of the Brazilian mining State, and that it attacked
the people, more especially the children, at night, biting the face.
On this account the insect is called “barbeiro” by the inhabitants.
The bite is somewhat painful. The disease has since been found in other
parts of Brazil, _e.g._, Matta de São João in Bahia province, Goyaz,
Matto Grosso and São Paulo provinces, as well as in Minas Geraes.
_Morphology._--The trypanosome has a large blepharoplast or kinetic
nucleus. It is stated to occur both free and in the red blood
corpuscles in the peripheral blood. It is about 20 µ long, on an
average.
Two forms of the parasite (fig. 33, _6_, _7_) are described in the
human blood. In one free form there is a large egg-shaped blepharoplast
and the posterior (aflagellar) end of the parasite is drawn out. The
blepharoplast (kinetic nucleus) may have a chromatin appendage. The
nucleus is oval or band-like, containing a karyosome. The flagellum,
starting close to the blepharoplast or its appendage, has a free
portion of variable length. The other free form in the blood has a more
or less round, terminal blepharoplast, smaller than in the first form,
without a chromatin appendage as a rule. The body of this second form
is decidedly broader than that of the first mentioned.
[Illustration: FIG. 33.--_Trypanosoma cruzi_. Schizogony. _1_,
merozoite in red blood corpuscle; _2_, parasite totally enclosed in
red cell, no flagellum or undulating membrane; _3_-_5_, parasites
partially enclosed in red cell; _6_, _7_, parasites in human blood;
_8_-_11_, parasites in lungs of the monkey, _Callithrix_; _12_, _13_,
initial forms of schizogony; _14_, _15_, schizogony in the lungs of
_Callithrix_. (After Chagas.)]
The dimorphism has been interpreted sexually, the first mentioned forms
being termed males, the second ones females. The correctness of this
interpretation is very doubtful.
No sign of longitudinal division was ever seen in the peripheral
blood or in the internal organs. The “endocorpuscular” forms may be
completely or partially enclosed in the red cell or only attached
thereto (fig. 33, _1_-_5_). At the beginning of infection the
endocorpuscular forms are the more numerous. Some authorities, however,
doubt these stages.
_Life-history in the Vertebrate Host._--Chagas found fluctuations in
the number of the parasites in the peripheral blood. He believes the
increase of the parasites to be periodic.
The investigations of Chagas and of Hartmann have revealed two types
of multiplication which take place in the internal organs of the
vertebrate host.
(_a_) The first type--which possibly belongs to another organism,
_Pneumocystis carinii_, see p. 90--occurs in the capillaries of the
lungs. The flagellate parasite entering the lung capillaries loses
its flagellum and undulating membrane. Its body becomes curved, and
the two ends fuse, and so an oval mass is formed (fig. 33, _8_-_11_).
In some cases the blepharoplast disappears, in other cases it blends
or fuses with the nucleus. The nucleus of the rounded parasite then
divides into eight by successive divisions (fig. 33, _12_-_15_). Next
the body, which is surrounded by its own periplast, also divides,
giving rise to eight tiny daughter individuals or merozoites (fig. 33,
_15_). The merozoites lie inside the periplast, which acts as a sort of
“cyst wall.” The merozoites are said to exhibit dimorphism, and Chagas
has interpreted the dimorphism in terms of sex. The daughter forms,
produced by the parent trypanosomes which kept their blepharoplasts,
themselves have blepharoplasts as well as nuclei, and have been
termed “males” or “microgametes.” The merozoites, arising from parent
trypanosomes which lost their blepharoplasts, have themselves only
nuclei, and have been called “females” or “macrogametes.” In the case
of the so-called “female” forms the single nucleus divides into two
unequal parts, of which the smaller becomes the blepharoplast, and
a flagellum is formed later. The so-called “males” possess early a
rudiment of a flagellum. Both kinds of merozoites escape from the
parent periplast wall, and enter red blood corpuscles. They grow into
flagellates within the corpuscles, and then become free as adult
trypanosomes in the blood-stream.
[Illustration: FIG. 34.--_Trypanosoma cruzi_. Transverse section of a
striated muscle containing rounded forms of the parasite in the central
portion. × 1,000 approx. (After Vianna.)]
(_b_) The second mode of multiplication is one of asexual reproduction
(schizogony or agamogony). It was first described by Hartmann from
hypertrophied endothelial cells of the lungs. It has since been found
in the cardiac muscle, in the neuroglia of the central nervous system,
and in striped muscle (fig. 34). In laboratory animals it has also
been found in the testicle and suprarenal capsules. In these tissues
the parasite is intracellular, appearing as a small rounded body with
nucleus and blepharoplast, without flagellum or undulating membrane. In
other words the parasite is _Leishmania_-like in the body tissues, and
recalls the organism of kala-azar.
Chagas considers this second mode of multiplication to be strictly
asexual. By this means the number of parasites in the vertebrate host
is increased, and symptoms are produced. On the other hand the first
mode of multiplication, seen in the lung capillaries, is considered
by Chagas to be a process of gametogony, in which sexual forms are
differentiated. He finds that (1) the adult trypanosomes exhibit
a dimorphism in human blood rarely seen in artificially infected
guinea-pigs. In these guinea-pigs (infected from guinea-pigs) the
so-called gametogony in the lungs is seldom seen. (2) The intermediate
host, _Triatoma_ (_Conorhinus_), becomes infective if fed directly on
infected human blood, but very rarely so if fed on guinea-pigs. Chagas
is led to believe that the occurrence of sexual forms constantly in
the blood of man implies a greater resistance to infection on the part
of man than on the part of guinea-pigs or other animals, assuming the
general hypothesis that the formation of gametes represents a reaction
of the Protozoön to unfavourable conditions. In human infection the
number of parasites is always less than in laboratory animals, and
their presence in the blood is transitory, lasting from fifteen to
thirty days in acute cases. In many cases examination of the tissues
at death has shown the presence of parasites in patients who did not
exhibit them in the general circulation.
[Illustration: FIG. 35.--_Trypanosoma cruzi_. Development in _Triatoma
megista_. _1_-_6_, forms found in the mid gut of _Triatoma_; _7_
flagellate forms found in the posterior part of the gut of _Triatoma_.
(After Chagas.)]
_Life History in the Invertebrate Host._--About six hours after the
ingestion of infected blood by the bug (_Triatoma megista_), the
kinetic nucleus of the trypanosome moves towards the nucleus, and the
flagellum is usually lost (fig. 35, _1_-_5_). The parasite becomes
rounded and _Leishmania_-like (fig. 35, _3_-_5_), and multiplies
rapidly by division. After a time, multiplication having ceased,
the rounded forms become pear-shaped and develop a flagellum at the
more pointed end. Crithidial forms (fig. 35, 7) are thus produced
and pass into the intestine, where they multiply and may be seen in
about twenty-five hours after the ingestion of blood. The crithidial
forms may also be found in the rectum and fæces. The last stage in the
invertebrate is a small, trypanosome-like type, long and thin with a
band-like nucleus and conspicuous kinetic nucleus. These parasites
are found in the hind gut and in the body cavity. They find their
way into the salivary glands, and are the forms (fig. 36) which are
transmissible to a new vertebrate host. The development in the bug
takes about eight days altogether, after which time the bugs are
infective.
There are thus three principal phases in the development of _T. cruzi_
in _Triatoma megista_: (1) A multiplicative phase (_Leishmania_-like)
in the stomach of the bug, (2) a crithidial phase, which is also
multiplicative, in the hind-gut, and (3) a trypanosome phase, which is
“propagative,” and apparently passes through the wall of the alimentary
canal into the body cavity and so into the salivary glands.
[Illustration: FIG. 36.--_Trypanosoma cruzi_. Forms found in the
salivary glands of _Triatoma megista_. (After Chagas.)]
Brumpt found that _T. cruzi_ could live in _Cimex lectularius_,
_C. boueti_, and _Ornithodorus moubata_. The _Cimex_ fæces may be
infective. Blacklock found multiplication of the parasite in _C.
lectularius_.
_Culture._--The trypanosome can be cultivated on Novy-MacNeal’s blood
agar, and the cultural forms resemble those described in the bug.
_Possible Reservoir._--Chagas thinks that probably the armadillo or
“tatu” (_Dasypus novemcinctus_) may be the reservoir of _T. cruzi_.
He also thinks that _Triatoma geniculata_ is a transmitter; it lives
in the burrows of the armadillo. Other carriers may be _Triatoma
infestans_ and _T. sordida_.
_Clinical Features._--The trypanosomiasis of Brazil, produced by _T.
cruzi_ and spread by _Triatoma_ spp. has received various names, such
as oppilação, canguary, parasitic thyroiditis, and coreotrypanosis. It
is also known as the human trypanosomiasis of Brazil, South American
trypanosomiasis, and Chagas’ disease.
Chagas[88] reports two principal forms--acute and chronic. The _acute
infection_ is rare, and is characterized by increase in the volume
of the thyroid gland, pyrexia, a sensation of crackling in the skin,
enlarged lymphatic glands in the neck, axilla, etc., while the liver
and spleen are increased in volume. Sclerosis of the thyroid gland is
found at autopsy and fatty degeneration of the liver. During an attack
of fever, trypanosomes are found in the blood. The acute form was only
observed in children.
[88] _Brazil Medico_, Nov. 15, 1910. Longer account in _Mem. Inst.
Oswaldo Cruz_, iii, pp. 219–275. See _Sleep. Sick. Bull._, Nos. 35 and
40.
_In the chronic form_ Chagas reports several varieties: (_a_) A
pseudo-myxœdematous form, occurring in most cases, especially up to
the age of 15. There is hypertrophy of the thyroid gland or at least
signs of hypothyroidism, general hypertrophy of glands, disturbance
of heart rhythm, and nervous symptoms. (_b_) The myxœdematous form
is characterized by similar symptoms, especially by considerable
swelling of the thyroid body, and myxœdema of the subcutaneous cellular
tissue; sometimes there is a true pachydermic cachexia. (_c_) In the
nervous form there are motor disturbances, aphasia, disturbances of
intelligence or signs of infantilism, athetosis of the extremities
and idiocy. There are also paralytic symptoms of bulbar origin,
disturbances of mastication, phonation and deglutition, and in some
cases convulsive attacks. (_d_) The cardiac form, characterized by
disturbance of the heart rhythm. In all these forms the parasite is
found at autopsy in the nervous substance, brain, bulb and heart.
Vianna (1911)[89] has studied the histopathology of the disease.
Some of the chief points are: in the heart muscle destruction of the
sarcoplasm, followed by interstitial myocarditis; in the central
nervous system invasion of the neuroglia cells and inflammatory
reaction; in the suprarenal capsule invasion of medulla or cortex;
inflammatory reaction can also be seen in the kidneys, the hypophysis
and thyroid gland.
[89] _Mem. Inst. Oswaldo Cruz_, iii, p. 276.
Recently Chagas states[90] that “schizotrypanosomiasis” has been found
in a child 15 to 20 days old, and that _Trypanosoma cruzi_ has also
been found in a fœtus--the mother being infected with the trypanosome.
The trypanosomiasis can, then, be transmitted hereditarily.
[90] _Rev. Med. S. Paulo_ (1912), xv, p. 337.
*Trypanosoma lewisi*, Kent, 1881.
The trypanosome has a nucleus somewhat displaced anteriorly, about
one-third of the way from the anterior (flagellar) end of the body, a
relatively straight edge to the undulating membrane, and a rod-shaped
blepharoplast (fig. 37, A). It averages about 25 µ long and 1·5 µ broad.
Much attention has been devoted in recent years to the elucidation
of the life history of the rat parasite, _Trypanosoma lewisi_. It
is usually non-pathogenic to its host. It has been shown that the
trypanosome can be transmitted from rat to rat by the rat-flea,
_Ceratophyllus fasciatus_, and by _Ctenocephalus canis_ (the so-called
dog-flea). (See also p. 92). The flagellate may also persist, but
doubtfully develop, in the rat-louse, _Hæmatopinus spinulosus_. These
researches may now be summarized.
[Illustration: FIG. 37.--_Trypanosoma lewisi_, from rat’s blood. A,
ordinary form; B, small form; C, D, stages in equal binary fission; E,
elongate form (_longocaudense_ type), resulting from division as seen
in D; F, unequal binary fission; G, H, multiple fission into four and
eight; I, small form; J, binary fission of small form; K, division
rosette. × 2,000. (After Minchin and Thomson.)]
_Life Cycle in the Vertebrate Host._--After infection of a rat, the
trypanosomes usually appear in the animal’s blood in five to seven
days. This incubation period applies either to a natural or an
artificial infection. The trypanosomes first observed in the rat’s
blood are diverse in form (fig. 37), being small, medium and large
in size. This diversity is explained by the rapid multiplication
taking place. A trypanosome may divide by equal longitudinal fission
(fig. 37, C, D), but more commonly multiple fission occurs (fig. 37,
G, H), and is unequal. Rosette forms are produced, in which the parent
form can be recognized by its long flagellum (fig. 37, H) and attached
to it are daughter individuals, smaller in size, from which flagella
are growing. Minchin and J. D. Thomson (1912) find that the daughter
forms may be set free sometimes with a crithidia-like facies (fig. 37,
I), the blepharoplast being anterior but near to the nucleus. The
daughter forms, when set free, may themselves divide by binary or
multiple fission, in the latter case forming rosettes (fig. 37, K).
Rosette forms were described by Moore, Breinl and Hindle in 1908.
Lingard, some years ago, described as a distinct species, _T.
longocaudense_, certain forms with markedly elongate posterior ends
(fig. 37, E). According to Minchin, “these forms appear to arise
by binary fission” (fig. 37, D). These long drawn-out forms “are
of constant occurrence and very numerous at a certain stage of the
multiplication period.” It is about the eighth or tenth day after
infection that the multiplication of _T. lewisi_ is at its maximum in
the rat’s blood. About the twelfth or thirteenth day the trypanosomes
seen in the blood appear uniform. According to Minchin (1912)[91] the
rat “gets rid of its infection entirely sooner or later, without having
suffered, apparently, any marked inconvenience from it, and is then
immune against a fresh infection with this species of trypanosome.”
There is, then, a cycle of development in the vertebrate host. Minchin
notes that the records of the pathogenicity of _T. lewisi_ in rats,
causing their death, need further investigation.
[91] “Protozoa,” p. 294.
_T. lewisi_ inoculated into dormice (_Myoxus nitela_) and jerboas may
become pathogenic thereto.
Carini found cysts in the lungs of rats infected with _T. lewisi_.
He thought the cysts were schizogonic stages of the trypanosome,
comparable with those found in the lungs of animals sub-inoculated
with _T. cruzi_. Delanoë (1912)[92] has found, however, that such
cysts, containing eight vermicules, occurred in rats uninfected with
_T. lewisi_. Delanoë concludes that the pneumocysts are independent of
_T. lewisi_, and represent a new parasite, _Pneumocystis carinii_. The
pneumocysts may be allied to the Coccidia, and must be considered when
investigating the life-cycle of a trypanosome in a vertebrate host.
Some of the stages of _T. cruzi_ may possibly be of this nature.
[92] _C. R. Acad. Sci._, clv, p. 658.
_Life-cycle in the Invertebrate Host._--This occurs in fleas, and has
been investigated in considerable detail by Minchin and Thomson in
_Ceratophyllus fasciatus_, and by Nöller in _Ctenocephalus canis_ and
_Ctenopsylla musculi_.
When infected rat’s blood is taken up by the flea, the parasites pass
with the ingested blood direct to the mid-gut of the Siphonapteran.
In the flea’s stomach they multiply in a somewhat remarkable manner,
namely, by penetration of the cells of the lining epithelium, and
division inside the epithelial cells. Inside these lining cells the
trypanosomes first grow to a large size and then form large spherical
bodies, within which nuclear multiplication occurs (fig. 38, A-F).
Any one of these large spherical bodies contains at first a number of
nuclei, blepharoplasts and developing flagella, the original flagellum
still remaining attached for a time. The cytoplasm then divides into
daughter trypanosomes which are contained within an envelope, formed
by the periplast of the parent parasite. Inside the periplast envelope
are a number of daughter trypanosomes “wriggling very actively; the
envelope becomes more and more tense, and finally bursts with explosive
suddenness, setting free the flagellates, usually about eight in
number, within the host-cell” (fig. 38, F). The daughter forms escaping
from the host cell into the stomach lumen of the flea are fully formed,
long trypanosomes.
[Illustration: FIG. 38.--_Trypanosoma lewisi_. Developmental stages
from stomach of rat flea. O, ordinary blood type; A-F, stages occurring
in gut-epithelium of flea, when the trypanosome becomes rounded and
undergoes multiplication, forming in F eight daughter trypanosomes; G,
type of trypanosome resulting from such division which passes back to
the rectum. × 2,000. (After Minchin.)]
The trypanosomes (fig. 38, G) pass into the flea’s rectum. The next
phase is a crithidial one. The parasites become pear-shaped, in which
the blepharoplast (kinetic nucleus) has travelled anteriorly past the
nucleus towards the flagellum (fig. 39). The crithidial forms attach
themselves to the wall of the rectum, and multiply by binary fission
(fig. 39, D). A stock of parasites is thus formed which, according to
Minchin and Thomson, “persist for a long time in the flea--probably
under favourable conditions, for the whole life of the insect”
(fig. 39, A-I).
From the crithidial forms of the rectum, according to Minchin,
small infective trypanosomes arise by modification morphologically
(fig. 39, J--M). The flagellum grows longer and draws out more the
anterior part of the body, the blepharoplast migrates posteriorly,
behind the nucleus, and carries with it the flagellar origin. These
trypanosomes are small, but broad and stumpy (fig. 39, N), and can
infect a rat. Minchin and Thomson formerly considered that the small,
stumpy, infective trypanosomes pass forwards from the rectum into the
stomach, and “appear to be regurgitated into the rat’s blood when the
flea feeds.” However, the small infective trypanosomes were previously
described by Swellengrebel and Strickland.[93] They may be found in the
flea’s fæces. Nöller (1912)[94] has found that the development of _T.
lewisi_ proceeds quite well in the dog flea (_Ctenocephalus canis_) in
Germany. Wenyon confirms this, and states that the human flea, _Pulex
irritans_, and the Indian rat-flea, _Xenopsylla cheopis_, are also able
to serve as true hosts for _T. lewisi_.
[93] _Parasitology_, iii, p. 360.
[94] _Arch. f. Protistenkunde_, xxv, p. 386.
[Illustration: FIG. 39.--_Trypanosoma lewisi_. Developmental stages
from rectum of rat-flea. A, early rectal form; C, D, division of
crithidial form; E, group of crithidial forms; F--I, crithidial forms
without free flagella, some becoming rounded; J--M, transitional forms
to trypanosome type seen in N, which represents the final form in the
flea. × 2,000. (After Minchin.)]
Nöller stated that rats were not infected with _T. lewisi_ by infective
fleas biting them, but by the rats licking up the fæces passed by
the fleas while feeding. This is not in agreement with Minchin and
Thomson’s earlier views of regurgitation, which, apparently, they have
now abandoned.[95] Wenyon (1912) confirms Nöller’s experiments. He took
a dog flea, containing infective trypanosomes in its fæces, and allowed
it to feed on a clean rat. The fæces of the flea, passed while feeding,
were carefully “collected on a cover glass and taken up in culture
fluid with a fine glass pipette.” The contents of the pipette were
discharged into the mouth of a second clean rat. Injury to the rat’s
mouth was carefully avoided. The first rat, on which the infective flea
was fed, did not become infected, while the second rat, in whose mouth
infective flea fæces were placed, became infected in six days.
[95] Report to Advis. Comm. Trop. Dis. Research Fund for 1913, p. 74.
When infective forms of _T. lewisi_ have been developed within the gut
of a rat flea, they may enter and infect the vertebrate host by[96]
(_a_) being crushed and eaten by the rodent; (_b_) the rat may lick
its fur on which an infected flea has just passed infective excrement;
or (_c_) the rat may lick, and infect with flea excrement, the wound
produced by the bite of the flea.
[96] Nuttall, _Parasitology_, v, p. 275.
The time taken for the full development of _T. lewisi_ in the flea is
about six days. The intracellular phase is at its height about the end
of the first day; the crithidial phase, in the flea’s rectum, begins
during the second day; the stumpy, infective trypanosomes are developed
in the rectum about the end of the fifth day.
Wenyon[97] writes that, “the fleas, when once infected with _T.
lewisi_, remain infected for long periods, for though many small
infective trypanosomes are washed out of the gut at each feed, those
that remain behind multiply to re-establish the infection of the hind
gut. Further, the infection is still maintained even if the flea is
nourished on a human being, so that fresh human blood does not appear
to be destructive to the infective forms in the flea.”
[97] Report to Advis. Comm. Trop. Dis. Research Fund, October, 1912,
p. 91. See also _Journ. Lond. Sch. Trop. Med._, ii, p. 119.
The best method of controlling fleas during experiments is that due to
Nöller. He adopted the method of showmen who exhibit performing fleas,
and secure them on very fine silver wire.
Of fleas fed on an infected rat only about 20 per cent. become
infective. About 80 per cent. are immune. If fleas are examined
twenty-four hours after feeding, trypanosomes will be found in all, so
that many of the parasites are destined to degenerate.
It may be of interest to note that Gonder[98] (1911) has shown
that a strain of _T. lewisi_ resistant to arsenophenylglycin loses
its resistance after passage through the rat-louse, _Hæmatopinus
spinulosus_. These experiments suggest that physiological “acquired
characters” may be lost by passage through an invertebrate host.
[98] _Centralbl. f. Bakt._, Orig., lxi, p. 102.
*Trypanosoma brucei*, Plimmer and Bradford, 1899.
_Trypanosoma brucei_ was discovered by Sir D. Bruce in 1894 in cattle
in Zululand and was named _T. brucei_ by Plimmer and Bradford in 1899
in honour of its discoverer. This trypanosome is of considerable
economic importance, as it is responsible for the fatal tsetse fly
disease, or “nagana,” in cattle, horses and dogs. The disease is widely
distributed in Africa and is transmitted from host to host by the
tsetse, _Glossina morsitans_, and other species of _Glossina_. The
virus is maintained in nature in certain big game, such as wildebeest,
bushbuck and koodoo, which thus act as living reservoirs of disease
from which the tsetse may become infected. These reservoir hosts are
not injured, apparently, by the presence of the parasites.
_T. brucei_ is rapidly fatal to the small laboratory animals, such as
rats and mice. Horses, asses and dogs practically always succumb to its
attacks, while a very small number of cattle recover from “nagana.” The
disease is characterized by fever, destruction of red blood corpuscles,
severe emaciation and by an infiltration of coagulated lymph in the
subcutaneous tissue of the neck, abdomen and extremities giving a
swollen appearance thereto. The natural reservoirs in which _T.
brucei_ has been long acclimatized are unaffected by the trypanosomes,
while the newer hosts, such as imported cattle in Africa, are rapidly
destroyed by their action.
[Illustration: FIG. 40.--_Trypanosoma brucei._ × 2,000. (After Laveran
and Mesnil.)]
The general morphology and life history in the vertebrate host is that
of a typical trypanosome (fig. 40). Its length is from 12 µ to 35 µ,
its breadth from 1·5 µ to 4 µ. Multiplication by longitudinal division
proceeds in the peripheral blood (fig. 26), while latent, leishmaniform
bodies are produced in the internal organs.
Bruce and colleagues[99] have quite recently (June, 1914) described
the development of a Zululand strain of _T. brucei_ in _G. morsitans_.
The tsetse flies were bred out in Nyasaland. In vertebrate blood
the _brucei_ strain was polymorphic. The development was like that
found for _T. gambiense_ in _G. palpalis_ (fig. 30), and by Bruce
and colleagues for _T. rhodesiense_ in _G. morsitans_ in Nyasaland.
Long trypanosomes were found in the proventriculus of the tsetse.
Crithidial, rounded or encysted, and immature “blood forms” occurred in
the salivary glands; and finally infective, stumpy, “blood forms” were
differentiated in the salivary glands. The period of development of _T.
brucei_ in _G. morsitans_ takes about three weeks, and then the fly
becomes infective. Bruce believes that _T. rhodesiense_ of Nyasaland
and _T. brucei_ of Zululand are the same, their cycles of development
in _G. morsitans_ being “marvellously alike.” (But see Laveran, p. 80.)
[99] _Proc. Roy. Soc._, B, lxxxvii, p. 526.
_T. brucei_ has been cultivated with difficulty by Novy and MacNeal,
using blood agar. The best treatment for nagana is arsenic in some form.
It is probable that more than one trypanosome has been confused under
the name _T. brucei_, more especially as the occurrence of many species
of trypanosomes in various animals in Africa was not suspected
until comparatively recent times. It has been shown by Stephens and
Blacklock (1913) that the original Zululand strain of _T. brucei_
was monomorphic, while the organism sent from Uganda, and at the
time believed by Bruce to be the same as the Zululand trypanosome,
has been found to be polymorphic, with morphological resemblances
to _T. rhodesiense_. Stephens and Blacklock[100] have suggested the
name _T. ugandæ_ for the polymorphic trypanosome, which, however, has
marked resemblances with *Trypanosoma pecaudi*, and they are, perhaps,
identical. _T. pecaudi_ was the name given by Laveran[101] in 1907 to
the causal agent of “baleri” in equines and sheep in the French Sudan.
_T. pecaudi_, which is dimorphic, is widely distributed in Africa.
An extremely small number of both _T. pecaudi_ and _T. ugandæ_ have
been shown to possess posterior nuclei. _T. pecaudi_ is transmitted by
various species of _Glossina_, and is said to develop in the gut and
proboscis of the fly.
[100] _Proc. Roy. Soc._, B, lxxxvi, p. 187.
[101] _C.R. Acad. Sci._, cxliv, p. 243.
On the other hand, Bruce and colleagues (1914), examining a strain sent
from Zululand in 1913, state that _T. brucei_ is polymorphic. Bruce
(1914) suggests that passage through laboratory hosts has influenced
and altered the morphology of the parasite.
*Trypanosoma evansi*, Steel, 1885.
Syn.: _Spirochæta evansi_, Steel, 1885; _Hæmatomonas evansi_,
Crookshank, 1886; _Trichomonas evansi_, Crookshank, 1886.
_Trypanosoma evansi_, first found by Evans in 1880, in India, is the
causal agent of the disease known as “surra.” The malady affects more
particularly horses, mules, camels and cattle in India and neighbouring
countries, such as Burma and Indo-China. It occurs also in Java, the
Philippines, Mauritius and North Africa. Elephants may be affected.
A serious outbreak among cattle in Mauritius occurred in 1902, the
disease being imported into the island. The symptoms are fever,
emaciation, œdema, great muscular weakness and paralysis culminating in
death.
_T. evansi_ varies from 18 µ to 34 µ in length and 1·5 µ to 2 µ in
breadth. It has a pointed posterior extremity, and, anteriorly,
there is a free portion to the flagellum (fig. 41). It is possibly
monomorphic, but a few broad forms occur. The trypanosome multiplies by
longitudinal fission in the blood. Rounded leishmaniform stages occur
in the spleen of the vertebrate host, which stages Walker[102] (1912)
considers to be phases of schizogony.
[102] _Philippine Journ. Sc._ (Sect. B), vii, p. 53.
The parasite is transmitted in nature by various species of _Tabanus_
and _Stomoxys_, though at present little is known of the life-history
within these invertebrate hosts.
Dogs are said to contract the disease by feeding on animals dead of
surra.
A variety of _T. evansi_ is the cause of “mbori” in dromedaries in
Africa (Sahara and Sudan). Another possible variety, or closely allied
form, is _T. soudanense_, the causal agent of “el debab” in camels and
horses in North Africa, especially Algeria and Egypt.
[Illustration: FIG. 41.--_Trypanosoma evansi_. × 2,000. (Original. From
preparation by Fantham.)]
An extraordinary example of the possible infection of a human being
with an animal trypanosome is recorded in the case of Professor
Lanfranchi, of the Veterinary School, Parma. The Professor became
infected with trypanosomes, although only nagana and surra were
maintained in his laboratory, and he himself had never visited the
tropics. He suffered from irregular attacks of fever and was œdematous,
but his mind remained clear. The identification of the trypanosome
from Lanfranchi’s blood has been a matter of great difficulty.
Apparently Mesnil and Blanchard (1914)[103] consider the strain found
in the patient is almost indistinguishable in its reactions from _T.
gambiense_, though the parasite is monomorphic. Lanfranchi considers
that he was infected with _T. evansi_.
[103] _Bull. Soc. Path. Exot._, vii, p. 196.
*Trypanosoma equinum*, Voges, 1901.
Syn.: _Trypanosoma elmassiani_, Lignières.
_Trypanosoma equinum_ was found by Elmassian to be the cause of the
fatal disease, “mal de caderas,” of horses and dogs, in South America
(Paraguay, Argentine, Bolivia). The name refers to the fact that in
the disease, as in other trypanosomiases, the hind quarters become
paralysed. Cattle are refractory to inoculation.
[Illustration: FIG. 42.--_Trypanosoma equinum_. × 2,000. (After Laveran
and Mesnil.)]
_T. equinum_ is about 22 µ to 24 µ long and about 1·5 µ broad
(fig. 42). Although this trypanosome is very active, yet it is
characterized by the blepharoplast (kinetic nucleus) being very minute
or even absent, as the granule sometimes seen may be the basal granule
of the flagellum.
The mode of transmission of _T. equinum_ is not known with absolute
certainty. Migone has shown that the parasite causes a fatal disease
in the large South American rodent, the capybara (_Hydrochœrus
capybara_). This animal appears to be a reservoir of the parasite. Dogs
may become infected by eating diseased capybaras, and it is suggested
that the infection is spread from the dogs to horses by the agency of
fleas. Some authorities consider that _T. equinum_ may be spread by
various _Tabanidæ_ and by _Stomoxys_. Neiva (1913)[104] doubts all
these modes of transmission in Brazil, and suggests _Chrysops_ or
_Triatoma_ as vectors.
[104] _Brazil Medico_, xxvii, p. 366.
*Trypanosoma equiperdum*, Doflein, 1901.
Syn.: _Trypanosoma rougeti_, Laveran and Mesnil.
The malady of horses known as “dourine” or “mal du coït” is due
to a trypanosome, _T. equiperdum_, discovered by Rouget in 1894.
“Dourine”--also known as “stallion disease” or “covering disease”--is
found among horses and asses in Europe, India, North Africa and North
America. The trypanosome is transmitted by coitus, and so far as is
known not by insect agency.
[Illustration: FIG. 43.--_Trypanosoma equiperdum._ × 2000
approximately. (Original. From preparation by Fantham.)]
The progress of the disease may be considered under three periods. The
_period of œdema_, when signs of œdema of the genitalia are seen. The
œdema is generally painless and non-inflammatory. This period lasts
about a month. It is succeeded by the _period of eruption_, which
sets in about two months after infection. Circular œdematous areas
(“plaques”), often about the size of a two-shilling piece, appear
under the skin of the sides and hind quarters, and also, at times,
under the skin of the neck, thighs and shoulders. The eruption is
variable, but usually lasts about a week and leaves the animal in an
enfeebled condition. Gland enlargement and swelling of the joints and
synovia also may occur. The third period of the disease is described
as that _of anæmia and paralysis_. The animal becomes very anæmic,
emaciation is marked, superficial non-healing abscesses often form, and
conjunctivitis and ulcerative keratitis can occur. Paralysis ensues,
and in from two to eighteen months the animal dies. In the acute form
of the disease the animal may die after the first period from acute
paralysis.
It is difficult to find the trypanosomes in naturally infected animals,
and they are best obtained from the plaques of the eruption. Apparently
the parasite occurs more in the lymph than in the blood.
Ruminants are said to be refractory to this trypanosome.
_T. equiperdum_ is about 25 µ to 28 µ in length on an average, but
varies from 16 µ to 35 µ. Its cytoplasm is relatively clear, and does
not show chromatic granules (fig. 43). It is stated to be monomorphic.
It has been shown recently by Blacklock and Yorke (1913)[105] that
there is another trypanosome giving rise to dourine in horses. This
trypanosome is dimorphic (resembling _T. pecaudi_ and _T. ugandæ_), and
is named _T. equi_. Previously _T. equiperdum_ and _T. equi_ had been
confused.
[105] _Proc. Roy. Soc._, B, lxxxvii, p. 89.
Uhlenhuth, Hübner and Worthe have demonstrated the presence of
endotoxins in _T. equiperdum_. These endotoxins may be set free by
trypanolysis.
*Trypanosoma theileri*, Bruce, 1902.
This parasite, 60 µ to 70 µ long, and 4 µ to 5 µ broad, is
distinguished for its large size, though it is not so large as _T.
ingens_ from Uganda oxen, whose length may be 72 µ to 122 µ, and
breadth 7 µ to 10 µ. The posterior end of _T. theileri_ is drawn out.
Small forms of the flagellate are known, 25 µ to 53 µ in length.
Probably other forms of the parasite have the nucleus posterior, and
these flagellates were formerly separated as _T. transvaaliense_
(Laveran, 1902). Myoneme fibrils may be seen on its body. The
pathogenicity of this organism is doubtful, it was formerly thought
to be the causal agent of “gall-sickness” in cattle in South Africa.
_T. theileri_ also occurs in Togoland, German East Africa, and
Transcaucasia. Allied or identical parasites occur in cattle in India.
[Illustration: FIG. 44.--_Trypanosoma theileri._ × 2,000. (After
Laveran and Mesnil.)]
_Trypanosoma theileri_, specific to cattle, is perhaps transmitted by
the fly _Hippobosca rufipes_ in South Africa.
*Trypanosoma hippicum*, Darling, 1910.
_Trypanosoma hippicum_ causes the disease of mules known as
“murrina.”[106] It was found in mules imported to Panama from the
United States. It can live in other equines. The parasite varies
from 18 µ to 28 µ in length, and is from 1·5 µ to 3 µ broad. Its
undulating membrane is little folded. The trypanosome has a noticeable
blepharoplast. It can penetrate mucous membranes, and it is thought
that the trypanosome may be transmitted during coitus. It may also
be spread mechanically by species of _Musca_, _Sarcophaga_ and
_Compsomyia_, sucking the wounds of infected animals and carrying over
the trypanosomes to wounds on healthy ones.
[106] _Bull. Soc. Path. Exot._, iii, p. 381.
*Endotrypanum schaudinni*, Mesnil and Brimont, 1908.
This organism was discovered in the blood of a sloth (_Cholœpus
didactylus_), in South America (French Guiana).[107] It possesses
special interest, in that the best known form of the organism is
endoglobular, inhabiting the erythrocytes of the sloth. A free
trypanosome in the same animal was considered to be different from the
endoglobular form, which was somewhat like a peg-top, and possessed a
short flagellum. Darling[108] (November, 1914) has seen the organism in
Panama. He describes free crithidial forms in shed blood, but not in
the blood-stream of the sloth.
[107] _C. R. Soc. Biol._, lxv, p. 581.
[108] _Journ. Med. Research_, xxxi, p. 195.
*Trypanosoma boylei*, Lafont, 1912.
This is a parasite of the Reduviid bug, _Conorhinus rubrofasciatus_.
The insect attacks man in Mauritius, Réunion and other places.
Lafont infected rats and mice by intraperitoneal injection with the
gut-contents of infected bugs. Trypanosomes appeared in the mice. Other
flagellate types were assumed by the parasites in the bug.
MONOMORPHIC TRYPANOSOMES.
A number of trypanosomes, characterized by relative uniformity in
size and structure, may be considered under this heading. They occur
in cattle, sheep, goats and horses in Africa, especially West Africa.
Morphologically, they are characterized by the posterior (aflagellar)
part of the body being swollen, while the anterior part narrows. The
nucleus is central and situated at the commencement of the narrowing of
the body. The blepharoplast is almost terminal, the undulating membrane
is narrow and not markedly folded, so that the flagellar border lies
close to or along the body. The flagellum may or may not possess a free
portion.
Some recent workers have considered that _T. brucei_ (Zululand strain)
and _T. evansi_ are also monomorphic, but they do not exhibit the
general characteristics outlined above. _T. brucei_ and _T. evansi_
have already been considered separately.
The monomorphic trypanosomes, as defined above, include:--
*Trypanosoma vivax*, Ziemann, 1905.
This trypanosome[109] occurs in cattle, sheep and goats, and was
first found in the Cameroons. It is fatal to cattle. Equines are also
affected. Antelopes are the possible reservoirs of the trypanosome. It
is probably transmitted by _Glossina palpalis_ and other tsetse flies.
Its movement is very active. It possesses a free flagellum (fig. 45)
and it averages 23 µ to 24 µ in length. _T. cazalboui_ (Laveran,
1906)--the causal agent of “souma” in bovines and equines in the French
Sudan--is probably synonymous with _T. vivax_.
[109] See Bruce and colleagues (1910), _Proc. Roy. Soc._, B, lxxxiii,
p. 15.
[Illustration: FIG. 45.--_Trypanosoma vivax_. × 2,000. (Original. From
preparation by Fantham.)]
*Trypanosoma capræ* (Kleine, 1910) is allied, but is somewhat broader
and more massive. It was found in goats in Tanganyika.
*Trypanosoma congolense*, Broden, 1904.
Probable synonyms.--_Trypanosoma dimorphon_, Laveran and Mesnil,
1904; _Trypanosoma nanum_, Laveran, 1905; _Trypanosoma pecorum_,
Bruce, 1910; _Trypanosoma confusum_, Montgomery, 1909.
This trypanosome causes disease among horses (_e.g._, Gambia horse
sickness), cattle, sheep, goats, pigs, and dogs. It is widely
distributed in Central Africa (_e.g._, Gambia, Congo, Uganda,
Nyasaland), the strain probably being maintained naturally in big game.
It is transmitted by various _Glossinæ_, and perhaps by _Tabanus_
and _Stomoxys_. It is said to develop in the gut and proboscis of
_Glossina palpalis_ and _G. morsitans_. The trypanosome averages 13 µ
to 14 µ in length and has no free flagellum (fig. 46). It is about 2 µ
broad. Formerly _T. nanum_ and _T. pecorum_ were said to differ in
their pathogenicity, the former being said not to infect the smaller
laboratory animals. Yorke and Blacklock (1913), however, consider that
the virulence varies and that these trypanosomes are probably the same.
[Illustration: FIG. 46.--_Trypanosoma congolense_. × 2,000. (Original.
From preparation by Fantham.)]
[Illustration: FIG. 47.--_Trypanosoma uniforme_. × 2,000. (Original.
From preparation by Fantham.)]
The _T. dimorphon_ originally obtained by Dutton and Todd (1903) in
Gambian horse sickness has been shown to be a mixture of _T. vivax_ and
_T. congolense_.
*Trypanosoma simiae* (_T. ignotum_) is like _T. congolense_. It
averages 17·5 µ long. It is virulent to monkeys and pigs.
*Trypanosoma uniforme*, Bruce, 1910.
This trypanosome was found in oxen in Uganda.[110] It can be inoculated
to oxen, goats and sheep, but is refractory to dogs, rats and
guinea-pigs. It has been found in antelopes. It resembles _T. vivax_,
but is smaller (fig. 47), averaging 16 µ in length. A free flagellum is
present. It is transmitted by _Glossinæ_.
[110] _Proc. Roy. Soc._, B, lxxxiii, p. 176.
[Illustration: FIG. 48.--_Trypanosoma rotatorium_, from blood of a
frog. × 1,400. (After Laveran and Mesnil.)]
Many other trypanosomes occur in mammals, while birds, reptiles,
amphibia (fig. 48) and fish also harbour them. The discussion of these
forms does not come within the scope of the present work. They are
dealt with in Laveran and Mesnil’s “Trypanosomes et Trypanosomiases,”
2nd edit., 1912.
GENERAL NOTE ON DEVELOPMENT OF TRYPANOSOMES IN GLOSSINA.
Before concluding the account of trypanosomes, it may be of interest to
remark that several African trypanosomes develop in various species of
_Glossina_, and are found in different parts of the alimentary tract
and in the proboscis. Thus (_a_) _T. vivax_, _T. uniforme_ and _T.
capræ_ develop in the fly’s proboscis (labial cavity and hypopharynx)
only; (_b_) _T. congolense_, _T. simiæ_ and _T. pecaudi_ develop first
in the gut of the fly and then pass forward to its proboscis; and (_c_)
_T. gambiense_ and _T. rhodesiense_ develop first in the gut and later
invade the salivary glands of the tsetse. The proboscis or the salivary
glands in such cases are termed by Duke[111] the _anterior station_ of
the trypanosome, wherein it completes its development.
[111] _Repts. Sleeping Sickness Commission Roy. Soc._ (1913), xiii,
p. 82.
ADAPTATION OF TRYPANOSOMES.
These flagellates may exhibit power of adaptation to changes of
environment, such as those due to the administration of drugs,
change of host, etc. A few examples of such mutations may be briefly
considered:--
(1) _Blepharoplastless Trypanosomes_.--_T. brucei_ may become resistant
to pyronin and oxazine. Accompanying this drug resistance is a change
in morphology, namely, the loss of the blepharoplast (Werbitzki).[112]
A race or strain of blepharoplastless trypanosomes may be thus produced
which retains its characteristic feature after as many as 130 passages
(Laveran).[113] Oxazine is the more powerful drug, and it acts directly
on the blepharoplast. (Compare the natural blepharoplastless character
of _T. equinum_.)
[112] _Centralbl. f. Bakt._ (1910), Orig., liii, p. 303.
[113] _Bull. Soc. Path. Exot._, iv, p. 233.
(2) Reference has been made on p. 93 to the experiments of Gonder,
who showed that a strain of _T. lewisi_ rendered resistant to
arsenophenylglycin lost its resistance after passage through the rat
louse. This is in marked contrast with the retention of drug resistance
during passage by inoculation from rat to rat.
(3) _T. lewisi_ from the blood of a rat when transferred to a snake
seems largely to disappear, as very few flagellates are seen. When
blood from the snake is inoculated into a clean rat, then trypanosomes
reappear in the rat, but they are not all like those originally
inoculated. It seems certain that, in such a case, changes in form and
virulence of the trypanosome have occurred. Similar experiments were
made with _T. brucei_ from rats to adders and other animals and back to
rats. Changes in the form and virulence of _T. brucei_ occurred.
These interesting experiments were performed by Wendelstadt and
Fellmer.[114]
[114] _Zeitschr. f. Immunitatsforschung_, iv, p. 422 (1909), and v,
p. 337 (1910).
Genus. *Herpetomonas*, Saville Kent, 1881.
_Herpetomonas_ is a generic name for certain flagellates possessing a
vermiform or snake-like body, a nucleus placed approximately centrally,
and a blepharoplast (kinetic nucleus) near the flagellar end. There
is no undulating membrane (fig. 49, _a_). The organisms included
in this genus certainly possess one flagellum, while according to
Prowazek (1904) _Herpetomonas muscæ-domesticæ_, the type species,
possesses two flagella united by a membrane. Patton,[115] Porter[116]
and others affirm, however, that the biflagellate character of _H.
muscæ-domesticæ_ (from the gut of the house-fly) is merely due to
precocious division. The matter is further complicated by the generic
name _Leptomonas_, given by Kent in 1881, to an uniflagellate organism
found by Bütschli in the intestine of the Nematode worm, _Trilobus
gracilis_. This parasite, _Leptomonas bütschlii_, has not yet been
completely studied. Until these controversial points relating to
the identity or separation of _Herpetomonas_ and _Leptomonas_ have
been satisfactorily settled, we may retain the better known name
_Herpetomonas_ for such uniflagellate, vermiform organisms. However,
the name _Leptomonas_, having been used by Kent two pages earlier
in his book (“Manual of the Infusoria”) than _Herpetomonas_, would
have priority if the two generic names were ultimately shown to be
synonymous.
[115] _Arch. f. Protist._, xiii, p. 1.
[116] _Parasitology_, ii, p. 367.
A full discussion of these interesting and important flagellates hardly
comes within the purview of the present work; brief mention can only be
given here to certain species.
The Herpetomonads occur principally in the digestive tracts of insects,
such as Diptera and Hemiptera. They are also known in the guts of
fleas and lice, but are not confined to blood-sucking insects. One
example, _H. ctenocephali_ (Fantham, 1912)[117] occurs in the digestive
tracts of dog fleas, _Ctenocephalus canis_, in England, France,
Germany, Italy, India, Tunis, etc. It is a natural flagellate of the
flea, and might easily be confused with stages of blood parasites in
the gut of the dog flea. Dog fleas are stated by Basile to transmit
canine kala-azar, which is believed to be the same as human infantile
kala-azar. Confusion is further likely to arise since herpetomonads
pass through pre-flagellate, flagellate and post-flagellate or
encysted stages; pre- and post-flagellate stages being oval or rounded
and _Leishmania_-like. The post-flagellate stages are shed in the
fæces, and are the cross-infective stages by means of which new hosts
are infected by the mouth. The possible presence of such natural
flagellates must always be considered when experimenting with fleas,
lice, mosquitoes, etc., as possible vectors of pathogenic flagellates
like _Leishmania_ and _Trypanosoma_. _H. pediculi_ (Fantham, 1912)
occurs in human body lice.[118] See further remarks on pp. 107, 112.
[117] _Bull. Path. Exot._, vi, p. 254.
[118] _Proc. Roy. Soc._, B, lxxxiv, p. 505.
[Illustration: FIG. 49.--_a_, _Herpetomonas_; _b_, _Crithidia_; _c_,
_Trypanosoma_. (After Porter.)]
Laveran and Franchini (1913–14)[119] have recently succeeded in
inoculating _Herpetomonas ctenocephali_, from the gut of the dog flea,
intraperitoneally into white mice, and producing an experimental
leishmaniasis in the mice. A dog was also infected. They have also
succeeded in infecting mice with _H. pattoni_--a natural flagellate of
the rat flea--by mixing infected rat fleas with the food of the mice,
and by causing them to ingest infected fæces of rat fleas. Further,
they have shown that infection with the herpetomonas occurs naturally
by this method, that is, by the rodents eating the fleas and not by the
insects inoculating the flagellates into the vertebrates when sucking
blood. These experiments shed an interesting light on the probable
origin of _Leishmania_ and its cultural herpetomonad stage, which were
very probably once parasitic flagellates in the gut of an insect.
[119] _C. R. Acad. Sci._, clvii, pp. 423, 744. _Ibid._, clviii,
pp. 450, 770. _Bull. Soc. Path. Exot._, vii, 605.
Fantham and Porter[120] (1914–15) have shown that young mice may be
inoculated or fed with _Herpetomonas jaculum_, from the gut of the
Hemipteran, _Nepa cinerea_ (the so-called “water-scorpion”), with fatal
results. The pathogenic effects are like those of kala-azar. They also
showed that the post-flagellate stages of the herpetomonads seemed most
capable of developing in the vertebrate.
[120] _Proc. Camb. Philosoph. Soc._, xviii, p. 39.
A herpetomonad, _H. davidi_, has been found in the latex of species
of the plant-genus _Euphorbia_ in Mauritius, India, Portugal, etc. It
is apparently transmitted to the plants by _Hemiptera_. The plants
sometimes suffer from “flagellosis.”
Franchini (1913)[121] has described a new parasite, _Hæmocystozoon
brasiliense_, from the blood of a man who had lived in Brazil for many
years. It possesses flagellate and rounded stages, and is closely
allied to the herpetomonads.
[121] _Bull. Soc. Path. Exot._, vi, pp. 156, 333, 377.
Genus. *Crithidia*, Léger, 1902, emend. Patton, 1908.
_Crithidia_ is the generic name of vermiform flagellates with a central
nucleus, a blepharoplast or kinetic nucleus in the neighbourhood of the
principal nucleus, and a rudimentary undulating membrane bordered by a
flagellum arising from a basal granule, which is the centrosome of the
kinetic nucleus (fig. 49_b_). The anterior or flagellar end of the body
is attenuated and fades off as the undulating membrane.
_Crithidia fasciculata_, the type species, was found by Léger in the
alimentary canal of _Anopheles maculipennis_. Crithidia occur in
bugs, flies, fleas,[122] and ticks. Some of them are found in the
body-fluid of the invertebrate host as well as in the gut. Others
may be restricted to the body cavity or intestine respectively. _C.
melophagia_ from the sheep-ked, _Melophagus ovinus_, and _C. hyalommæ_
from the hæmocœlic fluid of the tick, _Hyalomma ægyptium_, pass into
the ovaries and eggs of their hosts, and the young keds or ticks are
born infected.
[122] See Porter, _Parasitology_, iv, p. 237.
_C. fasciculata_ has been shown by Laveran and Franchini to be
inoculable into white mice, producing a sort of experimental
leishmaniasis therein. In one case cutaneous lesions were produced like
those of Oriental sore.
Crithidia are natural flagellates of Arthropoda, with their own
pre-flagellate, flagellate and post-flagellate stages, and must not be
confused with transitory crithidial stages of trypanosomes.
Genus. *Leishmania*, Ross, 1903.
With an oval body containing nucleus and blepharoplast (kinetic
nucleus) but no flagellum. An intracellular parasite in the vertebrate
host.
Included in the genus _Leishmania_ are three species, namely:--
(1) _Leishmania donovani_, Laveran and Mesnil, 1903, the parasite
of Indian kala-azar, a generalized systemic disease, usually
fatal, occurring in subjects of all ages.
(2) _Leishmania tropica_, Wright, 1903, the parasite of Delhi boil,
Oriental sore, Aleppo button--a localized, cutaneous disease,
usually benign.
(3) _Leishmania infantum_, Nicolle, 1908, the parasite of infantile
kala-azar, occurring in children (and a few adults) around
the shores of the Mediterranean. The disease is perhaps a
form of Indian kala-azar, and the parasite is probably identical
with _L. donovani_.
These diseases may be termed collectively leishmaniases. The morphology
of the various species is practically identical.
*Leishmania donovani*, Laveran and Mesnil, 1903.
Syn.: _Piroplasma donovani_, Laveran and Mesnil.
The parasite of Indian kala-azar was demonstrated in 1900 by Leishman
from a _post-mortem_ examination of a case of “Dum-Dum fever,” but
details were not published till May, 1903. In July, 1903, Donovan found
similar bodies from cases in Madras. Rogers succeeded in cultivating
the parasite in July, 1904.[123] The original centre of the disease was
probably Assam; it occurs also in Madras, Ceylon, Burma, Indo-China,
China and Syria. A variety of this leishmaniasis is found in the Sudan.
The patient becomes emaciated, with a greatly enlarged spleen. There is
anæmia and leucopenia.
[123] The literature up to 1912, on kala-azar and other leishmaniases
is reviewed in the _Kala-azar Bulletin_. Afterwards in the _Tropical
Diseases Bulletin_.
The parasite, commonly known as the Leishman-Donovan body, is
intracellular (fig. 50, 2, 3). It is found in the endothelial cells
of the capillaries of the liver, spleen, bone-marrow, lymphatic
glands and intestinal mucosa, and in the macrophages of the spleen
and bone-marrow. Some host cells may contain many parasites. It is
rather rare in the circulating blood, but may be found in the blood
from the femoral, portal and hepatic veins. It does not occur in
the red blood corpuscles as was formerly thought. The parasites
liberated from the endothelial cells are taken up by the mononuclear
and polymorphonuclear leucocytes. The Leishman-Donovan body is the
resting stage of a flagellate. As found in man it is a small, oval
organism, about 2·5 µ to 3·5 µ in length by 2 µ in breadth, and
containing two chromatinic bodies, corresponding to the nucleus and
kinetic nucleus (blepharoplast) of a flagellate. The latter element
is the smaller and more deeply staining, and is usually placed at the
periphery, transversely to the longer axis of the oval organism.
There is sometimes a very short, slightly curved filament to be seen,
which may be a rhizoplast. Multiplication takes place by binary or
multiple fission. The presence of the parasite used to be demonstrated
by splenic or hepatic puncture; nowadays it can be demonstrated in
peripheral blood, _e.g._, of the finger, or by culture of infected
blood.
[Illustration: FIG. 50.--_Leishmania donovani_. _1_, Free forms,
each with nucleus and rod-shaped blepharoplast (after Christophers);
_2_, endothelial cell and leucocytes containing parasites (after
Christophers); _3_, capillary in the liver showing endothelial cells
containing parasites (after Christophers); _4_, two parasites escaping
from a leucocyte in the alimentary canal of the bug (after Patton);
_5_, further development in bug (after Patton); _6_, young flagellate
forms in bug (after Patton); _7_-_11_, culture forms (after Leishman);
_7_, _8_, _9_, show development of flagellum.]
_L. donovani_ can be cultivated in citrated splenic blood, under
aerobic conditions, at 22° to 25° C. This was first accomplished by
Rogers (1904). It is not so easily culturable as _L. infantum_ on the
Novy-MacNeal-Nicolle medium.[124] _L. donovani_ is inoculable with
some difficulty into experimental animals--in India, white rats, white
mice, dogs and monkeys (_Macacus spp._), have been inoculated. The
Sudan variety, somewhat less virulent, is inoculable to monkeys. Row
also produced a local lesion in _Macacus sinicus_ by subcutaneous
inoculation of _L. donovani_. Parasites taken from such a local lesion
were found to be capable of producing a generalised infection in
_Macacus sinicus_ and white mice.
[124] For the composition of this medium, see Appendix.
In cultures the various species of _Leishmania_ all grow into
herpetomonad, uniflagellate organisms (fig. 50, 10), about 12 µ to
20 µ in body length. On this account Rogers[125] and Patton place the
Leishman-Donovan body within the genus _Herpetomonas_. The method of
culture may be used in diagnosing leishmaniases.
[125] _Proc. Roy. Soc._, B, lxxvii, p. 284.
Kala-azar is very probably an insect-borne disease. Patton[126]
suspects the bed-bug to be the transmitter and finds (fig. 50, _4_-_6_)
that the Leishman-Donovan body can develop into the flagellate stage
in the digestive tract of the bed-bug. Feeding experiments are
unsatisfactory, since there are very few cases in which the parasites
occur in sufficient numbers in the peripheral blood to make the
infection of the insect possible, or at any rate easy. In examining
the alimentary tracts of insects for possible flagellate stages of
_Leishmania_, it must be remembered that in many insects natural
flagellate parasites, belonging to the genus _Herpetomonas_, may occur
therein; such natural insect flagellates may be harmless, and have no
connection with the life-cycle of _L. donovani_. Natural herpetomonads
are known to occur in the alimentary tracts of flies, mosquitoes,
sand-flies, fleas and lice, but not in bed-bugs. Further, if such
flagellates are able to be inoculated into and live within vertebrate
hosts, producing symptoms like those of leishmaniasis, the origin of
kala-azar is indicated (see pp. 104, 112).
[126] _Sci. Mem. Govt. India_, Nos. 27, 31 (1907–08).
*Leishmania tropica*, Wright, 1903.
Syn.: _Helcosoma tropicum_, Wright, 1903; _L. wrighti_, Nicolle,
1908; _Ovoplasma orientale_, Marzinowsky and Bogrow.
It is believed by some that the parasite was first described by
Cunningham in 1885, and studied by Firth in 1891, being called by
him _Sporozoon furunculosum_. If these earlier studies were of the
parasite, then its correct name is _L. furunculosa_, Firth, 1891.
The benign disease produced by this parasite has received many names,
among the best known being Oriental sore, Tropical sore, Delhi boil and
Aleppo button. These names, however, are not happy ones, as cutaneous
leishmaniasis (_e.g._, on the ear) is now known to occur in the New
World, for example in Mexico, Venezuela, Brazil and neighbouring
States. However, it may be necessary to subdivide cutaneous
leishmaniases later.
In the Old World the disease occurs in India, Persia, Arabia and
Transcaucasia. It is also known in Algeria, Northern Nigeria, Egypt,
Sudan, Crete, Calabria, Sicily and Greece.
The boils often occur on the face, and before ulceration the parasites
may be found in the cells at the margin and floor of the “button.” In
searching for parasites the scab should be removed and scrapings made
from the floor and edges. Where lesions occur atrophy of the epidermis
takes place, and infiltration of mononuclear cells (_e.g._, plasma
cells, lymphoid and endothelial cells) follows. The parasites are
intracellular, being found inside mononuclear cells. In non-ulcerating
sores, Cardamitis found some free parasites. Non-ulcerating forms
are said to occur in the Sudan. In the Old World the sores are often
limited to exposed surfaces of the body. Infection of mucous membranes
(such as the lip, palate, buccal and nasal membranes) may occur,
especially in South America, and are often known there as “Espundia.”
Christopherson (1914) has recorded a case in Khartoum.
_Leishmania tropica_ is equally well cultivated on Novy-MacNeal-Nicolle
medium or on citrated blood. The usual temperature for cultivation
is 22° to 28° C., though Marzinowski claims to have cultivated the
parasite at 37° C. _L. tropica_ can be inoculated into monkeys and
dogs, with the production of local lesions. Material from a human sore
or flagellates from a culture may be thus successfully inoculated. Also
infected material may be rubbed directly into a scarified surface. The
incubation period is long, extending over several months. The duration
of the disease may be from twelve to eighteen months. Recovery from
one attack of tropical sore confers immunity, and the Jews in Bagdad
inoculate their children with the disease on a part of the body which
will be covered, and so secure immunity in adult life.
The mode of transmission of _L. tropica_ is unknown. Wenyon (1911)[127]
has found that the parasite develops into the flagellate stage in the
digestive tract of _Stegomyia fasciata_ in Bagdad. Patton (1912)[128]
has found similar development in the bed-bug in Cambay. The house-fly,
_Phlebotomus_ and _Simulium_ have been suspected as transmitters in
different parts of the world.
[127] _Parasitology_, iv, p. 387.
[128] _Sci. Mem. Govt. India_, No. 50.
An interesting announcement has been made recently (May, 1913), that
Neligan has found that _L. tropica_ occurs in dogs in Teheran, Persia,
producing ulcers on the dogs’ faces (_cf._ natural occurrence of _L.
infantum_ in dogs--see p. 110). Yakimoff and Schokhor (1914),[129] have
found the disease in dogs in Tashkent.
[129] _Bull. Soc. Path. Exot._, vii, p. 186.
Gonder[130] (1913) has performed some interesting experiments showing
the relation of infantile kala-azar to Oriental sore. Gonder infected
mice with _L. infantum_ and with _L. tropica_. He used culture material
and injected intraperitoneally or intravenously. In each a general
infection resulted, with enlargement of the liver and spleen. Later,
however, mice injected with Oriental sore (North African variety)
developed peripheral lesions on the feet, tail and head, and the
lesions contained _Leishmania_. No such peripheral lesions developed
in the case of the mice infected with the kala-azar virus. Gonder
suggested that Oriental sore, like kala-azar, is really a general
infection overlooked in its earlier stages, and that it is in the
later stages that peripheral lesions on the skin are developed. Row
(1914)[131] also obtained a general infection in a mouse by the
injection of cultures of _L. tropica_ from Oriental sore of Cambay.
[130] _Arch. f. Schiffs- u. Trop. Hyg._, xvii, p. 397.
[131] _Bull. Soc. Path. Exot._, vii, p. 272.
*Leishmania infantum*, Nicolle, 1908.[132]
Infantile splenic anæmia has been long known in Italy. It also
occurs in Algeria, Tunis, Tripoli, Syria, Greece, Turkey, Crete,
Sicily, Malta,[133] Spain and Portugal. This leishmaniasis is, then,
distributed along the Mediterranean littoral; also in Russia. Cathoire
(1904) in Tunis and Pianese (1905) in Italy were among the first to see
the parasite. Nicolle then found the parasite in patients in Tunis, and
further found spontaneous infection in dogs. The patients are usually
children between the ages of 2 and 5 years. There are a few cases known
in which the infantile type of leishmaniasis occurred in youths and
adults of the ages of 17 to 19, while one patient in Calabria was 38
years old. The symptoms are like those of Indian kala-azar. Several
Italian investigators and others consider that _L. infantum_ is the
same as _L. donovani_, and that the latter name should be used for the
parasite of Mediterranean leishmaniasis. This view, as to the identity
of _L. donovani_ and _L. infantum_, seems coming into general favour.
[132] _Arch. Inst. Pasteur Tunis_, i, p. 26.
[133] _See_ Wenyon (1914), _Trans. Soc. Trop. Med. and Hyg._, vii,
p. 97; also Critien (1911), _Annals Trop. Med. and Parasitol._, v,
p. 37.
There are, however, differences between the Indian and infantile
kala-azars, in addition to the ages of the patients affected,
thus: (_a_) As regards cultures, it is found that _L. infantum_ is
readily grown on the Novy-MacNeal-Nicolle (“N.N.N.”) medium (saline
blood-agar), and that sub-cultures are easily obtained; in citrated
blood _L. infantum_ grows with difficulty. The reverse is the case with
regard to culture media for _L. donovani_, which grows with difficulty
on the N.N.N. medium, but relatively easily in citrated splenic blood.
(_b_) Considering inoculability into experimental animals, it is found
that _L. donovani_ is inoculated generally with some difficulty into
white rats, white mice and monkeys, and with greater difficulty into
dogs, while _L. infantum_ can be inoculated into several experimental
animals, especially into dogs and monkeys, with ease. (_c_) At present
_L. donovani_ is not known to occur spontaneously in animals, but _L.
infantum_ is found naturally in dogs in the Mediterranean region, and
the disease in dogs is often referred to as canine kala-azar. Kittens
have occasionally been found infected. However, these differences must
not be emphasized too much.
The material for cultivation is obtained from punctures of spleen,
liver or bone-marrow of cases infected with _L. infantum_. It is
not always easy, however, to infect from cultures, as the cultural
flagellates inoculated into the body are often phagocytosed.
Similarly, the material for animal inoculation is obtained from
emulsions of infected spleen, liver or bone-marrow. Dogs and monkeys
are easily inoculated with such material; Nicolle inoculates into the
liver or the peritoneal cavity. Mice, white rats, guinea-pigs and
rabbits only show slight infections after such inoculations.
Dogs infected experimentally with infantile leishmaniasis may show
either acute or chronic symptoms. The acute course occurs more often in
young dogs, and is usually fatal in three to five months. The chronic
course is found more commonly in older dogs, and may last seventeen to
eighteen months. In acute forms there is irregular fever, progressive
wasting, diarrhœa occasionally, motor disturbances involving the hind
quarters, and the animal dies in a comatose condition. In the chronic
form the animal may appear well, except for loss of weight. The
parasites may be found in the internal organs of these experimental
dogs, but are not numerous in the peripheral blood except at times of
high fever. Experimental monkeys live about three months.
It may be interesting to record the number of dogs found to be infected
naturally with leishmaniasis in various countries. In Tunis, Nicolle
and Yakimoff found about 2 per cent. infected out of about 500 dogs
examined. Sergent in Algiers found 9 infected out of 125 dogs examined.
In Italy and Sicily, Basile found about 40 per cent. of the dogs to be
infected out of 93 examined at Rome and Bordonaro. Cardamitis found
15 infected out of 184 examined in Athens. In Malta, Critien found 3
infected out of 30 dogs examined. Alvares found 1 infected dog out of
19 examined in Lisbon. Pringault has recently (December, 1913) found
an infected dog in Marseilles.[134] Yakimoff and Schokhor found 24 per
cent. infected out of 647 dogs examined in Turkestan.
[134] _Bull. Soc. Path. Exot._, vii, p. 41.
The distribution of the parasites in the body of the human patient is
much the same as in the case of Indian kala-azar. Critien records
the finding of parasites in the mucous flakes of the stools of a
three-year-old Maltese child.[135] Intestinal lesions rarely occur in
infantile leishmaniasis.
[135] Quoted by Leishman (1911) in his interesting review of
Leishmaniasis, _Journ. Roy. Army Med. Corps_, xvii, p. 567, xviii,
pp. 1, 125. Also _Quart. Journ. Med._ v, pp. 109–152.
_Ætiology._--Infantile leishmaniasis is stated to be transmitted
by fleas, especially dog fleas, _Ctenocephalus canis_ (= _Pulex
serraticeps_), and by _Pulex irritans_. Children living in contact with
infected dogs may be bitten by infected dog fleas, and so contract
the disease. Basile (1910–11) and Sangiorgi (1910) state that they
found _L. infantum_ parasites in the digestive tract of the dog flea.
After searching they found infected dog fleas on the beds, mattresses,
and pillows used by children suffering from the disease. Franchini
(1912) thinks that _Anopheles maculipennis_ may be concerned in the
transmission.
Basile[136] tried a number of experiments to show that infantile
leishmaniasis is transmitted by fleas, thus:--
[136] Numerous papers in _Rendiconti R. Accad. dei Lincei_ (Rome), xix,
xx (1910–11).
(1) Fleas were taken from a healthy dog. They were placed in vessels
containing infected spleen-pulp and allowed to feed thereon. The fleas
were then killed and dissected, and portions of the gut-contents
examined for parasites. The remainder of the gut was emulsified
and injected into a young puppy, whose bone-marrow had been shown
previously to be uninfected. Basile states that the puppy became
infected. The parasites are said to increase in number in the flea’s
gut.
(2) Two healthy pups, each a month old, and born in the laboratory,
were placed in a disinfected, flea-proof cage. A few days after, an
infected dog was placed in the cage, so that fleas from the infected
dog could pass on to the puppies. A month later the two pups became
infected, parasites being found in them after liver puncture. A number
of control puppies from the same litter remained uninfected and in good
health.
(3) Basile next used other laboratory-born puppies, a month old. Four
of the litter were placed in a disinfected, flea-proof gauze cage in
Rome. The cage was isolated from other dogs. Fleas obtained from an
infected area in Sicily were placed in the cage. The puppies were
examined by hepatic puncture, but were found to be negative for two
months. Then two of the puppies showed infection, and six days later
the remaining two puppies were found to be infected, and all four died.
They showed irregular temperatures, and were getting thin. Control
puppies remained healthy.
From these experiments Basile concludes that fleas transmit
leishmaniasis. However, Basile did not exclude the possible occurrence
of natural herpetomonads in the gut of the fleas.[137] _Herpetomonas
ctenocephali_ is known to occur in the gut of _Ctenocephalus canis_. A
natural _Herpetomonas_ is also known in the gut of _Pulex irritans_,
as well as a _Crithidia_ (_C. pulicis_, Porter). These natural
flagellates of the fleas pass through non-flagellate stages, like the
Leishman-Donovan body. In consequence Wenyon and Patton, among others,
have criticized Basile’s results. Further, other investigators, such as
Wenyon and Da Silva (1913), have repeated Basile’s flea experiments and
been unable to confirm them.
[137] See Fantham, _Brit. Med. Journ._, 1912, ii, p. 1196.
In feeding and inoculation experiments the incubation period of the
parasite may be long, and so it is necessary to wait a long time to see
whether the parasite will develop.
_Immunity._--Nicolle has tried some experiments with _L. infantum_ and
_L. tropica_. He finds that in animals recovery from an attack of the
former confers immunity against infection by the latter and vice-versâ.
Laveran[138] records that a monkey having an immunity against _L.
infantum_ was also immune to _L. donovani_.
[138] _Annales Inst. Pasteur_ (1914–15), xxviii, pp. 823, 885; xxix,
pp. 1, 71.
As mentioned on p. 103, Laveran and Franchini (1913), working in Paris,
have succeeded in inoculating _Herpetomonas ctenocephali_, a natural
flagellate in the gut of the flea, _Ctenocephalus canis_, into white
mice. Leishmaniform stages of the flea flagellate were recovered
from the peritoneal exudate, blood and organs of the mice some weeks
after inoculation. The parasites may also be conveyed by way of the
digestive tract of the vertebrate. Similar experiments have succeeded
with _H. pattoni_. These experiments go to show, together with those
of Fantham and Porter with _H. jaculum_ (see p. 104), that, in the
words of the latter authors, “it may be expected that the various
leishmaniases, occurring in different parts of the world, will prove to
be insect-borne herpetomoniases.”
Genus. *Histoplasma*, Darling, 1906.
Under the name _Histoplasma capsulatum_,[139] Darling described
small round or oval parasites, enclosed in a refractile capsule, and
each containing a single nucleus. The bodies were found in cases of
splenomegaly in Panama. They occurred in the endothelial cells of
the small blood-vessels of the liver, spleen, lungs, intestine and
lymphatic glands, and also within the leucocytes. A few flagellates
were stated to occur in the lungs. The parasite has usually been
placed near _Leishmania_, but recently Rocha-Lima has stated that
_Histoplasma_ is a yeast.
[139] _Journ. Amer. Med. Assoc._, xlvi, p. 1283: _Journ. Exptl. Med._
(1909), xi, p. 515.
Genus. *Toxoplasma*, Nicolle and Manceaux, 1908.
The genus was created for crescentic, oval or reniform parasites,
2·5 µ to 6 µ by 2 µ to 3 µ, possessing a single nucleus and
multiplying by binary fission. They occur in mononuclear and
polymorphonuclear cells in the blood, spleen, liver, peritoneum etc.
(fig. 51). The parasites have been found in the gondi, dog, rabbit,
mole, mouse, pigeon and other birds. Although various species names
have been given to the parasites in these hosts, it seems probable,
from cross infection experiments, that there is but one species with
several physiological races. Splendore[140] (1913) has described a
flagellate stage.
[140] _Bull. Soc. Path. Exot._, vi, p. 318.
[Illustration: FIG. 51.--_Toxoplasma gondii_, endocellular or free in
the peritoneal exudate of infected mice. 1, 2, mononuclear leucocytes
containing toxoplasms. 3, polynuclear, containing parasites. 4, 5,
6, endothelial cells containing toxoplasms, agglomerated in 6. 7,
agglomeration forms. 8–11, free forms. 12–13, division stages. × 1,600.
(After Laveran and Marullaz.)]
[Illustration: FIG. 52.--_Toxoplasma pyrogenes._ 1, body found in
blood. 2–7, bodies found] in spleen. [1 is about the size of a red
blood corpuscle, as drawn in the figures]. Magnification not stated.
(After Castellani.)]
Castellani (1913–14)[141] has described similar parasites from a case
of splenomegaly, with fever of long standing, in a Sinhalese boy. The
bodies were found in the spleen and more rarely in the blood (fig. 52).
Castellani has named them _Toxoplasma pyrogenes_. Further researches
are needed.
[141] _Journ. Trop. Med. and Hyg._, xvii, p. 113.
THE SPIROCHÆTES.
The Spirochætes are long, narrow, wavy, thread-like organisms, with
a firm yet flexible outer covering or periplast. There is a diffuse
nucleus internally in the form of bars or rodlets of chromatin
distributed along the body. In some forms there is a membrane or crista
present (fig. 53), which in the past was compared with the undulating
membrane of a trypanosome, but the membrane of a spirochæte does not
undulate. Progression is very rapid, corkscrew-like and undulatory
movements occurring simultaneously.
The genus _Spirochæta_ was founded by Ehrenberg in 1833 for an organism
which he discovered in stagnant water in Berlin. Ehrenberg named
the organism _Spirochæta plicatilis_. According to Zuelzer (1912)
_S. plicatilis_ does not possess a membrane or crista, but an axial
filament. _S. gigantea_ has been described by Warming from sea-water.
Spirochætes occur in the crystalline style and digestive tract of many
bivalve molluscs. The first molluscan spirochæte to be studied was
that of the oyster, named by Certes (1882) “_Trypanosoma_” _balbianii_
(fig. 53). Similar spirochætes, probably belonging to the same species,
occur in various species of _Tapes_ and in _Pecten_ (the scallop).
_S. balbianii_ has rounded ends (fig. 53). Other spirochætes occur
in freshwater mussels (_Anodonta_ spp). _S. anodontæ_, studied by
Keysselitz (1906) and by Fantham (1907), has pointed ends. Gross (1911)
suggested the generic name _Cristispira_ for molluscan spirochætes,
because they possess a well-marked membrane or “crista,” which appears
to be absent from _S. plicatilis_, according to Zuelzer’s researches.
[Illustration: FIG. 53.--_Spirochæta balbianii._ _a_, basal granule
or polar cap. _b_, chromatin rodlets. _c_, membrane (“crista”). _d_,
myonemes in membrane. (After Fantham and Porter.)]
Schaudinn in 1905 founded the genus _Treponema_ for the parasite of
syphilis (_T. pallidum_), discovered by him and by Hoffmann. According
to Schaudinn the Treponemata have no membrane or crista. The pathogenic
agent of yaws or frambœsia, discovered by Castellani, is also placed in
the genus _Treponema_, as _T. pertenue_.
There remain the blood spirochætes. It is somewhat disputed as to
whether these organisms possess a membrane. The present writer
considers that they have a slight membrane or crista. The name of
the genus in which to place the blood-inhabiting forms is somewhat
uncertain and disputed. Various generic names given to them are
_Spirochæta_, _Treponema_, _Spiroschaudinnia_ (Sambon) and _Borrelia_
(Swellengrebel). Included in this division are the causal agents
of relapsing or recurrent fever. These Protists will be named, for
description, Spirochætes without prejudice as to the ultimate correct
generic name.
It is sometimes made a matter of argument as to whether the spirochætes
are Protozoa or Bacteria. Such arguments are somewhat unprofitable.
Morphologically the spirochætes are like the Bacteria in possessing a
diffuse nucleus. They differ from _Spirillum_, an undoubted bacterial
genus, in being flexible and not possessing flagella. Molluscan
spirochætes, however, may appear to have flagella if their membrane
becomes frayed or ruptured, when the myonemes therein (fig. 53),
becoming separated, form apparent threads or flagella (Fantham,
1907–08).[142]
[142] _Quart. Journ. Microsc. Sci._, lii, p. 1.
Again, the mode of division of spirochætes has been used as a criterion
of their bacterial or protozoal affinity. They have been stated to
divide transversely, longitudinally, and by “incurvation,” or bending
on themselves in the form of a *U*, “a form of transverse fission.”
The present writer believes that they divide both transversely and
longitudinally, and that there is a periodicity in their mode of
division at first longitudinal (when there are few spirochætes in, say,
the blood) and then transversely (when spirochætes are numerous in
the blood).[143] Some authors consider that longitudinal division is
explained by “incurvation.”
[143] _Proc. Roy. Soc._, B, lxxxi, p. 500.
The spirochætes of relapsing fever show a remarkable periodic increase
and decrease in numbers in the blood. They are transmitted by ticks
or by lice. They react to drugs (_e.g._, salvarsan or “606”) rather
like trypanosomes, and--like Protozoa, but unlike Bacteria--they
are cultivated with difficulty. These and other criteria have
been used to endeavour to determine whether they are Protozoa or
Bacteria. The present writer believes that they are intermediate in
character, showing morphological affinities with the Bacteria and
physiological and therapeutical affinities with the Protozoa. The group
Spirochætacea, as an appendix to the Protozoa, has been created for
them by the present writer (Jan., 1908). Others have placed them in the
Spirochætoidea of the Bacteria or with the Spirillacea. Doflein (1909)
called them Proflagellata. Further discussion is unnecessary, as they
are undoubtedly Protista (see p. 29).
There is no true conjugation, sex or encystment in spirochætes, but
morphological variation may occur.[144] They may agglomerate.
[144] Fantham, _Parasitology_, ii, p. 392.
The Spirochætes form an interesting chapter in the evolution of
parasites. There are free living forms, parasitic forms in the guts
of both vertebrates and invertebrates, and blood-inhabiting forms.
These probably represent the order of evolution of parasitism. The
blood-inhabiting forms are pathogenic to warm-blooded hosts.
We must now consider the blood Spirochætes and the Treponemata
(organisms of syphilis and of yaws).
THE SPIROCHÆTES OF THE BLOOD.
There are at least two important human parasites included hereunder:--
(_a_) _Spirochæta recurrentis_ (=_S. obermeieri_), (_b_) _Spirochæta
duttoni_.
More is known of the life-cycle of _Spirochæta duttoni_, and it will be
convenient to consider that first.
*Spirochæta duttoni*, Novy and Knapp, 1906.
The specific name _duttoni_ was also given, independently, to this
parasite in 1906 by Breinl and Kinghorn.
_S. duttoni_ is the pathogenic agent of African tick fever in man,
prevalent in the Congo State and other parts of Africa. The full-grown
organism is about 16 µ to 24 µ long, and has pointed ends. It is 0·25 µ
to 0·5 µ broad. P. H. Ross and Nabarro were among the earliest to see a
spirochæte in the blood of patients in Uganda. It is transmitted by the
tick, _Ornithodorus moubata_.
In the blood of the patient some of the spirochætes may show, after
staining, lighter and darker portions (chromatin dots) and evidence
of the possession of a very narrow membrane (fig. 54). The mode of
division has already been discussed. Periodicity in the direction
of division was first described by Fantham and Porter,[145] (1909).
Just before the crisis in African tick fever, Breinl has stated that
_S. duttoni_ becomes thinner in the spleen and bone-marrow and rolls
up into skein-like forms, which are surrounded by a thin “cyst” wall
(probably the periplast). Such occur in apyrexial periods. Inside
the cyst the spirochæte breaks up into granules. Balfour and Sambon
have described somewhat similar rolled up forms, breaking into
granules, inside the red blood cells of Sudanese fowls in the case
of _S. granulosa_ (possibly only a variety of _S. gallinarum_). The
intracorpuscular stage is not definitely established.
[145] _Proc. Roy. Soc._, B, lxxxi, p. 500.
The granule phase, however, is an essential one in the invertebrate
transmitter (fig. 54_c_). In 1905,[146] Dutton and Todd proved
experimentally that _O. moubata_ transmitted _S. duttoni_. They fed
ticks, obtained from Congo native huts in which infected persons
lived, on monkeys and the latter became infected. Dutton and Todd also
found the offspring of infected ticks to be capable of transmitting the
infection to experimental animals. They concluded that _O. moubata_ was
a true intermediate host.
[146] _Liverpool Sch. Trop. Med._, _Memoir_ xvii; _Lancet_, Nov. 30,
1907, p. 1523.
[Illustration: FIG. 54.--_Spirochæta duttoni_. _a_, blood form showing
slight membrane; _b_, granules or coccoid bodies clearly formed within
the organism; _c_, beginning of extrusion of coccoid bodies in the
tick. (After Fantham.)]
A little later in 1905, Koch stated that spirochætes from the gut of
the tick penetrated the gut wall and tissues and found their way into
the eggs in the ovary. Koch figured tangled masses of spirochætes as
occurring in the tick eggs. He found ticks infective to the third
generation. He thought that the infection was spread by the salivary
fluid of the tick, in the act of biting. (This is now known to be
incorrect.) Markham Carter (1907) corroborated Koch’s work on the
spirochætes in the tick eggs, and they have been seen since by Kleine
and Eckard (1913).
Sir William Leishman,[147] in 1909–10, found that at ordinary
temperatures the salivary glands of infected ticks (_O. moubata_) were
not themselves infective, and that the infection occurred by way of the
ticks’ excretion. The spirochætes (contained in the ticks’ excrement)
found their way into the vertebrate host through the wound made by
biting. While feeding, ticks pass large quantities of clear fluid from
the coxal glands; in this fluid an anticoagulin occurs. Some of the
ticks also pass thick, white Malpighian secretion, that is, excrement,
towards the end of the feed. Leishman, using experimental monkeys,
showed that if infected ticks were interrupted while feeding, then no
infection resulted in the monkeys. If, however, the ticks were allowed
to finish their feed, and the Malpighian secretions were passed, then
the experimental monkeys became infected. Fantham[148] and Hindle[149]
(1911), independently, have repeated the experiments with mice.
[147] _Journ. Roy. Army Med. Corps_, xii, p. 123; _Lancet_ (1910),
clxxviii, p. 11.
[148] _Annals Trop. Med. and Parasitol._, v, p. 479.
[149] _Parasitology_, iv, p. 133.
Leishman’s methods and results may be summarized thus: Saline emulsions
of the organs of infected ticks were made, after the organs had been
most carefully dissected out. The ticks were first kept for several
days at certain constant temperatures, such as 24° to 25° C. or blood
heat, 37° C. The saline emulsions of the organs were inoculated,
separately, into experimental animals, and the results recorded:--
At 24° C. At 37° C.
Salivary glands Negative Positive
Malpighian tubules Positive Positive
Gut and contents Positive Positive
Excrement Positive Positive
Genital organs Positive Positive
Coxal fluid is usually negative; thick, white excrement from Malpighian
tubes is positive.
When the ticks were incubated at 21° to 24° C. no spirochætes, as such,
were seen in the organs, except perhaps in the gut, where they often
disappeared in a few days. When the ticks were previously incubated at
35° to 37° C. for two to three days, spirochætes, as such, reappear in
the gut, organs and hæmocœlic fluid. The infection proceeds, not from
the salivary gland, but from the infective excrement, that is, from the
thick, white material voided by the tick while feeding, usually towards
the end of the meal. This Malpighian excrement passes into the wound
caused by the bite, being greatly aided by the clear and more limpid
coxa fluid, which bathes the under surface of the tick’s body, and
mixes with and carries the infective excrement into the wound. Ticks
remain infective for a long time.
[Illustration: FIG. 55.--_Spirochæta duttoni_ and its coccoid bodies
in the tick (_O. moubata_).--Mononuclear cells of the tick (_O.
moubata_) containing (_a_) Spirochæte breaking up into coccoid bodies;
(_b_) Similar tick-cell containing coccoid bodies or granules. Such
mononuclear cells occur in various organs of ticks and in developing
Malpighian tubules. (Original. From preparations by Fantham.)]
The spirochætes in the gut of infected ticks divide by a process
of multiple transverse fission into granules, which are composed
of chromatin (fig. 54). These granules--sometimes known as coccoid
bodies--are capable of multiplication. Leishman first found them in
clumps inside the cells of the Malpighian tubules (_cf._ fig. 55).
To summarize, when spirochætes are ingested by a tick, some of them
pass through the gut-wall into the hæmocœlic (body) fluid. They then
bore their way into the cells of various organs (fig. 55_a_) and break
up into coccoid bodies. In this manner the granules find their way
into the ovaries and ova, thus explaining how the young ticks are born
infected. Inoculation of these chromatinic granules usually produces
infection. Infective granules are also seen in the rudiments of the
Malpighian tubules of embryo ticks. Bosanquet and Fantham (1911),
independently, have shown that molluscan spirochætes also break up
into similar granules or coccoid bodies. Gross has also demonstrated
multiple transverse fission in molluscan forms. Marchoux and Couvy
(1913) and Wolbach (1914) consider the granules or coccoid bodies to be
degeneration products. This is unlikely (see below).
Schuberg and Manteufel have found that certain _O. moubata_, perhaps
30 per cent. of the specimens of a given neighbourhood, may acquire a
natural active immunity against infection with _S. duttoni_.
_S. duttoni_, or a closely allied form (by some termed _S. novyi_),
occurs in Colombia, and is spread by the tick _Ornithodorus turicata_.
In Panama a similar spirochæte is probably spread by _O. talaje_.
*Spirochæta gallinarum*, Stephens and Christophers, 1905 (= *Spirochæta
marchouxi*, Nuttall, 1905).
This Spirochæte, which occurs in fowls and is pathogenic, is
transmitted by the tick _Argas persicus_. It is about 10 µ to 20 µ
long. There is a pathogenic spirochæte known to occur in geese, named
by Sakharoff (1891) _S. anserina_, and found in Caucasia. This may be
the same as _S. gallinarum_, in which case the name _S. anserina_ will
have priority. These organisms cause fever, diarrhœa, anæmia and death.
The life history of the avian pathogenic spirochætes has been studied
by Balfour, by Hindle[150] and by Fantham.[151] It is essentially
similar to that of _S. duttoni_.
[150] _Parasitology_, iv, p. 463.
[151] _Annals Trop. Med. and Parasitol._ (1911), v, p. 479.
Marchoux and Couvy[152] (1913) consider that the “fragmentation of
the chromatin” in spirochætes is a process of degeneration. Working
with _A. persicus_ and _S. gallinarum_, they state that a large number
of the spirochætes ingested by the Argas almost immediately pass
through the wall of the alimentary canal and appear in the hæmocœlic
fluid. Marchoux and Couvy consider that Leishman’s granules may be
found in the Malpighian tubules of various Arachnids. They found
spirochætes in the cephalic glands of infected Argas. They consider
that spirochætes remain as wavy spirochætes within the tick, if they
are to be infective, though the spirochætes may become so thin as to
be invisible! The latter argument is obviously weak, and it was never
asserted that all granules in the Malpighian tubules of infected ticks
were derived from spirochætes. With dark-ground illumination small,
refractile spirochætal granules may be seen to grow into spirochætes.
The granule phase of spirochætes has recently been discussed by
Fantham[153] (1914).
[152] _Annales Inst. Pasteur_, xxvii, pp. 450, 620.
[153] _Annals Trop. Med. and Parasitol._, viii, p. 471.
*Spirochæta recurrentis*, Lebert, 1874.
Syn.: _Spirochæta obermeieri_, Cohn, 1875.
This organism was discovered by Obermeier (1873) in cases of relapsing
fever in Berlin. Short forms 7 µ to 9 µ long, and longer (probably
adult) forms, 16 µ to 19 µ, are found in the blood. The width is
0·25 µ. Parasites 12 µ or 13 µ long are often observed.
The spirochæte is found in the blood during febrile attacks and
relapses, but not during intervening periods. It can be inoculated
into monkeys, rats and mice. It can live in the bed-bug, _Cimex
lectularius_, and Nuttall has succeeded in transmitting _S.
recurrentis_ from mouse to mouse by the bites of the same bug. The
French investigators Sergent and Foley (1908–9) in Algeria, and
Nicolle, Blaizot and Conseil (1912) in Tunis, have shown experimentally
that _S. recurrentis_ (var. _berbera_) is transmitted by lice. The
latter workers also demonstrated the method of infection that commonly
occurs, namely, by the scratching of the skin and crushing of lice
containing spirochætes on the excoriated surface of the body.
Lice as transmitting agents for relapsing fever were indicated
by Mackie[154] in 1907. An epidemic among Indian school children
furnished the materials.[155] It was noted that out of 170 boys, 137
were infected, and the boys were very verminous. Among the girls, 35
out of 114 suffered, and few lice were found on them. Twenty-four
per cent. of the lice taken from the boys contained spirochætes as
compared with 3 per cent. of those from the girls. As the epidemic
died out among the boys, the lice also became fewer, and an increase
in the number of cases among the girls coincided with an increase in
the number of lice. Spirochætes were found in the gut, Malpighian
tubules and genital organs of the lice. Mackie thought that infection
of the patients was brought about by the regurgitation of the
spirochætes when the lice fed, but proof of this was lacking.
[154] _Brit. Med. Journ._, Dec. 14, 1907, p. 1706.
[155] See also Nuttall, Herter Lecture on Spirochætosis,
_Parasitology_, v, p. 269.
In 1912, Nicolle, Blaizot and Conseil,[156] working in Tunis and using
chiefly an Algerian strain of relapsing fever spirochætes (sometimes
called _S. berbera_), showed by direct experiments that infection by
means of the bites of _Pediculus vestimenti_ and _P. capitis_ was
untenable. As many as 4,707 infected lice were fed on one man, and
6,515 on another occasion were allowed to bite a man after they had
fed on a monkey heavily infected with spirochætes, yet no infection of
the man followed. Examination of the lice showed that the spirochætes
left the gut soon after they were ingested, and passed into the body
cavity, which swarmed with spirochætes. The contents of the alimentary
tract and the fæces of the lice alike were uninfective. The spirochætes
did not reappear in the gut till eight days after an infective feed,
but some persisted as late as the nineteenth day when kept at 28° C.
[156] _C.R. Acad. Sci._, cliv, p. 1636; clv, p. 481.
It was noted that the irritation due to the lice caused scratching,
and that thereby lice became crushed on to the skin. An emulsion was
made of two infected lice and rubbed on to the slightly excoriated
skin of one of the above workers. Infection followed five days later.
A drop of emulsion placed on the conjunctiva of the human eye produced
spirochætosis after an incubation of seven days. The body contents of
such lice, then, produce infection when they reach the blood by any
excoriated or penetrable surface. The stages leading up to infection
in nature briefly are: The irritation due to the louse bites causes
scratching, and the lice are crushed on to the skin. The slight
abrasion is quite sufficient to permit the entry of the parasite. The
louse bite alone is harmless. Infection by way of the eye is quite
probable in Africa, remembering the constant trouble due to sand, dust,
insects, etc., resulting in frequent touching of the eyes.
The spirochætes occur in the body fluid of the lice and can pass in
it to the adjacent organs. Thus they probably find their way into
the genital organs, and into the eggs of the lice. Eggs laid twenty
to thirty days after the parent became infected have retained the
infection, and the larvæ issuing from such eggs must have contained
some form of spirochætes, for an emulsion of either the eggs or the
larvæ produced spirochætosis when inoculated into monkeys. Further
details regarding the spirochætosis in the eggs of the lice and
in the larvæ are needed. Hereditary infection, however, has been
demonstrated, but is not very common. Sergent and Foley (1914) state
that the spirochæte possesses a very small and virulent form which it
assumes during apyrexial periods in man and during a period following
an infecting meal in the louse. Nicolle and Blanc (1914) find that
the organisms are infective in the louse just before they reappear
as spirochætes. Nicolle and Blaizot found that female lice were more
susceptible to spirochætes than males, four times as many females as
males being infected.
Tictin (1897) found _S. recurrentis_ in bugs recently fed on
patients, and infected a monkey with the fluids of crushed bugs.
Karlinski (1902) found the spirochætes in bed-bugs in infected
houses. There is some other evidence to show that bugs may transmit
the spirochæte in Nature. Further researches are needed regarding the
relationship of bed-bugs and human spirochætosis.
Multiplication of _S. recurrentis_ is by longitudinal and transverse
division (including so-called “incurvation”), and the organism forms
small, ovoid bodies (“coccoid” bodies) in the same way as _S. duttoni_.
_S. recurrentis_ is the cause of European relapsing fever, and a number
of possible varieties of it are associated with relapsing fevers in
other parts of the world. Such spirochætes only differ by biological
reactions, such as acquired immunity tests. They include:--
_S. rossii_, the agent of East African relapsing fever; _S. novyi_, the
agent of North American relapsing fever; _S. carteri_, the agent of
Indian relapsing fever; _S. berbera_, the agent of North African and
Egyptian relapsing fever.
OTHER HUMAN SPIROCHÆTES are:--
_S. schaudinni._ This organism, according to Prowazek, is the agent of
ulcus tropicum. It varies in length from 10 µ to 20 µ.
_S. aboriginalis_ has been found in cases of granuloma inguinale in
British New Guinea and Western Australia. It also occurs in dogs, and
may not be truly parasitic.
_S. vincenti._ This spirochæte is 12 µ to 25 µ in length, tapers
at both ends and has few coils. It has been associated with angina
vincenti. It often occurs in company with fusiform bacilli.
_S. bronchialis_, found by Castellani in 1907 in cases of bronchitis in
Ceylon. The parasites are delicate, but show morphological variation.
This organism is important and has since been found in the West Indies,
India, Philippine Islands and various parts of Africa, such as the
Anglo-Egyptian Sudan, Uganda and West Africa. It has recently been the
subject of research by Chalmers and O’Farrell, Taylor, and Fantham.
_S. phagedenis_ was found by Noguchi in a ten days old ulcerated
swelling of the labium. The organism shows much variation in size,
being 4 µ to 30 µ in length.
_S. refringens_ (Schaudinn, 1905) occurs in association with _Treponema
pallidum_ in syphilitic lesions, but is non-pathogenic. It is 20 µ to
35 µ long and 0·5 µ to 0·75 µ broad, being larger than _T. pallidum_
and more easily stained.
Various spirochætes have also been notified in vomits, chiefly in
Australia; others from the human intestinal tract, _e.g._, _S.
eurygyrata_; _S. stenogyrata_ (Werner); _S. hachaizæ_ (Kowalski), in
cholera motions; _S. buccalis_ (Cohn, 1875) and _S. dentium_ occurring
in the human mouth and in carious teeth (_S. dentium_, Koch, 1877,
being the smaller); _S. acuminata_ and _S. obtusa_ found by Castellani
in open sores in cases of yaws.
Animal spirochætes of economic importance include:--
_S. anserina_, highly pathogenic to geese.
_S. gallinarum_ (= _S. marchouxi_) in fowls. (See p. 119.)
_S. theileri_ in cattle and _S. ovina_ in sheep also occur in Africa;
their pathogenicity is not clear.
_S. laverani_ (= _S. muris_), occurring in the blood of and pathogenic
to mice, is probably the smallest spirochæte from the blood, being only
3 µ to 6 µ long.
Numerous spirochætes have been recorded from the guts of various
mammals, birds, fishes, amphibia and insects.
CULTIVATION OF SPIROCHÆTES.--Cultures of spirochætes have been made
with little success or with great difficulty until comparatively
recently, when Noguchi (1912) devised a means whereby he has cultivated
most of the pathogenic spirochætes as well as some Treponemata.
Noguchi has now cultivated _S. duttoni_, _S. recurrentis_, _S. rossii_,
_S. novyi_ and _S. gallinarum_ from the blood; _S. phagedenis_[157]
from human phagedænic lesions; _S. refringens_[158] and spirochætes
from the teeth.
[157] _Journ. Exptl. Med._, xvi, p. 261.
[158] _Journ. Exptl. Med._, xv, p. 466.
His method is as follows:--
A piece of fresh, sterile tissue, usually rabbit kidney, is placed in
a sterile test-tube. A few drops of citrated blood from the heart of
an infected animal, _e.g._, rat or mouse, is added, and about 15 c.c.
of sterile ascitic or hydrocœle fluid is poured quickly into the tube.
Some of the tubes are covered with a layer of sterile paraffin oil,
others are left uncovered. The tubes are incubated at 37° C. The best
results are obtained if the blood is taken from an animal forty-eight
to seventy-two hours after it has been inoculated, that is, before
the spirochætes reach their maximum multiplicative period in the
blood. The presence of some oxygen seems indispensable for these blood
spirochætes, and they fail to develop _in vacuo_ or in an atmosphere of
hydrogen.
For subcultures, 0·5 c.c. of a culture is added to the medium instead
of citrated blood, and it is useful to add a little fresh, normal
blood, either human or from an animal, such as a rat.
Noguchi found that the events in cultures were:--
_S. duttoni_,[159] maximum multiplication on the eighth to ninth day;
disintegration beginning on the tenth day, spirochætes disappeared
after about the fifteenth day. No diminution of virulence was found at
the ninth day.
[159] _Journ. Exptl. Med._, xvi, p. 202.
_S. rossii_ (= _S. kochi_).[160] Maximum development on the ninth day,
after which the virulence diminishes. The incubation period is also
prolonged.
[160] _Ibid._, p. 205.
_S. recurrentis_[161] (= _S. obermeieri_). Maximum growth on the
seventh day.
[161] _Ibid._, p. 205.
_S. novyi._[162]--Maximum development on the seventh day. It is more
difficult to grow than the preceding forms.
[162] _Ibid._, p. 208.
All the above spirochætes showed undoubted longitudinal division and
transverse division was observed in part.
_S. gallinarum_[163] can be cultivated as above, but transverse
division was usual here. Maximum growth occurred in the culture about
the fifth day.
[163] _Ibid._, p. 620.
TREPONEMATA.
The genus _Treponema_ (Schaudinn, 1905), includes minute, thread-like
organisms, with spirally coiled bodies, the spirals being preformed
or fixed. No membrane or crista is present, according to Schaudinn,
though a slight one is said by Blanchard to be present in the
organism of yaws. The ends of the organisms are tapering and pointed.
Multiplication is by longitudinal and transverse division. The most
important members of the genus are _T. pallidum_, the agent of
syphilis, and _T. pertenue_, which is responsible for frambœsia or yaws.
*Treponema pallidum*, Schaudinn, 1905.
Syn.: _Spirochæta pallida_.
_Treponema pallidum_ was first described by Schaudinn and Hoffmann
in 1905 under the name of _Spirochæta pallida_. It has also been
described under the names of _Spironema pallida_, _Microspironema
pallida_ and _Trypanosoma luis_. Siegel in 1905 described an organism
which he called _Cytorhyctes luis_ and considered to be the agent
of syphilis. Schaudinn reinvestigated Siegel’s work and found _T.
pallidum_, which he considered to be the causal agent of the disease,
and pronounced against _Cytorhyctes luis_. It is probable now that
both workers were correct, for Balfour (1911) has seen the emission
of minute granules or “coccoid” bodies from _T. pallidum_ and these
granules probably correspond to the _C. luis_ of Siegel. Recently E. H.
Ross, having observed a spirochæte stage in the development of Kurloff
bodies, thinks that _T. pallidum_ is a stage in the life-history of a
Lymphocytozoon. MacDonagh has also described a complicated and somewhat
similar cycle, but these observations require further study and
confirmation.
[Illustration: FIG. 56.--_Treponema pallidum_. (After Bell, from
Castellani and Chalmers.)]
_T. pallidum_ varies from 4 µ to 10 µ in length, its average length
being 7 µ, while its width is usually about 0·25 µ. Longer individuals
of 16 µ to 20 µ have been recorded. The body has from eight to ten
spiral turns and forms a tapering process at each end (fig. 56). The
organism is most difficult to stain, and its internal structure is
little known. It is possibly like that of _Spirochæta duttoni_ or _S.
balbianii_, as the “granule shedding” observed by Balfour is strongly
suggestive of the formation of resistant bodies by those spirochætes.
Hoffmann (1912) has seen the formation of spores in _T. pallidum_.
The Treponemata occur in the primary and secondary sores, but are
difficult to find in the tertiary eruptions of syphilis. Noguchi and
Moore (1913) and Mott[164] (1913) have demonstrated _T. pallidum_
in the brain in cases of general paralysis of the insane. Marie and
Levaditi (1914), however, consider that the treponeme found in the
brain in such cases is different from _T. pallidum_.
[164] _Brit. Med. Journ._, Nov. 15, 1913. p. 1, 271.
CULTIVATION _of T. pallidum_.--This has been accomplished successfully
by Noguchi,[165] using a modification of his method for spirochæte
cultivation, for _T. pallidum_ is much more difficult to grow than
spirochætes, being a strict anaerobe.
[165] _Journ. Exptl. Med._, xv, p. 90; xvi, p. 211.
[Illustration: FIG. 57.--Diagram of apparatus for cultivation of
_Treponema pallidum_ by Noguchi’s method. (After Noguchi.)]
The apparatus consists of two glass tubes, the upper being connected to
the lower by a narrower tube passing through a rubber cork (fig. 57).
Both tubes are carefully sterilized.
A piece of fresh, sterile rabbit’s kidney is placed in the lower tube,
which is filled with ascitic fluid, or ascitic fluid and bouillon
mixture. The tube is inoculated with syphilitic material and corked
by inserting the upper tube. In the bottom of the upper tube a piece
of sterile rabbit’s kidney is placed and syphilitic material poured
over it. A mixture of one part ascitic fluid and two parts of slightly
alkaline agar is then poured over the tissue and allowed to solidify.
When solid, a layer of sterile paraffin oil is poured on top of it,
and the top plugged with cotton wool (fig. 57). The whole is then
incubated at 37° C. for two or three weeks. The tissue removes traces
of oxygen from the lower levels of the medium and also probably
provides a special form of nourishment. At first _T. pallidum_ grows in
the solid medium, and then when the cultural conditions in the lower
fluid portion become favourable, the organisms migrate thither and
multiply abundantly. At first the culture is impure, but after several
transferences a pure culture is obtained readily.
The syphilitic material for culture is prepared by cutting off pieces
of tissue from the lesions, washing in sterile salt solution containing
1 per cent. sodium citrate, and then emulsifying the tissue in a mortar
with sodium citrate.
Good cultures show rapid multiplication, which is invariably by
longitudinal division.
In his various cultivation experiments Noguchi[166] found morphological
and pathogenic variations in _T. pallidum_. Three forms of the organism
were found, namely, thicker, average and thinner types. The lesions
caused in the testicle of the rabbit differ according to the variety
inoculated, but more work is necessary on the subject.
[166] _Journ. Exptl. Med._, xv, p. 201.
Noguchi[167] has cultivated a separate organism, _T. calligyrum_, from
the surface of human genital or anal lesions, either syphilitic or
non-syphilitic. It is apparently non-pathogenic, and is 6 µ to 14 µ
long.
[167] _Journ. Exptl. Med._, xvii, p. 89.
Hata (1913)[168] has modified the Noguchi technique for the cultivation
of spirochætes and treponemes, with a view to simplification and
convenience. Hata substitutes normal horse serum for ascitic fluid
and the “buffy coat” of the clot of horse blood in place of the small
pieces of rabbit’s kidney. It is unnecessary to place sterile paraffin
on the surface of the medium.
[168] _Centralbl. f. Bakt._, Orig., lxxii, p. 107.
The horse serum is mixed with twice its volume of physiological
saline solution. The mixture is placed in tubes which are heated on
a water-bath at 58° C., the temperature being raised gradually until
it reaches 70° or 71° C. in three hours. The tubes are then heated at
71° C. for half an hour. After cooling, the contents will consist of
an opaque semi-coagulated mass. This semi-coagulated serum and saline
mixture may be substituted for Noguchi’s ascitic fluid.
The buff coagulum is cut into small pieces, about 1 c.c. in volume.
They must be forced with a sterile glass rod to the bottom of the
semi-coagulated serum and saline mixture. The medium is inoculated with
a small quantity of infected blood and kept at 37° C. In the case of
_S. recurrentis_, growth of spirochætes is observed on the second day,
reaching a maximum in five to seven days. The growth of the organisms
proceeds rather more slowly, they live for a longer period and maintain
their virulence better than in Noguchi’s medium.
*Treponema pertenue*, Castellani, 1905.
Syn.: _Spirochæta pertenuis_; _S. pallidula_, Castellani, 1905.
Castellani discovered the organism in 1905, in scrapings of yaws
pustules. He first described it under the name of _Spirochæta
pertenuis_.
[Illustration: FIG. 58.--_Treponema pertenue_. (After Castellani and
Chalmers.)]
_Treponema pertenue_ (fig. 58), though delicate and slender, shows
great morphological variation both in length and thickness. It may be
short, _e.g._, 7 µ, but can attain 18 µ to 20 µ in length and may be
even larger. In cultures made by Noguchi, thick, medium and thin forms
were found, each giving rise to a different type of frambœsial lesion
when inoculated into the testicles of rabbits, thus suggesting the
possibility of the occurrence of varieties of _T. pertenue_.
The organism is difficult to stain, but occasionally deeper staining
granules are found along its body. They may represent a diffuse
nucleus. Granule formation similar to that of _T. pallidum_ has been
observed by Ranken, using dark-ground illumination.
Many experiments have been made with a view to establishing the
identity of the organism of yaws and also of differentiating between
the causative agents of yaws and syphilis. Both monkeys and the human
subject have been experimentally inoculated with yaws material and have
developed the disease.
In an early experiment, negroes were inoculated with the secretion
from lesions of yaws. All of them developed the disease, nodules
appearing, chiefly at the seat of inoculation, in from twelve to twenty
days, followed by the usual eruption. Similar results were obtained
with thirty-two Chinese prisoners, who were inoculated with yaws,
twenty-eight becoming infected.
A naturally infected yaws patient when inoculated with syphilis,
contracted that infection, thus showing that yaws does not confer
immunity to syphilis. This has also been observed naturally, when yaws
patients have contracted syphilis.
Experiments with monkeys have been successfully performed. The
incubation period varies from sixteen to ninety-two days. Lesions
appear first at the seat of inoculation, and in some monkeys the
eruption is localized to this spot, though the infection is general,
_T. pertenue_ occurring in the spleen, lymphatics, etc. Monkeys
inoculated with splenic blood of a yaws patient, and also sometimes
with blood from the general circulation, have become infected.
Castellani and others have shown that monkeys successfully inoculated
with syphilis do not become immune to yaws, and vice-versâ.
Craig and Ashburn, using the monkey _Cynomolgus philippinensis_, found
these animals susceptible to yaws but not to syphilis.
The ulcerated lesions of frambœsia are rapidly invaded by numerous
bacteria as well as by different spirochætes, of which Castellani has
described three distinct species. One is identical with _Spirochæta
refringens_, Schaudinn, the other two are thin and delicate. One, _S.
obtusa_, has blunt ends; the other _S. acuminata_, has pointed ends.
_T. pertenue_ is also present.
The reasons for considering _T. pertenue_ to be the specific cause of
frambœsia are:--
(1) _T. pertenue_ is the only organism present in non-ulcerated
papules, in the spleen and in the lymphatics of yaws patients, or of
monkeys artificially infected with the disease. By no method has any
other organism been obtained.
(2) Extract of frambœsia material, free from all organisms other than
_T. pertenue_, reproduces the disease if inoculated.
(3) Extract of frambœsia material deprived by filtration of _T.
pertenue_ is no longer infective on inoculation.
The method of infection is contaminative, by direct contact. Women
in Ceylon are frequently infected by their children. Any slight skin
abrasion is sufficient to admit the parasite. In some cases, insects
may carry the disease from person to person, and even in hospitals,
when dressings are removed, it has been noticed that flies greedily
suck the secretion from the ulcers. _T. pertenue_ has been recovered
from flies that have fed on yaws, and monkeys have contracted the
disease when flies were placed and retained on them for a short time,
after the insects had fed on yaws material.
CULTIVATION.--_T. pertenue_ has been cultivated by Noguchi, who finds
three types of parasites in his cultures, as before mentioned. Its
multiplication is by longitudinal division.
Noguchi[169] (1912), has cultivated species of Treponema from the human
mouth, e.g., _T. macrodentium_, _T. microdentium_ and _T. mucosum_, the
latter from pyorrhea alveolaris. These parasites in the past may have
been confused under the name _Spirochæta dentium_.
[169] _Journ. Exptl. Med._, xv, p. 81; xvi, p. 194.
Class III. *SPOROZOA*, Leuckart, 1879.
The third group of the Protozoa consists entirely of parasitic
organisms forming the class known as the Sporozoa or spore-producing
animals. The members of this class are characterized by possessing
very great powers of multiplication, coupled with a capacity for
producing forms that serve for the transference of the organisms
to other hosts. These reproductive bodies, whether for increase of
numbers within one host or for transmission to another host, are called
spores. But, strictly, the term spore should be used only in the latter
connection, when a protective or resistant coat known as a sporocyst
envelops the body of the spore.
The Sporozoa are widely distributed, occurring in various tissues and
organs of Annelids, Molluscs, Arthropods, and Vertebrates. Their food,
which is fluid, is absorbed osmotically. The life-cycle of a Sporozoön
may be completed within one host or may be distributed between two
different hosts.
The Sporozoa were divided by Schaudinn into two groups or sub-classes,
called (1) the *Telosporidia*, and (2) the *Neosporidia*.
The Telosporidia are Sporozoa in which the reproductive phase of the
parasites is distinct from the growing or trophic phase, and follows
after it. The Neosporidia include Sporozoa in which growth and
spore-formation go on simultaneously. This classification is not final,
for certain exceptions and difficulties are already known with regard
to it. It is possible that the class Sporozoa is not a natural entity,
but should be replaced by two classes of equal rank, corresponding in
most respects with the Telosporidia and Neosporidia.
The *Telosporidia* comprise the *Gregarinida*, the *Coccidiidea*, and
the *Hæmosporidia*. Doflein combines the two latter orders into one
known as the *Coccidiomorpha*.
The *Neosporidia* comprise the *Myxosporidia*, the *Microsporidia*, the
*Actinomyxidia*, the *Sarcosporidia*, and the *Haplosporidia*. Doflein
combines the first three orders into one, the *Cnidosporidia*.
Sub-Class. TELOSPORIDIA, Schaudinn.
Sporozoa in which the reproductive phases follow completion of growth.
Order. *Gregarinida*, Aimé Schneider emend. Doflein.
Knowledge of the Gregarinida probably goes back as far as the year
1684, when Redi observed gregarines in the crab, _Cancer pagurus_.
Von Cavolini (1787) found them in _Cancer depressus_. The name
_Gregarina_ was created by L. Dufour (1828), who observed masses
of these organisms in the gut of insects of different orders.
Hammerschmidt (1838) and von Siebold found rich infestations in
insects, while Dujardin (1835) and Henle described various genera
from segmented worms. Henle (1835) also observed cysts containing
“navicellæ” in the sperm-sacs of segmented worms, and attention was
drawn to his researches by the discovery by von Siebold (1839) of
“pseudonavicellæ” in the gut of _Sciara nitidicollis_. Up to this
time many workers considered the gregarines to be worms, but Kölliker
(1845) investigated many of them and maintained their unicellular
nature, while Stein’s work (1848) showed the interrelation of the
pseudonavicellæ and the gregarines. The discovery of amœboid germs
in the pseudonavicellæ by Lieberkühn (1855) and the demonstration of
myonemes further aided in the elucidation of their true systematic
position. The entire process of conjugation, of which Dufour had seen
one phase, was followed by Giard under the microscope.
From 1873 onwards Aimé Schneider made important additions to the
knowledge of the morphology, life-history, and systematic position
of numerous gregarines. Bütschli (1881) and L. Léger (1892) also
contributed much work on the subject. The discoveries of Schaudinn
with regard to the life-cycle of Coccidia gave a fresh stimulus to
the study of the Gregarines, whereby the life-cycles of numerous
forms and the phases thereof have been elucidated.
Asexual multiplication is not common among the Gregarines, but is
known to occur in the sub-order Schizogregarinea, formerly known as
the Amœbosporidia.
Although the Gregarinida are not known to be parasitic in man or
other vertebrates, they are of great interest, inasmuch as they are
among the earliest known Sporozoa, and therefore will be briefly
described here.
[Illustration: FIG. 59.--_Monocystis agilis_ from seminal vesicles of
_Lumbricus_ × 250. (After Stein.)]
[Illustration: FIG. 60.--_Gregarina longa_ from larva of crane-fly
(_Tipula_). _a_, in epithelial cell of host; _b_, _c_, gradually
leaving host-cell; _d_, adhering to host-cell; _e_, fully developed
free trophozoite.]
The Gregarines are usually elongate, somewhat flattened organisms
(figs. 59, 60), whose bodies are enclosed in an elastic and often
thick cuticle. The enclosed living substance shows a separation into
ectoplasm and endoplasm, as is common among Protozoa. The cuticle is
sometimes regarded as the outer portion or epicyte of the ectoplasm.
A single, vesicular, spherical, or elliptical, large nucleus, with
its chromatin concentrated to form a spherical karyosome, is present.
The body of some gregarines may be divided by ingrowing ectoplasmic
partitions or septa, and are then said to be “septate” or “polycystid”
(fig. 61). Other gregarines remain simple and non-septate, and are
termed “monocystid” (fig. 59). The monocystid gregarines occur
especially in the body cavity of Chætopoda and Insecta, more rarely
in Echinodermata, in the parenchyma of Platyhelminthes, also in the
gut of Tunicata and Insecta (fig. 60) and in the seminal vesicles
of Annelida. In the polycystid gregarines a single septum only is
present as a rule, and thus the body presents two portions: (1) an
anterior portion termed the protomerite; (2) a posterior, larger
portion, known as the deutomerite, which generally contains the
nucleus. The protomerite is often modified anteriorly to form an organ
of attachment, termed the epimerite (fig. 61), which is developed
from the pointed rostrum of the sporozoite or primary infecting young
gregarine. The structure of the epimerite may be complicated, being
provided with hooks, spines, knobs, and other appendages. An extension
of the polycystid condition is seen in _Tæniocystis mira_ Léger (from
the dipteran larva, _Ceratopogon solstitialis_), whose body shows a
number of partitions, giving the organism a superficial resemblance to
a tapeworm.
[Illustration: FIG. 61.--_Xyphorhynchus firmus_ with epimerite in
intestinal epithelial cell of host. (After Léger.)]
The ectoplasm of a gregarine exhibits three layers: (1) An epicyte
(cuticle) externally of which the epimerite is composed; (2) a
sarcocyte which forms the septa if present; (3) the deeper myocyte
layer containing contractile elements in the form of fibrils or threads
termed myonemes (fig. 62).
[Illustration: FIG. 62.--_Gregarina munieri_ (from the beetle,
_Chrysomela hæmoptera_). Section through surface layers. _Cu_, cuticle;
_E_, ectoplasm proper; _G_, gelatinous layer; _My_, myonemes in myocyte
layer. × 1500. (After Schewiakoff.)]
The endoplasm is fluid and granular, containing many enclosures,
which are of the nature of reserve food materials. They consist of
fat droplets or of paraglycogen, and give the organisms an opaque
appearance. _Lithocystis_ contains crystals of calcium oxalate in its
endoplasm.
Many gregarines are capable of active movements, though they do not
possess obvious locomotor organs. The movement is of a smooth, gliding
character and two suggestions have been put forward to explain it.
According to Schewiakoff, a gelatinous substance is secreted between
the layers of the ectoplasm. This is extruded posteriorly and thus the
animal is pushed forward. On the other hand, Crawley considers that
the movements are produced by contractions of the myonemes. These two
explanations are probably correct as far as each goes, and are to be
regarded as supplementary to one another.
[Illustration: FIG. 63.--_Monocystis agilis_. Spores from vesicula
seminalis of the Earthworm. _a_, Sporoblast with single nucleus,
enclosed in sporocyst; _b_, mature spore containing sporozoites; _c_,
diagrammatic cross-section of spore, showing eight sporozoites round
residual protoplasm. (After Bütschli.)]
Occasionally, temporary associations of gregarines are formed by
a number of individuals adhering to one another end to end. Such
temporary associations are examples of syzygy. Such syzygies must not
be confused with true associations which form an essential part of the
life-cycle.
The life-cycle of a relatively simple gregarine, such as _Monocystis
agilis_ (fig. 59), parasitic in earthworms, may now be considered.
The gregarines, being members of the Sporozoa, produce spores at one
phase of the life-cycle. Each gregarine spore (fig. 63) develops
within itself a number of minute, sickle-shaped or vermicular bodies,
known as sporozoites or primary infecting germs. Eight sporozoites are
often formed within each spore. When absorbed by a new host, the spore
softens and the sporozoites issue from it. They are capable of active
movement and may or may not enter a cell, such as one of those of the
digestive tract, or, as in _Monocystis_, a cell lining the vesicula
seminalis which becomes a sperm-cell aggregate (sperm morula). When the
sporozoite has reached the place of its choice in the host it ceases
active movements and proceeds to feed passively on the fluid substances
around it, whether they be those of tissues or body fluids. This
passive, growing and feeding form is known as the trophozoite. After a
trophic existence of longer or shorter duration, the trophozoite ceases
to feed and prepares for reproduction. Two trophozoites associate
together, each of them first becoming somewhat rounded. The two
trophozoites, now known as sporonts or gametocytes, become invested
in a single common envelope or cyst (fig. 64, _a_). The nucleus of
each gametocyte then divides by a series of binary fissions (fig. 64,
_b_), and the daughter nuclei thus produced arrange themselves at the
periphery of the parent cells (fig. 64, _c_). Cytoplasm collects around
each of these nuclei, and thus a number of gametes are formed within
each gametocyte. The gametes for a time exhibit active movements, and
ultimately ripe gametes of different parentage fuse in pairs, that is,
conjugation occurs (fig. 64, _d_). In this way zygotes are produced,
the nucleus of each zygote being formed by the fusion of two gamete
nuclei.
[Illustration: FIG. 64.--Schematic figures of conjugation and spore
formation in Gregarines. For details see text. (After Calkins and
Siedlecki, modified.)]
[Illustration: FIG. 65.--_Stylorhynchus oblongatus_. _a_, cyst
containing two sporonts or gametocytes, each full of gametes, those in
the upper one being male. _b_, ripe male and female gametes. × 1,600.
(After L. Léger.)]
The zygote grows slightly and becomes oval or elongate, and at this
period is often called the sporoblast. It then secretes an external
membrane, the sporocyst. Nuclear division occurs inside the sporocyst
by a series of three binary fissions (fig. 64, _e_), so that each
sporocyst, now usually referred to as a spore, contains eight nuclei.
The cytoplasm collects around each nucleus and eight vermicular
sporozoites are produced within each spore (fig. 64, _f_), thus
completing the life-cycle.
It will be noticed that in the above life-cycle no asexual
multiplication occurs. These organisms, such as _Monocystis_, are known
as the Eugregarines, and include the majority of the gregarines. The
remainder, which have introduced schizogony into their life-cycle, are
known as the Schizogregarines.
[Illustration: FIG. 66.--Spores of various Gregarines. _a_,
_Xiphorhynchus_. _b_, _Ancyrophora_. _c_, _Gonospora_. _d_,
_Ceratospora_. (After Léger.)]
There are variations in the morphology and life-cycle of gregarines
besides those that have been mentioned. It is not within the scope of
this book to discuss them in detail, but the following may be noted:--
Morphological differentiation of gametes may occur as in _Stylorhynchus
oblongatus_ (fig. 65), which differentiation is probably of a sexual
nature.
The sporocyst really consists of two layers, an epispore and an
endospore. Externally the spores of different gregarines show great
variety in shape and markings, and spines, or long processes may be
present (fig. 66).
The resistant spores serve for the transmission of the gregarines
from host to host. The mode of infection is contaminative, the spores
expelled with the dejecta of one host being absorbed with the food of a
new host.
The Gregarinida may be classified as follows:--
Sub-order I.--*Eugregarinea*, without schizogony.
Tribe 1.--_Acephalina_.--Without an epimerite and non-septate; often
“cœlomic” (body-cavity) parasites. _E.g._: _Monocystis_, with several
species parasitic in the seminal vesicles of earthworms. Many other
genera parasitic in Echinodermata, Tunicata, Arthropoda, etc.
Tribe 2.--_Cephalina_.--With an epimerite, either temporarily
or permanently, in the trophic phase. Usually septate (except
_Doliocystidæ_). Many families, genera and species. Common in the
digestive tracts of insects. _E.g._: _Gregarina_, with several
species, _Gregarina ovata_ in the earwig, _Gregarina blattarum_ in the
cockroach, _Stylorhynchus_ in beetles, _Pterocephalus_ in centipedes,
etc.
Sub-order II.--*Schizogregarinea*, with schizogony.
Tribe 1.--_Endoschiza_.[170]--With schizogony occurring in the
intracellular phase, _e.g._, _Selenidium_ (from Annelida and Gephyrea),
_Merogregarina_ (from an Ascidian).
[170] See Fantham (1908), _Parasitology_, i, p. 369.
Tribe 2.--_Ectoschiza_.--In which the schizont is free, and schizogony
is extracellular, _e.g._, _Ophryocystis_ (from _Blaps_, a beetle), and
_Schizocystis_ (from _Ceratopogon_ larva).
Order. *Coccidiidea*.
Hake (1839) first saw the organisms now termed Coccidia during
his investigations on the so-called coccidial nodules of rabbits.
The opinions as to the nature of these peculiar formations were
very diverse. The discoverer considered them to be a sort of pus
corpuscle; Nasse (1843) took them for epithelial cells of the biliary
passages, others for helminthes, especially the ova of trematodes
(Dujardin, Küchenmeister, Gubler, etc). Remak (1845) was the first to
draw attention to their relation to the Psorospermia (Myxosporidia),
and this investigator found them also in the small intestine and
vermiform appendix of rabbits. Lieberkühn (1854), who examined
not only the coccidia of rabbits, but found similar forms in the
kidneys of frogs, likewise called them definitely psorosperms. To
differentiate Müller’s psorosperms, which are found in fishes, from
those of rabbits, etc., the latter were called egg-shaped psorosperms
(Eimer), until R. Leuckart (1879) named them _Coccidia_ and placed
them in a group of the Sporozoa analogous to that of the Gregarinida,
Myxosporidia, etc. Numerous works confirmed the occurrence of
coccidia, not only in all classes of vertebrate animals, but also in
invertebrates (Mollusca, Myriapoda, Annelida, etc.). A large number
of genera and species have in the course of time been described
which inhabit the epithelium of the intestine and its appendages for
choice, but are also found in other organs (kidneys, spleen, ovaries,
vas deferens, testicles). Some also live in the connective tissue of
various organs, more particularly of the intestine.
The knowledge of the development of the coccidia was of particular
importance in determining their classification. By means of encysted
coccidia from the liver of rabbits, Kauffmann (1847) first confirmed
the fact that the cyst, which was partly or entirely filled with
granular contents, divided into three or four pale bodies (fig. 71)
after a long sojourn in water. Lieberkühn observed the same process
in the host in the case of the coccidia of the kidney of the frog.
Stieda (1865) studied more minutely the changes that occur within
the encysted coccidia of the liver of rabbits after the death of
the host. He discovered that the bodies now known as “spores” were
oval formations pointed at one pole, and surrounded by a delicate
membrane, which exhibited a certain thickness at the pointed
extremity and enclosed a slightly bent rodlet, expanding at either
end into a strongly light-refracting globule; a finely granular
globule was present in the middle of the spore. Waldenburg (1862) saw
the same phenomenon in coccidia from the epithelium of the villi and
Lieberkühn’s glands of the intestine of the rabbit; but the process
in this case took place in a much shorter time.
According to the discovery of Kloss (1855), the spores of the
coccidia of the urinary organ of the garden snail were formed in far
greater numbers: the round spores also harboured several (five to
six) rodlets, which after the bursting of the spore-envelope became
free. Eimer’s researches (1870) afforded information regarding a
Coccidium from the intestine of the mouse, which was transformed
_in toto_ into a “spore,” containing small sickle-shaped bodies.
The fact was, moreover, established that the little bodies left the
delicate envelope when in the intestine, made movements of flexion
and extension, and were finally transformed into amœboid organisms,
which apparently penetrated the epithelial cells; at all events,
similar bodies of various sizes were seen in these cells. Taking the
immense number of these parasites into account and the lack of any
other cause, Eimer attributed the sudden death of his mice to the
_Gregarina falciformis_, as the parasite was then called, just in the
same way as a few years previously Reincke ascribed the acute and
fatal intestinal catarrh of rabbits to the invasion of intestinal
coccidia.
All that had become known about coccidia up to 1879 was then
compiled by Leuckart, and completed by his own observations on
the coccidia of the liver of the rabbit. Experimental infections
had already been conducted by Waldenburg (1862) with intestinal
coccidia of rabbits, and by Rivolta (1869–73) with the coccidia of
fowls, which experiments confirmed the importance of the spores,
or bodies enclosed in them, in the transmission of the parasites
to other animals. Accordingly, it was assumed that after the entry
of the spores into the intestine the sporozoites were set free,
actively penetrated into the intestinal cells, where they grew into
coccidia, and finally became encysted. The further development,
_i.e._, the formation of spores, took place outside the host’s body
in these cases; in other cases (Kloss, Eimer) it took place within
the host. Although much regarding the cycle of development was still
hypothetical, the ideas coincided with the observations, and were
therefore universally regarded as established. Further research
confirmed this view in numerous new forms.
L. Pfeiffer’s statements (1891) on the part that certain coccidia or
their sporozoites played, or seemed to play, as causes of disease
gave a renewed impetus to the investigation of the coccidia. The
ingestion of even very numerous spores did not appear to account for
the mass infection so frequently observed, even after Balbiani had
confirmed the fact that there were two, and not one, sporozoites
contained in every spore of the coccidia of rabbits (fig. 72). The
hypothesis was therefore advanced that the sporozoites or young
coccidia were able to divide once again by sporulating. The question
was finally solved quite differently. R. Pfeiffer (1892) first
confirmed the fact that in addition to the well-known method of
sporulation in the coccidia of the rabbit that causes the infection
of fresh hosts (“exogenous sporulation”), an enormous increase may
follow in the already infected host in a manner that Eimer first
observed in the coccidia of the intestine of the mouse (“endogenous
sporulation”). It had hitherto been believed that some of the
species of coccidia increased like the rabbit parasite, then known
as _Coccidium oviforme_, and others like _Eimeria falciformis_, and
this difference had been made the foundation of a classification. R.
Pfeiffer was successful in observing the occurrence of both kinds
of development in the same species, and expressed the opinion that
endogenous sporulation (fig. 73), which takes place within the host,
was the cause of the mass-infection that is mostly accompanied by
serious consequences (fig. 74). L. Pfeiffer sought, especially, to
demonstrate the correctness of this view as regards other species of
coccidia and for this purpose he utilized the experiences already
published. Coccidia were known to exist in a number of different
hosts, and to propagate in some according to the _Coccidium_ type,
in others according to the _Eimeria_ type. It therefore was reasoned
that in this case it was not a question of two species belonging
to different genera living side by side, with a different mode of
development, but of one species, in the life of which both forms of
development occurred alternately.
This interpretation of facts was combated especially by A. Schneider
(1892) and by Labbé, but has, nevertheless, proved true, apart from
the circumstance that Schuberg succeeded in discovering the hitherto
unknown _Coccidium_ form in the intestine of the mouse; and that,
moreover, Léger confirmed the fact that there are no Arthropoda in
which Eimeria are not found together with coccidia. The question
was finally settled by experiments made by Léger with the coccidia
of _Scolopendra cingulata_, by Schaudinn and Siedlecki with those
of _Lithobius forficatus_, and by Simond with the coccidia of the
rabbit. On Simond’s suggestion the sickle-shaped germs corresponding
to the sporozoites, which are formed by endogenous sporulation, are
generally termed merozoites; and in accordance with Schaudinn’s
suggestion, those individuals which form merozoites are termed
schizonts, and those which produce spores are called sporonts. In
contradistinction to sporogony (exogenous sporulation), the term
schizogony (endogenous sporulation) is used.
The more minute examination of these processes at last led to the
discovery of sexual dimorphism, of copulation and of alternation of
generations in the coccidia. Schuberg was the first to consider the
possibility of copulation in coccidia; in addition to the formations
which now are termed merozoites, he observed very diminutive
bodies (“microsporozoites”) in the coccidia of the intestine of
the mouse, which were able eventually to copulate. Labbé confirmed
this observation in some of the species, and Simond expressed
the opinion that bodies termed “chromatozoites” occurred in all
coccidia. Copulation itself was then observed by Schaudinn and
Siedlecki (1897). The copulating bodies were termed gametes. As,
however, they differed considerably one from the other, the males
were called microgametes (_i.e._, the microsporozoites of Labbé and
the chromatozoites of Simond) and the females macrogametes. After
copulation was completed sporogony took place, and in the cycle of
development of one species this regularly alternated with schizogony
(asexual multiplication). Schaudinn in 1900 described in detail the
life-cycle of _Eimeria_ (_Coccidium_) _schubergi_.
The recognition of this unsuspected complicated process was bound to
effect reforms in the classification of the coccidia; and all the
forms that had been regarded as developmental stages (_Eimeria_,
etc.) had to be reconsidered.
_Occurrence._--The Coccidiidea in their mature condition usually live
within the epithelial cells of various organs, and by choice inhabit
those of the intestine and of its associated organs. They also occur
frequently in the excretory organs of mammals, birds, amphibia,
molluscs, arthropods, and may also be found in the testes and vas
deferens, but the statement that they live in hen’s eggs, as well as
in the oviducts of fowls, has not been confirmed.[171] Some species
inhabit the nuclei of cells, others live in the connective tissue, but
their presence in the latter situation is probably only secondary,
that is, they have only reached it from the epithelium of the affected
organs.
[171] Notwithstanding the progress made during the last decades, the
ova of helminthes and more particularly of trematodes, have been
mistaken for Coccidia. Thus Poschinger (_Zool. Anz._, 1819, ix, p. 471)
and Gebhard (_Virchow’s Arch._, 1897, No. 147, p. 536) mistook the ova
of _Distoma turgidum_, Brds., for Coccidia. Podwyssotzki (_Centralbl.
f. allg. Path._, 1890, i, p. 135) made a similar error with the ova
(and vitelline sacs) of a species of _Prosthogonimus_ (_Distoma ovatum_
of the authors); von Willach (_Arch. f. wiss. u. prakt. Thierheilk._,
1892, xviii, p. 242) mistook the ova of a nematode for Coccidia.
The size of the Coccidiidea, corresponding as a rule to the capacity
of their habitat, is usually small, but there are said to be species
that attain a diameter of 1 mm. Their form[172] is globular, oval,
or elliptical. External appendages are lacking, at least during
the trophic or vegetative period of their life, which is spent in
epithelial cells, within which they increase in size. Frequently one
only is present in each cell, but more can occur. The body substance
is composed of a more or less finely granular or distinctly alveolar
protoplasm which exhibits no differentiation into ecto- and endoplasm.
All species possess a nucleus that enlarges with their growth;
sometimes it only shows through the cytoplasm as a lighter spot, or may
even be quite concealed. It is vesicular, and besides containing very
delicate threads of chromatin in the clear nucleoplasm, it contains
generally only one large karyosome.
[172] The life-cycle given here is based on that of _Eimeria_
(_Coccidium_) _schubergi_, after Schaudinn (1900). See “Untersuchungen
über den Generationswechsel bei Coccidien,” _Zool. Jahrb., Abt. f.
Anat._, xiii, pp. 197–292, 4 plates.
The infected epithelial cells degenerate sooner or later as the
parasite feeds on them (fig. 67, II-IV). After their form has been
changed by the action of the growing parasite, they finally perish.
The cell membrane then alone surrounds the coccidia, which, at least
in the species sufficiently known, begin to propagate by an asexual
process (schizogony), the parasites themselves becoming schizonts, as
the initial stage is usually called. They differ from later stages
(sporonts or gametocytes), which resemble them in form, by the absence
of granulations in the cytoplasm, as well as by the vesicular nucleus.
The form is not always the same, for in some cases, at least, many
schizonts assume a globular form.
Schizogony (fig. 67, V-VII) commences with a division of the nucleus,
which takes place in different ways in the various species. This
finally leads to the formation of numerous daughter nuclei which
become smaller and smaller, and which collect beneath the surface of
the schizonts. In some species the daughter nuclei collect only in one
half of the schizont. A part of the protoplasm of the periphery now
divides around each daughter nucleus, the remaining part (residual
body) being left in the centre or on one side. The segments of the
divided cytoplasm, each containing a nucleus, assume a fusiform shape
and become merozoites, which very soon become free (fig. 67, VIII) and
leave the residual body. They are distinguishable from the very similar
sporozoites (fig. 67, I), as the merozoites possess a karyosome.
[Illustration: FIG. 67.--Life-cycle of _Eimeria_ (_Coccidium_)
_schubergi_, Schaud., from the intestine of _Lithobius_. (After
Schaudinn.) The infection is caused by a cyst (XX), containing spores,
which reaches the intestine of a _Lithobius_, where it discharges the
sporozoites (I). II, A sporozoite invading an intestinal epithelial
cell; III, intestinal epithelial cell with young trophozoite; IV,
intestinal epithelial cell with a globular schizont; V, nuclear
segmentation within the schizont; VI, the daughter nuclei arranging
themselves superficially; VII, formation of the merozoites; VIII,
merozoites that have become free, and which, penetrating into other
epithelial cells of the same intestine, repeat the schizogony
(II-VIII); IX and X, merozoites which, likewise invading the epithelial
cells of the same intestine, become sexually differentiated; XIa,
young macrogametocyte; XIb, older macrogametocyte; XIc, mature
macrogametocyte (discharging particles of chromatin); XIIa, young
microgametocyte; XIIb, older microgametocyte; XIIc, increase of nuclei
in the microgametocyte; XIId, the globular residual body around which
numerous microgametes have formed; XIIe, an isolated microgamete; XIII,
the mature macrogamete surrounded by numerous microgametes and forming
a cone of reception or fertilization prominence; XIV, shows the nucleus
of a microgamete that has penetrated and fused with the nucleus of the
macrogamete (fertilization)--the latter forms a membrane and becomes
an oöcyst; XV, XVI, XVII, nuclear segmentation in the oöcyst; XVIII,
oöcyst with four sporoblasts; XIX, the sporoblasts transformed into
spores, each containing two sporozoites; XX, the cyst introduced into
the intestine and liberating the sporozoites by bursting.]
The merozoites move in a manner similar to that of the sporozoites.
The movements consist either of slow incurvations with subsequent
straightenings, or annular contractions along the entire extent
of the body. In addition, there are gliding movements similar to
those of many gregarines, and brought about in a like manner by the
secretion at the posterior extremity of a gelatinous substance that
hardens rapidly.
The merozoites do not gain the open in the usual way, but are destined
to infect still further the same host by actively penetrating into
other epithelial cells of the affected organ. Here they continue their
growth and may again and again undergo schizogony. In the Infusoria
the repeated segmentations finally cease and are renewed only after
a conjugation. This is likewise the case with the Coccidia, with the
difference that in the latter the two conjugating individuals (gametes)
are differently constituted one from the other, whereas in the
Infusoria they are almost always similar.
When the schizogony ceases, the merozoites, that had penetrated
the epithelial cells and become trophozoites there, consist of two
kinds of differently constituted individuals. One kind possesses a
clear cytoplasm (fig. 67, XII), the other an opaque, richly granular
cytoplasm (fig. 67, XI), while both possess a vesicular nucleus
with a karyosome. In order to continue their development, the more
granular individuals must be fertilized, and are therefore termed
either female gametes or, on account of their size, macrogametes.
The male individuals (microgametes) necessary to conjugation, are
formed in greater numbers from the less dense microgametocytes or
male mother-cells (fig. 67, XIId). They are slender bodies consisting
chiefly of nuclear substance, and in most species bear two flagella
of unequal length directed backwards, the place of insertion of which
varies according to the species (fig. 67, XIIe).
While the development of the microgametes is rapidly advancing a change
occurs in the nucleus of the female parent forms or macrogametocytes.
Parts of the karyosome are extruded (fig. 67, XIc), and the nucleus
loses at the same time its vesicular form. One macrogamete results,
after nuclear maturation, from one macrogametocyte. By this time
the macrogametes are capable of conjugation, and the process takes
place within the host, generally, however, outside the affected and
degenerated host cells. The microgametes that have now become free from
the very large residual body, crowd around the mature macrogametes,
which often send out a small prominence (“cone of reception” or
fertilization protuberance) for their reception (fig. 67, XIII). As
soon as a microgamete comes in contact with this and penetrates into
the cytoplasm of the macrogamete, the latter surrounds itself with
a membrane which prevents the intrusion of other microgametes. The
nucleus of the microgamete that has gained entry unites with the
nucleus of the macrogamete, which latter is afterwards capable of
forming the well-known spores. The parasite is now called an encysted
zygote or oöcyst. The oöcysts of some other members of the Coccidiidea,
_e.g._, _Eimeria avium_, can form their walls prior to fertilization.
In such cases, a weak spot is left at one place in the cyst wall,
forming a micropyle, that permits of the entry of the male, immediately
after which the micropyle is closed.
The reduced nucleus of the macrogamete elongates on the entry of the
microgamete, and becomes a fertilization spindle to which the male
pronucleus (from the microgamete) becomes attached (fig. 67, XIV and
XV). Thereupon the spindle divides into two daughter nuclei (fig. 67,
XVI) which assume a round shape. The protoplasm at this stage may
at once divide, or another segmentation of the daughter nuclei may
first occur. In the former case the two halves divide again, so
that finally four nucleated segments, the sporoblasts, are formed,
whereas in the latter case the four sporoblasts appear simultaneously
(fig. 67, XVII). In both cases a residual body of varying size is
separated from the protoplasm of the oöcyst. As a rule the oöcysts
have already been discharged from the body of the host, and in the
manner described above, form the sporoblasts after a longer or
shorter period of incubation.
The sporoblasts are originally naked, but each soon secretes a
homogeneous membrane, the sporocyst, in which it becomes enveloped
(fig. 67, XVIII). After the segmentation of the nucleus the contents
divide into two sickle-shaped sporozoites, in addition to which there
is generally also a residual body (fig. 67, XIX).
This terminates the development. The spores are intended for the
infection of other hosts. If they reach the intestine of suitable
hosts, either free or enclosed in the oöcyst wall, the action of the
intestinal juices causes them to open and permits the escape of the
sporozoites (fig. 67, XX). The latter move exactly like the merozoites
and soon make their way into epithelial cells (fig. 67, I), where they
become schizonts, and thus repeat the life cycle.
Although our knowledge of the development of the coccidia is but of
recent date, yet it already extends to a large number of species,
which exhibit various deviations from the cycle of development
described above. For instance, in addition to differences in the
gametocytes, the schizonts of _Adelea_ and _Cyclospora_ also show
differentiation and give rise to macromerozoites and micromerozoites,
whilst in _Adelea_ and _Klossia_ a precocious association of the
gametocytes precedes the true copulation of the ripe gametes.
The classification of the Coccidiidea is based chiefly on the number of
sporozoites found in each spore, and the number of sporocysts (spores)
found in one oöcyst. Léger[173] recognises two great legions, the
Eimeridea and the Adeleidea, the former comprising the greater number
of genera, including the genus of most economic importance, _Eimeria_.
It must be noted that, though a member of this genus may be frequently
referred to as _Coccidium_, strictly it should be termed _Eimeria_,
that name having priority. The name of the disease resulting from
the action of such parasites is, however, established and remains as
coccidiosis.
[173] _Arch. f. Protistenkunde_ (1911), xxii, p. 71.
Certain of the more important of the Coccidiidea may now be considered.
Genus. *Eimeria*, Aimé Schneider, 1875.
Syn.: _Psorospermium_, Rivolta, 1878; _Cytospermium_, Rivolta,
1878; _Coccidium_, R. Leuckart, 1879; _Pfeifferia_, Labbé, 1894;
_Pfeifferella_, Labbé, 1899.
The Eimeria belong to Léger’s old family, the Tetrasporocystidæ, which
comprises forms producing oöcysts with four sporocysts, each containing
two sporozoites. The cysts are spherical or oval, as are also usually
the schizonts. The members of the genus are confined chiefly to
vertebrate hosts, the more important economically occurring in mammals
and birds. From the mammalian hosts very rarely the parasites may reach
man. _Eimeria_ (_Coccidium_) _avium_ of wild birds and poultry, and
_Eimeria stiedæ_ parasitic in rabbits, may be considered. There is a
general similarity in their life-cycles and each is of great practical
importance.
*Eimeria avium*, Silvestrini and Rivolta.
_Eimeria avium_ is responsible for fatal epizoötics among game birds
such as grouse, pheasants and partridges, and domestic poultry such
as fowls, ducks, pigeons and turkeys, and can pass from any one of
these hosts to any of the others with the same effect. The organism
is parasitic in the alimentary tract of the host, affecting more
especially the small intestine (duodenum) and the cæca, but in
some cases penetrating to the liver and multiplying there (as in
turkeys), producing necrotic cheesy patches, that ultimately become
full of oöcysts. The gut is rendered very frail by the action of
the parasites, its mucous membrane is greatly injured, and is often
reduced to an almost structureless pulp, riddled with parasites
(fig. 68). Infection is conveyed from host to host by the ingestion
of food or drink contaminated with the oöcysts voided in the fæces of
infected birds. Oval oöcysts from 24 µ to 35 µ long and from 14 µ to
20 µ broad are the means of infection. The oöcysts develop internally
four sporocysts or spores, from each of which two sporozoites are
produced. The life-history[174] presents two phases: (1) The asexual
multiplicative phase, schizogony, for the increase in numbers of the
parasites within the same host; (2) the reproductive phase, following
the formation of gametes (gametogony), leading to the production of
resistant oöcysts, destined for the transference of the parasite to
new hosts (sporogony).
[174] Fantham, H. B. (1910), “The Morphology and Life History of
_Eimeria_ (_Coccidium_) _avium_, a Sporozoön causing a fatal disease
among young Grouse,” _Proc. Zool. Soc. Lond._, 1910, pp. 672–691, 4
plates. Also Fantham, H. B. (1911), “Coccidiosis in British Game Birds
and Poultry,” _Journ. Econ. Biol._, vi, pp. 75–96.
The oöcysts usually reach the duodenum unharmed, with food or
drink. Under the influence of the powerful digestive juices
(especially the pancreatic) now encountered, the oöcysts soften,
as do the sporocysts, and ultimately two sporozoites emerge from
each sporocyst. The sporozoites are from 7 µ to 10 µ long, and each
is vermicular with a uniform nucleus (fig. 69, A). After a short
period of active movement in the gut, each sporozoite penetrates an
epithelial cell (figs. 68 _spz_, 69, B), and once within, gradually
becomes rounded (fig. 69, B, C). It grows rapidly, feeding on the
contents of the host cell and living as a trophozoite (fig. 69,
_D_). When the parasite is from 10 µ to 12 µ in diameter, usually
multiplication by schizogony (fig. 69, E-H) begins. The nucleus
of the parent cell, now called a schizont, divides into a number
of portions that become arranged at the periphery (fig. 69, E).
Cytoplasm collects around each nucleus (fig. 69, E, F) and gradually
a group of daughter individuals (merozoites) is produced (fig. 69,
G), the nucleus of each merozoite showing a karyosome.
[Illustration: FIG. 68.--Small piece of epithelial lining of gut of
heavily infected Grouse chick, showing various stages in life history
of the parasite _Eimeria avium_; _par_, parasite (trophozoite); _mz_,
merozoite; _sch_, schizont; _spz_, sporozoite; _ooc_, oöcyst; ♂, male
gametocyte; ♀, female gametocyte. × 750. (After Fantham.)]
The merozoites of _Eimeria avium_ are arranged “en barillet,” like
the segments of an orange (figs. 68 _mz_, 69, G), therein differing
from those of _E. schubergi_, which are arranged “en rosace.” They
separate from one another (fig. 69, H), penetrate other epithelial
cells, where they may, in turn, become schizonts. Eight to fourteen
merozoites are usually formed by each schizont, twenty have been
found, while in cases of intense infection when space has become
limited, the number may be only four.
After a number of generations of merozoites have been formed, a limit
is reached both to the multiplicative capacity of the parasite and to
the power of the bird to provide the invader with food. Consequently,
resistant forms of the parasite are necessary, and the trophozoites
begin to show sexual differentiation instead of forming schizonts,
that is, gametogony commences.
[Illustration: FIG. 69.--_Eimeria avium_. Diagram of life-cycle. For
explanation see text. (After Fantham.)]
Certain trophozoites store food and become large and granular. These
are macrogametocytes (fig. 69, I, ♀). The microgametocytes (fig. 69,
I, ♂) are smaller and far less granular. The macrogametocyte
continues to grow, and becomes loaded with chromatoid and plastinoid
granules (fig. 69, J, ♀), while the microgametocyte has its nucleus
divide to form a number of bent, rod-like portions (fig. 69, J, ♂).
The macrogametocyte gives rise to a single macrogamete, which forms
a cyst wall for itself, leaving a thin spot (micropyle) for the
entry of the male (fig 69, K, ♀). The microgametocyte gives rise to
numerous small, biflagellate microgametes (fig. 69, K, ♂) around a
large, central residual mass, from which they ultimately break free,
and swim away. When a macrogamete is reached, the microgamete enters
through the micropyle (fig. 69, L)--which then closes, thus excluding
the other males--and applies itself to the female nucleus (fig. 69,
M). Nuclear fusion occurs, the oöcyst (encysted zygote) being thus
produced. Sporogony then ensues. The oöcyst (fig. 69, N) at first
has its contents completely filling it. They then concentrate into
a central spherical mass (fig. 69, O) which gradually becomes
tetranucleate (fig. 69, P). Cytoplasm collects around each nucleus,
and four sporoblasts are thus formed (fig. 69, Q). Each sporoblast
becomes oval (fig. 69, R) and produces a sporocyst. Ultimately two
sporozoites are formed in each sporocyst or spore, at first lying
tête-bêche (fig. 69, S), but finally twisting to assume the position
most convenient for emergence (fig. 69, T) when they reach a new
host. The period of the life-cycle of _Eimeria avium_ (as well as
the details of the life-cycle) was determined by Fantham to be from
eight to ten days, of which period schizogony occupies four to five
days.
The method of infection[175] is contaminative, by way of food or
drink. Young birds are especially susceptible to infection. Certain
birds, particularly older ones, may act as reservoirs of oöcysts,
being continuously infected themselves, without showing any marked
ill effects from the parasite, but being highly infectious to
other birds. Much moisture retards the development of sporocysts
considerably. The duration of vitality of the infective oöcysts has
been determined experimentally to extend well over two years, and in
certain cases longer. _Eimeria avium_ is the causal agent of “white
diarrhœa” or “white scour” in fowls, and of “blackhead” in turkeys.
[175] Fantham, H. B. (1910), “Experimental Studies on Avian
Coccidiosis, especially in relation to young Grouse, Fowls and
Pigeons,” _Proc. Zool. Soc. Lond._, 1910, pp. 722–731, 1 plate.
_Eimeria avium_ of birds and _E. stiedæ_ of rabbits closely resemble
one another, but are not the same parasite, for _E. avium_ is not
infective to rabbits, nor _E. stiedæ_ to poultry.
*Eimeria stiedæ*, Lindemann, 1865.
Syn.: _Monocystis stiedæ_, Lindemann, 1865; _Psorospermium cuniculi_,
Rivolta, 1878; _Cytospermium hominis_, Rivolta, 1878; _Coccidium
oviforme_, Leuckart, 1879; _Coccidium perforans_, Leuckart, 1879;
_Coccidium cuniculi_.
[Illustration: FIG. 70.--_Eimeria stiedæ_. Section through an infected
villus of rabbit’s intestine. × 260.]
_Eimeria stiedæ_ is parasitic in the gut epithelium (fig. 70), liver,
and epithelium of the bile ducts of rabbits, and is usually considered
to be the parasite very occasionally found in man. The life-cycle
resembles that of _Eimeria avium_ in its general outlines (see fig. 69)
and therefore will not be detailed in full here. The oöcysts (fig. 71)
are large, elongate-oval, greenish in fresh preparations and vary in
size from 24 µ to 49 µ long and 12·8 µ to 28 µ broad, the gut forms
being usually smaller than those occurring in the liver, owing to the
more confined space in which they are formed. Formerly, the parasites
in the liver were described under the name of _Coccidium oviforme_,
while those from the intestine were termed _Coccidium perforans_. This
distinction has now broken down.
[Illustration: FIG. 71.--_Eimeria stiedæ_, from the liver of the
rabbit, oöcysts in various stages of development. (After Leuckart.)]
[Illustration: FIG. 72.--_a_, _b_, spores of _Eimeria stiedæ_ (Riv.),
with two sporozoites and residual bodies; _c_ represents a free
sporozoite. (After Balbiani.)]
[Illustration: FIG. 73.--So-called swarm cysts (endogenous sporulation
or schizogony) of the Coccidium of the rabbit. The daughter forms are
called merozoites. (After R. Pfeiffer.)]
The oöcysts[176] are thick-walled, somewhat flattened at one pole,
where a large micropyle is present. Four egg-shaped spores (sporocysts)
are formed within, each about 12 µ to 15 µ long and 7 µ broad
(fig. 72). The oöcysts are voided with the fæces. Sporogony takes,
in nature, about three days in the excrement. Fæcal contamination of
the food of rabbits results, and coccidian oöcysts are swallowed.
Under the influence of the pancreatic juice of a new host, the
sporozoites (fig. 72, _a_--_c_) are liberated from the spores and
proceed to attack the epithelium and multiply within it, as in the
case of _Eimeria avium_. From the gut, infection spreads to the liver,
where multiplication of the parasite goes on actively, resulting in
the formation of the whitish coccidial nodules, which may be very
conspicuous (fig. 74). Proliferation of the connective tissue may occur
around the coccidial nodules, which then contain large numbers of
oöcysts in various stages of development. It is said that the oöcysts
in the older nodules do not seem to be capable of further development.
Schizogony (fig. 73) and gametogony in all stages can be found in both
liver and gut.
[176] For an account of the life-cycle of _Eimeria stiedæ_ consult
Wasielewski, Th. von (1904), “Studien und Photogramme zur Kenntnis der
pathogenen Protozoen,” Heft. 1 (Coccidia), 118 pp., 7 plates, Leipzig:
J. A. Barth. Also, Metzner, R. (1903), _Arch. f. Protistenk._, ii,
p. 13.
Young rabbits often die of intestinal coccidiosis before infection of
the liver occurs. The repeated schizogony of _Eimeria stiedæ_ in the
gut is sufficient to cause death.
[Illustration: FIG. 74.--_Eimeria stiedæ_. Section through coccidian
nodule in infected rabbit’s liver. × 55.]
The disease of cattle popularly known as “red dysentery” is also
ascribed to the action of _Eimeria stiedæ_. The fæces of infected
cattle show blood clots of various sizes and in severe cases watery
diarrhœa is present. Acute cases end fatally in about two days.
Numerous oöcysts, considered to be those of _Eimeria stiedæ_, occur
in the fæces, and there is a heavy infection of the gut, especially
the large intestine and rectum, all stages of the parasite being
found in the epithelium. It is suspected that cattle contract the
disease by feeding on fresh grass contaminated with oöcysts. The
disease is recorded from Switzerland and from East Africa.
As before mentioned, _Eimeria stiedæ_ is considered to be the
organism found in a few cases in man, possibly acquired by eating the
insufficiently cooked livers of diseased rabbits. These cases may now
be described.
(_a_) *Human Hepatic Coccidiosis.*
(1) Gubler’s Case. A stone-breaker, aged 45, was admitted to a Paris
hospital suffering from digestive disturbances and severe anæmia.
On examination the liver was found to be enlarged and presented a
prominent swelling, which was regarded as being due to Echinococcus.
At the autopsy of the man, who succumbed to intercurrent peritonitis,
twenty cysts were found averaging 2 to 3 cm. in diameter, and one
measuring 12 to 15 cm. The caseous contents consisted of detritus,
pus corpuscles, and oval-shelled formations, which were considered to
be Distoma eggs, but which, in accordance with Leuckart’s conjecture,
proved to be Coccidia.[177]
[177] Gubler, A., “Tumeurs du foie déterm. par des œufs d’helm....”
_Mem. Soc. Biol._, Paris, 1858, v, 2; and _Gaz. med. de Paris_, 1858,
p. 657; Leuckart, R., _Die menschl. Paras._, 1863, 1ST edition, i,
pp. 49, 740.
(2) Dressler’s Case (Prague). Relates to three cysts, varying from
the size of a hemp-seed to that of a pea, and containing Coccidia,
found in a man’s liver.[178]
[178] Leuckart, R., _Die menschl. Paras._, 1863, 1st edition, i, p. 740.
(3) Sattler’s Case (Vienna). Coccidia were in this case observed in
the dilated biliary duct of a human liver.[179]
[179] Leuckart, R., _Die Paras. d. mensch._, 1879, 2nd edition, p. 281.
(4) Perls’ Case (Giessen). Perls discovered Coccidia in an old
preparation of Sömmering’s agglomerations.[180]
[180] Leuckart, R., _ibid._, p. 282.
(5) Silcock’s Case (London).[181] The patient, aged 50, who had
fallen ill with serious symptoms, exhibited fever, enlarged liver
and spleen, and had a dry, coated tongue. At the autopsy numerous
caseous centres, mostly immediately beneath the surface, were found,
while the contiguous parts of the liver were inflamed. Microscopical
examination demonstrated numerous Coccidia in the hepatic cells as
well as in the epithelium of the biliary ducts. A deposit of Coccidia
was likewise found in the spleen, which the parasites had probably
reached by means of the blood-stream.[182]
[181] Silcock, “A Case of Parasit. by Psorospermia,” _Trans. Path.
Soc._, London, 1890, xli, p. 320.
[182] Pianese has confirmed the fact that Coccidia actually occur in
the blood of the hepatic veins of infected rabbits.
(_b_) *Human Intestinal Coccidiosis.*
In two cadavers at the Pathological Institute in Berlin, Eimer[183]
found the epithelium of the intestine permeated by Coccidia. Railliet
and Lucet’s case may be traced back to intestinal Coccidia, which
were found in the fæces of a woman and her child, who had both
suffered for some time from chronic diarrhœa.[184] In other cases
(Grassi, Rivolta), where only the existence of Coccidia in the fæces
was known, it is doubtful whether the parasites originated in the
intestine or in the liver.
[183] _Die ei- u. kugelf. Psorosp. d. Wirbelt._, 1870, p. 16.
[184] Railliet and Lucet, “Obs. s. quelq. Cocc. intest.,” _C. R. Soc.
Biol._, Paris, 1890, p. 660; Railliet, _Trait. Zool. med. et agric._,
2e éd., 1895, p. 140.
(_c_) *Doubtful Cases.*
To these belong Virchow’s case[185] where, in the liver of an elderly
woman, a thick walled tumour measuring 9 to 11 mm. was found.
Among the contents of this tumour there were oval formations 56 µ
long, surrounded by two membranes and enclosing a number of round
substances. Virchow considered these foreign bodies to be eggs of
pentastomes in various stages of development, others consider them to
be Coccidia.
[185] _Arch. f. path. An._, xviii, 1860, p. 523.
The Coccidia which Podwyssotzki claims to have seen in the liver of
a man, not only in the liver cells, but also in the nuclei, are also
problematic.[186] The parasite was called _Caryophagus hominis_.
[186] Podwyssotzki, “Ueb. d. Bedeut. d. Coccid. in d. Path. Leber des
Menschen,” _Centralbl. f. Bakt._, vi, 1889, p. 41.
Again, other explanations can be given to an observation by Thomas,
on the occurrence of _Coccidium oviforme_ in a cerebral tumour of a
woman aged 40. The growth was as large as a pea and surrounded by a
bony substance.[187]
[187] Thomas, J., “Case of Bone Formation in the Human Brain, due to
the Presence of _Coccidium oviforme_,” _Journal Boston Soc. Med. Sc._,
iii, 1899, p. 167; _Centralbl. f. Bakt._ [I] xxviii, 1900, p. 882.
Genus. *Isospora*, Aimé Schneider, 1881.
Syn.: _Diplospora_, Labbé, 1893.
Belonging to the section _Disporea_, that is, forming only two spores,
each with four sporozoites.
*Isospora bigemina*, Stiles, 1891.
Syn.: “_Cytospermium villorum intestinalium canis et felis_,”
Rivolta, 1874; “_Coccidium Rivolta_,” Grassi, 1882; _Coccidium
bigeminum_, Stiles, 1891.
This parasite lives in the intestinal villi of dogs, cats, and the
polecat (_Mustela putorius_, L.). According to Stiles,[188] the oöcyst
divides into two equal ellipsoidal portions or sporoblasts which
become spores and then each forms four sporozoites. The oöcysts of
this species vary from 22 µ to 40 µ in length and from 19 µ to 28 µ in
breadth. Each spore is 10 µ to 18 µ long and contains four sporozoites.
The parasites live and multiply, not only in the gut epithelium, but
also in the connective tissue of the intestinal submucosa. Wasielewski
has seen merozoites in the gut of the cat.
[188] “Notes on Paras.,” No. II, _Journ. of Comp. Med. and Vet. Sci._,
1892, xiii, p. 517.
_Isospora bigemina_ (fig. 75) appears to occur also in man, for Virchow
published a case which was communicated to him by Kjellberg, and
attributed the illness to this parasite.[189] Possibly also it would be
more correct to ascribe the observation of Railliet and Lucet, which
is mentioned under “Human Intestinal Coccidiosis,” p. 148, to this
species, as the Coccidia in that case were distinguished by their
diminutive size (length 15 µ, breadth 10 µ). The case communicated by
Grunow may also possibly refer to _Isospora bigemina_.[190] Roundish
or oval structures of 6 µ to 13 µ in diameter occurred in the mucous
membrane of the gut and in the fæces of a case of enteritis.
[189] _Arch. f. path. An._, 1860, xviii, p. 527.
[190] Grunow, “Ein Fall von Protozoën (Coccidien?) Erkrankung des
Darmes,” _Arch. f. exper. Path. und Pharm._, 1901, xlv, p. 262.
[Illustration: FIG. 75.--_Isospora bigemina_, Stiles (from the
intestine of a dog). _a_, Piece of an intestinal villus beset with
Isospora, slightly enlarged; _b_, _Isospora bigemina_ (15 µ in
diameter), shortly before division; _c_, divided; _d_, each portion
encysted forming two spores; _e_, four sporozoites in each part, on the
left seen in optical section, together with a residual body--highly
magnified. (After Stiles.)]
DOUBTFUL SPECIES.
In literature many other statements are found as to the occurrence
of Coccidia-like organisms in different diseases of man. In some
of the cases the parasites proved to be fungi. This was the case
with the parasites of a severe skin disease of man, formerly called
_Coccidioides immitis_ and _Coccidioides pyogenes_. Other statements
are founded on misapprehensions, or are still much disputed. If
reference is here made to “_Eimeria hominis_,” R. Blanchard, 1895,
this is done on the authority of the investigator mentioned. The
structures in question are nucleated spindle-shaped bodies of very
different lengths (18 µ to 100 µ), which either occurred isolated or
were enclosed in large globular or oval cysts, alone or with a larger
tuberculated body (“residual body”). These formations were found by
J. Künstler and A. Pitres in the pleural exudation removed from a man
by tapping. The man was employed on the ships plying between Bordeaux
and the Senegal River.
Blanchard looks upon the fusiform bodies as merozoites and the cysts
as schizonts of a Coccidium. On the other hand, Moniez declares the
spindle bodies to be the ova and the supposed residual bodies to be
“floating ovaries” of an Echinorhynchus.
Severi’s “monocystid Gregarines,” which were taken from the lung
tissue of a still-born child, are also quite problematical.
No less doubtful are the bodies which Perroncito calls _Coccidium
jalinum_, and which he found in severe diseases of the intestine in
human beings, pigs, and guinea-pigs; Borini also reported another
case.
Order. *Hæmosporidia*, Danilewsky emend. Schaudinn.
The Hæmosporidia are a group of blood parasites, comprising forms
differing greatly among themselves. Some of the forms need much further
investigation. However, there are certain true Hæmosporidia which
present close affinities with the Coccidia, leading Doflein to use the
term *Coccidiomorpha* for the two orders conjoined.
The Hæmosporidia present the following general characteristics:--
(1) They are parasites of either red or white blood corpuscles of
vertebrates during one period of their life-history.
(2) They exhibit alternation of generations--asexual phases or
schizogony alternating with sexual phases or sporogony--as do the
Coccidia.
(3) There is also an alternation of hosts in those cases which have so
far been completely investigated. The schizogony occurs in the blood or
internal organs of some vertebrates while the sporogony occurs in an
invertebrate, such as a blood-sucking arthropod or leech.
(4) Unlike the Coccidia, resistant spores in sporocysts are not
generally produced, such protective phases in the life-cycle being
unnecessary, as the Hæmosporidia are contained within either the
vertebrate or invertebrate host during the whole of their life.
The Hæmosporidia may be considered for convenience under five main
types:--
(1) The _Plasmodium_ or _Hæmamœba_ type. This includes the malarial
parasites of man and of birds. The asexual multiplicative or
schizogonic phases occur inside red blood corpuscles and are amœboid.
They produce distinctive, darkish pigment termed melanin or hæmozoin.
Infected blood drawn and cooled on a slide may exhibit “exflagellation”
of the male gametocytes, _i.e._, the formation of filamentous male
gametes. The invertebrate host is a mosquito. The malarial parasites
of man are discussed at length on p. 155. Similar pigmented hæmamœboid
parasites have been described in antelopes, dogs, and other mammals,
and even reptiles.
(2) The _Halteridium_ type. The trophozoite stage inside the red blood
corpuscle is halter-shaped. Pigment is produced, especially near the
ends of the organism. The parasites occur in the blood of birds. The
invertebrate host of _H. columbæ_ of pigeons in Europe, Africa, Brazil
and India, is a hippoboscid fly, belonging to the genus _Lynchia_.
Halteridium parasites are common in the blood of passerine birds,
such as pigeons, finches, stone owls, Java sparrows, parrots, etc.
The Halteridium embraces or grows around the nucleus of the host red
cell without displacing the nucleus. Young forms and multiplicative
stages of _H. columbæ_ have been found in leucocytes in the lungs of
the pigeon (fig. 76, _8_-_12_). Male and female forms (gametocytes)
are seen in the blood (fig. 76, _3a_, _3b_). The cytoplasm of the
male gametocytes is pale-staining and the nucleus is elongate, while
the cytoplasm of the females is darker and the nucleus is smaller and
round. Formation of male gametes from male gametocytes (the so-called
process of “exflagellation”) may occur on a slide of drawn infected
blood, also fertilization, and formation of the oökinete, as first seen
by MacCallum. The correct generic name for Halteridia is, apparently,
_Hæmoproteus_. Wasielewski (1913), working on _H. danilewskyi_ (var.
_falconis_), in kestrels, finds that the halteridium may be pathogenic
to nestlings. The cycle of _H. noctuæ_ described by Schaudinn (1904)
lacks confirmation. The account of the life-cycle of _H. columbæ_ given
by Aragão (1908) is illustrated in fig. 76. It agrees with the work of
Sergent (1906–7) and Gonder (1915). Mrs. Adie (1915) states that the
cycle in _Lynchia_ is like that of a _Plasmodium_.
[Illustration: FIG. 76--_Hæmoproteus_ (_Halteridium_) _columbæ_.
Life-cycle diagram: 1, 2, stages in red blood corpuscle of bird; 3,
4, gametocytes (3_a_ ♂, 3b ♀); 5_a_, formation of microgametes; 6,
fertilization (in fly’s gut); 7, oökinete; 8–12, stages in mononuclear
leucocytes in lungs. (After Aragão.)]
(3) The _Leucocytozoön_ type. The trophozoites and gametocytes occur
within mononuclear leucocytes and young red cells (erythroblasts) in
the blood of birds. Laveran and França consider that the Leucocytozoa
occur in erythrocytes. The host cells are often greatly altered by
the parasites, becoming hypertrophied and the ends usually drawn into
horn-like processes (fig. 77), though some remain rounded. Leucocytozoa
are limited to birds, and very rarely produce pigment. Male and female
forms (gametocytes) are distinguishable in the blood (fig. 77), and the
formation of male gametes (“exflagellation”) may occur in drawn blood.
[Illustration: FIG. 77.--_Leucocytozoön lovati_. _a_, Male parasite
(microgametocyte), within host cell, whose ends are drawn out; _b_,
female parasite (macrogametocyte) from blood of grouse. × 1,800. (After
Fantham.)]
The Leucocytozoa were first seen by Danilewsky in 1884. They are
usually oval or spherical. It is not easy sometimes to distinguish the
altered host cell from the parasite, as the nucleus of the former is
pushed to one side by the leucocytozoön. The cytoplasm of the female
parasite stains deeply, and the nucleus is rather small, containing a
karyosome. In the male the cytoplasm stains lightly and the nucleus is
larger, with a loose, granular structure.
Many species of Leucocytozoa are recorded, but schizogony has only
been described by Fantham (1910)[191] in _L. lovati_ in the spleen of
the grouse (_Lagopus scoticus_), and by Moldovan[192] (1913) in _L.
ziemanni_ in the internal organs of screech-owls.
[191] _Annals Trop. Med. and Parasitol._, iv, p. 255.
[192] _Centralbl. f. Bakt._, Orig., lxxi, p. 66.
M. and A. Leger[193] (1914) propose to classify Leucocytozoa,
provisionally, according as the host cells are fusiform or rounded.
[193] _Bull. Soc. Path. Exot._, vii, p. 437.
(4) The _Hæmogregarina_ type. Included herein are many parasites of red
blood corpuscles, with a few (the leucocytogregarines) parasitic in the
white cells of certain mammals and a few birds. They are not amœboid
but gregarine-like, vermicular or sausage-shaped (fig. 78). They do
not produce pigment. They are widely distributed among the vertebrata,
but are most numerous in cold-blooded vertebrates (fishes, amphibia
and reptiles). The hæmogregarines of aquatic hosts are transmitted by
leeches, those of terrestrial hosts by arthropods.
The nucleus of hæmogregarines is usually near the middle of the
parasite, but may be situated nearer one end. The body of the
parasite may be lodged in a capsule (“cytocyst”). There is much
variation in size and appearance among hæmogregarines. Some are
small (_Lankesterella_); some attack the nucleus of the host cell
(_Karyolysus_); others have full grown vermicules larger than the
containing host corpuscle, and so the hæmogregarines bend on themselves
in the form of *U* (fig. 78, _b_). Schizogony often occurs
in the internal organs of the host, sometimes in the circulating blood.
The hæmogregarines occurring in the white cells (mononuclears or
polymorphonuclears) of mammals have been referred to a separate
genus, _Leucocytogregarina_ (Porter) or _Hepatozoön_ (Miller). Such
leucocytogregarines are known in the dog (fig. 79), rat, mouse,
palm-squirrel, rabbit, cat, etc. Schizogony of these forms occurs in
the internal organs, such as the liver, lung and bone-marrow of the
hosts. They are apparently transmitted by ectoparasitic arthropods,
such as ticks, mites, and lice.
[Illustration: FIG. 78.--Hæmogregarines from lizards, _a_, _H.
schaudinni_, var. _africana_, from _Lacerta ocellata_; _b_, _H. nobrei_
from _Lacerta muralis_; _c_, _H. marceaui_ in cytocyst, from _Lacerta
muralis_. (After França.)]
A few hæmogregarines are known to be parasitic in the red blood
corpuscles of mammals. Such are _H. gerbilli_ in the Indian field rat,
_Gerbillus indicus_; _H. balfouri_ (_jaculi_) in the jerboa, _Jaculus
jaculus_, and a few species briefly described from marsupials. These
parasites do not form pigment.
Strict leucocytic gregarines have been described from a few birds by
Aragão and by Todd.
The sporogony of hæmogregarines is only known in a few cases, and
in those affinity with the Coccidia is exhibited. In fact, the
Hæmogregarines are now classified by some authors with the Coccidia.
(5) The _Babesia_ or _Piroplasma_ type. These are small parasites of
red blood corpuscles of mammals. They do not produce pigment. They
are pear-shaped, round or amœboid in Babesia, bacilliform and oval
in other forms referred to this group. Piroplasms are transmitted by
ticks. These parasites are described at length on p. 172.
[Illustration: FIG. 79.--_Leucocytogregarina canis_. Life-cycle
diagram. Constructed from drawings by Christophers. (After Castellani
and Chalmers.) Schizogony occurs in the bone-marrow. The parasite is
transmitted from dog to dog by the tick, _Rhipicephalus sanguineus_,
development in which, so far as known, is shown on the right.]
THE MALARIAL PARASITES OF MAN.
Malaria, otherwise known as febris intermittens, chill-fever, ague,
marsh fever, paludism, etc., is the name given to a disease of man,
which begins with fever. It has been known since ancient times and is
distributed over almost all the world, although very unevenly, but does
not occur in waterless deserts and the Polar regions. In many places,
especially in the civilized countries of Central Europe, the disease
is extinct or occurs only sporadically, and large tracts of land have
become free from malaria.
The rhythmical course of the fever is characteristic. It begins
apparently suddenly with chilliness or typical shivering, whilst the
temperature of the body rises, the pulse becomes low and tense and the
number of beats of the pulse increases considerably. After half to
two hours the heat stage begins. The patient himself feels the rise
of his temperature (shown by feeling of heat, dry tongue, headache,
thirst). The temperature may reach 41°C or more. At the same time there
is sensitiveness in the region of the spleen and enlargement of that
organ. After four to six hours an improvement takes place, and with
profuse perspiration the body temperature falls rapidly, not often
below normal. After the attack the patient feels languid, but otherwise
well until certain prodromal symptoms (heaviness in the body, headache)
which were not noticed at first, denote the approach of another attack
of fever, which proceeds in the same way.
The intervals between the attacks are of varying length which permit of
a distinction in the kinds of fever. If the attacks intermit one day,
occurring on the first, third and fifth days of the illness and always
at the same time of day, it is termed _febris tertiana_; if two days
occur between fever days, it is called _febris quartana_. In the case
of the fever recurring daily, later writers speak of typical _febris
quotidiana_. But a quotidian fever may arise when two tertian fevers
differing by about twenty-four hours exist at the same time (_febris
tertiana duplex_). The patient has a daily attack, but the fever of the
first, third and fifth days differs in some point (hour of occurrence,
height of temperature, duration of cold or hot stage) from the fever
of the second, fourth and sixth days. Similarly, two or three quartan
fevers which differ by about twenty-four hours each may be observed
together (_febris quartana duplex_ or _triplex_); in the latter case
the result is also a quotidian fever.
Two kinds of tertian fever are differentiated--a milder form occurring
especially in the spring (spring tertian fever), and a more severe form
appearing in the summer and autumn in warmer districts, especially in
the tropics (_summer or autumn fever_, _febris æstivo-autumnalis_,
_febris tropica_, _febris perniciosa_). The latter often becomes a
quotidian fever.
All the afore-mentioned infections are termed acute. They are
distinguished from the very different _chronic malarial infection_ by
the frequent occurrence of relapses, which finally lead to changes
of some organs and particularly of the blood. The relapses are then
generally marked by an irregular course of fever.
The term masked malaria is used when any disturbance of the state
of health of a periodic character shows itself and disappears after
treatment with quinine.[194] Generally it is a question of neuralgia.
[194] Quinine is still almost exclusively the remedy used in the
treatment of malaria. It is prepared from the bark of the cinchona
tree. This important remedy was introduced into Europe in 1640 from
Ecuador by Juan del Vego, physician of the Countess del Cinchon.
That intermittent fever was an infectious disease, although
not one which was transmitted direct from man to man, had been
assumed for a long time. Therefore it was natural, at a time when
bacteriology was triumphing, to look for a living agent causing
infection in malaria, which search was, seemingly, successful (Klebs,
Tomasi-Crudeli, 1879). Hence it was not surprising that the discovery
of the real malarial parasites in November, 1880, by the military
doctor A. Laveran[195] in Constantine (Algeria), at first met with
violent opposition, even after Richard (1882) had confirmed it and
Marchiafava, Celli, Grassi and others, had further extended it.
Not that the existence of structures found in the blood of malaria
patients by Laveran and Richard was denied; on the contrary, the
investigations of the opponents furnished many valuable discoveries,
but the organisms were differently interpreted and considered to be
degeneration products of red blood corpuscles. Only when Marchiafava
and Celli (1885) saw movements in the parasites, which Laveran called
_Oscillaria malariæ_ and later _Hæmatozoön malariæ_, was their animal
nature admitted and the parasites were named _Plasmodium malariæ_.
Shortly before this, Gerhardt (1884) had stated that the disease
could be transmitted by the injection of the blood of a malarial
patient to a healthy person.
[195] The discovery of Laveran is in no way lessened by the fact that
one investigator or another (according to Blanchard [_Arch. de Paras._,
vii, 1903, p. 152], P. F. H. Klencke in 1843) had seen, mentioned and
depicted malarial parasites. (_Neue phys. Abhandl. auf. selbständ.
Beob. gegr._, Leipzig, 1843, p. 163, fig. 25). In 1847 Meckel had
recognized that the dark colour of the organs in persons dead of
malaria was due to pigment. Virchow in 1848 stated that this pigment
occurred in blood cells. Kelsch in 1875 recognized the frequency of
melaniferous leucocytes in the blood of malarial patients. Beauperthuy
(1853) noticed that in Guadeloupe there was no malaria at altitudes
where there were no “insectes tipulaires,” and suggested that the
disease was inoculated by insects.
This supplied the starting point for further investigations, which
were made not exclusively, but principally, by Italian investigators
(Golgi, Marchiafava and Celli, Bignami and Bastianelli, Grassi and
Feletti, Mannaberg, Romanowsky, Osier, Thayer and others). In 1885
Golgi described the asexual cycle in the blood, in the case of the
quartan parasite. These investigations, after attention had been
drawn by Danilewsky (1890) to the occurrence of similar endoglobular
parasites in birds, were extended to the latter (Grassi and Feletti,
Celli and Sanfelice, Kruse, Labbé and others).
The result was as follows: Malaria in man (and birds) is the result
of peculiar parasites included in the _Sporozoa_ by Metchnikoff,
which parasites live in the erythrocytes, grow in size and finally
“sporulate,” that is, separate into a number of “spores” which leave
the erythrocytes and infect other blood corpuscles. Morphologically
and biologically several species (and respectively several varieties)
of malarial parasites may be distinguished, on which the different
intermittent forms depend. Transmission of the blood of patients to
healthy people produces a malarial affection which corresponds in
character to the fever of the patient from whom the inoculation was
made. The combined types of fever (tertiana duplex, quartana duplex
or triplex) are explained by the fact that the patient harbours
two or three groups of parasites which differ in their development
by about twenty-four hours, whilst the irregular fevers depend on
deviation from the typical course of development of the parasites. In
addition to stages of the parasites which could easily be arranged
in a developmental series concurrent with the course of the disease,
other phases of the parasites also became known, such as spheres,
crescents, polymitus forms, which seemed not to be included in the
series and, therefore, were very differently interpreted.
The decision reached at the beginning of the last decade of the
last century, which found expression in comprehensive statements
(Mannaberg, Ziemann and others), only concerned a part of the
complete development of the malarial parasites. No one could with
any degree of certainty demonstrate how man became infected, nor
were there reliable hypotheses based on analogy with other parasites
concerning the exit of the excitants of malaria from the infected
person and their further behaviour. Numerous hypotheses had been
advanced, but none was able to elucidate the various observations
made from time to time in dealing with malaria. One hypothesis only
seemed to have a better foundation. Manson (1894), who knew from
his own experience the part played by mosquitoes in the development
of Filaria from the blood of man, applied this also to the malarial
parasites living in the blood, whereby at least the way was indicated
by which the Hæmosporidia could leave man. The parasites were said
finally to get into water through mosquitoes which had sucked the
blood of malarial patients, and the germ spread thence to men who
drank the water. In some cases the parasites were supposed to reach
man by the inhaling of the dust of dried marshes. On the other
hand, Bignami believed that the mosquitoes were infected in the
open air by malarial parasites which occurred there in an unknown
stage and the insects transmitted the germs to man when biting. R.
Koch combined both hypotheses, without, however, producing positive
proof. R. Ross, then (1897–8) an English military doctor in India,
was the first to succeed in this. He had been encouraged by Manson
to study the fate of malarial _Plasmodia_ which had entered the
intestine of mosquitoes with malaria-infected blood, especially in
the case of the _Plasmodium_ (_Proteosoma_) living in the blood of
birds. He showed that the _Proteosoma_ penetrate the intestinal wall
of the mosquitoes, grow and develop into large cysts which produce
innumerable rod-like germs, which burst into the body cavity and
penetrate the salivary glands. Ross allowed mosquitoes to suck the
blood of birds affected by malaria, and some nine days later, let
the infected mosquitoes which had been isolated suck healthy birds.
After five to nine days _Proteosoma_ were found to occur in the blood
of the birds used. The _Proteosoma_ and _Halteridium_ of birds were
also further investigated by MacCallum (1897–8), Koch and others, and
important results followed.
In any case Ross (1898) had clearly established the importance
of mosquitoes in the spread of malaria among birds. It was now
only a question of proving whether, and how far, mosquitoes were
concerned with human malaria. Ross himself worked to this end. Here
the experiments of Italian investigators (Bignami, Bastianelli,
Grassi)[196] were of importance. These investigators studied the fate
of malarial parasites in man, produced malaria in men experimentally
by the bites of infected mosquitoes, and established that only
mosquitoes belonging to the genus _Anopheles_ were concerned, and
not species of _Culex_. These latter are only able to transmit
_Proteosoma_ to birds. It is true that _Culex_ can ingest the
human malarial parasites, but the latter do not develop in them.
Development only occurs in species of _Anopheles_. In _Anopheles_
(and similarly for _Proteosoma_ in _Culex_) sexual reproduction takes
place; crescents, spheres and polymitus forms are necessary stages of
development in the mosquito.
[196] Grassi, B. (1901), “Die Malaria,” 250 pp., 8 plates. G. Fischer,
Jena.
With these discoveries the campaign against malaria became more
definite. It was directed partly against the transmitters, whose
biology and life-cycle were more thoroughly investigated, instead of
merely against the infection of the adult _Anopheles_. The latter do
not, as was believed for some time, transmit the malarial germs to
their offspring. They always infect themselves from human beings,
whereby the relapses appearing in early summer, and the latent
infection, especially of children of natives, play a principal part
(Stephens and Christophers, Koch). Further, the crusade was directed
against the infection of man by the bites of _Anopheles_. Important
results have been obtained in these directions. Low and Sambon in
1900 lived in a mosquito-screened hut in a malarial part of the
Roman Campagna for three of the most malarious months and did not
contract the disease. In the same year Dr. P. T. Manson was infected
with malaria by infected mosquitoes sent from Italy. The rôle of
mosquitoes having been proved, it may be hoped that ultimately the
eradication of malaria, or at least a considerable restriction of it,
will be achieved.
It is of importance to record that, although malarial parasites occur
in mammals (monkeys, bats, etc.) the human ones are not transmissible
to mammals, not even to monkeys. The species, therefore, are specific
to the different hosts (Dionisi, Kossel, Ziemann, Vassall).
An important work dealing with the modern applications of the
mosquito-malaria theory in all parts of the Tropics was published by
Sir Ronald Ross in 1911. It is entitled “The Prevention of Malaria”
(John Murray, London, 21s.).
DEVELOPMENT OF THE MALARIAL PARASITES OF MAN.
The commencement of the developmental cycle and of the infection of
man, is the sporozoites (fig. 80, _1_) which are passed into the
blood of a person by the bite of an infected mosquito. Prior to this
the parasites collect in the excretory ducts of the salivary glands
(fig. 80, _27_) of the _Anopheles_. The sporozoites are elongate
and spindle-shaped, 10 µ to 20 µ long and 1 µ to 2 µ broad, with an
oval nucleus situated in the middle. They are able to glide, perform
peristaltic contractions, or curve laterally. Schaudinn has studied
the penetration of the red blood corpuscles (fig. 80, _2_) by the
sporozoites in the case of the living tertian parasite. The process
takes forty to sixty minutes in drawn blood. After its entrance the
parasite, which is now called a trophozoite, contracts, and becomes an
active amœbula (fig. 80, _3_). It develops a food vacuole and grows at
the expense of the invaded blood corpuscle (fig. 80, _4_), which is
shown by the appearance of pigment granules (transformed hæmoglobin)
in it. When the maximum size is attained, multiplication by schizogony
(fig. 80, _5_-_7_) begins with a division of the nucleus, which is
followed by further divisions of the daughter nuclei, the number of
which varies up to 16 or even 32, depending on the species of the
parasite. Then the cytoplasm divides into as many portions as there
are nuclei, the result being a structure suggestive of the spokes of a
wheel or of a daisy, the centre of the resulting rosette being occupied
by dark pigment. Finally, the parts separate from one another, leaving
behind a residual body containing the pigment, and the daughter forms
issue into the blood plasma as merozoites (fig. 80, _7_). They are
actively amœboid (fig. 80, _8_) and soon begin to enter other blood
corpuscles of their host, for the entry into which thirty to sixty
minutes are necessary, according to Schaudinn’s observations.[197]
[197] It should be remembered that some authors (Laveran, Argutinsky,
Panichi, Serra) argue against the intra-globular position of
malarial parasites and state that they only adhere outwardly to
the red blood corpuscles. These views have recently been revived
by Mary Rowley-Lawson, and she states that the malarial parasite
is “extracellular throughout its life-cycle and migrates from red
corpuscle to red corpuscle destroying each before it abandons it.”
(_Journ. Exper. Med._, 1914, xix, p. 531.)
Here they behave like sporozoites which previously entered and again
produce merozoites. This process is repeated until the number of
parasites is so large that, at the next migration of the merozoites,
the body of the person infected reacts with an attack of fever,[198]
which is repeated with the occurrence of the next or following
generations.
[198] The incubation period, that is, the time between infection
and the first attack of fever, is ten to fourteen days; with severe
infection fewer days (minimum 5 to 6) are needed.
[Illustration: FIG. 80.--Life-cycle of the tertian parasite
(_Plasmodium vivax_). Figs. 1 to 17, × 1,200; figs. 18 to 27, × 600.
(After Lühe, based on figures by Schaudinn and Grassi.) 1, sporozoite;
2, entrance of the sporozoite into a red blood corpuscle; 3, 4, growth
of the parasite, now sometimes called a trophozoite; 5, 6, nuclear
division in schizont; 7, free merozoites; 8, the merozoites which have
developed making their way into blood corpuscles, (arrow pointing to
the left) and increase by schizogony (3–7); after some duration of
disease the sexual individuals appear; 9_a_-12_a_, macrogametocytes;
9_b_-12_b_, microgametocytes, both still in the blood-vessels of
man. If macrogametocytes (12_a_) do not get into the intestine of
_Anopheles_ they may perhaps increase parthenogenetically according
to Schaudinn (12_a_; 13_c_-17_c_). The merozoites which have arisen
(17_c_) become schizonts 3–7. The phases shown underneath the dotted
line (13–17) proceed in the stomach of _Anopheles_. 13_b_ and 14_b_,
formation of microgametes; 13_a_ and 14_a_, maturation of the
macrogametes; 15_b_, microgamete; 16, fertilization; 17, oökinete; 18,
oökinete in the walls of the stomach; 19, penetration of the epithelium
of the stomach; 20–25, stages of sporogony on the outer surface of
the intestinal wall; 26, migration of the sporozoites to the salivary
gland; 27, salivary gland with sporozoites.]
The growth and schizogony last different times, according to the
species of the parasite, about forty-eight hours in the case of the
parasite of febris tertiana or tropica, and seventy-two hours for the
quartan parasite. The various intermittent forms produced by them
depend on this specific difference in the malarial parasites.
The schizogony can, however, only be repeated a certain number of
times, supposing that the disease has not been checked prematurely by
the administration of quinine, which is able to kill the parasites.
It appears that after a number of attacks of fever the conditions of
existence in man are unfavourable for the malarial parasites, and
this brings about the production of other forms which have long been
known, but also long misunderstood (spheres, crescents, polymitus). The
merozoites in this case no longer grow into schizonts, or at least not
all of them, but become sexual individuals called gametocytes (fig. 80,
_9_-_12_), which only start their further development when they have
reached the intestine of _Anopheles_. This does not take place in
every case, nor with all the gametocytes which exist in the blood of
patients with intermittent fever. Of those parasites which remain in
the human blood the male ones (microgametocytes) soon perish, the
females (macrogametocytes) persist for some long time, and perhaps at
last acquire the capacity of increasing by schizogony. They might thus
form merozoites which behave in the body as if they had proceeded from
ordinary schizonts (fig. 80, _13c_-_17c_). If their number increases
sufficiently, in course of time the patient, who was apparently
recovering, has a new series of fever attacks, or relapses, without
there having been a new infection. This is the view of Schaudinn, who
from researches of his own concluded that relapses were brought about
by a sort of parthenogenetic reproduction of macrogametocytes. R. Ross,
on the contrary, believes that in the relatively healthy periods the
number of parasites in the blood falls below that necessary to provoke
febrile symptoms; relapses then result merely from increase in the
numbers of the parasites present in the individual. Ross’s view is now
generally accepted.
[Illustration: FIG. 81.--Stages of development of pernicious
or malignant tertian parasites in the intestine of _Anopheles
macultpennis_. (After Grassi.) _a_, macrogametocyte (crescent) still
attached to human blood corpuscles; _b_, macrogametocyte (sphere)
half an hour after ingestion by the mosquito; _c_, microgametocyte
(crescent) attached to the blood corpuscle; _d_, microgametocyte
(sphere) half an hour after ingestion; the nucleus has divided several
times; _e_, microgametes attached to the residual body (polymitus
stage).]
[Illustration: FIG. 82.--Oökinete of the malignant tertian parasite
in the stomach of _Anopheles maculipennis_, thirty-two hours after
ingestion of blood. (After Grassi.)]
If the gametocytes, which are globular, or in the pernicious or
malignant tertian parasite crescentic (fig. 81), gain access to the
intestine of an Anopheline,[199] they mature. The macrogametocytes
extrude a part of their nuclear substance (fig. 80, _13a_, _14a_) and
thereby become females or macrogametes. The microgametocytes, on the
other hand, undergo repeated nuclear division, preparation for this
being made apparently whilst in the blood of man. This results in the
formation of threadlike bodies which move like flagella and finally
detach themselves from the residual body (fig. 80, _13b_, _14b_). These
are the males or microgametes[200] (fig. 80, _15b_).
[199] Schizonts ingested about the same time perish in the intestine of
the mosquito.
[200] If the microgametocytes are sufficiently mature the formation of
microgametes occurs in the blood of man as soon as it is taken from the
blood-vessel and has been cooled and diluted. Such a stage is called a
_Polymitus_ form, and the process has been called “exflagellation.”
Copulation takes place in the stomach of the Anopheline (fig. 80,
_16_). A microgamete penetrates a macrogamete and coalesces with it.
The fertilized females elongate very soon and are called oökinetes
or “vermicules” (figs. 80, _17_; 82). They penetrate the walls of the
stomach, pierce the epithelium (fig. 80, _18_, _19_), and remain lying
between it and the superficial stratum (tunica elastico-muscularis).
Then they become rounded and gradually develop into cysts which grow
larger and are finally visible to the naked eye, being called oöcysts
(figs. 80, _20_-_24_; 83). Their size at the beginning is about 5 µ,
the maximum that they attain is 60 µ, only exceptionally are they
larger.
[Illustration: FIG. 83.--Section of the stomach of an _Anopheles_, with
cysts (oöcysts) of the malignant tertian parasite. (After Grassi).]
The sporulation (figs. 80, _21_-_25_; 84), which now follows, begins
with repeated multiple fission of the nucleus. Long before the
definitive number of nuclei, which varies with the individual, is
attained the protoplasm, according to Grassi, begins to segment around
the individual large nuclei but without separating completely into cell
areas. According to Schaudinn, however, there is a condensation of the
outstanding protoplasmic strands. It is certain that the number of
nuclei increases with simultaneous decrease in size. They soon appear
on the surface of the strands or sporoblasts, surround themselves
with some cytoplasm and then elongate (fig. 84). In this manner the
sporozoites are formed and break away from the unused remains of the
cytoplasmic strands of the sporoblasts (fig. 80, _26_). The number
of the sporozoites in an oöcyst varies from several hundreds to ten
thousand.
[Illustration: FIG. 84.--Four different sporulation stages of malarial
parasites from _Anopheles maculipennis_, much magnified. _a_-_c_, of
the malignant tertian parasite; _a_, four to four and a half days after
sucking; _b_ and _c_, five to six days after sucking; _d_, of the
tertian parasite, eight days after sucking. (After Grassi.)]
The sporulation is influenced in its duration by the external
temperature (Grassi, Jansci, Schoo). In the tertian parasite it takes
place quickest at a temperature of 25° to 30° C. and takes eight to
nine days. A temperature a few degrees lower has a retarding effect
(eighteen to nineteen days at 18° to 20° C). A still lower one has a
restraining or even destructive effect. Temperatures over 35° C. also
exercise a harmful effect. The malignant tertian parasite seems to
need a somewhat higher temperature and the quartan parasite a lower
one.
The sporozoites of the various malarial parasites show no specific
differences. They were stated by Schaudinn to occur in three forms,
and these were described as indifferent (neuter), female and male.
There is, however, little or no evidence for this hypothetical
differentiation. The last were said to perish prematurely, that is, in
the oöcyst. The others after the rupture of the oöcysts enter the body
cavity of the Anophelines, whence they are carried along in the course
of the blood. Finally they penetrate the salivary glands (fig. 80,
_27_) probably by their own activity, break through their epithelia and
accumulate in the salivary duct (fig. 80, _27_). At the next bite by
the mosquito they are transmitted to the blood-vessels of man.
THE SPECIES OF MALARIAL PARASITES OF MAN.
In view of the differences in opinion regarding “species” and
“varieties,” the dispute whether the malarial parasites of man
represent one species with several varieties, or several species is
almost superfluous. If necessary two genera may be distinguished.
The parasites of the tertian and quartan fever are alike in that
their gametocytes have a rounded shape (figs. 80, _12_, _13_), whilst
the corresponding stages of the pernicious or malignant tertian
parasites are crescentic (figs. 81, 88). These differences are used
by some writers as the distinguishing characteristic of two genera:
_Plasmodium_, Marchiafava and Celli, 1885, for the first mentioned
species; _Laverania_, Grassi and Feletti, 1889, for the pernicious or
malignant tertian parasite. Whether there is a genuine quotidian fever
and accordingly a special quotidian parasite is still disputed.
These parasites are treated in practical detail in Stephens and
Christophers’ “Practical Study of Malaria,” 3rd edition, 1908.
*Plasmodium vivax*, Grassi and Feletti, 1890.
Syn.: _Hæmamœba vivax_, Grassi and Feletti, 1890; _Plasmodium
malariæ_ var. _tertianæ_, Celli and Sanfelice, 1891; _Hæmamœba
laverani_ var. _tertiana_, Labbé, 1894; *Hæmosporidium tertianum*,
Lewkowitz, 1897; _Plasmodium malariæ tertianum_, Labbé, 1899:
_Hæmamœba malariæ_ var. _magna_, Laveran, 1900, p.p.; _Hæmamœba
malariæ_ var. _tertianæ_, Laveran, 1901.
This species, _P. vivax_,[201] is the causal agent of the simple or
spring tertian fever and is, therefore, named directly the tertian or
benign tertian parasite (figs. 80, _3_-_8_; 85). During the afebrile
period in the patient, the young trophozoites or amœbulæ appear on or
in the red blood corpuscles as pale bodies of 1·5 µ to 2 µ diameter
which at first show only slow amœboid movements. Their nucleus is
difficult to recognize in the early stage. Soon the food vacuole is
formed and this grows concomitantly with the trophozoite and the
parasite has a ring-like appearance. Afterwards the vacuole diminishes,
and at this period the first brownish melanin granule appears. From
this time the activity and number of the pigment granules increase
with continuous growth. When the parasite has grown to about one-third
the diameter of the erythrocyte the latter shows characteristic red
Schüffner’s dots or “fine stippling,” after staining with Romanowsky’s
solution. Later, after about twenty-four hours, the blood corpuscles
begin to grow pale, then to increase in size, and after thirty-six
hours, that is, about twelve hours before the next attack of fever,
schizogony of the parasite is initiated by the division of the nucleus.
The parasite at this time occupies half to two-thirds of the enlarged
blood corpuscle. The daughter nuclei continue dividing until sixteen,
and occasionally twenty-four, daughter nuclei are produced. The pigment
which, up till now lies nearer the periphery, moves to the middle,
while the nuclei lie nearer the surface.
[201] See Schaudinn, F. (1902), _Arb. a. d. kaiserl. Gesundheits._,
xix, pp. 169–250, 3 plates.
[Illustration: FIG. 85.--Development of the tertian parasite in the red
blood corpuscles of man; on the right a “Polymitus.” (After Mannaberg.)
See also fig. 80, _3_--_7_.]
Around each nucleus a portion of cytoplasm collects and thus young
merozoites are produced. These separate from each other and from the
little residual masses[202] which contain the melanin and pass from
the blood corpuscles, which now can hardly be recognized, to the blood
plasma, where they soon attack new erythrocytes.
[202] The pigment masses (melanin or hæmozoin) are taken up by the
leucocytes, particularly the mononuclear ones, and are carried
especially to the spleen, and also to the liver and the bone-marrow.
From this circumstance arises the well-known pigmentation of the spleen
in persons who have suffered from malaria.
The migration of the merozoites initiates a new attack of fever and two
groups of tertian parasites in the blood, differing in development by
about twenty-four hours, are the conditions for febris tertiana duplex.
After a lengthy duration of fever the gametocytes (figs. 80, _9_--_12_)
appear. They are uninucleate. The microgametocytes are about the size
of fully developed schizonts, the macrogametocytes are somewhat larger.
Their further development takes place in Anophelines.
The chief distinctive characteristics of the simple tertian parasite,
as seen in infected blood, are:--(1) The infected red-cell is usually
enlarged; (2) the presence of fine red granules known as Schüffner’s
dots in the red blood corpuscles, after Romanowsky staining; (3)
the fragile appearance of the parasite compared with other species.
Large forms are pigmented, irregular and “flimsy-looking,” sometimes
appearing to consist of separate parts. Irregularity of contour is
common.
Ahmed Emin[203] (1914) has described a small variety of _P. vivax_.
[203] _Bull. Soc. Path. Exot._, vii, p. 385.
*Plasmodium malariæ*, Laveran.
Syn.: _Oscillaria malariæ_, Laveran, p.p., 1883; _Hæmamœba malariæ_,
Gr. et Fel., 1890; _Plasmodium malariæ_ var. _quartanæ_, Celli et
Sanfel., 1891; _Hæmamœba laverani_ var. _quartana_, Labbé, 1894;
_Hæmosporidium quartanæ_, Lewkowitz, 1897; _Plasmodium malariæ
quartanum_, Labbé, 1899; _Plasmodium golgii_, Sambon, 1902;
_Laverania malariæ_, Jancso, 1905 nec Grassi et Fel. 1890; _Hæmomœba
malariæ_ var. _quartanæ_; Lav., 1901.
_Plasmodium malariæ_ is the parasite of quartan malaria (fig. 86). The
trophozoites of the quartan parasite differ from the corresponding
stages of the tertian parasite in that their motility is less and
soon ceases. They differ also in their slower growth, by the early
disappearance of the food vacuole, by the more marked formation of
the dark brown pigment, and by the fact that the red blood corpuscles
attacked are not altered either in colour or size.
[Illustration: FIG. 86.--Development of the quartan parasite in the red
corpuscles of man--asexual stages. (After Manson.)]
When the parasites have grown almost to the size of the erythrocytes
schizogony occurs. The pigment granules arrange themselves in lines
radiating towards the centre and the merozoites are also radially
disposed in groups of 6, 8, 10 or even 12, but are often arranged less
regularly. The whole development, growth and schizogony, occupies
seventy-two hours.
The appearance of quartana duplex or triplex is conditional on the
presence in the blood of the patient of two or three groups of
_Plasmodia_ differing in their development by twenty-four hours.
The chief distinctive characters of the quartan parasite are: (1)
The erythrocyte is unchanged in size; (2) the rings are compact and
show pigment early; in the larger forms the chromatin is dense and
relatively plentiful; (3) the pigment, which is relatively well-marked,
may be arranged at the periphery.
*Laverania malariæ*, Grassi and Feletti, 1890 = *Plasmodium
falciparum*, Welch, 1897.
Syn.: _Plasmodium malariæ_ var. _quotidianæ_, Celli et Sanf., 1891;
_Hæmamœba malariæ præcox_, Gr. et Fel., 1892 (nec _H. præcox_,
Gr. et Fel., 1890); _Hæmamœba laverani_, Labbé, 1894; _Hæmatozoön
falciparum_, Welch, 1897; _Hæmosporidium undecimanæ_ and _H.
sedecimanæ_ and _H. vigesimo-tertianæ_, Lewkowitz, 1897; _Hæmamœba
malariæ parva_, Lav., 1900; _Plasmodium præcox_, Dofl., 1901;
_Plasmodium immaculatum_, Schaud., 1902; _Plasmodium falciparum_,
Blanch., 1905.
The names most commonly used for the parasite of malignant tertian
malaria are _Plasmodium falciparum_ and _Laverania malariæ_.
The summer and autumn fever (_febris æstivo-autumnalis_), also called
malignant tertian or sub-tertian, is caused by a malarial parasite
which is distinguished by the small size of its schizont, while the
gametocytes are crescentic (figs. 81, 88).
Most authors identify this kind of fever or the parasites which
cause it (_Laverania malariæ_) with the pernicious malaria of the
tropics. Ziemann, however, repeatedly has drawn attention to certain
small but definite differences between the usual malignant tertian
or pernicious parasites which occur in the tropics and the tropical
parasites of some malarial districts, particularly of West Africa,
and insists that at least two varieties or sub-species occur. Other
investigators distinguish from this or these forms a quotidian
parasite. On the other hand, the assertion is made that there are no
specific differences, but that the malignant or pernicious tertian
parasite which normally needs forty-eight hours for its development
in the blood of man, can also develop in twenty-four hours. The
establishment of the duration of the development is a matter of
especial difficulty, because the stages of schizogony are far less
numerous in the peripheral blood than in that of the internal
organs. It is also stated that the tropical parasite very seldom
forms crescentic but rather rounded gametocytes. According to such
an observation the organism would belong to _Plasmodium_ and not to
_Laverania_. The question whether the tropical fevers are caused by
two different parasites does not seem to be definitely settled.
The young trophozoite of the malignant, pernicious tertian, or
sub-tertian parasite (fig. 87) are but slightly active and are very
small, even after the formation of the comparatively large food
vacuole, which makes the body appear annular (“signet ring” stage).
Often two and even more parasites are found in one blood corpuscle.
Fully grown they only attain two-thirds or less of the diameter of
the erythrocytes, which display an inclination to shrink and then
appear darker than the normal (brass-coloured). In the early stage
dots or stippling--sometimes called Maurer’s dots--appear on the blood
corpuscles as in those attacked by the ordinary tertian parasite
(_Plasmodium vivax_), but the Maurer’s dots are relatively coarse and
few, and are not easily stained. These dots were first described by
Stephens and Christophers in 1900, and subsequently by Maurer in 1902.
About thirty hours after the entrance into the blood corpuscles, the
parasites are rarely found in the peripheral blood, but they are
present in the internal organs, and especially in the spleen. The
schizogony, which now begins in the internal organs, proceeds on the
same lines as that of the quartan parasite, that is, usually with the
merozoites radially arranged around a central agglomeration of dark
brown pigment.
[Illustration: FIG. 87.--The pernicious malignant or sub-tertian
parasite in the red corpuscles of man, asexual stages. (After Manson.)]
The number of merozoites formed is quoted differently, _e.g._, 8 to
24, on an average 12 to 16. However, according to the recent cultural
researches of J. G. and D. Thomson[204] (1913) the number of merozoites
of _P. falciparum_ is 32. D. Thomson, from examination of spleen smears
at autopsy, also concludes that the number of merozoites may reach 32.
During their formation the blood corpuscle which is attacked gets paler
and disintegrates.
[204] _Proc. Roy. Soc._, B, lxxxvii, p. 77.
[Illustration: FIG. 88.--The crescents of the malignant tertian
parasite. (After Mannaberg.) See also fig. 81.]
The gametocytes which finally appear are attenuated, curved bodies,
rounded at each end and known as crescents (figs. 81, 88), and are
provided with a nucleus and with coarse pigment masses. In the males
the pigment is more scattered than in the females, where it is around
the nucleus. Their length is 9 µ to 14 µ, and their breadth is 2 µ to
3 µ. At first they are still in the pale blood corpuscles, later they
free themselves and are found in numbers in the peripheral blood in
cases of pernicious malaria of Southern Europe and the tropics, while,
on the other hand, they occur much more rarely in the peripheral blood
in West African malignant tertian. Their further development takes
place under the same conditions as in the other malarial parasites.
[Illustration: FIG. 89.--Section through a tubule of the salivary gland
of an _Anopheles_ with sporozoites of the malignant tertian parasites;
on the left at the top a single sporozoite greatly magnified. (After
Grassi).]
D. Thomson (1914),[205] from studies of autopsy smears, has shown that
crescents develop chiefly in the bone-marrow and spleen, and take
about ten days to grow into the adult state in the internal organs.
He believes that crescents are produced from ordinary asexual spores.
Quinine, he states, has no direct destructive action on crescents, but
it destroys the asexual source of supply.
[205] _Annals Trop. Med. and Parasitol._, viii, p. 85.
The sporozoites of _Laverania malariæ_ (_P. falciparum_) are
represented in fig. 89.
The principal distinctive characters of the malignant tertian parasite
are: (1) The ring forms are very small, occasionally bacilliform, and
may be marginal (“accolé” of Laveran); (2) the larger trophozoites
are often ovoid, and about one-third or one-half of the erythrocyte
in size; (3) the infected red cells sometimes show coarse stippling
(Maurer’s dots); (4) the gametocytes, or sexual forms, are crescentic
in shape.
J. W. W. Stephens (1914) has described a new malarial parasite of
man; it is called _Plasmodium tenue_. It is very amœboid, with scanty
cytoplasm and much chromatin, sometimes rod-like or irregular. The
parasite was described from a blood-smear of an Indian child. The
creation of a new species for this parasite has been criticized by
Balfour and Wenyon, and by Craig.
*Plasmodium relictum*, Sergent, 1907.
Syn.: _Plasmodium præcox_, Grassi and Feletti, 1890; _Plasmodium
danilewskyi_, Gr. et Fel., 1890; _Hæmamœba relicta_, Gr. et Fel.,
1891; _Proteosoma grassii_, Labbé, 1894.
Hæmamœboid, pigment-producing, malarial parasites are often found in
birds. Like the human malarial parasites they have been variously
named. Labbé created the genus _Proteosoma_ for them, and this name
is still often used as a distinctive one unofficially. The correct
name is stated to be either _Plasmodium relictum_ or _P. præcox_,
or possibly even _P. danilewskyi_, assuming that there is only one
species. The nomenclature of the malarial parasites is most confused.
The avian malarial parasites are transmitted by Culicine mosquitoes.
The organism was discovered by Grassi in the blood of birds in Italy,
and causes a fatal disease in partridges in Hungary. Sparrows are
affected in India, and it was this Plasmodium in which Ross first
traced the development of a malarial parasite in a mosquito. The
parasite may be transmitted from bird to bird by blood-inoculation,
canaries being very susceptible.
The principal stages of the avian plasmodium closely resemble those
of the malarial parasites of man. In its earliest stage _P. relictum_
is unpigmented, but soon the trophozoite grows and becomes pigmented,
meanwhile displacing the nucleus of the avian red-blood corpuscle,
a characteristic feature, distinguishing it from _Halteridium_.
Schizonts are formed, each of which gives rise to about nine
merozoites in the circulating blood. Sexual forms or gametocytes also
occur in the blood. These develop in _Culex fatigans_, _C. pipiens_
and _C. nemorosus_. Oökinetes or vermicules are formed in twelve
to fifteen hours in the stomach of the mosquito, and in one to two
days well-developed round oöcysts may be seen. In three to four days
sporoblasts have formed within the oöcysts and young sporozoites
begin to develop. In nine to ten days the oöcysts are mature, being
filled with sporozoites. The oöcysts then burst and the sporozoites
travel through the thoracic muscles to the salivary glands of the
Culicine.
Neumann, experimenting with canaries, found that _Stegomyia fasciata_
could transmit the infection, but less efficiently than species of
_Culex_.
THE CULTIVATION OF MALARIAL PARASITES.
The successful cultivation of malarial parasites _in vitro_ was first
recorded by C. C. Bass and by Bass and Johns (1912).[206] Since then,
J. G. and D. Thomson,[207] and McLellan (1912–13), Ziemann[208] and
others have repeated the experiments.
[206] _Journ. Exptl. Med._, xvi, p. 567.
[207] _Annals Trop. Med. and Parasitol._, vi, p. 449; vii, pp. 153, 509.
[208] _Trans. Soc. Trop. Med. and Hyg._, vi, p. 220.
DIFFERENTIAL CHARACTERS OF THE HUMAN MALARIAL PARASITES.
=======================================================================
| | |_Laverania malariæ_
Character | _Plasmodium |_Plasmodium vivax_| _Plasmodium
| malariæ_ | (Benign tertian) | falciparum_
| (Quartan) | |(Malignant tertian)
-------------+------------------+------------------+-------------------
Schizogony |Complete in |Complete in forty-|Complete in forty-
| seventy-two | eight hours | eight hours
| hours | | or less
-------------+------------------+------------------+-------------------
Trophozoite |Smaller than _P. |Young trophozoite |Young trophozoite
| vivax_larger than| large. | small
| _L. malariæ_ | |
|Pseudopodia not |Long pseudopodia |
| marked or long | |
-------------+------------------+------------------+-------------------
Movements |Rather slow in |Active amœboid |Sometimes actively
| immature forms | movements | motile
-------------+------------------+------------------+-------------------
Pigment |Coarse granules, |Fine granules, |Granules fine and
| peripherally | with active | scanty, movement
| arranged, little | movement | oscillatory
| movement | |
-------------+------------------+------------------+-------------------
Schizont |Smaller than red |Larger than red |Smaller than red
| corpuscle | blood corpuscle | corpuscle
-------------+------------------+------------------+-------------------
Merozoites |6 to 12 forming |15 to 20 regularly|8 to 32 (according
| rosette | arranged | to different
| | | authors) arranged
| | | irregularly
-------------+------------------+------------------+-------------------
Gametocytes |Spherical |Spherical |Crescentic
-------------+------------------+------------------+-------------------
Distribution |About equal number|Larger numbers in |Scanty in periph-
of | in peripheral and| visceral blood | eral blood com-
parasites in| visceral blood | | pared with the
vertebrate | | | enormous numbers
host | | | in the internal
| | | organs. The latter
| | | part of the cycle
| | | (schizogony) may
| | | occur in the in-
| | | ternal organs only
-------------+------------------+------------------+-------------------
Alterations |Almost normal |Pale and |Corpuscle may be
in | | hypertrophied. | shrunken and dark,
erythrocytes| |Schüffner’s dots | or may be colour-
| | seen in deeply | less. Maurer’s
| | stained specimens| coarse dots some-
| | | times seen
-------------+------------------+------------------+-------------------
Essentially the method of cultivation, as used by Thomson, is
as follows: 10 c.c. of infected blood are drawn from a vein and
transferred to a sterile test tube, in which is a thick wire leading
to the bottom of the tube. One-tenth of a cubic centimetre of a 50 per
cent. aqueous solution of glucose or dextrose is placed in the test
tube, preferably before adding the blood. The blood is defibrinated
by stirring gently with the wire. When defibrination is complete the
wire and the clot are removed, and the glucose-blood is transferred,
in portions, to several smaller sterile tubes, each containing a
column of blood about one inch in height. The tubes are plugged and
capped and then transferred, standing upright, to an incubator
kept at a temperature of 37° C. to 41° C. The blood corpuscles soon
settle, leaving a column of serum at the top, to the extent of about
half an inch in each tube. The leucocytes need not be removed by
centrifugalization. J. G. Thomson (1913) and his collaborators did not
find it necessary to destroy the complement in the serum, and they
found that the malarial parasites developed at all levels in the column
of corpuscles, and not merely on the surface layer of the corpuscles as
first stated by Bass and Johns.
So far only the asexual generation of the malarial parasites has been
grown _in vitro_. Thomson rarely observed hæmolysis in the cultures.
Clumping of the malignant tertian parasites occurred. In cultures of
the benign tertian parasite (_Plasmodium vivax_) clumping was not
observed. J. G. and D. Thomson consider that this difference as regards
clumping explains why only young forms of malignant tertian are found
in peripheral blood, as the clumping tendency of the larger forms
causes them to be arrested in the finer capillaries of the internal
organs. It also explains the tendency to pernicious symptoms, such as
coma, in malignant tertian malaria. Further it was found from cultures
that _P. falciparum_ was capable of producing thirty-two spores
(merozoites) in maximum segmentation, while _P. vivax_ produced sixteen
spores (merozoites) as a rule, though the number might be greater than
sixteen. (Quartan parasites produce eight spores or merozoites in
schizogony.)
It may also be mentioned here that _Babesia_ (_Piroplasma_) _canis_ has
been successfully cultivated _in vitro_ by Bass’s method. This has been
accomplished by Thomson and Fantham,[209] Ziemann, and Toyoda in 1913.
J. G. Thomson and Fantham used the simplified Bass technique recorded
above, namely, infected blood and glucose, incubating at 37° C. In
one of the _B. canis_ cultures, starting with heart blood of a dog
containing corpuscles infected with one, two, or, exceptionally, four
piroplasmata, Thomson and Fantham succeeded in obtaining a maximum of
thirty-two merozoites in a corpuscle. The cultures are infective to
dogs and sub-cultures have been obtained.
[209] _Annals Trop. Med. and Parasitol._, vii, p. 621.
Family. *Piroplasmidæ*, França.
The parasites included in this provisional family or group belong
to the Hæmosporidia. They are minute organisms, sometimes amœboid,
but usually possessing a definite form. They are endoglobular, being
contained within mammalian red blood corpuscles, but they produce no
pigment. The true Piroplasmata, belonging to the genus _Babesia_,
destroy the host corpuscles, setting free the hæmoglobin, which is
excreted by the kidneys of the cow, sheep, horse, dog, etc., acting
as host. The disease produced, variously called piroplasmosis or
babesiasis, is consequently characterized by a red coloration of the
urine known as hæmoglobinuria, or popularly as “red-water.” One of the
best known piroplasms is _Piroplasma bigeminum_ or _Babesia bovis_
(probably the latter name is correct), which is the causal agent of
“Texas fever” or “red-water” in cattle and is spread by ticks.
[Illustration: FIG. 90.--_Nuttallia equi_, life-cycle as seen in red
blood corpuscles in stained preparations of peripheral blood. (After
Nuttall and Strickland.)]
Of recent years, researches on the morphology of these blood parasites
has led to their separation into various genera and species. However,
our knowledge is still very far from complete. The various genera
recognized by França[210] (1909), and placed in a provisional family,
Piroplasmidæ, may be listed, though further research may lead to
emendations:--
[210] _Arch. Inst. Bact. Camara Pestana_, iii, p. 11.
(1) _Babesia_ (Starcovici) or _Piroplasma_ (Patton). Pyriform
parasites, dividing by a special form of budding or gemmation with
chromatin forking, as well as by direct binary fission. Parasitic in
oxen, dogs, sheep, horses, etc.
(2) _Theileria_ (Bettencourt, França and Borges). Rod-shaped and oval
parasites occurring in cattle and deer. _T. parva_ is the pathogenic
agent of African East Coast fever in cattle.
(3) _Nuttallia_ (França). Oval or pear-shaped parasites, with
multiplication in the form of a cross. _N. equi_[211] (fig. 90) of
equine “piroplasmosis” (nuttalliosis). _N. herpestidis_ in a mongoose.
[211] _Parasitology_, v (1912), p. 65.
(4) _Nicollia_ (Nuttall). Oval or pear-shaped parasites with
characteristic nuclear dimorphism, and with quadruple division at first
fan-like, then like a four-leaved clover. _N. quadrigemina_ from the
gondi.
(5) _Smithia_ (França). Pear-shaped, single forms stretching across the
blood corpuscle. Multiplication into four in the form of a cross. _S.
microti_ from _Microtus arvalis_, _S. talpæ_ from the mole.
(6) _Rossiella_ (Nuttall). This belongs to the family Piroplasmidæ
of França. It is intracorpuscular and non-pigment forming, occurring
singly, in pairs, or occasionally in fours. It is usually round and
larger than Babesia. The parasite multiplies by binary fission. _R.
rossi_ in the jackal.
The genus _Babesia_ is the best known and most important, and will be
considered next.
Genus. *Babesia*, Starcovici, 1893.
Syn.: _Pyrosoma_, Smith and Kilborne, 1893; _Apiosoma_, Wandolleck,
1895; _Piroplasma_, W. H. Patton, 1895; _Amœbosporidium_, Bonome,
1895.
The organisms belonging to this genus are pyriform, round or amœboid.
The characteristic mode of division is as follows: Just before division
the parasite becomes amœboid and irregular in shape, (fig. 91, _1–5_)
with a compact nucleus. The latter gives off a nuclear bud. This
nuclear bud divides into two by forking (fig. 91, _6_, _7_). The
chromatin forks grow towards the surface of the body of the rounded
parasite, and then two cytoplasmic buds grow out. The forking nuclear
buds, which are *Y*-shaped, pass into the cytoplasmic outgrowths[212]
(fig. 91, _8_, _9_). The buds gradually increase in size at the
expense of the parent form until they become two pear-shaped parasites
joined at their pointed ends. The connecting strand shrinks and the
two daughter forms separate (fig. 91, _10–14_). The pyriform parasites
after having exhausted the blood corpuscle escape from it (fig. 91,
_15_), and seek out fresh host corpuscles, entering by the rounded,
blunt end (fig. 91, _1_). It is the pyriform phase of the parasite
which penetrates red blood corpuscles, not rounded forms, which
die if set free. The pyriform parasite, however, becomes rounded
(fig. 91, _2_, _3_), soon after its entry into a fresh host cell. This
interesting mode of division by gemmation and chromatin forking has
been made diagnostic of the genus _Babesia_ by Nuttall.[213] Rounded
forms of _Babesia_ divide by binary fission, and this direct method can
also be adopted by the other forms of Babesia.
[212] Nuttall and Graham-Smith, _Journ. Hyg._, vii, p. 232.
[213] “Piroplasmosis,” Herter Lectures, _Parasitology_, vi, p. 302.
[Illustration: FIG. 91.--_Babesia_ (_Piroplasma_) _canis_, life-cycle
in stained preparations of infected blood of dog. (After Nuttall and
Graham-Smith.)]
The distribution of the chromatin in the pear-shaped _Babesia_,
as seen in _B. canis_ and _B. bovis_, is interesting. The main
nuclear body consists of a karyosome surrounded by a clear area.
There is also a loose (chromidial) mass of chromatin representing
the remains of the chromatin forks seen during the formation of the
parasite as a daughter form by gemmation. Occasionally there is
a small dot or point, the so-called “blepharoplast” of Schaudinn
and Lühe. This minute dot is not a flagellate blepharoplast, for
there is no flagellate stage in the life-history of Babesia. These
nuclear phenomena have been described by Nuttall and Graham-Smith
and Christophers (1907)[214] for _B. canis_, by Fantham (1907)[215]
for _B. bovis_, and by Thomson and Fantham (1913) from glucose-blood
cultures of _B. canis_.
[214] _Sci. Mems. Govt. India_, No. 29.
[215] _Quart. Journ. Microsc. Sci._, li, p. 297.
Babesia are tick borne, as was first shown by Smith and Kilborne
(1893). The developmental cycle in the tick is incompletely known. The
best accounts are those of Christophers (1907)[216] for _B. canis_ and
Koch (1906) for _B. bovis_, and these accounts are supplementary. The
principal stages, so far as known, may be summarized thus:--
[216] _Sci. Mems. Govt. India_, No. 29.
(1) The piroplasms taken by the tick in feeding on blood pass into
the tick’s stomach. The pyriform parasites, which alone are capable
of further development, are set free from the blood corpuscles. In
about twelve to eighteen hours they become amœboid, sending out long,
stiff, slender, pointed pseudopodia. The nucleus of each parasite
divides unequally into two. Similar forms have been obtained in
cultures. These stellate forms may be gametes, and according to Koch
fuse in pairs.
(2) A spherical stage follows, possibly representing the zygote. This
grows, and a uninucleate globular mass results. This form is found in
large numbers on the third day, according to the observations of Koch.
(3) A club-shaped organism is next formed. This may represent an
oökinete stage. The club-shaped bodies are motile and gregarine-like,
and are about four times the size of the blood forms. These
club-shaped bodies and subsequent stages were described by
Christophers in the development of _B. canis_ in the dog-tick,
_Rhipicephalus sanguineus_.
(4) The club-shaped bodies pass from the gut of the tick into the
ovary, and so get into the ova. There they become globular, and later
are found in the cells of the developing tick-embryo. The parasites
are, then, transmitted hereditarily. Similar globular bodies are
found in the tissue cells of the body of tick nymphs which have
taken up piroplasms. The globular stage was called the “zygote” by
Christophers, but it may correspond to the oöcyst of Plasmodia.
(5) The globular body divides into a number of “sporoblasts,” which
become scattered through the tissues of the larval or nymphal tick,
as the case may be.
(6) The sporoblasts themselves divide into a large number of
sporozoites, which are small uninucleate bodies, somewhat resembling
blood piroplasms. The sporozoites collect in the salivary glands of
the tick. They are inoculated into the vertebrate when the tick next
feeds.
The chief species of _Babesia_ and their pathogenic importance may be
listed thus:--
(1) _Babesia bovis_ (Babes) produces infectious hæmoglobinuria of
cattle in Europe and North Africa. It is transmitted by _Ixodes
ricinus_. A similar parasite also occurs in deer.
(2) _Babesia bigemina_ (Smith and Kilborne) produces Texas fever,
tristeza, or red-water in cattle in North and South America, South
Africa and Australia. It is transmitted by _Boöphilus annulatus_ in
North America, by _B. australis_ in Australia, South America, and the
Philippines, and by _B. decoloratus_ in South Africa.
The parasite is from 2 µ to 4 µ long, and from 1·5 µ to 2 µ broad.
_Babesia bigemina_ may be the same parasite as _B. bovis_.
(3) _Babesia divergens_ (MacFadyean and Stockman) is a small parasite.
It is found in cattle suffering from red-water in Norway, Germany,
Russia, Hungary, Ireland, Finland, and France, and is transmitted by
_Ixodes ricinus_.
(4) _Babesia canis_ (Piana and Galli-Valerio) gives rise to malignant
jaundice or infectious icterus in dogs in Southern Europe, India,
and other parts of Asia and North Africa, where it is transmitted by
_Rhipicephalus sanguineus_. In Africa generally, especially South
Africa, the disease is transmitted by _Hæmaphysalis leachi_. _Babesia
canis_ varies from 0·7 µ to 5 µ, the size depending partly on the
number of parasites within the corpuscle. It averages about 3 µ. It
has been cultivated in Bass’ medium (glucose and infected blood), see
p. 172.
In India _Piroplasma gibsoni_ (Patton) infects hunt dogs and jackals.
It is annular or oval in shape.
(5) _Babesia ovis_ (Babes) produces “Carceag,” a disease of sheep in
Roumania, the Balkan Peninsula, Italy, and Transcaucasia. It varies in
size from 1 µ to 3 µ. It is transmitted by _Rhipicephalus bursa_. The
parasite has recently been recorded from Rhodesia.
(6) _Babesia caballi_ (Nuttall and Strickland) causes “biliary
fever” in equines. The parasite occurs in Russia, Roumania, and
Transcaucasia. It varies in size from 1 µ to 2 µ. It is transmitted by
_Dermacentor reticulatus_.
It should be mentioned that _Nuttallia equi_ also causes
“piroplasmosis” in equines, with symptoms of hæmoglobinuria and
jaundice in Italy, Sardinia, many parts of Africa, Transcaucasia,
India, and Brazil. In Africa it is transmitted by _Rhipicephalus
evertsi_. It has been shown experimentally that a horse recovered
from _Babesia caballi_ was susceptible to the inoculation of
_Nuttallia equi_ blood.
(7) _Babesia pitheci_ (P. H. Ross) was found in a monkey,
_Cercopithecus_ sp., in Uganda. The pear-shaped forms measure 1·5 µ by
2·5 µ.
(8) _Babesia muris_ (Fantham)[217] was found in white rats. The
pyriform parasites are 2 µ to 3 µ long and 1 µ to 1·5 µ broad; oval
forms are 0·5 to 1·5 µ diameter.
[217] _Quart. Journ. Microsc. Sci._, 1, p. 493.
The usual symptoms of babesiasis (piroplasmosis) are high fever, loss
of appetite, hæmoglobinuria, icterus, anæmia, paralysis, and death in
about a week in acute cases. In chronic cases there is anæmia, and
hæmoglobinuria is less marked. When animals recover, there are still
some piroplasms left in the blood. “Recovered” or “salted” animals
are not susceptible to reinfection, but ticks feeding on them acquire
piroplasms, and are a source of danger to freshly imported animals.
_Treatment._--Trypan-blue is the best drug, as shown by Nuttall
and Hadwen[218] (1909). It should be administered intravenously
in 1 to 1·5 per cent. aqueous solution. A dose of 5 to 10 c.c. is
curative for dogs, one of 100 to 150 c.c. for horses and cattle.
Unfortunately, the tissues are coloured blue by the drug. The
“salted” animals, after trypan-blue treatment, still harbour the
parasites in their blood for years.
[218] _Parasitology_, ii, p. 156.
Genus. *Theileria*, Bettencourt, França and Borges, 1907.
The organisms belonging to this genus are rod-like or bacilliform,
and coccoid or round.
The best known of the species of Theileria is _T. parva_, the
pathogenic agent of East Coast fever or Rhodesian fever in cattle in
Africa.
*Theileria parva*, Theiler, 1903.
Syn.: _Piroplasma parvum_.
In the blood corpuscles of infected cattle minute rod-like and oval
parasites are seen. Some are comma shaped and others are clubbed
(fig. 92, _1–12_). The rod-like forms measure 1 µ to 3 µ in length
by 0·5 µ in breadth; the oval forms are 0·7 µ to 1·5 µ in diameter.
The intracorpuscular parasites are said by R. Gonder (1910) to be
gametocytes, the rod-like forms being thought to be males, the oval
forms to be females. Free parasites are practically never seen in the
blood. It is known that it is impossible to produce the disease in
a healthy animal by blood inoculation, but only by intraperitoneal
transplantation of large pieces of infected spleen (Meyer). There may
be as many as eight parasites in a corpuscle. The chromatin is usually
at one end of the organism. In some parasites the appearance of the
chromatin suggests division, but such division, if it takes place, must
be very slow, as it has not been actually seen in progress. The red
blood corpuscles appear merely to act as vehicles for the parasites
(Nuttall, Fantham, and Porter).[219]
[219] _Parasitology_, ii, p. 325; iii, p. 117.
[Illustration: FIG. 92.--_Theileria parva._ 1–12, intracorpuscular
parasites, stained. (After Nuttall and Fantham); 13–18, Koch’s blue
bodies, from stained spleen smear; 17–18, breaking up of Koch’s body.
(After Nuttall.)]
In the internal organs, especially the lymphatic glands, spleen
and bone-marrow, are found multinucleate bodies known as Koch’s
blue bodies (fig. 92, _13–18_). These are schizonts, according
to Gonder.[220] The actual Koch’s blue bodies are said to be
extracellular, but similar multinucleate bodies, schizonts, occur
in lymphocytes. The schizonts divide and the merozoites resulting
probably invade the red blood corpuscles in the internal organs.
Gonder considers that the sporozoites injected by the tick collect in
the spleen and lymphatic glands, penetrate the lymphocytes and give
rise to the schizonts.
[220] _Zeitschr. f. Infekt. paras. Krankh. u. Hyg. d. Haustiere_, viii,
p. 406.
Gonder has studied the cycle of _T. parva_ in the tick. He states
that the gametocytes leave the host corpuscles and give rise to
gametes, then conjugation occurs producing zygotes. The zygotes
are then said to become active to form ookinetes, and to enter the
salivary glands of the tick. Multiplication is said to occur therein,
producing a swarm of sporozoites. This work needs confirmation.
_T. parva_ is transmitted by _Rhipicephalus appendiculatus_, _R.
simus_, _R. evertsi_, _R. nitens_, and _R. capensis_. The parasites
are not hereditarily transmitted in _Rhipicephalus_, but when taken
by the transmitter at one stage of its development the tick is
infective in its next stage (_e.g._, if the larva becomes infected,
then the nymph is infective; if the nymph becomes infected, then the
adult is infective).
An animal recovered from _Theileria parva_ is incapable of infecting
ticks, but few animals recover from East Coast fever. Animals
suffering therefrom do not show hæmoglobinuria.
*Theileria mutans*, Theiler, 1907·
Syn.: _Piroplasma mutans_.
This is transmissible experimentally by blood inoculation. It
occurs in cattle in South Africa and Madagascar and is apparently
non-pathogenic. No Koch’s blue bodies are formed. It is transmitted
by ticks.
_Theileria annulata_ (Dschunkowsky and Luhs) occurs in cattle in
Transcaucasia.
A Theileria (_T. stordii_) has been found in a gazelle (França, 1912).
Genus. *Anaplasma*, Theiler, 1910.
This genus[221] may be mentioned here. The organisms included therein
are, according to Theiler, coccus-like, consisting of chromatin,
and are devoid of cytoplasm. They occur in the red blood corpuscles
of cattle, causing a disease characterized by destruction of red
cells, fever and anæmia, but with yellow urine. The disease is
tick transmitted. The bodies now called _Anaplasma marginale_ were
formerly described as marginal points. They multiply by simple
fission. They are said by Theiler to cause gall-sickness in cattle in
South Africa. Some authors doubt whether these bodies are organismal.
[221] _Bull. Soc. Path. Exot._, iii, p. 135.
Genus. *Paraplasma*, Seidelin, 1911.
Under this generic name Seidelin described certain bodies found
by him in cases of yellow fever in 1909. The type species is _P.
flavigenum_,[222] and is claimed by Seidelin to be the causal agent of
yellow fever.
[222] _Yellow Fever Bulletin_, i, p. 251.
_Paraplasma flavigenum_ occurs in the early days of the disease as
small chromatin granules with or without a faint trace of cytoplasm.
The bodies are usually intracorpuscular. Also, somewhat larger forms,
with distinct cytoplasm, are seen in small numbers. During the later
days of the disease still larger forms are found, and these occur
also in sections of organs (_e.g._, kidney) made post-mortem. Some of
these larger forms are perhaps schizonts. In the second period of the
disease possible micro- and macro-gametes may be found, some of which
are extracorpuscular. Some small free bodies have been seen. Recently
schizogony has been stated to occur in the lungs, and it is said that
guinea-pigs can be inoculated with _Paraplasma flavigenum_, and show
yellow pigment in the spleen.
Seidelin places _Paraplasma_ in the _Babesiidæ_, with resemblances
more particularly to _Theileria_. V. Schilling-Torgau and Agramonte
have criticized these findings; the former considers them to be the
resultant of certain blood conditions.
_P. subflavigenum_ was found by Seidelin in 1912 in a man suffering
from an unclassified fever in Mexico.
Further, it is now known that a Paraplasma occurs naturally in
guinea-pigs. More researches are needed on these matters, as some
writers (_e.g._, Wenyon and Low) claim that the bodies are not
organismal.
--------------------------------------------------------------------
|_Paraplasma flavigenum._--The Yellow Fever Commission (West Africa) |
|in their third report, dated 1915, have come to the conclusion that |
|there is no evidence that the bodies termed _Paraplasma flavigenum_ |
|are of protozoal nature or that they are the causal agents of yellow|
|fever. |
--------------------------------------------------------------------
Sub-class. NEOSPORIDIA, Schaudinn.
Sporozoa in which growth and spore formation usually go on together.
Order. *Myxosporidia*, Bütschli.
[Illustration: FIG. 93.--Upper figure, part of a gill of a roach,
_Leuciscus rutilus_ (natural size), with two myxosporidia. Lower
figures, _a_, _b_, _d_, spores of myxosporidia from a pike, _Esox
lucius_. _c_, Spore from _Platystoma fasciatum_. (After J. Müller.)]
[Illustration: FIG. 94.--The tailless spore of _Myxobolus mülleri_,
with the polar bodies and their nuclei and the sporozoite. (After
Bütschli.)]
These parasites, which were discovered by Johannes Müller (1841),
live principally in fishes, and occasionally cause destructive
epizoötics amongst their hosts. Müller first observed them in
the form of whitish-yellow pustules on the skin or on the gills
of various fishes. These pustules contained masses of small
shell-covered bodies with or without tails (“psorosperms,” see
fig. 93). Similar bodies were also found in the air bladders of
certain fish. Creplin (1842) demonstrated the resemblance of the
cysts (“psorosperm tubes”) harbouring the psorosperms to the
“pseudonavicella-cysts” of a gregarine, as described by v. Siebold.
Dujardin (1845) considered that there was possibly some connection
between the protoplasmic “psorosperm tubes” and the spores they
contained, and the developmental stages of monocystid gregarines
from the vesiculæ seminales of earth-worms. The relationship of the
“fish psorosperms” was placed on a firmer basis by Leydig (1851)
and Lieberkühn. The former found numerous forms in marine fish, and
he discovered in species which live free in the gall bladder of
cartilaginous fishes that the psorosperms originated in a manner
similar to the gregarines. Lieberkühn (1854) studied the Myxosporidia
in the bladder of the pike (fig. 93, _a_, _b_, _d_), and observed
their amœboid movements, as well as the formation of the spores,
from each of which a small amœboid body escaped, a discovery that
was confirmed by Balbiani. The same author also found that spiral
filaments were enclosed in the so-called polar body, _i.e._, the
polar capsule of the psorosperm spores, and that these could be
protruded (fig. 93, _d_, and fig. 95).
The term Myxosporidia, which at the present day is universally
applied to the “psorosperm tubes,” was introduced by Bütschli
in 1881, who studied not only the structure and development of
the spores, but also the protoplasmic body of the parasites
(fig. 96), and confirmed the occurrence of numerous nuclei. Many
authors have made important additions to our knowledge of the
Myxosporidia: Perugia, Thélohan, Mingazzini, L. Pfeiffer, L. Cohn,
Doflein, Mercier, Schröder and Auerbach; while the presence of this
parasite outside the class of fishes has become known through Lutz,
Laveran, and others. The species causing disease in fishes have been
described by Ludwig, Railliet, Weltner, L. Pfeiffer, Zschokke, Hofer,
Doflein, Gurley, Plehn, Schuberg, Fantham and Porter. With regard to
classification the works of Thélohan (1895) and Gurley (1894) may be
mentioned.
[Illustration: FIG. 95.--Schematic representation of a spore of
_Myxobolus_. One polar capsule has protruded its filament; two nuclei
and a “vacuole” in the sporozoite. (After Doflein.)]
[Illustration: FIG. 96.--_Chloromyxum leydigi._ Active trophozoite
(parasitic in gall-bladder of skates, rays, dog-fish). _Ect_,
ectoplasm; _ps_, pseudopodia; _end_, endoplasm; _y_, yellow globules in
endoplasm; _sp_, spores, each with four polar capsules. × 525. (After
Thélohan.)]
The Myxosporidia live either free on the epithelial surface of hollow
organs (gall or urinary bladder, renal tubules, but never in the
intestine), or are enclosed in the tissues of their host. The gills
and muscular system are their favourite habitat, but other tissues or
organs may be attacked. Species of Myxosporidia are also known from
Amphibia, Reptilia, and a few invertebrates.
The free forms, which are often amœboid (fig. 96), move by the
aid of variously shaped pseudopodia, have a constant form, or may
exhibit contractions of the body. The tissue parasites often reach
a considerable size, so that the integument of the host forms
protuberances over them. They are of a roundish or irregular shape.
Frequently they are enveloped in a connective tissue covering formed
by the host.
The protoplasmic body in the trophic phase (fig. 96) shows a distinct
ectoplasm which is finely granular or sometimes striated, and an
endoplasm which is coarsely granular and contains many nuclei as
well as cell inclusions, such as crystals, pigment grains and fat
globules. The nuclei originate by division from the primitive nucleus
of the amœboid germ that issues from the spore. This amœbula may
or may not live intra-cellularly during the early stages of its
existence.
The multinucleate trophozoite of a Myxosporidian forms spores in
its endoplasm practically throughout its whole period of growth
(fig. 96). Vegetative reproduction by a process of external budding
or plasmotomy may also occur, as in _Myxidium lieberkühni_ from the
urinary bladder of the pike.
The myxosporidian trophozoite may produce two spores within
itself, when it is placed in the sub-order _Disporea_, or it may
produce numerous spores, which is characteristic of the sub-order,
_Polysporea_. The phenomenon of spore formation is not simple
(fig. 97), and the spore itself is surrounded by a bivalved shell or
sporocyst and contains polar capsules in addition to the amœboid germ
(fig. 97, G, H). The valves of the sporocyst and the polar capsules
are really differentiated nucleate cells, so that each spore is an
aggregate of cells rather than one cell, though only a single amœbula
issues from a spore. The accounts of spore formation vary somewhat
according to the different workers.
Spore formation is usually very complicated and there are differences
of opinion as to the interpretation of various stages, particularly
as to whether conjugation occurs therein. The process is initiated
by the concentration of cytoplasm around one of the nuclei of the
endoplasm, so that a small spherical mass or initial corpuscle is
produced, the pansporoblast (Gurley) or primitive sphere (Thélohan).
Some authors state that a pansporoblast really results from a
conjugation of two initial corpuscles (fig. 97, A-D). Nuclear
multiplication occurs within the pansporoblast (fig. 97, E), and
sooner or later two multinucleate sporoblasts are formed within it
(fig. 97, F). Each sporoblast gives rise to a single spore, which
consists of a sporocyst or envelope composed of two valves each
secreted by a cell, two polar capsules each secreted by a cell, and
the sporoplasm or amœbula which becomes binucleate (fig. 97, G).
During the process of spore formation (fig. 97) various vegetative
and reduction nuclei may be produced, in addition to those which are
essentially involved in spore formation, and the sporocyst cells may
be developed early.
[Illustration: FIG. 97.--_Myxobolus pfeifferi._ Spore formation.
A, reproductive cell from plasmodial trophozoite; B, cell divided
unequally into two; C, smaller cell forming envelope to larger one; D,
pansporoblast formed by union of two forms like C; E, multinucleate
pansporoblast, two of the nuclei being those of the envelope; F,
pansporoblast divided into two multinucleate sporoblasts; G, spore
differentiation; _p_, two parietal cells forming sporocyst; _bc_, polar
capsules; _am_, binucleate amœbula; H, ripe spore in which the two
nuclei of the amœbula have fused. (After Keysselitz.)]
Each spore contains two (figs. 94, 95) or more polar capsules which
are clearly visible in the fresh condition. Each polar capsule is
a hollow, more or less pear-shaped body, secreted by a cell and
having a well defined contour. Within it, a long, delicate, elastic
filament, the polar filament, is formed, and lies spirally coiled
in the polar capsule until just before the emergence of the amœbula
from the spore (fig. 95). The polar filament is ejected, probably
under the influence of the digestive juice, when the spore reaches
a new host, and serves to anchor the spore to the tissue with which
it is in contact, and thus allow of the emergence of the amœbula in
a situation suitable for its development. The polar capsule with its
contained polar filament has been compared with the stinging cells or
nematocysts of the Cœlentera, but it has a totally different function.
The spores fulfil the purpose of effecting transmission to other
hosts. Infection occurs by the ingestion of the parasites per os
after their escape by some means from their host. Thélohan and
others have demonstrated that the valves of the spores soon open
under the influence of the digestive juices, thus allowing the young
myxosporidia to escape. Their further history is unknown; but it may
be surmised that they either travel direct to the organs usually
affected (gall bladder, urinary bladder), or are distributed in the
body by means of the circulatory or lymphatic systems.
The Myxosporidia that invade tissues are often deadly to their
hosts. They may be present in a state of “diffuse infiltration”
when practically every organ of the body may be infected, as in
barbel disease (due to _Myxobolus pfeifferi_). On the other hand,
the parasites may be concentrated at one spot, when cysts, either
large or small, are produced. Such cysts occur on the gills of many
fishes. A few additional important pathogenic forms are _Myxobolus
cyprini_, the excitant of “pockenkrankheit” of carp, and _Lentospora
cerebralis_, parasitic in the skeleton of Salmonidæ and Gadidæ.
The skeletons of the tail, fins and skull particularly are seats
of infection, and from the skull the Lentospora can spread to the
semicircular canals, resulting in loss of power to maintain its
balance on the part of the fish. On this account the malady is
termed “drehkrankheit.” Young fish are more particularly infected.
_Myxobolus neurobius_ infects the spinal cord and nerves of trout.
Myxosporidia are divided into two sub-orders--_Disporea_ and
_Polysporea_--according to whether they form only two or several
spores during their growth. The former include two genera limited to
fishes, which are easily distinguishable by the shape of the spores:
_Leptotheca_, Thél., with a rounded spore, and _Ceratomyxa_, Thél.,
with a very elongate spore. The larger number of genera belong to the
_Polysporea_, which are divided into three families:
(1) Amœboid germ with a vacuole {(a) With two polar capsules.--
the contents of which do { _Myxidiidæ._
not stain with iodine. {(b) With four polar capsules.--
_Chloromyxidæ._
(2) Amœboid germ with a vacuole stainable with iodine. Spores with
two polar capsules.--_Myxobolidæ._
For further subdivisions the differences in the spores are
principally utilized.
Order. *Microsporidia*, Balbiani.
These are the organisms discovered in the stickleback by Gluge in
1834, and in _Coccus hesperidum_ by Leydig in 1853. They have since
been found in numerous other arthropods, especially insects. They
acquired particular importance when it was discovered that they
were the cause of the “pébrine” disease (“gattina” of the Italians)
which caused so much destruction amongst silkworms (_Bombyx mori_).
Pasteur (1867–70) and especially Balbiani (1866) participated in the
researches on _Nosema bombycis_, and it was the latter who classed
the “pébrine bodies” or “psorospermia of the arthropoda” amongst the
Sporozoa as Microsporidia (1882).[223] The complete life cycle of
_N. bombycis_ was described in 1909 by Stempell. The Microsporidia
are not confined to insects and arachnoids, they are now known to
occur also in crustacea, worms, bryozoa, fishes, amphibians and
reptiles. Certain tumours in fishes, similar to those formed by many
Myxosporidia, are produced by Microsporidia. Fantham and Porter found
that _Nosema apis_ was pathogenic to bees and other insects, and
was the causal agent of the so-called “Isle of Wight” disease in
bees[224] in Great Britain.
[223] _C. R. Acad. Sci._, Paris, xcv, p. 1168.
[224] _Annals Trop. Med. and Parasitol._, vi, pp. 145–214, 3 pls.
The Microsporidia, as their name implies, form minute spores which
usually are oval or pear-shaped. Each spore contains a single polar
capsule which is not easily visible in the fresh state (fig. 98, _f_)
and a single amœboid germ issues from the spore (fig. 99, _b_).
[Illustration: FIG. 98.--_Nosema apis._ Various stages in life-cycle.
_a_, planonts or amœbulæ from chyle stomach of bee; _b_, amœboid
planont creeping over surface of gut epithelial cell; _c_, uninucleate
trophozoite within epithelial cell; _d_, meront with nucleus divided
into four, about to form four spores; _e_, epithelial cell crowded
with spores; _f_, young spore; _g_, spore showing five nuclei, polar
filament ejected, and amœbula, about to issue. × 1,500, _a-e_; × 2,150,
_f-g_. (After Fantham and Porter.)]
The life cycle of _Nosema apis_, parasitic in bees, may be taken
as an example of that of a microsporidian. The infection of the
host is initiated by the ingestion of spores of _N. apis_ in food
or drink contaminated with the excrement of other infected bees.
Under the influence of the digestive juice of the bee the spore-coat
(sporocyst) softens, the polar filament is ejected and anchors the
spore to the gut epithelium, and the minute amœbula contained in the
spore emerges. The amœbula is capable of active amœboid movements
(fig. 98, _b_) and so is termed the planont or wandering form
(fig. 98, _a_). After a short time each planont penetrates between
or into the cells of the epithelium of the gut, a few only passing
through into the body cavity. Within the cells the amœbulæ become
more or less rounded, lose their power of movement, and after a
period of growth of the trophozoite (fig. 98, _c_) commence to divide
actively, these dividing forms being known as meronts (fig. 98,
_d_). Various forms of fission occur, and during this phase, termed
merogony, the numbers of the parasite within the host are greatly
increased, with concomitant destruction of the epithelium (fig. 98,
_e_). After a time sporogony commences. The full-grown meront becomes
successively the pansporoblast and sporoblast. Nuclear multiplication
and differentiation ensue and five nuclei are ultimately produced. At
the same time a sporocyst is secreted, and two vacuoles are produced
within. One is the polar capsule, and within it the polar filament
is differentiated; the other forms the posterior vacuole (fig. 98,
_g_). Between the two vacuoles the body cytoplasm or sporoplasm forms
a girdle-like mass. Of the nuclei, one regulates the polar capsule,
two control the secretion of the sporocyst, and two remain in the
sporoplasm. The polar capsule and polar filament are not usually
visible in the fresh condition, but can be demonstrated by the use
of various chemical reagents (fig. 100). The sporoplasm ultimately
becomes the amœbula (fig. 98, _g_) which issues from the spore after
the ejection of the polar filament.
[Illustration: FIG. 99.--_a_, section through the abdominal wall of
a silkworm, whose epithelial cells contain Microsporidia (_Nosema
bombycis_); _b_, a spore, the contents of which are escaping. (After
Balbiani.)]
[Illustration: FIG. 100.--_Nosema bombycis_, Naeg. Spores treated with
nitric acid, thus rendering the polar capsule perceptible, and the
filament has protruded from one of the spores. (After Thélohan.)]
A trophozoite (meront) of _N. apis_ becomes a single pansporoblast
which gives rise to one sporoblast producing one spore, and this
procedure is characteristic of the genus _Nosema_. In other genera
the trophozoite may form more than one pansporoblast and each
pansporoblast may form a variable number of spores in different
cases. Various attempts at classification have been based on these
characteristics. It must suffice here to note that in the cases where
the trophozoite becomes one pansporoblast, the latter can produce
four spores in the genus _Gurleya_, eight spores in _Thélohania_ and
many spores in _Pleistophora_. In other cases, where the trophozoites
give rise to many pansporoblasts, each of the latter may form many
spores, as in the genus _Glugea_.
A few pathogenic microsporidian parasites other than _N. apis_ may
be mentioned. _N. bombycis_, causing pébrine in silkworms, may
infect any or all the tissues of the host (fig. 99). The larvæ of
the host, _i.e._, the “silkworms,” may become infected by eating
food contaminated with spore-containing excrement of already
infected silkworms. In cases of heavy infection the silkworm dies,
but should the infection be less intense the larva becomes a pupa
in which the parasite persists, so that the moth emerges from the
cocoon already infected. Not only is the moth parasitized itself,
but the Nosema reaches the generative organs of both sexes and
penetrates the ovaries of the female, with the result that the ova
are deposited infected. Such infected eggs are capable of developing,
so that infection may be transmitted hereditarily as well as by the
contaminative method. Infected eggs can be recognized by microscopic
examination, as Pasteur showed, and thus preventive measures may be
adopted.
A microsporidian parasite is known to occur on the roots of the
spinal and cranial nerves of _Lophius piscatorius_, the angler fish.
This parasite is variously referred to the genera _Nosema_ and
_Glugea_.
_Thélohania contejeani_, parasitic in the muscles of crayfish, is
believed by some to be the causal agent of recent epizoötics among
them, though others believe the disease to be really due to a
bacillus. It may be that the one organism aids in the entry of the
other into the host.
Order. *Actinomyxidia*, Stolč.
A brief mention may be made of the Actinomyxidia (fig. 101), which
were first described by Stolč in 1899 as parasites of Oligochætes.
They have also been investigated by Mrazek, and a detailed study
of certain species was made by Caullery and Mesnil (1905). The
trophozoite is small and amœboid. The spores are large, and exhibit
tri-radiate symmetry. Spore formation is complicated and sexual
processes occur therein. Many amœbulæ are set free from each spore.
[Illustration: FIG. 101.--Spore of _Hexactinomyxon psammoryctis_. At
top of figure three polar capsules, one with polar filament extended.
× 450. (After Stolč.)]
Order. *Sarcosporidia*, Balbiani.
The first member of this group was discovered by Miescher in 1843.
This author found white filaments running parallel with the direction
of the fibres in the voluntary muscles of mice. They were visible
to the naked eye, and proved to be cylindrical tubes tapering at
each end. They were as long as the muscular fibres, were enveloped
in a membrane, and contained innumerable elongate or kidney-shaped
bodies and a smaller number of little spherical forms. Th. v.
Hessling confirmed (1853) the occurrence of these “Miescher’s tubes”
within the muscular fibres, this author having discovered the same
structures in the heart muscles of deer, cattle, and sheep. Both
investigators considered them to be pathological transformations of
the muscles. v. Siebold, from his own experiences, regarded them as
fungus-like entophytes.
Rainey (1858) discovered similar structures in the muscular system
of pigs, and considered them to be early stages of _Cysticercus
cellulosæ_, which error Leuckart rectified, simultaneously
emphasizing their relationship with Myxosporidia. Both these authors
found them in the muscular fibres, and both observed that they
possessed a thick striated membrane. Manz (1867) published the
results of more minute investigations on the structure and contents
of the cylinders. This observer also recognized the disease in
rabbits and attempted to cultivate the parasites. He also tried to
induce experimental infection in guinea-pigs, rats, and mice, but the
result was negative.
However, domestic and wild mammals are not the only hosts of
Sarcosporidia; these parasites are also harboured by birds. Thus,
according to Kühn, they are found in the domestic fowl; according
to Rivolta in _Turdus_, _Corvus_, and other birds; according to
Stiles in North American birds; while Fantham found Sarcosporidia
in the African mouse-bird, _Colius_. Reptiles also are parasitized
occasionally. Bertram found them in the gecko, Lühe in the
wall-lizard. It was found also that the Sarcosporidia could develop
not only in the muscles but also in the connective tissue. This
led to the foundation of a new, but provisional, classification by
Blanchard, using the generic name _Miescheria_ for the parasites
in the muscles and _Balbiania_ for those in the connective tissue.
Finally, Sarcosporidia have also been observed in man.
The relation of these parasites to certain diseases of domestic
animals has been studied by veterinary surgeons. Sarcosporidia may
cause fatal epizoötics among sheep.
There is still a wide field open for research in regard to the
structure and development of these parasites, and the manner in which
the hosts become infected.
[Illustration: FIG. 102.--Longitudinal section of a muscle of the
domestic pig, with _Sarcocystis miescheriana_. × 30. (After Kühn.)]
[Illustration: FIG. 103.--Transverse section of the muscle of a pig,
with _Sarcocystis miescheriana_. × 38. (After Kühn.)]
The Sarcosporidia usually appear as elongate, cylindrical, or fusiform
bodies, rounded at both extremities and of various lengths and breadths
(fig. 102). In some species they may be from 16 mm. to 50 mm. long, as
in the sheep and roebuck. These bodies are the so-called sarcocysts or
Miescher’s tubes. They lie in transversely striated muscular fibres
which they distend more or less. The forms found in the connective
tissue are apparently parasites which originally inhabited the muscular
fibres, and only on disintegration of the fibres reached the connective
tissue, where they grow to large oval or globular bodies (fig. 105).
The mammalian muscles usually infected are those of the œsophagus,
larynx, diaphragm, body-wall, and the psoas muscles. The skeletal
muscles may be affected in acute cases, as well as those of the tongue
and eye. The heart muscles are sometimes parasitized.
In fresh material cut into thin slices the parasites are
frequently recognizable, even with the naked eye, because of their
yellowish-white colour. Under the microscope they appear to be
coarsely granular (fig. 103). Beginners may find some difficulty
in distinguishing them from other foreign bodies, such as dead and
calcified encapsuled Trichinæ, or from Cysticerci that have died
and become calcified in the early stages, more particularly as the
Sarcosporidia also occasionally may become calcified.
The Sarcosporidia are always enveloped in a membrane, which is
probably formed at an early stage. In a few cases it remains thin
and simple, in other cases a radially striated ectoplasmic layer is
present (figs. 104, 108), which has been variously described. From the
inner integument, which may be homogeneous or fibrous, thick or thin,
membranes or trabeculæ pass into the interior of the body, forming
anastomosing partitions, and so producing a system of chambers of
various sizes that do not communicate with one another (figs. 104,
108). These chambers are occupied by sickle- or bean-shaped bodies
(spores or sporozoites), or various developmental stages of them.
The oldest spores are found in the centre of the Miescher’s tubes or
trophozoites. If they are not liberated they die there, so that the
central chambers of the tube are empty and hollow.
[Illustration: FIG. 104.--_Sarcocystis miescheriana_ from pig. Late
stage in which body is divided into numerous chambers or alveoli, each
containing many spores. (From Wasielewski, after Manz.)]
In the youngest Sarcosporidia (40 µ in length) from the muscles of
the sheep there occur, according to Bertram, small roundish or oval
cells (4 µ to 5 µ), the nuclei of which are half their size, and are
embedded in a granular protoplasmic mass. In somewhat larger, and
therefore older, cylinders, the investing membrane of which already
shows both layers, the cells have become larger (to 7 µ) and are more
sharply outlined from each other (fig. 106). These uninucleate cells
may be considered as pansporoblasts. In each pansporoblast division
of the nucleus occurs (fig. 107), and meanwhile the pansporoblasts
become isolated within the chambers, the dividing partitions of which
originate from the granular protoplasm which is present between the
pansporoblasts. The numerous uninucleate daughter forms produced within
the chambers become spores direct (fig. 108).
The process commences in the centre of the cylinders or sarcocysts,
and then progresses towards the extremities, the parasites meanwhile
increasing in size, and new pansporoblasts being continually formed at
the extremities (fig. 107).
[Illustration: FIG. 105.--Transverse section of _Sarcocystis tenella_,
Raill. From the œsophagus of the sheep, _Ovis aries_. × 38. _a_,
marginal chambers filled with spores; _b_, connective tissue of the
œsophagus; _c_, muscles of the œsophagus.]
[Illustration: FIG. 106.--Young _Sarcocystis tenella_ of the sheep,
47 µ in length. (After Bertram.)]
[Illustration: FIG. 107.--End of a trophozoite of _Sarcocystis
miescheriana_ from the diaphragm of the pig, showing division in
pansporoblasts. × 800. (After Bertram.)]
[Illustration: FIG. 108.--_Sarcocystis blanchardi_ of the ox.
Longitudinal section of sarcocyst or Miescher’s tube. _a_, substance
of muscle fibre; _b_, envelope of sarcocyst; _c_, muscle nuclei; _d_,
spores in chambers; _e_, ground substance. × 400. (From Wasielewski,
after van Eecke.)]
The spores (sometimes called Rainey’s corpuscles), vary in shape
according to the species, but are also of different form individually.
They are mostly kidney-, bean- or sickle-shaped (fig. 109), and of
small size, sometimes reaching 14 µ by 3 µ to 5 µ. They are apparently
surrounded by a thin membrane, and at one extremity (according to the
discovery of L. Pfeiffer, confirmed by van Eecke, Laveran and Mesnil)
contain an obliquely striated body (fig. 109) often homologized with
the polar capsule, while the greater part of the spore is taken up by
the nucleate sporozoite. Several authors state that they have also
observed filamentous appendages (polar filaments) at one end of the
spores, and have seen two kinds of spores in the same Sarcosporidium.
Spores of various species of Sarcosporidia may contain metachromatic
granules, often centrally placed (fig. 109). These granules may be
metabolic or possibly may contain toxin (see below).
[Illustration: FIG. 109.--Spores of _Sarcocystis tenella_, Raill. _a_,
fresh, showing the polar capsule; _b_, stained, showing metachromatic
granules and nucleus. × 1,000. (After Laveran and Mesnil.)]
The gymnospores of _Sarcocystis muris_, from the mouse, show active
boring movements when kept in saline solution warmed to 35° or 37° C.
_S. muris_ is very deadly to its host. From their structure the
spores do not appear to have great powers of resistance to external
conditions. They measure 12 µ by 3 µ to 4 µ or less.
Laveran and Mesnil (1899) isolated a toxin from _S. tenella_ of
the sheep and called it sarcocystin. This substance is especially
pathogenic to experimental rabbits.
The duration of life of the Sarcosporidia is a comparatively long
one. The affected muscular fibres may remain intact and capable of
performing their functions for a long time, but at last they perish,
if the host lives long enough. Thus the Sarcosporidia of the muscles
are then enveloped only by sarcolemma, and finally, when this likewise
disappears, they fall into the intra-muscular connective tissue.
In many cases the Sarcosporidia die off within their hosts, this,
according to Bertram, being brought about by a disintegration of the
spores in the central chambers. In other cases the leucocytes play a
part in the destruction of the Sarcosporidia, and sometimes it happens
that lime salts are deposited in and around the vacant cylinders.
In some places pigs, sheep, mice and rats are infected with
sarcosporidiosis to a remarkable extent, in certain cases almost
reaching 100 per cent. Young animals also are infected, and perhaps
infection only takes place during youth.
Although the natural mode of transmission of the Sarcosporidia remains
to be determined, yet various experimental researches on the problem
are of interest and importance. Theobald Smith (1901) found that mice
could be experimentally infected with _S. muris_ by feeding them with
the flesh of other infected mice. The incubation period was a long one,
namely forty to fifty days. Thus, on the forty-fifth day after feeding
young Sarcosporidia were found, and seventy days after feeding spore
formation began. Ripe spores were found two and a half to three months
after the commencement of these experiments. This mode of infection--a
cannibalistic one--hardly seems likely to be the natural method for the
infection of sheep and ruminants generally. Smith’s researches have
been confirmed. Nègre[225] (1910) found that the fæces of mice fed on
infected muscular tissue were infective to other mice when ingested by
them. Negri[226] infected guinea-pigs with _S. muris_ by feeding them
on infected mouse flesh, and found that the parasite in guinea-pigs
showed different characters from those exhibited by it in mice.
Darling[227] also succeeded in infecting guinea-pigs with _S. muris_,
and Erdmann infected mice with _S. tenella_ (from the sheep).
[225] _C. R. Soc. Biol._, lxviii, p. 997.
[226] _Centralbl. f. Bakt._, Orig., xlvii, p. 612; see also xlvii,
p. 56; lv, p. 373.
[227] _Journ. Exptl. Med._, xii, p. 19.
According to Erdmann[228] (1910) the Sarcosporidian spore germinates
in the intestine of the host, which has recently ingested infected
material. The spore liberates its contained toxin--sarcocystin--which
acts upon the adjacent intestinal epithelium, whereby the latter is
shed, and an amœbula creeps out of the spore. The amœbula is able to
penetrate the denuded area and get directly into the lymph-spaces of
the submucous coat of the intestine. The first period of development,
lasting some twenty-eight to thirty days, is said to be passed in the
lymph-spaces of the intestine. Later the amœbula reaches a muscle
fibre. Writing in May, 1914, Erdmann[229] records the appearance of
small amœboid and schizogony forms six days after infection of the
host. Crawley[230] (1913) controverts some of these statements and
considers that the Sarcosporidian spore, still sickle-shaped, bores its
way into the epithelial cells of the intestine and comes to rest there.
The spore then becomes round or elliptical, and peripheral masses of
chromatin appear within it, suggesting schizogony. This happens about
twelve hours after feeding, and in twenty-four hours the spores appear
to have left the intestine. More recently (May, 1914), Crawley[231]
considers that there is sexual differentiation among the Sarcosporidian
spores, a few hours after their ingestion by the host.
[228] _Sitz. Gesell. naturf. Freunde zu Berlin_, p. 377.
[229] _Proc. Soc. Exper. Biol. and Med._, xi, p. 152.
[230] _Science_, xxxvii, p. 498.
[231] _Proc. Acad. Nat. Sci._, Philadelphia, May, 1914, p. 432.
Interesting discussions have occurred as to the site of the toxic
sarcocystin within the spore. Metachromatic granules occur in the
middle of the Sarcosporidian spore (fig. 109), and the toxin may be
contained in these grains, as they disappear, according to Erdmann,
before the amœbula penetrates the denuded intestinal wall. However, a
polar capsule, containing a polar filament, may be present at one end
of a Sarcosporidian spore. Laveran and Mesnil described a striated
area at the more pointed end of the spore of _S. tenella_, which area
they consider to represent a polar capsule. Fantham[232] (1913) found
a vacuole-like, polar capsule area in the spores of _S. colii_ from
the African mouse-bird. The sarcocystin may be contained in the polar
capsule. The nucleus of the spore is generally at the opposite, blunter
end.
[232] _Proc. Cambr. Philosoph. Soc._, xvii, p. 221.
Again, various authors have stated that Sarcosporidian spores may occur
in the blood of the host at times. If so, then an intermediate host may
be concerned in their transmission. Perrin suggested that Sarcosporidia
might be spread by blow-flies and flesh-flies.
The classification of the Sarcosporidia as proposed by R. Blanchard,
which was based on their various habitats, can no longer hold, because
the same species may occur in the muscles as well as in the connective
tissue. For the present, the few species that are known may be placed
in one genus, _Sarcocystis_, Ray Lankester, 1882.
The following species of _Sarcocystis_ are of interest:--
_S. miescheriana_, Kühn, 1865, in the pig.
_S. bertrami_, Doflein, 1901, in the horse.
_S. tenella_, Railliet, 1886, in sheep. _S. tenella bubali_ in
buffaloes in Ceylon and Egypt.
_S. blanchardi_, Doflein, 1901, in cattle.
_S. muris_, Blanchard, 1885, in the mouse, to which it is lethal.
_S. hueti_, Blanchard, 1885, in the seal.
_S. colii_, Fantham, 1913, in the African mouse-bird, _Colius
erythromelon_.
Also various Sarcosporidia from antelopes, monkeys, opossum, birds, the
gecko and wall-lizard are known.
The spores of _S. muris_, _S. bertrami_, _S. tenella_, and _S. colii_
can multiply by longitudinal fission.
SARCOSPORIDIA OBSERVED IN MAN.
(1) Lindemann[233] found on the valves and in the myocardium of a
person who had died of dropsy certain brownish masses, 3 mm. in length
and 1·5 mm. in breadth which he regarded as gregarines. If these were
actually independent animal organisms it may be suggested that they
were Sarcosporidia. Rivolta (1878) named the species _S. lindemanni_.
[233] “Ueb. d. hyg. Bdtg. d. Gregarinen,” _Dtsche. Ztschr. f.
Staatsarzneikunde_, 1868, xxvi, p. 326.
(2) Rosenberg[234] found a cyst 5 mm. in length and 2 mm. in breadth
in a papillary muscle of the mitral valve of a woman, aged 40, who had
died from pleuritis and endocarditis. The cyst contained no scolex nor
hooklets of tænia. Numerous small refracting bodies, round, oval or
kidney-shaped, were found in a daughter cyst, as well as sickle-shaped
bodies. The description hardly appears to indicate Sarcosporidia.
[234] “Ein Befund von Psorosp. in Herzmusk d. Menschen,” _Ztschr. f.
Hygiene_, 1892, xi, p. 435.
(3) Kartulis[235] observed Miescher’s cylinders of various sizes in the
liver (?) and in the muscular system, of a Sudanese who had succumbed
to multiple abscesses of the liver and abdominal muscles. This may be
considered as the first actual case of the occurrence of Sarcosporidia
in man. Koch in 1887 described a case in Egypt.
[235] Kartulis, “Ueb. pathog. Protoz. b. Menschen,” _Ztschr. f. Hyg.
u. Inf._, 1893, xiii, p. 1. Compare also Braun, M., _Die Thier. Par.
d. Mensch._, 2nd Edit., Wrzbg., 1895, p. 92; Braun, M., “Z. Vork. d.
Sarcosp., b. Menschen,” _Centralbl. f. Bakt._ 1895, xviii, p. 13.
(4) The case reported by Baraban and St. Remy[236] was at once
demonstrated as certain. It related to a man who had been executed,
and in the laryngeal muscles of whom Sarcosporidia were found; the
length of the parasites varied between 150 µ and 1,600 µ, their breadth
between 77 µ and 168 µ. The affected muscular fibres were distended
to four times their normal thickness. This species was described by
Blanchard as “_Miescheria_” _muris_, but according to Vuillemin, it was
more probably _Sarcocystis tenella_ of the sheep.
[236] “Sur un cas de Tub. Psorosp. ob. chez l’homme,” _C. R. Soc.
Biol._, Paris, 1894 (x), I, p. 201. “Le Parasitisme d. Sarcosp. chez
l’homme,” _Bibliogr. Anat._ 1894, p. 79.
(5) Vuillemin has also described a case of Sarcosporidia found in the
muscles of a man who died from tubercle at Nancy. The author considered
that the parasite corresponded to _S. tenella_.
(6) Darling[237] (1909) found Sarcosporidia in the biceps of a negro
from Barbados.
[237] _Arch. Internal Med._, III, p. 183.
The Myxosporidia, Microsporidia, Actinomyxidia and possibly the
Sarcosporidia may be included within the section *Cnidosporidia*
(Doflein), since they possess spores containing polar capsules.
Order. *Haplosporidia*, Caullery and Mesnil.
The Haplosporidia are a group of organisms having both a simple
structure and life-history. The simplicity may represent a primitive
condition or may be due to degradation resultant on parasitism, and
thus it is possible that the group is not a homogeneous one. The
order Haplosporidia was created by Caullery and Mesnil in 1899, and
includes parasites of rotifers, annelids (fig. 110), crustacea, fish,
prochordates and man. They may be present in the body cavity or
alimentary tract, and can also occur in the septum nasi of man, in
the nervous system of Cephalodiscus, and in tumours of fish.
As the name implies, the spores of the Haplosporidia are simple,
without polar capsules, and are uninucleate. In some genera, _e.g._,
_Haplosporidium_, _Urosporidium_ (fig. 111) there is a spore-coat
or sporocyst which may be elongate or spiny. The developmental
cycle of a Haplosporidian, such as _Haplosporidium_ or _Bertramia_,
begins with a small, uninucleate cell, often rounded, possessing a
cell membrane that may be prolonged into processes. Growth takes
place, coupled with an increase in the number of nuclei, so that a
multinucleate trophozoite is produced. Later, this multinucleate
trophozoite becomes segmented into a number of ovoid or spherical
pansporoblasts, which give rise to few (one to four) spores. Such a
spore, when set free, begins the life cycle over again.
More recently (1905–1907) two important organisms have been
described and included in this group, namely, _Neurosporidium
cephalodisci_[238] (Ridewood and Fantham) from the nervous system
of the prochordate, _Cephalodiscus nigrescens_, and _Rhinosporidium
kinealyi_ (or _seeberi_) from the septum nasi of man. In the case of
_Rhinosporidium_ and _Neurosporidium_, after the uninucleate spore
has grown into a multinucleate trophozoite, the latter segments into
uninucleate pansporoblasts, as in the preceding cases. A difference
then occurs, for each pansporoblast enlarges, its nucleus divides
and a “spore-morula” is formed. Thus a multinucleate pansporoblast
or spore-morula, divided into many uninucleate sporoblasts (spore
mother cells) is produced, and each sporoblast without further change
becomes a uninucleate spore.
[238] _Quart. Journ. Microsc. Sci._, li, p. 81.
The Haplosporidia have therefore been divided by Ridewood and Fantham
(1907)[239] into two sections:--
[239] See Fantham, _Brit. Assoc. Reports_, 1907, p. 553.
(1) The _Polysporulea_, wherein the pansporoblast gives rise to
a number of spores (nine or more), _e.g._, _Rhinosporidium_,
_Neurosporidium_.
(2) The _Oligosporulea_, wherein the pansporoblasts give rise
each to a few (four) spores or to only a single spore, _e.g._,
_Haplosporidium_, _Bertramia_, _Cœlosporidium_, _Ichthyosporidium_.
[Illustration: FIG. 110.--_Haplosporidium heterocirri._ Section
throughout wall of the Polychæte worm, _Heterocirrus viridis_, showing
various developmental stages of the Haplosporidium. × 550. (After
Caullery and Mesnil.)]
[Illustration: FIG. 111.--Haplosporidian spores. _a_, _b_,
_Haplosporidium heterocirri_. _a_, fresh; _b_, after immersion in sea
water; _c_, _d_, _Urosporidium fuliginosum_. × 1000. (After Caullery
and Mesnil.)]
*Rhinosporidium kinealyi*, Minchin and Fantham, 1905.
_Rhinosporidium kinealyi_, parasitic in man, must now be considered in
greater detail. This organism was found in nasal polypus in India, and
has since been recorded from the ear as small nodules in the external
auditory meatus. The Indian cases came from the neighbourhoods of
Calcutta and Madras, and the parasite has been seen in Ceylon. Similar
structures have since been described from the United States and South
America.
The Rhinosporidium polypus is said not to be particularly painful,
though nasal forms must interfere with breathing to some extent. The
first nasal polyp reported from India formed a vascular pedunculated
growth on the septum nasi and was about the size of a large pea or
raspberry. It was compared with a raspberry, being red in colour with a
number of small whitish dots upon its surface. When the tumour was cut,
a number of similar whitish dots were seen within. These were the cysts
of Rhinosporidium. According to Minchin and Fantham[240] (1905), they
vary considerably in size and measure up to 200 µ or 250 µ in diameter.
Each possesses a cyst wall which varies in thickness in different
cysts. Its outer wall is always firm and distinct, the inner limit
being less definite at times. Each large cyst is filled with numbers of
spherical or oval bodies, showing every gradation between small ones at
the periphery and large ones at the centre (fig. 112). Roughly, three
zones of parasites can be distinguished in a large cyst, a peripheral
set consisting of the youngest parasites, an intermediate group and a
central, oldest zone. A large cyst may possess a pore for the egress of
its contents. Some of the cysts show polar distribution of the zones.
[240] _Quart. Journ. Microsc. Sci._, xlix, p. 521.
The youngest forms of Rhinosporidium are difficult to detect. They are
small, granular masses, round, ovoid or irregular and at times even
amœboid in appearance. These are young trophozoites. They increase in
size, but encystment occurs early, the outer layer becoming firm so
that the organisms have a definite contour. Each is soon multinucleate
and the cytoplasm segments around the nuclei. The cyst thus becomes
full of uninucleate pansporoblasts or sporonts, with a peripheral
layer of undifferentiated protoplasm. The pansporoblasts grow in size.
In the larger cysts the formation of pansporoblasts progresses at
the expense of the peripheral layer of protoplasm, which, however,
continues to grow, so that the cyst as a whole increases in size. The
pansporoblasts at first are uninucleate (fig. 112, _a_), and then
undergo nuclear multiplication. This is well seen in the intermediate
zone of parasites, where the pansporoblasts show first one, then two,
then four or more spores (fig. 112, _b_), while in the oldest centrally
placed pansporoblasts, about a dozen or sixteen closely packed spores
(fig. 112, _c_), can be seen. The spore is small and rounded, and its
nucleus is clear and distinct. The fully formed pansporoblast or spore
morula becomes surrounded by a membrane.
Certain of the cysts have been found in a ruptured condition, whereby
the spores have been liberated into the surrounding tissue. It is
almost certain that the spores serve for the auto-infection of the
host, for though the tumours of Rhinosporidium seemed to have been
removed entirely, it has been found that they recur, some minute
fragment of the parasite having probably been left behind. The method
whereby the parasite reaches new hosts has not yet been determined,
and it would be of interest if its life-history could be more fully
investigated.
[Illustration: FIG. 112.--_Rhinosporidium kinealyi._ Portion of ripe
cyst containing pansporoblasts of various ages. × 480. (After Minchin
and Fantham.)]
The Asiatic specimens of _R. kinealyi_ were first described in detail
by Minchin and Fantham (1905) from material briefly reported to the
Laryngological Society of London in 1903, by O’Kinealy. Material
obtained by Dr. Nair, of Madras, was described by Beattie[241] in 1906.
This material came from Cochin. Castellani and Chalmers have found
similar polypi in Ceylon.
[241] _Journ. Pathol. and Bacteriol._, xi, p. 270; and _Brit. Med.
Journ._, Nov. 16, 1907, p. 1402.
Wright[242] has described the parasite from Memphis, Tennessee.
Seeber[243] in 1896 described nasal polypi in Buenos Ayres, and in
1900 Wernicke named the parasite therein _Coccidium seeberi_. Seeber’s
parasite is a Rhinosporidium, _R. seeberi_, and may ultimately be found
to be the same as _R. kinealyi_. Ingram[244] reports Rhinosporidium
cysts, with pores in the cyst walls, in conjunctival polypus and in
papilloma of the penis in India. Zschokke has reported the presence of
_Rhinosporidium_ in horses in South Africa.
[242] _New York Med. Journ._, December 21, 1907, p. 1149.
[243] _La Ciencia Medica_ (Buenos Ayres), 1912.
[244] _Lancet_, September 3, 1910, p. 726.
Class IV. *INFUSORIA*, Ledermüller, 1763.
The Infusoria (or Heterokaryota, Hickson, or Ciliophora, Doflein)
include the Ciliata and the Suctoria. A few authorities, including
Braun, raise the Suctoria (or Acinetaria) to separate rank as a class,
but this is not widely followed.
The body of the Ciliata usually is bilaterally symmetrical and is
enveloped in a cuticle which has numerous openings for the protrusion
of the cilia. Most kinds have a fixed shape, whilst changes in the form
of others are brought about by the contractions of the body substance.
The latter exhibits hyaline ectoplasm, in which myonemes, and
occasionally also trichocysts (minute spindle-shaped bodies) appear,
and granular endoplasm which may contain numerous vacuoles. The cilia,
on whose various arrangements the classification is based, are always
processes of the ectoplasm. Their form varies; they may be hair-like,
or more rarely thorn-like, spur-like, or hook-shaped; undulatory
membranes also may occur, which are probably composed of fused cilia.
With the exception of some of the parasitic species, an oral cavity,
peristome or cytostome, is always present. It is frequently beset with
cilia or provided with undulatory membranes, which help to waft the
food inwards; sometimes there is an anal aperture (cytopyge) generally
placed at the opposite pole of the organism. A cytopharynx fringed with
cilia or sometimes with a specialized supporting apparatus is connected
with the peristome. Vacuoles form round the ingested food, and in many
species a constant rotation goes on in the endoplasm. Often one, and
sometimes two contractile vacuoles are present, the frequency of the
pulsations of which depends on the surrounding temperature. Sometimes
special conducting channels lead to the vacuoles, or there are outlet
channels leading to the exterior.
There is in almost every case a large nucleus (macronucleus), and lying
close up to it a small nucleus (micronucleus). The form of the large
nucleus varies according to the species. Numerous nuclei are not very
common, but these occur in _Opalina_, which lives in the hind-gut of
amphibia, and is also distinguished by the absence of an oral aperture.
Reproduction is effected by binary fission; less commonly, after
encystment, by multiple division, or by budding. The divisions can
be repeated many times, but finally cease, and then the conjugation
of two specimens brings about a regeneration, particularly of the
nuclei. Numerous examinations (Bütschli, Hertwig, Maupas, Calkins) have
demonstrated that after two individuals have associated by homologous
parts of the body, the micronucleus separates from the macronucleus,
becomes larger and divides twice by mitosis, so that four micronuclei
are present in each one of the two individuals forming the couple.
Three of these nuclei perish and become absorbed, the fourth gradually
passes to the portion of protoplasm connecting the two conjugants,
which has originated by absorption of the cuticle at the point of
contact of the conjugants. After a further division one micronucleus of
each conjugant passes over into the other conjugant, and fusion ensues
between the two micronuclei of each individual. Complicated changes and
divisions may occur, but only the main principles can be noted here.
A new nuclear body is thus formed in each conjugant, and soon divides
into two. Of the segments thus produced one becomes a micronucleus, and
one or several of the others, as the case may be, form or amalgamate
into a new macronucleus, the old macronucleus usually perishing or
becoming absorbed during the conjugation. Usually, sooner or later,
the two conjugants separate, or may have separated already, and again
multiply independently by fission until a series of divisions by simple
fission is again followed by conjugation. The theoretical significance
of conjugation cannot be dealt with fully here. It may be remarked,
however, that the macronucleus plays no part in it, but governs
entirely the metabolism of the Infusorian, whereas the micronucleus is
essentially a generative nucleus from which macro- and micro-nuclei are
again and again produced.
Encystment amongst the Infusoria is very general, and is essentially
a means of protection when the surrounding medium dries up. Doubtless
these cysts are frequently carried long distances by the wind, which
explains the wide geographical distribution of most species. Also,
multiplication often takes place in the encysted condition.
Some Infusoria live a free life, others are sedentary; the latter
form colonies in fresh as well as in salt water. Numerous species are
parasites of various lower and higher animals,[245] and a few also are
parasitic in man.
[245] It may be stated that numerous peculiarly shaped species live
in the stomach of ruminants, others in the colon of horses. Several
species are found in the rectum of frogs and toads; others, again, on
the surface of the bodies of fishes; and various other species exist in
and on the bodies of invertebrate animals.
The Prague zoologist, v. Stein, introduced a classification of the
Infusoria that has been almost universally adopted. It is founded on
the different position of the cilia on the body. Though, no doubt,
artificial, it is a convenient system. Bütschli has compiled a better
one.[246] But for our purpose Stein’s system is sufficient:--
[246] Bronn’s _Cl. u. Ordn. d. Thierr._, i, Protozoa, Part 3, Infusoria.
Order 1. _Holotricha_, Infusoria with cilia that are evenly
distributed over the entire body.
Order 2. _Heterotricha_, ciliated all over like the _Holotricha_, but
having stouter cilia about the peristome.
Order 3. _Hypotricha_, only ciliated on the ventral surface.
Order 4. _Peritricha_, with only a ring of spiral cilia, mostly
sedentary.
The Infusoria observed in man belong to the order _Heterotricha_, with
few exceptions.
Genus. *Balantidium*, Claparède et Lachmann.
Heterotrichous Infusoria of oval or bag-like form and almost circular
on transverse section; the anterior extremity narrowed, the posterior
end broad and rounded off, or also narrowed; the peristome starting
at the anterior end is broadest there and becomes narrower as it
gradually obliquely approaches towards the posterior extremity. There
are coarse cilia along the entire left border and the anterior part
of the right border. Longitudinal striation is distinct and regular.
There are two contractile vacuoles on the right, and occasionally
also two or more to the left. The anus (cytopyge) is terminal. The
macronucleus is usually horse-shoe or kidney-shaped, sometimes oval;
the micronucleus contiguous. Reproduction is by binary fission and
conjugation, and encystment occurs. The cysts are spherical or oval.
These ciliates are parasitic in the large intestine of human beings
and pigs, in Amphibia, and in the body cavity of polychæte Annelida.
*Balantidium coli*, Malmsten, 1857.
Syn.: _Paramæcium coli_, Malmsten, 1857.
[Illustration: FIG. 113.--_Balantidium coli._ _a_, nucleus; _b_,
vacuole; _c_, peristome; _d_, bolus of food. (After Leuckart.)]
[Illustration: FIG. 114.--_Balantidium coli_, free and encysted;
_a_, anus or cytopyge; _n_, macronucleus; _b_, bolus of food. (After
Casagrandi and Barbagallo.)]
The body is oval, 60 µ to 100 µ in length (up to 200 µ according to
Janowski), and 50 µ to 70 µ in breadth. The peristome is funnel-shaped
or contracted, the anterior end being then broadened or pointed
according to the degree of contraction (figs. 113, 114). The ecto- and
endo-plasm are distinct, the latter is granular, containing drops of
fat and mucus, granules of starch, bacteria, and occasionally also red
and white blood corpuscles. There are usually two contractile vacuoles,
seldom more. The anus (cytopyge) opens at the posterior extremity. The
macronucleus is bean- or kidney-shaped, rarely oval; the micronucleus
is spherical.
_Balantidium coli_ lives in the large intestine of man, in the rectum
of the domestic pig, and has been found in monkeys. It propagates by
transverse division, but conjugation and encystment are known to take
place.[247] Transmission to other hosts is effected by the cysts of the
parasite (fig. 114).
[247] According to Gourvitch (“Bal. coli. Darmk. d. Menschen,” _Russ.
Arch. f. Path., klin. med. u. Bact._, Petrograd, 1896), the conjugated
Balantidia are supposed to fuse with each other and form oval cysts
two or three times the size of the free organisms, and to divide into
numerous globules within the cystic membrane; the process, however, has
hitherto not been confirmed. The supposed Balantidium cysts appeared in
two patients who were simultaneously suffering from _Dibothriocephalus
latus_, after the administration of anthelminthics. It therefore seems,
according to the description, that in reality these forms were actually
abnormally large, possibly swollen, young eggs of the tape-worm
mentioned.
_Balantidium coli_, first seen by Leeuwenhoek, was described by
Malmsten in 1857 in a man aged 35 years, who had two years previously
suffered from cholera, and since then had been subject to diarrhœa. The
examination showed an ulcer in the rectum above the mid sphincter ani,
in the sanguineous purulent secretion of which numerous Balantidia were
swimming about. Although the ulcer was made to heal, the diarrhœa did
not cease and the stools contained numerous Balantidia, the number of
which could only be decreased by extensive enemas of hydrochloric acid.
The second case related to a woman who was suffering from severe
colitis, and who died ten days after admission. The malodorous, watery
evacuations contained innumerable Balantidia, in addition to pus, and
at the autopsy the anterior portion of the large intestine was found to
be infested with them.
Subsequently this parasite has often been observed in human beings,
and various cases have been recorded. These occurred in Russia,
Scandinavia, Finland, Cochin China, Italy, Germany, Serbia, Sunda
Islands, Philippine Islands, China, and in other parts of Asia and in
America. Other cases were reported by Askanazy, Ehrnroth, Klimenko,
Nagel, Koslowsky, Kossler, Waljeff, Strong and Musgrave, Glaessner[248]
and others. Sievers found _B. coli_ very common in Finland.
[248] _Centralbl. f. Bakt._, Orig., xlvii, p. 351.
In the majority of the cases described by Sievers from Finland,
and in other cases from Central Europe, the patients suffered from
obstinate intestinal catarrh, which did not always cease even after
the Balantidia had disappeared. On the other hand, Balantidia have
occasionally still been found to persist, though in small numbers,
after the catarrh has been cured. Some authors, nevertheless, do
not regard Balantidia as the primary cause of the various diseases
of the large intestine, which often commence with the development of
ulcers, but they consider that they may aggravate these diseases and
render them obstinate. According to Solowjew, Askanazy, Klimenko and
Strong and Musgrave, however, the parasites penetrate the intestinal
wall, and give rise to ulcerations which may extend deeply into the
submucosa, and even be found in the blood and lymphatic vessels of the
intestinal wall. According to Stokvis, _B. coli_ occurs also in the
lung; at all events this author states that he found one living and
several dead paramæcia (?) in the sputum of a soldier, returned from
the Sunda Islands, who was suffering from a pulmonary abscess. Sievers
has shown that _B. coli_ might occur in persons not suffering from
intestinal complaints, but E. L. Walker[249] (1913) states that every
person parasitised with _B. coli_ is liable sooner or later to develop
balantidian dysentery.
[249] _Philip. Jl. Sc._, Sec. B, viii, p. 333.
Since Leuckart confirmed the frequent presence of _B. coli_ in the
rectum of pigs, and corresponding observations were made in other
countries, the pig is universally considered to be the means of the
transmission of Balantidium to man. The encysted stages only serve
for transmission, because, according to all observations, the free
parasites have a very small power of resistance. They perish when the
fæces have become cool; they cannot live in ordinary, slimy, or salt
water. As they are killed by acids even when much diluted, they cannot
pass through the normal stomach alive except under the most unusual
circumstances. The pigs, in whose intestines the Balantidium appears to
cause little or no disturbance, evacuate numerous encysted Balantidia
with the fæces, and their occasional transference to man brings about
their colonization there, but perhaps only when a disease of the colon
already exists.
Experimental transmission of the free parasites to animals (per os
or per anum) yielded negative results, even in the case of pigs.
Casagrandi and Barbagallo (1896), however, had positive, as well as
negative, results. They employed healthy young cats, or cats in which
catarrhal entero-colitis had been artificially induced (which in other
experiments is apt to cause the death of the animals experimented upon
in about six or seven days), or finally cats that had dilatation of
the rectum with alkaline reaction of the fæces. An attempt to infect
three healthy cats by injecting human fæces containing Balantidium
into the rectum proved negative, in so far as the fæces of the
experimental animals had an acid reaction and contained no Balantidia,
but at the autopsy performed eight days after infection a few encysted
parasites were found in the mucus of the ileum. In the case of four
cats suffering from entero-colitis, into which human fæces containing
Balantidia were introduced per os, Balantidium cysts were found in the
fæces three days after the last ingestion. Great numbers, moreover,
were found in the cæcum and the posterior part of the small intestine
at the autopsy of the animals, which died about eight days after the
commencement of the experiments. Actual colonization, therefore,
was not effected in either series of experiments. Free or encysted
Balantidia of pigs were used for further experiments. The experiments
proved negative when fæces containing cysts were injected into the
rectum of healthy cats (three experiments), or cats (two) suffering
from spontaneous intestinal catarrh, or when such material was
introduced per os into three healthy cats. In the case of two cats
with intestinal catarrh artificially produced, a small number of the
active Balantidia injected into the rectum remained alive. Larger
quantities of fæces containing encysted Balantidia were introduced into
two other cats affected with the same complaint. These, certainly, did
not appear in the fæces, but small numbers, free and alive, were found
in the cæcum. Similarly, encysted Balantidia were introduced into two
cats with dilated rectum, and whose fæces had an alkaline reaction.
In these cases no parasites appeared in the fæces, but three and five
days later, when the two animals were examined, a very small number
were discovered free in the large intestine. Klimenko did not succeed
in infection experiments with _B. coli_ on young dogs, whose intestines
had been artificially affected by disease.
More recent experiments by Brumpt have shown that young sucking pigs
can be infected with Balantidium from infected monkeys (_Macacus
cynomolgus_) and suffer heavily from the same, whereas the Balantidium
of the pig is rarely harmful to its host. This and previous experiments
may be thought to suggest that there are perhaps several pathogenic
species, and also that harmless strains of Balantidium may occur.
At the same time, it must be remembered that a large proportion of
the cases recorded of Balantidian colitis occur among swineherds
and butchers, that is, among people in frequent contact with pigs.
Morphologically, there are practically no differences between the
Balantidia found in man, monkeys and pigs, and it is probable that
one species only, under slightly different environmental conditions,
may be responsible for the colitis observed. In any case, efficient
prophylactic measures should be taken against balantidiasis in
countries where it may occur, by confining the pigs and not allowing
them to run in yards and dwellings.
E. L. Walker (1913) has given a good summary of work on balantidiasis.
His own researches in the Philippines showed that monkeys could be
infected by Balantidia both from pigs and men. Parasites may appear
in the stools only at infrequent intervals. He believes that the
ciliates are the primary etiologic factor in the symptoms and lesions
of balantidian dysentery.
Behrenroth (1913) has given an interesting account of _Balantidium
coli_ and its pathogenic significance.
*Balantidium minutum*, Schaudinn, 1899.
The body is of oval form, with the anterior extremity pointed, and
posterior extremity broad and rounded (fig. 115). The length is 20 µ
to 32 µ, and the breadth is 14 µ to 20 µ. The peristome, which is
fissure-like, extends to the centre of the body (fig. 115). The right
lateral border of the peristome is beset with cilia the same length as
those of the body, the left side terminates in a thin hyaline membrane
that extends towards the back, and can pass over to the right side. A
row of longer and stronger cilia (cirri) are on the left border of the
peristome. The cuticle is refractile, the ectoplasm hyaline and the
endoplasm granular, with numerous food vacuoles.
[Illustration: FIG. 115.--_Balantidium minutum._ _P_, peristome; _N_,
nucleus; _M_, micronucleus; _V_, contractile vacuole. Food vacuoles are
represented in the endoplasm. (After Schaudinn.)]
A single contractile vacuole lies dorsally and to one side at the
posterior extremity. The macronucleus, which is always spherical, is
central and is 6 µ to 7 µ in diameter. The micronucleus, close in front
of it, only measures 1 µ (fig. 115). The cysts are oval.
These parasites were found in numbers in the evacuations of a man
aged 30, who was born in Germany and had repeatedly travelled between
Hamburg and North America, where he made long stays. The patient came
to the Charité in Berlin to seek advice for constipation alternating
with diarrhœa accompanied by abdominal pain.
A second case (the parasite of which was described as _Colpoda
cucullus_ by Schulz) was observed in a patient in the same institution.
As, in both cases, the parasites only appeared during the diarrhœa,
and disappeared as soon as the fæces had assumed a normal consistency,
or could only be demonstrated in a few encysted specimens, it may be
assumed that the small intestine or the duodenum is their habitat.
Genus. *Nyctotherus*, Leidy, 1849.
Flat, heterotrichous Infusoria, kidney- or bean-shaped. The peristome
commences at the anterior pole of the body and extends along the
concave side to the middle, where the oral aperture is situated. The
cytopharynx is oblique and is more or less curved. The cytopyge is at
the posterior extremity, where a single contractile vacuole is also
situated. The macronucleus is almost in the centre of the parasite.
The members of this genus live parasitically in the intestine of
amphibia, insects and myriapods, and at least one species is found in
man.
*Nyctotherus faba*, Schaudinn, 1899.
The body is bean-shaped, and a little flattened dorso-ventrally. It
is 26 µ to 28 µ long, 16 µ to 18 µ broad, and 10 µ to 12 µ thick
(fig. 116). The peristome is on the right border and extends to the
middle; at the left there are large adoral cilia, the cilia on the
right border not being larger than those on the body. The cytopharynx
is short, slightly curved and turned backwards. The contractile vacuole
is large, spherical, situated at the posterior extremity, and its
contents are voided through the anus at its left. The macronucleus is
in the centre of the body; it is globular (6 µ to 7 µ in size), and
contains four or five chromatin masses. The micronucleus lies close
to it, and is spherical or somewhat elongate measuring 1 µ to 1·5 µ
(fig. 116). The cysts are oval.
[Illustration: FIG. 116.--_Nyctotherus faba._ _P_, peristome;
_N_, nucleus; _M_, micronucleus; _V_, contractile vacuole. (After
Schaudinn.)]
This species has hitherto only been seen once in the same patient in
whom _Balantidium minutum_ was discovered.
*Nyctotherus giganteus*, P. Krause, 1906.
Under the name _Balantidium giganteum_ n. sp., P. Krause described
an Infusorian which was repeatedly observed with _Trichomonas
intestinalis_ in the alkaline evacuations of a typhoid patient in
Breslau. The body is ovoid, narrower and rounded anteriorly and
broader and stunted posteriorly. The peristome lies to one side; the
macronucleus is bean-shaped, the micronucleus small and globular;
one or two vacuoles are present. The anus is at the farther end. The
organism is 90 µ to 400 µ long, 60 µ to 150 µ broad (fig. 117). After
a prolonged stay outside the body, it becomes rounded and encystment
occurs. In the thermostat the Infusoria remain alive at 37° C. for five
weeks.
The species, however, hardly belongs to _Balantidium_, but to all
appearances is a _Nyctotherus_ and is distinguished from _N. faba_ by
the difference in size.
[*Nyctotherus*] *africanus*, Castellani, 1905.
In the fæces of a native of Uganda who suffered from sleeping sickness
and diarrhœa and had in his intestine _Ascaris lumbricoides_,
_Trichocephalus trichiurus_ and _Ancylostoma duodenale_, Castellani
found a curiously shaped Infusorian, 40 µ to 50 µ long, and 35 µ
to 40 µ broad, with spherical macro- and micronucleus and a
contractile vacuole (fig. 118). He included the organism in the genus
_Nyctotherus_, perhaps wrongly, or the parasite may have been deformed.
After the patient’s death the same parasite was found in the intestine
and especially in the cæcum.
[Illustration: FIG. 117.--_Nyctotherus giganteus._ (After Krause.)]
[Illustration: FIG. 118.--_Nyctotherus africanus._ (After Castellani.)]
G. Lindner, in Cassel, studied certain peritrichal Infusoria
(stalkless Vorticella), and connected them, probably incorrectly,
with the most varied diseases of man and domestic animals, even
with Sarcosporidia of pigs. It may be mentioned that according to a
communication by letter from Schaudinn, Vorticella may be found in
freshly evacuated fæces, but always only after the administration of
a water enema. In spite of this, several other investigators mention
Vorticellæ as intestinal parasites of man.
The _Chilodon dentatus_ (Ehrenberg) recorded in 1903 by J. Guiart as
a parasite of man, which may be found in all infusions, can hardly
have lived in the man from whose fæces it was cultivated, but may
represent a chance admixture both in the fæces and the cultivations.
_C. uncinatus_ was also found as a chance parasite of man by Manson
and Sambon. According to Doflein[250] (1911) certain Chilodon-like
organisms have been found by Selenew in prostate secretions in
gonorrhœa. Other species of the genus _Chilodon_ are known, but only
as ectoparasites (_e.g._, _Chilodon cyprini_, Moroff, 1902, from the
skin and gills of diseased carp).
[250] _Lehrbuch der Protozoenkunde_, 3rd ed., p. 963.
A number of other parasitic Ciliates are known, among which
_Ichthyophthirius multifiliis_, destructive to fish, is important. It
lives in the skin and the layers immediately below it, forming small
whitish pustules which may become confluent. The pustules are most
common on the head and fins, but occur also on the eyes and gills of
the host. The young parasite, which is one of many formed in a cyst,
is very small. At first it is free swimming, but soon attaches itself
to the skin of a fish. It bores inwards and becomes surrounded by the
irritated skin. There it attains a relatively large size, being 500 µ
to 750 µ and occasionally more in diameter. The body has a rounded
terminal mouth, short cytopharynx and a number of minute contractile
vacuoles. The macronucleus is large and horseshoe-shaped; the small
micronucleus is only seen in the very young animal. When full grown,
the organism encysts and forces its way to the surface and bursts
through, leaving a small, gaping wound behind. The cyst sinks to the
bottom of the water, nuclear multiplication occurs and a number of
young parasites are produced, which leave the cyst and either attack
new hosts or else perish.
_Opalina ranarum_, parasitic in the rectum and urinary bladder of
frogs and toads, shows great degradation and simplification due
to parasitism, possessing no separate micronuclei, no cytostome,
cytopharynx or cytopyge. It has many macronuclei, and is a large
parasite. During summer and autumn nuclear multiplication followed
by division of the body occurs, the process being repeated after the
daughter forms have grown to the size of their parent. In spring, the
Opalina divide rapidly, but do not grow much before dividing again.
Finally, tiny forms, containing three to six nuclei, encyst and pass
from the host with the fæces. As these latter are greedily devoured
by tadpoles, the _Opalina_ gain new hosts in which they develop.
THE CHLAMYDOZOA.
The name Chlamydozoa was proposed by Prowazek in 1907 for a number of
minute, problematic organisms (fig. 119) believed to be the causal
agents of certain diseases in man and animals, such as vaccinia
and variola, trachoma, inclusion blenorrhœa in infants, molluscum
contagiosum, and bird epithelioma contagiosum. Other diseases possibly
due to Chlamydozoa[251] are hydrophobia, measles, scarlet fever,
foot-and-mouth disease, the “Gelbsucht” disease of silkworms, and
perhaps even typhus (Prowazek, 1913). The subject is difficult and
controversial and can only be briefly discussed here. It is known that
the viruses in all these diseases can pass through ordinary bacterial
filters, that is, they belong to the group of “filterable viruses.”
At such periods the organisms are extracellular or free. It is also
known that in many of these cases the virus produces definite and
characteristic reaction-products or cell-inclusions in the infected
cells, during the intracellular phase of the life-history of the
organism. As the organisms to be considered are problematic, it will be
convenient to summarize their history:--
[251] For a detailed account of the Chlamydozoa see Prowazek’s
_Handbuch der Pathogenen Protozoen_, Bd. i (1911–12). Leipzig, J. A.
Barth.
(1) Cell-inclusions, usually named after their discoverers, have been
found in certain diseases, thus: In vaccinia Guarnieri’s bodies, in
scarlet fever Mallory’s bodies, in hydrophobia Negri’s bodies, in
trachoma Prowazek’s bodies occur.
(2) At first these characteristic cell-inclusions were considered to
be actual parasitic organisms causing the diseases in question. The
bodies received zoological names and attempts were made to work out
their supposed development cycles. The supposed parasites of vaccinia
and variola were referred to a so-called genus _Cytoryctes_, those
of hydrophobia to _Neuroryctes_, of scarlet fever to _Cyclasterium_,
while those of molluscum contagiosum were referred to the Coccidia.
Calkins in 1904 studied in detail the cell-inclusions of vaccinia
and small-pox, calling them _Cytoryctes variolæ_, Guarnieri. Calkins
considered that in the stratified cells of the epidermis they passed
through two cycles, the one cytoplasmic, the other intranuclear. The
first is the vaccinia cycle, the second the pathogenic (intranuclear)
variola cycle. It is hardly necessary to follow all Calkins’ stages
here.
Negri (1909) described a cycle for _Neuroryctes hydrophobiæ_. Calkins
refers both _Cytoryctes variolæ_ and _Neuroryctes hydrophobiæ_ to the
Rhizopoda.
Siegel (1905) described quite different organisms under the name
_Cytorhyctes_. He listed several species: _C. vacciniæ_; of vaccinia
and small-pox, _C. scarlatinæ_ of scarlet fever, _C. luis_ of syphilis
(this is probably the granule stage of _Treponema pallidum_), and _C.
aphtharum_ of foot-and-mouth disease.
(3) The afore-mentioned views were criticized, and the bodies were
not considered to be living organisms but merely reaction products or
cell-inclusions due to the effects of the virus on the host cells.
Thus Guarnieri’s bodies were stated to consist of extruded nucleolar
or plastin material, having no developmental cycle. It was further
asserted that infection could be produced by lymph in which Guarnieri’s
bodies had been destroyed. Similar assertions have been made regarding
the Negri bodies, and others. The _Cytoryctes_, _Neuroryctes_, etc.,
are considered, according to these views, to be degeneration products
of the nucleus or to be of a mucoid nature.
(4) More recently a positive belief has gained ground that there
are true parasitic organisms causing these diseases, and that the
parasites are very minute, being termed Chlamydozoa by Prowazek and
Strongyloplasmata by Lipschütz.
The Chlamydozoa are characterized by (_a_) their very minute size,
smaller than any bacteria, so that they can pass through bacterial
filters; (_b_) they pass through intracellular stages, in the cytoplasm
or the nucleus of the host cell, producing therein the reaction
products or inclusions in the cell already recorded as characteristic
or diagnostic of the diseases produced; (_c_) they pass through
definite developmental cycles. Such a cycle consists essentially of
growth and division. The mode of division of the Chlamydozoa resembles
that of the centriole of a cell, by the formation of a dumb-bell-shaped
figure. Two dots are observed connected by a fine line or strand which
becomes drawn out and finally snaps across the middle. Prowazek and
Aragão (1909) working on smallpox in Rio de Janeiro found that the
chlamydozoal granules passed through a Berkefeld filter and that the
filtrate was virulent. But if an “ultra-filter” were used, _i.e._, one
coated with agar, then the granules were retained and the filtrate
was no longer virulent. The surface of the ultra-filter was found to
contain many granules.
The Chlamydozoa are parasites of epiblastic tissues (_e.g._, epidermal
cells, nerve cells, conjunctival cells).
[Illustration: FIG. 119.--Chlamydozoa. Trachoma bodies in infected
epithelial cells of the conjunctiva. (_a_) initial bodies (above) and
cluster of elementary bodies (touching the nucleus); (_b_) cluster
of granules surrounded by mantles. × 2,000 approx. (Original. From
preparation by Fantham.)]
The life-history of a Chlamydozoön (fig. 119), such as that of
vaccinia, is, according to Prowazek, Hartmann and their school, as
follows:--
1. The infection begins with _elementary bodies_ or _elementary
corpuscles_ which live at first extracellularly. An elementary body
is a minute speck of chromatin, apparently devoid of cytoplasm, which
can pass through a bacterial filter. It can enter a host cell, but the
entry is not a process of phagocytosis.
2. Inside the host cell the elementary body grows in size, and becomes
an _initial body_ (fig. 119, _a_).
3. A reaction on the part of the host cell results, for nucleolar,
plastin substance is extruded from the cell-nucleus and surrounds the
parasitic initial body. The latter is thus enveloped in a mantle (hence
the name Chlamydozoa, from χλαμὑς, a mantle), and the characteristic
cell-inclusion (Guarnieri’s body, Negri’s body, etc.) is produced. The
nucleolar, mantle substance probably represents the “cytoplasm” of
_Cytoryctes_, described by Calkins.
4. The body next breaks up into a number of smaller bodies known as
_initial corpuscles_. These, in their turn, divide by simple division
(in the manner already described) into numerous elementary bodies
(fig. 119). Thus, the life-cycle is completed.
The Chlamydozoa are, then, the minute granules inside the body of the
_Cytoryctes variolæ_ or the _Neuroryctes hydrophobiæ_, so that the
whole body of the _Cytoryctes_ or _Neuroryctes_ corresponds to the
mantle and parasite of the Chlamydozoön. The Cytoryctes group is said
to cause destruction of the host cell. The Cytoöikon group (_e.g._,
trachoma bodies) causes proliferation of the host cell.
In September, 1913, Noguchi[252] described the cultivation of the
parasite of rabies in an artificial medium, similar to that used by
him for the cultivation of _Spirochæta recurrentis_. The cultures were
stated to be infective to dogs, rabbits and guinea-pigs. Levaditi, in
December, 1913, stated that he had succeeded in cultivating spinal
ganglia of rabid monkeys in monkey plasma.
[252] _Journ. Exptl. Med._, xviii, p. 314.
Noguchi and Cohen (November, 1913)[253] have succeeded in cultivating
the so-called trachoma bodies, or at any rate bodies very closely
resembling them morphologically. The medium employed was Noguchi’s
ascitic fluid and rabbit kidney medium, as used for spirochætes. The
coarser cultural forms stained blue with Giemsa’s solution, the finer
ones stained red. Attempts to infect monkeys from the culture tubes
failed.
[253] _Idem_, p. 572.
From their behaviour on treatment with such reagents as saponin, bile
and sodium taurocholate, Prowazek considers that the Chlamydozoa
approach the Protozoa.
* * * * *
PROTOZOA INCERTÆ SEDIS.
*Sergentella hominis*, Brumpt, 1910.
Et. and Ed. Sergent in 1908 found vermiform bodies about 40 µ long by
1 µ to 1·5 µ broad in the blood of an Algerian suffering from nausea
and cold sweats, without other symptoms. The bodies were pointed at
each end, with a somewhat ill-defined nucleus in the middle. Their
systematic position is doubtful.
-----------------------------------------------------------------
|NOTE.--An Appendix on Protozoology will be found on pp. 733–752. |
|This has been prepared in order to incorporate a number of new |
|additions to knowledge made since the body of the book was |
|printed off. |
-----------------------------------------------------------------
B. *PLATYHELMINTHES*, or Flat Worms.
BY
J. W. W. STEPHENS, M.D., B.C., D.P.H.
DEFINITION: Bilaterally symmetrical animals without limbs, the form
of which is leaf or tape-like, rarely cylindrical, and whose primary
body cavity (segmentation cavity) is absent, the cavity being filled
by a mesenchymatous tissue (parenchyma).
The mouth is either situated at the anterior end of the body, or is
shifted more or less backwards on to the flat ventral surface. The
alimentary canal consists of a short fore-gut, which is frequently
provided with a muscular pharynx, and of a simple forked or branched
mid-gut; there is neither a hind-gut nor an anus; in one class, the
Cestodes, the alimentary canal has entirely disappeared except for
muscular remnants in the scolex.
The INTEGUMENT OF THE BODY consists either of a ciliated epithelium
of only one layer (Turbellaria), or of a cuticle and gland-like
cells embedded in the parenchyma, or subcuticular layer (Cestodes,
Trematodes). The dermo-muscular layer consists of annular,
longitudinal, and even diagonal fibres, while the parenchyma is
traversed by dorso-ventral fibres.
The central NERVOUS SYSTEM, which is embedded in the parenchyma of
the body, consists of cerebral ganglia, united together in the shape
of dumb-bells, and of two or more longitudinal MEDULLARY FASCICLES,
often forming transverse anastomoses. Organs of sense usually occur
only in the free-living species, more rarely during the free-living
stages of a few parasitic species and in a few ectoparasitic forms.
[In Platyhelminthes simple eye-spots frequently occur, and in a few
an auditory vesicle.]
BLOOD-VESSELS and definite RESPIRATORY ORGANS are lacking [except
in _Nemertinea_]; the EXCRETORY APPARATUS (formerly termed
water-vascular system) is typical of the entire class. It commences
in the interstices of the parenchyma, with peculiar terminal cells
(ciliated funnels), which will be described later (p. 219), the
capillary processes of which go on uniting into larger branches,
and finally form two large collecting vessels, which, sometimes
separately and sometimes united, open to the exterior through one,
two, or numerous pores.
Nearly all the Platyhelminthes are HERMAPHRODITIC, and in nearly all
there are, in addition to the ovaries producing ova, other glands
attached to the female genital apparatus, namely, the vitellaria or
yolk glands, which provide a substance termed yolk, which serves
as nourishment for the embryo. The fully formed eggs have shells
and are “compound,” _i.e._, composed of the egg or ovarian cell,
which is surrounded by numerous yolk cells or their products of
disintegration. The two sexual openings usually lie close together,
frequently in the fundus of a genital atrium; they are rarely
separated from one another. Shell glands also usually occur (p. 221).
Reproduction is sexual, often, however, combined with asexual methods
of propagation (segmentation, budding). The Platyhelminthes live
partly free in fresh or salt water, exceptionally also on land. The
greater part, however, live as parasites on or in animals.
CLASSIFICATION OF THE PLATYHELMINTHES.
_Class I._--*Turbellaria* (or Eddy Worms). Flat worms for the most
part, free living, and always covered with a ciliated epithelium.
_Order 1._--_Rhabdocœlida_, gut unbranched.
_Order 2._--_Tricladida_, gut with three main branches.
_Order 3._--_Polycladida_, a central gut with lateral cæca.
Development direct or through metamorphosis. They live in fresh and
salt water or on land; very seldom as parasites.
_Class II._--*Trematoda* (Sucking Worms[254]). [Usually known as
Flukes.--F. V. T.] Flat worms, living as ecto- or endoparasites, that
are only ciliated in the larval condition, and in their adult state
are covered with a cuticle, the matrix cells of which lie in the
parenchyma. They have either one, a few, or several suckers,[255] and
frequently also possess chitinous fixation and adhesive organs. The
intestine is single, but generally bifurcated, and not uncommonly there
are transverse anastomoses between the forks or diverticula on them.
Excretory organs double, with two orifices at the anterior extremity
or a single one at the posterior end. Development takes place by a
metamorphosis or alternation of generations (p. 283). These worms are
almost always hermaphroditic, with two or more female and one male
sexual orifice. They live, almost without exception, as parasites on
vertebrate animals, but the intermediate generations are passed in
molluscs.
[254] This grouping goes back to the year 1800, and was made by
J. G. H. Zeder, a physician and helminthologist of Forchheim, who
divided the helminths, which until 1851 were generally regarded as
a special class of animals, into the groups of round, hook, sucker,
tape and bladder worms, as which they are recognized up to the present
time. In 1809, K. A. Rudolphi gave them the names _Nematodes_,
_Acanthocephali_, _Trematodes_, _Cestodes_ and _Cystici_.
[255] A sucker or acetabulum (little cup) is a round, cup-shaped
muscular organ, the muscles of which are _sharply defined_ from those
of the body.
_Class III._--*Cestoda* (Tapeworms). Endoparasitic flat worms without
an alimentary canal. The larval stages are rarely ciliated, but are
usually provided with six spines; the adult worm is covered with a
cuticle, the matrix cells of which are embedded in the parenchyma. The
body consists of a single segment (Cestodaria) or a chain of segments,
in which case it consists of the scolex and the segments containing
the sexual organs (proglottides) (Cestodes s. str.). The scolex is
provided with various adhesive and fixation organs, and there are
calcareous corpuscles in the parenchyma. Excretory organs symmetrical,
opening at the posterior end. These worms are always hermaphroditic,
and then possess one or two female and one male sexual orifice. During
development a larval intermediate stage (“measle”) occurs and almost
always in a different host to that in which the adult sexual worm
lives. The adult stage is parasitic in vertebrate animals; but the
larval stage may occur in invertebrates.
Class II. *TREMATODA*, Rud.
These worms are usually leaf- or tongue-shaped, but also barrel-shaped
or conical; they vary from 0·1 mm. to almost 1 m.[256] in length; most
of them, however, are small (5 mm. to 15 mm.). The surface on which
the orifice of the uterus and the male sexual opening are situated is
termed the ventral surface; the oral aperture, which also acts as anus,
is always at the anterior end in the sub-order _Prostomata_ (p. 230),
but in the sub-order _Gasterostomata_ it is ventral.
[256] _Nematobothrium filarina_, van Bened., on the branchial chamber
of the Tunny.
Suckers are always present and occur in varying numbers and positions
at the anterior extremities as well as on the ventral surface, and
occasionally on the lateral margin and on the dorsum; the beginning
of the intestine (mouth) is always surrounded by a sucker in the
_Prostomata_.
In or near the suckers there may be chitinous hooks, claws or claspers,
or the surface of the body is more or less covered with spines, scales
or prickles; in one genus (_Rhopalias_) there are projectile tentacles
beset with spines on the sides of the anterior part of the body.
The body of adult Trematodes is covered by a homogeneous layer of
varying thickness, which either lies directly over the external layer
(basement membrane) of the parenchyma, or over the muscles embedded
in the parenchyma. This investing membrane (cuticle) arises from
pear-shaped or spindle-shaped cells arranged singly or in groups (which
lie between or internal to the diagonal muscles), and is connected with
them by processes; these cells one may regard as epithelial cells which
have sunk down, or possibly as parenchymatous cells. An epithelium of
one layer is also found on the body of young stages, but it disappears
during growth, and only occasionally do its nuclei persist until adult
life. In its place we then find the cuticle, which, moreover, extends
into all the body openings more or less deeply.
It is thus a debatable point whether the “investing layer” of flukes
is a cuticle--that is, consists of modified epithelial cells--or
whether it is a basement membrane, _i.e._, compressed and modified
connective tissue cells; in this latter case the true epidermis and
cuticle have been cast off. In the former case the epidermal cells are
the pear-shaped cells referred to above. According to recent authors
it consists of two parts, an outer true cuticle and an inner basement
membrane. There are also unicellular cuticular glands, lying isolated
or in groups, which are termed cephalic, abdominal, or dorsal glands
according to the position of their orifice.
The PARENCHYMA is a connective substance, the structure of which is
still a matter of dispute. It consists, according to some authors, of
multipolar cells, the offshoots from which anastomose with each other
so that a network, permeating the entire body and encompassing all the
organs, is produced. There exists also, as part of it, a homogeneous
matrix, in the form of lamellæ and trabeculæ that border small cavities
communicating with each other and filled with fluid. According to
other authors, the parenchyma of the Trematodes consisted originally
of cells, of which, however, only the cell membranes remain, while
the protoplasm has been liquefied except for small residua around
the nucleus. Between these cells an intercellular mass has appeared.
By partial absorption of the walls, adjoining spaces unite, and the
originally flat cell walls become transformed into trabeculæ. According
to this view the cavities filled with fluid are _intra_-cellular,
according to the former view _inter_-cellular. Pigment cells occur only
in a few species.
The MUSCULAR SYSTEM of the Trematodes is composed of (1) a
dermo-muscular tube, (2) the dorso-ventral or parenchymal muscles, (3)
the suckers, and (4) the special muscles of certain organs.
The dermo-muscular tube, which lies fairly close to the cuticle,
consists of annular, diagonal, and longitudinal fibres which surround
the entire body in one or several layers, and as a rule are more
strongly developed on the ventral surface as well as in the anterior
part of the body. The MUSCLES OF THE PARENCHYMA are found chiefly in
the lateral parts of the body and pass through the parenchyma in a
dorso-ventral direction; their diverging brush-like ends are inserted
on the inner surface of the cuticle (fig. 120).
[Illustration: FIG. 120.--Half of a transverse section through
_Fasciola hepatica_, L. 25/1. _Cu._, Cuticle with scales; under the
cuticle are circular muscles, and adjoining them the longitudinal
and diagonal muscles; internal to the latter are the matrix cells of
the cuticle; _I._, gut; the other similarly contoured cavities are
gut diverticula that have been transversely or obliquely sectioned;
_F.v.s._, vitellaria; _Ex.v._, excretory vessels; _T._, testes; _Md._,
median plane; the fibres passing from the ventral to the dorsal surface
are the muscles of the parenchyma. The parenchyma itself is omitted.]
The suckers are specially differentiated parts of the dermo-muscular
tube. Their concave inner surface is lined by the continuation of the
cuticle and their convex external surface is covered by a more dense
tissue that frequently takes the form of a refractive membrane, thus
separating them from the parenchymal muscles.
The principal mass of the suckers consists of muscular fibres which
run in three directions--equatorial, meridional and radial. The
equatorial fibres correspond to the annular muscles, the meridional
fibres to the longitudinal muscles, and the radial fibres to the
muscles of the parenchyma; the radial fibres are always the most
strongly developed. The function of these muscles is evident from
their position; the meridional fibres flatten the suctorial disc and
diminish the depth of its cavity, so that the internal surface may
adhere to the object to be held; if the equatorial fibres now contract,
the sucker rises by elongating longitudinally, and its inner surface
is drawn in by the contraction of the radial muscles. Thus the sucking
disc becomes adherent. Usually also there is a sphincter at the border
of the suckers, which plays its part during the act of adhesion by
constricting in a circular manner that part of the mucous membrane to
which it is attached. The loosening of the fixed sucker is effected
by relaxation chiefly of the radial fibres, by the contraction of the
meridional fibres and certain bundles of muscles situated at the base
and at the periphery of the suckers. The connective and elastic tissues
between the muscles of the suckers probably also take part in the
process.
[Illustration: FIG. 121.--_Harmostomum leptostomum_, Olss., an immature
specimen from _Helix hortensis_. _Nervous system_, according to
Bettendorf. _A.s._, ventral sucker; _C.g._, cerebral ganglion; _Ex.p._,
excretory pore; _G.p._, genital pore; _O.s._, oral sucker; _M.d._,
dorsal medullary nerve; _M.l._, lateral medullary nerve; _N.ph._,
pharyngeal nerve; _M.v._, ventral medullary nerve. Magnified.]
Of the muscles of the organs which have developed from the parenchyma
muscles we may briefly mention those bundles that are attached to
certain parts of the genital apparatus, to the suckers, to the hooks
and claws, and also, at all events in _Fasciola hepatica_, to the
spines. The sheaths used for the projection of the tentacles of the
_Rhopaliadæ_ are also muscular.
The contractile elements consist of fibres of various lengths that are
mostly parallel to one another, and frequently anastomose; a cortical
substance finely fibrillated can usually be distinguished from an
internal homogeneous mass; large nucleated cells of uniform size are
always connected with them; these have been variously interpreted,
but have been proved to be myoblasts, one or more of their processes
constituting the muscular fibres.
The MOVEMENTS of the Trematodes consist in alterations of form and
position of the body, as well as in creeping movements.
In the NERVOUS SYSTEM (fig. 121) can be distinguished a cerebral
portion as well as strands (medullary strands) running from it, and
peripheral nerves. The cerebral portion always consists of two large
ganglia situated in the anterior end of the body which pass dorsally
over the œsophagus and are connected by means of a broad and thick
commissure composed of fibres only. From each ganglion three nerves
run anteriorly--the inner and dorsal nerve for supplying the anterior
dorsal part of the body; the median and ventral for the oral sucker;
and the exterior and lateral likewise for the supply of the sucker.
In a similar manner three strands run backwards from each ganglion--one
dorsal, one lateral and one ventral. The dorsal and ventral strands
become united and curve backwards; the symmetrical lateral strands
are connected by means of transverse commissures, the number of which
vary according to the species. Such commissures also exist between the
lateral and the two other strands on each side. There are ganglion
cells along the entire course of the posterior cords, more particularly
at the points of origin of the commissures. There also appears to be in
addition a fourth anterior and posterior pair of nerves, the front pair
for the oral sucker and the hind pair for the pharynx.
The peripheral nerves, which spring from the posterior strands as well
as from the commissures, either pass directly to the muscular fibres or
to the sensory cells that are situated at the level of the subcuticular
cells, or they reach these after the formation of a plexus situated
immediately beneath the dermo-muscular layer; the processes directed
outwards terminate in small vesicles in the cuticle.
As to other ORGANS OF SENSE, simple eyes, two or four in number, are
known in several ectoparasitic species as well as in a few free-living
larval stages (Cercariæ) of endoparasitic forms. In the adult stage,
however, they usually undergo complete atrophy.
The ALIMENTARY CANAL commences with an oral aperture, generally
terminal or sub-terminal (ventral) at the anterior extremity, which
leads into an oral cavity usually surrounded by a sucker; the
œsophagus, of various lengths, is directed backwards and is generally
surrounded by a muscular pharynx (fig. 122). In some cases there exists
between the sucker and pharynx, pharyngeal pouches (præpharynx). Sooner
or later the intestine divides into two lateral branches directed
backwards, both of which end blindly (cæca) at the same level.[257]
In many ectoparasites (_Monogenea_ [p. 222]) a connection exists
between the genital glands and one of the intestinal branches (ductus
vitello-intestinalis [fig. 123]).
[257] The following conditions represent deviations from this type: (1)
In _Gasterostomum_ the oral aperture is situated in the middle of the
ventral surface, and occasionally is even nearer to the posterior than
to the anterior end. There is no proper oral sucker, but the pharynx is
thus termed. (2) A few genera, such as _Gasterostomum_, _Aspidogaster_,
_Diplozoon_, etc., have only _one_ intestinal diverticulum, which is
undoubtedly to be taken as representing the primitive condition, as
it is also often found in the young stages of the _Trematoda_. (3)
The branches of the intestines are curved and united behind (several
_Tristomidæ_ and _Monostomidæ_), while in _Polystomum integerrimum_
(in the bladder of frogs) there are several commissures between the
intestinal branches, and in the _Schistosomidæ_ the united intestinal
branches proceed as one channel towards the posterior end. (4) The
termination of the two intestinal branches is not always on a level;
they are therefore of different lengths. (5) When the œsophagus is
very long the intestinal branches extend both forward and backward, so
that the gut exhibits the form of an *H*. (6) In the broad and flat
species the gut-forks form diverticula mostly externally but also
internally; these again may branch (fig. 139). (7) In a few cases
(_Nematobothrium_, _Didymozoon_) the intestine completely disappears up
to the pharynx.
The oral cavity, pharyngeal pouches, pharynx, and œsophagus are
lined with a continuation of the cuticle of the body; the gut cæca
are lined with tall cylindrical epithelium (fig. 120). The œsophagus
and intestinal branches often have also one layer of annular and
longitudinal muscles; the pharynx has essentially the structure of a
sucker (fig. 122).
[Illustration: FIG. 122.--Median section through the anterior part of
_Fasciola hepatica_: the oral sucker, pharyngeal pouches, pharynx,
œsophagus, cuticle with spines, and the body parenchyma.]
The accessory organs of the alimentary canal consist of groups of
unicellular SALIVARY GLANDS that discharge into the œsophagus in front
of or behind the pharynx, or even into the pharynx itself.
The food of the Trematodes consists of mucus, epithelial cells, the
intestinal contents of the hosts, and often also of blood, and this
not only in those species living in the vascular system, but also in
species living as ectoparasites or in the intestine or biliary passages
of their hosts.
[Illustration: FIG. 123.--_Polystomum integerrimum_, a monogenetic
fluke from the urinary bladder of the frog. _i._, intestine; _h._,
large hooks of the sucking disc; _h.k._, smaller hooklets; _l.c.v._,
longitudinal vitelline ducts; _o._, oral orifice; _Oot._, oötype;
_ov._, ovary; _s.p._, suckers of the disc; _tr.c.v._, transverse
vitelline ducts; _Ut._, uterus with ova; _v._, entrance to the vagina;
_v.d.e._, vas deferens; _v.d.i._, ductus vitello-intestinalis; the
vitellaria and testes are not shown. Magnified. (After Zeller.)]
[Illustration: FIG. 124.--_Allocreadium isoporum_, Looss. Excretory
apparatus. Of the other organs, the oral sucker, pharynx, genital pore,
ventral sucker, ovary and testes are shown; the cylindrical excretory
bladder is in the posterior end. 38/1. (After Looss.)]
The final products of assimilation dissolved in the fluids of the body
are distributed throughout the parenchyma and are thence expelled
by a definite tubular system (excretory apparatus, proto-nephridia,
formerly also termed the water-vascular system). This system, which is
distributed throughout the entire body (fig. 124), is symmetrically
developed, and, in the ectoparasitic Trematodes, it opens, right and
left, at the anterior end on the dorsal surface; in all other flukes,
however, it opens singly into the excretory pore (foramen caudale) at
the centre of the posterior border; in those cases, however, where a
sucker is present at the posterior end, as in the Amphistomata, the
excretory pore is situated on the dorsal surface close in front of the
sucker.
The EXCRETORY SYSTEM[258] consists of several parts: (1) of the more or
less numerous terminal “flame” cells or funnel cells (figs. 124, 125);
(2) of the capillaries ending in them; (3) of larger vessels receiving
the capillaries; and (4) of the excretory bladder. Terminal cells and
capillaries may be compared to unicellular glands with long excretory
ducts; the cellular body (fig. 125) is comparatively large, stretched
longitudinally, more rarely transversely, and provided with numerous
processes, that are lost in the parenchyma; within is a conical cavity
(analogous to the secretory cavity of unicellular glands) which is
continued directly into the structureless capillary; at its blind end
is a bunch of cilia projecting into the cavity, and which, during life,
shows a flickering motion (ciliary flame). The nucleus is situated in
the protoplasm of the terminal cell at its blind end.
[258] The following description relates in the main to the _Distomata_.
The entire apparatus thus begins blindly--_i.e._, within the terminal
cells, to which must be ascribed the capacity of taking up from the
fluid that permeates the parenchyma the products which are first
collected into their own cavities and thence excreted by means of the
capillaries and vessels.
[Illustration: FIG. 125.--Terminal flame cell of the excretory system.
_n._, nucleus of cell; _c._, bundle of cilia forming the “flame”; _p._,
processes of cell extending into parenchyma; _d._, excretory capillary.
(Stephens.)]
The vessels possess definite walls, consisting of a membrane and a
nucleated protoplasmic layer. They unite at many points on either side,
and again pass into other canals (COLLECTING TUBES), which finally,
travelling towards the posterior end, discharge into the excretory
bladder (fig. 124).
The form and size of the bladder vary much according to the different
species, but it always possesses its own flattened epithelium,
surrounded by circular and longitudinal muscles, the circular muscles
forming a sphincter around the opening. Frequently also the structure
of the bladder extends to the tubules discharging into it, which
therefore are not to be regarded as separate “vessels,” but rather
as tubular diverticula of the bladder, directed anteriorly. In some
few species the diverticula also branch and the branches anastomose,
so that a network of tubules ensues which receives the vessels or
capillaries. In such cases there are also ciliary tracts in the tubules.
The contents of the entire apparatus usually consist of a clear or
sometimes reddish fluid; in some species there are larger or smaller
granules, and occasionally also concretions occur.
[Illustration: FIG. 126.--Diagram of female genitalia. _Ov._, ovary;
_ovd._, oviduct; _L.c._, Laurer’s canal; _Rec. sem._, receptaculum
seminis; _Vit. R._, vitellarian reservoir; _t.v.d._, transverse
vitelline duct; _Oo._, oötype; _Sh. gl._, shell gland; _Rec. ut._,
receptaculum uterinum; _ut._, uterus. (The various parts are not to the
same scale.) (Stephens.)]
[Illustration: FIG. 127.--Diagram of male and part of female genitalia.
_ut._, uterus; _vag._, vagina; ♀, opening of vagina; _g.s._, genital
sinus; _g.p._, genital pore; ♂, opening of ejaculatory duct or vas
deferens; _c.s._, cirrus sac; _c._, cirrus; _p.p._, pars prostatica;
_s.v._, seminal vesicle; _e.j._, ejaculatory duct or vas deferens;
_v.e._, vas efferens; _t._, testis. (Stephens.)]
_Sexual Organs._--Nearly all the Trematodes are hermaphrodites,
and only a few (_Schistosomidæ_, _Koellikeria_) are sexually
differentiated. The sexual organs usually lie in the “central field”
limited by the gut cæca; the vitellaria, on the other hand, are, as a
rule, external to the gut cæca in the “lateral fields.”
The male apparatus[259] is composed of two variously formed testes
(fig. 127) (globular, oval, indented, lobed, or ramified), which may
lie side by side or one behind the other; from each testicle a tube
(vas efferens) originates; sooner or later, both tubes as a rule unite
to form the ejaculatory duct or vas deferens, which is frequently
enclosed in a muscular CIRRUS SAC, or more rarely passes directly into
the genital pore. The cirrus, which is the thick muscular terminal
portion of the vas deferens, can be everted and protruded from the
cirrus sac and serves as an organ of copulation. The walls of the
muscular portion of the tube (the cirrus) are attached to the walls of
the cirrus sac, and hence when the sac contracts the cirrus cannot be
protruded except by evagination of its lumen. Opening into the middle
portion of the vas deferens, and as a rule enclosed in the cirrus
sac, is found a mass of unicellular glands (prostate), the vesicula
seminalis (which is likewise within, or may also be outside the sac)
being the dilated first portion of the vas.
[259] The following description relates mainly to the _Distomata_.
The female genitalia (fig. 126) consist of an ovary, usually situated
in front of the testes, the form of which varies according to the
species, the usually double vitellaria, the ducts and a number of
auxiliary organs; the short oviduct directed towards the centre
arises from the ovary, and is connected in the median line with the
excretory duct of the vitelline glands. These grape-like glands possess
longitudinal excretory ducts, which assume a transverse direction
behind the ovary, unite together at the median line and form a single
duct, often dilated into a vitelline receptacle, that unites with
the oviduct. Near this point, moreover, there frequently opens a
canal (Laurer’s canal) which begins on the dorsal surface, and on the
inner end of which a vesicle filled with sperm (receptaculum seminis)
usually occurs (fig. 126). Moreover, there are also numerous radial
unicellular glands (shell glands) at or beyond the point of junction
of the oviduct, vitelline ducts and Laurer’s canal. In this portion
of the duct (oötype), which is usually dilated, the ovarian cells are
fertilized, surrounded with yolk cells and shell material, and as
ova with shells they pass into the uterus (a direct continuation of
the oviduct), which, with its many convolutions, occupies a larger
or smaller portion of the central field, and runs either direct to
the genital pore or, forming convolutions, first runs posteriorly and
then bends forward (descending and ascending limbs). In both cases
the terminal part lies beside the cirrus pouch and discharges beside
the male orifice either on the surface of the body or into a genital
atrium. The terminal portion of the uterus, which is often of a
particular structure, serves as a vagina (METRATERM).
The cirrus sac may include (1) the genital atrium (_i.e._, the common
sinus, into which the vas deferens and vagina may open), or (2) a
variable extent of the vas from cirrus to seminal vesicle. Thus the
latter may be outside the sac. In the absence of a sac, the genital
sinus may be surrounded by a pseudo-sucker, as in _Heterophyes_ (in
some cases the ventral sucker itself, from its close proximity to the
genital pore, serves as an accessory copulatory organ). In other cases
copulatory organs are formed by hooks projecting into the lumen of the
terminal portion of the vas.
The GENITAL PORE, which is the opening from the genital sinus on to
the surface, is generally situated at or near to the median line on
the ventral surface and in the anterior region of the body; in most of
the _Distomata_ it is in front of the ventral sucker, in other cases,
_e.g._, in the _Cryptocotylinæ_, it is behind.[260]
[260] The typical position of the genitalia is subject to many
deviations, which are of importance in the differentiation of the
genera and families. The following are some few of these deviations:
(1) The genital pore remains on the ventral surface, but is situated
beside or behind the ventral sucker, or it becomes marginal, and is
then found in front of or beside the oral sucker, or at a lateral edge,
or, finally, in the centre of the posterior border; the ducts also
correspondingly alter their direction. (2) The ovary usually lies in
front of the testes, not rarely, however, behind them or between them.
(3) The three genital glands mostly lie together close in front of, or
behind, the centre of the body; they may be moved far back, and may
incidentally become separated one from the other. (4) The vitellarium
may be single, in which case it then may lie in the central field.
(5) A few forms possess but one, others several or numerous testes.
Amongst the ectoparasitic trematodes there are also species with but
one testis; but they mostly have several. As a rule, their uterus is
short, but the oötype well developed. Special canals (vagina), single
or double, are used for copulation, not the uterus. The vitelline
ducts also communicate with the intestine through the canalis
vitello-intestinalis (fig. 123).
The spermatozoa do not differ essentially in their structure from those
of other animals; the ovarian or egg cells are cells without integument
and contain a large nucleus and a little protoplasm; the vitellaria
also produce nucleated cells, in the plasm of which there are numerous
yellow yolk granules; the yolk cells detach themselves, like the
ovarian cells, from the ovarium, and pass into the oviduct to surround
each ovarian cell in the oötype. They disintegrate sooner or later in
the completely formed egg and are utilized as food by the developing
embryo.
DEVELOPMENT OF THE TREMATODES.
(1) _Copulation._--Observation has demonstrated that the one or
two vaginæ occurring in the ectoparasitic Trematodes are utilized
as female organs of copulation, and that the copulation is cross;
it is also known that Laurer’s canal, which was formerly generally
regarded as the vagina, has only quite exceptionally, if at all,
served the digenetic Trematodes as such--it appears to be homologous
with the canalis vitello-intestinalis of the _Monogenea_[261]--but
the terminal portion of the uterus, termed the metraterm, is used
for copulation. Cross-copulation occurs as well as auto-copulation
and auto-fecundation. The spermatozoa subsequently pass through the
entire uterus, which is still quite short at the time the male organs
are matured; the maturation of which, as usually is the case in
hermaphrodites, precedes that of the female organs. It is only later
with the onset of egg formation that the uterus is fully developed.
Copulation, however, takes place also in the case of fully grown forms
with completely developed uteri.
[261] _Monogenea_: Trematoda in which the anterior sucker, if present,
is double. Development without an intermediate host.
[Illustration: FIG. 128.--Ovum of _Fasciola hepatica_, L., cut
longitudinally. The lid has been lifted in the process. Within the
egg are numerous yolk cells, and at the lid end there is the still
unsegmented ovum (dark). 240/1.]
[Illustration: FIG. 129.--Miracidium of _Fasciola hepatica_ that
has just hatched from the egg, with a distinct cuticular ciliated
epithelium. Magnified. (From Leuckart.)]
(2) _Formation of the Ova._--The ovarian cells arising from the
ovary first become mature after their entry into the oötype by the
formation of three polar bodies, fertilization then taking place. At
the same time as the ovarian cell a number of yolk cells from the
vitellarium and secretion, drop by drop, from the shell gland reach
the oötype.[262] The shell is then formed during the generally active
contractions of the oötype walls and then passes on into the uterus.
In the uterus of the endoparasitic trematodes the eggs accumulate more
and more, often in large quantities, while in ectoparasitic species
generally only one or some few eggs can be found. The completed ova
are of various forms and sizes. They are mostly oval, at all events in
the digenetic trematodes, and the yellowish or brown shell is provided
with an opening at one pole which is closed by a watch-glass-shaped
lid (operculum). Appendages (filaments) on the shell--at one or both
poles--are uncommon, but are the rule in the ova of the _Monogenea_
(ectoparasitic species).
[262] [Recent work (_e.g._, Goldschmidt, _Zool. Anzeiger_, xxxiv,
p. 482) has shown that the older views regarding the formation of
the egg must be modified. In certain species, at any rate, the shell
material is formed by the yellow droplets of the yolk glands and not
by the so-called shell gland (Mehli’s gland) secretion, which is clear
and watery. The function of this secretion accordingly still requires
explanation; according to Looss it serves as a covering secretion for
the egg-shell proper. It appears also that other granules, the yolk
granules as distinct from the shell drop granules, are not always used
up during the development of the embryo and hence do not function as
yolk, so these also when they exist, and frequently they are wanting,
must serve some other purpose, possibly that of imbibing water for the
use of the embryo.--J. W. W. S.]
(3) _Deposition of the Ova._--Soon after their formation, the
_Monogenea_ (ectoparasitic trematodes) deposit round the place of
their attachment on the skin or the gills or other organs of their
hosts, eggs which attach themselves by means of their filaments. The
embryonic development thus takes place outside the parent. This also
holds good for the eggs of many endoparasitic species, although as a
rule in these the eggs are always retained for a longer time in the
uterus. Moreover, they usually here undergo a part or a whole of their
development, and are eventually deposited in those organs in which the
adult forms are parasitic, but this is not always the case, as the egg,
_e.g._, of _F. hepatica_ appears in bile (and fæces) quite unchanged.
By the natural passages they eventually get out of the body, and in
cases where such do not exist, as in the case of the blood-vessels, the
eggs pass out by means of the kidneys.
(4) _The embryonic development_, after irregular segmentation of the
ovum into a number of blastomeres, leads to the formation of a solid
blastosphere or morula, which is surrounded by a cellular investing
membrane (yolk envelope), while the principal mass of the cells forms
the embryo, which uses for its nourishment the yolk cells, which have
in the meantime disintegrated (_cf._ footnote, p. 223). Usually,
after the ova have reached water the embryos hatch out, leaving the
yolk envelope in the egg-shell; in other cases, however, the embryos
only hatch out after having been subjected to the influence of the
intestinal juices, that is to say, in the intestine of an intermediate
host which has ingested with its food the ova that have escaped from
the primary host.
(5) _The post-embryonic development_ of the Trematodes is accomplished
in various ways; the process is the most simple in the ectoparasitic
species (_Monogenea_), the young of which should certainly be
regarded as larvæ, because they possess characteristics (cilia,
simple gut, etc.) that are lacking in the adult worms, but which,
nevertheless, pass into the adult state direct after a relatively
simple metamorphosis. In the _Holostomata_,[263] a group found chiefly
in the intestine of aquatic birds, and which rarely occur in other
vertebrates, the ova develop in water. The young are ciliated all over,
and, after having entered an intermediate host (leeches, molluscs,
arthropods, amphibians, fishes) living in the water, they undergo a
metamorphosis into a second larval stage; they then encyst and await
transmission into the final host, where they become adult Metastatic
trematodes, _i.e._, trematodes without asexually produced generations
(p. 229).
[263] _Holostomata_: Prostomata with (in addition to the oral and
ventral suckers) a third fixation apparatus, generally on a separate
part of the body.
In the remaining so-called digenetic trematodes (p. 230) one or two
asexual generations interpose between the miracidium and terminal
stage, so that quite a number of adult worms may originate from one
egg. Usually the young, which are termed MIRACIDIA[264] (fig. 129),
hatch in water, where they move with the aid of their cilia. Sooner
or later they penetrate into an intermediate host, which is always a
snail or a mussel, and while certain of their organs disappear, they
grow into a gutless germinal tube (SPOROCYST, fig. 131). These are
simple elongated sacs with a central body cavity. They may or may
not have excretory tubules. In these, according to the species, the
larval stages (CERCARIÆ) that will ultimately become adult worms are
produced, or another intermediate generation is first formed, _viz._,
that of the REDIÆ[265] (figs. 132, 133), which are always provided with
an intestine, and these then give rise to cercariæ (figs. 130, 134).
The cercariæ, as a rule, leave their host and move about in the water
with the assistance of their rudder-like tails. After a little time,
however, they usually again invade an aquatic animal (worms, molluscs,
arthropods, fishes, amphibians), then they lose their tails and become
encysted (fig. 135); here they wait until they attain, together with
their host, the suitable terminal host, and in this new situation they
establish themselves and reach maturity. Or, again, the cercariæ may
themselves encyst in water or on foreign bodies (plants) and wait until
they are taken up directly by the terminal host, _e.g._, sheep.
[264] [Also known as ciliated embryos.--F. V. T.]
[265] [In _Fasciola hepatica_ in the summer months the rediæ give rise
to daughter rediæ, which then give rise to cercariæ.--J. W. W. S.]
[Illustration: FIG. 130.--A group of cercariæ of Echinostoma sp. (from
fresh water). 25/1.]
Accordingly the following conditions are necessary for the completion
of the entire development: (1) The terminal host in which the adult
stage lives; (2) an intermediate host into which the miracidia
penetrate and in which they become sporocysts; (3) a second
intermediate host in which the cercariæ become encysted. In certain
species, as in _Fasciola hepatica_, this second host is omitted, as the
cercariæ spontaneously encyst on plants, or again (in other species)
encystment may occur within the first intermediate host, when, in
fact, the cercariæ (which in this case do not acquire an oar-like tail)
do not swarm out of, but encyst themselves within their sporocysts. The
development, moreover, may be further complicated by rediæ appearing
in addition to the sporocysts, though this occurs in the first
intermediate host and not in a second one.
Animals that harbour adult digenetic Trematodes thus become infected by
ingesting encysted cercariæ, which either occur (1) in certain animals
(second intermediate hosts) on which they feed, or (2) in water, or
(3) on plants, or finally (4) in the first intermediate host; whereas
animals harbouring encysted cercariæ have been directly infected by
the corresponding tailed stage, and animals harbouring germinal tubes
(sporocysts or rediæ) have been infected by the miracidia.
[Illustration: FIG. 131.--Development of _Fasciola hepatica_, L. _a_,
the miracidium in optical section showing cephalic lobe, X-shaped
eye-spot resting on the cerebral ganglion, two germ balls; below each
of these a flame cell, and still lower germ cells lying in a cavity
(primitive body cavity). _b_, young sporocyst with two eye-spots, and
germ balls; the cells lining the cavity are not shown. _c_, older
sporocyst with a young redia. Magnified. (After Leuckart.)]
Thus certain species of ducks and geese become infected with
_Echinostoma echinatum_ by devouring certain water-snails (_Limnæus_,
_Paludina_) in which the encysted cercariæ occur. Oxen become infected
with _Paramphistomum cervi_ (= _Amphistomum conicum_) by swallowing
with water, cysts of this species which occur at the bottom of puddles
and pits. Sheep are infected with _Fasciola hepatica_ by eating grass
to which the encysted cercariæ of the liver-fluke are attached;
our song-birds infect themselves or their young with _Urogonimus
macrostomus_ by tearing off pieces containing the corresponding
sporocysts which are full of encysted cercariæ from snails (_Succinea
amphibia_), which act as the first intermediate hosts, and eating, or
offering their young these pieces.
(1) The MIRACIDIA of the digenetic Trematodes are comparatively highly
organized, and the mode of their formation from the segmentation cells
of the ovum is only imperfectly known. They have a cuticular epithelium
(fig. 129) entirely or partly covered with cilia, beneath this a
dermo-muscular tube composed of circular and longitudinal muscles;
also, a simple gut sac with an œsophagus, occasionally also with
pharynx, salivary glands and boring spine, also a cerebral ganglion
on which, in some species, there are eyes (fig. 131, _a_). As to the
excretory organs, they are represented by two symmetrically placed
terminal flame cells, with excretory vessels opening separately; there
is a more or less ample (primary) body cavity between the parietes of
the body and the gut; from the cellular parietal lining of this cavity
single cells (germ cells) become free (fig. 131, _a_, _b_), and become
rediæ or cercariæ.
[The germ cells of the miracidium and the germ balls of the
sporocyst arise, according to some observers, by further division of
undifferentiated blastomeres; according to others from the cells of the
lining wall of its body cavity. It is from these free germ balls that
the redia stage is developed.
[In the germ ball or morula appears an invagination, giving rise to
the cup-shaped gastrula stage. This elongates and forms the REDIA
(fig. 131, _c_).
[In the interior of the redia cells are budded off and develop into
gastrulæ, as in the case of the sporocyst. These become a fresh
generation of rediæ or give rise to the third stage (CERCARIA).]
[Illustration: FIG. 132.--Young redia of _Fasciola hepatica_, with
pharynx and intestine, with a circular ridge anteriorly and a pair of
processes posteriorly and masses of cells (germ balls) in the interior.
Magnified. (From Leuckart.)]
[Illustration: FIG. 133.--Older redia of _Distoma echinatum_, with
rudimentary intestine _i._; cercariæ, _c._; germ balls, _b._; and birth
pore, _g._ Magnified.]
(2) The SPOROCYSTS, on the contrary, which are produced direct from the
miracidia, are very simple, as all the organs of the latter disappear,
even to the muscles and excretory organs, during or after penetration
into the intermediate host, whereas the budded and still budding cells
of the wall of the (primary) body cavity continue to develop rapidly
and form germ balls. The sporocysts when fully developed have the
appearance of tubes or fusiform bodies with rounded edge; they are
frequently of a yellow colour. Their length rarely exceeds a few
millimetres; in some species their size increases exceedingly through
proliferation, and they then occupy a large portion of the body of the
intermediate host.
(3) The REDIÆ (figs. 132, 133), on the other hand, are more cylindrical
and always have a simple intestine of varying length, provided with
a pharynx; they likewise possess, situated near the circular ridge,
a “birth pore” which serves for the exit of the cercariæ originating
within them.
[Illustration: FIG. 134.--Cercaria of _Fasciola hepatica_; the
cutaneous glands at the side of the anterior body. Magnified. (After
Leuckart.)]
[Illustration: FIG. 135.--Encysted cercaria of _Fasciola hepatica_.
Magnified. (After Leuckart.)]
(4) The CERCARIÆ[266] are very different; typically they consist of the
anterior body and the oar-like tail at the posterior end (fig. 134).
The former, even to the genitalia, has the organization of the adult
digenetic Trematodes, and thus allows the easy recognition of at least
the characters of that large group to which the species in question
belongs. On the other hand, however, there are also organs that are
lacking in the adult form, such as, in many, the boring spine in the
oral sucker, or the eyes situated on the cerebral ganglion; moreover,
also, cutaneous glands (fig. 134), the secretion of which forms the
cyst membrane. The oar-like tail may be long or short (stumpy-tailed
cercaria) or entirely absent; its free end may be partly split (furcate
cercaria), or split to its base (_bucephalus_); in various forms also
the anterior end of the tail is hollow, and has enclosed within it the
anterior body, which is otherwise free. The size also of the cercaria
belonging to the different species is very diverse; in addition
to forms swimming in the water that have the appearance of minute
milky-white bodies, there are forms which measure as much as 6 mm. in
length.
[266] The cercaria is the characteristic larval stage of the
Trematodes, and corresponds to a cysticercus or cysticercoid, though
there is the important difference that the cercaria has an enteric
cavity. According to some observers the enteron is represented by the
frontal sucker of some Cestodes, and by the rostellum of the majority
of others.
The sporocyst and redia are regarded as intercalated stages, _viz._,
as cercariæ exhibiting _pædogenesis_, _i.e._, development of young by
a parthenogenetic process from individuals (_i.e._, cercariæ) not yet
adult.
The encysted cercariæ (fig. 135) are globular or oval, and are
surrounded by a homogeneous membrane, which may be striated or contain
granules. The tail is always cast off when encystment occurs, and
organs peculiar to the cercaria stage (boring papilla, eyes) almost
entirely disappear. On the other hand, the genitalia appear or become
more or less highly developed, in extreme cases to such an extent that
they become functional, and after autocopulation the creatures produce
ova within the cysts.
The cycle of development of the digenetic Trematodes has hitherto
been generally explained as a typical ALTERNATION OF GENERATIONS, one
sexual generation regularly alternating with one or two asexually
reproducing generations. Recent authors, however, regard the cells
in the sporocysts from which rediæ or eventually cercariæ arise as
parthenogenetically developing ova, and the sporocysts as well as the
rediæ as generations propagating parthenogenetically. In this case,
however, it is an alternation of a sexual not with an asexual but with
firstly a parthenogenetic generation (the sporocyst), the central cells
of which are regarded as ova which develop parthenogenetically into the
redia, and this the second parthenogenetic generation finally produces
larvæ (cercariæ) capable of developing into the sexually mature form.
Other authors, again, regard the development of the Digenea as only a
complicated metamorphosis (p. 283), which is distributed over several
generations before it is concluded.
BIOLOGY.
Endoparasitic Trematodes, as fully developed organisms, occur in
vertebrate animals only, with very few exceptions; they inhabit almost
all the organs (with the exception of the nervous and osseous systems
and the male genitalia), but by preference the intestine in all its
extent from the oral cavity to the anus; and, further, certain species
or groups inhabit only quite restricted parts of the intestine.
Besides in the intestine other species live in the liver, or in the
bile-ducts, or in the gall-bladder; other accessory organs of the
intestine, such as the pancreas, bursa Fabricii (of birds), are only
infected by a few species. Many inhabit the lungs, or the air sacs in
fowls, a few the trachea. Trematodes have also been known to occur in
the urinary bladder, the urethra and the kidneys of all classes of
vertebrates; they are also present in the vascular system of a few
tortoises, birds and mammals; in birds they even penetrate from the
cloaca into the oviducts, and are occasionally found enclosed in the
laid eggs; one species is known to occur in the cavum tympani and in
the Eustachian tube of a mammal (Dugong), another in the frontal sinus
of the polecat; several species infest the conjunctival sac under the
membrana nictitans of birds, one species even lives in cysts in the
skin of song-birds. In an analogous manner the ectoparasitic Trematodes
are not entirely confined to the surface of the body or the trachea
of the lower vertebrate animals; a few species appear exclusively in
the urinary bladder, in the œsophagus, and in the case of sharks in an
accessory gland of the rectum.
Trematodes live free and active within the organs attacked, though they
may attach themselves by suction for a longer or shorter period; in
other cases, however, they bore more or less deeply into the intestinal
wall with their anterior end, or lie in cysts of the intestinal wall
which only communicate with the lumen through a small opening; in those
species living in the lungs of mammals the host likewise produces a
cyst, which usually encloses two specimens; such association of a pair
is also observed in other situations, and, though this is the rule in
species sexually distinct, it is not entirely confined to these.
As regards the AGE attained by endoparasitic Trematodes, there are but
few reliable records, and these differ considerably; the overwhelming
majority of species certainly live about a year, or perhaps a little
longer, but there are some whose term of life extends to several or
many years.
Trematodes are but rarely found encysted in the higher vertebrate
animals; the condition, however, is more frequent in amphibians, and
especially in fishes, as well as in numerous invertebrate animals.
CLASSIFICATION OF THE TREMATODES OF MAN.
The following classification, partly artificial, partly natural,
embraces only the flukes found in man:--
Order. *Digenea*, v. Beneden, 1858.
Anterior sucker single and median, present. Eggs few. The
(specialized) terminal portion of the uterus serves as a vagina.
Development indirect, _i.e._, an intermediate host is required.
Sub-order. *Prostomata*, Odhner, 1905.
Mouth surrounded by the anterior sucker.
Group. *Amphistomata*, Rudolphi, 1801, ep., Nitzsch, 1819.
Gut forked, two suckers, the posterior sucker (acetabulum) terminal
or ventro-terminal behind the genitalia, or at most embraced by the
vitellaria. Skin with no spines. Excretory bladder a simple sac
opening dorsally near hind end. Testes in front of ovary. Genital
pore, median in anterior third of body. Thick flukes, almost circular
in cross section.
Family. *Paramphistomidæ*, Fischoeder, 1901.
Amphistomata: Body not divided into a conical anterior portion and
disc-like caudal portion. Ventral pouch absent.
Sub-family. *Paramphistominæ*, Fisch., 1901.
Paramphistomidæ: Oral sucker without evaginations. Not in man.
Sub-family. *Cladorchiinæ*, Fisch., 1901.
Paramphistomidæ: Oral sucker with evaginations; testes, two, deeply
cleft (fig. 137). Genera: _Watsonius_, _Cladorchis_, etc.
Family. *Gastrodisciidæ*, Stiles and Goldberger, 1910.
Amphistomata: With body divided into a conical cephalic and disc-like
caudal portion (fig. 138). Posterior sucker ventro-terminal. Oral
sucker with evaginations. Genera: _Gastrodiscus_ and _Homalogaster_.
Group. *Distomata*, Retzius, 1782.
Gut forked, two suckers, the posterior sucker (acetabulum) ventral.
It is always separated from the hind end by at least a part of the
genitalia.
Family. *Fasciolidæ*, Railliet, 1895.
Large flat forms, genital pore _in front_ of ventral sucker, the
latter powerful. Vitellariæ of numerous follicles, united by
branching vitellarian ducts, at the sides of the body meeting
posteriorly and extending ventrally and dorsally. Cirrus and vagina
without spines. No crown of strong spines around sucker. Testes much
branched. Uterus not well developed. Excretory bladder much branched.
Eggs large.
Sub-family. *Fasciolinæ*, Odhner, 1910.
Large or median forms, gut much branched. Body has a shoulder
separating head from body. Receptaculum seminis absent. Ovary
branched, ventral sucker in anterior part of body. Genus: _Fasciola_.
Sub-family. *Fasciolopsinæ*, Odhner, 1910.
Shoulder absent. Receptaculum seminis present. Ovary branched, gut
takes a zig-zag course with kinks on it, ventral sucker in anterior
part of body. Genus: _Fasciolopsis_.
Family. *Opisthorchiidæ*, Braun, 1901, emend. auctor.
Ovary in front of testes. Small to medium flukes, very transparent,
tapering anteriorly. Vitellaria moderately developed not extending
in front of sucker. Cirrus absent. Seminal vesicle a twisted tube
free in parenchyma. Testes near hind end one behind the other, lobed
or branched, but not dendritically. Excretory bladder *Y*-shaped,
the two limbs short, the stem *S*-shaped passing between the testes.
Receptaculum seminis well developed. Laurer’s canal present. Uterine
coils transverse, numerous. Eggs small.
Sub-family. *Opisthorchiinæ*, Looss, 1899, emend. auctor.
_Opisthorchiidæ_ in which the excretory pore is terminal. Excretory
bladder long, dorsal to testes. Uterine coils not overlapping gut
forks. Genera: _Opisthorchis_, _Paropisthorchis_, _Clonorchis_,
_Amphimerus_, etc.
Sub-family. *Metorchiinæ*, Lühe, 1909.
_Opisthorchiidæ_ in which the excretory pore is ventral. Excretory
bladder short, ventral to testes. Uterine coils partly overlapping
gut forks and extend anteriorly beyond the sucker. Vitellaria
compressed on the sides of the body. Genus: _Metorchis_.
Family. *Dicrocœliidæ*, Odhner, 1910.
Ovary _behind_ testes. Testes behind the ventral sucker, between it
and the ovary. Body thin and transparent. Cirrus sac encloses the
pars prostatica and seminal vesicle. Skin smooth. Gut forks do not
reach posterior end. Receptaculum seminis and Laurer’s canal present.
Vitellaria, moderate, lateral in mid-body slightly overlapping the
gut. Uterus with an ascending and descending branch and numerous
transverse coils extending to hind end. Eggs dark brown, 25 µ to
60 µ. Excretory bladder tubular in posterior third or half of body.
Parasitic in bile-ducts of mammals and birds. Genus: _Dicrocœlium_.
Family. *Heterophyiidæ*, Odhner, 1914.
Ovary _in front_ of testes. Genital pore _behind_ or on a level with
ventral sucker. Genital pore surrounded by a pseudo-sucker (_i.e._,
its muscle is not sharply separated from but blends with the body
muscles). Cirrus sac absent, consequently vesicula seminalis and pars
prostatica lie free. Vagina and ejaculatory duct unite into a common
duct before opening. Small and very small forms. Body covered with
scales. Genera: _Heterophyes_, _Metagonimus_, etc.
Family. *Troglotremidæ*, Odhner, 1914.
More or less flattened Distomes of compact form, 2 to 13 mm. long.
Ventral surface flat or somewhat hollowed, dorsal surface _arched_.
Skin completely covered with pointed spines. Musculature weakly
developed also in the suckers in those forms that inhabit cysts. Gut
with pharynx and a not very long œsophagus and cæca, which end more
or less shortly before the hind end. Excretory bladder *Y*-shaped or
tubular. Pars prostatica and seminal vesicle always distinct. Testes
elongated, symmetrically placed in or behind the middle of the body.
Ovary directly in front of the testes, right-sided, generally much
lobed. Receptaculum seminis and Laurer’s canal present. Vitellaria
generally well developed, exclusively or for the most part confined
to _the dorsal surface_, leaving only a median band unoccupied.
Uterus either very long, coiling here and there, or shorter and more
convoluted. Eggs in first case small 17 µ to 25 µ, in the second much
larger 63 µ to 85 µ or even 120 µ (?) long. Parasitic in carnivora or
birds, generally occurring in pairs in cyst-like cavities. Genera:
_Paragonimus_, _Pholeter_, _Collyriclum_, _Troglotrema_.
Family. *Echinostomidæ*, Looss, 1902.
_More or less elongated flukes, small or very large, much flattened
anteriorly, less so posteriorly, or even round. Suckers near one
another, the anterior small and weak, the posterior large and
powerful directed obliquely backwards. Surrounding the oral sucker
dorsally and laterally but not ventrally is a fold or “collar”
bearing a row or rows of pointed spines which are continued round
laterally on to the ventral corners, the number being constant
for each species, the corner spines large or specialized, skin
anteriorly scaled or spiny. Alimentary canal consists of a pharynx,
epithelial “pseudo-œsophagus” and gut cæca reaching to posterior
end. Testes behind one another in hind body. Ovary on right side
or median directly in front of the testes. Vitellaria lateral,
usually extending to the hind end and not beyond the ventral sucker
anteriorly. Genital pore just in front of ventral sucker. Uterus
in transverse loops. Genital sinus absent or present. Receptaculum
seminis and Laurer’s canal present. Eggs thin shelled and large,
bright yellow, 65 µ to 120 µ long. Excretory bladder *Y*-shaped.
Parasitic in gut of vertebrates, especially birds._
Sub-family. *Echinostominæ*, Looss, 1899.
_Cirrus sac usually reaching to centre of ventral sucker, but not
beyond. Cirrus long, usually without spines, coiled when retracted.
Seminal vesicle tubular, twisted. On the head a ventral uniting ridge
between the angles of the collar. Dorsal circlet of spines, single or
double, not interrupted unless the collar itself is dorsally divided.
Genera_: Echinostoma, etc.
Sub-family. *Himasthlinæ*, Odhner, 1910.
Cirrus sac reaching far beyond ventral sucker. Cirrus armed with
strong rose-thorn-shaped hooks. Vesicula seminalis tubular not
coiled. Cervical collar not continued across ventral aspect. Spines
on collar in one row. Body armed with fine needle-shaped spines.
Family. *Schistosomidæ*, Looss, 1899.
Sexes separate. Genital pore behind the ventral sucker. Ventral
sucker elevated above the surface. Pharynx absent. Gut forks reunite
to form a single stem. In ♂ four or more testicular follicles. In ♀ a
single ovary, just in front of the union of the gut forks. Vitellaria
on either side of the united gut stem.
THE TREMATODES OBSERVED IN MAN.
Family. *Paramphistomidæ*, Stiles and Goldberger, emend. 1910.
Sub-family. *Cladorchiinæ*, Fisch., 1901.
Genus. *Watsonius*, Stiles and Goldberger, 1910.
_Cladorchinæ_.--Body pyriform. Ventral pouch absent. Acetabulum
ventral or (?) ventro-subterminal, very large, margins projecting,
aperture small. Genital pore in front of bifurcation of gut, not
surrounded by a sucker; ductus hermaphroditicus apparently absent.
Excretory pore at posterior end of excretory vesicle, behind Laurer’s
canal. Oral sucker with a pair of irregularly globular suctorial
pouches; œsophagus thickened distally; cæca long, not wavy; end in
acetabular region.
_Male Organs_.--Testes two lobed, smaller than acetabulum;
longitudinally, nearly or quite coinciding; transversely they abut or
slightly overlap; preovarial in equatorial and caudal thirds. Pars
musculosa not largely developed; cirrus pouch absent.
_Female Organs_.--Ovary and shell gland post-testicular. Vitellaria
extend from gut fork to slightly beyond gut ending; uterus
intercæcal, partly post-testicular. Laurer’s canal in front of
excretory vesicle.
_Type Species_.--_Watsonius watsoni_, Conyngham, 1904.
*Watsonius watsoni*, Stiles and Goldberger, 1910.
Syn.: _Amphistomum watsoni_, Conyngham, 1904; _Cladorchis watsoni_,
Shipley, 1905.
_Body_, 8 to 10 mm. long, by 4 to 5 mm. broad, by 4 mm. thick; tapers
anteriorly to 2·5 mm. Caudal extremity bluntly rounded, venter
surrounded by an elevated ridge, surface with transverse ridges best
defined ventrally. Genital pore median about one-quarter of body length
from anterior end at level of suctorial pouches. Acetabulum 1 mm. in
diameter, margin projecting, aperture small. Mouth in a groove with
digitate papillæ. Oral sucker very large, one-fifth of length of body,
with a pair of irregularly globular pouches. Œsophagus somewhat longer
than sucker. Excretory pore at the level of the acetabular aperture.
The vesicle extends from the plane of the transverse vitelline ducts to
centre of acetabulum.
[Illustration: FIG. 136.--_Watsonius watsoni_: ventral view. 4/1.
(After Shipley.)]
_Male Organs_.--Testes deeply notched adjoining one another. Vesicula
seminalis much coiled and dilated, pars musculosa not coiled. Pars
prostatica (?) dilated, ejaculatory duct long and narrow, opening on a
papilla; genital atrium papillated.
_Female Organs._--Ovary dorso-posterior of posterior testis. Shell
gland dorsal to ovary. Vitellaria ventral and lateral to gut cæca
extending from gut fork to equator of acetabulum. Uterus dorsal to
testes, ductus hermaphroditicus absent. Laurer’s canal opens in
dorso-median line slightly behind anterior border of sucker.
[Illustration: FIG. 137.--_Watsonius watsoni_: ventral projection
composed from a series of transverse sections. _o.s._, oral sucker;
_s.p._, suctorial pouch; _ga._, genital atrium; _d.e._, ejaculatory
duct; _es._, œsophagus; _e.g._, œsophageal ganglion; _p.p._, pars
prostatica; _p.m._, pars musculosa; _i._, gut; _ut._, uterus; _v.e._,
vas efferens; _v.e.s._, left vas efferens; _v.e.d._, right vas
efferens; _v.g._, vitellarium; _t._, testes; _ov._, ovary; _s.g._,
shell gland; _t.vd._, transverse vitelline duct. (After Stiles and
Goldberger.)]
_Eggs._--123 µ to 133 µ long by 75 µ to 80 µ broad.
_Habitat._--Jejunum and duodenum of man, German West Africa. The
parasite has only been found once in man. The patient, a negro from
German West Africa, died at Zola, Northern Nigeria. The symptoms were
persistent watery diarrhœa without blood or mucus. The parasites were
also passed in the stools. It occurs also in monkeys.
Family. *Gastrodisciidæ*.
Genus. *Gastrodiscus*, Lkt., 1877.
Acetabulum small, caudal and ventral margin raised, aperture
relatively large. Genital pore without sucker. Excretory pore
post-vesicular, posterior to opening of Laurer’s canal. Œsophagus
with muscular thickening; cæca not wavy, long, end post-equatorial
and post-testicular.
_Male Genitalia._--Testes two, branched pre-ovarial.
_Female genitalia._--Ovary and shell gland post-testicular.
Vitellaria extracæcal; uterus intercæcal; Laurer’s canal entirely
prevesicular.
_Type._--_Gastrodiscus ægyptiacus_, Cobbold, 1876.
*Gastrodiscus hominis*, Lewis and McConnell, 1876.[267]
Syn.: _Amphistomum hominis_, Lew. and McConn.
[267] Leiper places this species in a new genus _Gastrodiscoides_.
Genus _Gastrodiscoides_, Leiper, 1913, distinguished from
_Gastrodiscus_ by: (1) large genital cone; (2) position of genital
orifice; (3) disc without papillæ; (4) testes one behind the other.
[Illustration: FIG. 138.--_Gastrodiscus hominis._ Slightly magnified.
(After Lerckart.)]
_Body_, reddish in the fresh, 5 to 8 mm. long; posteriorly, 3 to 4 mm.
broad. The disc has incurved edges which are interrupted in front where
it joins the anterior cylindrical portion and posteriorly behind the
ventral sucker. The disc itself and ventral surface are covered with a
number of (microscopic) papillæ. Pharynx provided with two diverticula
or pouches. The bifurcation of the gut lies sometimes above, sometimes
below the level of the genital pore. The gut cæca end about the level
of the centre of the acetabulum.
_Genital Pore._--About the middle of the conical anterior portion. (It
appears to be surrounded by a muscular sucker.) Leiper (1913) describes
the ducts as discharging at the tip of a large fleshy papilla, the
surface of which bears cuticular bosses.
_Testes_ much lobed, the anterior is smaller than the posterior and
lies at about the level where the anterior conical portion joins the
disc. The posterior testis just in front of the anterior margin of the
acetabulum separated from it by the ovary. The ovary, somewhat oval in
shape or slightly constricted in the middle, lies slightly to the right
of the median line. Dorsal to it lies the well-developed shell gland,
Laurer’s canal opening in front of the excretory bladder. The excretory
bladder is a long sac with its opening at its posterior extremity
about the level of the middle of the acetabulum. The vitellaria are
restricted in extent. They do not extend forward beyond the anterior
border of the posterior testis. They are best developed in the area
between the acetabulum and the termination of the gut cæca.
The eggs are oval and measure 150 µ in length by 72 µ in breadth.
_Habitat._--Cæcum and large intestine of man. Also in the pig (5 per
cent.) in Annam.
_Distribution._--This parasite has been recorded from Assam (not
uncommon), British Guiana (Indian immigrants), and Cochin China.
_Gastrodiscus ægyptiacus_, Cobbold, 1876, and _G. secundus_, Looss,
1907, occur in the horse; _G. minor_, Leiper, 1913, in the pig in
Nigeria and Uganda.
Family. *Fasciolidæ*, Raill., 1895.
Sub-family. *Fasciolinæ*, Odhner, 1910.
Genus. *Fasciola*, L., 1758.
The ventral sucker is situated at the level of the junction of the
cone with the body, _viz._, at the level of the “shoulder,” and is
large and powerful. The cuticle is covered with strong spines; the
gut cæca run in the mid-line to the hind end, and are provided with
numerous long lateral and fewer and shorter median branches. The
ovary lies on one side in front of the transverse vitelline duct;
the testes lie obliquely one behind the other. The uterus, in the
shape of a rosette, lies in front of the genitalia. Laurer’s canal
is present; the vesicula seminalis lies in the cirrus pouch; the ova
are large, not very numerous, and only develop after they have been
deposited. Parasites of the biliary ducts of herbivorous animals.
*Fasciola hepatica*, L., 1758.
Syn.: _Distomum hepaticum_, Retz., 1786; _Fasciola Humana_, Gmel.,
1789; _Distomum caviæ_, Sons., 1890; _Cladocœlium hepaticum_, Stoss.,
1892.
Length 20 to 30 mm., breadth 8 to 13 mm., cephalic cone 4 to 5 mm.
in length and sharply differentiated from the body by a shoulder on
each side. Spines in alternating transverse rows and extending on
the ventral surface to the posterior border of the testes, and on
the dorsal surface not quite so far. The spines are smaller on the
cephalic cone than on the posterior part of the body, where they are
discernible with the naked eye. The suckers are hemispherical, and
near each other; the oral sucker is about 1 mm. and the ventral sucker
about 1·6 mm. in diameter. The pharynx, which includes almost the
entire œsophagus, measures 0·7 mm. in length and 0·4 mm. in breadth.
The intestine bifurcates at the limit of the cephalic cone and the
branches are even here furnished with diverticula directed outwardly.
The ovary is ramified and situated in front of the transverse vitelline
duct, usually on the right side; the shell gland lies near the ovary
in the median line; posterior to the transverse vitelline ducts are
the greatly ramified testes, which occupy the greater portion of the
posterior part of the body, with the exception of the lateral and
posterior border; the long vasa efferentia only unite as they enter the
cirrus pouch. The vitellaria occupy the sides of the posterior part of
the body, commencing at the level of the ventral sucker and uniting
behind the testes. The ova are yellowish-brown, oval, operculated,
130 µ to 145 µ in length, 70 µ to 90 µ in breadth (average size 132 µ
by 70 µ).
[Illustration: FIG. 139.--_Fasciola hepatica_, L. From a specimen that
is not yet mature, showing the gut and its branches. 5/1.]
The Liver Fluke inhabits the bile-ducts of numerous herbivorous mammals
(sheep, ox, goat, horse, ass, rabbit,[268] guinea-pig, squirrel,
beaver, deer, roe, antelope, camel, kangaroo, and others), and is
distributed over the whole of Europe, though not to an equal extent. It
is further known in North Africa, in North and South America, as well
as in Australia; it is also found in Asia, as it has been reported from
Japan, China, and Tonkin (Gaide, two cases in man). In some districts
of Germany it is very frequent, and the slaughter-house statistics of
various places show that it is of daily occurrence. _Fasciola magna_
occurs in herbivora in America.
[268] [There does not seem to be any direct evidence of either rabbits
or hares normally being invaded by this fluke.--F. V. T.]
The liver fluke, however, is by no means a harmless parasite, for it
produces in domestic animals, more especially in sheep, a disease of
the liver that appears epidemically in certain years and districts, and
commits great ravages amongst the flocks.
[The following records show the enormous loss caused in sheep by this
parasite. In 1812, in the Midi, principally in the Departments of
the Rhône, Herault, and Gard, the disease was rampant; 300,000 sheep
perished in the Arles territory, and 90,000 in the Arrondissements of
Nîmes and Montpellier. In 1829 and 1830, in the Department of the
Meuse and near localities, not only sheep but oxen died in enormous
numbers; for instance, in the Arrondissement of Verdun out of 50,000
sheep 20,000 died, and out of 20,000 cattle 2,200 died. In England, in
1830, 2,000,000 sheep were carried off; whilst in 1862 60 per cent.
of the sheep died in Ireland; and in 1879 over 300,000 were lost in
England; whilst as late as 1891 one owner in the same country lost over
10,000 sheep (_Live Stock Journal_, October 30, 1891).--F. V. T.]
[Illustration: FIG. 140.--_Fasciola hepatica._ _M._, mouth; _Ut._,
uterine rosette; _Tr.c._, transverse vitelline ducts uniting to form a
vitelline receptacle in the mid-line; _E.d._, longitudinal vitelline
ducts; _V.s._, vitellaria. The clear space in the centre represents the
position of the ramifying testes and part of the gut. Natural size.
(Mull. fluid, alcohol, creosote, Canada balsam.)]
[Illustration: FIG. 141.--_Fasciola hepatica_, L. _I._, intestine;
_Vs._, vitellaria; _Ov._, ovary; _O._, oral aperture; _Ut._, uterus;
_S._, ventral sucker; _T._, testes. In front of the testes are seen
the transverse vitelline ducts uniting to form the pyriform vitelline
receptacle. Immediately in front of this the spherical shell gland. The
two vasa efferentia can also be seen running up in the mid-line. The
branches of the gut are only shown in the cephalic cone. (After Claus.)]
The disease usually commences towards the end of summer with an
enlargement of the liver, induced by the invasion of numerous
young flukes; in the autumn and winter the animals suffer from the
consequences of disordered biliary secretion; they become feverish,
emaciated, and anæmic, and lose their appetite. In consequence of the
consecutive atrophy of the liver, œdema and ascites set in, and many
animals succumb to this “liver rot.” On examination the liver is found
to be shrunken, the bile-ducts are enormously dilated and in parts
saccular and full of flukes. Should the animals survive this stage,
spontaneous recovery ensues in consequence of the flukes commencing to
leave the liver in the spring, but the liver remains changed and its
sale is prohibited[269] when the changes are extensive.[270]
[269] [This is not the case in Great Britain; fluky sheep are sent to
market, there being no danger to man from eating the flesh.--F. V. T.]
[270] As an example, this occurred in Berlin in the case of 19,034
oxen, 15,542 sheep, 1,704 pigs, and 160 calves in the period of
1883–1893; during which time 719,157 oxen, 1,519,003 sheep, 2,258,110
pigs, and 567,964 calves were slaughtered. As a matter of fact,
however, the number of infected beasts was really larger.
[The following stages may be noticed in sheep suffering from
fascioliasis. Gerlach recognized four stages, based on the varied
relations that the flukes contract with the liver of their host. These
periods are sometimes very marked, but at others, owing to subsequent
infections, the features become merged and so obliterated. But when a
single infestation occurs they are very marked.
[The first period is called the PERIOD OF IMMIGRATION. This occurs at
the fall of the year and generally passes unperceived, as the young
flukes do little harm to the liver. It varies from four to thirteen
weeks. Gerlach has remarked upon cases of death from apoplexy at this
period.
[The second period is the PERIOD OF ANÆMIA. This occurs in November
and December. The sheep at first fatten rapidly, but later the mucous
membranes become pale and of a yellowish hue, and the sheep become
sluggish and cease to feed. The fæces are normal, but may contain fluke
ova.
[Illustration: FIG. 142.--_Fasciola hepatica_: egg from liver of sheep.
_o_, operculum, _e_, segmenting ovum. The rest of the space is occupied
by yolk cells, the granules in three only being shown. × 680. (After
Thomas.)]
[Illustration: FIG. 143.--_Limnæus truncatulus_, Müll., the
intermediate host of _Fasciola hepatica_. _a._, natural size; _b._,
magnified. (From Leuckart.)]
[The third period is the PERIOD OF WASTING. This corresponds with the
beginning of January--about three months after the entry of the larvæ.
Emaciation now becomes very marked, the skin and mucous membranes
blanched, temperature variable and marked by an irregular curve;
respiration laboured and quick; appetite regular; abortion frequently
occurs in pregnant ewes; pressure on the back causes the animals to
fall; local œdemas occur, the most perceptible in the submaxillary
space, extending below the larynx and over the cheeks and parotids
(called “bourse,” “boule” in France; “watery poke” or “cockered” in
England). Death usually occurs at this period, but a fourth stage may
occur.
[The fourth period is the PERIOD OF MIGRATION OF THE FLUKES. This
is a period of convalescence and recovery, generally in May and
June.--F. V. T.]
Oxen suffer less in general, but even in these animals “stray” hepatic
flukes are occasionally found in the lungs, enclosed in thick-walled
cysts.
_Pathological Anatomy._--The bile-ducts are conspicuous on the surface
of the liver. They are thickened and much dilated and in parts
saccular, and considerable atrophy of the liver cells accompanies
the condition. Histologically there is immense proliferation of the
epithelium of the bile-ducts leading to “adenomata.”
The LIFE-HISTORY of the liver fluke was discovered by R. Leuckart and
P. Thomas. According to these investigators the elongated miracidium
(fig. 131, _a_) ciliated all over develops from the eggs a few weeks
after the latter (fig. 142) have reached the water, and after it has
become free the embryo penetrates and becomes a sporocyst (fig. 131,
_b_) in a water-snail (_Limnæus truncatulus_, Müll. = _L. minutus_,
Drap.) that is common in fresh water, and can live in the smallest
collection of water as well as in fields that have been flooded. The
sporocyst first of all produces rediæ, which remain in the same host
(and under certain circumstances, _e.g._ in summer, these develop
a second generation of rediæ), and these finally form cercariæ
(fig. 134). The latter become encysted on blades of grass and are taken
up by the respective hosts with their food; this takes place towards
the end of summer, while the sheep feeding on the pasture land in the
spring spread the eggs of the fluke, and sometimes the fluke itself, by
passing them with their fæces.
In districts where _Limnæus truncatulus_ is absent, analogous species
act as the intermediary hosts, of which one example according to Lutz
is _Limnæus oahuensis_ in the Sandwich Islands.
[The host in Europe is _Limnæus truncatulus_. This snail extends from
Siberia to Sicily and Algeria, and according to Captain Hutton is a
native of Afghanistan. It also occurs in Thibet, Amoor, Morocco,
Tunis, Canary Islands and the Faroe Islands. It deposits its eggs or
spawn upon the mud around ponds, ditches and streams. The eggs are laid
in batches of thirty to a hundred, each snail laying as many as 1,500
eggs; they are united into strips of a gelatinous substance. In about
two weeks young snails appear. It is amphibious, being more frequently
met with out of the water than in it. It occurs in elevated spots as
well as in low-lying districts. Moquin-Tandon found it at 4,000 feet
in the Pyrenees. In the allied species, _L. peregra_, the fluke will
develop up to a certain stage, but never completes all its varied
phases.
[In South America the host is probably _Limnæus viator_, Orb., and in
North America _Limnæus humilis_, Say.--F. V. T.]
In human beings as well as in some of the mammals quoted above, the
liver fluke is only a casual parasite, and hitherto only twenty-eight
cases have been observed in man; the infection was mostly a mild one
and there were no symptoms, or only very trifling ones; a few isolated
cases were only discovered _post mortem_. Occasionally, however, even
when the infection was inconsiderable, severe symptoms were set up,
which in isolated cases led to death. The symptoms (enlargement and
painfulness of the liver, icterus) merely pointed to a disease of the
liver.
_Diagnosis_ can only be established by finding eggs in the fæces. Care
should be taken not to confuse them with those of _Dibothriocephalus
latus_.
HALZOUN.
[Illustration: FIG. 144.--Young _Fasciola hepatica_, soon after
entry into the liver. The intestinal cæca have lateral diverticula.
Magnified. (From Leuckart.)]
In North Lebanon, the liver fluke is, according to A. Khouri, a
frequent parasite of man, not in the liver, however, but in the
pharynx. The occurrence in this unusual site is effected by the eating
of raw infected livers, especially those of goats (_Capra hircus_). The
flukes thus taken in do not all reach the stomach, where they would
be soon killed, but some of them attach themselves to the pharyngeal
mucosa and to the adjoining parts, and there cause inflammation and
swelling, which lead to dyspnœa, dysphagia, dysphonia and congestion of
the head, sometimes even to still more severe symptoms, and even death.
The affection termed “Halzoun” lasts some hours or several days, and
after vomiting recovery sets in. In other cases man becomes infected in
the usual way by ingesting cysts attached to grass or the underside of
leaves of plants (_e.g._, Rumex sp.), where they are overlooked from
their scanty size (0·2 to 0·3 mm.).
[Illustration: FIG. 145.--_Fasciola gigantica._ × 6-1/2 (After Looss.)]
As the liver fluke feeds on blood it is possible that it also reaches,
particularly when young, the circulatory system, and cases have been
known in which it has been carried by the blood into organs far
from its original situation. Such cases also have been repeatedly
observed in men. Probably the parasite described by Treutler, 1793, as
_Hexathyridium venarum_, which protruded from the ruptured anterior
tibial vein of a man, was a young liver fluke. A few adult specimens
were found by Duval in the portal and other veins _post mortem_ at
Rennes (1842) in a man, aged 49, and a similar statement is reported
by Vital from Constantine (1874). Giesker, in 1850, found two hepatic
flukes in a swelling on the sole of the foot of a woman. Penn Harris
states that he observed six specimens in Liverpool in a spontaneously
ruptured abscess of the occiput of a two months old infant. Another
case which, like the previous one, is reported by Lankester,[271]
relates to a sailor who suffered from an abscess behind the ear, and
from which a liver fluke was expelled. Finally, Dionis de Carrières
reports the case of a man, aged 35, in whose right hypochondriac region
a tumour the size of a pigeon’s egg had formed, and from which a young
liver fluke was extracted.
[271] In the English translation of Küchenmeister’s work on
Parasitology (London, 1857). The specimen is preserved in the Hunterian
Museum, London, and is an adult liver fluke, measuring 18 mm. in length
and 7 mm. in breadth.
From such records it is not impossible that _Distomum oculi humani_,
Ammon, 1833, as well as _Monostomum lentis_, v. Nordm., 1832, may
have been very young hepatic flukes that had strayed. Ammon found
four specimens (length 0·5 to 1 mm.) of his species (named _Distomum
ophthalmobium_ by Diesing in 1850) between the opaque lens and the
capsule of a five months old child in Dresden, and von Nordmann
discovered his _Monostomum lentis_ to the number of eight specimens
(only 0·3 mm. in length) in the opaque lens of an old woman. Minute
white bodies which Greef found in the cortex of the lens of a
fisherman, aged 55, removed on account of cataract, were with some
reserve regarded as Trematode larvæ. The fact that Ammon found that
the intestinal cæca of the worm discovered by him had no lateral
branches does not negative the above opinion, as in the liver fluke
the intestinal cæca are originally unbranched, and according to Lutz
they only develop lateral ramifications later, between the twelfth and
twenty-second day of infection (fig. 144).
*Fasciola gigantica*, Cobbold, 1856.
Syn.: _Distomum giganteum_, Diesing, 1858; _Fasciola gigantea_,
Cobbold, 1858; _Cladocœlium giganteum_, Stoss., 1892; _Fasciola
hepatica_ var. _angusta_, Raill., 1895; _Fasciola hepatica_ var.
_ægyptiaca_, Looss, 1896.
This species is closely allied to _Fasciola hepatica_, but is
distinguished by its elongated body, short cephalic cone, almost
parallel sides, larger ventral sucker, which is also closer to the oral
sucker, and by its larger eggs. Length up to 75 mm., width up to 12 mm.
Oral sucker 1 to 1·2 mm., ventral sucker up to 1·7 mm. in diameter.
Eggs 150 µ to 190 µ long by 75 µ to 90 µ broad.
_Habitat._--Bile-ducts of _Camelopardalis giraffa_, _Bos taurus_, _Bos
indicus_, _Bos bubalis_, _Ovis aries_ and _Capra hircus_.
_Distribution._--Africa.
This species has once been observed in man by Gouvea, in Rio de
Janeiro, in a French naval officer who became ill with fever, cough
and slight blood-spitting. The lungs were normal except for a sharply
circumscribed spot at the base of the left lung. Twenty days later
during a fit of coughing the patient spat up a fluke 25 mm. long,
characterized by its slender aspect and by the size of its ventral
sucker, and its close proximity to the oral sucker. Considering the
fact that Gouvea’s patient had spent many weeks in July of the same
year in Dakar (Senegambia), where according to Railliet _Fasciola
gigantica_ is common in slaughtered animals, and considering also the
characters of the fluke, Railliet rightly assumes that one had to do
with the African giant fluke and that the patient had infected himself
in Dakar.
Sub-family. *Fasciolopsinæ*, Odhner, 1910.
Genus. *Fasciolopsis*, Looss, 1898.
Ventral sucker large, and elongated posteriorly into a sac. Cirrus
pouch long and cylindrical, its greatest length being occupied by the
sinuous tubular seminal vesicle, on which exists a peculiar cæcal
appendage. Laurer’s canal present.
*Fasciolopsis buski*, Lank., 1857.
Syn.: _Distomum buski_, Lank., 1857; _Dist. crassum_, Cobbold, 1860,
_nec_ v. Sieb., 1836.
[Illustration: FIG. 146.--_Fasciolopsis buski_, Lank. _V.s._,
ventral sucker; _C.p._, cirrus pouch; _I._, intestinal fork; _S.v._,
vitellaria; _T._, testes; _O._, ovary; _Ms._, sucker; _Shg._, shell
gland; _Ut._, uterus. Magnified. (After Odhner.)]
The length of the body varies; it may measure 24 to 37 or even attain
70 mm.; the breadth is from 5·5 to 12 to 14 mm. In the pig the fresh
parasites measure, smallest, 12 to 8 mm.; largest, 35 to 16 mm. (Mathis
and Léger). Skin without spines, but according to Heanly always
present in man and pig specimens. The oral sucker measures 0·5 mm.
in diameter; the ventral sucker is three to four times as large; the
pharynx is globular, 0·7 mm. in diameter; the prepharynx is provided
with a sphincter; the intestinal cæca extend to the posterior border
with two characteristic curves, one at the anterior border of the
anterior testis, the other between the two testes. The genital pore is
at the anterior border of the ventral sucker; the cylindrical cirrus
pouch extends from behind the ventral sucker to half-way to the shell
gland. The seminal vesicle extends forwards within the cirrus pouch
as a convoluted tube. From its anterior portion is given off the
cæcal appendage, which has itself short lateral diverticula. It runs
backwards, ending blindly about 0·5 mm. from the posterior end of the
cirrus sac. The seminal vesicle is continued as the pars prostatica (?)
0·5 mm. long, and this by the very short ejaculatory duct (13 µ), and
finally by the fairly long cirrus, which is beset with very fine spines
except at either extremity. The ovary and shell gland are situated
at about the middle of the body with the testes behind them, and the
uterus in front. The vitellaria extend from the ventral sucker to the
posterior border. The eggs measure 120 µ to 130 µ in length and 77 µ to
80 µ in breadth, and resemble those of Echinochasma sp. in dogs. The
larval stages are said to occur in shrimps.
_Habitat._--Intestine of pig and man.
_Distribution._--In man: India, Siam, China, Assam, Sumatra. It is
common in Cochin China (16 out of 133 Annamites, Noc.), in Tonkin very
rare. Dr. J. Bell has sent me [J. W. W. S.] human specimens from Hong
Kong. In pigs: very common in South China (Heanly). Common in pigs in
Hong Kong. Sixteen out of 248 pigs (_i.e._, 6 per cent.) infected in
Hanoi.
*Fasciolopsis rathouisi*, Ward, 1903.
Syn.: _Distomum rathouisi_, Poirier, 1887.
[Illustration: FIG. 147.--_Fasciolopsis rathouisi_, Poir.: the mouth at
the top, and under it the genital pore and ventral sucker, behind which
again is the uterus. The vitellaria are at the sides, and posteriorly
in the central field the ramified testes; the ovary is in front of the
right testis. (After Claus.)]
Fifteen to 19 mm. long by 8·5 to 10·5 mm. broad by about 3 mm. thick.
Skin with spines (Leiper). Bluntly oval or elliptical with short
cephalic cone which is absent in _Fasciolopsis buski_. Oral sucker
subterminal, 0·25 to 0·29 mm. broad by 0·2 mm. in antero-posterior
diameter. Distant from ventral sucker by about twice its diameter.
Ventral sucker 1·32 to 1·38 mm. broad by 0·68 to 0·7 mm. in
antero-posterior diameter. Œsophagus extremely short. Cirrus sac
not conspicuous and straight as in _Fasciolopsis buski_, but is
convoluted. Testes one behind the other (according to Poirier they
lie beside one another), more compactly branched, broader and denser
than in _Fasciolopsis buski_. Ovary on right side, small, coarsely
branched. Uterus in broad, closely grouped coils, packed with ova
anterior to ovary. Vitellarian acini more numerous and somewhat
differently distributed. Eggs 150 µ by 80 µ, thin shelled. [H. B.
Ward, who has examined this species, and from whose account the
above is mainly taken, considers that it is a good species, although
the differences between it and _Fasciolopsis buski_ are slight,
while Odhner, who examined the original species, is of the opposite
opinion.--J. W. W. S.] The parasite appears to cause diarrhœa, wasting
and occasionally jaundice.
_Habitat._--Intestine of man.
_Distribution._--China, common in some parts (Goddard).
*Fasciolopsis goddardi*, Ward, 1910.
Twenty-one to 22 mm. long, 9 mm. broad. Skin with spines (Leiper).
Uterus very closely coiled, most striking character is the large size
of the vitelline acini. Imperfectly known.
_Distribution._--China (Shanghai).
*Fasciolopsis fülleborni*, Rodenwaldt, 1909.
The fully extended fluke is tongue-shaped, 50 by 14 mm.; two contracted
specimens measured 40 by 15 mm. and 30 by 16 mm. respectively. Skin
without spines, with according to Leiper cephalic cone not clearly
defined. Oral sucker circular, 0·75 mm. in diameter, slightly larger
than that of _Fasciolopsis buski_. Ventral sucker 2·6 mm. in diameter
(that of _Fasciolopsis buski_ 1·6 to 2 mm.). Length 2·9 mm. (as in
_Fasciolopsis rathouisi_), the excess of length over breadth being
due to the posterior elongated sac-like prolongation of the sucker.
Prepharyngeal sphincter present. Pharynx 0·7 mm. in diameter. Œsophagus
practically absent. Gut cæca similar to those of _Fasciolopsis buski_.
_Testes_--regularly branched, separated by an incurving of the cæca,
the anterior occupying a smaller area than the posterior.
_Ovary_--very small, as in _Fasciolopsis buski_, on the right side.
_Shell Gland_--almond-shaped, 2·3 by 1·2 mm. In _Fasciolopsis buski_ it
is round and smaller, 1 to 1·5 mm. in diameter.
_Vitellaria_--similar in distribution to those of _Fasciolopsis buski_,
but the acini are strikingly small.
[Illustration: FIG. 148.--_Fasciolopsis fülleborni_, ventral aspect.
(After Fülleborn.)]
_Cirrus Sac_--is the most characteristic feature of this species. It is
a powerfully built, convoluted sac standing out clearly on the body.
It is not a uniform, straight cylinder 0·25 to 0·33 mm. in diameter, as
in _Fasciolopsis buski_, but even in fully extended flukes is typically
convoluted. It is 1 mm. thick in the middle, but in other parts varies
much from this. The posterior end of the cirrus sac is at two-thirds or
more of the distance from ventral sucker to shell gland. In the case of
_Fasciolopsis buski_ the posterior end of the sac only extends half-way.
_Seminal Vesicle_--has a peculiar convoluted, saccular and angular
course, but the cæcal appendage characteristic of the genus appears to
be absent!
_Excretory System._--The main stem gives off very regular transverse
branches which are well seen posteriorly.
_Eggs._--100 µ by 73 µ. Thin shelled.
_Habitat._--Intestine. Mahommedan from Calcutta.
[It is evident that a re-examination of fresh material is required
before the validity of all these species can be accepted.--J. W. W. S.]
Family. *Troglotremidæ*, Odhner, 1914.
Genus. *Paragonimus*, Braun, 1899.
Body egg-shaped or somewhat elongated, generally more broadly
rounded in front than behind. Covered all over with spear-shaped
spines _arranged in groups_. Gut cæca winding with dilatations
or constrictions in parts. Ventral sucker in or in front of the
middle of the body. Excretory bladder cylindrical, very long and
broad, reaching in front to the bifurcation of the gut. The lateral
excretory canals join the bladder only a little in front of the
excretory pore. Genital pore median just behind the ventral sucker.
Genital sinus duct-like. Cirrus sac absent. Male terminal organs very
small. Ejaculatory duct present. Testes and ovary deeply lobed, the
testes in or just behind the middle, the ovary somewhat laterally
placed just _behind_ the ventral sucker. Uterus forms a coil behind
the ventral sucker. Eggs rather large, thin shelled, the ovarian cell
still unsegmented on deposition. Receptaculum seminis, small.
Parasitic in the lungs of mammals, enclosed in cyst-like cavities,
generally in pairs.
_Type Species._--_P. westermanii_ in the tiger.
*Paragonimus ringeri*, Cobb., 1880.
Syn.: _Distoma ringeri_, Cobb., 1880; _Distoma pulmonale_, Baelz,
1883; _Distoma pulmonis_, Suga, 1883.
The body is of a faint reddish-brown colour and plump oval shape. The
ventral surface a little flattened; 7·5 to 12 mm. in length, 4 to 6 mm.
in breadth, and 3·5 to 5 mm. thick (in man). The oral sucker (0·75 mm.)
is subterminal; the ventral sucker (0·8 mm.) somewhat in front of the
middle of the body. Pharynx spherical, 0·3 mm. in diameter, or 0·4 by
0·3 mm.; œsophagus, 0·02 mm.; intestinal cæca convoluted, asymmetrical,
the first part having the same structure as the œsophagus. The cuticle
is covered with spines in groups; the excretory pore opens at the
posterior end rather on the ventral surface, the excretory ducts open
into the elongated bladder at the hind end near the pore. Genital pore
behind the ventral sucker and median. Genital sinus 0·2 mm. long with
thick wall, ejaculatory duct 0·13 mm., pars prostatica 0·2 mm., seminal
vesicle duct-like of irregular outline. Behind the sucker the ovary
on the left, and the closely packed uterine coil on the right (though
amphitypy of these two organs is common); the two irregularly lobed
testes lie side by side posteriorly. Vitellaria extensive, leaving only
a median dorsal and ventral space free. Seminal receptacle probably
absent; Laurer’s canal present. The eggs are oval, brownish-yellow,
fairly thin shelled, and measure on an average 81·2 µ by 49·2 µ.
[Illustration: FIG. 149.--_Paragonimus ringeri_, Cobb.: to the right,
dorsal aspect; to the left, ventral aspect. Natural size. (After
Katsurada.)]
[Illustration: FIG. 150.--_Paragonimus ringeri_, Cobb.: diagram of
the internal organs. _a_, œsophagus; _b_, vitellaria (a portion only
shown); _c_, common genital duct; _d_, shell gland with oviduct,
Laurer’s canal and vitelline duct; _e_, ovary; _f_, vitelline
receptacle; _g_, excretory pore; _h_, oral sucker; _i_, pharynx; _k_,
gut; _l_, ventral sucker; _m_, uterine coils; _n_, vitellarian ducts;
_o_, vas efferens; _p_, testis. (After Kubo.)]
[Illustration: FIG. 150A.--_Paragonimus westermanii_, Kerb.: seen from
the ventral surface. Mouth, pharynx, intestinal cæca, at the sides
of which the vitellaria are observed. The genital pore is behind the
ventral sucker, and next to it, on the left, the ovary; on the right,
the uterus; the two testes posteriorly; the excretory vessel in the
middle, 10/1. (After Leuckart.)]
The following species are also known:--_P. westermanii_, Kerb., 1878,
in the tiger, and _P. kellicotti_, Ward, 1908, in the pig, dog, and
cat (N. America). Ward and Hirsch give the following differences
between the spines of the three forms:--
_P. ringeri._ _P. westermanii._ _P. kellicotti._
Shape Chisel-shaped, Lancet-shaped, Chisel-shaped,
moderately heavy. very slender. heavy.
Distribution Circular rows, in Circular rows, Circular rows,
groups. in groups. singly.
Two other species, _P. rudis_, Diesing, 1850, in a Brazilian otter
(_Lutra brasiliensis_) and _P. compactus_, Cobbold, 1859, in the Indian
ichneumon, are but little known.
_Habitat._--Lungs, pleuræ, and especially the bronchi of man and
dog. The alleged occurrence (of eggs) in other organs may be due to
confusion with those of _Schistosoma japonicum_.
_Distribution._--China, Korea, and especially in Japan, where,
according to Katsurada, there are no districts that are entirely
free from pulmonary flukes. The _mountainous_ provinces of Okayama,
Kumamoto, Nagano and Tokushima are the principal centres.
[Illustration: FIG. 151.--Egg of _Paragonimus ringeri_, Cobb., from
the sputum. Showing the ovarian cell and vitelline cells and granules.
1,000/1. (After Katsurada.)]
_Pathology._--The number present in the lung varies from two to twenty,
about. Usually one cyst contains one worm, but in the dog each cyst
contains two. The cysts admit the tip of the finger, and have a fibrous
wall 1 mm. thick. They originate partly from dilatation of bronchi and
bronchioles. Others arise from the inflammatory reaction of lung tissue
into which the worms have wandered. The worms and their eggs cause
bronchitis and peribronchitis, catarrhal, hæmorrhagic, or purulent,
and areas of consolidation. Areas containing eggs in their centre
resembling tubercle nodules are not uncommon, and extensive cirrhosis
of the lung may be found. As a result of these changes, emphysema and
bronchiectasis also occur.
As to the development, only the following details are known: that the
eggs, which before segmentation of the ovum reach the open in the
sputum and through being swallowed also in the fæces, develop in water
into a miracidium ciliated all over, which hatches and swims about
freely. According to Manson this takes place in four to six weeks.
Sub-family. *Opisthorchiinæ*, Looss, 1899.
Genus. *Opisthorchis*, R. Blanch., 1845.
Opisthorchiinæ with lobed testes. Laurer’s canal present. Parasitic
in the bile-ducts of mammals and birds.
*Opisthorchis felineus*, Riv., 1885.
Syn.: _Distoma conus_, Gurlt, 1831 (_nec_ Creplin, 1825); _Distoma
lanceolatum_, v. Sieb., 1836, v. Tright, 1889 (_nec_ Mehlis, 1825 =
_Fasciolo lanceolata_, Rud., 1803); _Distoma sibiricum_, Winogr.,
1892; _Distoma tenuicolle_, Mühl., 1896.
This parasite is yellowish-red in the fresh condition, and almost
transparent. The body is flat, with a conical neck at the level of the
ventral sucker marked by a shallow constriction; this, however, is only
noticeable in fresh and somewhat contracted specimens. Posteriorly
to the ventral sucker the lateral borders run fairly parallel; the
posterior end is either pointed or rounded off. The length and breadth
vary according to the contraction, being usually 8 to 11 mm. by 1·5
to 2 mm. The suckers are about one-fifth to one-sixth of the length
of the body distant from each other, and of about equal size (0·23 to
0·25 mm.). The œsophagus is hardly any longer than the pharynx, which
lies close behind the oral sucker; the intestinal cæca reach almost to
the posterior border and are often filled with blood. The excretory
pore is at the posterior extremity, and the excretory bladder forks in
front of the anterior testis. The testes in the posterior fourth of
the body lie obliquely one behind the other; the anterior one has four
lobes, the posterior one five lobes; the ovary is in the median line
transversely, simple or slightly lobed; behind it lies the large pear-
or retort-shaped receptaculum seminis and Laurer’s canal. The uterus
is in the median field. The vitellaria occupy the fairly broad lateral
areas, in about the central third of the body, beginning behind the
ventral sucker and terminating at about the level of the ovary; the
acini are small and arranged in groups of seven to eight, separated by
interstices. The genital pore is close in front of the ventral sucker.
The eggs are oval with sharply defined operculum at the pointed pole,
30 µ, by 11 µ.
This species, which is frequently confused with others, inhabits
the gall-bladder and bile-ducts of the domestic cat especially;
but is also found in the dog, in the fox, and in the glutton
(_Gulo borealis_). It has been observed in France, Holland, North
Germany (being particularly frequent in East Prussia), in Russia,
Scandinavia, Siberia, Japan, Tonkin, Hungary, and Italy. The North
American form (from cats and _Canis latrans_) is a distinct species
(_Opisthorchis pseudofelineus_).
In man this species was first found by Winogradoff in Tomsk (nine
cases), then by Kholodkowsky in a peasant from the neighbourhood of
Petrograd who had travelled a great deal in Siberia, and finally by
Askanazy in five persons who were natives of the East Prussian district
of Heydekrug. In Tomsk, _Opisthorchis felineus_ is the most frequent
parasite of man that comes under observation at _post mortem_ (6·45
per cent.), whereas _Tænia saginata_ has only been found in 3·2 per
cent., Echinococcus in 2·4 per cent., _Ascaris lumbricoides_ in 1·6 per
cent., and _Oxyuris vermicularis_ in 0·8 per cent. of the autopsies.
In the district of Heydekrug, however, the species in question is also
frequent, as in a few years five cases came to our knowledge (of which
three were diagnosed by the discovery of the eggs in the fæces).
[Illustration: FIG. 152.--Egg of _Opisthorchis felineus_, Riv. 830/1.]
[Illustration: FIG. 153.--_Opisthorchis felineus_: from the cat. _m._,
mouth; _p.b._, pharynx; _i._, gut; _g.p._, genital pore; _ac._, ventral
sucker; _ut._, uterus; _v.g._, vitellarium; _ov._, ovary; _s.g._, shell
gland; _r.s._, receptaculum seminis; _t._ testes; _ex. p._, excretory
pore. (After Stiles and Hassall.)]
In none of Winogradoff’s nine cases had the death of the patient been
caused direct by the parasites, yet more or less extensive changes
in the liver were found in all of them; such as dilatation of the
bile-ducts with inflammation and thickening of their walls, and foci
of inflammation or atrophy in the liver substance; icterus was present
five times and atrophy of the liver an equal number of times; ascites
was observed three times, and in two cases, probably of recent date,
the organ was enlarged. The number of parasites found fluctuated
between a few and several hundreds.
In two of Askanazy’s cases, which he examined more closely, carcinoma
which had developed at the places most invaded by flukes was found
at the _post-mortem_, so that perhaps there may be grounds for the
connection which the author seeks to establish between cancer of the
liver and the changes induced by the parasites; these changes consist
of numerous and even ramified proliferations of the epithelium
of the biliary duct into the connective tissue, which is likewise
proliferated. The number of worms found in one case amounted to over
100; in a second case, in which the parasites had also invaded the
pancreatic duct, their number was even larger.
Winogradoff as well as Askanazy found isolated flukes in the intestine
also.
[Illustration: FIG. 154.--_Opisthorchis pseudofelineus_: from the
bile-duct of the cat (Iowa), _m._, oral sucker; _p.b._, pharyngeal
bulb; _es._, œsophagus; _i._, intestine; _va._, vagina; _g.p.m._, male
orifice; _ac._, ventral sucker; _ut._, uterus; _v.g._ vitellarium;
_s.g._, shell gland; _v.dt._, vitelline duct; _ov._, ovary; _r.s._,
receptaculum seminis; _L.c._, Laurer’s canal; _t._, testis; _ex.c._,
excretory bladder; _ex.p._, excretory pore. (After Stiles.)]
Unfortunately, nothing much is known of the history of the development
of _Opisthorchis felineus_; we only know that when deposited the eggs
already contain a ciliated miracidium, which, however, according to my
experience, does not hatch out in water, but only after the entry of
the eggs into the intestine of young _Limnæus stagnalis_; no further
development, however, occurs. Winogradoff states that he has seen the
miracidia hatch after the eggs had been kept in water for a month at
37° C.; and has even observed free miracidia in the bile of man and of
a dog respectively. Although the whole post-embryonal development of
the cat fluke remains yet to be investigated, Askanazy by a series of
experiments on cats and dogs has discovered the mode of infection. The
intermediate hosts are fish, and mainly the ide, in this country called
Tapar (_Idus melanotus_, H. and Kr.), and of subsidiary importance the
roach (_Leuciscus rutilus_). Both species of fish as well as others
are readily eaten raw by man on the Courland lagoon (Baltic). It is,
moreover, significant that those persons whom Askanazy found infected
with the cat fluke were also infected with _Dibothriocephalus latus_,
the intermediate host of which is also fish (Lota sp., Esox sp., Perca
sp.).
In one of his nine cases Winogradoff also saw a small fluke covered
all over with spines, which he conjectured to be the young stage of
_Opisthorchis felineus_; as, however, according to my experience, this
species, even in smaller specimens, is always without spines, the above
hypothesis cannot be accepted. It is much more probable that one of
the other species that also invade the liver of cats may accidentally
be introduced into man; we know, in fact, that _Metorchis albidus_,
Braun, and _Metorchis truncatus_, Rud., are both covered with spines.
As, however, the spines of the first-named species are rather apt to
fall off, and also as it possesses a different shape (spatula-shaped),
it may be assumed that probably Winogradoff had found _Metorchis
truncatus_, Rud., 1819, in his patient.
Genus. *Paropisthorchis*, Stephens, 1912.
Structure as in Opisthorchis, except that the ventral sucker and
genital pore occur on the apex of a process or pedicle projecting
from the anterior portion of the body. This process is about 1/2 mm.
long, and is retractile.
*Paropisthorchis caninus*, Barker, 1912.
Syn.: _Distoma conjunctum_, Lewis and Cunningham, 1872; _Opisthorchis
noverca_, M. Braun, 1903 (_pro parte_); _Opisthorchis caninus_,
Barker, 1912 (?).
Length varies from 2·75 to 5·75 mm. in preserved specimens, average
3·6 to 5·2 mm. Body uniformly spinose, though as a rule spines are not
present on the pedicle. Body slightly concavo-convex, the concavity
being ventral. Oral sucker 0·28 mm. Pharynx 0·224 by 0·184 mm.
Œsophagus 0·04 mm. Ventral sucker 0·176 mm. in diameter. Pedicle about
1/2 mm. long, may be completely retracted.
_Genital Pore_--opens on the apex of the pedicle in front of the
ventral sucker. Its exact position varies with the state of contraction
of the parts. In certain cases it actually opens within the cuticular
border of the sucker, in other cases it opens externally to the sucker
and anterior to it. The opening is covered with scales. The vas
deferens and uterus run alongside one another until they merge near the
apex of the pedicle into a common sinus.
_Vitellaria_--consist of eight acini on each side, extending from
slightly behind the base of the pedicle to the anterior border of the
ovary, or as far back as a line separating the posterior border of the
ovary from the anterior border of the anterior testis.
[Illustration: FIG. 155.--_Paropisthorchis caninus_: from the
bile-ducts of the pariah dog, India. _Acet. v._, ventral sucker; _Ut._,
uterus; _V. ex. lat_., longitudinal excretory duct; _V. sem._, seminal
vesicle; _Sem. rec._, seminal receptacle; _Ov._, ovary; _V. ex._,
excretory bladder; _Test. l._, left testis; _Test. r._, right testis;
_P. ex._, excretory pore. × 40. (After Stephens.)]
_Testes._--Anterior testis 0·496 by 0·44 mm.; posterior testis 0·52
by 0·48 mm., usually ovoid, though both may be regularly lobed. The
anterior testis is usually on the left side.
_Ovary_--multilobular, the lobes 6 to 8 being irregular in size and
shape.
_Shell Gland_--extensive and diffuse, occupying an area which
approximately corresponds with the loop of the transverse vitelline
ducts.
_Seminal Receptacle_--globular, to the right of and dorsal to the
posterior lobe of the ovary.
_Laurer’s Canal_--generally runs from the end of the receptacle with a
single curve medially and backwards.
_Uterine Coils_--form loosely packed transverse coils terminating
slightly in front of the level of the first vitelline acini. From here
the uterus passes forwards into the pedicle to the left and ventral to
the seminal vesicle.
_Seminal Vesicle_--commences about the level of the first vitelline
acini. The coils displace the uterus ventrally and to the left. In
the pedicle the vesicle diminishes in extent and lies in its dorsal
(anterior) side.
_Habitat._--Liver of pariah dogs, India. In North-Western Provinces
about 40 per cent. are infected. This fluke appears to be different
from _Amphimerus_ (_Opisthorchis_) _noverca_ in man, as the latter
has not the pedicle on the summit of which lie the sucker and common
genital pore.
Genus. *Amphimerus*, Barker, 1912 (?).
Structure as in Opisthorchis, except that the vitellaria are
separated into two portions, an ant-ovarial and a post-ovarial.
[Illustration: FIG. 156.--_Amphimerus noverca_, Braun. o.s., oral
sucker; p.b., pharynx; ac., ventral sucker; ut., uterus; v.g.,
vitellarium; ov., ovary; v.d., vas efferens; ex.c., excretory canal;
t., testis. (After McConnell.)]
*Amphimerus noverca*, Barker, 1912 (?).
Syn.: _Distomum conjunctum_, McConnell, 1876 (_nec_ Cobbold, 1859);
_Opisthorchis noverca_, M. Braun, 1903 _pro parte_.
At the autopsy of two Mahommedans who died in Calcutta, McConnell found
a large number of Distomata in the thickened and dilated bile-ducts.
The worms were lancet-shaped, covered with spines, and measured 9·5
to 12·7 mm. in length and 2·5 mm. in breadth. The two suckers lie
very close to one another, the anterior one being larger than the
ventral; the genital pore opens immediately in front of the ventral
sucker; pharynx spherical; intestinal cæca extending far back. At
the commencement of the posterior third of the body the two testes,
somewhat apart, the anterior one roundish, the posterior one distinctly
lobed. The transverse and slightly lobed ovary in front of the
bifurcation of the *Y*-shaped excretory bladder, whence the uterus, in
convolutions barely spreading beyond the central field, extends to the
pore; the vitellaria in the lateral areas commence behind the ventral
sucker and extend to the testes. Cirrus pouch absent. Eggs oval, 34 µ
by 21 µ.
Genus. *Clonorchis*, Looss, 1907.
Structure as in Opisthorchis, distinguished, however, by the branched
testes situated one behind the other, the branches of which ventrally
encroach upon the gut forks; dorsal to the testes the *S*-shaped
excretory bladder, the main branches of which, arising at the level
of the bifurcation of the gut, open into the bladder below its
anterior end. Parasitic in the bile-ducts of mammals and man.
[Illustration: FIG. 157.--_Metorchis conjunctus_,[272] (Syn.: _Distomum
conjunctum_, Cobb., _nec_ Lew. and Cunn., _nec_ McConn.): from _Canis
fulvus_. _Vs._, ventral sucker; _I._, intestine; _Vsc._ vitellaria;
_Ex._, excretory bladder; _T._, testes; _O._, ovary; _Ms._, oral
sucker; _Ph._, pharynx; _Ut._, uterus. (After Cobbold.)]
[272] This species from _Canis fulvus_ was for long thought to be the
same as that here described as _Amphimerus noverca_. It probably does
not belong to the genus Metorchis.
*Clonorchis sinensis*, Cobbold, 1875.
Syn.: _Distoma sinense_, Cobbold, 1875; _Distoma spathulatum_, R.
Leuckart, 1876 (_nec_ Rudolphi, 1819); _Distoma hepatis innocuum_,
Baelz, 1883.
In shape resembles _Opisthorchis felineus_, 13 to 19 mm. long, 3 to
4 mm. broad, at the beginning of sexual maturity 12 to 13 mm. long, 2·5
to 3 mm. broad. Oral sticker 0·58 to 0·62 mm., ventral sucker 0·45 to
0·49 mm. in transverse diameter. In the parenchyma numerous yellowish
or brownish granules, especially behind the oral sucker and at the
posterior end. Testicular branches very long, in the anterior testis
often four, in the posterior testis five branches. Ovary generally
with three large lobes and a smaller lobe. Vitellaria not always
symmetrical, generally extending laterally from the ventral sucker to
the ovary, interrupted in parts.
Eggs 26 µ to 30 µ by 15 µ to 17 µ. Average 29 µ by 16 µ.
[Illustration: FIG. 158.--_Clonorchis sinensis._ _C.L._, Laurer’s
canal; _Dst._, vitellaria; _Ex._, excretory bladder; _H._, testes;
_K._, ovary; _R.s._, receptaculum seminis; _Vd._, terminal section of
vas deferens. Magnified 4-1/2 times. (After Looss.)]
[Illustration: FIG. 159.--Ova of _Clonorchis sinensis_. The knobs on
the ends of the eggs are not shown. 900/1. (After Looss.)]
This (?) species was discovered in 1874 by McConnell, in Calcutta, in
the bile-ducts of a Chinaman who died shortly after being admitted into
hospital.
_Habitat._--Bile-ducts of man, dog and cat.
_Distribution._--Especially in China, apparently rare in Japan.
*Clonorchis endemicus*, Baelz, 1883.
Syn.: _Distoma sinense_ s. _spathulatum p.p._; _Distoma hepatis
endemicum_ s. _perniciosum_, Baelz, 1883; _Distoma japonicum_, R.
Blanchard, 1886.
Very similar to the previous species and consequently generally
confused with it. Length between 6 and 13 mm., width varying between
1·8 and 2·6 mm. Oral sucker 0·37 to 0·5 mm., usually 0·43 to 0·45 mm.
in transverse diameter; ventral sucker 0·33 to 0·45 mm., usually 0·37
to 0·40 mm. No pigment in parenchyma; anterior testis with four,
posterior testis with five branches. Vitellaria continuous, ova 26 µ by
13 µ to 16 µ.
_Habitat._--Bile-ducts of man, dog, cat and pig.
_Distribution._--This species occurs very frequently in man, in certain
districts of Japan, especially in the province of Okayama, Central
Japan, in particular localities of which above 60 per cent. of the
population are infected. The worms are sometimes found in enormous
numbers in the liver (upwards of 4,000), also in the pancreas and
rarely in the duodenum. It is common in Tonkin and Indo-China. Léger
in Tonkin found 50 per cent. of people apparently in normal health
infected, so that probably symptoms only arise when the infection is
intense. [The exact distribution of these two species is, however,
not precisely defined at present, as commonly no distinction is made
between them.--J. W. W. S.]
[Illustration: FIG. 160.--_Clonorchis endemicus._ × 6 about. (After
Looss.)]
[Illustration: FIG. 161.--_Clonorchis endemicus_: eggs. The knobs on
the eggs are not shown. × 900. (After Looss.)]
Verdun and Bruyant deny, in opposition to Looss, the possibility of
being able to distinguish within the genus Clonorchis the two species
described, but they admit the justification for the new genus. They
also report the occurrence of _Opisthorchis felineus_ in man in Tonkin
(_Compt. Rend. Soc. de Biol._, lxii, 1907).
_Pathology._--Both species of Clonorchis give rise to grave symptoms.
The liver is generally enlarged, though when the infection has
lasted some time it begins to contract. The surface of the organ
is studded with white vesicles, and on cutting into it one sees
numerous cavities with thickened walls (distended bile-ducts) filled
with a brownish fluid containing innumerable eggs, which cause its
colour. Microscopically, the epithelium of the bile-ducts is either
(1) entirely destroyed, or (2) actively proliferates, forming an
adenomatous outgrowth. Occasionally this proliferation is not limited
by the wall of the bile-duct but penetrates it and leads to a growth
of numerous new ducts, forming a malignant biliary adenoma. The
bile-ducts have their connective tissue wall greatly sclerosed. These
fuse with one another, forming areas of sclerosis devoid of liver
tissue. As a result of these changes the liver cells atrophy and
undergo fatty pigmentary and granular degeneration. Besides these
changes, due probably to the toxic action of the flukes, mechanical
obstruction due to the actual plugging of the ducts by the flukes
causes retention of bile and icterus, and through pressure on veins,
ascites and hypertrophy of the spleen.
To what extent blood or bile respectively forms the food of the flukes
is uncertain.
_Life-history._--(Kobayashi, 1911, _Mitteilungen aus dem kaiserlichen
Institut für Infektions-Krankheiten zu Tokio_, pp. 58–62.)
It results from the work of Kobayashi in Japan that fresh-water fish
form the _second_ intermediate host for _Clonorchis endemicus_. He
fed cats with encysted flukes (cercariæ) from various fish and easily
succeeded in infecting them, _e.g._ a kitten, proved to be uninfected
by repeated examination of its fæces, was fed on infected fish; a month
later innumerable flukes were found in the bile-ducts, gall-bladder,
pancreas and even in the duodenum. The fish infected were _Leucogobis
güntheri_, _Pseudorasbora parva_, and to a less extent _Acheclognathus
lanceolata_, _Acheclognathus limbata_, _Paracheclognathus rhombea_,
_Pseudoperilampus typus_, _Abbottina psegma_, _Biwia zezera_ and
_Sarcocheilichthys variegatus_. The cysts occur throughout the muscles
and subcutaneous tissue of the fish. Length 0·13 mm., breadth 0·1 mm.
The cercaria lies folded in the cyst, length 0·5 mm. breadth 0·1 mm.
It tapers posteriorly. Skin at first covered with fine spines,
disappearing as they grow older. Body dotted with fine pigment.
The _first_ intermediate host is still unknown.
Sub-family. *Metorchiinæ*, Lühe, 1909.
Genus. *Metorchis*, Looss, 1899, emend. auctor.
Hind end rounded. Gut forks reach extreme end. Testes only slightly
lobed, filling the hind end.
*Metorchis truncatus*, Rud., 1819.
This species, which attains a length of 2 mm., is slender and conical,
the anterior end is pointed and the posterior truncated, and provided
with a muscular tuberosity that resembles a terminal sucker; for
this reason the discoverer of the species (Rudolphi) classed it with
the Amphistomes. The cuticle in the young, as well as in the adult
specimens, is entirely and closely covered with spines. Suckers about
equal in size (0·134 to 0·172 mm.); the ventral sticker lies somewhat
in front of the middle of the body. The pharynx is small (0·09 mm.),
the œsophagus minute, the intestinal cæca reach to the posterior
extremity. Between them, and in front of their blind ends, lie the two
elliptical testes, one generally a little in front of the other. In
front of them, either in the median line or somewhat laterally, the
spheroidal ovary is situated; in front, again, is the uterus, the coils
of which usually extend beyond the median field. The vitellaria are at
the sides of the central third of the body, thus commencing in front of
the ventral sucker; cirrus pouch absent; the genital pore is close in
front of the acetabulum. The excretory pore is terminal (?). Eggs 29 µ
by 11 µ.
_Metorchis truncatus_ lives in the bile-ducts of the seal, cat, dog,
fox, and glutton (_Gulo borealis_). The source of infection is unknown,
although one would suspect fish. Askanazy did not succeed in getting
this fluke in his feeding experiments, but another species, _Metorchis
albidus_, not uncommon in cats by feeding them on roach (_Leuciscus
rutilus_).
[Illustration: FIG. 162.--_Metorchis truncatus_, Rud.: from the biliary
ducts of the domestic cat. _V.s._, ventral sucker; _I._, gut; _V.sc._,
vitellaria; _T._, testes; _O._, ovary; _R.s._, receptaculum seminis;
_Ut._, uterus. 25/1.]
Family. *Heterophyiidæ*, Odhner, 1914.
Genus. *Heterophyes*, Cobbold, 1866.
Syn.: _Cotylogonimus_, Lühe, 1899; _Cænogonimus_, Looss, 1899.
No crown of spines on head. Body divided into a narrow, movable,
anterior part (neck), and a broader, less movable, posterior
portion, which contains the genitalia. The suckers separated from
one another by a space equal to half the length of the body or more;
the pharynx is close behind the oral sucker; the œsophagus is long;
the intestinal cæca extend to the posterior border; the genital pore
is placed laterally, and behind the ventral sucker. Genital sucker
provided with a circlet of chitinous rodlets, shaped like stags’
horns. The testes are at the posterior end, the ovary in a median
position in front of them. Laurer’s canal with receptaculum seminis
present; the small vitellaria are at the sides of the posterior part
of the body. Parasitic in the intestine of mammals and birds.
*Heterophyes heterophyes*, v. Sieb., 1852.
Syn.: _Distomum heterophyes_, v. Siebold, 1852; _Heterophyes
ægyptica_, Cobbold, 1866; _Mesogonimus heterophyes_, Railliet, 1890;
_Cœnogonimus heterophyes_, Looss 1900; _Cotylogonimus heterophyes_,
Braun, 1901.
Length up to 2 mm., breadth 0·4 mm.; the neck not sharply defined; in
life it stretches to double the length of the hind body. The scales
are rectangular, 5 µ to 6 µ by 4 µ, their posterior margin serrate
with seven to nine teeth. Cuticular glands are numerous on the ventral
surface, especially in the fore part of the body, and partly discharge
at the anterior border of the oral sucker. The oral sucker is 0·09 mm.,
the ventral sucker 0·23 mm. in diameter; the pharynx measures 0·05
to 0·07 mm. in length; the œsophagus is about three times as long;
posteriorly the intestinal cæca are directed one towards the other and
terminate beside the excretory bladder. Close in front of the posterior
ends of the intestinal branches are the two elliptical testes, which
are not exactly on the same level. In the middle in front of them is
the receptaculum seminis, and in front of the latter lies the spherical
or elliptical ovary. The two vasa efferentia unite to form the vas
deferens, which after a short course passes over into the angularly
bent seminal vesicle; after the entry of the prostatic glands it
becomes united with the metraterm (vagina), and the common duct opens
into the genital sucker. The latter is somewhat smaller than the
ventral sucker, lateral to and close (0·15 mm.) behind it, and bears
a not entirely closed ring of from seventy-five to eighty chitinous
rods (20 µ in length). The vitellaria on either side consist of about
fourteen acini. The uterus is spread almost throughout the entire
posterior part of the body. The eggs have thick shells with a knob
resembling that of Clonorchis eggs but not so prominent, and measure
30 µ by 17 µ; they contain a completely ciliated miracidium with a
rudimentary intestinal sac.
[Illustration: FIG. 163.--_Heterophyes heterophyes_, v. Sieb. _C._,
cerebral ganglion; _I._, intestinal cæca; _Ct.g._, cuticular glands;
_V.sc._, vitellaria; _Ut._, genital sucker; _T._, testes--the excretory
bladder between them; _L.c._, Laurer’s canal; _R.s._, receptaculum
seminis, with the ovary in front of it; _G.c._, ventral sucker; _Vs._,
vesicula seminalis, 53/1. On the left side above, an egg, 700/1, is
depicted, and below it three chitinous rodlets from the genital sucker.
700/1. (After Looss.)]
This species was discovered in 1851 by Bilharz in the intestine of
a boy who died in Cairo; a second case was only found in 1891 and
published by R. Blanchard, so that it appeared as if the species were
very scarce. According to Looss, this is, however, not the case, but
the species easily escapes notice on account of its small size. Looss
found it in Alexandria twice in nine autopsies, and once in Cairo, and
has recently stated that in man “it is not at all uncommon to meet with
the parasite in cadavers, and the eggs of the worm in the stools of the
patients.” Leiper records one case from Japan and one from China. The
parasites occupy the middle third of the small intestine, and even when
present in large numbers appear to be harmless.
This small species, according to Looss, frequently occurs in Egyptian
dogs, less so in cats, and has also been found in the fox, as well as
once in _Milvus parasiticus_; Janson also reports this species from the
intestine of the dog in Japan.
*Metagonimus*, Katsurada, 1913; Yokogawa, Leiper, 1913.
Resembles in general structure Heterophyes. In the arrangement of
its ventral genital suckers resembles but differs from that of
Tocotrema,[273] Looss. The ventral and genital suckers lie laterally
and on the right.
[273] In the genus Tocotrema the common genital duct opens into the
ventral sucker.
*Metagonimus yokogawai.* Katsurada, 1913.
Syn.: _Yokogawa yokogawai_, Leiper, 1913.
[Illustration: FIG. 164.--_Metagonimus yokogawai_, Katsurada, 1913: the
spines are only shown over a small part of the skin. (After Leiper.)]
One to 1·5 mm. long, seldom 2·5 mm., and 0·4 to 0·7 mm. broad;
elliptical in shape. The body is thickly covered with nail-shaped
spines about 10 µ long. Oral sucker 77 µ, to 85 µ in diameter. Ventral
sucker characteristic and peculiar 0·12 to 0·14 mm. by 0·08 to 1 mm.
It is a sac-like organ placed deeply in the body, but does not open as
in other flukes on the ventral surface. Testes elliptical, not quite
symmetrically placed at the hind end of the body. Vesicula seminalis
retort-shaped, situated transversely, internal to the ventral sucker.
Pars prostatica present. Ejaculatory duct opens with the uterus into
a genital sinus, which, together with the internal opening of the
ventral sucker, opens into a pit at the front of the ventral sucker.
The opening of the genital sinus and that of the ventral sucker are
furnished with a complex muscular apparatus. Ovary spherical, 0·12 to
0·13 mm. in diameter, lies in the middle of the hind body. Receptaculum
seminis and Laurer’s canal present. Vitellaria in the hind half of the
body, consisting of about ten acini on each side. Shell gland to the
left of the ovary. Uterus forms three to four transverse coils. Eggs
elliptical, double contoured, yellowish-brown in colour. There is no
shoulder below the operculum as in the eggs of _Cl. sinensis_. At the
rounder end there is a thickening or knob different from the spine-like
or hook-like process seen in _Cl. sinensis_. Dimensions 28 µ by 16 µ.
_Habitat._--Mainly in upper or middle portion of jejunum, rarely in
cæcum. They penetrate deep into the mucosa, but not into the submucosa,
and _post mortem_ appear as a number of small brown points. They
frequently occur in the solitary glands, which they destroy. They cause
chronic catarrh of the gut. Parasitic in man and mammals.
_Geographical Distribution._--Japan.
_Life-history._--The cercarial stage occurs in a trout (_Plecoglossus
altivelis_) and seldom in Crassius sp. and Cyprinus sp. Infection takes
place through the eating of the fish raw. Seven to sixteen days later
eggs appear in the fæces (of dog).
Family. *Dicrocœliidæ*, Odhner, 1910.
Genus. *Dicrocœlium*, Dujardin.
_Dicrocœliidæ_, with leaf-shaped bodies, pointed posteriorly and
anteriorly. Greatest width behind the mid-line. Vitellaria double.
The testes smooth or indented, lying symmetrically or obliquely
beside or behind the ventral sucker. The ovary approaches the median
line behind one testis. Parasitic in the liver and gall-bladder
(rarely in the intestine) of members of all classes of vertebrate
animals--by preference in birds and mammals.
[Illustration: FIG. 165.--_Dicrocœlium dendriticum_, Rud. _V.s._,
ventral sucker; _Cb._, cirrus pouch; _I._, intestinal cæca; _V.sc._,
vitellaria; _T._, testicles; _O._, ovary; _M.s._, oral sucker; _Ut._,
uterus. 15/1.]
*Dicrocœlium dendriticum*, Rud., 1819.
Syn.: _Dicrocœlium lanceatum_, Stil. and Hass., 1896; _Fasciola
lanceolata_, Rud., 1803 (_nec_ Schrank, 1790); _Distomum
lanceolatum_, Mehlis, 1825; _Dicrocœlium lanceolatum_, Dujardin, 1845.
[Illustration: FIG. 166.--Eggs of _Dicrocœlium dendriticum_, Rud. To
the left seen flat, to right lying on one side. 600/1.]
[Illustration: FIG. 167.--Miracidia of _Dicrocœlium dendriticum_. _a_,
from the dorsum; _b_, from the side. (After Leuckart.)]
Body lancet-shaped, narrowing especially at the anterior extremity;
length 8 to 10 mm., breadth 1·5 to 2·5 mm., the greatest breadth
usually behind the middle of the body. Suckers distant from each
other by about one-fifth the length of the body; oral sucker about
0·5 mm., ventral sucker about 0·6 mm. Pharynx globular, adjoining
the oral sucker; œsophagus 0·6 mm. in length; intestinal cæca reach
to four-fifths of the body length. Genital pore at the level of the
bifurcation of the intestine; cirrus pouch small and slender. The
large, slightly lobed testes lie obliquely one behind the other behind
the ventral sucker; the ovary, which is considerably smaller, is placed
behind the posterior one; the vitellaria, commencing at the level
of the posterior testis, terminate far before the cæca. The uterus,
situated behind the ovary, extends throughout the posterior end, not
confined to the central field, but overlapping the lateral fields with
its transverse coils; at the posterior edge of the body it turns back
again and winds forwards to the ovary in transverse loops, then between
the testes, and finally, dorsal to the ventral sucker, terminates in
the genital pore. The thick-shelled eggs when young are yellowish,
when older dark brown. They measure 38 µ to 45 µ by 22 µ to 30 µ.
They contain an oval or roundish miracidium, only the anterior part
of which is ciliated, and which possesses a rudimentary intestinal
sac with a boring spine. The miracidia do not hatch out in water
spontaneously, but, according to Leuckart, in the intestines of slugs
(_Limax_, _Avion_), but they do not develop either in these (slugs) or
in water-snails.
The lancet fluke inhabits the biliary duct of herbivorous and
omnivorous mammals (sheep, ox, goat, ass, horse, deer, hare, rabbit,
pig), and is often found associated with the liver fluke; it is not,
however, so common nor so widely disseminated, nevertheless, it has
been met with outside of Europe, namely, in Algeria, Egypt, Siberia,
Turkestan, and North and South America.
In man it is still more uncommon than the liver fluke, and has hitherto
only been observed seven times (Germany, Bohemia, Italy, France, and
Egypt); it may, however, have occurred more frequently, and have been
overlooked, as in slight infections it produces no special symptoms.
The intermediate host is still unknown. Leuckart for some time held
the opinion that small species of _Planorbis_ from fresh water, which
contain encysted Distomata, were to blame, and he supported his views
by a feeding experiment which seemingly yielded positive results; this,
however, is not definitely proved. Piana’s statement that small land
snails are the intermediate hosts has also not been proved.
Family. *Echinostomidæ*, Looss, 1902.
Sub-family. *Echinostominæ*, Looss, 1899.
Genus. *Echinostoma*, Rud. 1809; Dietz, 1910.
Fore-body not bulging. Greatest width at or behind the ventral sucker.
Oral sucker not atrophied. Collar kidney-shaped with a double dorsally
unbroken row of spines, terminating in four to five angle spines. The
border spines of the aboral series not larger than the oral. Skin
spined or smooth. Body elongated. Uterus long with numerous transverse
coils. Ventral sucker in the anterior quarter of body. Cirrus sac
small, almost completely in front of the ventral sucker. Testes round
or oval, smooth incurved or lobed, in the hinder half of body. Ovary
median or lateral in front of testes. Vitellaria from hinder margin of
ventral sucker to end of body. Eggs oval, 84 µ to 126 µ by 48 µ to 82 µ.
The spines placed most ventrally, or those placed most medially on
ventral surface, are from differences of position or form termed
“angle” spines, the rest “border” spines.
_Type._--_Echinostoma echinatum_, Rud.
*Echinostoma ilocanum*, Garrison, 1908.
Length 4 to 5 mm., breadth 1 to 1·35 mm., thickness 0·5 to 0·6 mm. The
circum-oral disc 0·3 mm. broad, separated by a shallow groove from the
body. Crown of forty-nine spines and five to six angle spines on each
side continuous with an irregularly alternating series of fourteen
spines on the dorsum. Largest spines are 34 µ long, 8 µ thick at the
base. The remainder of the dorsal spines are 24 µ by 6 µ. Skin thickly
covered with scales on the margins of the body as far back as the
level of the hind testis. Oral sucker, 0·18 mm.; ventral sucker, 0·4
to 0·46 mm. Its anterior border about 0·07 mm. from the anterior end.
Pharynx 0·17 mm. long, 0·11 mm. broad. Testes about mid-line of the
body, much lobed; the lobes of the anterior testis run transversely,
while the axis of the posterior testis is longitudinal, as often
occurs in the _Echinostomidæ_. Cirrus sac reaches to the centre of
the ventral sucker. Ovary transversely oval in front of the testes.
Vitellaria commence about half-way between the ventral sucker and ovary
and extend to the posterior end. Eggs numerous, 92 µ to 114 µ by 53 µ
to 82 µ.
_Average._--99·5 µ by 56 µ.
_Habitat._--Gut of man (Filipinos), Philippine Islands.
[Illustration: FIG. 168.--_Echinostoma ilocanum._ _Vo._, oral sucker;
_Ph._, pharynx; _Cirre_, cirrus; _V.v._, ventral sucker; _Ut._, uterus;
_G.c._, ovary; _Ov._, shell gland; _T._, testes; _T.d._, vitellarium;
_C.ex._, excretory vesicle. (After Brumpt.)]
[Illustration: FIG. 169.--_Echinostoma ilocanum_, Garrison, 1908: head
end showing collar of spines, ventral view. (After Leiper.)]
*Echinostoma malayanum*, Leiper, 1911.
Twelve millimetres long, 3 mm. broad, 1·3 mm. thick. Ends bluntly
rounded. At the anterior end a ventral furrow on either side, one-third
the width of the body, marking off the circum-oral collar. Along its
edge is a row of forty-three spines extending across the middle line
dorsally but not ventrally. The spines vary in size from 0·07 mm.
in length (ventrally) to 0·05 to 0·016 mm. (dorsally). Cuticular
spines also exist on the ventral side as far back as posterior end
of body, but dorsally limited to a triangular area ending in front
of the ventral sucker. Oral sucker 0·07 mm. thick, occupying the
middle third of the circum-oral disc; pharynx 0·25 mm. in diameter;
œsophagus 0·04 mm. long; gut cæca simple, extending to end of body;
ventral sucker 0·9 mm. long by 0·75 mm. broad by 0·7 mm. deep; wall
about 0·25 mm. thick. The sucker is inclined at an angle of 40° to the
ventral surface. Testes lobed, one behind the other, behind the ventral
sucker. Cirrus pouch well developed, reaching to the posterior edge of
the sucker. Genital pore in the angle between neck and anterior lip
of ventral sucker. Ovary smooth, 0·3 mm. in diameter, 0·85 mm. behind
ventral sucker. Vitellaria very numerous, extending from posterior
margin of sucker to posterior end of body, where they intermingle. Eggs
few in number, brown and large.
_Habitat._--Gut of man (Tamils), Malay States.
[Illustration: FIG. 170.--_Echinostoma malayanum_, Leiper, 1912:
anterior end showing collar of spines, ventral view. (After Leiper.)]
Sub-family. *Himasthlinæ*, Odhner, 1910.
Genus. *Artyfechinostomum*, Clayton-Lane, 1915.
Crown of thirty-nine spines, continuous over dorsum. Two corner spines
long. Vitellaria extend from posterior margin of sucker to posterior
end of fluke. Eggs without filament. [Although the possession of strong
rose-thorn hooks is given by Odhner as a sub-family characteristic,
yet in this genus assigned to this sub-family they have not been
seen.--J. W. W. S.]
*Artyfechinostomum sufrartyfex*, Clayton-Lane, 1915.
Spirit specimens: 9 by 2·5 by 0·8 mm. thick. Ventral sucker
conspicuous, 1 mm. in diameter. Cirrus sac 2 mm. long. Testes lobed,
about 1·5 mm. in diameter. Posterior border of posterior testes 1 mm.
from posterior end. Vitellaria meet posteriorly behind the posterior
testis.
Family. *Schistosomidæ*, Looss, 1899.
Genus. *Schistosoma*, Weinl, 1858.
Syn.: _Gynæcophorus_, Dies., 1858; _Bilharzia_, Cobb., 1859;
_Thecosoma_, Moq. Tandon, 1860.
The males have bodies that widen out considerably behind the ventral
sucker, the lateral parts of which in-roll ventrally, forming the
almost completely closed canalis gynæcophorus, within which the
female is enclosed. There is no cirrus pouch. The male has five or
six testes, the females are filiform; the uterus is long. There
is no Laurer’s canal. The ova almost equally attenuated at either
extremity; they have a small terminal spine, and are not provided
with a lid. They contain a miracidium, ciliated on all sides, which
is characterized by the possession of two large glandular cells,
which discharge anteriorly beside the gastric sac. They live in the
vascular system of mammals. (An allied genus [Bilharziella] lives in
the blood-vessels of birds.)
*Schistosoma hæmatobium*, Bilharz, 1852.
Syn.: _Distoma hæmatobium_, Bilh.; _Distoma capense_, Harley, 1864.
[Illustration: FIG. 171.--_Schistosoma hæmatobium_, Bil.: male carrying
the female in the canalis gynæcophorus. 12/1. (After Looss.)]
_The Male_ is whitish, 12 to 14 mm. in length, but is already
mature when 4 mm. long. The anterior end is 0·6 mm. or a little
over in length. The suckers are near each other, the oral sucker is
infundibular, and the dorsal lip is longer than the ventral one. The
ventral sucker is a little larger, 0·28 mm., and is pedunculated.
A little behind the ventral sucker the body broadens to a width of
1 mm., decreasing, however, in thickness; the lateral edges in-roll
ventrally, so that the posterior part of the body appears almost
cylindrical, 0·4 to 0·5 mm. in diameter; the posterior extremity is
somewhat more attenuated. The dorsal surface of the posterior part of
the body is covered with spinous papillæ. There are delicate spines
on the suckers, and larger ones invest the entire internal surface of
the gynæcophoric canal, as well as a longitudinal zone at the edge of
that side of the external surface that is covered by the other side
rolling over it. The œsophagus is beset with numerous glandular cells
(fig. 173), and presents two dilatations; the intestinal bifurcation is
close in front of the ventral sucker, the two branches uniting sooner
or later behind the testes into a median trunk, which may again divide
at short intervals. The excretory pore is at the posterior end, but
placed somewhat dorsally; the genital pore is at the beginning of the
gynæcophoric canal, thus behind the ventral sucker; into it opens the
vas deferens which, posteriorly, broadens into the seminal vesicle
and then continues as the vasa efferentia of the four or five testes
(fig. 173).
[Illustration: FIG. 172.--Transverse section through a pair of
_Schistosoma hæmatobium_ in copulâ. In the male the point of reunion of
the intestinal forks has been cut across. (After Leuckart.)]
[Illustration: FIG. 173.--Anterior end of the male _Schistosoma
hæmatobium_, Bilh. _V.s._, ventral sucker; _I._, gut cæca; _G.p._,
genital pore; _T._, testes; _O.s._, oral sucker; _Oe._, œsophagus with
glandular cells; _V.s._, vesicula seminalis. 40/1. (After Looss.)]
_The Female_--filiform, about 20 mm. in length, pointed at each
end, and measuring 0·25 mm. in diameter in the middle. Their colour
varies according to the condition of the contents of the intestine.
(Posteriorly they are dark brown or blackish.) The cuticle is smooth
except in the sucker, where there are very delicate spines, and at the
posterior end, where there are other larger spines. The oral sucker
is a little larger than the pedunculated ventral sucker (0·07 and
0·059 mm. respectively). The anterior part of the body, 0·2 to 0·3 mm.
in length; the œsophagus is as in the male. The intestinal bifurcation
is in front of the ventral sucker, the two branches uniting behind the
ovary and the trunk running in a zigzag manner to the posterior border.
There are indications of diverticula at the flexures. The ovary is
median. In young females it is of an elongated oval shape; in older
females the posterior end becomes club-shaped, whereas the anterior
end becomes attenuated; the oviduct originates at the posterior end,
but immediately turns forwards and joins the parallel vitelline duct
in front of the ovary (fig. 174), where the shell gland cells open;
the common canal becomes dilated to form the oötype, and then proceeds
as the uterus, with only slight convolutions, along the central field
to the genital pore, which lies in the middle line immediately behind
the ventral sucker. The single vitellarium starts behind the ovary and
extends to the posterior end. The acini are situated at the sides of
the excretory duct, which runs a median course. The eggs are compact
spindles, much dilated in the middle; they have no lid, and are
provided with a terminal spine (rudimentary filament) at the posterior
end, measuring 120 µ to 150 µ in length and 40 µ to 60 µ in breadth,
but vary in size and shape (fig. 175).
_Distribution._--In order to understand the distribution of the worms
and eggs in the body, it may be well to recall the blood supply of the
abdominal and pelvic organs. It is generally assumed that the early
life (? cercarial stage) of the worms occurs in the liver, and that
the young worms travel from here, where they are invariably found, to
their various sites along the portal vein and its tributaries and so
_against_ the blood stream. The tributaries of the portal vein are:--
(1) _Superior mesenteric_, the tributaries of which are: (_a_) the
veins of the small intestine; (_b_) ileo-colic; (_c_) right colic;
(_d_) middle colic; (_e_) right gastro-epiploic; and (_f_) inferior
pancreatic. By these paths infection of the small intestine, ascending
and transverse colon and pancreas would occur.
(2) _Splenic._ (Ova have been recorded by Symmers in the spleen.)
(3) _Inferior mesenteric_, the tributaries of which are (_a_)
superior hæmorrhoidal veins from the upper part of the hæmorrhoidal
plexus; (_b_) sigmoid veins from sigmoid flexure and lower portion of
_descending_ colon; (_c_) left colic vein draining descending colon.
The superior hæmorrhoidal veins form a rich plexus in the rectum, and
below this level in the upper and middle parts of the anal canal. The
plexus forms two networks, an _internal_ plexus in the submucosa and
an external on the outer surface. The _internal_ plexus opens at the
anal orifice into: (_a_) branches of the inferior hæmorrhoidal vein
(from the pudic); (_b_) the external plexus. The _external_ plexus
gives off: (_a_) inferior hæmorrhoidal opening into internal pudic
(of _internal iliac_ vein); (_b_) mid-hæmorrhoidal into _internal
iliac_ or its branches; and (_c_) superior hæmorrhoidal opening into
inferior mesenteric. The external plexus further communicates with the
vesico-prostatic plexus. The vesico-prostatic (vaginal) plexus opens
into the _vesical veins_, which drain into the interior iliac vein.
This plexus also receives afferents from the pudendal plexus, the chief
tributary of which is the dorsal vein of the penis. The pudendal plexus
also receives branches from the inferior pudic and the anterior surface
of the bladder.
There is thus a communication between the portal vein and the vena cava
by means of these plexuses, _viz._, through the inferior and middle
hæmorrhoidals, and by the inferior hæmorrhoidals to the bladder and
thence by the vesical veins or the pudic to the caval system (interior
iliac).
It is thus by the inferior mesenteric and its tributaries that the
worms reach the descending colon, rectum, anal canal, and eventually
the bladder, and in some cases the caval system.
Before considering what is actually found _post mortem_ in these veins
and the organs drained by them, we may further recall the fact that the
calibre of “medium” veins is 4 to 8 mm., “small” veins less than 40 µ
in diameter and capillaries 8 µ to 20 µ. Further, the maximum diameter
of the male worm is 1 mm., that of the female 280 µ and eggs _in utero_
80 µ to 90 µ long by 30 µ to 40 µ.
_Liver and Portal Vein._--Here worms are most easily found _post
mortem_. Often only males are found and these of the same size, and
if females occur only a few worms are found in copulâ. The worms are
frequently not full size and the males may contain no free spermatozoa
in their testes, and as regards the females some may be fertilized,
others not, as shown by the presence or absence of spermatozoa in
the seminal receptacle or uterus. In either case they may contain
eggs--_lateral-spined_--usually one, less often two, but there may be
as many as five or six. These eggs may also show some abnormality,
which takes the form of: (1) abnormal contents, _viz._, disintegrating
yolk cells with or without an ovarian cell; (2) abnormal shape but with
normal contents and probably represented by the collapsed and empty
egg-shells which are found in the tissues.
As to the interpretation of these facts, Looss believes that these
lateral-spined eggs are products of young females whose egg-laying is
not at first properly regulated. The shape that the eggs take, _viz._,
with a lateral spine, is determined by an excess of material--ovarian
and yolk cells--being present in the oötype. The shape of eggs depends
upon the position they have in the oötype during their formation. In
young females an excess of cells--yolk cells especially--accumulates,
distending not only the dorsal wall but a portion also of the short
duct joining the oötype to the uterus. The result of this is that
the axis of the oötype and egg is almost transverse to the body, and
the posterior funnel-shaped portion of the oötype, instead of being
terminal, has now a lateral or rather a ventral position, so that the
spine which occupies this portion, instead of being terminal, is now
lateral. It is noteworthy that these lateral-spined eggs are thicker,
owing to the excess of material present, and not uncommonly have a
curved anterior border, due to a projection of the anterior end into
the anterior opening of the oötype.
As these eggs are being laid by females in the portal vein they are
carried back to the liver by the blood stream. The liver is one of the
commonest sites for these eggs; also terminal-spined eggs may be found
here for the same reason.
_Hæmorrhoidal Veins._--Mature worms, generally in copulâ, are usually
found here, though young not fully grown females may also occur. The
tissues of the rectal wall (or colon) show, as a rule, large quantities
of lateral-spined eggs, though less often only terminal-spined eggs may
be found.
_Vesico-prostatic Plexus._--Worms in copulâ are found in the veins of
the submucosa in the bladder, and the eggs in the mucosa, and those
voided are usually terminal-spined, though lateral-spined eggs are not
so rare as generally thought. The problem next arises as to how the
eggs get to the lumen of the gut or bladder.
The female worm is 280 µ in diameter. Veins in the submucosa of the
rectum less than 178 µ in diameter are not affected with endophlebitis.
It is probable that the female even by stretching could not penetrate
much beyond this. Eggs are probably then laid in the submucosa as near
the muscularis mucosa as possible. Now if the eggs are laid in a vein
of larger calibre than the worm fills, the eggs would be carried back
to the inferior mesenteric vein, so that presumably the worm must
succeed in blocking the vein already narrowed by endophlebitis, so that
by the stasis which ensues the eggs may escape from the veins. How this
occurs is not exactly known; it is not necessarily due to the spine,
as the same escape into the tissues occurs in spineless eggs, such
as those of _Schistosoma japonicum_. The eggs, then, pass as foreign
bodies through the tissues. Another hypothesis is that the worms leave
the veins in order to lay their eggs, but the evidence is against this.
_Caval System._--Occasionally worms that have passed through the
vesical plexus may be found in the iliac vein, inferior vena cava, and
even the lungs. If the worms are young they contain a lateral-spined
egg; if adult, numerous (50 to 100) terminal-spined eggs.
_Lungs._--When the liver is strongly infected with (terminal-spined)
eggs it is possible that by passive movements some may pass into the
intralobular veins, and thence by the inferior vena cava to the lungs.
_Gall-bladder._--Similarly terminal-spined eggs pass into the
bile-capillaries and gall-bladder (where they may be abundant), and so
into the fæces.
_Detection of Eggs._--Occasionally eggs may be found in various other
parts of the body. They are best detected by macerating pieces of the
tissue in question in about 1/4 per cent. hydrochloric acid at 50 to
60°C. (Looss).
Pathological changes:--
_Rectum._--These have been studied thoroughly by Letulle in the case of
an apparently pure infection of the rectum.[274] They take the form of
a chronic diffuse inflammation, which may result in--(1) ulceration, or
(2) hyperplasia of the mucosa, producing adenomata.
[274] It is noteworthy that in this almost classical case no worms were
found in any of the sections. It is further noteworthy that the eggs in
the rectum showed great irregularity of form. Eggs with a spine at each
end were not uncommon; exceptionally eggs with two polar spines and one
lateral.
_Ulcerative Form._--The _mucosa_ is transformed into a mass of vascular
connective tissue. The connective tissue spaces next become invaded
by numerous mononuclear cells. The tissue itself undergoes diffuse
sclerosis, becoming hard and fibroid. Eventually ulcerative necrosis
sets in. During these changes the Lieberkühn glands are destroyed. The
process does not extend to the submucosa, in this respect differing
from that in chronic dysentery.
_Hyperplastic Form._--The Lieberkühn glands of the mucosa at first
hypertrophy; then there is an actual hyperplasia resulting in
adenomata. The interstitial tissue of the glands is also greatly
hypertrophied, giving rise to very vascular granulations. These growths
are often hollow and contain worms. Many eggs are found in the mucosa
on their way to the lumen of the gut.
The _muscularis mucosa_ is thickened up to twice or even ten times the
normal. Its vessels are dilated (36 µ to 80 µ), but they do not allow
of the passage of worms.
The _submucosa_ is profoundly changed; rigid and hard instead of
supple. It is here that the greatest number of eggs occur. A remarkable
condition of endophlebitis exists in the veins of the submucosa, not
only in the smaller ones but also in the larger ones (370 µ by 270 µ).
This endophlebitis results in a more or less complete occlusion of the
vessels of the lumen.
The _muscular coats_ are free from change, also their veins.
The _Serous Coats_.--The veins about 1,900 µ, also show endophlebitis.
Besides the rectum, in extreme cases even the transverse colon, the
cæcum and small intestine may be affected.
_Bladder._--In the early stages the mucosa is deep red and swollen
like velvet, or there may be localized patches of hyperæmia or
extravasation. The subsequent changes take two chief forms:--
(1) _Sandy Patches._--The mucosa looks as if it were impregnated with a
fine brownish or yellowish powder (myriads of ova). This is accompanied
by a gradual hypertrophy and new formation of connective tissue, so
that dry, hard or plate-like patches with this sandy appearance arise;
the thickening eventually affects all the coats of the bladder. In the
older patches many of the eggs are calcified. These patches sooner
or later break down, ulcerate and necrose. Phosphatic deposits are
abundant and stone is common. These patches are not found in the rectum.
(2) _Papillomata._--Where the inflammatory change produced by the eggs
gives rise to hypertrophy and hyperplasia of the mucosa, papillomata
result, the axis of which is formed by connective tissue of the
submucosa. These are most variable in shape and form and bleed readily,
and sometimes contain cavities of extravasated blood.
As in the rectum, it is in the submucosa that eggs are most abundant,
and worms in copulâ occur in the veins of this layer, but endophlebitis
is not as general as described in the rectum. Malignant disease of
the bladder is not an uncommon sequela of bilharziasis. Besides the
bladder, the ureters and kidneys may in advanced cases be involved. The
prostate and vesiculæ seminales are commonly diseased. Eggs have been
recorded in the semen. The urethra is frequently attacked; the vagina
in the female.
Eggs also occur in the lymphatic glands of the gut.
_Geographical Distribution._--East Africa: Nile Valley, Red Sea Coast,
Zanzibar, Portuguese East Africa, Delagoa Bay, Natal, Port Elizabeth.
South Africa: Cape Colony, Orange Free State, Transvaal, Mauritius,
Bourbon, Madagascar.
West Africa: Angola, Cameroons, Gold Coast, Gambia, Senegal, Sierra
Leone, Lagos, Nigeria.
North Africa: Tripoli, Tunis, Algeria, parts of the Sahara.
Central Africa: Sudan, various portions. Uganda, Nyasaland.
It occurs with varying frequency in these regions. It is probably more
widely spread than this list implies, as undoubtedly many cases are
seen which are not recorded.
Isolated cases have been recorded from Arabia, India,[275] Greece,
Cyprus.
[275] In a case from Madras, recorded by Stephens and Christophers,
the eggs were long and spindle-shaped, quite unlike the eggs of
_Schistosoma hæmatobium_.
[Illustration: FIG. 174.--_Schistosoma hæmatobium_, Bilh.: genitalia of
the female. _V.s._, ventral sucker; _I._, gut cæca; _V.d._, vitelline
duct; _V.sc._, vitellarium; _O._, ovary; _Oe._, œsophagus; _Sh._, shell
gland; _U._, uterus. Magnified. (After Leuckart.)]
The means by which infection is brought about are still uncertain; we
only know that the miracidia (fig. 175) enclosed in the discharged
eggs do not hatch if the eggs remain in the urine, but after cooling
perish. As soon, however, as the urine is diluted with water the shell
swells, generally bursting lengthways, and releases the miracidium from
its investing membrane, so that it can swim about with the aid of its
cilia. In its structure it differs but little from the miracidium of
_Fasciola hepatica_, as, for instance, in the lack of eyes; the two
large gland cells situated on either side of the intestinal sac are
also present in the miracidia of _Fasciola hepatica_.
_Sarcode Globules._--This is a term applied to certain globules which
at times appear in the miracidium and are later ejected. Some authors
consider them as indicative that the miracidium has developed into a
sporocyst, but Looss considers them to be degeneration products.
The Bilharzia mission, under R. T. Leiper, sent to Egypt by the War
Office early in 1915, reports that cercariæ of bilharzia type were
recognized in four of the commonest fresh-water molluscs around Cairo.
With material obtained from naturally infected _Planorbis boissyi_
acute bilharziosis was experimentally produced in rats, mice, and
monkeys. Infection takes place experimentally through the skin and also
through the mucous membrane of the mouth and œsophagus. The miracidium,
after entering the mollusc, develops into a sporocyst. This gives rise
not to rediæ, but to secondary sporocysts, which, in turn, produce
cercariæ. These, like the adult worm, differ from other distomes in
lacking a muscular pharynx.
*Schistosoma mansoni*, Sambon, 1907.
According to Manson, Sambon and others, the eggs with lateral spines
belong to a species different from _Schistosoma hæmatobium_. Infections
with this species only are said to occur in the Congo, Southern States
of North America, West Indies (Guadeloupe) and Brazil (Bahia). The
following characters, according to Flu, differentiate this species: (1)
In the male the transition from the anterior portion of the worm to
the lateral fields (the infolded portions which form the gynæcophoric
canal) is not a gradual one as in _Schistosoma hæmatobium_, but in this
case the lateral fields rise suddenly, almost at right angles to the
anterior portion. (2) The ovaries have a well-marked convoluted course
as in no other schistosome. (3) The oötype is symmetrical in reference
to the long axis of the body, its duct being lateral on the ventral
side (Looss’ explanation of this we have already given). (4) The worms
live exclusively in portal vein and tract. (As lateral-spined eggs
occur also in the bladder, this is not exactly true.)
[Illustration: FIG. 175.--Ovum of _Schistosoma hæmatobium_, Bilh., with
miracidium, which has turned its anterior end towards the posterior end
of the egg. 275/1. (After Looss.)]
------------------------------------------------------------------
|*Schistosoma hæmatobium*, Bilharz, 1852. |
| |
|Male, four or five large testes. Gut forks unite late, so that the|
|single gut stem is short. Female, ovary in posterior half of body.|
|Uterus very long, voluminous, with many terminal-spined eggs, some|
|lying in pairs. Vitellaria in posterior fourth of body. Cercariæ |
|in _Bullinus contortus_ and _Bullinus dybowski_ (syn.: _Physa |
|alexandrina_) in Egypt. |
| |
| |
|*Schistosoma mansoni*, Sambon, 1907. |
| |
|Male, eight small testes. Gut forks unite early, so that the |
|single gut stem is very long. Females, ovary in anterior half of |
|body. Uterus very short; usually only one lateral-spined egg at a |
|time _in utero_. Vitellaria occupy posterior two-thirds of body. |
|Cercariæ in _Planorbis boissyi_ in Egypt. |
| |
|The above morphological descriptions are founded on worms of each |
|species, derived from experimentally infected mice (Leiper, R. T.,|
|_Brit. Med. Journ._, March 18, 1916, p. 411). |
------------------------------------------------------------------
*Schistosoma japonicum*, Katsurada, 1904.
Syn.: _S. cattoi_, Blanchard, 1905.
_Male._--Eight to 19 mm., but extreme limits are 5 to 22·5 mm.
Consists of a short fore-body, separated by the ventral sucker from
the hind-body. The ventral sucker is stalked and somewhat larger than
the oral sucker. Both suckers are larger than the corresponding
ones in _S. hæmatobium_. Body usually smooth, but in the fresh
state numerous fairly evident spines along the margin of the canal.
Œsophagus: two bulbs. The junction of the gut forks more posterior than
in _S. hæmatobium_, the median united gut stem occupying a quarter to
one-fifth to one-sixth of the body length. An excretory canal runs
along each side of the body, opening into the dorsal excretory pore.
Testes irregularly elliptical, six to eight in number, in the anterior
part of hind-body. The vasa efferentia unite into a common vas deferens
which opens directly behind the ventral sucker. The seminal vesicle
lies just behind this.
[Illustration: FIG. 176.--_Schistosoma japonicum_: anterior end with
testes; posterior end with point of union of cæca. Length of worm about
10 mm. (After Katsurada.)]
_Female._--Up to 26 mm., generally thinner than the male. Surface
smooth. Suckers armed with fine spines. Ventral sucker larger than
oral. Body thicker behind the region of the ovary. The gut forks unite
immediately behind the ovary. The united gut much thicker than in _S.
hæmatobium_. Ovary elliptical, almost in the mid-body, its hinder
portion dilated. The oviduct arises from its posterior end and then
runs sinuously forward, where it is joined by the vitellarian duct;
the vitellarium well developed, extending from behind the ovary almost
but not quite to the posterior end as in _S. hæmatobium_. Shell gland
ducts enter at the junction point of oviduct and vitelline duct. The
canal here forms an oötype and then proceeds as the uterus to open
directly behind the ventral sucker. The uterus occupies almost half
the hind-body. In _S. hæmatobium_ this is not so. The uterine canal is
cleft-like, _i.e._, its dorso-ventral diameter is much greater than its
lateral diameter. The number of eggs varies from about 50 to 300 from
observations made in various hosts.
_Eggs._--_In utero_ assume various shapes, as they are soft; the lumen
of the uterus is narrow. Outside they are oval, faint yellow, double
contoured. In fæces the eggs measure 83·5 µ, by 62·5 µ (man); 85 µ by
61·5 µ (cattle); 98·2 µ by 73·8 µ (dog). The eggs have either small
lateral spines or thickenings, and Looss at the opposite side has
described cap-like thickenings. The eggs in the tissues undergo various
deformities, and may contain a miracidium, as also the eggs in fæces
do; or the contents may consist of granular matter or amorphous masses
or they may be calcified. Lymphocytes and giant cells may also invade
the eggs.
[Illustration: FIG. 177.--_Schistosoma japonicum_, male and female in
copulâ. × 60. (After Katsurada.)]
[Illustration: FIG. 178.--_Schistosoma japonicum_: eggs from human
liver, showing “spines” and “hoods” at opposite pole. (After Looss.)]
_Mode of Infection._--The miracidia hatch in water in as little as
fifteen minutes, but the majority in one to three hours. They will
live in water for about twenty-four hours. In water they undergo a
transformation into “larvæ,” which then penetrate the skin, as has been
shown by Japanese writers to hold good for man, cattle, dog and cat.
The penetration of the skin is attended with an eruption on the legs,
“Kabure.” The exact route by which the worms reach the portal vein
is uncertain. Infection in Japan takes place from spring to autumn,
especially May to July, when the soil is contaminated with manure
of cattle infected with _S. japonicum_. They also appear to develop
in molluscs. Leiper and Atkinson found cercariæ (in sporocysts) in
the liver of a mollusc, _Katayama nosophora_. They infected mice by
immersing them in water containing liver emulsion and so free cercariæ,
thus confirming the similar results of Miyairi and Suzuki.
[Illustration: FIG. 179.--_Schistosoma japonicum_: from dog. Uterine
egg. × c. 800. (After Katsurada.)]
[Illustration: FIG. 180.--_Schistosoma japonicum_: from dog. × c. 800.
(After Katsurada.)]
[Illustration: FIG. 181.--_Schistosoma japonicum_: from dog. Egg from
fæces. × c. 800. (After Katsurada.)]
_Habitat._--The worm occurs in Japan, China, and the Philippines. The
normal host is man and mammals. Cattle, dog and cat are often found
naturally infected. Mice can also be experimentally infected. Their
seat of election is the portal vein and its branches, especially the
mesenteric veins. They either swim free in the blood or remain fixed
by their suckers to the intima of the vessels. They have also been
found in the vena cava and right heart of a cat, but not so far in the
vesical plexus.
Eggs are found in the submucosa and mucosa of the gut, especially the
colon, and at times in the serosa and subserosa of the small intestine,
where they give rise to new growths. Occasionally eggs are found in the
brain. The life of the worms is at least two years.
_Pathogenic Effects._--Anæmia through loss of blood due to worms;
enlarged spleen, toxic in origin (?); phlebitis, thrombosis, due to
portal stasis; the eggs, however, cause the greatest mischief. They
are carried by the circulation to various organs where they produce
inflammation, granulation tissue, and later connective tissue.
_Liver._--The eggs reaching this organ give rise to granulomata and
hence enlarged liver, and later, when connective tissue is formed, to
contraction. The surface is rough and irregularly granular, “parasitic
embolic cirrhosis” of Yamagiwa.
[Illustration: FIG. 182.--_Schistosoma japonicum_: section through the
gut of a Chinaman showing eggs. × 58. (After Catto.)]
_Gut._--The eggs in the mucosa and submucosa cause catarrh and
destruction of tissue or new growth. In the small intestine the eggs
are mainly in the serosa and subserosa, where they give rise to
polypoid or branched growths.
_Spleen._--Enlarged, at first due to toxin (?) and later due to portal
stasis. Eggs in the spleen are uncommon.
_Ascites_ also arises from the portal stasis, and is generally present
in advanced cases.
Eggs may be found in many other situations: glands (numerous),
mesentery, stomach, pancreas, kidney, etc. The bladder remains free.
[Illustration: FIG. 183.--_Schistosoma japonicum_: liver showing eggs
in the intra- and interlobular connective tissue. × c. 80. (After
Katsurada.)]
Class III. *CESTODA*, Rud., 1808.
Tapeworms have been known from ancient times--at all events, the
large species inhabiting the intestines of man--and there has never
been a doubt as to their animal nature. The large cysticerci of the
domestic animals (occasionally of man also) have been known for an
equally long period, but they were generally regarded as growths,
or “hydatids,” until almost simultaneously Redi in Italy, and
Hartmann and Wepfer in Germany, concluded from their movements and
organization that they were of animal nature. From that time the
cysticerci have been included amongst the other intestinal worms, and
Zeder (1800) established a special class (_Cystici_, Rud., 1808) for
the bladder worms. Things remained in this condition until the middle
of the last century, when Küchenmeister, by means of successful
feeding experiments, demonstrated that the cysticerci were definite
stages of development of certain tapeworms. Before Küchenmeister, E.
Blanchard, van Beneden, and v. Siebold had held the same opinion in
regard to other asexual Cestodes.
Since the most remote period another question has again and
again occupied the attention of naturalists, the question of the
morphological nature--that of the INDIVIDUALITY OF THE TAPEWORM. The
ancients, who were well acquainted with the proglottids (_Vermes
cucurbitani_) that are frequently evacuated, were of the opinion
that the tapeworm originated through the union of these separate
proglottids, and this view was maintained until the end of the
seventeenth century. In 1683 Tyson discovered the head with the
double circlet of hooks in a large tapeworm of the dog; Redi (1684)
was also acquainted with the head and the suckers of several Tæniæ.
Andry (1700) found the head of _Tænia saginata_, and Bonnet (1777)
and Gleichen-Rusworm (1779) found the head of _Dibothriocephalus
latus_. Consequently most authors, on the ground of this discovery,
considered the tapeworm as a single animal, that maintains its hold
in the intestine by means of the head, and likewise feeds itself
through it. The fact was recognized that there were longitudinal
canals running through the entire length of the worm, and it was
thought that these originated in the suckers, and that the entire
apparatus was an intestine. As, moreover, the segments form at the
neck, and are cast off from the opposite extremity, the tapeworm
was also compared with the polyps, which were formerly regarded as
independent beings.
Steenstrup, in his celebrated work on the alternation of generations
(1841), was the first to give another explanation. This has been
elaborated still further by van Beneden, v. Siebold and Leuckart,
and until a few years ago all authorities adopted his views.
According to this view, the tapeworm is composed of numerous
individuals, something like a polyp colony, and, in addition to the
proglottids--the sexual individuals which are usually present in
large numbers--there is ONE individual of different structure, the
_scolex_, which not only fastens the entire colony to the intestine,
but actually produces this colony from itself, and therefore is
present earlier than the proglottids. The scolex is a “nurse,”
which, though itself produced by sexual means, increases asexually
like a _Scyphistoma_ polyp; the tapeworm chain has therefore been
termed a _strobila_. Consequently the development of the tapeworms
was explained by an alternation of generations. In support of this
opinion it was demonstrated not only that the adult sexual creatures,
the proglottids, can separate from the colony and live independently
for a time, but that in certain Tæniæ, and especially in many
Cestodes of the shark, the proglottids detach themselves long before
they have attained their ultimate size, and thus separated continue
to develop, grow and finally multiply; the scolex also exhibits a
certain independence in so far as, though not, as a rule, capable of
a free life, yet it in some cases lives as a free being, partly on
the surface of the body of marine fishes and partly in the sea. With
the more intimate knowledge of the development of the cysticerci,
the independent nature of the scolex was recognized. It is formed by
a budding of the bladder that has developed from the oncosphere, in
some cases (Cœnurus) in large numbers, in other cases (Echinococcus)
only after the parent cyst has developed several daughter cysts.
Released from its mother cyst and placed in suitable conditions,
it goes on living, and gives rise at its posterior end by budding
to the strobila, the proglottids of which eventually become sexual
individuals.
In order to make this clearer we will briefly summarize what takes
place in the jelly-fishes.
By _metamorphosis_ is meant a developmental change in the _same_
individual, while alternation of generations, or _metagenesis_,
implies a stage in which _reproduction_ of individuals takes place by
a process of budding or fission. This _asexual_ reproductive stage
_alternates_ with the _sexual_ mode of reproduction. Thus in the
development of the Scyphozoa (jelly-fishes) we have:--
(1) The fertilized egg cell divides regularly and forms a _morula_.
(2) By accumulation of fluid in the interior this becomes a closed
sac with a wall formed of a single layer of cells, forming the
_blastosphere_ or _blastula_.
(3) One end of the sac is invaginated, forming a _gastrula_.
(4) The gastrula pore or mouth closes, forming again a sac, the walls
of which have two layers, forming a _planula_.
(5) This becomes fixed to a rock, an invagination forms at one end,
a depression--the stomodæum--communicating with the enteric cavity.
Tentacles grow out and we have a _Scyphozoön polype_, _Scyphistoma_
or _Scyphula_. It is to this stage that Steenstrup gave the name
“nurse” (“wet-nurse”), because it nourished or produced asexually the
succeeding forms.
(6) _Asexual reproduction_ by transverse fission occurs in this,
forming a pile of saucer- or pine-cone-like animals which before this
time had been considered to be a distinct animal, which was called
_strobila_ from its resemblance to a pine-cone. This is the alternate
generation.
(7) The individuals of the strobila become free and are called
_Ephyrulæ_.
(8) These develop finally into adult sexual jelly-fish, _Scyphozoa_,
so that comparing a tapeworm with this we have (_a_) egg, (_b_)
scolex (= Scyphula or “nurse”), (_c_) asexual reproduction of the
tapeworm chain (= strobila), (_d_) development of the individuals of
the chain (proglottids) into sexual adults.
Van Beneden’s terminology for these stages is the following: Ciliated
embryo = protoscolex; scyphistoma = deutoscolex (or scolex); free
Ephyrula = proglottis. According to this view, as is the case in many
endoparasitic Trematodes, asexual reproduction by budding occurs
at two stages of the whole cycle of development, _viz._ (1) in the
formation of the scolex by budding from the bladder (“nurse”), (2) in
the formation of the strobila by budding from the scolex (“nurse”).
But in cysticercal larval forms it appears that the scolex does not
arise in this way but is simply a part of the proscolex (hexacanth
embryo), becoming invaginated into it for protection, so that there
is no asexual gemmation here. It has been questioned also whether
the strobila also arises by gemmation. If it does, the tapeworm is a
_colony_ of zoöids produced by budding from the asexual scolex; if
it is not produced in this way, then the tapeworm is to be regarded
as an _individual_ in which growth is accompanied by segmentation.
Against the “colony” view are the facts that the muscular, nervous,
and excretory systems are continuous throughout the worm, and that
some tapeworms, such as _Ligula_, are unsegmented.
Finally, if the tapeworm is an individual the question arises
which is the head end. As new segments are formed at the neck,
and as this point in annelids is the antepenultimate segment, the
scolex must be the last or posterior segment. The caudal vesicle
or bladder of larval forms is consequently anterior. According to
this view, in tapeworms as among many endoparasitic flukes, an
_asexual_ multiplication occurs at two points of the whole cycle
of development, which is as follows: (1) egg, (2) oncosphere or
hexacanth embryo, (3) bladder (cysticercus or hydatid), (4) (after
digestion of the bladder) by budding, the scolex, (5) by budding from
the scolex the sexual proglottids, (6) the egg; (4) and (5) being the
two asexual stages.
ANATOMY OF THE CESTODA.
If we except the tapeworms with only one proglottis, the CESTOIDEA
MONOZOA, Lang = _Cestodaria_, Monticelli, we can always distinguish in
the Cestodes, in the narrower sense, one scolex or head and a large or
small number of segments (proglottids). The SCOLEX serves the entire
tapeworm for fastening it to the internal surface of the intestinal
wall, and therefore carries at its end various organs which assist
in this function, and which are as follows: (i) SUCTORIAL ORGANS,
_i.e._, the four suckers (acetabula), which are placed crosswise at the
circumference of the thickened end of the scolex; further, the double
or quadruple groove-like suckers (bothridia), which are diversely
shaped in the various genera and families.[276] (2) FIXATION ORGANS
(hooklets)[277] that likewise occur in varying numbers and different
positions; they may be in the suckers, or outside them on the apex of
the scolex; for instance, in many of the _Tæniidæ_ they appear in a
circle around a single protractile organ, the rostellum, or the latter
may be rudimentary, and is then replaced by a terminal sucker. (3)
PROBOSCIS. One family of the Cestodes, the _Rhynchobothriidæ_, carries
four proboscides, moved by their own muscular apparatus, on the scolex,
and they are beset with the most diverse hooks. (4) TENTACLE-LIKE
formations are only known in one genus (Polypocephalus).
[276] They may remain simple, and are then not separated from the
remaining muscles of the scolex; or they project as roundish or
elongated structures over the scolex, hollow on their free surface, and
often divided into numerous areas by muscular transverse ribs. They may
also carry accessory suckers on their surface.
[277] The various parts of a hooklet are thus named from the point
backwards: (1) blade or prong, (2) guard or ventral or posterior root,
(3) handle or dorsal or anterior root.
The thickened part of the scolex that carries the suckers is usually
called the head; the following flat (unsegmented) part connecting
it with the proglottids is called the neck, and is sometimes quite
small. In a few cases the entire scolex (or head) disappears, and its
function is then undertaken by the contiguous portion of the chain of
proglottids, which is transformed into a variously shaped PSEUDO-SCOLEX.
The proglottids are joined to the scolex in a longitudinal row, and are
arranged according to age in such a manner that the oldest proglottis
is farthest from the scolex, and the youngest nearest to it.
The number of segments varies, according to the species, from only a
few to several thousands; they are either quadrangular or rectangular;
in the latter case their longitudinal axis falls either longitudinal
or transverse to that of the entire chain, according as the segments
are longer than broad or broader than long. When the number of segments
is very large, the youngest ones are, as a rule, transversely oblong,
the middle ones are squarish, and the mature ones longitudinally
oblong. The posterior border of the segments, as a rule, carries a
longitudinal groove for the reception of the shorter anterior border
of the following proglottis. The two lateral borders of the segment
are rectilinear, but converge more or less towards the front, or they
are bent outwards. In most of the Cestodes the segments, just as the
neck, are very flat; in rare cases their transverse diameter is equal
to their dorso-ventral diameter. As a rule the segments, singly or
several united together, detach themselves from the posterior end, in
many cases only after complete maturity is attained, and in others
much earlier; they then continue to live near their parent colony, to
still call it by that name, in the same intestine and continue their
development. Even when evacuated from the intestine the proglottids
under favourable circumstances can continue to live and creep about,
until sooner or later they perish.
The first proglottis formed, and which in a complete tapeworm [_i.e._,
sexually complete] is the most posterior, is as a rule smaller and
of different shape, it also frequently remains sterile, as likewise
happens in the next (younger) segments in a few species; otherwise,
however, sooner or later the generative organs develop in all the
segments, mostly singly, sometimes in pairs; in the latter case they
may be quite distinct from each other or possess some parts in common.
The term “mature” is used for a proglottid that has the sexual organs
fully developed, while “gravid” is used for one containing eggs. Most
of the species combine male and female genitalia in the same segment,
only a few are sexually distinct (Diœcocestus). In the hermaphrodite
species one male and one female sexual orifice are always present,
and, in addition, there may be a second female orifice, the uterine
opening; as a rule, however, this is lacking, and in one sub-family,
the _Acoleinæ_, to which also the genus Diœcocestus belongs, the other
sexual orifice, the opening of the vagina, is also absent. The position
of these orifices varies; the cirrus and vagina usually open into a
common atrium on one lateral border or on a surface of the segments;
the orifice of the uterus may be on the same surface or on the opposite
one.
The surface on which the uterus opens is termed the VENTRAL SURFACE;
if this orifice is absent, one must depend on the ovary, which almost
always approaches one of the two surfaces; this surface is then called
the ventral.
The length of the Cestodes--independently of their age--depends on the
number and size of the segments, as well as on their contraction; the
smallest species (_Davainea proglottina_) is 0·5 to 1·0 mm. in length;
the largest may attain a length of 10 m., and even more.
The entire superficial surface of the tapeworms is covered with a
fairly resistant and elastic layer, which exhibits several indistinctly
limited layers and which is usually called a cuticle, which also covers
the suckers, and is reflected inwardly at the sexual orifices. In
some species fine hairs appear, either on the entire body or only in
the region of the neck, on the external surface. In the cuticle there
can be recognized, besides the pores, which no doubt are concerned
with nutrition, spaces in which lie the ends of sensory cells. Close
under the cuticle lies the external layer of the parenchyma (basal
membrane), and below this the circular and longitudinal muscles forming
the dermo-muscular coat. The matrix cells of the cuticle occur as in
the Trematodes, only on the inner side of the peripheral muscles in
the external zone of the parenchyma; they are fusiform cells, forming
one or two layers, but are not arranged in the manner of epithelial
cells (fig. 184, _Sc.c._). They have fine branching processes which
run between the dermal muscles, pass through the basal membrane and
penetrate the internal surface of the cuticle with small pistil-like
enlargements, expanding on the internal surface of the cuticle into a
thin plasma layer.
[Illustration: FIG. 184.--Schematic representation of a small part of
a transverse section of _Ligula_ sp. _Bs._, basal membrane; _Cu._,
cuticle; at its base are the endplates of the subcuticular (epithelial)
cells; in the centre a cuticular sense organ, _O.s._; _F.v.s._,
vitelline follicle; _Exc._, excretory vessel; _C._, calcareous
corpuscle; _L.m._, longitudinal muscles; _M.c._, myoblast; _P.m._,
parenchymatous or dorso-ventral muscles; _Pl._, plexus of nerve fibres;
_A.m._, circular muscles; _Sc.c._, subcuticular or matrix cell; _T.c._,
terminal flame cell. 500/1. (After Blochmann.)]
In addition to the above mentioned, there are other cuticular
formations occurring on the cuticle of some Cestodes, such as immobile
hairs and variously formed hooks, such as are seen principally on the
scolex. Their development is only roughly known in a few species;
they are usually already present in the larval stage, and of the same
arrangement and shape as in the fully developed tapeworms; a matter
of importance, because by these structures larvæ can be recognized as
being those of a certain species of tapeworm.
The CUTICULAR GLANDS in Cestodes are scarce.
The PARENCHYMA forms the chief tissue of the entire body, and in all
essentials its structure is similar to that of the Trematodes.
The same doubt exists here also as to the nature of the parenchyma.
Recent authors consider that it consists of highly branched cells,
the processes of which ramify in all directions. These cells lie in a
non-cellular matrix containing fluid vacuoles. This matrix spreads in
between and so breaks the continuity of the epidermal cells.
[Illustration: FIG. 185.--Half of a transverse section through a
proglottis of _Tænia crassicollis_. Cu., cuticle; _Ex.v._, external
excretory vessel, to the right of which there is the smaller internal
one; _T._, testicular vesicles; _L.m._, longitudinal muscles (outer
and inner); _M.f._, lateral nerve with the two accessory nerves;
_Sc.c._, subcuticular matrix cells; _Sm.f._, submedian nerve; _Tr.m._,
transverse muscles; _Ut._, the uterus, and the middle of the entire
transverse section. 44/1.]
In the parenchyma of almost all the Cestodes there are found in adult
specimens, as well as in larvæ, light-refracting concentrically
striated structures, of a spherical or broad elliptical shape, which,
on account of their containing carbonate of lime, are termed CALCAREOUS
CORPUSCLES (fig. 184, _C._). Their size, between 3 µ and 30 µ, varies
according to the species; their frequency and distribution in the
parenchyma also varies, but they are chiefly found in the cortical
layer. They are the product of certain parenchymatous cells, in the
interior of which they lie like a fat globule in a fat cell, but
according to others they are _intercellular_ in origin.
The MUSCULAR SYSTEM of the proglottids is composed of--(1) the
subcuticular muscles (figs. 184 and 185), as a rule consisting of
a single layer of annular muscles; (2) longitudinal muscles; (3)
dorso-ventral fibres extending singly from one surface to the other,
and at both ends expanding in a brush-like manner, and inserted into
the basal membrane, consisting of an outer, more numerous, and an
inner, less numerous but more powerful layer (the number of bundles
in this layer being in certain cases of specific importance); (4)
transverse fibres, the elements of which penetrate to the borders
of the segments, thus passing through the longitudinal muscles and
reaching the cuticle. In the region of the septa the transverse and
dorso-ventral muscles form a kind of plate.
The mass of parenchyma bounded by the transverse muscles is termed
the MEDULLARY layer, while the mass lying outside them is termed the
CORTICAL LAYER.
It was known long ago that the myoblasts adhere to the dorso-ventral
fibres as thickenings, but it is only recently that large star-shaped
cells (fig. 184), separated from but connected with them by processes,
have been recognized as the myoblasts of other fibres (Blochmann,
Zernecke).
Within the scolex the direction and course of the muscular layers
change.
The SUCKERS are parts of the musculature, locally transformed, with a
powerful development of the dorso-ventral muscles, now become radial
fibres.
The ROSTELLUM of the armed Tæniæ, like the proboscis of the
_Rhynchobothriidæ_, also belongs to the same category of organs.
[Illustration: FIG. 186.--_Dipylidium caninum_: from the cat. In the
upper figure the rostellum is retracted, in the lower protruded, _a_,
sucker; _b_, hooks of rostellum; _B_, enlarged hook; _c_, apical
aperture on scolex; _d_, longitudinal muscles; _e_, circular muscles.
(After Benham.)]
In the simplest form, the rostellum, or top of the head (as in
_Dipylidium caninum_), appears as a hollow oval sac, the anterior part
of which, projecting beyond the upper surface of the head, carries
several rows of hooks (fig. 186). The entire internal space of the sac
is occupied by an elastic, slightly fibrous mass, while the anterior
half of the surface of the rostellum is covered by longitudinal fibres
and the posterior half by circular fibres. On contraction of the latter
the entire mass is protruded through the apical aperture, the surface
of the rostellum becomes more arched, and the position of the hooks is,
in consequence, altered. The rostellum of the large-hooked _Tæniidæ_,
which inhabit the intestine of man and beasts of prey, is of a far more
complicated structure, for, in addition to the somewhat lens-shaped
rostellum carrying the hooks on its outer surface, there are secondary
muscles grouped in a cup-like manner (fig. 187). Every change in the
curvature of the surface of the rostellum induces an alteration in the
position of the hooks. In the hookless _Tæniidæ_ the muscular system of
the rostellum is altered in a very different manner; in a few forms a
typical sucker appears in its place.
The NERVOUS SYSTEM commences in the scolex and runs through the
neck and the entire series of proglottids. Within the proglottids it
consists of a number of longitudinal nerve fibres of which those at
each lateral border are usually the largest. In the Tæniæ the lateral
nerves are accompanied both dorsally and ventrally by a thinner nerve
(accessory nerve) (fig. 185); on each surface, moreover, between the
lateral nerve and the median plane, there are two somewhat stronger
bundles (sub-median), so that there is a total of ten longitudinal
nerve bundles. They lie externally to the transverse muscle plates,
and the lateral and accessory bundles lie externally to the principal
excretory vessels, and are everywhere connected by numerous anastomoses
and secondary anastomoses; one typical ring commissure is usually found
at the posterior border of the segments. In the _Bothriocephalidæ_ the
distribution of the nerve bundles is different (for instance, two lie
in the medullary layer), or they are split up into a larger number
of branches. In the scolex the nerve bundles are connected in a very
remarkable manner by commissures with that which is generally termed
the central part of the entire nervous system. There occurs normally
a commissure between the two lateral nerves; at the same level, the
dorsal and ventral median nerves are also connected at each surface as
well with each other as with the lateral nerves, so that a hexagonal or
octagonal figure is formed. The so-called apical nerves pass from this
commissural system anteriorly, embrace the secondary muscular system of
the rostellum semicircularly, and form an annular commissure (rostellar
ring) at the inner part of the rostellum.
[Illustration: FIG. 187.--Longitudinal section of the head and neck of
_Tænia crassicollis_, showing the lens-shaped muscular rostellum, with
two hooks lying in the concentric cup-like mass of muscles. _L.m._,
longitudinal muscles of the neck; _L.f._, left lateral nerve; _G._,
ganglion; _S.c._, subcuticular layer; _W_{1}_, external, _W_{2}_,
internal excretory vessel. 30/1.
The peripheral nerves arise from the nerve bundles as well as from the
commissures situated in the scolex; some go direct to the muscles,
while others form a close plexus of nerves external to the inner
longitudinal muscles, which plexus likewise sends out fibres to the
muscles, but principally to numerous fusiform sense organs (fig. 184,
_Pl._); they lie internal to the subcuticular cells and, piercing the
cuticle with their peripheral processes, end as projecting “receptor”
hairs. Higher organs of sense are not known.
The EXCRETORY APPARATUS of the Cestodes is similar to that of other
flat worms. The terminal (flame) cells, which hardly differ in
appearance from those of the Trematodes, are distributed throughout
the parenchyma, but are more common in the cortical than in the
medullary layer (fig. 184, _T.c._). Before opening into a collecting
tube, the capillaries run straight, tortuously, or in convolutions,
anastomosing frequently with one another or forming a _rete mirabile_.
The collecting tubes, which have their own epithelial and cuticular
wall, and which also appear to be provided with muscular fibres, occur
typically as four canals passing through the entire length of the worm
(fig. 189); they lie side by side, two (a wider thin-walled ventral,
and a narrower thick-walled dorsal one) in either lateral field; in
the head the two vessels on each side unite by means of a loop, at
the posterior extremity they open into a short pyriform or fusiform
terminal bladder which discharges in the middle of the posterior edge
of the original terminal proglottis.
[Illustration: FIG. 188.--_Tænia cœnurus_, head and part of neck
showing nervous system. Enlarged. (After Niemiec.)]
This primitive type (fig. 189) of arrangement of collective tubes is
subject to variation in most Cestodes, in the scolex as well as in
the segments. Indeed, even the lumen of the four longitudinal tubes
does not remain equal, as the dorsal or external tubes are more fully
developed and become thicker, whereas the ventral or internal ones
remain thin, and in some species quite disappear in the older segments
(figs. 185, 187). Moreover, very frequently connections are established
between the right and left longitudinal branches, as in the head,
where a “frontal anastomosis” develops, which in the _Tæniidæ_ usually
takes the form of a ring encircling the rostellum (fig. 190), and in
the segments of a transverse anastomosis at each posterior border,
especially between the larger branches, and more rarely between the
smaller collecting tubes also (fig. 191).
The so-called “island” formation is another modification, _i.e._, at
any spot a vessel may divide and after a longer or shorter course the
two branches reunite, and this may appear in the collecting tubes
themselves as well as in their anastomoses. The above-mentioned ring
in the frontal commissure of the _Tæniidæ_ is such an island; similar
rings also frequently encircle the suckers (fig. 190). In extreme cases
(_Triænophorus_, _Ligula_, _Dibothriocephalus_, etc.) this island
formation extends to all the collecting tubes and their anastomoses.
Instead of two or four longitudinal canals only, connected by
transverse anastomoses at the posterior border of the segments, there
is an irregular network of vessels, situated in the cortical layer,
from which the longitudinal branches, having again subdivided, can only
be distinguished at intervals, and even then not in their usual number.
[Illustration: FIG. 189.--Young _Acanthobothrium coronatum_, v.
Ben., with the excretory vessels outlined. Slightly enlarged. (After
Pintner.)]
[Illustration: FIG. 190.--Scolex of a cysticercoid from _Arion sp._,
with the excretory vessels outlined. (After Pintner.)]
The opening of the longitudinal branches at the posterior end requires
more accurate investigation; it is true that a single terminal
bladder is mentioned as being present in many species, but this is
also disputed; when the original end proglottis has been cast off,
the longitudinal branches discharge separately. Some species possess
the so-called foramina secundaria, which serve as outlets for the
collecting tubes; they are generally at the neck, but may be situated
on the segments.
The contents of the excretory vessels is a clear fluid, the
regurgitation of which is prevented by the valves present at the points
of origin of the transverse anastomoses. The fluid contains in solution
a substance similar to guanine and xanthine.
_Genital Organs._--With the exception of one genus (_Diœcocestus_,
Fuhrm.), in which the species are sexually differentiated, all the
Cestodes are hermaphroditic; the genitalia develop gradually in the
segments (never in the scolex), the male organs, as is usual in
hermaphroditic animals, forming earlier than the female. The youngest
proglottids generally do not exhibit even traces of genitalia: these,
as a rule, develop first in the older segments, and the development
proceeds onwards from segment to segment. In a few exceptional cases
(_Ligula_) the sexual organs are already developed in the larval stage,
but are only functional after the entry of the parasite into the final
host.
[Illustration: FIG. 191.--Proglottis of _Tænia saginata_, Goeze,
showing genitalia. _C._, transverse excretory canal; _N._, lateral
longitudinal nerve; _W._, longitudinal excretory canal; _T._, testicles
scattered throughout the proglottis; _Ut._, opposite the central
uterine stem (a closed sac); _Ss._, genital pore leading into the
genital sinus; above the cirrus and coiled vas deferens (_V.d._), below
the vagina (_Vag._), bearing near its termination a dilatation, the
seminal receptacle; _Vsc._, the triangular vitellarium, and above it
(_Shg._) the shell gland; leading from this to the uterus is seen the
short uterine canal, on either side of this the two lobes of the ovary
(_Ov._). 10/1.]
With the exception of the end portions of the vagina, cirrus and
uterus, all the parts of the genital apparatus lie in the medullary
layer, except only the vitellaria, which in many species are in the
cortical layer. The male apparatus consists of the testes, of which,
as a rule, there are a large number,[278] and which lie dorsal to the
median plane (fig. 185, _T._); a vas efferens arises from each testis,
unites with contiguous vasa, and finally discharges into the muscular
vas deferens that is situated in about the middle of the segment.
According to the position of the genital pore, the vas deferens opens
on the lateral margin or in the middle line in the front of the
segment; it is much convoluted or twisted, and frequently possesses a
dilatation termed the vesicula seminalis. It finally enters the cirrus
pouch, which is usually elongated; within the cirrus pouch lies the
protrusible cirrus, which is not uncommonly provided with hooklets.
[278] There are, however, tapeworms with only one, others with only two
or three testes in each segment.
[Illustration: FIG. 192.--_Dibothriocephalus latus._ Upper figure:
female genitalia, ventral view. Lower figure: male genitalia, dorsal
view. The central portion only of the proglottis is shown. _a_,
cirrus sac; _b_, partly everted cirrus; _c_, genital atrium and pore;
_d_, vaginal pore; _e_, uterus; _f_, uterine pore; _g_, vagina; _h_,
ovary; _i_, shell gland; _j_, vitelline duct; _k_, lateral nerve; _l_,
vitellarium; _n_, vas deferens (muscular portion); _p_, vas deferens;
_q_, seminal vesicle; _r_ and _x_, vasa efferentia; _s_, lateral
excretory canal; _t_, testicular follicles. (After Benham and Sommer
and Landois.)]
The male sexual orifice almost always opens with that of the vagina
into a genital atrium, the raised border of which rises above the edge
of the segment and forms the genital papilla (fig. 191).
[Illustration: FIG. 193.--Diagram of genitalia of a Cestode. _g.p._,
genital pore; ♀ ♂, male and female ducts opening into genital sinus;
_c.s._, cirrus sac; _v.d._, coiled vas deferens (“outer seminal
vesicle”); _vag._, vagina; _sem. rec._, seminal receptacle; _sp. d._,
spermatic duct; _C.c._, fertilization canal; _vit. d._, vitelline duct;
_sh. g._, shell gland; _ut. c._, uterine canal; _ut._, uterus; _Ov._,
ovary; _p_, pumping organ. _Cf._ figs. 191 and 233. (Stephens.)]
The vagina, like the vas deferens, usually runs inwardly and
posteriorly, where it forms a spindle-shaped dilatation (receptaculum
seminis); its continuation, the spermatic duct, unites with the
oviduct, the common duct of the ovaries (fig. 191). The ovaries,
usually two in number, are compound tubular glands in the posterior
half of the proglottis, which extend into the medullary layer, but
ventral to the median plane.
At the origin of the oviduct there is frequently a dilatation provided
with circular muscles (suction apparatus), which receives the ovarian
cells and propels them forward. After the oviduct has received the
spermatic duct the canal proceeds as the fertilization canal, and after
a very short course receives the vitelline duct or ducts, and then the
numerous ducts of the shell glands (oötype). [Although the nomenclature
of these parts varies, we may consider the oviduct as extending from
the ovary to the shell gland and as receiving the spermatic duct and
then the vitelline duct and the ducts of the shell gland. The short
piece into which the shell gland ducts open corresponds to the oötype
in the flukes, but in the tapeworms this portion of the canal is seldom
dilated. From this point the oviduct is continued as a shorter or
longer tube, the uterine canal or true oviduct opening into the uterus
proper.--J. W. W. S.] The vitellarium may be single, but often exhibits
its primitive duplication more or less distinctly, in which case it is
situated at the posterior border of the segments in the medullary layer
(fig. 191). The original position of the double organ is, moreover, the
same as in the Trematodes, _i.e._, at the sides of the proglottids, and
thence eventually extending more or less on both surfaces (figs. 192
and 194); the gland is then distinctly grape-like and the follicles lie
mostly in the cortical layer.
[Illustration: FIG. 194.--Part of a transverse section through a
proglottis of _Dibothriocephalus latus_. _Ct._, cuticle; _C._,
cirrus; _Vvs._, vitelline follicles; _L.M._, longitudinal muscles;
_T._, testicles; _M._, medullary nerve; _S.c._, subcuticle; _T.m._,
transverse muscles; _Ut._, uterus. 20/1.]
The egg cell that has been fertilized and supplied with yolk cells
receives the shell material at the point of entry of the shell gland
ducts, and, as a complete egg, then moves onward to the uterus. In
those cases in which the uterus in its further course presents a
convoluted canal, and may form a rosette (pseudo-phyllidea), there is
an external opening which is usually separate from the genital pore,
and lies on the same or the opposite surface. In all other cases,
however, the uterus terminates blindly and is represented by a longer
or shorter sac lying in the longitudinal axis (fig. 191), but in many
forms transversely. With the accumulation of eggs it becomes modified
in various ways: (1) it sends out lateral branches (fig. 241), or
(2) forms numerous isolated sacs (PARENCHYMAL CAPSULES) containing
single eggs or groups of eggs (fig. 217); further, (3) in some cases
at the blind end one or more special thick-walled cavities are formed
(PARUTERINE ORGANS or UTERINE CAPSULES), in which all or most of the
eggs are collected, the uterus then undergoing atrophy.
In species in which the uterus lacks an opening, simultaneously with
the growth of this organ an atrophy of the male apparatus, at least
of the testes and their excretory ducts, takes place; this atrophy
also frequently occurs in the female glands, so that the entire mature
segments have besides the uterus only traces of the genitalia left.
In the _Acoleïnæ_ the vagina is more or less extensively atrophied, and
in any case has no external opening.
A number of genera are distinguished by the duplication of the
genitalia in every segment; the genital apparatus in its entirety, or
with the exception of the uterus, is double, or the genital glands and
the uterus are single, but the cirrus, vas deferens and vagina are
double.
On comparing the genitalia of the Trematodes and Cestodes the parts
will be found to agree, but the vagina of the Cestodes corresponds
with the uterus of the Trematodes, and the uterus of the tapeworms to
Laurer’s canal of the Trematodes, which in most of the Cestodes has
lost its external orifice.
DEVELOPMENT OF THE TAPEWORMS.
_Copulation._--As each proglottis possesses its own genital apparatus,
and male as well as female organs are present, the following processes
may occur: (1) self- or auto-fecundation (without immissio cirri); (2)
self- or auto-copulation (with immissio cirri); (3) cross-copulation
between proglottids of the same or different chains (of the same
species); and (4) cross-copulation in the same proglottis in species
with double genital pores. These various modes have actually been
observed.
In those species which lack the vagina (_Acoleïnæ_) it appears that
the cirri, which are always furnished with hooks, are driven into the
tissues and for the most part reach the receptaculum seminis.
The _eggs_ of all Cestodes are provided with shells, but the shells,
like their contents, vary. In genera that possess a uterine pore the
mature eggs frequently do not differ from those of the Distomata; they
have a brown or yellow shell of oval form provided with an operculum,
and contain a number of yolk cells in addition to the fertilized
ovarian cell (fig. 128), but in other genera (with a uterine pore) the
lid is absent and the egg-shell is very thin, the eggs of these genera
resembling those of Cestodes in which the secretion of the vitellarium
is a light albumin-like substance that contains only a few granules,
and in which the egg-shell is very delicate and without operculum.
The eggs of _Tæniidæ_, for example, at first consist of egg-shell
(oötype), ovum and yolk cells. The egg-shell is as a rule soft,
colourless and frequently deciduous, and the yolk is scanty in amount
and contains few granules. The eggs are, moreover, more complicated
than this. They enlarge and change their shape and various envelopes
are developed around the embryo. The egg-shell proper often disappears,
and one or more embryonal envelopes, or protoplasmic layers, arise,
so that eventually it is difficult to say whether the whole egg is
present, and, if not, what the layers that remain really are.
[Illustration: FIG. 195.--Egg of _Diplogonoporus grandis_, showing the
morula surrounded by yolk cells and granules. 440/1. (After Kurimoto.)]
[Illustration: FIG. 196.--Uterine egg of _Tænia saginata_, G. Uterine
shell with filaments; the oncosphere with embryonal shell (embryophore)
in the centre. 500/1. (After Leuckart.)]
The _embryonal development_ in most species takes place during the stay
of the eggs in the uterus; in other species it takes place after the
eggs have been deposited and are in water. Separate cells or a layer
of cells always separate from the segmentation cells, as well as from
the cells of the developing embryo, and form one or more envelopes
round the embryo; usually two such envelopes are formed, the inner
one of which stands in intimate relationship with the embryo itself
and is often erroneously termed the egg-shell, but more correctly the
embryonal shell or _embryophore_. In some species it carries long
cilia, as in _Dibothriocephalus latus_, by aid of which the young swim
about when released from the egg-shell; as a general rule, however,
there are no cilia and this envelope is homogeneous, or is composed
of numerous rods and is calcified, as in _Tænia_ spp. (fig. 197). The
second outer envelope (“yolk envelope”) (fig. 207, 3) lies close within
the true (oötype) egg-shell, and remains within it when the embryo
hatches out, and in many species, as in _Tænia_ spp., it perishes at
the end of the embryonal development with the delicate egg-shell which
was formed in the oötype, so that one observes not the entire egg with
egg-shell but only the embryo in its embryonal shell, _viz._, the
embryophore (fig. 197, _a._).
The embryo (the ONCOSPHERE) enclosed within the embryonal shell
(embryophore) is of spheroidal or ovoid form (fig. 197, _b._), and
is distinguished by the possession of three pairs of spines, a few
terminal (flame) cells of the excretory system, and muscles to move the
spines.
NO FURTHER DEVELOPMENT of the oncosphere takes place, either in the
parent organism or in the open; in fact, in all cases in which the
oncospheres are already formed within the proglottids they do not
become free, but remain in their shell; it is only when the oncospheres
are provided with a ciliated embryophore that they leave the egg-shell,
and they even cast this ciliated envelope after having swum about in
water by its means for a week or so. Sooner or later, however, all the
oncospheres leave the host that harbours the parental tapeworm and
reach the open, either still enclosed in the uterus of the evacuated
proglottids, after the disintegration of which they then become free,
or after being deposited as eggs in the intestine of the host; they
then leave it with the fæces. In the former case also, the slightest
injury to the mature proglottids while still in the intestine suffices
to allow a part of the oncospheres in their embryophores to be released
and mingled with the fæces. Here they are the generally, but falsely,
so-called Tæniæ “eggs.” For, as stated above, the “yolk” envelope and
the true shell deposited in the oötype have before this disintegrated.
[Illustration: FIG. 197.--_a._, oncosphere, in its radially striated
embryophore (erroneously termed egg-shell) of _Tænia africana_. Greatly
magnified. (After von Linstow.) _b._, freed oncosphere of _Dipylidium
caninum_. (After Grassi and Rovelli.) Both oncospheres show six spines.]
In other cases, _e.g._, _Hymenolepis_ spp., the uterine (oötype) shell
persists in fæces (fig. 230).
In any case the oncospheres must be transmitted into suitable animals
to effect their further development; in only very rare cases might
an active invasion be possible, as, for instance, takes place with
the miracidia of many Trematodes. The entry into an animal is, as a
rule, entirely passive, that is to say, the oncospheres are swallowed
with the food or water. Many animals are coprophagous and ingest the
oncospheres direct with the fæces; others swallow them with water,
mud, or food contaminated by such fæces. Infection is easily produced
artificially by feeding suitable animals with mature proglottids of
certain Cestodes or introducing the oncospheres with the food. As
the mature tapeworm frequently finds the conditions suitable for
its development in only one species of host, or in species nearly
related, and perishes when artificially introduced into other hosts,
experiment has taught us that to succeed in cultivating the oncospheres
certain species of animals are necessary. Thus we are aware that the
oncospheres of _Tænia solium_, which lives in the intestine of man,
develop only in the pig, and only quite exceptionally develop into the
stage characteristic of all Cestodes--the cysticercus in the wide sense
of the word--in a few other mammals. The oncospheres of _T. saginata_
develop further only in the ox; those of _T. marginata_ (of the dog) in
the pig, goat, and sheep; those of _T. serrata_ (of the dog) in hares
and rabbits; those of _Dipylidium caninum_ (of the dog and cat) in
parasitic insects of the dog and cat, etc. It is not unusual that young
animals only appear to be capable of infection, while older animals of
the same species are not so.
Once introduced into a suitable animal, which is only exceptionally
the same individual or belongs to the same species as the one which
harbours the adult tapeworm, the oncosphere passes into the larval
stage common to all Cestodes, but varying in structure according to the
species. In the simplest case--as, _e.g._, in _Dibothriocephalus_--such
a larva resembles the scolex of the corresponding tapeworm, only that
the head, provided with suckers, is retracted within the fore-part of
the neck. Such a larval form is known as a _plerocercoid_ (πλήερης,
full; κέρκος, tail). They differ from the cysticercoids in being solid
larval forms, elongated, tape-like or oval, with the head invaginated.
The conditions appear to be similar in _Ligula_, _Schistocephalus_,
_Triænophorus_, but here the larvæ are very large, indeed as large in
the first-mentioned genera as the tapeworms originating from them,
and the sexual organs are already outlined; doubtless, however, this
stage is preceded by one that corresponds to the scolex of the genus in
question, and which represents the actual larval stage. In such cases
the development of the body of the tapeworm from the scolex has already
begun within the first or intermediate host; in other cases, except in
the single-jointed (monozootic) Cestodes, this only takes place in the
definitive host. The direct metamorphosis of the oncosphere into the
larval forms termed PLEROCERCOID has hitherto not been investigated,
although _Ligula_, _Schistocephalus_ and _Bothriocephalus_ are very
common parasites, but many circumstances point to the conclusions
arrived at by us and by other observers. In the larval stages of other
tapeworms we can always distinguish the scolex and a caudal-like
appendage, vesicular in the cysticerci (fig. 200), compact in the
cysticercoids (fig. 231). The scolex alone forms the future tapeworm,
the variously formed appendage perishing.
It has now been proved that the appendage, the caudal vesicle,
originates direct from the body of the oncosphere, and therefore
is primary, and that the scolex only subsequently forms through
proliferation on the surface of this appendage. On account of this
origin the scolex is generally regarded as the daughter, and the part
usually designated as the appendage as the mother, originating from the
oncosphere.
Accordingly, two modes of development of the larval stage may be
distinguished; in the one case, plerocerci and plerocercoids, the
oncosphere changes directly into the scolex, thus forming the body of
the tapeworm within the primary host; in the other case, cysticerci and
cysticercoids, the scolex only forms secondarily in the transformed
body of the oncosphere, which later on perishes, the scolex alone
remaining as the originator of the tapeworm colony.
We may summarize briefly what has been said regarding these larval
forms. We have, firstly, solid larval forms without any bladder. These
arise _directly_ from the oncosphere and are of two kinds, plerocercus
and plerocercoid. _Plerocercus_ is a solid _globular_ larva with the
head invaginated into the posterior portion. _Plerocercoid_ (fig. 208)
is a solid _elongated_ larva also with the head invaginated into
the posterior portion, which is sometimes very long. Secondly, we
have larval forms with bladders from which the scolices arise thus
_indirectly_ from the oncosphere. They are of two kinds, cysticercoid
and cysticercus.
_Cysticercoid._--The bladder is but slightly developed and is usually
absorbed again. The anterior portion is, moreover, retracted into
the posterior, and in some cases there is a long or a stumpy tail
(figs. 220, 231).
_Cysticercus_, or true bladder worms. (These may be divided into
(1) cysticercus proper, consisting of a bladder and one scolex; (2)
cœnurus, a bladder and many scolices; (3) echinococcus, a bladder in
which daughter bladders or cysts are developed, and then in these
multiple scolices.)
[Illustration: FIG. 198.--Diagram of a cysticercoid. _Cf._ figs. 220,
227. _c.v._, caudal vesicle or bladder (small); _sec. c._, secondary
cavity caused by the growth forward of the hind-body; _t._, tail
bearing six spines. (Stephens.)]
[Illustration: FIG. 199.--Diagram of a cysticercus. _c.v._, caudal
vesicle or bladder; _i._, invagination of wall of bladder. (Stephens.)]
In the case of cysticerci a papilliform invagination forms, projecting
into the interior of the bladder (fig. 201). The layer of cells forming
the papilla becomes divided into two laminæ, the outer[279] of which
forms a kind of investing membrane (receptaculum capitis) for the
papilla. The head and suckers are now developed on the walls bounding
the axial lumen of the papilla. The papilla eventually evaginates, so
that the receptaculum capitis now forms the inner surface of the hollow
head, which eventually becomes solid.
[279] _I.e._, regarded from the interior or centre of the invagination.
Our knowledge of the development of cysticerci in the wide sense of
the word is limited almost exclusively to that of a few true “bladder
worms” (cysticerci); in other cases we know either only the terminal
stage, _i.e._, the complete larva, or, exceptionally, one of the
intermediate stages, but we are not acquainted with a complete series;
the description must therefore be incomplete.
We know from feeding experiments that, after the introduction of mature
proglottids or of the fully developed ova of _Tænia crassicollis_ (of
the cat) into the stomach of mice, the oncospheres escape from the
shell in the middle portion of the small intestine, and a few hours
later penetrate into the intestinal wall by means of a boring movement;
they have been found in this position twenty-seven to thirty hours
after the infection. By means of this migration, for which purpose they
employ their spines, they attain the blood-vessels of the intestine;
indeed, already nine hours after the infection and later they are found
in the blood of the portal vein, and in the course of the second day
after infection they are found in the capillaries of the liver, which
these larvæ do not leave.
Leuckart, in experimental feeding of rabbits with oncospheres of
_Tænia serrata_ (of the dog), found free oncospheres in the stomach of
the experimental animal, but not in the intestine: however, he came
across them again in the blood of the portal vein. The passage through
the blood-vessels to the liver is the normal one for those species
of _Tænia_ the eggs of which become larvae in mammals; even in those
cases in which the oncospheres develop further in the omentum or in
the abdominal cavity (_Cysticercus tenuicollis_, _C. pisiformis_),
there are distinct changes observable in the liver that lead one to the
conclusion that there has been a secondary migration out of the liver
into the abdominal cavity. Indeed, one must not imagine that the young
stages of the Cestodes are absolutely passive; once they have invaded
an organ they travel actively, and leave distinct traces of their
passage.
In other cases the oncospheres leave the liver with the circulation,
and are thus distributed further in the body; they may settle and
develop in one or more organs or tissues. Many oncospheres may, by
travelling through the intestinal wall, penetrate through it and
attain the abdominal cavity direct; some, perhaps, pass also into the
lymph stream. Where there are no blood and lymphatic vessels in the
intestinal wall, as in insects, the oncospheres attain the body cavity
or its organs direct; in short, they never remain in the intestinal
lumen itself, and only rarely--as in _Hymenolepis murina_ of the
rat--do they remain in the intestinal wall.
When the infection has been intense, and the body is crowded with
numerous oncospheres, acute feverish symptoms, are induced, to which
the infected animals usually succumb (“acute cestode tuberculosis”);
while in other cases the alterations in the organs attacked--as the
liver in mice and the brain in sheep--may cause death.
Sooner or later the oncospheres of tapeworms come to rest, and are
first transformed into a bladder, which may be round or oval according
to the species. The embryonal spines disappear sooner or later, or
remain close together or spread over some part of the bladder wall
(fig. 200). Their discovery by V. Stein in the bladder worm of the
“meal worm” (the larva of a beetle, _Tenebrio molitor_) first led to
the conclusion that bladder worms (cysticerci) actually originate from
the oncospheres of _Tæniidæ_.
[Illustration: FIG. 200.--Diagram of development of a cysticercus. 1,
solid oncosphere with six spines; 2, bladder formed by liquefaction of
contents; 3, invagination of bladder wall; 4, formation of rostellum
(with hooklets) and suckers at the bottom of the invagination; 5,
evagination of head; 6, complete evagination effected by pressure.
(Stephens.)]
The bladder may remain as a bladder, and then by proliferation the
scolex forms on its wall (fig. 202), or it may divide into an anterior
so-called “cystic” portion and a solid tail-like appendage of various
lengths, on which the embryonal hooks are to be found, and this is
particularly the case in those larval forms (cysticercoids), _e.g._,
those of _Dipylidium caninum_, that develop in invertebrate animals,
such as Arthropoda.
As mentioned above one may regard the scolex as an individual that
originates through proliferation of the wall of the parent cyst, mostly
singly, but in those cysticerci that are termed cœnurus (fig. 201)
many scolices occur, whereas in those called echinococcus the parent
cyst originating from the oncosphere of _Tænia echinococcus_ (of the
dog) first produces a number of daughter cysts, which in their turn
form numerous scolices. Echinococcus-like conditions also occur in
cysticercoids, as, for instance, in those peculiar to earthworms; and
similar conditions prevail in a larval form known as _Staphylocystis_,
found in the wood-louse (_Glomeris_). Thus it happens in these cases
that finally _one_ tapeworm egg produces not _one_, but numerous
tapeworms, for, under favourable conditions, each scolex can form a
tapeworm.
[Illustration: FIG. 201.--Section through a piece of a _Cœnurus
cerebralis_, with four cephalic invaginations in different stages of
development. At the bottom of the invaginations the rostellum, hooks
and suckers develop. (From a wax model.)]
[Illustration: FIG. 202.--Median section through a cysticercus, with
developed scolex at the bottom of the invagination. (After Leuckart.)]
The rudiment of the scolex appears as a hollow bud, the cephalic
invagination usually directed towards the interior of the bladder
cavity; on its invaginated surface arise the four suckers, and the
rostellum with the hook apparatus is formed in its blind end; we
thus get a Tænia head, but with the position of the parts reversed
(fig. 201). In many cysticerci the head rises up from the base of the
cephalic invagination and is then surrounded by the latter. A more
or less elongated piece of neck also develops, and even proglottids
may appear, as in _Cysticercus fasciolaris_ (the larva of _Tænia
crassicollis_ of the cat) of the Muridæ, a process somewhat analogous
to that of Ligula, etc.
The period that elapses from the time of infection till the cysticercus
is fully developed varies according to the species; the cysticercus of
_Tænia saginata_ requires twenty-eight weeks, that of _T. marginata_
seven to eight weeks, that of _T. solium_ three to four months, and
that of _T. echinococcus_ longer still.
[Illustration: FIG. 203.--_Cysticercus pisiformis_ in an evaginated
condition, with neck, fore-body and bladder, with excretory network in
its wall. 18/1.]
With one single exception (_Archigetes_) the larvæ do not become
sexually mature in the organ where they have developed; they must
enter the terminal host, a matter that is usually purely passive, the
carriers of the larvæ or infected parts of them being usually devoured
by other animals. In this manner, for instance, the larvæ (_Cysticercus
fasciolaris_) found in mice and rats reach the intestine of cats;
those of the hare and rabbit (_C. pisiformis_) reach the intestine
of dogs; those of the pig (_C. cellulosæ_) are introduced into man;
those of insects are swallowed by insectivorous birds; those of
crustaceans are ingested by ducks and other water fowl; perhaps, also,
the infection of herbivorous mammals is caused by their accidentally
swallowing smaller creatures infected by larvæ. Indeed, the researches
of Grassi and Rovelli have taught us that such an intermediate host
is not always necessary; _Hymenolepis murina_ of rats and mice in its
larval stage lives in the intestinal wall of these rodents, and as a
larva it passes into the intestinal lumen and develops into a tapeworm
in exactly the same way as the larvæ of other species that reach the
intestine of the terminal host by means of an intermediate carrier.
Probably this curtailed manner of transmission also occurs in many
other species. In some cases the larvæ actively quit the body of the
intermediate host, as in the case of _Ligula_ and _Schistocephalus_,
which travel out of the body cavity of infected fish and reach the
water, where they may be observed in hundreds in summer, at all events
in some localities. The larval stage of _Calliobothrium_--wrongly
termed _Scolex_--has been observed swimming free in the sea, and
the scolices of _Rhynchobothrium_, without their mother cysts, have
been observed free within the tissues of several marine animals.
In any case there is almost always a change of hosts, even in the
single-jointed Cestodes, for the larva of _Caryophyllæus_, which lives
in fishes of the carp family, is found in limicoline Oligochætes,
that of _Gyrocotyle_ (Chimæra) in shell-fish (Mactra), and different
conditions can hardly be possible for _Amphilina_. _Archigetes_ alone
becomes sexually mature in the larval stage, but the life-history of
this creature is not well known, so that it is not impossible that the
attainment of sexual maturity as a larva in invertebrates (Oligochætes)
is perhaps abnormal, and somewhat analogous to the maturity of some
encysted Trematodes.
The METAMORPHOSIS OF THE LARVA into the tapeworm is rarely accomplished
in a simple manner; the transformation, however, is not complex in
the single-jointed Cestodes, nor in _Ligula_ and _Schistocephalus_;
the latter is swallowed by birds (_Mergus_, _Anas_, etc.), produces
eggs after only a few days, and very soon quits the intestine of
its terminal host. In all other cases it is the scolex only which,
by proliferating at its posterior extremity, forms the proglottids,
after having invaded as a larva the intestine of a suitable host.
The mother cysts, or what corresponds to them, die, are digested,
absorbed, or perhaps even eliminated; on the contrary, segments found
on the scolex during the larval stage, also in the case of _Cysticercus
fasciolaris_, are retained. It is not certain whether the larvæ of
_Dibothriocephalus_ lose any part.
The time required by the scolex to complete the entire chain of
proglottids does not depend only on the number it has to produce,
for _Tænia echinococcus_, which, as a rule, only possesses three or
four segments, takes quite as long a time for their growth (eleven to
twelve weeks) as _T. solium_ with its numerous segments; _T. cœnurus_
is fully developed in three to four weeks, and the same holds good for
_Dibothriocephalus latus_, which possesses many more segments than the
above-mentioned Tænia of the dog. In a number of species it has been
possible to determine fairly accurately the average daily growth; for
instance, in _Dibothriocephalus latus_ the daily growth is 8 cm., in
_Tænia saginata_ 7 cm., etc.
The history of the development of the Cestodes demonstrates that
persons and beasts harbouring larval tapeworms have become infected by
having swallowed the oncospheres of the species of tapeworm to which
they belong. In regard to _Hymenolepis murina_ alone, it is known that
the introduction of the oncospheres into those species of animals which
harbour the adult tapeworm leads to the formation of the latter after
the development of a larval stage in the intestinal wall; nevertheless,
only young animals (rats) are capable of infection, for a previous
infection, or the presence of mature tapeworms in the intestine,
appears to produce a kind of immunity.
BIOLOGY.
In their adult stage, the tapeworms inhabit almost exclusively the
alimentary canal of vertebrate animals, with but few exceptions the
small intestine, and a few species select definite parts of it. A small
number of _Rhynchobothriidæ_ of marine fishes live apparently always
in the stomach, while in rays and sharks the spiral intestine is their
exclusive site. Bothriocephali generally attach themselves with their
head on to the appendices of the pylorus of fishes; other species
(_Hymenolepis diminuta_) occasionally fix their head in the ductus
choledochus, and this is more frequent still in the tapeworms of the
rock badger (_Hyrax_), which occasionally penetrate entirely into the
biliary ducts. _Stilesia hepatica_, Wolffh., has so far only been found
in the bile-ducts of its host (sheep and goat, East Africa).
In the disease of sheep induced by Cestodes, the worms have been
observed also in the pancreas. Specimens found in the large intestines
were probably being evacuated.
The Cestodes are looked upon as fairly inert creatures, this opinion
having been formed by observing their condition in the cold cadavers of
warm-blooded animals. Actually, however, they are exceedingly active,
and accomplish local movements within the intestine, for they have been
found in the ducts communicating with the bowel, or in the stomach,
and may even make their way forward into the œsophagus.
They also invade other abdominal organs through abnormal
communications, or through any that may be temporarily open between the
intestine and such organs; they thus reach the abdominal cavity or the
urinary bladder, or they work their way through the peritoneum.
They produce changes in the intestinal mucous membrane at the place of
their attachment, the alterations varying in intensity according to the
structure of the fixation organs. The mucous membrane is elevated in
knob-like areas by the suckers; the epithelial cells become atrophied
or may be entirely obliterated. _Dipylidium caninum_ bores into the
openings of Lieberkühn’s glands with its rostellum, dilating the
lumen to two or three times its normal size, while the suckers remain
fixed between the basal parts of the cells. Species with powerful
armatures penetrate deeper into the submucosa, and some that are not
provided with exceptionally strong armatures, or are even unarmed,
may be actually found with the scolex embedded in the muscles of the
intestinal walls or even protruding beyond (_Tænia tetragona_, Mol., in
fowls, etc.). Other species, again, even cause perforation of the walls
of the intestine of their hosts.
It is generally assumed that tapeworms, which almost without exception
live in the gut of vertebrates, get their nutriment from the gut
contents, which apparently they absorb through the whole body surface
(cuticular trophopores). In favour of this view is the existence
of fat drops in the proglottids, the identity in colour in certain
forms between that of the fresh worm and the gut contents and the
passage of certain substances derived from medicines (iron and mercury
preparation) into the worms in the gut, etc. Whether the suckers are
concerned in the absorption of nutriment and to what extent is still
questionable.
THE LENGTH OF LIFE OF THE ADULT TAPEWORM certainly varies; as a rule
it appears to last only about a year; in other cases (_Ligula_) it
averages only a few days, but we are likewise aware that certain
species of Cestodes of man attain an age of several or many years
(thirty-five). The natural death of Cestodes often appears to be
brought about by alterations in the scolex, such as loss of the hooks,
atrophy of the suckers and rostellum, finally the dropping off of the
scolex; it is unknown whether a chain of segments deprived of its
scolex then perishes or whether it first attains maturity. It has
already been mentioned that in a few species the foremost proglottids
are transformed into organs of fixation on the normal loss of the
scolex.
Abnormalities and malformations are encountered relatively frequently
in the Cestodes--such as abnormally short or long segments;
the so-called triangular tapeworms, which--if belonging to the
_Tæniidæ_--always possess six suckers; often also club-shaped
segments occur between normal ones, or there may be a defect in
one segment or in the centre of a number following one another
(fenestrated segments); bifurcated chains of segments have likewise
been observed, as well as incomplete or complete union of the
proglottids, abnormal increase of the genital pores, reversion of
the genitalia. Besides the above-mentioned increase of the number
of suckers on the scolex (in Tæniæ), there may be a decrease in
the number; in other cases the crown of hooks may be absent, or
abnormally shaped hooks may be formed.
CLASSIFICATION OF THE CESTODA OF MAN.
Order. *Pseudophyllidea*, Carus, 1863.
Scolex without proboscis or rostellum. Head “stalk” absent.
Scolex never with four, generally with two (or one terminal)
bothria.[280] Vitellaria numerous. Uterine opening present. Genitalia
do not atrophy when uterus is developed. In large majority of
proglottids eggs (or, if formed, their contents) are at the same
stage of development.
[280] _Bothridia_ or “_phyllidia_” are _outgrowths_ from the scolex.
They are concave and extremely mobile. By some authors the term
“_phyllidium_” is used for the outgrowth, and the term “_bothridium_”
is restricted to the muscular cup. _Bothria_, on the other hand, are
grooves more or less wide, the musculature of which is only slightly
developed and is not separated off internally from the parenchyma.
_Acetabula_, or suckers in the usual sense, are hemispherical cups,
without lips and with musculature separated internally from the
parenchyma.
Family. *Dibothriocephalidæ*, Lühe, 1902.
Syn.: _Diphyllobothriidæ_, Lühe, 1910.
Genitalia repeated in each proglottid (polyzootic Cestodes). Ventral
and dorsal surfaces flat. Cirrus unarmed. Cirrus and vagina if
non-marginal open on the same surface as the uterus. Uterus long,
convoluted, often forming a “rosette,” never dilates into a uterine
cavity. Eggs thick shelled, operculated, constantly being formed in
mature proglottids.
Sub-family. *Dibothriocephalinæ*, Lühe, 1899.
Syn.: _Diphyllobothriinæ_, Lühe, 1910.
Segmentation distinct. Scolex unarmed, elongated, sharply separated
(generally by a neck) from the first proglottis. Cirrus and vagina
open ventrally. Genital pores non-alternating. Vas deferens
surrounded by a muscular bulb. Receptaculum seminis large, sharply
separated from the spermatic duct.
Order. *Cyclophyllidea*, v. Beneden.
Four suckers always present. Uterine opening absent. Vitellarium
single. Genitalia atrophy when uterus is fully developed.
Family. *Dipylidiidæ*, Lühe, 1910.
Rostellum if present armed. Suckers unarmed. Uterus breaks up into
egg capsules. Paruterine organs absent.
Family. *Hymenolepididæ*, Railliet and Henry, 1909.
Segment always broader than long. Genitalia single. Longitudinal
muscles in two layers. Genital pores unilateral. Testes one to four.
Uterus persistent, sac-like. Eggs with three shells.
Family. *Davaineidæ*, Fuhrmann, 1907.
Rostellum cushion-shaped. Armed with numerous (sixty to several
thousand) hammer-shaped hooks in two (rarely one) rows.
Sub-family. *Davaineinæ*, Braun, 1900.
Suckers armed. Uterus breaks up into egg capsules. Paruterine organs
absent.
Family. _Tæniidæ_, Ludwig, 1886.
Suckers unarmed. Uterus with median longitudinal stem and lateral
branches. Female genitalia at the hind end of the proglottis. Genital
pore irregularly alternating. Testes numerous in front of female
genitalia. Ovary with two lobes (wings). Vitellarium behind the
ovary. Embryophore radially striated.
THE CESTODES OF MAN.
Most of the species to be mentioned live in man in their adult stage
and occupy the small intestine; man is the definite host of these
parasites, but is not the specific host for all the species; some of
these species, as well as others (of mammals), may occur in man also in
the larval stage.
Family. *Dibothriocephalidæ.*
Sub-family. *Dibothriocephalinæ.*
Genus. *Dibothriocephalus*, Lühe, 1899.
Syn.: _Diphyllobothrium_, Cobbold, 1858; _Bothriocephalus_, p. p.
Rud., 1819; _Dibothrius_, p. p. Rud., 1819; _Dibothrium_, p. p.
Dies., 1850.
Scolex egg-shaped; dorsal and ventral bothria elongated, moderately
strong, cutting rather deeply into the head; genitalia single in
each proglottis; papillæ in the vicinity of the genital atrium; the
testes and vitellaria are in the lateral fields, the former in the
medullary layer, the latter in the cortical layer on both surfaces,
and occasionally extending to the median line; the ovary ventral,
the shell gland dorsal. The uterus is in the central field, taking a
zigzag course, and frequently forms a rosette.
*Dibothriocephalus latus*, L., 1748.
Syn.: _Tænia lata_, L., 1748; _Tænia vulgaris_, L., 1748;
_Tænia grisea_, Pallas, 1796; _Tænia membranacea_, Pall., 1781;
_Tænia tenella_, Pall., 1781; _Tænia dentata_, Batsch, 1786;
_Bothriocephalus latus_, Bremser, 1819; _Dibothrium latum_,
Dies., 1850; _Bothriocephalus cristatus_, Davaine, 1874[281];
_Bothriocephalus balticus_, Kchnmstr., 1855; _Bothriocephalus
latissimus_, Bugn., 1886.
[281] Until recently this worm, which was understood to belong
to a separate species, was proved on examination by R. Blanchard
(“Mai. Par.,” 1896), to be _Dibothriocephalus latus_. Compare also
Galli-Valerio, in _Centralbl. f. Bakt., Path. und Infektionskr._, 1900
(1), xxvii, p. 308.
Length 2 to 9 m. or more; colour yellowish-grey; after lying in water
the lateral areas become brownish and the uterine rosette brown. The
head is almond-shaped, 2 to 3 mm. in length, the dorso-ventral axis is
longer than the transverse diameter; the head, therefore, generally
lying flat, conceals the suctorial grooves at the borders; these
suckers are deep and have sharp edges (fig. 205). The neck varies in
length according to the degree of contraction and is very thin; there
are 3,000 to 4,200 proglottids and there may be more; their breadth is
usually greater than their length, but in the posterior third of the
body they are almost square, and the very oldest are not uncommonly
longer than they are broad. There are numerous testes situated dorsally
in the medullary layer of the lateral fields; the vas deferens
(fig. 192) passes dorsally in transverse loops in the central field
anteriorly and forms a seminal vesicle before its entry into the large
cirrus pouch.
The orifice of the vagina is close behind the orifice of the cirrus;
the former passes almost straight along the median line posteriorly,
and widens into a receptaculum seminis shortly before its junction
with the oviduct; the ovary is bilobed, in shape like the wings of
a butterfly, ventrally in the medullary layer; the shell glands lie
in the posterior recess of the ovary; the uterus, forming numerous
transverse convolutions, passes ventral to the vas deferens forwards.
Eggs (fig. 207) large, with brownish shells and small lids, 68 µ to
71 µ by 45 µ; the ovarian cell, which is already, as a rule, in process
of segmentation, is surrounded by numerous large yolk cells; the
proglottids nearest the posterior extremity are frequently eggless.
[Illustration: FIG. 204.--Various chains of segments of
_Dibothriocephalus latus_, showing the central uterine rosette.
(Natural size.)]
[Illustration: FIG. 205.--Transverse section of the head of
_Dibothriocephalus latus_. 30/1.]
[Illustration: FIG. 206.--Fairly mature proglottis of
_Dibothriocephalus latus_. The vitellaria are at the sides; the uterus,
filled with eggs, is in the middle, also the vagina (the dark stripe
passing almost straight from the front to the back), and the vas
deferens (almost hidden by the uterus). Above in the centre is the
cirrus sac, and below the shell gland and ovary are seen. 15/1. (From a
stained preparation.)]
The eggs, which are deposited in the intestine and evacuated with
the fæces, hatch in water after a fortnight or more; the embryonal
integument (embryophore) of the oncosphere is provided with cilia;
after bursting open the lid of the egg the oncosphere in its
embryophore (fig. 207) reaches the water and swims slowly about; often
it slips out of its ciliated embryophore, sinks to the bottom and is
capable of a creeping motion; sooner or later it dies in the water.
The manner and means of its invasion of an intermediate host are
still unknown; yet we are aware that the larval stage (plerocercoid,
fig. 208), which resembles the scolex and may reach a length of 30 mm.,
lives in the intestine, in the intestinal wall, in the liver, spleen,
genital glands and muscular system (fig. 209) of various fresh-water
fish, the pike (_Esox lucius_), the miller’s thumb (_Lota vulgaris_),
the perch (_Perea fluviatilis_), _Salmo umbla_, _Trutta vulgaris_, _Tr.
lacustris_, _Thymallis vulgaris_ (grayling), _Coregonus lavaretus_,
_C. albula_ (in Europe) and _Onchorhynchus perryi_ (in Japan). The
transmission of the plerocercoids from these fish to the dog, cat and
man (Braun, Parona, Grassi and Ferrara, Grassi and Rovelli, Ijima,
Zschokke, Schroeder) leads to the development of the broad tapeworm,
the growth of which is rapid. In my experiments on human beings the
average number of proglottids formed per diem averaged thirty-one to
thirty-two for five weeks, with a length of 8 to 9 cm. According to
Parona the eggs appear twenty-four days after man has been infected.
Zschokke found the average growth in the experimental infection of man
between 5·2 and 8·2 cm. per diem, and the person experimented upon by
Ijima evacuated a piece of a _Dibothriocephalus latus_, 22·5 cm. in
length, only twenty-one days after the infection.
[Illustration: FIG. 207.--_Dibothriocephalus latus_: development of
egg. 1, segmentation complete; some cells of the blastosphere have
migrated through the yolk and have flattened to form _c_, the yolk
envelope; others form a layer of flattened cells (_e_) forming the
embryophore; the remaining cells (_d_) of the blastosphere form the
hexacanth embryo. 2, embryophore (_e_) is becoming thicker. 3, the
ciliated embryo has been pressed out of the shell; _s′_, the operculum;
_c_, the yolk envelope remaining in the shell (_s_); _y_, the yolk
consisting of separate cells. 4, a free-swimming larva much swollen by
the water. (After Benham and Schauinsland.)]
The “broad tapeworm” is a frequent parasite of man in some districts,
but it also occurs in the domestic dog, and on rare occasions is found
in the domestic cat (together with _Dibothriocephalus felis_, Crepl.)
and fox. French Switzerland and the Baltic Provinces of Russia are the
centres of distribution; from the former districts the distribution
radiates to France and Italy (Lombardy, Piedmont); from the Baltic
Provinces over Ingermanland to Petrograd, over Finland to Sweden (on
the shore of the Gulf of Bothnia), in a southerly direction to Poland,
and into the Russian Empire and across it to Roumania, and towards
the west along the coast of the Baltic Sea to the North Sea, where,
however, its frequency considerably diminishes (Holland, Belgium, and
the North of France).
In Turkestan and Japan the “broad tapeworm” is the most frequent
parasite of man; it has been reported in Africa from the vicinity
of Lake N’gami as well as from Madagascar; cases, in part at least
imported, have also come under observation in North America.
[Illustration: FIG. 208.--Plerocercoid of _Dibothricephalus latus_.
_A._, with the head evaginated; _B._, with the head invaginated. From
the muscle of the pike.]
[Illustration: FIG. 209.--A piece of the body wall of the Burbot, _Lota
vulgaris_. The tangential section has exposed the muscles of the trunk,
with a plerocercoid of _Dibothriocephalus latus_. Natural size.]
In Germany _Dibothriocephalus latus_--apart from the fact that it
is undoubtedly imported from Switzerland, Russia or Italy--is
particularly frequent in East Prussia amongst the inhabitants of the
Courland Lagoon district, on the Baltic; it is, moreover, also found in
the Province and even in the City of Königsberg. In West Prussia and
Pomerania it is very much scarcer.
It is also found in Munich and in the vicinity of the Lake of Starnberg
(Bollinger).
Krabbe found it in 10 per cent. of the sufferers from tapeworms in
Denmark; Szydlowski found the ova of this worm in Dorpat in 10 per
cent. of the fæces examined; Kruse found the worm in 6 per cent. of
_post-mortems_; Kessler, in Petrograd, found the eggs in the fæces in
7·8 per cent.; at _post-mortems_ he found the worms in 1·17 per cent.,
though Winogradoff only found it in 0·8 per cent. In Moscow, according
to Baranovsky, 8·9 per cent. of the fæces examined contained the ova of
_Dibothriocephalus_. In the interior and southern provinces of Sweden
the worm, according to Lönnberg, is only found sporadically, but, on
the other hand, in Angermanland about 10 per cent. of the population
is affected; while again in Norbotten the majority of persons are
affected, and in Haparanda the entire population (with the exception
of infants) harbour this parasite. In Switzerland _D. latus_ is very
frequent in close proximity to the lakes of Bieler, Neuchatel, Morat
and Geneva (according to Zaeslin 10 to 15 to 20 per cent. of the
population are affected); the parasite is less frequent in districts
one to four hours removed from these lakes.
Of the fish from Swiss lakes examined by Schor those from Lake Geneva
were most commonly infected, and especially _Lota_ sp. and _Perea_ sp.
The frequency and distribution have, nevertheless, decreased
perceptibly in places; at the commencement of the eighteenth century
the broad tapeworm was very common in Paris, at the present date it
only occurs when imported (Blanchard); in Geneva, also, according to
Zschokke, it has become rarer (formerly 10 per cent., now only 1 per
cent.).
The disturbances produced in man by the presence of broad tapeworms
are, as a rule, very trifling; in other cases they produce partly
gastric disorders and partly nervous symptoms; in a number of cases,
again, they set up severe anæmia, apparently caused by toxins
produced by the worms and absorbed by the host. There is no danger
of auto-infection, as the larval stage lives only in fishes, not in
warm-blooded animals. The case reported by Meschede (ova like those of
_Dibothriocephalus latus_ in the brain of a man who had suffered from
epilepsy for six years) must be otherwise explained.
Human beings, like other hosts, can only acquire the broad tapeworm by
ingesting its plerocercoids with the previously mentioned fresh-water
fishes; the opportunity for such infection is afforded the more readily
by the fact that not only do the lower classes not pay sufficient
attention to the cooking of fish, so that all the larvæ that are
present may be killed, but also in certain localities the custom exists
of eating some parts of these fishes in a raw condition; even the
mere handling of the usually severely infected intermediary hosts may
occasionally cause infection. The plerocercoids are as well known as,
but differ materially in appearance from, the cysticerci (_Cysticercus
cellulosæ_) of pig’s flesh. In Germany the occurrence of the
plerocercoids of _Dibothriocephalus latus_ has been confirmed in the
pike, miller’s thumb and perch of East Prussia, and more particularly
in those taken from the Courland Lagoon.
The life of _D. latus_ is a very long one (six to fourteen years), as
is deduced from persons who have left _D. latus_ regions after they
have been infected.
According to the experiments of M. Schor, plerocercoids of _D. latus_
placed in slowly warmed water completely lose their movement at 54° to
55° C.; they survive the death of their host for several days; they
are killed by low temperatures -3° to +1° C. in two days; strong acids
and salt solutions kill them at once, also high temperatures, but all
the same at least ten minutes is required in boiling or frying fish in
order to kill the plerocercoids with certainty.
*Dibothriocephalus cordatus*, R. Lkt., 1863.
Syn.: _Bothriocephalus cordatus_, R. Lkt.
[Illustration: FIG. 210.--Cephalic end of _Dibothriocephalus
cordatus_; on the left viewed sideways, on the right from the dorsal
surface, showing a suctorial groove. (After Leuckart.)]
Length, 80 to 115 cm.; the head is heart-shaped and measures 2 by 2 mm.
The suctorial grooves are on the flat surface; the segments commence
close behind the head and increase rapidly in breadth. At only 3 cm.
behind the head they are already mature; the greatest breadth attained
by them averages 7 to 8 mm., the length 3 to 4 mm.; the number of
proglottids averages 600; the most posterior ones are usually square.
The uterine rosette is generally formed of six to eight lateral loops.
The eggs are operculated and measure 75 µ by 50 µ.
_Dibothriocephalus cordatus_ is a common parasite of the seal, the
walrus and the dog in Greenland and Iceland, occasionally of man also.
No doubt its larva lives in fishes.
The statement that _D. cordatus_ also occurs in Dorpat in human
beings has been proved erroneous (_Zool. Anzeiger_, 1882, v,
p. 46), as also has the report that this worm lives in hares in the
neighbourhood of Berlin, whither it was supposed to have been carried
by Esquimaux dogs (Rosenkranz in _Deutsch. med. Wochenschr._, 1877,
iii, p. 620). The parasite stated by the author to be _D. cordatus_
is _Tænia pectinata_, Goeze, which has been known since 1766.
*Dibothriocephalus parvus*, Stephens, 1908.
Largest gravid segments 5 by 3 mm. Uterus forms a central rosette
with four to five loops on each side of median line. In a proglottid
measuring 3·5 by 2·25 mm. the genital atrium is situated 0·4 to
0·5 mm. behind the anterior margin and the uterine opening the same
distance behind the genital atrium. Calcareous corpuscles absent in the
preserved specimens. Eggs operculated, 59·2 µ by 40·7 µ.
Distinguished from _Dibothriocephalus latus_--(1) by the size of gravid
segments (the minimum width of gravid segments of _D. latus_ is 10
to 12 mm., so that _D. parvus_ is a much smaller worm); (2) quadrate
segments of _D. latus_ measure 6 by 6 mm., those of _D. parvus_ 4 by
4 mm.; (3) by the eggs.
From _D. cordatus_ it is distinguished by--(1) _D. cordatus_ has only
fifty immature segments, _D. parvus_ has at least 200, possibly more;
(2) mature segments of _D. cordatus_ measure 7 to 8 mm., maximum width
of _D. parvus_ is 5 mm.; (3) quadrate segments of _D. cordatus_ measure
5 to 6 mm.; (4) _D. cordatus_ has six to eight uterine loops; (5) _D.
cordatus_ measures 75 µ to 80 µ by 50 µ.
_Habitat._--Intestine of man (Syrian, in Tasmania).
Genus. *Diplogonoporus*, Lönnbrg., 1892.
Syn.: _Krabbea_, R. Blanch., 1894.
The scolex is short and has powerful suctorial grooves; no neck; the
proglottids are short and broad; there are two sets of genital organs
side by side in each segment, which in all essentials resemble the
single one of _Dibothriocephalus_.
Parasitic in whales and seals, occasionally in man.
*Diplogonoporus grandis*, R. Blanch., 1894.
Syn.: _Bothriocephalus_ sp., Ijima et Kurimoto, 1894; _Krabbea
grandis_, R. Blanch.
Scolex unknown; chain of proglottids over 10 m. in length, 1·5 mm.
broad anteriorly, 25 mm. broad posteriorly. The proglottids are very
short (0·45 mm.), but 14 to 16 mm. broad. On either side to the right
and left of the worm, along the entire ventral surface, there is a
longitudinal groove; these grooves are nearer to each other than to
the lateral margin; in them lie the genital pores, and they are in the
same sequence as in _Dibothriocephalus_; corresponding to the scanty
length (0·45 mm.) of the proglottids, the ovary is only developed
transversely; the uterus only makes a few loops. Eggs (fig. 195) thick
shelled, brown, 63 µ by 48 µ to 50 µ. This parasite has hitherto been
observed twice in Japanese. Similar species are known in Cetacea and
seals.
[Illustration: FIG. 211.--_Diplogonoporus grandis_, Lühe, 1899: ventral
view of a portion of the strobila, showing two rows of genital pores
and partially extruded cirri. (After Ijima and Kurimoto.)]
[Illustration: FIG. 212.--_Diplogonoporus grandis_: ventral view
(diagrammatic) of genitalia of left side; _cir_, cirrus; _cir.o_,
cirrus opening; _dtg._, vitelline duct; _ov._, ovary; _ovd._, oviduct;
_sb._, receptaculum seminis; _ut._, uterus; _ut.o._, uterine pore;
_vag._, vagina; _vag.o._, vaginal pore; _vd_, vas deferens. × 150.
(After Ijima and Kurimoto.)]
*Sparganum*, Diesing, 1854.
The term _Sparganum_, invented by Diesing, is used as a group name of
larval bothriocephalid Cestodes whose development is not sufficiently
advanced to enable them to be assigned to any particular genus.
*Sparganum mansoni*, Cobb., 1883.
Syn.: _Ligula mansoni_, Cobbold, 1883; _Bothriocephalus linguloides_,
R. Lkt., 1886; _Bothriocephalus mansoni_, R. Blanch., 1886.
These plerocercoids were discovered in 1882 by P. Manson during
the _post-mortem_ on a Chinaman who had died in Amoy, twelve
specimens being found beneath the peritoneum and one free in the
abdominal cavity. Cobbold described them as _Ligula mansoni_, and
Leuckart, who contemporaneously reported a case in Japan, termed them
_Bothriocephalus liguloides_. Ijima and Murata reported eight further
cases, and Miyake records nine further cases, seven of which are
recorded in Japanese literature.
[Illustration: FIG. 213.--Cephalic end of _Sparganum mansoni_, Cobb.
(After Leuckart.)]
[Illustration: FIG. 214.--_Sparganum mansoni_: on the right in
transverse section. Natural size. (After Ijima and Murata.)]
The plerocercoid, which hitherto alone is known to us, attains a length
of 30 cm. and a breadth of 3 to 6 to 12 mm. The ribbon-shaped body is
wrinkled, the lateral borders are often somewhat thickened, so that
the transverse section has the form of a biscuit; the anterior end
is usually wider and has the head provided with two weak suctorial
grooves, either retracted or protracted.
The parasite makes migrations within the body, and thus may reach the
urinary passages; then it is either evacuated with the urine or has
to be removed from the urethra; not rarely it causes non-inflammatory
tumours on various parts of the skin, which are at times painful and at
times vary in size.
Nothing is known of its development and origin.
*Sparganum proliferum*, Ijima, 1905.
Syn.: _Plerocercoides prolifer_, Ijima, 1905; _Sparganum prolifer_,
Verdun, Manson, 1907.
These plerocercoids produce an acne-like condition of the skin.
The condition is really one of capsules in great abundance in the
subcutaneous tissue and less so in the corium and in the intermuscular
connective tissue. The encapsuled worms in the corium feel like
embedded rice grains and raise the epidermis, giving rise to an
acne-like condition. Many thousands occur scattered over the body; in
Ijima’s Japanese case there were over 10,000 in the left thigh. The
worms when they first appear in the skin cause itching. The capsules
are ovoid, generally about 1 to 2 mm. in diameter, but they may be
smaller and also much larger. The larger ones occur in the subcutaneous
tissue. The capsules consist of dense tough connective tissue.
Each capsule, as a rule, contains one worm, but as many as seven may
occur. The skin of areas that have been long infected is swollen and
indurated or adherent, giving a somewhat elephantoid appearance. The
subcutaneous tissue is thick and filled with slimy fluid or in other
parts sclerosed.
[Illustration: FIG. 215.--_Sparganum prolifer_: left with buds, right
extended. × 4. (After Ijima.)]
[Illustration: FIG. 216.--_Sparganum proliferum._ × 10. (After Stiles.)]
_The Worm._--The chief peculiarity is its irregular shape and its
reproduction in the larval stage by forming supernumerary heads, which
are supposed to wander about the body.
The simplest forms are thread-like bodies, flat or round, 3 mm. long
and 0·3 mm. in diameter, but they may be 12 mm. long by 2·5 mm. broad.
The narrow end is the head, which in life invaginates and evaginates,
but there is no indication of any suckers, except an inconstant
terminal depression. In addition to these simple forms the most
complicated and irregular forms occur, due to the formation of buds
(heads) at various parts. The detachment and growth of a head account
for the presence of more than one worm in a cyst. The irregularity in
form is also increased by the presence in the subcuticular tissue of
the worm of _reserve food bodies_. These bodies are supposed to be of
this nature and are spherical, 100 µ to 300 µ in diameter, but also
much elongated.
_Calcareous bodies_ in the Japanese worms were 7·5 µ to 12 µ; in the
Florida worms 8·8 µ to 17·6 µ.
_Mode of Infection._--Probably from eating uncooked fish.
_Distribution._--Japan, Florida.
Family. *Dipylidiidæ*, Lühe, 1910.
Genus. *Dipylidium*, R. Lkt., 1863.
Rostellum retractile, with several rings of alternating hooks; the
latter with a disc-like base, having the shape of the thorns of a
rose. Genital pores opposite; genitalia double. Testes very numerous
in the central field; ovary with two lobes; the vitellaria, which are
smaller, behind them; the uterus forms a reticulum, in the network of
which the testicular vesicles lie; later on it breaks up into sacs
enclosing one or several eggs. The eggs have a double shell.
*Dipylidium caninum*, L., 1758.
Syn.: _Tænia canina_, L., 1758, p. p.; _Tænia moniliformis_, Pallas,
1781; _Tænia cucumerina_, Bloch, 1782; _Tænia elliptica_, Batsch,
1786; _Dipylidium cucumerinum_, Lkt., 1863.
[Illustration: FIG. 217.--_Dipylidium caninum_: on the left, the
scolex, neck and the first proglottids; on the right, at the top, a
packet of ova; below, hooks of the rostellum, side and front views;
below, an ovum. Various magnifications. (After Diamare.)]
[Illustration: FIG. 218.--_Dipylidium caninum_; egg showing _a_,
egg-shell (vitelline membrane of Moniez); _b_, albuminous coat; _c_,
internal shell formed of or secreted by an outer layer of blastomeres
(Moniez); _d_, hexacanth embryo. (After Benham and Moniez.)]
This worm measures 15 to 35 cm. in length and 1·5 to 3 mm. in breadth.
The scolex is small, rhomboidal, and has a club-shaped rostellum on
which there are, in three to four rings, forty-eight to sixty hooks
resembling rose thorns, the size of those in the foremost being 11 µ
to 15 µ and those in the hindmost ring 6 µ. The neck is very short,
the most anterior segments broad and short, the middle as long as they
are broad; the mature segments are longer than wide (6 to 7 mm. by 2
to 3 mm.), fairly thick, are frequently of a reddish colour, and when
cast off resemble cucumber seeds. The genital pores lie symmetrically
at the lateral margins; the roundish egg sacs, arising from the
uterine reticulum, contain eight to fifteen eggs embedded in a reddish
cement substance (in life). The eggs are globular (43 µ to 50 µ,); the
embryonal shell (embryophore) is thin, the oncosphere measures 32 µ to
36 µ. Surrounding the embryophore is an albuminous coating, and outside
this the thin vitelline envelope (fig. 218).
[Illustration: FIG. 219.--_Dipylidium caninum_: central portion of a
proglottis. _C.p._, cirrus sac; _V.s._, vitellaria; _Ex.v._, excretory
vessels; _T._, testicles lying in the meshes of the uterine reticulum
which laterally forms pouches; _O._, ovary; _U._, reticulum of uterus;
_V._, vagina and seminal receptacle (below ovary). Magnified. (After
Neumann and Railliet.)]
[Illustration: FIG. 220.--_Dipylidium caninum_: development of embryo.
1, solid hexacanth embryo; 2, primitive lacuna (_a_) in the embryo; 3,
elongation of hinder part, rudiments of sucker and rostellum appearing;
4, “body” and “tail” distinct, (_b_) and (_c_) excretory system; 5,
fore-body invaginates into hind-body, excretory bladder has a pore; 6,
tail has dropped off; scolex growing up into secondary cavity formed by
fore-body; the primitive cavity has been absorbed at stage 4. (After
Benham, Grassi and Rovelli.)]
_Dipylidium caninum_ is a common intestinal parasite of dogs, in
which it grows larger (_Tænia cucumerina_, Bloch) than in cats (_T.
elliptica_, Batsch); it has, however, also been found in jackals, as
well as in human beings, though in the latter it is of comparatively
rare occurrence (twenty-four cases), and almost always affects
children, generally of tender age. One-third of all the cases in
children were sucklings, about a quarter of all the cases recorded were
adults, and these occurred throughout all Europe with the exception of
Spain and Italy.
[Illustration: FIG. 221.--Larva (cysticercoid) of _Dipylidium caninum_,
consisting of body and tail. The latter is solid and bears on it the
embryonal spines. The bladder, which was only slightly developed, has
disappeared, and the fore-part of the body bearing the rostellum is now
seen invaginated into the hind portion. The hooklets are shown in front
of the excretory system which has now developed. At a further stage
the tail drops off; the head now evaginates, but is still enclosed in
a double-walled sac formed by the prolongation upwards on each side of
the topmost parts of the body shown in the figure. _Cf._ fig. 220, 6.
Enlarged. (After Grassi and Rovelli.)]
The proglottids, which leave the intestine spontaneously, are
recognizable by the naked eye on account of their form and reddish
colour, as well as their two genital pores. As a rule, the presence of
this parasite sets up no marked symptom in the patient.
The corresponding larval form (cysticercoid) lives in the louse of
the dog (_Trichodectes canis_), a fact that was first established by
Melnikow and Leuckart; according to Grassi and Rovelli, as well as
Sonsino, it also lives in the flea of the dog (_Ctenocephalus canis_)
and in the flea of man (_Pulex irritans_), but not in its larva.
The adult segments, which also leave the rectum of dogs and cats
spontaneously, creep about around the anus and get into the hair, and
are thus partly dried and disintegrated. Part of the segments, or the
oncospheres released by disintegration, are then taken up by lice and
fleas, within which they develop into larvæ (cysticercoids). Dogs and
cats are thus infected by their own skin parasites, which they bite
and swallow whilst gnawing at their fur. The infection of human beings
must occur in an analogous manner, by transmission of the cysticercoids
present on the lips or tongue of dogs when the latter lick them, or it
may be that the vermin of cats and dogs harbouring cysticercoids are
accidentally and directly swallowed by human beings.
Family. *Hymenolepididæ*, Railliet and Henry, 1909.
Genus. *Hymenolepis*,[282] Weinland, 1858.
[282] The genus is by some authors divided into two
sub-genera--Hymenolepis, s. str., and Drepanidotænia, Raill.
_Drepanidotænia._--Body, broad lanceolate, testes three, female
genitalia antiporal beside the testes. Scolex small, with eight
hooks. Neck very short, longitudinal muscle bundles very numerous. No
accessory sac opening into genital atrium.
_Hymenolepis._--Narrow, female genitalia ventral to or between testes.
Accessory sac (opening into genital atrium) usually absent. Vas
deferens with an external (outside cirrus sac) and an internal
(inside cirrus sac) “seminal vesicle.” Three testes in each
proglottis. The eggs are round or oval with two to four distinct
envelopes. In mammals and birds.
*Hymenolepis nana*, v. Sieb., 1852.
Syn.: _Tænia nana_, v. Sieb., 1852, _nec_ van Beneden, 1867; _Tænia
ægyptiaca_, Bil., 1852; _Diplacanthus-nanus_, Weinld., 1858; _Tænia_
(_Hymenolepis_) _nana_, Lkt., 1863.
The worm is 10 to 45 mm. in length and 0·5 to 0·7 mm. in breadth; the
head is globular, 0·25 to 0·30 mm. in diameter. The rostellum has a
single circlet consisting of twenty-four or twenty-eight to thirty
hooks, which are only 14 µ to 18 µ in length. The neck is moderately
long; the proglottids are very narrow, up to 200 in number, 0·4 to
0·9 mm. in breadth, and 0·014 to 0·030 mm. in length. The eggs are
globular or oval, 30 µ to 37 µ to 48 µ; the oncospheres measure 16 µ
to 19 µ in diameter, with two coats, separated by an intervening
semi-fluid substance (fig. 224).
This species was discovered by Bilharz in Cairo in 1851; it was found
by him in great numbers in the intestine of a boy who had died of
meningitis. For several years this was the only case, until 1885,
since when numerous cases have come to light. Spooner (1873) even
reported a case from North America, which may, however, have related
to _Hymenolepis diminuta_. In Europe the worm is particularly frequent
in Sicily, but it has also been repeatedly observed in North Italy;
it has, moreover, been reported from Russia, Servia, England, France,
Germany, North and South America, the Philippines, Siam and Japan, in
all over 100 cases. Notwithstanding its small size this worm causes
considerable disorders in its hosts--mostly children--as it sets up
loss of appetite, diarrhœa, various nervous disturbances, and even
epilepsy; all these symptoms, however, disappear after the expulsion of
the parasites, which are generally present in large numbers.
[Illustration: FIG. 222.--_Hymenolepis nana_, v. Sieb. About 12/1.
(After Leuckart.)]
[Illustration: FIG. 223.--_Hymenolepis nana_: head. Enlarged. (After
Mertens.)]
[Illustration: FIG. 224.--_Hymenolepis nana_: an egg. Highly magnified.
(After Grassi.)]
[Illustration: FIG. 225.--Longitudinal section through the intestinal
villus of a rat, with the larva (cysticercoid) of _Hymenolepis murina_.
Magnified. (After Grassi and Rovelli.)]
[Illustration: FIG. 226.--_Hymenolepis nana_ (_murina_): cross section
of proglottis from a rat. _c.p_., cirrus sac; _rec. sem._, receptaculum
seminis; _s.g._, shell gland; _ov._, ovary; _t._, testis; _cort.
par._, cortical parenchyma; _m.l.n._, main lateral nerve; _ex. can._,
excretory canal; _y.g._, vitellarium. (After v. Linstow.)]
[Illustration: FIG. 227.--_Hymenolepis nana_: longitudinal section of
an embryo. _bl.p._, anterior opening of secondary cavity; _caud._,
caudal appendage; _pr. cav._, primary cavity; _sec. cav._, secondary
cavity. Enlarged. (After Grassi and Rovelli.)]
The development as well as the manner of infection is still unknown;
Grassi is of opinion that _Hymenolepis nana_ is indeed merely a variety
of _Hymenolepis murina_, Duj., which lives in rats. According to
Grassi direct development takes place with omission of the intermediate
host, but with the retention of the larval stage; that is to say, rats
infect themselves directly with _Hymenolepis murina_, by ingesting the
mature segments or oncospheres of this species, from which subsequently
the small larvæ originate in the intestinal wall (fig. 225); when fully
developed they fall into the intestinal lumen and become tapeworms.
The identity of the two forms has nevertheless been disputed (Moniez,
R. Blanchard, v. Linstow), though their near relationship cannot be
denied. Grassi gave mature segments of _Hymenolepis murina_ to six
persons, but only one person evacuated a tapeworm. This, however,
proves nothing in a district where _Hymenolepis nana_ frequently
occurs in man; it was, moreover, not possible to infect rats with
segments of _Hymenolepis nana_ (of man). Accordingly this form may
represent an independent species, which, however, like _Hymenolepis
murina_, also omits an intermediate host.
*Hymenolepis diminuta*, Rud., 1819.
Syn.: _Tænia diminuta_, Rud., 1819; _Tænia leptocephala_, Crepl.,
1825; _Tænia flavopunctata_, Weinld., 1858; _Tænia varesina_, E.
Parona, 1884; _Tænia minima_, Grassi, 1886.
This species measures 20 to 60 cm. in length, and up to 3·5 mm. in
breadth; there are from 600 to 1,000 segments. The head is very small
(0·2 to 0·5 mm.), it is club-shaped and has a rudimentary unarmed
rostellum; the neck is short; the mature segments are 3·5 mm. in
breadth, 0·66 mm. in length; the eggs are round or oval. The outer
egg-shell is yellowish and thickened, with indistinct radial stripes;
the inner embryonal shell (embryophore) double, thin; the outer layer
is somewhat pointed at the poles; oncosphere 28 µ by 36 µ. Between the
inner and outer shells is a middle granular layer.
[Illustration: FIG. 228.--_Hymenolepis diminuta_: scolex. Magnified.
(After Zschokke.)]
[Illustration: FIG. 229.--_Hymenolepis diminuta_: two proglottids
showing testes (3), ovary and vagina. Slightly enlarged. (After
Grassi.)]
[Illustration: FIG. 230.--_Hymenolepis diminuta_: egg from man. (After
Bizzozero.)]
_Hymenolepis diminuta_ lives in the intestine of rats--_Mus decumanus_
(the sewer rat), _Mus rattus_ (the black rat), and _Mus alexandrinus_,
rarely in mice; it is occasionally also found in human beings.
Weinland described it from specimens collected by Dr. E. Palmer in
1842, in Boston, from a child aged 19 months, as _T. flavopunctata_.
A second case relating to a three year old child, from Philadelphia,
was only reported in 1889 by Leidy; a third case was simultaneously
reported of a two year old girl in Varese (_T. varesina_); and Grassi
described another case relating to a twelve year old girl from Catania
(Sicily). Sonsino and Previtera reported the same species in Italy,
Zschokke in France, Lutz and Magalhães in South America, and Packard
in North America: a total of twelve cases, five from America, the rest
from Europe (Ransom).
According to Grassi and Rovelli the larval stage lives in a small
moth (_Asopia farinalis_), as well as in its larva, in an orthopteron
(_Anisolabis annulipes_), and in coleoptera (_Acis spinosa_ and
_Scaurus striatus_). Experimental infections have been successful on
rats as well as on human beings. In America other species of insects
may be the intermediary hosts.
[Illustration: FIG. 231.--_Hymenolepis diminuta_: cysticercoid from the
rat flea (_Ceratophyllus fasciatus_). _a_, remains of primary vesicle;
_b_, fibrous layer; _c_, radially striated layer resembling cuticle;
_d_, layer of columnar cells; _e_, parenchymatous layer of irregularly
disposed cells; _f_, parenchymatous layer. (Stephens, after Nicoll and
Minchin.)]
Nicoll and Minchin[283] found in the body cavity of 4 per cent. of rat
fleas (_Ceratophyllus fasciatus_) the cysticercoid of _Hymenolepis
diminuta_. That it belonged to this species was shown by its unarmed
rostellum and by feeding; 340 fleas were fed to white rats and
fourteen worms obtained, _i.e._, about 4 per cent., thus corresponding
to the infection of the fleas. The development in the flea probably
begins in the pupal stage, the eggs being ingested by the older flea
larvæ. The larva is 0·31 by 0·25 mm.; tail 0·8 mm., scolex 0·075 by
0·09 mm., suckers, 0·055 mm. in diameter. Microscopically it shows--(1)
externally a radially striated layer resembling cuticle, (2) a layer of
columnar cells, (3) parenchymatous layer continuous with the tail, (4)
fibrous layer around the small caudal vesicle, then the parenchymatous
scolex at the bottom of the secondary cavity.
[283] _Proc. Zool. Soc._, 1911, p. 9.
Nicoll and Minchin (_loc. cit._) found a cysticercoid[284] in the rat
flea _Ceratophyllus fasciatus_ which was probably that of _Hymenolepis
murina_. Body 0·16 mm., tail 0·19 mm., scolex 0·096 mm. in diameter.
Rostellum has twenty-three spines in a single row. Length 0·017 mm.,
handle 0·01 mm., guard 0·007 mm., prong 0·007 mm. Sucker 0·042 mm.
Although this cycle, then, for _H. murina_ also exists, it is not
probable that rats (or man in the case of _H. nana_ if this be
considered distinct) infect themselves in this way, as they hardly
ingest all the necessary fleas to account for the massive infection
which frequently exists in rats (and man), so that Grassi’s cycle holds
good as the predominant method. _Xenopsylla cheopis_ has also been
found by Johnston to harbour both cysticercoids in Australia.
[284] A third cysticercoid resembling this, but without hooks, has also
been found.
*Hymenolepis lanceolata*, Bloch, 1782.
Syn.: _Tænia lanceolata_, Bloch, 1782; _Drepanidotænia lanceolata_,
Railliet, 1892.
[Illustration: FIG. 232.--_Hymenolepis lanceolata_. Natural size.
(After Goeze.) To the right above, two hooks. 120/1. (After Krabbe.)]
[Illustration: FIG. 233.--_Hymenolepis lanceolata_: diagram of female
genitalia. _ov._, ovary; _ovd._, oviduct; _rec. sem._, receptaculum
seminis; _s.g._, shell gland; _ut._, uterus; _y.g._, vitellarium.
(After Wolffhügel.)]
The parasite measures 30 to 130 mm. in length and 5 to 18 mm. in
breadth; the head is globular and very small; the rostellum is
cylindrical, with a circlet composed of eight hooks (31 µ to 35 µ in
length). The neck is very short. The short segments increase gradually
and equally in breadth, but only a little in length; the female
glands lie on the side opposite to that on which the genital pore is
situated; the three elliptical testes are on the same side as the
pores; the cirrus is armed and slender. The eggs have three envelopes
and are oval (50 µ by 35 µ), the external envelope is thin, the middle
intermediate layer or envelope is not so marked as in _H. diminuta_,
and the internal one is very thin and sometimes has polar papillæ, as
in _Hymenolepis diminuta_ and _H. nana_.
It inhabits the intestine of the following birds: Domesticated ducks
and geese, the Muscovy duck (_Cairina moschata_), white-headed duck
(_Erismatura leucocephala_), the pochard (_Nyroca rufina_), and the
flamingo (_Phœnicopterus antiquorum_). It has been recorded from Great
Britain, France, Denmark, Austria and Germany.
Zschokke reports the receipt of two specimens which a twelve year old
boy in Breslau evacuated spontaneously at two different times.
The corresponding larva, according to Mrázek, lives in fresh water
_Cyclops_; according to Dadai it is likewise found in another copepod,
_Diaptomus spinosus_, but the hooks of Dadai’s larva differed in size.
Family. *Davaineidæ*, Fuhrmann, 1907.
Sub-family. *Davaineinæ*, Braun, 1900.
Genus. *Davainea*, R. Blanch., 1891.
The large scolex is more or less globular, much wider than the
rostellum, which is furnished with two rings of very small and
numerous hooks. Neck absent, proglottids few, genitalia single.
Parasitic chiefly in birds.[285]
[285] [The larval stage of the Davaineas occurs in slugs (_Limax_) and
snails (_Helix_).--F. V. T.]
*Davainea madagascariensis*, Davaine, 1869.
Syn.: _Tænia madagascariensis_, Dav.; _Tænia demerariensis_, Daniels,
1895.
This worm measures 25 to 30 cm. in length; the head has four large
round suckers; the rostellum has ninety hooks (18 µ in length); there
are 500 to 700 segments, of which the last 100 are filled with eggs and
form half of the entire worm. The segments, when mature, measure 2 mm.
in length by 1·4 mm. in breadth; genital pores unilateral; about fifty
testes; the uterus consists of a number of loops, which at each side
are rolled up into an almost spherical ball; when filled with eggs the
convolutions unwind, permeate the segment and then lose their wall; the
eggs lying free in the parenchyma become finally surrounded, one, or
several together, by proliferating parenchymatous cells; this is how
the 300 to 400 egg masses, taking up the entire mature segment, are
formed. The globular oncosphere (8 µ) is surrounded by two perfectly
transparent shells, the outer of which terminates in two pointed
processes.
[Illustration: FIG. 234.--Scolex of _Davainea madagascariensis_. The
hooks have fallen off. 14/1. (After Blanchard.)]
_Davainea madagascariensis_ has hitherto been found in man only (eight
times). Davaine described this species from fragments sent to him from
Mayotta (Comoro Islands), which were found in two Creole children.
Chevreau observed four cases in Port Louis (Mauritius), likewise
in children; Leuckart received the first perfect specimen--it was
obtained from a three year old boy, the son of a Danish captain, in
Bangkok; Daniels, at the _post-mortem_ of an adult native of George
Town, Guiana, found two specimens (_Tænia demerariensis_); and finally
Blanchard describes another perfect specimen which was in Davaine’s
collection of helminthes in Paris, and which was obtained from a little
girl 3 years old, of Nossi-Bé (Madagascar). The intermediate host is
unknown.
*Davainea (?) asiatica*, v. Linst., 1901.
Syn.: _Tænia asiatica_, v. Linstow.
There exists only one headless specimen of this species, which is
not quite adult, and which is preserved in the Zoological Museum of
the Imperial Academy of Science in Petrograd. It came from a human
being and was found by Anger in Aschabad (Asiatic Russia, near the
northern frontier of Persia). The specimen measures 298 mm. in length.
The breadth anteriorly is only 0·16 mm., the posterior part measures
1·78 mm. across. The number of segments is about 750. The genital pores
are unilateral; the testes are globular and lie in a dorsal and ventral
layer in the medullary layer; the cirrus pouch is pyriform, 0·079 mm.
in length and 0·049 mm. in breadth; the female glands lie in the
fore-part of the segments, the ovary reaching to the excretory vessels;
the vitellarium is small and round. The vagina has a large fusiform
receptaculum seminis; the uterus breaks up into sixty to seventy large,
irregularly polyhedric eggsacs.
Family. *Tæniidæ*, Ludwig, 1886.
Genus. *Tænia*, L., 1758.[286]
With the characters of the family. In the genus Cladotænia recognized
by some authors, the testes encroach on the mid field and the uterine
stem reaches the anterior end of the segment.
[286] The Greeks termed the tapeworms ἕλμινθες πλατεῖαι, more rarely
χηρία (= fascia); the Romans called them _tænia_, _tinea_, _tæniola_,
later _lumbrici_, usually with the addition _lati_, to distinguish
them from the _Lumbrici teretes_ (_Ascaridæ_). The proglottids were
called _Vermes cucurbitini_; the cysticerci χάλαζαι (hailstones),
later hydatids. Plater (1602) was the first to differentiate _Tænia
intestinorum_ (= _Bothriocephalus latus_) amongst the _Lumbrici lati_
of man from _Tænia longissima_ (= _Tænia solium_). The term _solium_
was already used by Arnoldus Villanovanus, who lived about 1300; and,
according to him, it signifies “cingulum” (belt, chain), while N.
Andry, in 1700, traces this word from “solus,” because the worm occurs
always singly in man. Leuckart and Krehl derive the word “solium”
from the Syrian “schuschl” (the chain), which in Arabian has become
“susl” or “sosl,” and in Latin has become “sol-ium.” What Linnæus
described under the term _Tænia solium_ was really _Tænia saginata_;
the latter was first distinguished by Goeze, but was forgotten until
Küchenmeister, in 1852, again called attention to the differences.
*Tænia solium*, L., _p. p._, 1767.
Syn.: _Tænia cucurbitina_, Pall., 1781; _Tænia pellucida_, Goeze,
1782; _Tænia vulgaris_, Werner, 1782; _Tænia dentata_, Gmel., 1790;
_Halysis solium_, Zeder, 1800; _Tænia humana armata_, Brera, 1802;
_Tænia_ (_Cystotænia_) _solium_, Lkt., 1862.
The average length of the entire tapeworm is about 2 to 3 m., but may
be even more; the head is globular, 0·6 to 0·8 to 1·0 mm. in diameter.
The rostellum is short with a double circlet of hooks, twenty-two to
thirty-two in number, usually twenty-six to twenty-eight; large and
small hooks alternate regularly; the length of the large hooks is
0·16 to 0·18 mm., of the small ones 0·11 to 0·14 mm. The rostellum is
sometimes pigmented. The suckers are hemispherical, 0·4 to 0·5 mm.
in diameter. The neck is fairly thin and long (5 to 10 mm.). The
proglottids, the number of which averages from 800 to 900, increase in
size very gradually; at about 1 m. behind the head they are square and
have the genitalia fully developed. Segments sufficiently mature for
detachment measure 10 to 12 mm. in length by 5 to 6 mm. in breadth. The
genital pores alternate fairly evenly at the lateral margin a little
behind the middle of each segment. The fully developed uterus consists
of a median trunk, with seven to ten lateral branches at either side,
some of which are again ramified. The eggs are oval, the egg-shell
very thin and delicate; the embryonal shell (embryophore) is thick,
with radial stripes; it is of a pale yellowish colour, globular, and
measures 31 µ to 36 µ in diameter; the oncospheres, with six hooks, are
likewise globular, and measure 20 µ in diameter (fig. 238).
Malformations are not so common as in _T. saginata_; they consist in
two or several proglottids being partly or entirely fused, formation
of single club-shaped segments, fenestration of long or short series
of segments and so-called double formation, in which the head has six
suckers and the segments exhibit a *Y*-shaped transverse section. The
oncospheres occasionally also possess more than six hooklets. Very
slender specimens have led to the description of a particular species
or variety (_T. tenella_).
In its fully developed condition _T. solium_ is found exclusively in
man; the head is usually attached in the anterior third of the small
intestine and the chain, in numerous convolutions, extends backwards;
a few mature detached proglottids usually lie at the most posterior
part, and these are usually evacuated during defæcation. In exceptional
cases single proglottids or whole worms may reach contiguous organs
if abnormal communications with them exist; thus they may reach the
abdominal cavity and the urinary bladder, or they may be found in a
so-called worm abscess of the peritoneum; occasionally, in vomiting,
single segments or several together may be brought up. Exceptionally it
induces severe anæmia.
[Illustration: FIG. 235.--Two fairly mature proglottids of _Tænia
solium_, showing ovaries (one bi-lobed), vitellaria, central uterine
stem, cirrus and vas deferens (above), vagina (below), testes
(scattered), longitudinal and transverse excretory vessels.]
[Illustration: FIG. 236.--Head of _Tænia solium_. 45/1.]
The _larval stage_ (_Cysticercus cellulosæ_) that gives rise to _Tænia
solium_ lives normally in the intramuscular connective tissue and other
organs of the domestic pig, but it is known to exist also in a few
other mammals, such as the wild boar, the sheep,[287] the stag, dog,
cat, brown bear and monkey, as well as in man. The cysticercus of
the pig is an elliptical vesicle with a longitudinal diameter of 6 to
20 mm., and a transverse diameter of 5 to 10 mm.
[287] The larvæ which on rare occasions are found in the muscular
system of sheep are either strayed specimens of _Cysticercus
tenuicollis_, which normally develop in organs of the abdominal cavity,
and appertain to _Tænia marginata_ of the dog, or actually _Cysticercus
cellulosæ_. (_Cf._ Bongert, in _Zeitschr. f. Fleisch- u. Milchhyg._,
1899, ix, p. 86.)
Even with the naked eye a white spot may be observed in the centre
of the long equator, this being the invaginated head; it is easy to
make it project by pressing on the vesicle (after tearing off with the
finger-nail the investing connective tissue), and on examining it under
the microscope one can convince oneself that it corresponds with the
head of _Tænia solium_.
[Illustration: FIG. 237.--Large and small hooks of _Tænia solium_.
280/1. (After Leuckart.)]
[Illustration: FIG. 238.--_Tænia solium._ 21, Egg with external
membrane; 22, without (embryophore). (After Leuckart.)]
[Illustration: FIG. 239.--Two mature proglottids of _Tænia solium_ with
fully developed uterus. 2/1.]
Numerous experiments have proved that the _Cysticercus cellulosæ_
of the pig, if introduced into the intestine of man, grows to a
_Tænia solium_ (Küchenmeister, 1855; Humbert, 1856; Leuckart, 1856;
Hollenbach, 1859; Heller, 1876); the cysticercus has frequently also
been cultivated purposely by feeding pigs with mature proglottids of
_T. solium_ (P. J. van Beneden, 1853; Haubner and Küchenmeister, 1855;
Leuckart, 1856; Mosler, 1865; Gerlach, 1870; etc.), but success did not
attend the efforts to make _Cysticercus cellulosæ_ establish themselves
in the intestines of pigs, dogs, guinea-pigs, rabbits and monkeys
(_Macacus cynomolgus_), and so become adult Tæniæ; the attempts, also,
to infect dogs with cysticerci by means of ova were likewise, as a
rule, abortive.[288]
[288] According to Gerlach only young pigs (up to 6 months old) are
capable of infection, and perhaps the failure may have been due to the
animals chosen for experiment being of the wrong age.
The development of _Cysticercus cellulosæ_ takes two and a half
to three or four months; it is not known how long the cysticerci
remain alive in animals; not uncommonly they perish at earlier or
later stages, and become calcified or caseated. Extracted cysticerci
die in water at a temperature of 47° to 48° C., in flesh at normal
temperature they remain alive for twenty-nine days or more. On
account of the present rapid means of pickling and smoking meat, the
cysticerci as a rule are not killed, also the effect of cold on them
for some time in cold chambers of slaughterhouses is not lethal, but
freezing is fatal (Ostertag).
There is not the least doubt that human beings are almost exclusively
infected with _Tænia solium_ by eating pork containing cysticerci in
a condition that does not endanger the life of the cysticerci. The
infection may likewise be caused in man by eating the infected meat of
other animals subject to this species of bladder worm, mainly, as a
matter of fact, deer and wild boar.
The frequency of cysticerci in pigs’ flesh has considerably decreased
since the introduction of meat inspection; in the Kingdom of Prussia
there was on an average 1 infected pig to every 305 slaughtered
between 1876 to 1882; from 1886 to 1889, there was 1 to 551; from
1890 to 1892, there was 1 to 817; in 1896, 1 to 1,470; and in 1899, 1
to 2,102; in the Kingdom of Saxony in 1894 there was 1 infected pig
to every 636; in 1895 there was 1 to every 2,049, and in 1896 only 1
infected pig was found of 5,886 slaughtered. In South Germany pigs
with cysticerci are very rare, but are more frequent in the eastern
provinces of Prussia; in 1892 the number of infected pigs compared
with the total slaughtered was as follows:--
In the district of Marienwerder 1 : 28
" " Oppeln 1 : 80
" " Königsberg 1 : 108
" " Stralsund and Posen 1 : 187
" " Danzig, Frankfort a. O. and Bromberg 1 : 250
As compared with the district of Arnsberg 1 : 865
" " " Coblenz 1 : 975
" " " Düsseldorf 1 : 1,070
" " " Münster and Wiesbaden 1 : 1,900
The average for the whole of Prussia in the same year was 1 : 1,290;
for the eastern provinces, on the other hand, 1 : 604. Even more
unfavourable are the proportions in Russian Poland (over 1 per
cent. of pigs measly), in Prague (over 3 per cent.), in Bosnia and
Herzegovina (6 to 7 per cent.). The cause for this is most likely
attributable to the manner in which the pigs are kept. When allowed
to be in the farmyards of the small farmers for the whole day, or
allowed to wander in the village streets and pasture lands, they are
more liable to take up the oncospheres of the _T. solium_ than when
shut up in good pig-styes.
The geographical distribution of _T. solium_ generally corresponds
with that of the domestic pig and the custom of eating pork in any
form insufficiently cooked or raw. There are, or were, some isolated
districts in Germany, France, Italy and England where the “armed
tapeworm” was frequent (for instance, Thuringia, Brunswick, Saxony,
Hesse, Westphalia, whereas it is and was very scarce in South Germany);
it is thus easily understood why it occurs very rarely in the East, in
Asia and in Africa, in consequence of the Mahommedans, Jews, etc.,
not eating pork. In North America, also, _T. solium_ is very rare; the
tapeworm which is known there by this name is generally _T. saginata_,
Stiles. During the last decade _T. solium_ infection has, however,
very markedly decreased in North and East Germany in consequence of
the precautions exercised by the public in the choice of pork to avoid
trichinosis, especially, however, because measly meat must be sold as
such and must be thoroughly cooked before being placed on the market;
indeed, if badly infected it may not be sold for food, but can be
turned to account for industrial purposes.
The occurrence of _Cysticercus cellulosæ_ in man has been known since
1558 (Rumler, _Obs. med._, liii, p. 32); there is hardly an organ in
man in which cysticerci have not been observed at some time; they are
most frequently found in the brain,[289] where they grow to a variety
known as _Cysticercus racemosus_; next in frequency they are found in
the eye, in the muscular system, in the heart, in the subcutaneous
connective tissue, the liver, lungs, abdominal cavity, etc. The number
of cysticerci observed in one man varies between a few and several
thousands. Of the sexes, men are most subject (60 to 66 per cent. of
the number attacked). The disturbances caused in man by cysticerci
vary according to the nature or position of the organs attacked; when
situated in the cerebral meninges they have the same effect as tumours.
[289] Dressel, for instance, examined eighty-seven persons suffering
from cysticercus, and found it seventy-two times in the brain, thirteen
times in the muscles; K. Müller, in thirty-six cases, found it
twenty-one times in the brain, twelve times in the muscles, three times
in the heart; Haugg, in twenty-five cases, found it thirteen times in
the brain, six times in the muscles, twice in the skin, etc. According
to Graefe, amongst 1,000 ophthalmic cases in Halle and Berlin, there
was one with cysticercus in the eye; in Stuttgart there was only one in
4,000, in Paris one in 6,000, and in Copenhagen one in 8,000.
During the last decades, however, these cases have also become less
common. In Rudolphi’s time 2 per cent. of _post-mortems_ in Berlin
showed cysticerci; in the ’sixties, according to Virchow, about the
same; in 1875 the number fell to 1·6 per cent.; in 1881 to 0·5 per
cent.; in 1882 to 0·2 per cent.; in 1900 to 0·15 per cent., and in
1903 to 0·16 per cent. Hirschberg between 1869 and 1885 discovered
cysticerci in the eye seventy times in 60,000 ophthalmic cases, but
during the following six years the parasite was only present twice
amongst a total of 46,000 cases of ophthalmic diseases, and since 1895
no ophthalmic case has been met with.
The infection of human beings with the cysticerci can only take place
by the introduction of the oncospheres of _Tænia solium_ into the
stomach with vegetable foods, salads that have been washed in impure
water containing oncospheres, also by drinking contaminated water;
the carriers of _T. solium_, moreover, infect themselves still more
frequently through uncleanliness in defæcation, the privies in public
localities and many private houses affording striking testimony of
this. The minute oncospheres can thus easily reach the fingers and
thence the mouth (as in twirling the moustache, biting the nail).
More rarely a third manner of transmission or internal auto-infection
may possibly take place, as when, in the act of vomiting, mature
proglottids near the stomach are drawn into it; the oncospheres or
segments there retained are then in the same position as if they had
been introduced through the mouth.
On account of these dangers of internal or external auto-infection,
it is therefore the duty of the medical attendant, after recognizing
the presence of tapeworms, to expel them,[290] and in doing so to
employ every possible means to prevent vomiting setting in; it is,
however, equally important to take the necessary steps to destroy the
parasites evacuated. It may be incidentally mentioned that in using
certain remedies the scolex not rarely remains in the intestine; the
cure in such cases has not been accomplished, as the scolex again
produces new proglottids, and after about eleven weeks the first
formed ones are again mature and appear in the fæces.
[290] The diagnosis as a rule is not difficult; the patients themselves
frequently observe the pumpkin seed-like segments in the fæces. But in
such cases the diagnosis must still be confirmed. In other cases the
discovery of the oncospheres in their embryonal shells (embryophores),
which cannot be confounded with the other constituents of the fæces,
gives complete certainty, although the differential diagnosis between
_T. solium_ and _T. saginata_ is hardly possible from the embryophores;
but, if evacuated segments are placed between two slides and lightly
pressed, the species is easily recognizable by the shape of the uterus
(_cf._ figs. 239 and 241).
Amongst the cysticerci also many malformations appear; thus absence
of the rostellum and the hooks, or double formation with six suckers,
or abnormalities of growth on account of the surroundings, which have
had a special name given to them, _viz._, _Cysticercus racemosus_,
Zenk. (= _C. botryoides_, Hell.; _C. multilocularis_, Kchnmstr.);
these forms are more especially found at the base of the brain, are
irregularly ramified and often without the head.
A certain interest is attached to those forms that have led to the
establishment of a distinct species:--
*Cysticercus acanthotrias*, Weinld., 1858.
In making the autopsy of a white Virginian woman who had died of
phthisis, a cysticercus was found in the dura mater, and eleven or
twelve specimens in the muscles and subcutaneous tissue. Weinland
and Leuckart, who examined the specimens, found that they resembled
_Cysticercus cellulosæ_ in form and size, but that they carried on
the rostellum a triple crown, each consisting of fourteen to sixteen
hooks, which differed from the hooks of _C. cellulosæ_ or of _Tænia
solium_ by the greater length of the posterior root process and the
more slender form of the hooks; the large hooks measured 0·153 to
0·196 mm., the medium-sized hooks, 0·114 to 0·14 mm., and the small
ones 0·063 to 0·07 mm.
On account of these differences a distinct species of cysticercus was
established, and this naturally presupposed a corresponding species
of Tænia (_T. acanthotrias_, Lkt.); this could be done with justice
so long as the case remained isolated, _i.e._, in America, as there
was the possibility of the corresponding Tænia being found. In this
respect, however, the position has changed; Delore first described a
cysticercus the size of a nut from the biceps muscle of the arm of a
silk-worker in Lyons; according to Bertolis this specimen possessed
hooks of three different sizes, the dimensions of which corresponded
with the figures given by Weinland and Leuckart; the correctness of
the diagnosis could hardly be doubted, as Bertolis was known to be a
very exact observer. A second case has become known through Cobbold,
who regards a specimen of a cysticercus in Dallinger’s collection as
likewise belonging to _Cysticercus acanthotrias_; this specimen also
came from a man’s brain; finally a third case, also from France, has
been published by Redon. This author, amongst numerous _C. cellulosæ_
of a man, found one that had forty-one hooks in three rows, and he
was the first to express the opinion that _C. acanthotrias_ does
not represent a distinct species, but is only an abnormality of _C.
cellulosæ_. This view was also taken by Blanchard and Railliet, and is
probably correct, as the discovery of the large corresponding Tænia
furnished with three rows of hooks is not to be expected in European
beasts of prey, and in Redon’s case _C. acanthotrias_ as well as _C.
cellulosæ_ occurred simultaneously.
The duration of life of _C. cellulosæ_ in man is very long; cysticerci
of the eye have been known to persist for twenty years, and in
cysticercus of the brain ten to nineteen years may elapse from the
first appearance of cerebral symptoms until death. Dead cysticerci may
shrivel up or become calcified, perhaps also undergo fatty degeneration
and then absorption. Finally, it may be mentioned that if particular
proof is required that _C. cellulosæ_ of man belongs to the cycle of
development of the _Tænia solium_, such proof has been furnished by
Redon.
NOTE.--_Tænia tenella_, mentioned on p. 332, was ascribed by Cobbold
to cysticerci of the muscular system of sheep. It has, however,
been demonstrated that these cysticerci belong to the cycle of
development of _Tænia marginata_ (dog) (_Cysticercus tenuicollis_,
from the omentum of sheep); but as already stated _C. cellulosæ_ also
occurs in sheep. Chatin himself swallowed the cysticercus, which
Cobbold termed _C. ovis_, without causing a Tænia to develop in his
intestine. Müller also vainly sought to induce infection with _C.
tenuicollis_ in his own person. On the other hand, the feeding of
a dog with _Cysticercus ovis_ resulted in the production of _Tænia
marginata_.
*Tænia bremneri*, Stephens, 1908.
Characterized by the large size of the gravid segments. The largest was
32 by 9 mm. Smallest 21 by 6 mm. Average 28·6 by 8·5 mm. Mode 21 by
6 mm. Uterine branches twenty-two to twenty-four in number. Calcareous
bodies numerous, 15·2 µ in diameter. Eggs maximum 45·6 µ by 41·8 µ.
Smallest 34·2 µ by 30·4 µ. Mode 38 µ by 30·4 µ.
*Tænia marginata*, Batsch, 1786.
Syn.: T. e. _Cysticerco tenuicolli_, Küchenmeister, 1853.
This species, which in structure resembles _Tænia solium_, lives
in the intestine of the dog and the wolf. It attains 1·5 to 4 m.
in length, possesses a double crown of thirty to forty hooks, on
an average thirty-six to thirty-eight hooks, and in its larval
stage (_Cysticercus tenuicollis_) lives in the peritoneal cavity of
ruminants and the pig, occasionally in the monkey and squirrel.
[Illustration: FIG. 240.--Large and small hooklets of _Tænia
marginata_. 280/1. (After Leuckart.)]
It is included in this work because, according to one statement,
_C. tenuicollis_ is supposed to have been observed in man in North
America; but the case is not quite certain, as the number of hooks
was less than in _C. tenuicollis_ and coincided with _C. cellulosæ_,
although the size of the cysticercus appeared to point to _C.
tenuicollis_. A yet earlier statement of Eschricht, that _Cysticercus
tenuicollis_ had been observed in Iceland in the liver of a man, is
undoubtedly due to an error.
*Tænia serrata*, Goeze, 1782.
This parasite attains a length of from 0·5 to 2 m., possesses a
double crown of thirty-four to forty-eight (mostly forty) hooks. It
lives exclusively in the intestine of the dog, the corresponding
cysticercus (_Cysticercus pisiformis_) living in the mesentery of the
hare and rabbit. We mention this species with all reserve amongst
the parasites of man, because Vital states that he has observed it
twice in Constantine (Algeria) in human beings. The data, however,
are not sufficient to characterize the species. It is highly probable
that they relate to _Tænia solium_. Galli-Valerio even swallowed five
specimens of _Cysticercus pisiformis_, but without result.
*Tænia crassicollis*, Rud., 1810.
I only mention this species from the intestine of the domestic cat
because Krabbe regards its occurrence in man as possible. It attains
a length of 60 cm. and is armed; its cysticercus (_Cysticercus
fasciolaris_) lives in the liver of mice and rats. In Jutland,
according to Krabbe, chopped-up mice (spread on bread) are eaten
raw, being a national remedy for retention of urine, and this custom
affords the possibility of the introduction of _C. fasciolaris_ into
the intestine of man (_Nord. med. Arkiv_, 1880, xii).
*Tænia saginata*, Goeze, 1782.
Syn.: _Tænia solium_, L., 1767 (_pro parte_); _Tænia cucurbitina_,
Pallas, 1781 (p.p.); _Tænia inermis_, Brera, 1802. Moquin-Tandon,
1860; _Tænia dentata_, Nicolai, 1830; _Tænia lata_, Pruner,
1847; _Bothriocephalis tropicus_, Schmidtmuller, 1847; _Tænia
mediocanellata_, Küchenmeister, 1855; _Tænia zittavensis_,
Küchenmeister, 1855; _Tænia tropica_, Moquin-Tandon, 1860; _Tænia_
(_Cystotænia_) _mediocanellata_, Leuckart, 1863.
The length of the entire tapeworm averages 4 to 8 to 10 m. and more,
even up to 36 m. According to Bérenger-Feraud it attains a length of
74 m. (?) The head is cubical in shape, 1·5 to 2 mm. in diameter; the
suckers are hemispherical (0·8 mm.) and are frequently pigmented;
there is a sucker-like organ in place of the rostellum, and this also
is frequently pigmented. The neck is moderately long and about half
the breadth of the head; the proglottids, the number of which averages
more than 1,000, gradually increase in size; the mature detached
segments are shaped exactly like pumpkin-seeds, and are about 16 to
20 mm. in length and 4 to 7 mm. in breadth. The genital pores alternate
irregularly and are situated somewhat behind the middle of the lateral
margin. There are twenty to thirty-five lateral branches at each side
of the median trunk of the uterus, and these again ramify. The eggs
are more or less globular, the egg-shell frequently remains intact and
carries one or two filaments; the embryonal shell (embryophore) is
thick, radially striated, is transparent and oval; it is 30 µ to 40 µ
in length, and 20 µ to 30 µ in breadth. Several segments simultaneously
are usually passed spontaneously with defæcation.
[Illustration: FIG. 241.--Mature segment of _Tænia saginata_, G., with
distended uterus. 2/1.]
[Illustration: FIG. 242.--Cephalic end of _Tænia saginata_ in the
contracted condition. 8/1.]
[Illustration: FIG. 243.--_Tænia saginata._ 19, egg with external
shell. 20, without (embryophore). (After Leuckart.)]
Malformations are not uncommon, and resemble those of _Tænia solium_;
a triangular form has been termed _T. capensis_ by Küchenmeister, and
_T. lophosoma_ by Cobbold, names that naturally possess as little
value as does the term _T. fenestrata_ for fenestrated specimens.
Moreover, _T. solium_, var. _abietina_, Weinld., 1858, which was
evacuated by an Indian, was probably a _T. saginata_ with somewhat
close uterine branches. It is regarded by Stiles and Goldberger as a
doubtful subspecies.
_T. saginata_ in its adult condition lives exclusively in the
intestinal canal of man.[291] The corresponding cysticercus is
_Cysticercus bovis_, and is found almost exclusively in the ox; it is
small, 7·5 to 9 mm. in length and 5·5 mm. in breadth, may easily escape
notice, and requires from three to six months for its development.
Numerous experiments have confirmed the connection of _Cysticercus
bovis_ with _Tænia saginata_; indeed, the cysticercus was only
discovered by feeding experiments after attention had been called to
the ox as the probable intermediary host of this Tænia.
[291] Abnormal migrations of this species have also been known.
Compare, amongst others, Stieda, A., “Durchbohr. d. Duod. u.
d. Pancreas durch eine Tænia,” _Centralbl. f. Bakt., Path. und
Infektionsk._, 1900, xxviii (1), p. 430.
Medical men observed that weakly children who were ordered to eat
raw scraped beef to strengthen them contracted _T. saginata_. It
was found, moreover, that Jews, who are prohibited from eating pork
from religious motives, suffered especially from _T. saginata_;
when _T. solium_ was found to occur in a Jew he often confessed to
having eaten pork; and finally it was found that certain nations--for
instance, the Abyssinians--frequently harbour _T. saginata_, and only
eat beef--raw by preference.
These observations led Leuckart, in 1861, to feed young calves
with the proglottids of _T. saginata_ in order to discover the
corresponding cysticercus, which was then not known. This experiment
was successful. Similar experiments, with similar results, were
then conducted by Mosler (1863), Cobbold and Simonds (1864 and
1872), Röll (1865), Gerlach (1870), Zürn (1872), Saint Cyr, Jolicœur
(1873), Masse and Pourquier (1876), and Perroncito, in 1876. The
attempts to infect goats, sheep, dogs, pigs, rabbits and monkeys were
unsuccessful. Only Zenker and Heller were able to infect kids, and
Heller infected one sheep, but these are exceptions.
[Illustration: FIG. 244.--A piece of the muscle of the ox, with three
specimens of _Cysticercus bovis_. Natural size. (After Ostertag.)]
Artificial infections of human beings with _Cysticercus bovis_ to
obtain the tapeworm were less numerous, and indeed quite superfluous,
yet this was also done by Oliver (1869) in India, and Perroncito (1877)
in Italy. The experiments of the latter prove that the extracted
cysticerci of the ox certainly perish in water at 47° to 48° C.
It is a remarkable circumstance that, at least as regards Central
Europe, _C. bovis_ in the ox, after natural infection, was so seldom
found that almost every case was published as a rarity; whereas the
Tænia is very frequent in man. The reason for this is that in Germany
cattle are not severely infected, and that the small, easily dried-up
cysticerci easily escape notice in the large body of the host.
Hertwig, the late director of the town cattle market in Berlin, in
1888, pointed out that the cysticercus of the ox is found chiefly in
the musculi pterygoide externi and interni, and since that time a far
greater number of infected oxen have been found in Berlin.
---------+----------------+----------+------------
Year | Number of oxen | Infected | Proportion
| slaughtered | |
---------+----------------+----------+------------
1888–89 | 141,814 | 113 | 1 : 1,255
1889–90 | 154,218 | 390 | 1 : 395
1890–91 | 124,593 | 263 | 1 : 474
1891–92 | 136,368 | 252 | 1 : 541
1892–93 | 142,874 | 214 | 1 : 672
---------+----------------+----------+------------
Since 1892 an increase has taken place in the number of oxen infected
with cysticercus, but this is probably attributable to the more
general and searching examinations. In the slaughter-houses of
Prussia the number of infected beasts was as follows:--
1892 567
1893 686
1894 748
1895 1,143
1896 1,981
1897 2,629
The condition was most frequent in Neisse (3·2 to 4 per cent.),
Eisenach (1·91 per cent.), Ohlau (1·57 per cent.), Oels i. Schles.
(1 per cent.), Marienwerder (0·34 to 1·2 per cent.). The flesh of
oxen only slightly infected (containing not more than ten living
cysticerci) is sold in pieces of not more than 5 lb. to consumers
after having been rendered innocuous by cooking, or by pickling for
twenty-one days in 25 per cent. salt brine, or hanging for twenty-one
days in suitable refrigerators; oxen in which only one cysticercus is
found are allowed free commerce, and those strongly infected (_i.e._,
containing more than ten living cysticerci) may only be used for
industrial purposes.
It is a striking fact that more bulls than cows are infected
(according to Reissmann, in Berlin, from 1895 to 1902, 0·446 per
cent. bulls, 0·439 per cent. oxen, and 0·262 per cent. cows), the
explanation of which, according to Ostertag, is that most oxen are
killed when young, when also infection most readily takes place, and,
further, that the larva later on in life can be completely atrophied.
The cysticercus of the ox has hitherto been found in man on very rare
occasions. Arndt (_Zeitschr. f. Psychiat._, xxiv) mentions a case in
the brain, Heller in the eye, and Nabiers and Dubreith also in the
brain (_Journ. méd. Bordeaux_, 1889–1890, p. 209); but the diagnoses
are not quite certain, as absence of hooks occasionally occurs in
_Cysticercus cellulosæ_.
_Tænia saginata_ is the most frequent tapeworm of man (with the
exception of _Dibothriocephalus latus_ in a few districts), and the
parasite is widely distributed over the surface of the globe; it has
been known in the East for ages, so far as data are available; it is
frequent in Africa, America, and Europe. Its frequency has perceptibly
increased during the last few years, but a decrease should soon take
place in consequence of the extent and improvement of the official
inspection of meat.
The following table shows the relative frequency of the Cestodes of
man:--
----------------+---------+----------+----------+-------+------+-------+--------
| |Number of | _T. | _T. |_Dibr.|_Dipyl.|Undeter-
Author | Year | cases |saginata_ |solium_|latus_|canin._| mined
----------------+---------+----------+----------+-------+------+-------+--------
Parona (Milan) | 1899 | 150 | 121 | 11 | 4 | -- | 14
Parona (Italy) | 1868–99 | 513 | 397 | 71 | 26 | -- | 19
Krabbe (Denmark)| 1869 | 100 | 37 | 53 | 9 | 1 | --
" " | 1869–86 | 200 | 153 | 24 | 16 | 8 | --
" " | 1887–95 | 100 | 89 | -- | 5 | 6 | --
" " |1896–1904| 50 | 41 | 1 | 5 | 3 | --
Blanchard | 1895 | ? | 1,000 | 21 | -- | -- | --
(Paris) | | | | | | |
Stiles | 1895 |{more than|more than}| -- | 3 | -- | --
(United States)| |{ 300 | 300 }| | | |
Schoch | 1869 | 19 | 16 | 1 | 2 | -- | --
(Switzerland) | | | | | | |
Zaeslein | 1881 | ? | 180 | 19 | ? | |
(Switzerland) | | | | | | -- | --
Kessler | 1888 | ? | 22 | 16 | 47 | -- | --
(Petrograd) | | | | | | |
Mosler | 1894 | 181 | 112 | 64 | 5 | -- | --
(Greifswald) | | | | | | |
Bollinger | 1885 | 25 | 16 | 1 | 8 | -- | --
(Munich) | | | | | | |
Vierordt | 1885 | 121 | 113 | 8 | -- | -- | --
(Tübingen) | | | | | | |
Mangold | 1885–94 | 128 | 120 | 6 | 8 | -- | --
(Tübingen) | | | | | | |
----------------+---------+----------+----------+-------+------+-------+--------
*Tænia africana*, v. Linst., 1900.
[Illustration: FIG. 245.--Mature segment of _Tænia africana_. The ovary
is in the middle, and behind it are the shell gland and vitellarium;
at the sides are the testicles, and externally the excretory canals;
the cirrus pouch, the vas deferens and the vagina are on the left.
Magnified. (After v. Linstow.)]
This worm measures over 1·3 m. in length. The segments are all broader
than they are long. The scolex is unarmed and is provided with an
apical sucker (0·16 mm.). The parasite measures 1·38 mm. in breadth,
1·03 mm. in width; the suckers measure 0·63 mm. in diameter. The neck
is very short and somewhat broader than the scolex; number of segments
about 600; the hindmost segments measure 7 mm. in length and 12 to
15 mm. in breadth. The genital pores alternate irregularly in the
middle of the lateral margin; the testes are very numerous and occupy
the entire medullary layer; the vas deferens is much convoluted; the
cirrus pouch is pyriform and thick walled; the cirrus and vagina
are beset with bristles directed outwards; the receptaculum seminis
is fusiform; the ovary is large and double, and consists of radially
placed club-shaped tubes that do not anastomose and do not branch;
the vitellarium is at the posterior border of the proglottids, the
round shell gland in front of it; the uterus consists of a median
trunk and fifteen to twenty-four non-ramified lateral branches on each
side; the embryonal shell is thick and has radial stripes--it may be
round (31·2 µ to 33·8 µ) or oval (39 µ, by 33·8 µ); the spines of the
oncospheres measure 7 µ to 8 µ in length (fig. 197).
[Illustration: FIG. 246.--Proglottis of _Tænia africana_, with uterus.
Magnified. (After v. Linstow.)]
[Illustration: FIG. 247.--Head of _Tænia africana_; apical surface.
Magnified. (After v. Linstow.)]
At present only two specimens are known; they came from a black soldier
from the vicinity of Lake Nyasa. The cysticercus is unknown; perhaps it
lives in the zebu, the flesh of which the Askaris are in the habit of
devouring uncooked.
*Tænia confusa*, Ward, 1896.
Length 8·5 m., breadth about 5 mm. The scolex is unknown; there is
no neck; number of proglottids 700 to 800, always longer than they
are broad; the hindmost measure 35 mm. in length, 4 to 5 mm. in
breadth; the genital pores alternate irregularly behind the middle
of the lateral margin; testicles numerous; vas deferens not much
coiled; the cirrus pouch thick walled, elongated and club-shaped, with
globular vesicula seminalis; the cirrus is beset with little hairs;
the receptaculum seminis is globular; ovary small, double; each half
is bean-shaped; vitellarium narrow, triangular; shell gland globular;
uterus with median trunk and fourteen to eighteen short ramified
lateral branches on either side. The embryophores are oval (39 µ by
30 µ), thick and radially striated.
[Illustration: FIG. 248.--_Tænia confusa_: mature segment showing
central uterine stem, bilobed ovary, globular shell gland, triangular
vitellarium, scattered testes, cirrus, vas deferens, and vagina. 15/1.
(After Guyer.)]
[Illustration: FIG. 249.--_Tænia confusa_: gravid segment. 25/1. (After
Ward.)]
Of this species only two specimens have been recorded; they occurred in
human beings and were sent at different times to the first describer
of them by a doctor in Lincoln (Nebr.). Perhaps _Tænia solium_, var.
_abietina_, Weinld., which was found in a Chipeway Indian, is of the
same species in spite of the shorter segments.
*Tænia echinococcus*, v. Sieb., 1853.
Syn.: _Tænia nana_, v. Ben., 1861 (_nec_ v. Sieb., 1853);
_Echinococcifer echinococcus_, Weinld., 1861.
_Tænia echinococcus_ measures 2·5 to 5 or 6 mm. in length; the head
is 0·3 mm. in breadth, and has a double row of twenty-eight to fifty
hooklets (on an average thirty-six to thirty-eight) on the rostellum.
The size and form of these hooklets vary (the larger ones are 0·040
to 0·045 mm. in length, the smaller ones are 0·030 to 0·038 mm. in
length). The suckers measure 0·13 mm. in diameter; the neck is short;
there are only three or four segments, the posterior segment being
about 2 mm. in length and 0·5 mm. in breadth. The genital pores
alternate; there are forty to fifty testicles; the vas deferens
is spirally coiled; the cirrus pouch is pyriform. The ovary is
horseshoe-shaped with the concavity directed backwards; the vitellarium
double, each half almost bean-shaped, at right angles to the plane of
the segment; the shell gland is round. The median trunk of the uterus
is dilated when filled with eggs and (instead of lateral branches)
has lateral diverticula. It is not unusual for the eggs to form local
heaps. The embryonal shell (embryophore) is moderately thin, with
radial striæ, almost globular, 30 µ to 36 µ in diameter.
[Illustration: FIG. 250.--_Tænia echinococcus_: the cirrus sac, the
vagina, uterus, ovary, shell gland and vitellarium, and the testicles
at the sides are recognizable in the second proglottis; the posterior
proglottis shows the uterus partly filled with eggs, as well as the
cirrus sac and the vagina. 50/1.]
When mature this parasite lives in the small intestine of the domestic
dog, the jackal, and the wolf, and apparently also in _Felis concolor_,
and is usually present in great numbers; it can also be transmitted
experimentally to the domestic cat, one successful result out of seven
(Dévé).[292] The larval stage (_Echinococcus polymorphus_) lives in
various organs--chiefly in the liver and lungs--of numerous species
of mammals (twenty-seven), especially in sheep, ox and pig, and it is
even not uncommon in man, though the Tænia itself has never been found
in a human being; accordingly man can only acquire the echinococcus by
ingesting the eggs of the “dog worm.” The dogs disseminate the eggs of
_Tænia echinococcus_ wherever they go, or carry them to their mouths
and coats by biting up the evacuated segments, and are thus able to
transmit them directly to human beings (by licking them or making use
of the same crockery, etc.). In other cases the oncospheres, enclosed
in the embryophores, must withstand desiccation for a time and then (as
when the dogs are “kissed” or otherwise caressed) are transmitted into
or on to man. As echinococcus disease in man is always very dangerous,
it would be a matter of general interest to prevent dogs being
infected by destroying the echinococci,[293] and all measures would be
justifiable which would diminish the superfluous number of house-dogs
(for instance, high taxes); measures should also be adopted to limit
the association of men with dogs, particularly in such frequented
places as restaurants, railway carriages and tram-cars.
[292] In Iceland 28 per cent. of the dogs are infected with this Tænia,
in Lyons 7·1 per cent., in Zurich 3·9 per cent., in Berlin 1 per cent.,
and in Copenhagen 0·4 per cent. In Australia even 40 to 50 per cent. of
the dogs are affected. It is, however, a question whether, in addition
to _Tænia echinococcus_, a second analogous form is not involved, as
the form from _Canis dingo_ attains a length of 10 to 30 mm.
[293] Mosler, F., “Ueb. Mittel z. Bekampfg. endem. vork.
Echinococcuskrank.,” _Deutsch. med. Zeit._, 1889, No. 72.
Echinococcus is very common in slaughtered animals; in Germany,
however, the figures in the reports of the abattoirs present an
erroneous view in so far as, besides the total number of animals
slaughtered, only the numbers of those organs (liver and lungs) are
published that were so severely infected with echinococci that, even
when the parasites were “shelled” out, the flesh could not be placed
upon the market and was therefore “condemned.”
In Berlin the following animals were slaughtered:--
-------+---------+---------+---------+---------+---------+---------
Year | 1889–90 | 1890–91 | 1891–92 | 1892–93 | 1896–97 | 1902
-------+---------+---------+---------+---------+---------+---------
Oxen | 154,218 | 124,593 | 136,368 | 142,874 | 146,612 | 153,748
Sheep | 430,362 | 371,943 | 367,933 | 355,949 | 395,769 | 434,155
Pigs | 442,115 | 472,859 | 530,551 | 518,073 | 694,170 | 778,538
-------+---------+---------+---------+---------+---------+---------
During the same years the following were condemned in consequence of
being infected with echinococci:--
-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+------+-----
|Lung |Liver|Lung |Liver|Lung |Liver|Lung |Liver|Lung |Liver|Lung |Liver
-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+------+-----
Oxen |7,266|2,418|5,792|1,938|4,497|1,721|2,563| 739|3,284|1,156| 2,507| 791
Sheep|5,479|2,742|4,595|2,059|4,435|1,669|3,331|1,161|4,561|1,939|11,138|4,437
Pigs |6,523|5,078|5,083|3,735|6,037|4,374|6,785|4,312|7,888|5,398| 9,544|9,233
-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+------+-----
Nevertheless there are statistics that give the total number of
animals infected with echinococcus:--
--------+-------------+--------------+--------------+--------------
Author | Place | Oxen | Sheep | Pigs
--------+-------------+--------------+--------------+--------------
Längrich|Rostock i. M.|26·2 per cent.|37·0 per cent.| 5·4 per cent.
Olt |Stettin | 7·1 " |25·8 " | 7·3 "
Steuding|Gotha |24·6 " |35·4 " |21·4 "
Prettner|Prague |23·2 " | 5·5 " | ?
--------+-------------+--------------+--------------+--------------
In Güstrow, in Mecklenburg, half of the animals slaughtered are said
to be infected with echinococcus; in Wismar 25 per cent. of the oxen,
15 per cent. of the sheep and 5 per cent. of the pigs are infected;
according to Mayer, in Leipzig, 3·79 per cent. native pigs, 24·47
per cent. Hungarian pigs, and 13·09 per cent. of sheep were infected
with echinococcus; at the same time it was stated that in regard
to the native pigs the liver was more frequently affected than the
lungs (3·81 per cent. as compared with 0·26 per cent.); in sheep the
lungs were more frequently infected (12·71 per cent. to 3·73 per
cent.), whereas in the Hungarian pigs both organs were almost equally
infected (14·78 per cent. to 12·03 per cent.).
The data of Lichtenheld, in Leipzig, give the frequency with which
various organs were affected, as shown in the following table:--
-----------+---------+-------------------+---------+---------
| Cattle | Pigs | Sheep | Horses
-----------+---------+-------------------+---------+---------
| | ♂ | ♀ | |
|per cent.|per cent.|per cent.|per cent.|per cent.
Lungs | 69·3 | 16·2 | 21·4 | 52·2 | 5·5
Liver | 27·0 | 74·2 | 72·0 | 44·9 | 94·5
Spleen | 2·2 | 3·2 | 2·7 | 2·9 | --
Heart | 0·75 | 3·2 | 1·3 | -- | --
Kidneys | 0·75 | 3·2 | 1·3 | -- | --
Sub- | | | | |
peritoneal| | | | |
tissue | -- | -- | 1·3 | -- | --
-----------+---------+---------+---------+---------+---------
STRUCTURE AND DEVELOPMENT OF ECHINOCOCCUS (HYDATID).
[Illustration: FIG. 251.--_Echinococcus veterinorum_: the fibrous sac
enclosing the echinococcus has been opened and laid back in five parts,
so that the surface of the bladder worm may be seen, with the brood
capsules, visible to the naked eye, showing through it. Natural size.
(After Leuckart.)]
An echinococcus is a spherical or roundish bladder full of a watery
liquid, which originates by liquefaction of the oncosphere, and in man
may attain the size of a child’s head, but remains smaller in cattle
(the size of an orange or apple). The thin wall of the bladder is
composed of an external laminated cuticle (ectocyst) and an internal
germinal or parenchymatous layer (endocyst). The latter again exhibits
two layers: an outer layer of small cells that are less sharply
defined, and an inner layer of larger cells. It contains, in addition,
calcareous corpuscles, muscular fibres and excretory vessels. It is
rich in glycogen.
[Illustration: FIG. 252.
FIGS. 252 and 252A.--Diagrams of mode of formation of brood capsule and
scolices. (1) Wall of mother cyst, consisting of ectocyst and endocyst;
(2) theoretical stage of invagination of wall; (3) a brood capsule with
the layers of the wall in the reverse position to that in the mother
cyst; (4) evagination of wall; (5) invagination; (6) fusion to form the
solid scolex; (7) invagination of fore-part of scolex into hind-part.
(_Note._--The size of the scolex is much out of proportion to the brood
capsule.) (Stephens.)]
The development in cattle often remains stationary at the bladder
stage, and they are then called “acephalocysts,” or _Echinococcus
cysticus sterilis_. According to Lichtenheld, sterile cysts occur in
80 per cent. of cases in cattle, in 20 per cent. in pigs, and in 7·5
per cent. in sheep. In other cases large numbers of small, hollow
BROOD CAPSULES are formed in the germ layer, but are not arranged in
any particular order. The order of the layers is just the reverse
in them to what it is in the parent cyst, that is to say, they have
inside a thin non-laminated cuticle and the parenchymatous layer on
their external surface. These, theoretically at least, may be regarded
as invaginations of the bladder wall giving rise to a cavity with the
cuticle internal and the parenchymatous layer external. If we suppose
the orifice to close, we should then get an isolated cavity with
cuticle internal and parenchymatous layer external, as in the brood
capsule (fig. 252). If we next suppose an evagination of the wall of
the brood capsule to occur at one point we should get a hollow process
_lined_ with cuticle; at the bottom of this we get the scolex and
hooklets formed, and a little higher up the tube the suckers (fig. 252,
4). If this hollow scolex is now pictured as being invaginated we get
a hollow scolex _covered_ with cuticle and lined by a parenchymatous
layer projecting into the cavity of the brood capsule. The two sides of
this hollow scolex now fuse and we get a solid scolex projecting into
the cavity. Finally, if we imagine once more the rostellum and suckers
invaginated into the posterior part of the scolex we get the condition
as frequently found in the brood capsules, _i.e._, a scolex covered
with cuticle projecting into the cavity, with the rostellum and suckers
invaginated into the posterior portion of the scolex (fig. 252A, 7).
[Illustration: FIG. 252A.]
A large hydatid may contain many thousands of brood capsules. Each
brood capsule is about as big as a pin’s head, and may contain ten to
thirty or more scolices. The delicate wall of the brood capsules may
rupture, so that the scolices are now free in the mother cyst. These
free scolices and also free brood capsules constitute what is known as
“hydatid sand,” which settles at the bottom of a glass when hydatid
fluid is poured into it. This form occurs chiefly in domesticated
animals and is termed _E. veterinorum_, Rud., or _E. cysticus fertilis_.
In man, and only rarely in cattle, the mother cyst first forms
“daughter cysts” (_E. hominis_, Rud. [fig. 255]), which, though smaller
than the “mother cyst,” resemble it in the structure of their walls;
thus they are covered externally by a laminated cuticle and internally
by the parenchymatous layer. They originate:
[Illustration: FIG. 253.--Section through an invaginated echinococcus
scolex. _Cf._ fig. 252A, 7. × 300. (After Dévé.)]
[Illustration: FIG. 254.--A piece of the wall of an _Echinococcus
veterinorum_ stretched out and seen from the internal surface. A few
brood capsules (the outline of which is only faintly shown), with
scolices directed towards their interior and exterior. 50/1.]
(1) Between the laminæ of the cuticle of the mother cyst from small,
detached portions of the parenchymatous layer; during their growth
they bulge inwardly or outwardly and may separate themselves entirely
from their parent cyst. In the latter case they lie between the mother
cyst and the capsule of connective tissue formed by the host (_E.
granulosus_ or _E. hydatidosus exogenus_); when growing inwardly they
reach the interior of the mother cyst (_E. hydatidosus endogenus_).
Their number is very variable and does not depend on the size of the
mother cyst. They are as big as, or bigger than, gooseberries.
(2) According to some authors, endogenous daughter cysts arise also
from a _metamorphosis of scolices_ that have separated off from the
brood capsule. This takes place in the following way: Fluid accumulates
in the interior of the scolex, so that eventually nothing remains
except a sac consisting of cuticle lined by parenchyma. The cuticle
gradually thickens and several layers form (fig. 257).
[Illustration: FIG. 255.--_Echinococcus hominis_ in the liver. The
fibrous capsule and the wall of the echinococcus have been incised,
so that the endogenous daughter cysts may be seen. Reduced. (After
Ostertag, from Thoma.)]
[Illustration: FIG. 256.--Section through an echinococcus scolex in
process of vesicular metamorphosis, twenty-six days after insertion in
the pleural cavity. × 250. (After Dévé.)]
(3) _Transformation of Brood Capsules into Daughter Cysts._--This is
also held to be possible by various observers. New epithelial layers
are deposited between the cuticle which lines the brood capsule and
the outer parenchymatous layer. This parenchymatous layer gradually
disappears and a new parenchymatous layer forms in the interior from
the parenchyma of the scolex or scolices. Although it appears strange
that a completely formed scolex with specifically differentiated
tissues and organs should retrogress to more primitively organized
matter, and again become a proliferating bladder, yet we can hardly
doubt that the older observations, regarding such a vesicular
metamorphosis, of Bremser (1819), v. Siebold (1837), Naunyn (1862),
Rasmusser (1866), Leuckart (1881), Alexinsky (1898), Riemann (1899),
Dévé (1901), and Perroncito (1902) are correct.
(4) Further, _a fourth method_ of formation of daughter cysts is
described by Naunyn as occurring in sterile hydatids, _i.e._, those
containing no brood capsules. In this case a portion of the mother wall
of the hydatid gets constricted off.
[Illustration: FIG. 257.
Figs. _257_ and 257A.--Diagram of transformation of a scolex into a
daughter cyst (1 to 3): 1, scolex in brood capsule; 2, liquefaction
of scolex; 3, daughter cyst; and (4 to 6) of a brood capsule into
a daughter cyst; 4, brood capsule with scolex; 5, deposition of
new epithelial layers on the inner layer of the parenchyma; 6,
disappearance of outer parenchyma and formation of inner parenchyma
from the parenchyma of scolex, which has now disappeared. (_Note._--The
scolices are out of proportion to the brood capsules and to the
daughter cysts. Stephens.)]
It has also been established that not only daughter cysts transplanted
into animals develop further (Lebedeff, Andrejew, Stadnitzky,
Alexinsky, Riemann), but that this also holds good if only hydatid
_scolices_ from man or animals are transplanted into animals
(rabbits). They develop into echinococci and can then give rise to
brood capsules and scolices. As Dévé further established, hydatid
_scolices_ are not capable of developing in guinea-pigs, while
corresponding experiments with rabbits are in the large majority of
cases successful where the scolices are introduced subcutaneously
or into the pleural or peritoneal cavities. It is only in the case
of _daughter cysts_ that further growth is obtained in the case of
guinea-pigs. Finally it appears, as has been already stated, that brood
capsules can transform themselves into daughter cysts, but according to
Dévé only within the mother cyst, not after transplantation. Daughter
cysts that have been formed in the mother cyst of man and animals
behave themselves just as the mother cyst does, _i.e._, they can remain
sterile, or give rise to brood capsules and scolices, or even again
to fresh cysts--granddaughter cysts. The mother cyst can also die, so
that the daughter cysts then lie in the cavity of the connective tissue
capsule. The number of the daughter cysts in either case may attain
several thousands.
[Illustration: FIG. 257A.]
The echinococcus fluid, which originally is formed from the blood
of the host, is light yellow, with a neutral or slightly acid
reaction; its specific gravity averages 1009 to 1015. It contains
about 1·5 per cent. of inorganic salts, half of which is common salt;
in addition (besides water) it contains sugar, inosite, leucine,
tyrosin, succinic acid (associated with lime or soda) and albumens
which are not coagulated by heat; occasionally also the fluid has
been found to contain hæmatoidin and uric acid salts (in echinococcus
of the kidneys), which doubtless demonstrates that the echinococcus
liquid originates from the host. It has been generally assumed that
echinococcus fluid contains a toxic substance the escape of which
into the body cavity (at operation or by bursting of a hydatid
cyst) produces more or less severe symptoms (fever, peritonitis,
urticaria), so much so that one speaks of hydatid intoxication. The
investigations of Kobert, Joest, etc., have, however, shown the
harmlessness of fresh undecomposed hydatid and cysticercus fluid for
rabbits, mice and guinea-pigs, whether inoculated intraperitoneally,
subcutaneously or intravenously. Contrary data or clinical experience
must accordingly depend on other factors.
According to the researches of Leuckart, the growth of the echinococcus
is very slow; four weeks after infection the average size is only 0·25
to 0·35 mm., at the age of eight weeks it is 1 to 2·5 mm., and at this
period the formation of the central cavity commences; at the age of
five months, and with a size of 15 to 20 mm., the first brood capsules
with scolices are formed. The consequence of this gradual increase of
size is that the organ attacked can maintain its functions by vicarious
hypertrophy, and that many echinococci induce no special symptoms and
cannot even be diagnosed, the latter circumstance being due to their
hidden position.
The echinococcus cannot be said to be scarce in man, as is shown by the
following table for Central Europe:--
--------------------+-------+--------------+------------+----------
Place | | No. of |No. of cases|Percentage
|Period |_post-mortems_| of echino. |
--------------------+-------+--------------+------------+----------
Rostock |1861–83| 1,026 | 25 | 2·43
Greifswald |1862–93| 3,429 | 51 | 1·48
Jena |1866–87| 4,998 | 42 | 0·84
Breslau |1866–76| 5,128 | 39 | 0·761
Berlin |1859–68| 4,770 | 33 | 0·69
Würzburg | -- | 2,280 | 11 | 0·48
Göttingen | -- | 639 | 3 | 0·469
Dresden |1852–62| 1,939 | 7 | 0·36
Münich |1854–87| 14,183 | 35 | 0·25
Vienna | 1860 | 1,229 | 3 | 0·24
Prague | -- | 1,287 | 3 | 0·23
Kiel |1872–87| 3,581 | 7 | 0·19
Zürich, Basle, Berne| -- | 7,982 | 11 | 0·13
Erlangen |1862–73| 1,755 | 2 | 0·11
--------------------+-------+--------------+------------+----------
These, however, are only cases that have become known by _post-mortem_;
in addition, there are cases that have been treated medically, of which
there are a few statements, at all events relating to the principal
districts of Germany. According to Madelung, one case of echinococcus
occurs in every 1,056 inhabitants in the town of Rostock, in the
district of Rostock one to every 1,283, in Schwerin one to every 5,887,
and in Ludwigsort one to every 23,685; according to Peiper, in Upper
Pomerania one case occurs to every 3,336, in the district of Greifswald
one to every 1,535 inhabitants. The northern districts of Pomerania are
more affected than the southern ones.
Accordingly, echinococcus is also considerably more frequent in
cattle in Pomerania. On an average in Germany 10·39 per cent. oxen,
9·83 per cent. sheep, and 6·47 per cent. pigs are infected, whereas
in Upper Pomerania 37·73 per cent. oxen, 27·1 per cent. sheep, and
12·8 per cent. pigs are infected; in Greifswald, indeed, 64·58 per
cent. oxen, 51·02 per cent. sheep, but only 4·93 per cent. pigs are
infected. In accordance with these figures _Tænia echinococcus_ must
be frequent in dogs in Pomerania, especially in Upper Pomerania; on
the other hand, the conjecture that the frequency of echinococcus in
Mecklenburg is explained by the occurrence of _Tænia echinococcus_ in
foxes has not been confirmed, as the fox does not harbour this worm
in Mecklenburg.
Beyond the European continent, echinococcus is frequent in the
inhabitants of Iceland, Argentine, Paraguay and Australia. In Iceland,
according to Finsen, 1 in every 43 inhabitants is affected with
echinococcus; according to Jonassen the proportion is 1 to 63; this
is due to the habits of the people of Iceland or, in fact, to the
frequency of _Tænia echinococcus_ in dogs, and the prevalence of the
hydatid in cattle. In certain districts of Australia it is just as
frequent. In Cape Colony, Egypt and Algeria echinococcus is not rare,
but it is scarce in America and in Asia, with the exception of the
nomadic tribes of Lake Baikal.
[Illustration: FIG. 258.--Hooklets of echinococcus. _a_, of
_Echinococcus veterinorum_; _b_, of _Tænia echinococcus_, three weeks
after infection; _c_, of the adult _Tænia echinococcus_; _d_, the
three forms of hooklets outlined one within the other. 600/1. (After
Leuckart.)]
Echinococcus attacks persons of every age, though it is rare in
children up to 10 years of age and in old people. It occurs most
frequently between the ages of 21 and 40 years. According to all
statistics it preponderates in women (about two-thirds of the cases).
The liver is its favourite seat (57·1 per cent. of the cases); next
in order come the lungs (8 per cent.), kidneys (6 per cent.), cranial
cavity, genitalia, organs of circulation, spleen (3·8 per cent.), etc.
As a rule one organ only is invaded; multiple occurrence may originate
from one infection, or eventually from a later infection (?), or it may
come to pass that from some cause (through the spontaneous rupture of
an echinococcus, or the rupture of one caused by an injury or surgical
operation) daughter cysts, brood capsules or scolices escape into the
abdominal cavity,[294] where they settle or become transformed and
go on growing. In the distribution of this secondary echinococcus
the great powers of motility of the free scolices must be taken into
account (Sabrazès, Muratet, and Husnot).
[294] In such cases the toxic effects of the echinococcus fluid
usually--if not always--manifest themselves. Such effects are
manifested by severe symptoms of poisoning being set up, by urticaria,
peritonitis, and ascites, and not infrequently they cause a fatal
termination.
Human echinococci may also die at various stages of development,
become caseous or calcified, or may be absorbed, the cause for this
being either disease of the hydatid itself or inflammation of its
connective tissue capsule; the discovery of the laminated cuticle,
which has great powers of resistance, or the finding of the hooklets
of the scolices is sufficient to form a conclusion as to the nature
of such formations.
Siebold (1853) was the first to rear _Tænia echinococcus_ in the dog
by feeding it with the echinococcus of cattle and especially of sheep.
Küchenmeister, van Beneden, Leuckart, Railliet and others obtained
similar results, and Thomas, Naunyn, Krabbe and Finsen succeeded in
rearing _T. echinococcus_ in dogs from the bladder worms of human
beings; these grow comparatively slowly (one to three months[295])
and only during the process of growth develop their hooklets in their
definite form (fig. 258). It lies in the nature of things that dogs,
whether experimentally or naturally infected, almost always harbour
_T. echinococcus_ in large quantities. That cats exceptionally harbour
these worms has been already mentioned (Dévé). Finally, Leuckart
infected young pigs by feeding them with mature segments.
[295] According to Perroncito the scolices had not formed proglottids
nine days after feeding, but the latter were present twenty-four days
after feeding, although the formation of eggs had not begun.
*Echinococcus multilocularis* (alveolar colloid).
In addition to the form of echinococcus already described, and which is
also frequently termed _Echinococcus unilocularis_, there is a second
form which occurs in man as well as in animals, and which is termed _E.
multilocularis_, s. _alveolaris_ (alveolar colloid).
It was originally regarded as a tumour; its animal nature was first
established by Zeller and R. Virchow. The parasite, which varies in
size from that of a fist to a child’s head, presents a collection
of numerous cysts, measuring between 0·1 and 3 to 4 mm. to 5 mm. in
diameter, which are embedded at first in a soft, connective tissue
stroma; the cut surface has therefore a honeycomb appearance. The cysts
are surrounded by a pellucid and laminated cuticle, and each according
to its size encloses either a small-celled tissue or a cavity lined by
a parenchymatous layer; the fluid contained in such a cavity may be
transparent, or is rendered opaque by globules of fat, bile-pigment,
hæmatoidin and fat crystals. According to some authors all or most of
these cysts intercommunicate; others state that this is the case at
least as regards the cuticle. The scolices are by no means found in
all the cysts, and when present only a few, rarely half, of the cysts
contain scolices (one or more); it is supposed that at least some of
these scolices are formed in brood capsules, and that the former are
capable of undergoing a cystic metamorphosis.
One circumstance is peculiar to the multilocular echinococcus of man,
namely, the disintegration that sets in at certain stages; in the
centre of the parasite a cavity forms that frequently becomes very
large and is filled with a purulent or brownish or brownish-green
viscid fluid; in this fluid one finds shreds of the wall of the
cavity, calcareous bodies, echinococcus cysts, also scolices and
hooklets, as well as fat globules and crystals of hæmatoidin,
margarine and cholesterin and concretions of lime. Such ulcerative
processes, according to Ostertag, are never present in the multilocular
echinococcus of oxen,[296] in which the separate cysts are larger and
the connective tissue integument less powerfully developed.
[296] This may perhaps be explained by the fact that the hosts are
slaughtered before the parasites have attained the size or other
conditions necessary to disintegration.
[Illustration: FIG. 259.--_Echinococcus multilocularis_ in the liver of
the ox. Natural size. (After Ostertag.)]
Hardly anything positive is known with regard to the development of
the alveolar echinococcus; its peculiar conformation is attributed by
some to enormous infection of oncospheres, by others to the abnormal
situation of one oncosphere; a few authors ascribe it to infection
of lymphatic vessels, others to infection of the biliary ducts or to
peculiarities of the surrounding hepatic tissue; Leuckart ascribes it
to a grape-like variety of form which continues budding; a few more
recent authors consider multilocular echinococcus to be specifically
different from unilocular echinococcus, and therefore also different
the species of Tænia arising from them. Melnikow-Raswedenkow is also
of this opinion. According to this author the oncospheres infect
the lumen of a branch of the portal vein in Glisson’s capsule of
the liver and grow into an irregularly shaped formation (chitinous
coil), which breaks through the vascular walls and thus forms the
alveoli. So far the data coincide well with Leuckart’s opinion of
the original grape-like form of the _Echinococcus multilocularis_;
according to Melnikow-Raswedenkow the “granular protoplasmic
substance” (parenchymatous layer) is not only present in the interior
of the loculi but also outside, and, moreover, “ovoid embryos”
are supposed to develop in the chitinous coils, which, “thanks to
their amœboid movements, reach the lumen of a vessel, where, under
favourable circumstances, they begin to develop further,” that is to
say, they become “chitinous cysts with fantastic outlines,” or also
“single-chambered chitinous cysts”; scolices may develop in both. Dévé,
however, considers that these embryos are only prolongations of the
protoplasmic layer which secondarily cuticularize.
The multilocular echinococcus, which in man produces a severe disease
and almost always leads to premature death, infects most frequently
the liver, but may also be found primarily in the brain, the spleen
and the suprarenal capsule; from the liver by means of metastasis it
may reach the most various organs, especially those of the abdomen,
but also the lungs, the heart, etc. Up to 1902, 235 cases have been
described and up to 1906, 265, being 70 from Russia, 56 from Bavaria,
32 from Switzerland, 30 from the Austrian Alps, 25 from Würtemberg;
the remaining cases are distributed over Central Germany, Baden,
Alsace, France, Upper Italy, North America. In some the origin is
doubtful; in any case after Russia, the mountainous South of Europe
is the principal region of distribution. As to the domesticated
animals, the same parasite is found principally in the ox (according
to Meyer, in Leipzig, in 7 per cent. of the oxen affected with
echinococcus); it is rarer in the sheep and very scarce in the pig.
It has already been mentioned above that recently the multilocular
echinococcus has been stated to be specifically different from hydatid
or unilocular echinococcus. To this may be added the fact that
Mangold, who fed a young pig with oncospheres of a Tænia reared from
the multilocular echinococcus, found two growths in the liver four
months later, which he took to be _E. multilocularis_, and consequently
one has to assume the existence of two different worms. The chief
defender of this view, already put forward by Vogler, Mangold, and
Müller, is Possett. He bases his opinions on (1) the more restricted
distribution of the multilocular hydatid, the former occurring in
districts where only cattle are raised, the latter where sheep-breeding
is established; (2) that those engaged in looking after sheep are
attacked by multilocular, whereas those looking after cattle are
attacked by unilocular hydatid; (3) that among the cases of unilocular
hydatid occurring in the distribution areas of multilocular hydatid no
transitions between the two forms are observed; (4) on the difference
in the hooks both in the hydatid as well as in the Tænia stage; the
hooks of _Tænia echinococcus_ are plump, sharply curved, and have a
short posterior root process the length of which is to that of the
total length as 1 to 4·7, whereas on the contrary the hooks of the
alveolar echinococcus are more slender, slightly bent, and have a long
posterior root process (1 to 2·5); and (5) on the form of the uterus,
which in the alveolar Tænia has the form of a spherically distended sac
anteriorly.
SERUM DIAGNOSIS OF ECHINOCOCCUS.
(1) _Precipitin Reaction._--Mix equal parts of hydatid fluid (of
the sheep) and serum of patient. Keep at 37° C. The reaction is not
decisive as it may be given by normal sera.
(2) _Complement Deviation._--Required: (1) Hydatid fluid of sheep
(antigen), (2) guinea-pig complement, (3) patient’s serum, (4) red
cells of sheep, (5) hæmolytic serum (of rabbit) against sheep’s red
cells, (6) 0·8 per cent. salt solution. Mix the antigen + patient’s
serum (heated) + complement + salt solution at 37° C. for one hour. Add
red cells of sheep + hæmolytic serum. Allow to stand for half an hour
at 37° C. It is imperative to make adequate control observations. An
example will indicate the method. Salt solution 1·3 c.c. + patient’s
serum (heated) 0·2 c.c. + hydatid fluid 0·4 c.c. + complement 0·1 c.c.
of serum diluted to a quarter strength + hæmolytic serum and red cell
emulsion 1 c.c. Result: no hæmolysis, _i.e._, the patient’s serum
contains specific (echinococcus) antibodies.
C. *NEMATHELMINTHES*.
BY
J. W. W. STEPHENS, M.D., B.C., D.P.H.
Bilaterally symmetrical animals, without limbs and with a body
cavity in which the gut or other organs float. They are generally
cylindrical.
Class. *NEMATODA.*
Nemathelminthes with an alimentary canal.
Nematodes are as a rule elongated round worms of a filiform or
fusiform shape; their length varies according to the species from
about 1 mm. to 40 to 80 cm. The outer surface of the body is
smooth or annulated, and at certain points provided with papillæ,
occasionally also with bristles and alar appendages. The anterior end
carrying the oral aperture is usually rather slender, occasionally
quite thin; the posterior end is pointed or rounded; the anus, as a
rule, lies somewhat in front of the posterior extremity. The sexes
are almost always separate, and the male can as a rule be easily
distinguished from the female because the former is smaller and
more slender, its posterior extremity is often spiral or incurved,
or carries an alar appendage, whereas the female is larger and
thicker, and its posterior extremity is straight. In the male the
genitalia open into the anus; the sexual orifice of the female opens
ventrally along the median line in the anterior half of the body,
in the middle, or a little further back. Both sexes, moreover, have
an orifice, the excretory pore, which is situated ventrally in the
median line and about the level of the œsophageal nerve ring.
In large species, even with the naked eye, two lighter transparent
bands--the lateral lines--may be distinguished; they run along the
sides of the body from the anterior to the posterior end, while two
other bands, the median lines, running along the ventral and dorsal
mid-lines, are less evident; in exceptional cases there are also four
sub-median lines. These bands or lines are inward projections of the
ectoderm, and in them lie the nerves and excretory vessels (fig. 260).
Some Nematodes live free in fresh or salt water, in soil, mud or
decaying vegetable matter, others parasitically in the most various
organs of animals, frequently also in plants.
ANATOMY OF THE NEMATODES.
All the Nematodes are covered by (1) a CUTICLE, which in the small
species is thin and delicate, while in the larger species it is
thickened, and may consist of several layers of complicated structure.
Canalicular pores do not occur. According to general opinion, which
is confirmed by the history of development, the cuticle is a product
of (2) the EPITHELIUM or ectoderm that had formerly existed or is
still found beneath it; in young specimens and small species it is
perceptible, but in older worms it frequently alters so considerably
that not only do the borders of the cells disappear,[297] but a fine
fibrous differentiation appears in their cytoplasm. The matrix or
ectoderm then has the appearance of an ectodermal syncytium permeated
by fibres and strewn with nuclei, so that it is hardly distinguishable
from the tissue of (3) the CUTIS, which is always present, though
developed to a varying degree. Both layers, matrix and cutis, project
internally as ridges and form the lateral lines, while the less marked
median lines are produced apparently only by the ectoderm (fig. 260).
[297] In the _Ascaridæ_ isolated epidermal cells grow to a considerable
size, and have to do with the sensory apparatus of the lips
(Goldschmidt).
Unicellular cutaneous glands are known in parasitic as well as in
free-living species; they vary in number and arrangement, and are found
discharging some at the anterior extremity and others in the vicinity
of the genital orifices. In other cases large numbers of them are
present along the lateral lines; they are strongly developed in most
of the _Trichotrachelidæ_, where they discharge either along a part of
the ventral surface or along the lateral and median lines; they are
placed so closely together that the ridges of the cuticle perforated by
the orifices have long been known, and have been described, as “rodlet
borders,” or “fields of rods.”
As the cutis is immediately adjacent to (4) the DERMO-MUSCULAR TUBE
the simple layer of the muscular cells is divided into four quadrants
by the longitudinal lines--two dorsal and two ventral (fig. 260). The
MUSCLES are in the simplest cases large rhomboid cells that lie two
by two in each quadrant, so that on transverse section of the entire
worm only eight cells are perceptible. The outer border of the cells is
converted into contractile fibrils, while the contiguous inner portion
has remained protoplasmic, and contains the nucleus. In large species
the muscular cells do not only increase in length (up to 3 mm.) and in
number in every quadrant, but their contractile portion curves up to
form a groove (like that of a dead leaf) thereby even becoming thicker;
simultaneously space is gained for more cells, the protoplasmic parts
of these cells (on transverse section) project out of the grooves
like vesicles. In all cases there is only one layer of longitudinal
muscular cells, which, by contracting, can shorten the body or, by
contracting one side, can bend it. In the latter case the muscles of
the opposite side have an antagonistic effect, or when all the muscles
are contracted, the elasticity of the cuticle acts in the same way.
Special muscles exist at the beginning of the gut and at sections of
the genital apparatus.
The existence of a cavity between the body and the gut wall has
hitherto been generally assumed, and has been referred to the cleavage
cavity, and consequently designated as a primary body cavity. More
recent investigators, however, state that such a cavity does not
exist, but that the space between the longitudinal muscles or their
protoplasmic portions and the gut epithelium is filled by a complicated
“isolation tissue.” This in the main proceeds from a large cell
(_Is._, fig. 262) which lies directly behind the nerve ring dorsal to
the œsophagus, and consists of a system of lamellæ which sheathe the
muscles and penetrate through them to the cutis and also cover the gut
in a thin layer.
[Illustration: FIG. 260.--Diagram of a transverse section of _Ascaris
lumbricoides_, showing thick cuticle, and beneath it the matrix or
syncytial ectoderm. The flat intestine is in the middle, and to
the right and left near it in the body wall the lateral lines with
excretory vessel and lateral nerves; above and below in the centre
the dorsal or ventral median lines with the nerves radiating to the
muscles, also the muscle cells with their striated outer contractile
portion and inner nucleated vesicular protoplasmic portion. About 50/1.
(After Brandes.)]
[Illustration: FIG. 261.--Anterior end of an _Ascaris megalocephala_
cut open and showing the four tuft-like organs lying on the lateral
lines. Natural size. (After Nassonow.)]
We may now consider the “tuft-like” or “phagocytic” organs, which
attain 1 cm. in size, and consist of four, six, or even more ramified
cells, which lie close to the walls of the body (fig. 261). They
are found either only in the anterior part of the body (Ascaris),
or throughout the whole length of the body (Strongylus, syn.,
Sclerostomum), and their position usually corresponds to the lateral
lines. In some species there are small protoplasmic cells on the
processes of these organs. In consequence of their size they can be
recognized with the naked eye, especially when they are loaded with
granules of stain (carmine, Indian ink) injected into the body cavity.
INTESTINAL CANAL.--The oral aperture, which is situated at the tip
of the anterior extremity, is frequently surrounded by thick lips,
or small bristles, or papillæ; it leads to a more or less strongly
developed buccal cavity, which is lined by a continuation of the
body cuticle, and which in some species is provided with “teeth,”
representing differentiated portions of the cuticle.
THE ŒSOPHAGUS (fig. 262), which arises from the base of the oral
cavity, is as a rule a short, bottle-shaped tube with triradiate
lumen; its wall is chiefly composed of radiating muscular fibres,
which give it the appearance of being transversely striped when viewed
from the surface. There exist also in its wall three large gland cells
(œsophageal glands) and nerves arising from the lateral lines and
running forward. The radial fibres cause a dilatation of the lumen,
and exercise an effect antagonistic to the elasticity of the cuticle
lining the inner surface. The latter has its own particular layer,
which is not in direct connection with that of the oral cavity. Special
dilator muscles, arising from the dermo-muscular tube and situated at
the commencement of the œsophagus, are only known in a few species.
The posterior end of the œsophagus presents a bulb-like dilatation,
and is frequently provided with small chitinous movable valves. In a
few forms, which belong to the _Trichotrachelidæ_ (Trichocephalus,
Trichinella), the œsophagus is a very long cuticular tube, beset on
its dorsal surface with a series of large nucleated cells. In others
(Cucullanus, Ascaris, etc.), a tube, the so-called glandular stomach,
lined only by epithelial cells, follows behind the muscular œsophagus.
This glandular stomach is, from its structure, easily distinguished
from the mid-gut, or chyle intestine, which is likewise cellular. The
so-called mid-gut is a tube lined by flat, cubical, or cylindrical
cells (fig. 260) surrounded by “isolation tissue”; its transverse
section is circular or flattened dorso-ventrally; the lumen may run in
a straight line, or it runs a sinuous course through the alternating
prominences of the then flat epithelial cells.
The ectodermal hind gut is, as a rule, very short. At the anal opening
the cuticle and the subcuticular layers are reflected inwards, forming
the lining of the hind gut. In large species the subcuticular tissue
forms large cells on which anteriorly lie in addition large “glandular
cells.”[298] In the male the ejaculatory duct opens at this point.
Around the end part of the gut, either on the chyle intestine or at the
beginning of the end gut, there exists a sphincter muscle arising from
a muscle cell which acts antagonistically to the two diaphragm-like
dilator muscle cells which stretch from the gut to the body wall.
In many species large stretches of the gut are provided with dilator
muscles. There is sometimes a retrogressive absorption of the gut in
the adult stage of a few parasitic species.
[298] In Ankylostomes according to Looss these cells have no glandular
function, but are ligaments.
INTESTINAL CÆCA and ŒSOPHAGEAL GLANDS sometimes exist as intestinal
appendages; the former are tubular appendages of various size, running
backwards or forwards, and arising from the posterior extremity of the
œsophagus. They are lacking in many species. The œsophageal glands are
unicellular; a dorsal and two subventral glands may be distinguished
according to their position; as a rule they open into the œsophagus at
a distance from one another. The body of the gland lies in the bulb of
the œsophagus, or in the dorsal _cul-de-sac_ arising from it.
[Illustration: FIG. 262.--Transverse section through _Ascaris
lumbricoides_ at the level of the œsophagus behind the nerve ring.
_Cu._, cuticle; _Sc._, subcuticular layer; _Ex._, excretory vessel;
_Is._, isolation cell and the system of lamellæ proceeding from it;
_M._, muscles; _Ml._, median line; _Sl._, lateral line. Magnified.
(After Goldschmidt.)]
THE NERVOUS SYSTEM is sufficiently known in a few species only; it
consists of a ring containing fifty to sixty fibres closely surrounding
the œsophagus, various groups of ganglion cells, and a certain number
of nerves extending anteriorly as well as posteriorly. The remarkably
small number of fibres, as well as ganglion cells, is characteristic
of the nervous system of all Nematodes. Immediately behind the
œsophageal ring (fig. 263, _Lg._) an agglomeration of ganglion cells
lies at either side (lateral ganglia); part of their off-shoots form
the œsophageal ring, and part are directed posteriorly and ventrally,
and unite partly in front of and partly at the back of the excretory
pore, with fibres originating direct from the œsophageal ring, and
passing along the ventral median line to the back; these fibres then
together form the ventral median nerve (fig. 263, _V.m.n._). This
nerve, originally consisting of thirty to fifty fibres, becomes in
the female attenuated quite evenly in its further course. There is
also an agglomeration of ganglion cells close in front of the anus
(anal ganglia), and then the median nerve divides in order to combine
with the lateral nerves on either side. In the male the median nerve
enlarges to nearly the original number of fibres in front of the anal
ganglion, which contains seven cells; there is also an anal ring
embracing the terminal gut, and there are two ganglion cells in it on
each side. In the dorsal median line the dorsal median nerve is alike
in both sexes; arising in front with a single root from the œsophageal
ring, it gathers its fibres from the lateral ganglia; in the anterior
part of the body it consists of thirteen to twenty fibres; in the
posterior part of the body the fibres are reduced to four or six;
behind the anus it divides and combines with the lateral nerves; the
latter consists of two fascicles at either side right up to their most
posterior extent--one dorsal and one ventral--which in the greater part
of the body do not run in, but beside the lateral lines, and exhibit a
different origin anteriorly. The ventral fascicle at each side branches
off from the ventral median nerve in front of the excretory pore,
whereas the dorsal fascicles originate from the œsophageal ring close
to the lateral ganglia. Each of the four fascicles contains only two
or three fibres, which run backwards parallel to the lateral lines; a
few centimetres in front of the caudal extremity they enter the lateral
lines and remain separate from one another up to the level of the anal
ganglion; here they amalgamate on either side, after each interpolating
one ganglion cell, with the single short lateral nerve which first
takes up the forked ends of the ventral and then of the dorsal median
nerve; finally, both lateral nerves unite with each other at the back
in an arch-like manner.
[Illustration: FIG. 263.--Schematic representation of the nervous
system of a male _Ascaris megalocephala_. _A._, anus; _Ag._, anal
ganglion; _C._, commissures; _D.m.n._, dorsal median nerve; _Exp._,
excretory pore; _Pr._, œsophageal sensory ring; _Lg._, lateral ganglia;
_Ln._, lateral nerve; _Sp._, papilla; _V.m.n._, ventral median nerve.
(After Brandes.)]
In the male each ventral part of the lateral nerves becomes thickened
by taking up fibres from the ventral nerves, which become thickened
posteriorly to the nervus bursalis, which towards the middle gives off
a mass of fibres to the “genital papillæ” situated in front of and
behind the anus; the number of these fibres averages eighty to 100; in
its further course the bursal nerve resembles the corresponding ventral
part of the lateral nerves of the female.
The ventral and dorsal nerves are connected by a number of semicircular
commissures, which originate from the ventral nerves and serve to
supply the dorsal nerve, which is always being decreased by fibres
departing from it. It is remarkable that these commissures are not
placed symmetrically, and their position also is different in the
two sexes; in the female there are thirty-one on the right side and
only thirteen on the left side. In the male there are thirty-three
commissures on the right side and fourteen on the left, which run into
the subcuticular layer, generally in pairs, and usually cross at the
level of the lateral lines.
The fibres of the two median nerves are chiefly motor; fascicular
processes run from each protoplasmic part of the muscular cells to
the median nerves; from these they take up bundles of primitive
fibrils, which separate, pass through the protoplasmic part and enter
the contractile part (fig. 260). One part of the fibrils, however,
penetrates beyond the muscles into the subcuticular layer, where they
form a network, probably of a sensory nature, with contiguous fibrils.
Nerves directed anteriorly finally originate from the œsophageal ring;
they consist each of three fibres, carry three ganglion cells at their
point of origin, and enter the sensory organs of the three papillæ
surrounding the oral aperture. Two of these little trunks lie in the
lateral lines, the remaining four are situated in the middle of the
four quadrants (Nn. sub-mediani anteriores).
Parasitic species lack higher ORGANS OF SENSE; free-living worms
occasionally have two rust-red eyes, sometimes with lenses, at the
anterior part of the body. In addition to the above-mentioned sensory
papillæ surrounding the oral aperture and the genital papillæ of the
male at the end of the body, another pair exist in the vicinity of the
lateral ganglia, the “cervical papillæ,” and two dorsal papillæ in the
central region of the body and two lateral ones near the tip of the
tail (_Ascaridæ_). The differences in the distribution and number of
the sensory papillæ serve for characterizing the larger and smaller
groups of Nematodes.
THE EXCRETORY ORGANS of the Nematodes are variable. In a great many
cases the apparatus is symmetrical, and consists of a vessel commencing
in the posterior extremity in each lateral line (fig. 260), and passing
anteriorly. In the vicinity of the anterior extremity both tubes pass
out of the lateral lines, bend ventrally, and, in the median ventral
line, unite into a short vesicle formed by an ectodermal cell--the
cavity of which is lined by a continuation of the cuticle of the
body--which opens into the excretory pore (fig. 263, _Exp._). Asymmetry
is occasioned through the excretory duct proceeding from the ventral
pore to the lateral line, and it here proceeds as (or takes up) the
left excretory canal, which anteriorly is a broader tube and runs along
the left lateral line; shortly before its union with the excretory duct
it throws out a branch to the right towards the lateral line, which,
however, always remains weak, and runs posteriorly in the right lateral
line; a few smaller branches in addition spring from the left main
stem. In other species the right branch is completely suppressed; the
entire organ thus lies in the left lateral line, and consists of the
excretory duct, which occasionally opens quite in front near the lips,
as well as the excretory canal, which throws out a number of lateral
branches.
This excretory vesicle is a single elongated or horse-shoe-shaped
cell, with a large nucleus and an intracellular tubular system, which
is connected with the excretory duct arising from the excretory pore
on the outer surface (fig. 326). The so-called ventral gland is the
only excretory organ of marine Nematodes, and probably represents
a primitive form. Goldschmidt, who has investigated the excretory
apparatus of _Ascaris lumbricoides_, considers that the vessels running
in the lateral lines are only ducts to which belong a glandular system
hitherto overlooked or otherwise interpreted. This system also lies in
the lateral lines, and takes the form of two glandular tracts, forming
a syncytial tissue in which lie the ducts, one dorsal, one ventral.
In parts these tracts are connected by commissures, although their
junction with the excretory vessels cannot be clearly made out. These
statements, however, require confirmation. The author has further found
that the anterior ends of the lateral canals, directly before they bend
ventrally, anastomose with one another and give off anteriorly a small
blind process, which can be interpreted as a rudiment of a canal coming
from the head end, and as a matter of fact, according to Golowin, such
anterior excretory canals exist in a number of genera.
In a number of Nematodes (Cheiracanthus, Capillaria, Trichocephalus,
Trichinella, etc.), however, special excretory organs are lacking;
possibly the cutaneous glands, which are in these species generally
powerfully developed, replace these organs.
SEXUAL ORGANS.--With the exception of a few species, the Nematodes are
sexually differentiated.
(_a_) _Female Sexual Organs._--The sexual orifice (vulva), surrounded
by thick labia, is, as a rule, ventral and varies in position from
near the head to near the anus. It leads into a short or long vagina
(ectodermic), bifurcating into the two uteri, which may be long or
short; the long filiform ovaries are continuations of them (fig. 264).
Further there is often, _e.g._, in Ankylostoma, a differentiation into
the following parts: (1) _Ovejector_: the specialized portion of the
uterus before it joins the vagina; there may be a separate one for
each uterus, or a common one for both uteri. (2) _Seminal receptacle_:
at the other extremity of the uterus. (3) _Oviduct_: a narrow tube
connecting the ovary with the uterus proper. (For the explanation of
the terms _convergent_ and _divergent_ uteri _vide_ footnote p. 432.)
Uterus and ovaries, which arise in the first place from a single cell,
lie between the body wall and the gut and are surrounded by connective
tissue. In some species (for instance, Trichinella) the ovary is single.
[Illustration: FIG. 264.--Diagram of female genitalia. _Ov._, ovary (in
part); _Ovd._, oviduct; _Rec. sem._, seminal receptacle; _Ut._, uterus
(in part); _Ovj._, ovejector; _Vag._, vagina.]
[Illustration: FIG. 264A.--Diagram of male genitalia of a strongylid.
_Test._, testis (in part); _S.V._, seminal vesicle; _c.g._, cement
gland surrounding ejaculatory duct; _sp._, spicules; _cl._, cloaca;
_gub._, gubernaculum; _p.p.a._, pulvillus post-analis; _g.c._, genital
cone; _l.d._, dorsal lateral line; _l.v._, ventral lateral line (the
bursa is not shown).]
[Illustration: FIG. 265.--Transverse section through the ovarian tube
of _Belascaris cati_ of the cat at various levels. To demonstrate the
development (right to left) of the ova and of the rhachis. Magnified.]
At the blind end of the ovary there is a mass of protoplasm with
numerous nuclei that multiply continuously. Gradually the nuclei
arrange themselves in longitudinal rows (fig. 265) and the protoplasm
commences to leave the periphery and surround each nucleus. The
nearer to the uterus the more progressive is this loosening process,
until club-shaped cells each containing a nucleus are developed. The
most pointed end of each, however, is still attached to an axial
fibre of protoplasm, the _rhachis_; probably this has some connection
with the nutrition of the ova. Finally the ova fall off and reach the
uterus, where they are fertilized and enclosed in shells.
(_b_) _Male Sexual Organs._--There is never more than one testis
(fig. 266), which is a straight or sinuous tube of the same
construction as an ovary, and in which the mother cells originate
in the same manner as the ova. In the same way as the ovary passes
into the uterus, so does the testis pass into the spermatic duct; the
latter is often divided into the somewhat dilated seminal vesicle
and into the muscular ductus ejaculatorius, which, running ventral
to the intestine backward (fig. 267), finally opens into the cloaca.
In many species, _e.g._, _A. duodenale_, the ejaculatory duct is
surrounded for a greater or less portion of its extent by the cement
gland, the secretion of which (brownish or blackish in colour) serves
for copulation. The ejaculatory duct of the large _Ascaridæ_ is for
the most of its course surrounded by a muscular network which takes
its origin from the two dilator cells of the gut (fig. 268 _F_.).
The spermatozoa of the Nematodes, it may be noted, only attain their
full development after the sperm mother cells have been conveyed by
copulation into the uteri of the female genitalia. In their form
(sheathless, capable of amœboid motion) they differ from those of most
other animals.
SPICULES.--The male genital apparatus is also provided with one or
two sacs, situated on the dorsal side of the intestine, and opening
into the cloaca. In each sac there is a chitinous rod-like body, the
spicule. Further, in many cases there exists, more or less fixed in the
dorsal wall of the cloaca, a chitinous structure, the accessory piece
or _gubernaculum_, the latter name implying its function of guiding the
spicules during copulation (fig. 264A). A special muscular apparatus,
consisting of protractors and retractors, moves the spicules. The
protractors or exsertors in the large Ascaridæ consist of four flat
band-like muscles which surround the spicule sac. Two long muscle
cells which arise proportionally far forward on the dorsal side of
the lateral line and are inserted into the base of the spicules serve
as retractors. The spicules can be projected from the cloacal orifice
(anus) during copulation, and when they are introduced into the vagina
they serve as prehensile organs, perhaps also as stimulatory organs.
[Illustration: FIG. 266.--Male of the rhabditic form of _Angiostomum
nigrovenosum_. _A._, anus; _I._, mid-gut; _T._, testicular tube; _O._,
oral orifice; _P._, papillæ; _Sp._, spicule. Magnified.]
[Illustration: FIG. 267.--Transverse section through the posterior
extremity of the body of _Ascaris lumbricoides_ (male). The intestine
is in the middle, and the lateral lines are subjoined thereto; above
the intestine the two spicule sacs are seen; below is the ductus
ejaculatorius. The muscular fibres are between the lateral and median
lines. Magnified.]
BURSA COPULATRIX.--The males in many genera possess epidermal wing-like
appendages at their posterior extremity. These are supported by
elongated tactile papillæ called ribs. In the most highly developed
bursæ, _e.g._, in the _Strongylidæ_, the ribs are called rays, as
they consist not only of nerve fibres but mainly of “pulp,” _i.e._,
prolongations of the subcuticular layer. Bursæ are either open,
_i.e._, bilaterally symmetrical, or closed, when the posterior border
is continuous all round. A _pseudo-bursa_ is one unsupported by
ribs or rays, _e.g._, in Trichuris. The bursa serves as an organ of
prehension during copulation. Some forms, moreover, carry a sucker at
the posterior extremity (_e.g._, Heterakis); in others the spicules
and other prehensile organs are absent; they are then replaced by an
evertible cloaca, _e.g._, Trichinella.
DEVELOPMENT OF THE NEMATODES.
After impregnation, the ovum develops around itself a delicate membrane
(vitelline membrane), and subsequently an egg-shell is formed. This
is derived either as a secretion from the uterine wall or it is a
further differentiation of the vitelline membrane, the original single
membrane splitting into two, the outer becoming the egg-shell. Further
the uterus often secretes a special albuminous covering around the
egg-shell. The “yolk” granules of the ovum are secretions of the
protoplasm of the ovum itself and first appear when the rhachis is
formed. In certain cases ova lie in follicles or capsules formed
of epithelium cells derived from the ovarian tubes. These cells
subsequently fuse and form a membrane--the CHORION.
[Illustration: FIG. 268.--Hind end of a male _Ascaris lumbricoides_ cut
across at the level of the dilator cells of the gut. _D._, gut; _Dil._,
dilator cells of the gut; _F._, a process of the dilator cells forming
a network over the vas deferens; _Sl._, lateral line; _Sp._, spicule;
_Vd._, vas deferens. The anterior end of the worm lies to the right.
Magnified. (After Goldschmidt.)]
The shape of the completed eggs is characteristic of the different
species, and therefore a single egg often suffices to diagnose the
species. According to the species, the eggs may be deposited sooner
or later, either before or during segmentation, or with the embryo
perfectly developed. Only a few species are viviparous, _e.g._,
_Dracunculus mediensis_, _Trichinella spiralis_; in the other Nematodes
the further development of the extruded eggs takes place after various
lengths of time in the open, in moist earth, or in water. Thick-shelled
eggs can maintain their developmental capacity for a long time, even
after prolonged desiccation.
Finally, a nematode-like embryo develops, which usually lies somewhat
coiled up within the shell, and varies in its further development
according to the species to which it belongs.
In the simplest forms, as in the free-living Nematodes, the embryos,
apart from their size, resemble their parents, and grow up into these
after leaving the egg-shell. In many parasitical Nematodes, however,
the young must be called _larvæ_, as they present characters which are
subsequently lost.
The manner of conveyance of the eggs or the embryos contained in them
after they have left the body into the definite host is very different
in the various species.
(1) _Without Intermediate Host._--(_a_) In many the conveyance into
the definite host is effected directly after the larvæ have developed
within the eggs; thus, for instance, the feeding of suitable animals
with the embryo-containing eggs of species of Trichocephalus and
Ascaris leads to an infection of the gut, for the young Trichocephali
or Ascarides only leave the egg-shell when they have attained the
intestine of the final host, in which they become adult.
In other cases (_b_) Ancylostoma, Necator, the larvæ hatch in the open,
and live for a time free, changing their form; they grow, cast their
skin, and finally gain the intestine of the host by means of water or
through the skin, when they lose their larval characters and assume the
structure of the adult worm.
(_c_) In a number of Nematodes, however, HETEROGONY occurs. This terms
signifies a mode of development in which two structurally different
sexual generations of the same species alternate with each other. To
these appertains, for instance, _Angiostomum_ (syn.: _Rhabdonema_)
_nigrovenosum_, which lives in the lungs of frogs and toads; this
Nematode measures about 1 cm. in length and is hermaphrodite
(protandric). The eggs are deposited in the pulmonary cavity, and
through the cilia of the same reach the oral cavity, where they are
swallowed and thus conveyed into the intestine. They pass through the
entire gut, and are finally evacuated with the fæces; often, indeed,
the young themselves emerge from the egg-shell within the hind-gut
of the frogs. These young forms become sexually differentiated,
remain much smaller than the parent, their œsophagus is differently
constructed (rhabditis form), and they are non-parasitic (fig. 266).
After having grown in the open they copulate; the males die soon after
copulation, and the females in their own bodies develop a few young,
which, given the opportunity to get into frogs, infect them, and are
transformed into the hermaphroditic Angiostomum. The same manner of
development occurs in other species of the same genus, and also in the
case of _Strongyloides stercoralis_.
(2) _With Intermediate Host._--(_a_) Frequently, however, the larvæ
of Nematodes make use of one or even two intermediate hosts; their
condition then resembles that of Cestodes or Trematodes, excepting that
there is never a multiplication within the intermediate hosts. The
larvæ become encapsuled amongst the tissues of the intermediate host,
and wait till they are introduced with the latter into the final host.
For instance, _Ollulanus tricuspis_, the adult form of which is found
in cats, previously lives encysted in the muscular system of mice.
_Cucullanus elegans_, which attains the adult stage in fishes (perch,
etc.), is found encysted in species of Cyclops. Other examples of
species that require an intermediate host are _Filaria bancrofti_ and
_Dracunculus medinensis_.
[Illustration: FIG. 269.--A piece of the trunk muscle of the pig with
encapsuled embryonic Trichinæ. Magnified.]
Peculiar conditions prevail in the case of (_b_) _Trichinella
spiralis_. This species, which in its adult state lives in the
intestine of man and of various mammals, is viviparous; the young
Trichinæ, however, do not leave the intestine, but reach the intestinal
wall (Cerfontaine, Askanazy) in the following way: the female
intestinal Trichinæ bore into the intestinal wall, where they are found
in the submucosa, or in the lumen of the dilated lacteal vessels. Here
the young are born, in the intestinal wall, and leave this position
with the lymph stream. Some of them, no doubt, actively bore through
the intestinal wall, reaching the lymph or blood-stream, or even pass
into the body cavity. What occurs during their further migrations is
difficult to say at present. It has hitherto been maintained that
the wandering is entirely active; for instance, the ligaturing of an
artery would be no protection against the part of the body supplied
by such artery being invaded by Trichinella. This observation cannot
be otherwise explained than by the active progress of the young
Trichinella. The question, however, may be mooted as to where and when
the worms quit the blood-vessels, which they for the most part reach
through the thoracic duct, the natural connection between the vascular
system and the lymphatic system, to wander further independently, and
ultimately reach the muscular system, in which they become encysted
(fig. 269). Thus the progeny does not leave the body of the host
inhabited by the parents, as is generally the case amongst helminthes,
but uses it as an intermediate carrier to reach another host, which is
then the final host. The latter may belong to another species, or may
be another individual of the same species. This second migration is, of
course, purely passive.
CLASSIFICATION OF THE NEMATODA.
The Nematodes are usually divided into a number of families, some of
which it is at present impossible to define accurately; moreover, the
definition of many genera is also in an unsatisfactory state.
Family. *Anguillulidæ*, Gervais and van Beneden, 1859.
A “family” name not definable. They comprise a vast number of
small forms, most of which live free in fresh water, in soil, or
in macerating substances; amongst them there are some which live
parasitically on plants, more rarely on animals. They do not exceed
8 mm. in length. The large majority are only 1 to 2 mm., or even
0·5 mm. The uterus is straight. Eggs in the uterus at one time,
one to four. Genera very numerous, but many of them insufficiently
defined (Anguillula, Anguillulina, Rhabditis, Heterodera, etc.).
Family. *Angiostomidæ*, Braun, 1895.
Small Nematodes undefined morphologically, but characterized by
heterogony, _i.e._, there is a free-living “rhabditic” generation
and a parasitic “filariform” generation which succeed one another
(_e.g._, Angiostomum, Strongyloides, Probstmayria).
Family. *Gnathostomidæ.*
Cuticle covered totally or partly with cuticular laminæ fringed
posteriorly with multiple points. Head subglobular, covered with
simple spines. Two spicules. Vulva behind middle of body, parasitic
in vertebrates, especially mammals (_e.g._, Gnathostoma, Tanqua,
Rictularia).
Family. *Dracunculidæ*, Leiper, 1912.
Males very small in proportion to females. Anus absent. Vulva absent
(?). Genera: Dracunculus, Icthyonema (in body cavity of eel and other
fish).
Family. *Filariidæ*, Claus, 1885.
Long thread-like Nematodes. Anus present. Œsophagus without bulb.
Vulva usually in anterior half of body. Two ovaries. Generally
ovoviviparous. Development often requires an intermediate host. This
family is at present ill-defined, but has been already subdivided
into several sub-families, _Filariinæ_, _Onchocercinæ_, _Arduenninæ_.
Family. *Trichinellidæ*, Stiles and Crane, 1910.
Œsophagus consisting of a chain of single cells, the lumen of the
œsophagus passing through their centre. Ovary single. Vulva at
junction of anterior and posterior portions. Sub-families: (1)
_Trichurinæ_, (2) _Trichinellinæ_.
Family. *Dioctophymidæ.*
Body anteriorly armed with spines or unarmed; mouth without lips,
with six, twelve, or eighteen papillæ in one or two circles;
œsophagus very long without a bulb; anus terminal in female; one
ovary; vagina very long; spicule in male very long; bursa cup-shaped
without rays (Dioctophyme, Hystrichis, Eustrongylides).
Family. *Strongylidæ*, Cobbold, 1864.
Bursa, supported by rays, always present. Oviparous.
Family. *Physalopteridæ.*
Mouth with two large lips. Bursa with supporting papillæ in form of a
lanceolate cuticular expansion, with genus Physaloptera.
Family. *Ascaridæ*, Cobbold, 1864.
Rather thick Nematodes. Mouth with three lips--one dorsal, two
latero-ventral. Sub-families: (1) _Ascarinæ_, (2) _Heterakinæ_, etc.
Family. *Oxyuridæ.*
Smallish forms, 4 to 45 mm., with cuticle thickened on each side
for the whole length of body in the form of a lateral flange or
wing. Œsophagus long with a well-marked bulb containing a valvular
apparatus. Tail end of female drawn out into a long point. Eggs
asymmetrical. Males very small (about 2 mm.). One spicule. Genera:
Oxyuris, Passalurus, Ozolaimus, Atractis, etc.
_Mermithidæ_, greatly elongated “Nematodes,” which, in the larval
stage, are parasitic in insects, but in their adult condition are
free living. Cuticle with diagonal striation. Without an open
mouth or anus. Oral papillæ present. Characteristic eggs with two
processes, ending in a tuft of filaments. Larvæ with a movable boring
spine at the head end.
_Gordiidæ._--Long, thread-like “Nematodes.” Mouth and anterior
portion of gut atrophied in adult. Oral papillæ absent.
THE NEMATODES OBSERVED IN MAN.
Family Sub-family Genus Species
_Anguillulidæ_ -- _Rhabditis_ _R. pellio._
_R. niellyi._
_Rhabditis sp._
_Anguillula_ _A. aceti._
_Anguillulina_ _A. putrefaciens._
_Angiostomidæ_ -- _Strongyloides_ _St. stercoralis._
_Gnathostomidæ_ -- _Gnathostoma_ _Gn. siamense._
_Gn. spinigerum._
_Dracunculidæ_ -- _Dracunculus_ _D. medinensis._
_Filariidæ_ _Filariinæ_ _Filaria_ _F. bancrofti._
_F. demarquayi._
_F. taniguchi._
_F. (?) conjunctivæ._
Group. _Agamofilaria_ -- _Ag. georgiana._
_Ag. palpebralis._
_Ag. oculi humani._
_Ag. labialis._
_F. (?) romanorum-
orientalis._
_F. (?) kilimaræ._
_F. (?) sp. ?_
(_Mikrofilaria_) _Mf. powelli._
_Mf. philippinensis._
_Setaria_ _S. equina._
_Loa_ _L. loa._
_Acanthocheilonema_ _Ac. perstans._
_Dirofilaria_ _Di. magalhãesi._
_Onchocercinæ_ _Onchocerca_ _O. volvulus._
_Trichinellidæ_ _Trichurinæ_ _Trichuris_ _T. trichiura._
_Trichinellinæ_ _Trichinella_ _T. spiralis._
_Dioctophymidæ_ -- _Dioctophyme_ _D. gigas._
_Strongylidæ_ _Metastrongylinæ_ _Metastrongylus_ _M. apri._
_Trichostrongylinæ_ _Trichostrongylus_ _T. instabilis._
_T. probolurus._
_T. vitrinus._
_Hæmonchus_ _H. contortus._
_Mecistocirrus_
(_Nematodirus_) _M. fordi._
_Ancylostominæ_
Group. _Œsophagostomeæ_ _Ternidens_ _T. deminutus._
_Œsophagostomum_ _Œ. brumpti._
_Œ. stephanostomum_
var. _thomasi_.
_Œ. apiostomum._
Group. _Ancylostomeæ_ _Ancylostoma_ _A. duodenale._
_A. ceylanicum._
_A. braziliense._
Group. _Bunostomeæ_ _Necator_ _N. americanus._
_N. exilidens._
Group. _Syngameæ_ _Syngamus_ _S. kingi.
Physalopteridæ_ -- _Physaloptera_ _P. caucasica._
_P. mordens._
_Ascaridæ_ _Ascarinæ_ _Ascaris_ _A. lumbricoides._
_A. sp._
_A. texana._
_A. maritima._
_Toxascaris_ _T. limbata._
_Belascaris_ _B. cati._
_B. marginata._
_Lagocheilascaris_ _L. minor._
_Oxyuridæ_ -- _Oxyuris_ _O. vermicularis._
_Mermithidæ_ -- _Mermis_ _M. hominis oris._
(_Agamomermis_) _Ag. restiformis._
Family. *Anguillulidæ.*
Genus. *Rhabditis*, Dujardin, 1845.
Buccal cavity elongated, with lips. Its chitinous wall uniformly
thick. Lateral lines absent. Males with bursa.
*Rhabditis pellio*, Schneider, 1866.
Syn.: _Pelodera pellio_, Schn., 1866; _Rhabditis genitalis_,
Scheiber, 1880; _Rhabditis pellio_, Schn., 1866.
Males 0·8 to 1·05 mm. in length; females, 0·9 to 1·3 mm. in length. The
posterior extremity of the body of the male has a heart-shaped bursa,
and seven to ten ribs on each side; the bursa may, however, be lacking.
The spicules measure 0·027 to 0·033 mm. in length, but are never quite
alike. The posterior extremity of the female is long and pointed; the
vulva lies somewhat behind the middle of the body, the ovary is single,
the eggs are oval, 60 µ by 35 µ.
This species was found in Stuhlweissenburg by Scheiber in the acid
urine (containing albumin, pus and blood) of a woman suffering from
pyelonephritis, pneumonia and acute intestinal catarrh; the observer
was able to convince himself that the Nematodes which were found
during the whole period of the illness lived in the vagina, and were
evacuated with the urine.
Oerley proved that this species had long been known; during its larval
stage (_Anguillula mucronata_, Grube, 1849) it lives in earthworms;
in its adult stage it lives in decomposing matter in the soil. By
introducing individuals of this species into the vagina of mice, Oerley
succeeded in obtaining infection and multiplication (facultative
parasitism). These Nematodes must in some such way have got into the
vagina of Scheiber’s patient.
Two other cases described by Baginsky and Peiper probably belonged to
the same or a nearly related species.
*Rhabditis niellyi*, Blanchard, 1885.
Syn.: _Leptodera niellyi_, Blanchard, 1885.
In 1882 Nielly had a cabin-boy, aged 14, under observation in
Brest. The lad had never left the neighbourhood of Brest, and had
suffered from itching papules on the skin for five or six weeks; in
the papules the observer found one or several rhabdites, measuring
0·33 mm. in length by 0·30 mm. in breadth. Their cuticle presented a
delicate transverse striation; the intestine was the only internal
organ recognizable, and it opened somewhat in front of the posterior
extremity. Therefore, it must have belonged to the rhabditis-like larva
of a Nematode, the adult stage of which is unknown.
The manner of infection was established almost certainly by a further
observation of Nielly’s: at the commencement of the illness small
Nematodes were found in the blood of the patient; later on, however,
they disappeared, neither were Nematodes found in the fæces, urine
or sputum. Therefore it must be concluded that the cabin-boy, who
was in the habit of drinking water from brooks, had thus ingested
embryo-containing eggs of a Nematode; the young hatched out in the
intestine, perforated it, reached the blood and then settled in the
skin; but, on the other hand, the entry may have been direct through
the skin.
In connection with the foregoing, reference should be made to a
communication by Whittles, insufficient from a zoological point of
view. In a case of hypertrophic gingivitis occurring in a female
patient, aged 19, who had never left Birmingham, he found Nematode
larvæ in the periosteum of the upper jaw, which was excised after
extraction of the right premolar; the genital rudiment could be
recognized in them. Similar larvæ were found in the same patient in
abscesses in various regions of the skin, and in the case of her
mother in the blood. The author considers that the infection took
place through a dog, and refers to the case of O’Neil (1875), who
found Filariæ in the skin (in the condition known as “craw-craw”),
referred by Manson to _Filaria perstans_. O’Neil’s case was quoted,
and attributed to _Filaria sanguinis hominis_. In conclusion, the
author states that he has repeatedly found Nematode larvæ in the
blood of persons who suffered from pruritus; in his opinion the
parasite had been imported through the agency of troops returned
from South Africa. Glatzel found true Filaria larvæ in a pustule of
a cutaneous eruption of the trunk and extremities in a patient at
Dar-es-Salam.
Skin diseases which are caused by young Nematodes are also observed
in dogs (Siedamgrotzky, Möller, J. G. Schneider, Künnemann),
foxes (Leuckart), and horses (Semmer). Zürn found young Nematodes
(_Anguillulidæ_) also in pig’s flesh. In Künnemann’s case it was
shown that the adult Rhabdites lived in the straw upon which the dog
lay.
*Rhabditis*, sp.
In the fluid obtained by lavage from the stomach of a female
patient, aged 16, suffering from ozæna, O. Frese found during two
consecutive months Rhabdites of various ages, 0·275 to 0·64 mm. in
length, the adults all with eggs; males were not found; transmission
into rabbit’s stomach failed, but they could be kept alive in much
diluted hydrochloric acid (2 : 1,000) for several weeks. Neither eggs
nor larvæ appeared in the fæces of the patient. The nature of the
infection, which was perhaps of unique occurrence, remained doubtful.
Genus. *Anguillula*, Ehrenberg, 1826.
Buccal cavity very small, without lips. Males without bursa, but with
a series of papillæ. Lateral lines absent.
*Anguillula aceti*, Müller, 1783.
Cuticle unstriped, body cylindrical, anterior end tapering but little,
posterior end long, pointed. Male up to 1·45 mm. long, 0·024 to
0·028 mm. wide; two pre-anal papillæ, one post-anal; spicules equal,
curved, 0·038 mm. long; gubernaculum present; testis extending in front
of mid-line of body. Female up to 2·4 mm. long, 0·040 to 0·072 mm.
wide; anterior uterus reaching to near the œsophagus, posterior to hind
gut. Viviparous; embryos in both or only in one uterine horn, 0·22 mm.
long, 0·012 mm. broad.
The species is a frequent inhabitant of vinegar (prepared by older
methods), and was once observed for some time by Stiles and Frankland
in the urine of a woman; the urine had an acid reaction, and once had
a distinct odour of vinegar. It was assumed that the patient, who
was hysterical and suffered from chronic nephritis, employed vaginal
douches with diluted vinegar, perhaps to deceive her physician or
to protect herself against conception. According to Ward, Billings
and Miller are said to have reported on two other cases. Ill-effects
which might be connected with the vinegar eel (_Anguillula aceti_)
were not present.
Genus. *Anguillulina*, Gervais and Beneden, 1859.
Syn.: _Tylenchus_, Bastian, 1864.
Characterized by the possession in the buccal cavity of a spine
knobbed posteriorly; bursa present; uterus asymmetrical. Numerous
species parasitic in plants.
*Anguillulina putrefaciens*, Kühn, 1879.
Syn.: _Tylenchus putrefaciens_, Kühn; _Trichina contorta_, Botkin,
1883.
In 1883 Botkin (_Pet. klin. Wochenschr_., 1883) found a small
Nematode, which was, however, entirely mistaken, in the material
vomited by a Russian; this was not a species of Trichinella, but an
_Anguillulina_ living in onions which had already, in 1879, been
described by Kühn as _Tylenchus putrefaciens_; the Nematodes got into
the stomach with the onions, causing nausea and vomiting.
Family. *Angiostomidæ*, Braun, 1895.
Genus. *Strongyloides*, Grassi, 1879.
Syn.: _Pseudorhabditis_, Perroncito, 1881; _Rhabdonema_, Leuckart,
1882, _p.p._
The genus is insufficiently defined. The parasitic form possesses a
simple mouth opening directly into the long cylindrical œsophagus
which occupies the anterior third of the body. The free-living forms
possess a small buccal cavity; the œsophagus is short, with a double
bulb, in the hinder one there is a *Y*-shaped chitinous valve; two
spicules of equal size.
*Strongyloides stercoralis*, Bavay, 1877.
Syn.: _Anguillula intestinalis_ et _stercoralis_, Bavay, 1877;
_Leptodera intestinalis_ et _stercoralis_, Cobb.; _Pseudorhabditis
stercoralis_, Perroncito, 1881; _Rhabdonema strongyloides_, Leuckart,
1883; _Strongyloides intestinalis_, Grassi, 1883; _Rhabdonema
intestinale_, Blanchard, 1886.
[Illustration: FIG. 270.--_Strongyloides stercoralis_, female:
parasitic generation from gut of man. × 70. (After Looss.)]
[Illustration: FIG. 271.--_Strongyloides stercoralis_, male:
free-living generation. × 170. (After Looss.)]
In 1876, a number of French soldiers returned to Toulon from
Cochin China suffering from severe diarrhœa. Dr. Normand, under
whose treatment they were, discovered a large number of Nematodes
in the evacuated fæces, and Bavay described them as _Anguillula
stercoralis_. Soon after Normand, at the _post-mortem_ of five
patients who had died of Cochin China diarrhœa, found numerous other
Nematodes in the intestine, from the stomach to the rectum, in the
bile-ducts and in the pancreas, and these he handed over to Bavay.
The latter diagnosed another species, and described them as _A.
intestinalis_. Both forms were then regarded as the cause of Cochin
China diarrhœa until, in 1882, Leuckart was able to demonstrate
that the two forms are only two succeeding generations of the same
species, of which the one (_A. intestinalis_) lives parasitically in
the intestine, whereas its young (_A. stercoralis_) attain the open,
where they come to maturity and propagate. The young of these again
live parasitically. There thus exists the same heterogony as was
discovered by Leuckart in _Angiostomum nigrovenosum_ of frogs, which
heterogony, indeed, according to v. Linstow, appertains to the entire
family of the _Angiostomidæ_.
(1) The parasitic generation (strongyloid or filariform ♀) is quite
colourless and cannot be seen _in situ_ even with a lens. To detect
them it is necessary to scrape the mucosa of the jejunum and examine
the scrapings microscopically. It measures 2·2 mm. in length, and 34 µ
to 70 µ in breadth; the cuticle is finely transversely striated; the
mouth is surrounded by four lips; the œsophagus is almost cylindrical
and a third the length of the entire body. The anus opens shortly in
front of the pointed posterior extremity; the vulva is situated at
junction of middle and posterior thirds of the body; the uterus has no
special ovejector; the eggs measure 50 µ to 58 µ in length, and 30 µ to
34 µ in breadth, and lie in a chain one behind the other (fig. 270).
As in the case of _Angiostomum nigrovenosum_, Leuckart considers this
stage to be hermaphroditic, the testes degenerating after having
functioned; other authors (Rovelli) regard it as a female reproducing
by parthenogenesis.
(2) The free-living generation (♂ and ♀) has a smooth body,
cylindrical, somewhat more slender at the anterior extremity and
pointed at the tail end. The mouth has four indistinct lips; the
œsophagus is short with a double (rhabditis-like) bulb; there is a
*Y*-shaped valve in the posterior bulb; the anus opens in front of the
tail end. The males measure 0·7 mm. in length, 0·035 mm. in breadth.
Their posterior end is rolled up; the two brown spicules are small
(38 µ) and much curved. There is also a gubernaculum. The females
measure 1 mm. in length or a little over; 0·05 mm. in breadth. The tail
end is straight and pointed; the vulva lies somewhat behind the middle
of the body. The yellowish, thin-shelled ova measure 70 µ in length and
45 µ in breadth.
As Askanazy has shown, the parasitic form bores deeply into the
mucous membrane of the intestine, and frequently into the epithelium
of Lieberkühn’s glands, both for nourishment and oviposition. The
eggs then develop in the intestinal wall. The eggs which are found in
scrapings from the mucosa occur, at least in the case of Strongyloides
of the sheep, in chains enclosed in a thin tube or sheath, the origin
of which is doubtful; possibly it is the uterus. The eggs themselves
are only rarely found in stools, _e.g._, after a strong purge. The
larvæ, which are hatched out, and measure 0·2 to 0·25 mm. long by
0·016 mm. broad, again reach the lumen of the intestine,[299] and
grow to double or three times that size, until they are passed out
with the fæces. They already differ from the parent (♀) in the shape
(rhabditiform) of the œsophagus. When the external temperature is
sufficiently high (26° to 35° C.), they become sexually mature after
moulting. In about thirty hours they are completely developed and
copulate, now forming the free-living rhabditiform generation. At lower
temperatures the larvæ only moult, but do not escape from the old
cuticle and do not develop further. At a temperature of about 25° C.
only some of the larvæ attain maturity.
[299] As a case published by Teissier shows, they may also abnormally
appear in the blood (_Arch. méd. expér. et d’An. path._, 1895, vii,
p. 675).
[Illustration: FIG. 272.--_Strongyloides stercoralis_, female;
free-living generation, × 170. (After Looss.)]
[Illustration: FIG. 273.--_Strongyloides stercoralis_: larva from fresh
human fæces. × 310. (After Looss.)]
The females of the free-living generation (rhabditiform) deposit
from thirty to forty eggs, which develop rapidly, sometimes even
within the uterus in the case of old females. After the larvæ have
emerged from the egg-shell, they measure 0·22 mm. in length, and
possess the characteristics of the parents (rhabditiform larvæ). When
they have grown to 0·55 mm. they moult, and while losing their own
characteristics they acquire the characteristics of their parasitic
grandparents (strongyloid or filariform). After about eight days the
free-living adult generation in the cultures have disappeared, and
all the rhabditiform larvæ have been transformed into strongyloid or
filariform larvæ; they then die off unless they reach the intestine.
This cycle of development holds good for _Strongyloides stercoralis_ of
tropical origin (Bavay, Leuckart, Leichtenstern, Zinn). In the European
Strongyloides the free-living generation, as a rule, is absent (Grassi,
Sonsino, Leichtenstern, Braun); the rhabditis-like larvæ evacuated with
the fæces are transformed into the strongyloid or filariform type of
larva (in cultures which are easily made) which will only become adult
if introduced into man.
[Illustration: FIG. 274.--_Strongyloides stercoralis_: mature
filariform larva showing long transparent œsophagus, slender granular
intestine and characteristic tip to the tail ending in two small
points. × 620. (After Looss).]
So that we have these two cycles: (_A_) (1) ♀ parasitic, (2) eggs, the
rhabditiform larvæ in fæces, (3) free-living strongyloid or filariform
larva, (4) ♀ parasitic. (_B_) (1) (2) (3) as before, then (4) adult ♀
and ♂, free living, (5) eggs, (6) rhabditiform larva, (7) strongyloid
or filariform larva, (8) ♀ parasitic.
Infection of man results not only from direct entry into the stomach
but also, according to van Durme and Looss, through the skin.
_Occurrence in Man._--As already mentioned, _Strongyloides
stercoralis_ was first observed in persons suffering from so-called
Cochin China diarrhœa. From the enormous numbers of parasites
evacuated with the fæces, the cause of the disease was apparently
evident. It appeared, however, that only some of the soldiers
returning from Cochin China and Martinique, and suffering from
diarrhœa, harboured Strongyloides (Chauvin). Breton made the same
observations in Cochin China and found that only 10·4 per cent. of
cases of chronic dysentery, and 8·8 per cent. of chronic diarrhœa,
show Strongyloides. Normand, moreover, found that only a few of the
Europeans residing in Cochin China are exempt from _S. intestinalis_,
yet the people exhibit no intestinal symptoms; if, however, from any
cause a catarrhal condition of the intestine supervenes the condition
is changed, the parasites appear in larger numbers, and the disorder
is considerably intensified.
_S. intestinalis_, besides being present in the Indo-China region,
also occurs in the Antilles, in Brazil, Africa, and Europe; in 1878
it was discovered in Italy by Grassi and C. and E. Parona; in 1880 it
was also found in the labourers working at the St. Gothard tunnel. It
was imported into Germany, Belgium, and the Netherlands by Italian
labourers. One sporadic case has been observed in East Prussia, and
the worm has also been reported from Siberia.
In mammals the following species are found: _Probstmayria_
(_Strongyloides_) _vivipara_, Ransom, 1907, in _Equus caballus_;
_Strongyloides fülleborni_, v. Linst., in _Anthropopithecus
troglodytes_ and _Cynocephalus babuin_.
Their development is, so far as is known, the same as that of
_Strongyloides stercoralis_ (v. Linstow, _Centralbl. f. Bakt., Path.
u. Infektionsk._, 1905, Orig. xxxviii, p. 532).
Family. *Gnathostomidæ.*
Genus. *Gnathostoma*, Owen, 1836.
Syn.: _Cheiracanthus_, Diesing, 1839.
Easily recognizable by the numerous spines which cover the entire
body or only the anterior extremity, and terminate in several points;
head globular and beset with bristles; mouth with two lips; two
spicules; vulva situated behind the middle of the body.
*Gnathostoma siamense*, Levinsen, 1889.
Syn.: _Cheiracanthus siamense_, Lev., 1889.
Female measures 9 mm. in length, 1 mm. in breadth. There are eight
rows of simple spines on the head; the armature of spines extends over
the anterior third of the body only; each spine on the anterior region
of the body spreads into three points, of which the middle one is the
longest; the posterior spines are simple; they gradually become smaller
and then disappear entirely. The vulva is situated behind the middle of
the body.
_Male._--10·5 mm. long by 0·6 mm. broad. Head terminates in a globular
swelling with two large lips. Neck 3 mm. broad. In front of neck eight
rows of simple spines directed backwards. Anterior half of body with
cuticular laminæ, posterior unarmed. Two pre-anal and two post-anal
papillæ. Bursa wanting.
Spicules 1·1 and 0·4 mm. respectively.
Leiper considers _Gnathostoma siamense_ to be identical with
_Gnathostoma spinigerum_.
The single specimen described by Levinsen was found by Deuntzer in
Bangkok (Siam), and was obtained from a young Siamese woman who
suffered from a small tumour of the breast which had developed in the
course of a few days. After the disappearance of the tumour, nodules
the size of beans were found in the skin; out of one of these the
worm was obtained. The same observer saw this affection in two other
persons.
A closely related species, _Gnathostoma spinigerum_, Ow., lives in
the stomach of wild cat (_Felis catus_), puma (_Felis concolor_),
tiger (_Felis tigris_), and domestic cat (India); another species,
_Gnathostoma hispidum_, Fedsch., 1839, in the stomach of pigs in
Turkestan, Annam, Hungary, Congo, and by Collin in the stomach of an
ox (Berlin).
_Gnathostoma_ sp. in pariah dogs, Calcutta. _Gnathostoma_ sp. in
monkeys, French Guiana. They produce large fibrous thickenings in the
stomach wall.
[Illustration: FIG. 275.--_Gnathostoma siamense_: to the left, the
entire worm (8/1); to the right the head seen from above, with two
fleshy lips (about 40/1). (After Levinsen.)]
*Gnathostoma spinigerum*, Owen, 1836.
Cuticle of bulb with eight rows of chitinous laminæ with their
posterior edges notched into spines. The laminæ on the anterior portion
of the body are similar trident laminæ. In the middle of the body, the
laminæ are simple and conical, cuticle posteriorly is unarmed. Mouth
with two fleshy lips.
Male 5 mm. long by 0·5 mm. broad; tail spiral, four pairs of papillæ.
Female about twice as long; tail straight, trilobed.
Family. *Dracunculidæ*, Leiper, 1912.
Genus. *Dracunculus*, Kniphoff, 1759.
Anterior end rounded with a cuticular thickening or shield. Mouth
triangular with two lips. Alimentary canal atrophied.
*Dracunculus medinensis*, Velsch, 1674.
Syn.: _Vena medinensis_, Velsch, 1674; _Dracunculus persarum_,
Kämpfer, 1694; _Gordius medinensis_, Linné, 1758; _Filaria
dracunculus_, Bremser, 1819; _Filaria æthiopica_, Valenciennes, 1856;
_Dracunculus medinensis_, Cobbold, 1864; _Guinea worm_, _Medina worm_.
The females attain a length of 50 to 80 cm., or even more, and average
1·5 to 1·7 mm. in diameter. They are whitish or yellowish in colour.
The anterior extremity is roundish and bears a cuticular thickening or
shield. The triangular mouth opening is surrounded by two projections
or lips, behind which on the shield there are two lateral and four
sub-median papillæ; the posterior end terminates in a spine, ventrally
directed, and about 1 mm. in length; the alimentary canal below the
œsophagus is atrophied, but not entirely obliterated; anus absent; the
lateral lines are very flat. The greater part of the body is occupied
by the long uterus, in which a great number of young larvæ are always
found. The ovaries probably lie at the ends of the uterus; the vulva
lies just behind the cephalic shield. During parturition the uterus is
prolapsed through this opening.
The male is almost unknown. Leiper in an experimentally infected monkey
found two males 22 mm. long, one from the psoas muscle, the other from
the connective tissue behind the œsophagus.
_Occurrence._--_Filaria medinensis_ has been known since the most
remote period. The “fiery serpents” that molested the Israelites by
the Red Sea, and which Moses mentioned, were probably filariæ. The
term Δρακὁντιον occurs in Agatharchides (140 B.C.). Galen called
the disorder dracontiasis; the Arabian authors were well acquainted
with the worm. It is found not only in Medina or Arabia, but also
in Persia, Turkestan, Hindustan. The Guinea worm is also widely
distributed in Africa, on the coasts as well as in the interior. It
occurs in the Fiji Islands. It was carried to South America by negro
slaves, but is said at the present time to exist in only quite a
few places (British Guiana, Brazil [Bahia]); it is also observed in
mammals (ox, horse, dog, leopard, jackal [_Canis lapuster_], etc.).
_Dracunculus medinensis_ in its adult stage lives in superficial
ulcers on the body surface; it is seen most frequently on the lower
extremities, more especially in the region of the ankle, but it also
occurs in other parts of the body--on the trunk, scrotum, perineum, on
the upper extremities, and in the eyelids and tongue. Sometimes there
is only one ulcer and one worm, but more commonly several. It attacks
man without distinction of race, age or sex. It is observed most
frequently during the months of June to August.
[Illustration: FIG. 276.--Guinea worm (_Dracunculus medinensis_).
(After Leuckart.)]
[Illustration: FIG. 277.--Anterior extremity of Guinea worm, showing
dorsal and ventral lips, one lateral and two submedian papillæ and the
lateral line. (After Leuckart.)]
[Illustration: FIG. 278.--_Dracunculus medinensis_. _a_, anterior
extremity seen end on; O, mouth; P, papillæ; _b_, female reduced more
than half; _c_, larvæ enlarged. (After Claus.)]
_Life history._[300]--When about a year old the worm seeks the
surface of the body and produces there a thickening as big as a
florin. Over this a vesicle forms which eventually ruptures, and at the
bottom of the ulcer can be seen a hole from which a part of the worm
may project. On bathing the sides of the ulcer with water, a drop of
fluid, at first clear then milky, exudes. This contains numerous larvæ.
In other cases a thin tube an inch long is prolapsed (through the
vulva). This is probably the uterus, but the mechanism of parturition
is not clearly known. It lasts for about a fortnight. An abundant
supply of larvæ can be got by placing wet compresses on a _fresh_
ulcer. In a few hours a mass of larvæ is obtained.
[300] The larvæ resemble those of _Cucullanus elegans_ parasitic in
the perch (_Perca fluviatilis_). The larvæ of this species develop in
Cyclops sp. Fedschenko in 1870, at Leuckart’s suggestion, succeeded in
observing the invasion of Cyclops by Guinea worm larvae. They penetrate
not _per os_ but through the exoskeleton. Newly hatched larvæ (in
bananas) will cause infection of monkeys.
The larvæ are 500 µ to 750 µ by 15 µ to 25 µ, with a long slender
tail about one-third of the total length. The cuticle is transversely
striated. The body is flattened. They possess an œsophagus and gut. At
the anus there are apparently glandular structures.
[Illustration: FIG. 279.--Transverse section of female Guinea worm;
_u._, uterus containing embryos; _i._, intestinal canal; _o._, ovary.
(After Leuckart.)]
The larvæ live and move actively in water for about two days, the
majority dying on the third (Leiper). If a number of Cyclops sp. have
been collected and isolated in clean water, and the larvæ are now
added, the further development can be traced.
The larvæ enter the Cyclops, according to most authorities, by
penetrating the exoskeleton, but according to Leiper this is
impossible; they must enter by the mouth and penetrate the gut in
order to reach the body cavity. In eight days moult 1 takes place, the
striated cuticle being cast off. In ten days moult 2 takes place. In
five weeks the larva is mature. If now the infected Cyclops is placed
in 0·2 per cent. HCl solution the Cyclops is killed immediately, but
the larvæ are stirred into activity, escape from the body, and swim
about in the acid. This suggests that infection in nature probably
takes place by the swallowing of infected Cyclops; Leiper, by feeding
Cyclops containing mature larvæ to a monkey, found in it, _post mortem_
six months later, two immature females 30 cm. long and two males 22 mm.
long.
In certain areas the new cases occur principally in June. Five weeks
later the larvæ will become mature in Cyclops, so that infection of
Cyclops is taking place in July or August, and from then to June about
ten months elapse, giving the period of development in man.
_Pathology._--The initial induration is accompanied by itching.
Urticarial eruptions are described in Dahomey and Mauretania
accompanied by fever, rigors, blood-shot conjunctiva, and prostration
resembling fungus poisoning. Symptoms last for one to two days, later
the worms appear on the surface.
[Illustration: FIG. 280.--_Cyclops virescens_, ♀. 8, Female, ventral
view, × 120; 9, anterior antennæ × 240; 10, urosome and last thoracic
segment, × 240; 11, foot of first pair, × 320; 12, 15, 16, foot of
second, third and fourth pairs, × 240; 14, foot of fifth pair, × 440;
13, last thoracic segment and first segment of urosome of male, × 240.]
If the worm is ruptured in an attempt to extract it, disastrous results
may occur through the escape of the larvæ into the tissues: fever,
inflammation, abscess, sloughing, ankylosis, even death from sepsis.
Eosinophilia is often marked, 11 to 13 or even 50 per cent.
_Extraction._--(1) The native method consists in rolling the worm round
a stick; 1 in. to 2 in. are extracted each day, the process taking
about a fortnight; (2) Emily used injections of 1 in 1,000 sublimate
into the swelling or into the worm itself fixed by a ligature. (3)
Béclère chloroforms the worm; (4) the worm can be more easily removed
when all the embryos have been deposited (two to three weeks).
_Cyclopidæ._--Cephalothorax ovate, clearly separated from abdomen.
Anterior antennæ of female when bent back scarcely ever stretch beyond
the cephalothorax. The second antennæ are unbranched. First four pairs
of feet two-branched, outer branches three-jointed. The fifth pair of
limbs are rudimentary alike in both sexes, usually one-jointed. There
is no heart. The female has two egg sacs containing about fifty eggs.
Genus. *Cyclops*, Müller, 1776.
Mandible palp rudimentary, reduced to a tubercle bearing two branchial
filaments. Maxillary palp rudimentary (obsolete). Lower foot-jaw
non-prehensile. Head ankylosed to first thoracic segment.
Family. *Filariidæ.*
Sub-family. *Filariinæ.*
The residue after exclusion of the _Arduenninæ_ and _Onchocercinæ_.
Genus. *Filaria*, O. Fr. Müller, 1787.
Very long, slender Nematodes, without excretory vessels or excretory
pore, the males of which are usually considerably smaller than the
females. Mouth round, without lips, unarmed. The lateral lines occupy
one-sixth of the circumference of body. The tails of the males are
bent or spirally rolled, and bear little wing-like appendages. The two
spicules are unequal; almost always there are four pre-anal papillæ,
but the number of post-anal papillæ varies. The vulva is always
situated at the anterior extremity. Parasitic chiefly in the serous
cavities and in the subcutaneous connective tissue. Insufficiently
defined.
*Filaria bancrofti*, Cobbold, 1877.
Syn.: _Trichina cystica_, Salisbury,[301] 1868 (_nec Filaria
cystica_, Rud., 1819); _Filaria sanguinis hominis_, Lewis, 1872;
_Filaria sanguinis hominis ægyptiaca_, Sonsino, 1875; _Filaria
wüchereri_, da Silva Lima; _Filaria sanguinis hominum_, Hall,
1885; _Filaria sanguinis hominis nocturna_, Manson, 1891; _Filaria
nocturna_, Manson, 1891.
[301] C. W. Stiles (“American Medicine,” 1905, ix, p. 682) is of the
opinion that Salisbury’s _Trichina cystica_ is identical with _Oxyuris
vermicularis_.
These parasites of man were for a long time only known in their
larval stage. They were discovered in 1863 in Paris by Demarquay, in
the hydrocele fluid of a Havanese emptied by puncture; they were next
observed by Wücherer, in Bahia, in the urine of twenty-eight cases
of tropical chyluria; they were likewise observed in North America
by Salisbury, who gave them the name of _Trichina cystica_. The next
discoveries (in Calcutta, Guadeloupe, and Port Natal) related to
chyluria patients, until Lewis discovered the larvæ in the blood of
man (India), and found they were almost always present in persons
suffering from chyluria, elephantiasis, and lymphatic enlargements;
he also, in exceptional cases, found them in apparently healthy
persons (_Filaria sanguinis hominis_). Lewis and Manson studied the
disease and the filariæ of the blood very minutely, and became aware
that the filariæ were sucked up by mosquitoes with the blood. Manson
described the metamorphoses that take place within the body of the
mosquito. The adult female was discovered in Queensland by Bancroft,
and soon after Lewis found it in Calcutta; it was described by
Cobbold as _F. bancrofti_. The male was first seen by Bourne in 1888.
[Illustration: FIG. 281.--_Filaria bancrofti._ 1, Anterior portion
of male; 2, two rows of papillæ on head; 3, papillæ of tail of male;
4, cloaca of male showing tips of spicules and gubernaculum; 5, the
spicules and gubernaculum of male. (After Leiper.)]
Head bougie-like, _i.e._, separated by a narrowing from the neck,
having two rows of minute papillæ. Cuticle has extremely fine
striations.
_Female._--50 to 65 mm. long by 1·5 to 2 mm. broad. Vulva 0·4 to
0·7 mm. behind the head. Anus about 1/4 mm. from the tip of the tail
(vulva 1 to 1·3 mm. from head, and anus 0·17 to 28 mm. from tail
according to other authors). The vagina is a muscular tube forming
three bold loops, and has terminally a pyriform enlargement. Uterus
double (or single). Ovoviviparous.
_Male._--25 to 30 mm. long by 0·1 mm. thick (40 by 0·1 mm. according
to various authors). Probably two pairs of pre-anal papillæ, eight
pairs of peri-anal, two pairs of post-anal papillæ, and one pair
terminal. Tail curved. Two spicules, 0·2 and 0·6 mm. respectively, and
a cup-like gubernaculum. The long spicule is cylindrical, expanded
proximally and tapering distally to a filament with wings. At the tip
it is spoon-like. The short spicule is of the same diameter throughout.
It is gutter-like, coarsely marked. Testis uncoiled, terminating in a
snowdrop-like process (Leiper).
_Eggs._--40 µ by 25 µ. They do not appear to possess a true shell, but
only an embryonal or vitelline membrane secreted by the ovum.
_Embryos._--In the posterior part of the uterus eggs occur, in the
anterior part embryos; the larvæ at birth measure 127 µ to 200 µ by 8µ
to 10 µ. In the blood they measure in the fresh 260 µ by 7·5 µ to 8 µ.
In stained films, owing to shrinkage, there is great variation in size,
from 154 µ to 311 µ. Probably 260 µ to 285 µ is the average in stained
films.
_Geographical Distribution._--Europe: Two cases recorded, one from
near Barcelona. The patient suffered from hæmato-chyluria and enlarged
scrotum with mikrofilariæ in the blood. A second case from Siena.
Africa: The filarial index has not been estimated for various parts. In
Nigeria it is about 10 per cent.
_Habitat._--Lymphatic glands: _e.g._, inguinal, femoral, iliac, lumbar,
mesenteric, bronchial, superficial cervical, epitrochlear.
Lymphatic vessels: _e.g._, those draining into the receptaculum chyli
of the spermatic cord, in the thoracic duct and in various different
parts.
Organs, etc.: Testis, epididymis, spermatic cord, tunica vaginalis,
mammary cyst, and in abscesses.
They may occur in masses, but usually only a few (one to eight).
Females are commoner than males. Dead and calcified worms are common in
the various sites.
_Distribution of Larvæ in Body._--These are by no means uniformly
distributed, but occur in greater number in the capillaries of the
lungs. Besides the lungs they occur in the capillaries of other organs,
as the following data of Rodenwaldt show:--
Mikrofilariæ Mikrofilariæ
Lungs 134,821† Spleen 1,666
Liver 4,884 Brain 3,833
Kidneys 15,253 Glands 0
{Glomeruli 8,008 Marrow 0
{Parenchyma 7,245 Blood 3,000
† These figures refer to 1 c.c. of each organ, and were estimated by
cutting sections of definite thickness (30 µ to 40 µ) and counting
the filariæ in a definite area of section, _e.g._, 1/4 cm.^2 The
organs before removal from the body have their vessels tied, and are
then fixed in hot alcohol.
The following data of Rodenwaldt refer to the larvæ of _Filaria
immitis_ in the dog. They are commoner in organs than in vessels, and
especially in the _capillaries_ of the organs, but in the lungs they
appear to be equally distributed in capillaries, arteries and veins.
The length of life of larvæ is unknown, but they appear to be destroyed
in the kidneys, as dead calcified specimens are fairly numerous in the
capillaries of the vasa recta of the medullary substance.
Kidneys: mainly in the glomerular capillaries and those of the vasa
recta.
Liver: in the capillaries of the portal system, especially in those
between the interlobular and the central intralobular veins.
_Periodicity of Larvæ._[302]--Roughly speaking, the larvæ of _Filaria
bancrofti_ are found in the peripheral blood only during the night,
disappearing (but not entirely) during the daytime. Their periodicity
and that of _Loa loa_ larvæ is shown by the table on p. 394, based on
that of Smith and Rivas (_Amer. Journ. Trop. Dis. and Prev. Med._,
1914, vol. iii, p. 361).
[302] For determining periodicity measured quantities of blood,
_e.g._., 20 mm.^3, should be used. A thick film is made of the whole
quantity. The numbers present in this quantity may vary from three or
four to 300 or 400.
It was discovered by Mackenzie that this periodicity could be
reversed by making the patient sleep during the daytime, showing that
the phenomenon was in some way dependent on sleep or its attendant
phenomena. Rodenwaldt gives the following explanation of the phenomenon
of periodicity:--
Mikrofilariæ come to rest in capillaries. After passing up the thoracic
duct they would reach the capillaries of the lungs by the superior vena
cava. Here they occur in immense numbers. In the case of _Loa loa_
larvæ (which have a diurnal periodicity) some of these are forced out
by the increased force and rapidity of the pulmonary circulation during
the day, but are able to rest (owing to their sticky sheath?) in the
peripheral capillaries on their way to the capillaries of the organs.
During the night the force of the current through the lungs is relaxed
and consequently they are able to remain in the pulmonary capillaries
and do not appear in the capillaries of the systemic circulation. If
it is true that the periodicity of _Loa loa_ cannot be reversed by
changing the hours of sleep, then the explanation is incomplete. In
the case of the larvæ of _Filaria bancrofti_ (which have a nocturnal
periodicity), in order to apply the same explanation we must further
assume that the mikrofilariæ have less power of resisting the force of
the capillary current (_i.e._, are less sticky). They are washed out of
the pulmonary capillaries by day and by night, but it is only at night,
when the blood stream in systemic capillaries is less rapid, that they
are able to rest there. In the daytime they are washed on until they
reach the capillaries of the organs (possibly again the lungs). The
reversal of the periodicity by sleeping during the daytime admits of a
similar explanation. If this explanation be true, then a prolongation
of the day conditions, _e.g._, by continued exercise, should result
in still keeping the larvæ out of the circulation, but this does not
appear to be the case.
--------+----------+----------+----------+----------+----------+----------
| Larvæ of | Average | CASE 1. | Average | CASE 2. | Average
| _L.loa_ | 132. | _F. | 1,000 | _F. | 1,570
| in equal |Deviations|bancrofti_| (about). |bancrofti_| (about).
|quantities| from | larvæ |Deviations| larvæ |Deviations
| of blood | average |in 1 c.c. | from |in 1 c.c. | from
| | | of blood | average | of blood | average
--------+----------+----------+----------+----------+----------+----------
2 a.m. | 9 | - 123 | 3,500 | + 2,500 | 6,500 | + 3,930
4 a.m. | 11 | - 121 | 3,200 | + 2,200 | 5,200 | + 3,630
6 a.m. | 41 | - 91 | 2,800 | + 1,800 | 2,000 | + 430
8 a.m. | 168 | + 36 | 900 | - 100 | 1,100 | - 470
10 a.m. | 298 | + 166 | 210 | - 790 | 350 | - 1,220
12 noon | 531 | + 389 | 30 | - 970 | 50 | - 1,520
2 p.m. | 252 | + 120 | 20 | - 980 | 40 | - 1,530
4 p.m. | 146 | + 14 | 10 | - 990 | 30 | - 1,540
6 p.m. | 91 | - 41 | 40 | - 960 | 40 | - 1,530
8 p.m. | 23 | - 99 | 60 | - 940 | 100 | - 1,470
10 p.m. | 5 | - 127 | 600 | - 400 | 800 | - 770
12 mid- | 5 | - 127 | 750 | - 250 | 2,600 | + 1,030
night| | | | | |
--------+----------+----------+----------+----------+----------+----------
Total | 1,580 | -- | 12,120 | -- | 18,810 | --
--------+----------+----------+----------+----------+----------+----------
In certain countries, _e.g._, Fiji, Samoa, Philippines, West Africa,
larvæ, apparently those of _Filaria bancrofti_, show no periodicity.
In Fiji the usual intermediate host is _Stegomyia pseudoscutellaris_,
a day-biting mosquito, so that possibly, as Bahr suggests, the
mikrofilariæ have partly adapted themselves to the habits of their
intermediate host, as the nocturnal mikrofilariæ are adapted for
transmission by a nocturnal feeding mosquito, _e.g._, _Culex fatigans_,
but how this could come about is a mystery. It is not certain in all
cases whether the non-periodic mikrofilariæ really belong to _Filaria
bancrofti_; some may be _L. loa_ larvæ, or possibly unknown larvæ. An
exact morphological description of these larvæ is therefore always
necessary.
_Preservation of Living Larvæ._--Blood from the vein (or finger
puncture) is shaken up with twenty times its volume of sterile 0·9 per
cent. salt solution, and kept in an ice cupboard (Fülleborn).
_Concentration of Larvæ._--(_a_) The above mixture is hæmolysed with
water and then sufficient salt solution added to make up to 0·9 per
cent. The solution is allowed to stand or can be centrifugalized. (_b_)
The blood is mixed with sodium citrate and centrifugalized; the larvæ
are found in the leucocytic layer (Bahr). (_c_) Allow blood to clot in
a small tube; the larvæ appear on the surface of the clot and are so
got in pure serum. A drop of blood may also be allowed to clot on the
slide; the larvæ are found in the clear areas of serum. (_d_) Hæmolyse
blood with water or acetic acid. Centrifugalize, make smears from, or
examine the sediment.
_Removal of Red Corpuscles._--The blood film is allowed to stand for
some minutes in a moist atmosphere. The staining solution is sucked
through with blotting paper: the larvæ stick to the slide, while the
corpuscles are washed out.
_Morphology of Larvæ._--Wet staining: Azur II one part, 0·9 per cent.,
salt solution 3,000, or very dilute Giemsa or ripened methylene blue
or neutral red solutions. Place a drop on the slide and add a drop
of blood to this. The larvæ remain alive for one or more days; it
sometimes takes twenty-four hours to stain some particular structure.
Differentiation by drawing through weak eosin solution is often useful.
This method is the best for finest details. The excretory pore, anal
pore, excretory cell, and chief “genital” cell stain first, then the
matrix cells and finally the column of nuclei.
Wet fixation and staining: The blood is spread on a large
cover-glass--floated on the surface of 70 per cent. alcohol heated
to about 70° C. Wash in water, (1) overstain with 1 in 1,000 azur II
solution, warming slightly; (2) differentiate with (_a_) absolute
alcohol (containing, if necessary, a trace of HCl), or (_b_) with
absolute alcohol 96 per cent. ninety parts, anilin oil ten parts; (3)
clear in origanum, bergamot or cajeput oil; (4) mount in balsam. Or
stain with hæmatoxylin, _e.g._, Mayer’s glycerine alumhæmatein, heating
till slightly steaming. Differentiate with acid (2 per cent. HCl)
alcohol if overstained. Clear and mount as above.
Dry fixation and staining: (1) With azur II as above, or (2) with
hæmatein (warm). Examine the dried films in the usual way without a
cover-glass. The azur stains the excretory and genital cells clearly.
Thick films: (1) The blood is smeared out fairly thickly over an area
as big as a sixpence.
(2) Dry _quickly_ to prevent shrinking, using carefully a spirit lamp
in a moist climate.
(3) Place films downwards in water for a few minutes.
(4) Fix in alcohol.
(5) Stain with azur II, 1 in 1,000. Differentiate as above. Examine as
a dry film. This method suffices for showing the excretory cell and the
G1 cell; or
(6) Stain with hæmatein (slightly steaming), especially for the column
of nuclei and the sheath. The fixation in alcohol in this case may be
omitted.
(7) The removal of the hæmoglobin and the fixation may be combined by
using Ruge’s mixture (formalin 2 per cent., containing 1 per cent.
acetic acid) or acetic alcohol (glacial acetic 1, alcohol 3).[303]
[303] [Acetic alcohol does well for detecting crescents in thick films
of malaria blood.--J. W. W. S.]
_Structure of Larvæ._--(1) Subcuticular cells: By vital staining, at
intervals underneath the cuticle are seen a series of spindle-shaped
cells--the _subcuticular matrix cells_ of Rodenwaldt, the _muscle
cells_ of Fülleborn. There are thirty or forty or more of these.
(2) Nerve ring: Appears as a break in the nuclear column about 20 per
cent. of total length from the head.
(3) Excretory system: Consists of a lateral spherical hollow excretory
pore which shows a radial striation. Connected with the pore is an
excretory cell which appears to be canalized. _Excretory pore_, 29·6
per cent. of length from head. _Excretory cell_, 30·6 per cent. of
length from head.
(4) “Genital” cells and anal pore: Consists of a pore opening ventrally
on a very fine papilla with which are connected four other cells in
series, the chief “genital” cell (G1) being some distance from the
three others, which lie close to the pore. G1, 70·6 per cent., anal
pore, 82·4 per cent. of length from head.
(5) Internal body, viscus, or reserve material: Best shown by vital
staining with neutral red. This is a granular strand-like body
extending from 52·7 per cent. to 65 per cent. of length from head.
(6) Tail end: (i) Rod-like structures resembling those in the head, 90
per cent. of length. (ii) The column of nuclei extends to 95 per cent.
of length, so that the terminal portion is free from nuclei.
(7) Mouth: Terminal according to some authors, lateral according to
others. Some describe a fang on the head, others not. By vital staining
and eosin differentiation two rod-like structures with mushroom-like
caps can be seen behind the head.
(8) Cuticle: Transversely striated. There is a longitudinal break
in the striation on each side corresponding to the lateral lines.
The striation is best shown by vital staining with azur II and eosin
differentiation.
(9) Column of nuclei: These nuclei of the gut cells form the main
feature in ordinary dry films stained with hæmatoxylin. They are
separated by a space from the subcuticular cells.
[Illustration: FIG. 282.--_Mf. bancrofti_ in thick film, dried and
stained with hæmatoxylin: 1, shrunken; 2, unshrunken. × 1,000. (After
Fülleborn)]
DISTINCTION BETWEEN _Mikrofilaria bancrofti_ AND _Mikroloa loa_.
_Dry Films, Hæmatoxylin Staining_:--
_Mf. bancrofti._ _Ml. loa._
(1) In graceful curves (but only (1) Kinked.
if quickly dried).
(2) Tip of tail free from nuclei. (2) Nuclei extend to tip.
(3) Column of nuclei separated by (3) Not so distinctly.
a space from the cuticle.
_Azur Staining_:--
(4) G1 cell small, easily overlooked. (4) G1 cell large, stains
deep blue, cell
protoplasm = twice
width of larva,
easily seen.
(5) Excretory cell close to excretory (5) Excretory cell farther
pore, 2 per cent. of length. from pore, 4 per
cent. of length.
_Vital Staining with Neutral Red_:--
(6) Internal body or reserve material (6) Not shown.
clearly shown.
_Life History._--In the stomach of the mosquito the larvæ cast their
sheath in the thickened blood in one to two hours. In twenty-four hours
the majority have reached the thoracic muscles, where development
proceeds. They are at first immobile and of a “sausage” form (110µ by
13 µ), with a short spiky tail. In three to five days the œsophagus is
formed, the larva now being 0·5 mm. long. The larva appears to moult at
this time. After the gut is formed papillæ, three or four in number,
appear at the tail end. In two to three weeks the larvæ are 1·5 mm.
long. They now leave the thorax and reach the labium, but they may be
found in various parts of the body, _e.g._, the legs. They bore through
Dutton’s membrane and so arrive on the surface of the skin, which they
rapidly enter. Their development in man is unknown, but it may be very
long, as children are not infected till 4 to 5, or even 10 years old,
but this may be due to unknown causes.
Development takes place in numerous mosquitoes. Anophelines:
_Myzomyia rossii_, _Pyretophorus costalis_, _Myzorhynchus sinensis_,
_Myzorhynchus barbirostris_, _Myzorhynchus peditæniatus_.
Culicines: _Culex pipiens_, _Culex fatigans_, _Culex skusei_, _Culex
gelidus_, _Culex sitiens_, _Culex albopictus_, _Stegomyia fasciata_,
_Stegomyia pseudoscutellaris_, _Stegomyia gracilis_, _Stegomyia
perplexa_, _Mansonioides uniformis_, _Mansonioides annulipes_,
_Scutomyia albolineata_, _Tæniorhynchus domesticus_.
Partial development takes place in other species.
[Illustration: FIG. 283.--Schematic drawings of the anatomy of _Ml.
loa_ and _Mf. bancrofti_ combined from specimens stained in different
ways. The position of the organs has not been based on the average
values of a large series of specimens, but on that of a single
specimen. G1, chief genital cell; G2–4, other genital cells; Ex.-C.,
excretory cell; Ex.-P., excretory pore; A-P., anal pore; N., nerve
ring. Magnification circa 1,000. (After Fülleborn).]
_Pathology._--Among the conditions which _Filaria bancrofti_ is
believed to produce are lymphangitis, varicose glands, especially
inguinal and epitrochlear, chyluria, chylocele, lymph scrotum,
orchitis, abscess, and elephantiasis. The evidence that these so-called
“filarial diseases” are produced by _F. bancrofti_ is (1) geographical
and statistical; (2) pathological. Bahr has contributed evidence of
the former kind from his researches in Fiji, on which we may base the
following statements:--
(1) The prevalence of filarial diseases is proportional to the
prevalence of _Mikrofilaria bancrofti_ in the blood. Thus in four
villages examined by him he got the following figures:--
Village A Village B Village C Village D
per cent. per cent. per cent. per cent.
_Mf. bancrofti_ 12·5 25 31 33
Filarial diseases 29 39 58 34
Total population 168 114 425 222
(2) Out of 257 people with _Mf. bancrofti_ in the blood, 153 were
suffering from filarial diseases, _i.e._, 59 per cent.
(3) Whereas of 672 people without _Mf. bancrofti_ in the blood, only
263 were suffering from filarial diseases, _i.e._, 37·6 per cent.
(4) Again out of 416 people suffering from filarial disease, 153 showed
_Mf. bancrofti_ in their blood, _i.e._, 36·7 per cent.
It is generally assumed that all people suffering from filarial
disease show at some (presumably early) stage larvæ in the blood; but
we do not consider that this must necessarily be so. It appears to us
quite possible that living adult filariæ may be present in the body,
producing disease, without their larvæ appearing in the blood. The
absence of larvæ from the blood in 63·3 per cent. of persons suffering
from filarial disease is, however, generally explained otherwise. The
adults which occur in enlarged glands, etc., get eventually destroyed
by inflammatory reaction, so that larvæ are no longer being produced,
while the enlarged gland, etc., which the adults have produced remains.
This explanation assumes that the larvæ of the original worm die in
the circulation or elsewhere, _e.g._, kidney, but we have no evidence
as to the duration of life of larvæ in the human body; but also it
assumes that a person cannot be reinfected with filaria, for otherwise
there is no reason why the diseased should not be infected in the same
proportion as the non-diseased. But assuming the explanation to be
true, it would explain why a diseased population show larvæ in only
about one-third of the cases. It must be borne in mind also that the
figures are rather small.
_Pathology._--In order to explain the effects which do or may be
expected to occur from obstruction of lymphatics, it is necessary to
have an accurate knowledge of the distribution and connections of
lymphatic vessels (and glands) and the anastomoses of these vessels. We
can only briefly summarize our knowledge here.
We should recall also that considerable destruction or obstruction
of lymphatics or glands may occur without necessarily producing any
lymphatic obstruction, at least, of a permanent nature, _e.g._, when
a mass of lymphatic glands is destroyed by a bubo in the groin or,
again, when a carcinomatous mass of glands is removed from the axilla.
Again, to take the case of chyluria--where it is generally assumed
that obstruction must occur higher up than the point at which the
intestinal lacteals enter the juxta-aortic glands--this disease may
occur, _e.g._, in temperate regions, quite apart from such obstruction.
It is true that some of these cases of chyluria are not cases of chyle
in the urine, but, as little or no fat is present, lymphuria. These do
not require the above assumption, but seeing that true chyluria may
apparently occur without such obstruction, we should be cautious about
explaining this and other symptoms on the basis of obstructions which
theory may demand, for only too often there are no _post-mortem_ facts
at our disposal.
Lymphangitis: What this is due to is unknown. There is no actual
evidence of the occurrence of adults in the inflamed vessel. Complete
disappearance, not to reappear, of (non-periodic) mikrofilariæ from the
blood has been shown by Bahr and others to occur within twenty-four
hours after an attack of lymphangitis, orchitis adenitis or simply a
high temperature. This mysterious phenomenon requires explanation. If
the mikrofilariæ were being killed by the attack, their dead bodies
should still be found in the blood; or if the adults were being killed,
for all we know to the contrary, the larvæ might well survive. We
consider there is no evidence that either are affected, but that for
some reason, as little understood as in periodicity, the larvæ now
remain in the organs.
Abscess: In Fiji, by Bahr, they have been found in the substance
of various muscles, _e.g._, quadriceps extensor, latissimus dorsi,
serratus magnus, in the popliteal space, groin, axilla, and over the
internal condyle of the humerus, and in the upper extremity they are
frequently infected with cocci. They not infrequently contain fragments
of dead adult filariæ. Their mode of origin is not clear. They form
nearly 30 per cent. of cases of filariasis in Fiji. Of 95 cases, 41
showed mikrofilariæ in blood, 54 did not.
Hydrocele and enlarged testis: In Fiji they form about 10 per cent.
(36 out of 343) of cases of filariasis. The fluid is usually sterile;
mikrofilariæ were present in the fluid in 1 out of 11 cases. In
the wall numerous calcified adult filariæ may be found. The walls
consist chiefly of hypertrophied muscle with fibrous tissue, dilated
blood-vessels and lymphatics, the lining epithelium of which appears to
be absent; of 38 cases 14 had mikrofilariæ in the blood, 24 had not.
Most of the cases are associated with elephantiasis of the scrotum (11
out of 12 cases).
Enlarged glands form over 40 per cent. (153 out of 343) of cases of
filariasis, so that they are the commonest expression of filariasis
met with in Fiji. The glands are enlarged, fibrotic, and the trabeculæ
are thickened. The lymphatics are thickened or represented merely by
fibrous tissue. The gland also shows dilated blood-vessels and numerous
spaces filled with lymph. Giant-cells are common in those glands
which contain remnants of filariæ. Masses of lymphocytes enclosed by
inflammatory or fibrous tissue are common. Eosinophile cells are also
extremely common, not only in the fibrous tissue of the glands, but
in other inflammatory or fibrotic conditions: in other organs living
or calcified filariæ are “usually” present. Only about 33 per cent.
show mikrofilariæ in the blood. The epitrochlear gland is frequently
enlarged in Fiji.
Breinl has examined enlarged glands and finds loose vascular fibrous
tissue with lymphocytic invasion. In parts, the lymphocytes collect
into areas 200 µ to 800 µ in diameter. The lymph tissue surrounding the
spermatic cord showed abundance of vessels--(1) large, (2) small. The
large had thick walls and wide lumina. In other cases the lumina were
nearly filled by a thrombus of newly formed, fine, loose connective
tissue.
Varicose glands: In about 7 per cent. (24 out of 343 cases) of
filariasis, mikrofilariæ are found in the blood in 50 per cent. (12 out
of 24).
_Elephantiasis._--Elephantiasis scroti is associated with hydrocele
in 50 per cent. of cases (12 out of 23); in 65 per cent. of cases (15
out of 23) there are associated enlarged glands in one or both groins,
though also hydrocele and enlarged glands occur without elephantiasis
scroti. In 13 out of 27, _i.e._, about 50 per cent., cases of
elephantiasis in various regions, no associated enlargement of glands
is found. Elephantiasis forms in Fiji less than 10 per cent. of cases
of filariasis. Mikrofilariæ are present in the blood in 36 per cent.
(12 out of 33) of cases.
_Chyluria._--Exceedingly rare in Fiji. Theory would demand an
obstruction above the point of entry of the lacteals, _viz._, the
pre-aortic lymphatic glands, but in cases in temperate regions it
may occur without any such lesion. In some of these cases the fluid
is not chyle (fat absent), but presumably lymph. A discussion of the
mode of production of chyluria, lymph scrotum, elephantiasis, etc.,
is at present premature; theory has far outrun fact. Too much stress
had been laid on the mechanical action of the worms to the almost
total exclusion of their (or possibly their larval) toxic action. The
above analysis has been made in the hope of acquiring more extended
observations similar to those made by Bahr.
_Geographical Distribution._--_Filaria bancrofti_ is known in nearly
all tropical countries. It occurs in India, China, Indo-China, Japan,
Australia, Queensland, the Islands of Polynesia (with the exception of
the Sandwich Islands), Egypt, Algeria, Tunis, Madagascar, Zanzibar,
Sudan, etc., the south of the United States of America, Brazil,
the Antilles, etc. Whether it is the same species in all cases is
questionable.
*Filaria demarquayi*, Manson, 1895.
Syn.: _F. ozzardi_, Manson, 1897.
[Illustration: FIG. 284.--_F. demarquayi_: tail, showing paired large
fleshy papillæ. (After Leiper.)]
The adult female _F. demarquayi_ measures from 65 to 80 mm. in length
by 0·21 to 0·25 mm. in breadth. The head has a diameter of from 0·09
to 0·1 mm. The mouth is terminal. The genital pore opens at 0·76 mm.
from the head. The alimentary canal is nearly straight and terminates
in an anus, which is subterminal. The opening of the anus is marked by
a slight papilla. The tail is curved. It rapidly diminishes in size
just below the anal papilla. A characteristic pair of fleshy papillæ
project from the tip of the tail. The diameter near the tip of the tail
before its termination is 0·03 mm. _F. demarquayi_ is a thicker worm
than _Ac. perstans_. It differs from _F. bancrofti_ in the greater size
of the head, in the smaller tail, and particularly in the marked fleshy
papillæ at the tip of the tail. These papillæ are knobby, and not
simply cuticular as in _Ac. perstans_.
The male of _Filaria demarquayi_ has still to be found.
The adult female form of _F. demarquayi_ was found by Dr. Galgey in the
body of a native of St. Lucia in whose blood the larvæ had been found
during life. Five adult females were found in the connective tissue of
the mesentery.
The larva measures 200 µ in length by 5 µ in breadth; it is
sharp-tailed, and has no sheath. Its movements are very active, and
the absence of a sheath enables it to glide along freely all over the
slide. It observes no periodicity, being present in the peripheral
circulation both by day and by night. As a rule, some eight or ten
parasites are found in an ordinary preparation. Sometimes hundreds of
these larval filariæ may be counted on every slide.
The intermediate host has not been discovered.
_Geographical Distribution._--St. Vincent, Dominica, Trinidad, and St.
Lucia (West Indies), British Guiana, New Guinea (?).
[Illustration: FIG. 285.--_Mf. demarquayi_ in thick film, dried and
stained with hæmatoxylin. 6, unshrunken; 7, shrunken. × 1,000. (After
Fülleborn.)]
*Filaria taniguchi*, Penel, 1905.
Female 68 by 0·2 mm. in breadth. Cuticle non-striated. Mouth two pairs
of papillæ. Anus 23 mm. from extremity. Vulva 1·3 mm. from mouth. Larva
164 µ by 8 µ, sheathed. Tail truncated. Periodicity nocturnal.
_Habitat._--Lymphatic glands of man. Japan.
*Filaria (?) conjunctivæ*, Addario, 1885.
Syn.: _Filaria peritonei hominis_, Babes, 1880; _Filaria inermis_,
Grassi, 1887; _Filaria apapillocephata_, Condorelli-Francaviglia,
1892.
The female only of this species is known. It measures 16 to 20 cm.
in length and 0·5 mm. in breadth, and is of a whitish or brownish
tint. The cuticle is striated with fine transverse and more marked
longitudinal striæ with the exception of a small field surrounding
the mouth, which is terminal and has neither papillæ nor lips. The
œsophagus measures 0·6 mm. in length. The anus is 3 mm. in front of the
rounded posterior extremity, and behind it there are two (glandular?)
sacs. The vulva is close behind the oral aperture; the vagina soon
divides into two convoluted uteri, which are filled with eggs and
embryos. Embryos 350 µ by 5·5 µ.
[Illustration: FIG. 286.--_Filaria_ (?) _conjunctivæ_: to the left,
life size; to the right, the anterior extremity magnified. (After
Addario.)]
This species (115 mm. long) was first observed in Milan by Dubini
in the eye of a man; subsequently it was observed, encysted and
calcified (190 mm. long), by Babes in the gastro-splenic omentum of
a woman in Budapest, and finally one (95 mm. long) was extracted by
Vadela from a tumour the size of a pea in the ocular conjunctiva of a
woman in Catania (Sicily), which case has been described by Addario.
Possibly _Agamofilaria palpebralis_, Pace, 1867 (_nec_ Wilson, 1844),
and _A. oculi humani_, v. Nordm., 1832, are the same species.
[Illustration: FIG. 287.--_Filaria_ (?) _conjunctivæ_: anterior end
greatly magnified; the mouth with the pharynx in the middle; in the
cuticle on the right side the opening of the vagina, and behind it the
excretory pore. (After Grassi.)]
_Filaria_ (?) _conjunctivæ_ is certainly only an incidental parasite of
man; the horse and ass are its normal hosts, but it is not common in
these animals, or is frequently confused with _Hamularia equi_, Gmelin,
1789.
Group. *Agamofilaria*, Stiles, 1906.
Not a generic but a group name for immature _Filariidæ_ the development
of which does not admit of generic determination.
*Agamofilaria georgiana.*
Adult unknown, length from 32 to 53 mm. Maximum diameter 560 µ to
640 µ. Head no cephalic cone. Mouth small, circular, surrounded by
six papillæ (two small latero-median and four sub-median). The larger
papillæ are 24 µ from base to tip. Excretory pore about 0·5 mm. from
head. Anus 64 µ to 128 µ from tip. Cuticle fine striæ near anus,
occasionally elsewhere. Lateral lines clearly marked. Œsophagus 2·5 to
2·9 mm. Rectum 200 µ long.
_Habitat._--Superficial sores on the ankle of a negress, Georgia, U.S.A.
*Agamofilaria palpebralis*, Pace, 1867 (_nec_ Wilson, 1844).
100 by 1·5 mm., removed from a cyst in the left upper eyelid of a boy
by Pace, in Palermo.
*Agamofilaria oculi humani*, v. Nordmann, 1832.
Syn.: _Filaria lentis_, Diesing, 1851.
The sexless Nematodes observed in the lens of the human eye were
termed _Filaria oculi humani_. Only three cases are known. v. Nordmann
observed very small round worms in the lens of a man and woman with
cataract, and Gescheidt once found three specimens in the lens of a
woman similarly affected.
The demonstration of nematode-like formations in the vitreous remains
uncertain even when movements are observed, and when they cannot be
extracted and examined microscopically the doubt may occur that one may
have mistaken the remains of the hyaloid artery for a worm, which it
resembles in form, size and colour; the slightest movement of the eye
also causes it to move so that it simulates a living organism.
Accordingly it would be more correct to exclude all the cases known
only ophthalmoscopically (Quadri, 1857; Fano, 1868; Schoeler, 1875;
Eversbusch, 1891). There then remains only one positive case,
described by Kühnt in 1891. In this case it was possible to follow
the gradual growth of the parasite for some time, and the worm, which
measured only 0·38 mm. in length, was finally extracted.
*Agamofilaria labialis*, Pane, 1864.
The parasite measures 30 mm. in length; the anterior extremity is
pointed; the terminal oral aperture is surrounded by four papillæ; the
anus opens 0·5 mm. in front of the posterior extremity; the vulva is
2·5 mm. in front of the anus; the uterus is double; the anterior one
passes with convolutions forward to the cephalic end; the posterior one
is directed backwards and remains rudimentary.
Extracted from a small pustule on the inner surface of the upper lip.
Also found in Naples by Pierantoni in 1908.
The position of many of these worms is doubtful, and still more so is
that of many other imperfectly described “Filariæ,” which are hardly
more than useless and confusing names. These include the following:--
*Filaria (?) romanorum-orientalis*, Sarcani, 1888.
Observed in the blood of a Roumanian woman; 1 mm. in length, 0·03 mm.
in breadth; tail end pointed, a tongue-like appendage on the head. Eggs
the size of a red cell with developed embryo, apparently viviparous.
*Filaria (?) kilimaræ*, Kolb, 1898.
Several female specimens, 10 to 20 cm. long by 0·5 to 1 mm. broad, were
once found free in the abdomen of a fallen Kitú warrior; according
to Spengel, who examined them, the oral papillæ of these worms were
similar to those of _Dracunculus medinensis_. Moreover, Kolb classifies
together Nematodes that probably have no connection with each other.
*Filaria (?) sp.?*
Cholodkowsky calls attention to Filariæ that are still unknown which
cause tumours resembling whitlows on the fingers of peasants of the
Twer Government.
_Mikrofilaria powelli_, Penel, 1905. In Bombay.
_Mikrofilaria philippinensis_, Ashburn and Craig, 1906. In the
Philippines.
Genus. *Setaria*, Viborg, 1795.
Syn.: _Hamularia_, Treutler, 1793; _Tentacularia_, Zeder, 1800 (_nec_
Bosc, 1797).
Mouth with projecting peribuccal armature deeply notched on the lateral
margins, less so dorsally and ventrally. Tail in both sexes with
peculiar caudal appendages.
Parasitic in serous cavities, especially of ruminants.
*Setaria equina*, Abildg., 1789.
Syn.: _Gordius equinus_, Abildg., 1789; _Filaria equi_, Gmelin, 1789;
_Hamularia lymphatica_, Treutler, 1793; _Tentacularia subcompressa_,
Zedder, 1800; _Filaria papillosa_, Rud., 1802; _Filaria hominis
bronchialis_, Rud., 1819; _Filaria hominis_, Dies., 1851; _Strongylus
bronchialis_, Cobb., 1879.
The body is whitish, filiform, pointed posteriorly. The cuticle
presents a delicate transverse striation. The mouth is small, round,
and surrounded by a chitinous ring, the border of which carries, at the
sides, two semilunar lips, and there is on the dorsal as well as on
the ventral surface a papilliform process; on the tail, corresponding
with each sub-median line, is a conical papilla. The male measures
6 to 8 cm. in length; the posterior extremity ends in a corkscrew
spiral; there are on each side four pairs of pre-anal and four or five
post-anal papillæ; the spicules are unequal. The female measures 9 to
12 cm. in length and is viviparous; the embryos measure 0·28 mm. in
length and 0·007 mm. in breadth.
[Illustration: FIG. 288.--_Setaria equina_: left, male; right, female.
Natural size. (After Railliet.)]
[Illustration: FIG. 289.--_Setaria equina_: anterior end, magnified.
(After Railliet.)]
_Setaria equina_ is a frequent parasite of horses and asses; it
inhabits the peritoneal cavity, and from there occasionally invades
the female genitalia or even the liver; it is found more rarely in
the pleural cavity or in the cranium. The statement that it also
occurs in the subcutaneous connective tissue is probably due to
confusion with _Setaria_ (_Filaria_) _hæmorrhagica_, Raill., 1885
(_Filaria multipapillosa_, Cond. et Drouilly, 1878). _Setaria labiata
papillosa_ (immature form) occurs in the eye of the horse, adults in
the peritoneal cavity.
Treutler, in 1790, found a filaria in the enlarged bronchial lymphatic
gland of a patient suffering from phthisis. It measured 26 mm.
in length and had two spicules, which Treutler mistook for mouth
hooks, hence the name _Hamularia_. Blanchard mentions another case
from Geneva, Brera a third and v. Linstow a fourth. As shown by the
synonyms, a few authors consider this form to be a distinct species,
which is hardly probable.
Genus. *Loa*, Stiles, 1905.
Characterized by the possession of cuticular bosses in both sexes
(fig. 294).
*Loa loa*, Guyot, 1778.
Syn.: _Filaria oculi_, Gerv. et v. Ben., 1859; _Dracunculus
oculi_, Diesing, 1860; _Dracunculus loa_, Cobbold, 1864; _Filaria
subconjunctivalis_, Guyon, 1864.
The male measures 25 to 35 mm. in length, and 0·3 to 0·4 mm. in
breadth; the cuticle is not striated, but, with the exception of the
anterior and posterior extremities (1·5 mm.), is beset with numerous
irregularly distributed bosses (4 µ to 12 µ high by 12 µ to 27 µ
broad). The anterior extremity is somewhat attenuated, and in front
is conical and transversely truncated. At the anterior limit of the
conical part is a small papilla corresponding with the dorsal and
ventral median lines, and a little in front six non-projecting sensory
papillæ (two lateral, four sub-median). Excretory pore 0·65 mm. from
the anterior end. The posterior extremity is attenuated and somewhat
curved ventrally; the anus is 0·082 mm. distant from the rounded
posterior border. In front of the anus on each side are three globular
and pedunculated papillæ of different sizes, set close one behind
the other but asymmetrically; behind the anus on either side are two
smaller papillæ of a different shape; the anterior one resembles the
pre-anal papillæ in form, but is smaller; the posterior one is conical,
and rests with a broad base on the cuticle. The spicules are 0·113 and
0·176 mm. long.
The female measures 45 to 63 mm. in length by 0·5 mm. in breadth. It
is also beset with irregularly distributed bosses, which in places lie
close to each other, and extend to the anterior extremity; posteriorly
they become less frequent, but are not entirely absent. The anterior
extremity is conical, the posterior one straight, attenuated, rounded
off, 0·17 mm. from the anus. The uteri contain eggs in the most various
stages of development, as well as hatched-out larvæ, 253 µ to 262 µ
in length and 4·7 µ to 5 µ in breadth. The vulva lies about 2 mm.
from the head end. The vagina, 9 mm. long, divides into two branches,
which at first run posteriorly and parallel to one another for about
18 mm. One then bends forward, runs as far as the œsophagus, bends here
again and runs backward to end at the point of its first bending. The
other branch at first runs straight backward and then bends forward,
but before reaching the point of the first bend of the anterior tube
bends backward again, forms again a loop and ends at the level of the
anus. The tubes consist in the main of the uterus, then a club-shaped
swelling, the receptaculum seminis, then the oviduct 2 mm. long, and
finally the ovary.
[Illustration: FIG. 290.--_Loa loa_: the anterior end of the male,
magnified. (After R. Blanchard.)]
[Illustration: FIG. 291.--_Loa loa_: anterior portion of the female as
far as vulva. (After Looss.)]
[Illustration: FIG. 292.--_Loa loa_ in situ. Natural size. (After
Fülleborn and Rodenwaldt.)]
[Illustration: FIG. 293.--_Loa loa_: male on the left, female on the
right. × 2. (After Looss.)]
Unsegmented eggs measure 32 µ by 17 µ, in the morula stage 40 µ by
25 µ, and when containing embryos 50 µ by 25 µ. The vitelline “shell”
of the egg is, according to most authors, stretched by the embryo and
becomes the sheath of the hatched larva. While still in the vulva,
the larva measures 217 µ to 274 µ (average 246 µ) in fresh, 146 to
226 µ (average 192 µ) stained.
[Illustration: FIG. 294.--_Loa loa_: on the left, the hind end of a
male; on the right, of a female. Note the cuticular bosses shown in the
figure of the female. × 285. (After Looss.)]
[Illustration: FIG. 295.--_Loa loa_: lateral view of tail of male
showing papillæ. (After Lane and Leiper.)]
[Illustration: FIG. 296.--_Loa loa._ _a_, ventro-lateral aspect of tail
showing papillæ and one spicule; _b_ and _c_, terminations of the two
spicules. (After Leiper.)]
_Site of Worms._--In various localities; under the muscular aponeuroses
on extensor surfaces of arms and legs, fingers, trunk, eyelid,
conjunctiva, frænum linguæ, penis, pericardium, anterior chamber of
eye, and, according to some authorities, in lymphatic vessels, _e.g._,
those of spermatic cord. As many as thirty adults may be found. The
worms appear to be frequently immature, and it has been stated that
worms in superficial parts are immature, those situated deeply are
mature, but the data are few.
The first accounts of _Loa loa_--long since forgotten--were reported
by Pigafetta, and are contained in a book of travels on the Congo
printed in 1598. In an accompanying illustration is depicted, not
only the ancient method of extraction of the Medina worm, but
also the operative removal of the filaria from the conjunctiva.
Subsequently the presence of the worm in negroes was confirmed by
Bajon in Guiana (1768) and by Mongin in Mariborou (San Domingo),
likewise in a negro (1770). At about this time a French ship’s
doctor, Guyot, was cruising on the West Coast of Africa; he observed
the parasite termed “loa” by the natives, and learned that it was
frequent in the negroes of the Congo district. Since that time
numerous observations have been reported. It was formerly common in
South America, where the parasite was imported by slaves, but it
disappeared when the traffic ceased; it was particularly prevalent
in the Congo, where it occurs not only in natives, but also in
Europeans. During recent times it has repeatedly been observed in
Europe in negroes as well as in white men who have lived on the West
Coast of Africa.
Nematodes of different size have been repeatedly observed in the eye of
man, in the anterior chamber, lens and vitreous. For example, Mercier,
in 1771 and 1774, removed a filaria out of the anterior chamber of two
negroes in St. Domingo. One was 36 mm. long. Barkan, in 1876, in San
Francisco, removed one from the eye of an Australian. Again, Cappez
and Lacompte, in Brussels, in 1894, observed for some weeks immature
Nematodes in the eye of a negro girl, aged 2-1/2 years, and then
removed them. What these Nematodes actually were in these cases it is
impossible to say.
_Structure of Larvæ._--In dried films the larva varies in size from
140·5 µ to 166·5 µ, average, 152·5 µ; while another set of measurements
gave the values 131 µ, to 150 µ, average, 143·6. In films fixed with
hot alcohol the dimensions were 208 µ to 254 µ, average, 231 µ.
The nerve ring 21·4 to 21·8 per cent. Excretory pore 30·4 to 31·8 per
cent. Excretory cell 34·8 to 37·3 per cent. G1 cell 68·2 to 68·5 per
cent. Anal pore 81·6 to 82·4 per cent. of total length. For other
details _cf._ _Filaria bancrofti_.
_Larvæ in Blood._--These from their diurnal periodicity are known as
_Mikrofilaria diurna_. The evidence that these larvæ are the young
of the adult worm _Loa loa_ is: (1) They are identical in structure
with larvæ taken from the uterus of _L. loa_; (2) their geographical
distribution is the same as that of _L. loa_; (3) they eventually occur
in the blood of patients suffering from Calabar swellings, a condition
due to _L. loa_. Their occurrence in the blood in this latter condition
and in _L. loa_ infections we shall consider later.
_Periodicity._--Here, as in the case of the larvæ of _Filaria
bancrofti_, the larvæ that appear in the blood are probably the
overflow simply of the larvæ which we assume, on analogy, to have
their principal site in the lungs. They appear in the blood about the
time of getting up, 6 to 8 a.m. (10 in 20 mm.^3), at 12 noon there
are twenty-four, at 8 p.m. the number has fallen to eighteen, and at
midnight to one, while from 2 a.m. to 6 a.m. none, or one only, may be
found. This periodicity is, as a rule, a very constant one, but there
are exceptions, and in certain cases more have been found at midnight
than at 9 a.m. The periodicity is also lost in pathological conditions,
_e.g._, sleeping sickness (_vide_ also under _Filaria bancrofti_). The
possibility of non-periodic _Loa loa_ larvæ should also be considered.
[Illustration: FIG. 297.--_Mf. loa_: in thick film, dried and stained
with hæmatoxylin. × 1,000. (After Fülleborn.)]
_Pathology._--The parasite wanders about the body, and may be seen
under the skin in thin parts. Their advance is in some cases at the
rate of an inch in two minutes. During their progress they give rise
to creeping sensations and to a condition of transient œdematous areas
known as Calabar swellings on various parts of the body, _e.g._, arm.
These vary in diameter from 1 to 10 cm., and often shift their position
an inch or so a day. They give rise to a certain amount of redness,
tension and heat, and their development is promoted by muscular action
of the part. They disappear to reappear elsewhere. The condition is
associated with a high eosinophilia, 50 per cent. being not uncommon.
Patients known to harbour _L. loa_, _e.g._, native children,
frequently show no larvæ in their blood, but they may do so after years
of infection. Again, in patients having an infection of _Mikrofilaria
diurna_, there is frequently at the time no evidence of the presence of
_Loa loa_ adults. Here again they may appear later, but the conditions
which determine whether persons infected with _L. loa_ show larvæ in
the blood, or persons infected with _Mikrofilaria diurna_ also show _L.
loa_, are unknown, though explanations unsupported by facts abound.
Likewise also the mode of production of the swellings is unknown.
Not uncommonly _Mikrofilaria perstans_ occurs in the blood together
with _M. diurna_.
_Duration of Life._--This is long, as some cases have been observed
five to six years after leaving Africa. The incubation period is about
a year.
_Life-history._--Development of the larvæ takes place in the salivary
glands of Chrysops sp. as shown by Leiper.
_Geographical Distribution._-- West Africa, especially in Congo.
Genus. *Acanthocheilonema*, Cobbold, 1870.
Cuticle striated _longitudinally_. Œsophagus divided into two portions.
Tail in both sexes with short lateral conical cuticular appendages.
Spicules unequal, the larger membranous distally, the smaller hooked.
Vulva in œsophageal region.
*Acanthocheilonema perstans*, Manson, 1891.
Syn.: _Filaria perstans_, P. Manson, 1891; _Filaria sanguinis
hominis_ var. _minor_, Manson, 1891.
[Illustration: FIG. 298.--_Acanthocheilonema perstans._ 1, tail of
male; 2, tail showing cuticular flaps devoid of fleshy contents. (After
Leiper.)]
The adult female _Ac. perstans_ measures 70 to 80 mm. in length by
120 µ to 140 µ in breadth. The head is club-shaped and measures
0·07 mm. in diameter. The vulva opens at 0·6 to 1·0 mm. from the head.
The tail is curved and presents a cuticular thickening which forms two
triangular appendages. The anus opens at the apex of a papilla situated
in the concavity of the curve formed by the tail 150 µ from the end.
The diameter of the tail just before termination is 0·02 mm.
[Illustration: FIG. 299.--_Mf. perstans_ in thick film, dried and
stained with hæmatoxylin; 4, unshrunken; 5, shrunken. × 1,000. (After
Fülleborn.)]
The adult male measures 45 mm. in length by 60 µ to 80 µ in breadth.
The diameter of the head is 0·04 mm. The tail is much curved. There
are four pairs of pre-anal papillæ and two pairs of post-anal papillæ.
Spicules very unequal in size. Cloaca 121 µ from the tail end. At the
tail end two triangular cuticular appendages.
The adult worms inhabit the connective tissue at the base of the
mesentery, especially in the region of the pancreas, abdominal aorta
and suprarenals. To find them the mesentery should be removed, placed
in a 2 per cent. solution of formalin, and then carefully examined at
leisure.
_Mikrofilaria perstans._--160 µ to 210 µ by 5 µ to 6 µ broad. Has no
sheath. Cuticle transversely striated. Tail rounded off, not pointed.
Nerve ring at 34 µ. Excretory pore 49 µ, genital pore 125 µ from head.
Smaller larvæ 90 µ to 110 µ by 4 µ broad. A “fang” is also described on
the head.
_Mf. perstans._ _Mf. demarquayi._
(1) Tail stumpy. (1) Tail pointed.
(2) Column of nuclei extends to (2) Does not extend to tip.
tip of tail.
_Periodicity._--None.
_Life-history._--Unknown.
_Geographical Distribution._--Very common in many parts of Africa:
Sierra Leone, Dahomey, Northern Nigeria, Southern Nigeria, Cameroons,
Ivory Coast, Gold Coast, Old Calabar, Congo, Uganda. Absent from
Zululand, Basutoland. On the East Coast of Africa it is not found in
the towns of Zanzibar and Mombasa, neither is it found in the country
of the Masi, nor amongst the Kavirondo, who dwell along the north-east
shores of Lake Victoria.
In South America, _Ac. perstans_ is very common amongst the aboriginal
Indians in the interior of British Guiana. However, it is not found in
Georgetown and in New Amsterdam, neither is it found in the cultivated
strip of coast lying between these two towns, but it is common on the
coast farther north near the Venezuelan boundary, where the forests
stretch to the sea. The Waran Indians, who live at the mouth of the
Waini river, harbour this parasite. It is absent in the West Indies.
Topographically, _Ac. perstans_ is found only in areas covered by
dense forest growth and abounding in swamps. In Kavirondo, where the
forest disappears and the land is covered with scrub and short grass,
it is not found; likewise it is not found on the grassy plains of the
highlands of British East Africa. Towns and cultivated areas are free
from it.
Genus. *Dirofilaria.* Railliet and Henry, 1911.
Body very long, thread-like, cuticle transversely striated. Mouth
with six papillæ. Male tail spiral with voluminous pre-anal and some
large post-anal papillæ; spicules unequal. Vulva near the anterior
hundredth of body; viviparous. Parasitic in heart or blood-vessels and
subcutaneous tissue.
*Dirofilaria magalhãesi*, R. Blanchard, 1895.
Syn.: _Filaria bancrofti_, v. Linstow, 1892; _Filaria bancrofti_,
P. S. de Magalhães, 1892 (_nec_ Cobbold, 1877).
The male measures 83 mm. in length by 0·28 to 0·40 mm. in breadth.
The anterior extremity is rounded, and has no papillæ (?6); the
posterior extremity exhibits a double curve, with four pre-anal
and four post-anal papillæ on each side. These are large and have
a villous appearance. The mouth is round and unarmed, the pharynx
measures 1 mm. in length, is cylindrical, very muscular, and its hinder
part is dilated. The anus is situated 0·11 mm. in front of the hind
end. There are probably two unequal spicules; one only, however, is
known--apparently the shorter one--the length of which is given as 0·17
to 0·23 mm.
[Illustration: FIG. 300.--_Dirofilaria magalhãesi_: posterior
extremity. (After v. Linstow.)]
The female measures 155 mm. in length and 0·6 to 0·8 mm. in breadth;
the rings of the cuticle are 0·005 mm. apart (in the male 0·003 mm.
apart); the anterior extremity is slightly thickened and club-like, the
posterior extremity is slender, and terminates obtusely; the lateral
line is 0·127 mm. in breadth (that of the male 0·007 to 0·008 mm.);
the anus opens 0·13 mm. in front of the hind end, the vulva is 2·5 mm.
distant from the mouth, the ovaries are two much convoluted tubes. The
eggs measure 38 µ by 11 µ.
This species was first discovered at a _post-mortem_, in the left
ventricle, by J. P. Figueira de Saboia in Rio de Janeiro, and has
been described by P. S. de Magalhães.
_D. immitis_ occurs in the right ventricle of the heart of the dog in
Europe and the Tropics.
_D. repens_ is also a common subcutaneous Nematode in dogs in Annam.
Sub-family. *Onchocercinæ*, Leiper, 1911.
Cuticle with spiral thickenings.
Genus. *Onchocerca*, Diesing, 1841.
Male with four pre-anal papillæ. Female with vulva situated anteriorly.
*Onchocerca volvulus*, R. Leuckart, 1893.
Syn.: _Filaria volvulus_, R. Leuckart, 1893.
The adult male measures 30 to 35 mm. in length by 0·14 mm. in breadth.
The body is white, filiform, attenuated at both ends. The head is
rounded and has a diameter of 0·048 mm. The cuticle is distinctly
transversely striated. The mouth is unarmed. The alimentary canal is
straight, the anus opening 0·07 mm. from the tip of the tail. The tail
is strongly curved and somewhat flattened on the concave surface. There
are three papillæ, one large and two small, on each side of the cloaca
and one large and two post-anal small papillæ. Two curved spicules,
0·166 and 0·08 mm. respectively.
The adult female is of uncertain length, but much longer than the
male, probably about 10 to 12 cm. The head is rounded and truncated;
it measures 0·065 mm. in diameter. The tail is curved. The vulva opens
0·55 mm. from the head. The hand-like cuticular thickenings are well
marked. Eggs ovoid with a prolongation at each pole “like an orange
wrapped in tissue paper.” The larva measures about 300 µ by 7 µ to 8 µ;
it has no “sheath.” The body tapers from about the last fifth of its
length, and terminates in a sharply pointed tail. At about the anterior
fifth of the body there is a *V* spot.
_O. volvulus_ is found in peculiar subcutaneous tumours, the size of
a pea to that of a pigeon’s egg. The same patient may present one or
several of these tumours. The regions of the body most frequently
affected are those in which the peripheral lymphatics converge. Thus
they are usually found in the axilla, in the popliteal space, about the
elbow, in the sub-occipital region and in the intercostal spaces. The
tumours are never adherent to the surrounding structures, and can be
easily enucleated. They are formed of a dense connective tissue wall
and internally a looser fibrous meshwork. This is traversed by a series
of canals in which the worms lie, but they are also partly embedded
in the denser wall. The canals apparently dilate into cavities filled
with slimy pus-like fluid consisting largely of larvæ. According to
Brumpt the posterior extremity of the male, and the anterior extremity
of the female with its vaginal opening, are free in one of the spaces
for the purpose of copulation and parturition. If a tumour be cut into
and placed in salt solution, Rodenwaldt states that the undamaged males
wander out into the solution.
The formation of the tumours is elucidated by Labadie-Lagrave and
Deguy’s case. The authors found an immature female _Onchocerca
volvulus_ in a lymphatic vessel partly obstructed by an infiltration
of fibrin and leucocytes. It appears, therefore, that the presence
of the parasites within the lymphatics gives rise to an inflammatory
process, and that the consequent fibrinous deposit envelops the
parasites, obliterates the lumen of the vessel, and ultimately isolates
the affected tract. At any rate, in young tumours the worms appear
to lie in a structureless substance permeated by leucocytes in which
connective tissue is gradually organized from the periphery, thus
isolating the worms.
In cases of infection with _O. volvulus_ larvæ have been found by
Ouizilleau, Fülleborn, and Simon in lymph glands, and in the finger
blood if considerable pressure is used so as to squeeze lymph out
of the tissues. They are _sheathless_, and the following are the
dimensions in ordinary dried films: Length, 274 µ; nerve ring, 23·7
per cent.; G1 cell, 69·6 per cent.; end of last tail cell, 96·3 per
cent. The dimensions of larvæ of _O. volvulus_ taken from the uterus
and prepared in the same way are: Length, 224·5 µ; nerve ring, 24·3 per
cent.; G1 cell, 68·9 per cent.; end of the last tail cell, 95·5 per
cent. In all probability the larvæ in the glands and blood are those of
_O. volvulus_.
According to the natives, the tumours may last indefinitely and never
ulcerate. Some old patients told Brumpt that their tumours had been
present since childhood. Probably _Onchocerca volvulus_, like some
other _Filariidæ_, may live for many years.
_O. volvulus_ occurs in various parts of West Africa: Gold Coast,
Sierra Leone, Dahomey, Lagos, Cameroons. Brumpt, on the banks of the
Welle between Dongon and M’Binia (Belgian Congo), found about 5 per
cent. of the riverine population affected.
Family. *Trichinellidæ*, Stiles and Crane, 1910.
Sub-family. *Trichurinæ*, Ransom, 1911.
Male with a single long spicule, with sleeve-like sheath. One ovary.
Eggs with an opening at each pole closed by a plug-like operculum. Eggs
hatch on being swallowed by a new host. Genera: Trichuris, Capillaria.
Genus. *Trichuris*, Röderer and Wagler, 1761.
Syn.: _Trichocephalus_, Goeze, 1782 (_nec Trichiurus_, L., 1758);
_Mastigodes_, Zeder, 1803.
The anterior part of the body is very long and thread-like; the
posterior, much shorter part, is thicker, rounded posteriorly, and
the anus is terminal. The males have the posterior extremity spirally
rolled; the vulva is situated at the commencement of the posterior
part of the body. The Trichocephali live in the large intestine of
mammals, the cæcum by predilection; their development is direct,
infection occurs through the ingestion of embryo-containing eggs.
*Trichuris trichiura*, Linnæus, 1761.
Syn.: _Trichocephalus trichiurus_, L., 1771; _Ascaris trichiura_,
L., 1771; _Trichocephalus hominis_, Schrank, 1788; _Trichocephalus
dispar_, Rud., 1801.
The male measures 40 to 45 mm. in length, the spicule is 2·5 mm. long,
its retractile sheath is beset with spines. The female measures 45
to 50 mm. in length, of which two-fifths appertain to the posterior
part of the body. The ova are barrel-shaped and have a thick brownish
shell which is perforated at the poles. Each opening is closed by
a light-coloured plug. The eggs measure 50 µ to 54 µ in length and
23 µ in breadth; they are deposited before segmentation. _Trichuris
trichiura_ usually lives in the cæcum of man, and is also occasionally
found in the vermiform appendix and in the colon, exceptionally also
in the small intestine; usually only a few specimens are present, and
these do not cause any particular disturbance, although, as Askanazy
found, they feed on blood; in other cases cerebral symptoms of more
or less severity are observed when Trichocephali are present in large
numbers. At _post-mortems_ performed soon after death the filiform
anterior extremity of the worm is frequently found embedded in the
mucous membrane (Askanazy).
[Illustration: FIG. 301.--_Trichuris trichiura_: on the left, male; on
the right, female with the anterior extremity embedded in the mucous
membrane of the intestine; below, egg.]
The whip worm is one of the most common parasites of man and
appears to be distributed over the entire surface of the globe; it
is, however, more frequent in the warmer regions. It is found in
persons of both sexes and all ages with the exception of infants. In
autopsies it is found in the following numbers: In Dresden in 2·5 per
cent., in Erlangen in 11·1 per cent., in Kiel in 31·8 per cent., in
Munich in 9·3 per cent., in Petrograd in 0·18 per cent., in Göttingen
in 46·1 per cent., in Basle in 23·7 per cent., in Greenwich in 68 per
cent., in Dublin in 89 per cent., in Paris in about 50 per cent.,
and in Southern Italy in almost 100 per cent. On examining the fæces
the eggs of the whip worm were found as follows: In Munich in 8·26
per cent., in Kiel in 45·2 per cent., in Greifswald in 45 per cent.,
in North Holland in 7 per cent., in Novgorod in 26·4 per cent., in
Petrograd in 5 per cent., in Moscow in 5·3 per cent.
The development of the eggs is completed in water or in moist soil,
and occupies a longer or shorter time according to the season; the
eggs possess great powers of resistance, as do the larvæ, which,
according to Davaine, may remain as long as five years in the eggshell
without losing their vitality. Leuckart proved by experiment that
direct infection with _Trichuris ovis_ (_Ovis aries_) and _T. crenata_
(_Sus scrofa dom._) was produced by embryo-containing eggs; Railliet
obtained the same results with _T. depressiuscula_ of dogs, and Grassi
subsequently, by means of two experiments, demonstrated the direct
development of _Trichuris trichiura_. In one case embryo-containing
eggs were swallowed on June 27, 1884, and on July 24 the ova of
Trichocephali were found in the fæces for the first time.
_Trichuris trichiura_ is found not only in man, but also in various
monkeys (_T. palæformis_, Rud.), as well as in lemurs (_T. lemuris_,
Rud.).
Other species are _T. crenata_ in pig; _T. ovis_ in cattle, sheep,
goat, and pig (?); _T. depressiuscula_ in dog; _T. campanula_ in
cat; _T. unguiculata_ in rabbit and hare; _T. cameli_ in camel; _T.
discolor_ in humped cattle; _T. nodosus_ in mouse; _T. alcocki_ in the
thamin (India); _T. globulosa_ in camel; _T. giraffæ_ in giraffe.
Sub-family. *Trichinellinæ*, Ransom, 1911.
Male without spicule; females ovoviviparous. Larvæ penetrate muscles of
host and become encysted. Genus: Trichinella.
Genus. *Trichinella*, Railliet, 1895.
Syn.: _Trichina_, Owen, 1835 (_nec_ Meigen, 1830).
Very small _Trichinellinæ_, the males of which have two conical
appendages at the caudal extremity; the vulva is situated at the
border of the anterior fifth of the body. There is only one species.
*Trichinella spiralis*, Owen, 1835.
Syn.: _Trichina spiralis_, Owen, 1835.
The male measures 1·4 to 1·6 mm. in length and 0·04 mm. in diameter.
The anterior part of the body is narrowed, the orifice of the cloaca is
terminal and lies between the two caudal appendages; internal to these
are two pairs of papillæ, dorsal one behind the other. The cloaca is
evertible for copulation. The females measure 3 to 4 mm. in length and
0·06 mm. in diameter; anus terminal.
_Trichinella spiralis_ in its adult stage inhabits the small intestine
of man, pig, wild boar, rat. The young do not leave the body of the
host but become encysted in the muscles. Experimentally it develops
in the black rat (_Mus rattus_), the sewer rat (_M. decumanus_), the
domestic pig (_Sus scrofa dom._), the wild boar (_Sus scrofa ferox_),
the domestic dog (_Canis familiaris_), the fox (_C. vulpes_) the
badger (_Meles taxus_), the polecat (_Putorius fœtidus_), the marten
(_Mustela foina_), the raccoon (_Procyon lotor_), the hippopotamus and
the cat, and many other mammals (rodents and carnivora); Trichinellæ
have been artificially introduced, by administering the encysted stage,
into the dog, the mole (_Talpa europæa_), the mouse (_Mus musculus_),
the hare (_Lepus timidus_), the rabbit (_L. cuniculus_), the hedgehog
(_Erinaceus europæus_), the marmot (_Cricetus vulgaris_), the vole,
the dormouse, the sheep, the calf, the horse, etc. Human beings and
the pig, rat, mouse, guinea-pig and rabbit are most easily infected;
less easily the sheep, calf and horse; with difficulty the cat, dog
and badger. Trichinella can also be reared in birds (fowl, pigeon and
duck), but the young do not encyst in the muscular system, but are
expelled with the fæces. By cold-blooded animals as well as by insects
(_Calliphora vomitaria_), encysted Trichinellæ are evacuated without
undergoing any change, but they will still develop if subsequently
ingested, say, by rabbits. According to Gujon, however, Trichinella
can develop in salamanders, because he has found Trichinella of the
muscles in these animals after they had been fed on encysted specimens.
A high temperature (30°C.) must be provided in which to keep the
experimental animals to ensure the success of the infection.
[Illustration: FIG. 302.--_Trichinella spiralis_. ♀, mature female:
_E_, embryos; _V_, vulva; _Ov_, ovary. ♂, mature male: _T_, testes.
_c._, newly born larva. _d._, larva in the muscles. _e._, encapsuled
larva in the muscles. Magnified. (After Claus.)]
_History._--Encapsuled Trichinellæ had been observed in London by
Peacock (1828) and by J. Hilton (1833) in the muscular system of man;
soon after (1835), Paget found them in London in an Italian who had
died of tuberculosis, and recognized them to be encysted entozoa,
which R. Owen described as _Trichina spiralis_. Soon after, some
further observations were reported on the occurrence of encysted
Trichinellæ, in man, in England, Berlin, Heidelberg, Denmark, North
America; they were also found in the pig (Leidy, Philadelphia)
and the cat (Herbst, Göttingen, and Gurlt, Berlin). Herbst even
succeeded in infecting a badger with encysted Trichinellæ, and
subsequently infected two dogs with the flesh of this badger (1850).
In 1855 R. Leuckart (Giessen) also commenced feeding experiments,
and, like Küchenmeister and Virchow (1859), first went on the wrong
track because it was believed at that time that Trichinellæ were
the larvæ either of Trichocephalus or Strongylus. Nevertheless,
these experiments yielded some important results; they showed that
Trichinellæ become adult in the intestine within a few days, and that
the females are viviparous (Leuckart). Until that time Trichinellæ
had been regarded as fairly harmless guests of man, but opinions
soon changed when Zenker in Dresden (January, 1860), in performing
the autopsy of a girl, aged 10, who had entered the hospital with
typhoid symptoms and there died, found Trichinellæ (not yet encysted)
in the muscles; the intestinal lesions characteristic of typhoid
were lacking, but numerous adult Trichinellæ were found in the
intestine. Inquiries elicited the fact that at about Christmas time
the girl had been taken ill after eating pork, and at the same time
the butcher from whom the meat was bought as well as several of his
customers fell sick: the pickled pieces of the same meat were full
of Trichinellæ. In the face of this information it was not difficult
to ascertain the cause of the disease and the manner of infection
in Zenker’s case, and it was not long before Leuckart, Virchow and
Zenker were able by renewed experiments to demonstrate the cycle
of development of _Trichinella spiralis_. Similar investigations
followed by Claus in Würzburg, Davaine in Paris, Fuchs and
Pagenstecher in Heidelberg, etc.
Hardly had Zenker’s case been published than numerous observations on
trichinosis in man appeared, some referring to isolated cases, others
to small or great epidemics, and nearly all from North Germany.
The worst epidemic was that of Hadersleben (1865), in which place,
numbering hardly 2,000 inhabitants, 337 persons were taken ill within
a short time, and of these 101 died. The source of infection proved
to be a single pig, the flesh of which had been mixed with that of
three other pigs; 200 of the badly infected persons had exclusively
eaten raw pork.
Moreover, it soon became clear that epidemics of trichinosis had been
observed in Germany prior to 1860, but that their nature had not been
recognized, although in a few cases Trichinellæ had been found in the
muscles of those who had succumbed.
HISTORY OF THE DEVELOPMENT OF _Trichinella spiralis_.
Shortly after their introduction into the intestine of experimental
animals the encysted Trichinellæ escape from their capsules, which are
destroyed by the gastric juices, and they then enter the duodenum and
jejunum, where they become adult. During this period they do not grow
much, the males from 0·8 to 1·0 to 1·2 to 1·5 mm.; the females to 1·5
to 1·8 mm. Soon after copulation, which takes place in the course of
two days, the males die; the females, which during the following days
attain a length of 3 to 3·5 mm., either bore more or less deeply into
the villi or, by means of Lieberkühn’s glands, into the mucous membrane
(Askanazy, Cerfontaine, Geisse), and thus usually attain the lymph
spaces. A few also pierce the intestinal wall and are then found in
the mesentery and glands. The females deposit their young, the number
of which, according to Leuckart, averages at least 1,500, in the lymph
spaces; the newly born larvæ measure 90 µ to 100 µ in length, 6 µ in
diameter, and they do not appear to increase in size during their
migrations. The migrations are mostly passive, that is to say, the
larvæ are carried along mainly by the lymph stream to the heart, but
sometimes they are active, as may be inferred from the fact that young
Trichinellæ are found in various parts of the intestinal wall beyond
the chyle and lymph spaces, as well as in abundance in the abdominal
cavity. Trichinellæ occur in the heart’s blood of artificially infected
animals seven to twenty-three days after infection. If scanty, dilute
the blood with about ten times the amount of 3 per cent. acetic acid
and centrifugalize.
The young brood is distributed from the heart throughout the entire
body, but the conditions necessary to its further development are found
only in striated muscle; the young Nematodes penetrate the capillaries,
attain the intramuscular connective tissue and then invade the fibres
(Virchow, Leuckart, Graham[304]). On the ninth or tenth day after
infection the first Trichinellæ have reached their destination; but
further invasions are constantly taking place because the intestinal
Trichinellæ live from five to seven weeks, and continue to produce
their young.
[304] Trichinellæ that are unable to penetrate into muscular fibres
invariably die, no matter where else they settle; their occurrence
in the adipose tissue is disputed, but is still possibly correct, as
bundles of muscles are present in the fat of bacon. The Trichinellæ
do not settle in heart muscle, although they may reach it in cases of
heavy infection; they then die or wander into the pericardium, and
eventually into the heart cavities.
_Symptoms._--(1) Period of invasion: Gastro-intestinal
symptoms--nausea, vomiting, watery diarrhœa, colic. Muscular pains may
occur even at this period. Recurrent abdominal pains about the eighth
day, a _temporary_ œdema. Embryos are abundant in the serous cavities.
(2) Period of dissemination: Second week. Myositis, variable in amount,
is the predominant symptom. The biceps and calf may be hard and tender.
Mastication, speech, respiration, etc., may be difficult and painful.
Dyspnœa may be intense. Temperature 104° to 105° F.
(3) Period of encystment: Symptoms of marked cachexia. Third week:
Second period of œdema, especially of face. Delirium, somnolence, lung
affections. Death or gradual subsidence of symptoms in mild cases.
Eosinophilia (50 per cent. or more) is present.
In consequence of the new batches of young produced during several
weeks, the above-mentioned symptoms of disease are often considerably
aggravated; the fever increases, delirium may arise, and infiltration
of the lungs, fatty degeneration of the liver and inflammation of the
kidneys may ensue; the initial slight œdema may extend, the strength
dwindles, and in many cases the patients succumb to the trichinosis.
In severe cases improvement of the condition is only apt to occur in
the fourth or fifth week; the convalescence is always protracted.
[Illustration: FIG. 303.--_A._, isolated muscular fibre of a rat,
invaded by Trichinella. 510/1. _B._, section through the muscle of a
rat; the infected fibre has lost its transverse striation; its nuclei
are enlarged and multiplied. 310/1. _C._, portion of a Trichinella
capsule, at the pole of which connective tissue cells are penetrating
the thickened sarcolemma. (After Hertwig-Graham.)]
The muscular fibres attacked degenerate, the transverse striation at
first disappearing; the fibres then assume a granular appearance, the
nuclei multiply and become enlarged, and are surrounded by an area
of granular material, which stains more deeply than the remaining
contents of the sarcolemma. Two or three weeks after infection, the
spirally rolled-up Trichinellæ have grown to 0·8 to 1·0 mm., and in
their vicinity the muscular fibre is swollen, spindle-shaped, and the
sarcolemma is glassy and thickened. The inflammation also extends
to contiguous fibres, especially to the intramuscular tissue, which
proliferates greatly, especially in the vicinity of the degenerated
fibres. While the latter become more and more absorbed, the capsule
is formed by the inflamed connective tissue, which, penetrating into
the glassy and thickened sarcolemma from the poles of the spindle,
forms the cystic membrane. According to other authorities, the larvæ
settle in the _inter_muscular connective tissue which forms the cyst
and not in the muscular fibres within the sarcolemma. The cysts are
lemon-shaped and usually lie with their longitudinal axis in the
direction of the muscular fibres; on an average they measure 400 µ in
length by 250 µ in breadth.
Later on fat cells appear at their poles, and after about six or nine
months they commence to calcify, the process starting at the poles
(fig. 305). Finally, sometimes after the lapse of years, the captive
Trichinellæ themselves become calcified.
[Illustration: FIG. 304.--Calcified Trichinella in the muscular system
of a pig; the capsules are not calcified. (After Ostertag.)]
[Illustration: FIG. 305.--Various phases of the calcification of
Trichinella of the muscles, which starts at the poles of the capsule.]
According to experience, Trichinellæ are not evenly distributed in the
muscular system of pigs; the diaphragm, the muscles of the larynx,
tongue, abdomen and intercostal spaces are their favourite positions;
this predilection for the respiratory muscles is explained by their
regular contractions, owing to which regular narrowings of the
capillaries take place, thus favouring the settling of the circulating
Trichinellæ. The same circumstance probably explains the frequency of
the parasites in the tongue.
Possibly also the Trichinellæ that bore direct through the intestine
may, from the abdominal cavity, penetrate the muscles in the vicinity.
Frequently also encysted Trichinellæ are found in remarkable numbers
in the vicinity of the points of insertion of the tendons, this
proclivity being probably connected with the fact that the Trichinellæ
first of all wander into the muscular fibres and find a natural barrier
at the points of insertion of the tendons.
The Trichinellæ, in their encysted condition, may remain alive and
capable of development for many years--in the pig eleven years and in
man as much as twenty-five to thirty-one years. Encystment, however,
is not a necessary condition for the development of the brood, that
is to say, Trichinellæ which reach the gut of suitable animals become
sexually mature and multiply provided that they have developed so far
as to possess a rudimentary genital spot, which occurs when the body is
0·5 to 0·75 mm. long, but all the same a great part of non-encapsuled
Trichinæ perish on their passage through the stomach.
The black rat (_Mus rattus_), and more particularly the sewer rat (_Mus
decumanus_[305]), are the normal hosts of _Trichinella spiralis_.
These animals, especially the last-named species, infect themselves
very easily, as they are cannibalistic, and they also transmit
trichinosis to other species by which they are devoured, such as pigs,
dogs, cats, foxes, bears and martens. Rats are infected also by the
ingestion of fæcal matter from infected animals which contains trichinæ
(Höyberg). Man becomes infected with Trichinella by eating the flesh,
insufficiently cooked, of infected pigs, also, but more rarely, by
eating the infected flesh of wild boars, dogs, cats, bears and foxes.
[305] It is still a matter of dispute and can hardly be definitely
settled whether Trichinellæ were brought to Europe by the sewer rats
which invaded Europe at the end of the eighteenth century, or whether
they were imported with the Chinese pig in 1820 or 1830, when it was
introduced into England and Germany to cross with the native breeds, or
whether finally Trichinellæ are also indigenous to Europe.
The infection of pigs may likewise take place by their having access
to the offal of trichinous pigs, or being actually fed on it. These
are, however, exceptions, which, as a matter of course, are of great
importance in certain places. As a matter of fact, the rats examined
for Trichinella were always found to be severely infected. Thus
Billings, in the knackers’ yard at Boston, found that 76 per cent.
of the rats were infected, and in an export slaughterhouse 100 per
cent. were found to harbour the parasite; in the city of Boston 10
per cent. of the rats had trichinosis. Heller found that of 704 rats,
from twenty-nine different places in Saxony, Bavaria, Würtemberg and
Austria, 8·3 per cent. were infected with Trichinellæ; of the rats
caught in the knackers’ yards, 22·1 were diseased; of those taken in
slaughterhouses, 2·3 were infected, and of rats from other localities
only 0·3 per cent. harboured the parasite. Leisering found almost the
same figures, but in rats from slaughterhouses 5·3 per cent. were
infected.
The geographical distribution of _T. spiralis_ does not correspond with
the occurrence of trichinosis in man; local customs are an important
factor; for instance, the custom of eating pork in a condition that
does not affect the life of the enclosed trichinella. In places where
such customs do not prevail, epidemics do not occur--at the most there
are isolated cases of the disease, although there be a great number of
infected pigs. The following conditions prevail in North America: In
Boston, Billings found that 4 to 5·7 per cent. of the pigs examined
were trichinous; Belfield and Atwood found that 8 per cent. were
infected in Chicago; Salmon found on an average that 2·7 per cent. were
infected (but at various places the percentage fluctuated between 0·28
to 16·3 per cent.), yet epidemics of trichinosis hardly ever occur in
North America, and only isolated cases of the disease are met with in
German immigrants, who keep to their native customs.
This report, according to the researches of H. U. Williams, must be
considerably modified. This author has examined the muscular system
of human cadavers according to the method employed by inspectors of
meat for pigs. The investigations were conducted in the Pathological
Institute of the University of Buffalo, and the observer has examined
505 bodies since 1894, of which 27 (= 5·34 per cent.) were invaded by
Trichinella. The cases, according to the nationality, are divided as
follows:--
---------------------+----------+--------+---------+-------------
| | Trichinella | Percentage
| Examined +--------+---------+ of positive
| | Absent | Present | results
---------------------+----------+--------+---------+-------------
Americans: | | | |
(_a_) Whites | 207 | 201 | 6 | 2·89
(_b_) Negroes | 70 | 65 | 5 | 7·14
British and Irish | 62 | 57 | 5 | 8·06
Canadians | 12 | 10 | 2 | 16·66
Germans | 49 | 43 | 6 | 12·24
Italians | 12 | 10 | 2 | 16·66
Other nationalities | 27 | 27 | 0 | 0
Nationality unknown | 66 | 65 | 1 | 1·51
---------------------+----------+--------+---------+-------------
Total | 505 | 478 | 27 | 5·34
---------------------+----------+--------+---------+-------------
It is worthy of remark that half of all the positive cases were
mental patients, who were found to be affected with Trichinella
to well-nigh 12 per cent. Trichinosis was not, however, the cause
of death in any case. Very frequently the Trichinellæ were found
calcified and dead.
Conditions are similar in most countries of Europe, where, of course,
the number of infected pigs is considerably smaller, but the disease
depends less on this than on the way in which the pork is prepared.
Cases of trichinosis have been known to occur in nearly all the
countries of Europe; further, in Egypt, Algeria, East Africa, Syria,
India, Australia, and America. North Germany, more especially the
Saxe-Thüringian states, is the classical land for epidemics of
trichinosis; the mortality varies, but it may be very high.[306]
[306] For instance, extensive epidemics occurred in Hettstädt in
1863 (160 patients, 28 deaths); Hanover, 1864–1865 (more than 300
patients); Hadersleben, 1865 (337 patients, 101 deaths); Potsdam, 1866
(164 patients); Greifswald, 1866 (140 cases, 1 death); Magdeburg, 1866
(240 cases, 16 deaths); Halberstadt, 1867 (100 cases, 20 deaths);
Stassfurt, 1869 (over 100 cases); Wernigerode, 1873 (100 cases, 1
death); Chemnitz (194 cases, 3 deaths); Linden, 1874 (400 cases, 140
deaths); Niederzwohren, near Cassel, 1877 (half the population);
Diedenhofen, 1877 (99 cases, 10 deaths); Leipzig, 1877 (134 cases, 2
deaths); Ernsleben, 1883 (403 cases, 66 deaths); Strenz-Neuendorf,
1884 (86 cases, 12 deaths), etc. According to Johne, 109 epidemics,
with 3,402 cases and 79 deaths, occurred in Saxony between 1860 and
1889. Stiles, in a work recently published, states that there were
8,491 cases of trichinosis with 513 deaths (6·04 per cent.) in Germany
from 1860 to 1880; and 6,329 cases and 318 deaths (5·02 per cent.)
between 1881–1898. Of these latter, 1881–1898, 3,822 (225 deaths)
occurred in Prussia, 1,634 (76 deaths) in Saxony, and 873 (17 deaths)
in the remaining states. There is, however, no doubt that many deaths
from trichinosis were not recognized, as proved by experience at
_post-mortems_.
_Prophylaxis._--The grave nature of the disease and the comparatively
high mortality relating to trichinosis led the authorities to adopt
certain preventive measures, which are the more necessary as national
customs cannot be altered in a short time. As the usual process of
pickling and smoking, even when long continued, does not certainly
ensure the death of the Trichinellæ contained in the meat, and also
because in roasting and boiling large pieces of pork a considerable
time is necessary to permit the temperature required to kill off the
parasites (62° to 70° C.) to penetrate to the middle of the joint,
it appeared to be most practical to have all pigs microscopically
examined for Trichinellæ before they, or parts of them, were placed
on the market, and all infected meat condemned, no matter whether the
Trichinellæ were present in large or small numbers, still undeveloped
or calcified. Since 1877 obligatory examination of pork has been
introduced in Prussia, though as yet it is not thoroughly carried
out; other states of North Germany as well as the larger towns of
South Germany soon followed; a complete army of trichina inspectors,
officially examined and periodically controlled by experts, and
whose number in Prussia amounted to 27,602 in 1896, this being even
increased to 28,224 in 1899, have the charge of examining pork on
certain lines laid down. These are at the present time uniformly
administered. The proceeding is usually that the trichina inspector
himself goes to the slaughterhouses, or special samplers take pieces
of the muscles that are known to be the favourite seats of the
parasite (pillars of the diaphragm, the costal part of the diaphragm,
muscles of the tongue and larynx, intercostal and abdominal muscles);
six small portions are separated from each piece, pressed between
slides or special compressors, and carefully gone through by
examining them with a low power of the microscope. The pigs free
from Trichinellæ are passed for commerce; trichinous pigs, on the
other hand, in Prussia, are only allowed to be used for industrial
purposes, _i.e._, the hide and bristles are used, the fat is allowed
to be melted down, or certain parts are used for the manufacture of
soap or glue. In Saxony, however, it is still permitted to place
trichinous flesh on the market, fully declaring its nature, and after
having been heated to its deepest strata at a temperature of 100° C.
in a suitable apparatus, and under the supervision of a veterinary
surgeon.
AS TO THE PROPORTION OF TRICHINOUS PIGS to healthy ones, the
following tables give the figures for Prussia:--
------+---------------+-----------------+------------
| Number of | Number of |
Year | pigs examined | trichinous pigs | Proportion
------+---------------+-----------------+------------
1878 | 2,524,105 | 1,222 | 1 : 2,065
1879 | 3,164,656 | 1,938 | 1 : 1,632
1881 | 3,118,780 | 1,695 | 1 : 1,839
1882 | 3,808,142 | 1,852 | 1 : 2,056
1883 | 4,248,767 | 2,199 | 1 : 1,932
1884 | 4,611,689 | 2,624 | 1 : 1,741
1885 | 4,421,208 | 2,387 | 1 : 1,852
1886 | 4,834,898 | 2,114 | 1 : 2,287
1887 | 5,486,416 | 2,776 | 1 : 1,988
1888 | 6,051,249 | 3,111 | 1 : 1,945
1889 | 5,500,678 | 3,026 | 1 : 1,818
1890 | 5,590,510 | 1,756 | 1 : 3,183
1891 | 6,550,182 | 2,187 | 1 : 2,996
1892 | 6,234,559 | 2,085 | 1 : 2,992
1896 | 8,759,490 | 1,877 | 1 : 4,666
1899 | 9,230,353 | 1,021 | 1 : 9,040
1902 | 9,093,210 | 725 | 1 : 12,397
------+---------------+-----------------+------------
The proportion, however, is not only subject to variation in separate
years, but differs according to the district; thus, in 1884, in the
state district of Minden there was one trichinous pig to 30,146
healthy animals, in Erfurt 1 to 14,563, in the district of Gnesen 1
to 101, in Schrimm 1 to 86, and in Schroda 1 to 68.
In Germany Trichinella is becoming LESS COMMON in pigs (Ostertag):--
(_a_) _Prussia._
Pigs found
Year to be trichinous
1878–1885 0·061–0·048 per cent.
1886–1892 0·033–0·043 "
1896 0·021 "
1899 0·014 "
1902 0·011 "
(_b_) Saxony.
Number of pigs
Year found to be trichinous
1891 0·014 per cent.
1892 0·011 "
1893 0·008 "
1894 0·007 "
1895 0·012 "
1896 0·0102 "
1899 0·004 "
1902 0·0056 "
(_c_) City of Berlin.
Number of pigs
Year found to be trichinous
1883–1893 0·035–0·064 per cent.
1893–1897 0·022–0·015 "
1902 0·006 "
There is no doubt that the excellent preventive measure of official
inspection for Trichinella has led to the avoidance of grave disasters;
its introduction has not yet caused an entire cessation of trichinosis
in man, because inspection of pork is not obligatory everywhere, so
that human beings may become infected by unexamined trichinous pigs
from their own country or from abroad, and also because an infection
may occasionally escape notice. For these reasons the meat imported
into Berlin from abroad as free from Trichinæ is examined again and not
always in vain; finally, also, gross negligence may at times occur, or
fatal errors may be made.
In addition _private prophylaxis_ must not be neglected, and its chief
aim should be directed to the suitable preparation of pork.
Family. *Dioctophymidæ.*
Genus. *Dioctophyme*, Collet-Megret, 1802.
Syn.: _Eustrongylus_, Dies., 1851.
Large worms. Anterior extremity unarmed; the mouth is surrounded by
six papillæ. One ovary. The vulva is in the anterior region of the
body.
*Dioctophyme gigas*, Rudolphi, 1802.
Syn.: _Dioctophyme renale_, Goeze, 1782; _Ascaris canis_ et _martis_,
Schrank, 1788; _Ascaris visceralis_ et _renalis_, Gmelin, 1789;
_Strongylus gigas_, Rud., 1802; _Eustrongylus gigas_, Dies., 1851;
_Strongylus renalis_, Moq. Tand., 1860; _Eustrongylus visceralis_,
Raill., 1885.
Colour blood-red; the anterior extremity somewhat slender; there is a
series of about 150 papillæ along the lateral lines; the sub-median
lines are strongly developed, and from them spring the radial muscles
for the intestine.
The males attain a length of 40 cm. and a diameter of 4 to 6 mm.; the
posterior extremity is transversely truncated; the anal orifice is
within the base of the collar-like bursa, the thickened edges of which
are beset with papillæ; the spicule measures 5 to 6 mm. in length.
The females attain a length of 100 cm. and a breadth of 12 mm. The anus
is crescent-shaped and terminal. The vulva is 50 to 70 mm. distant
from the anterior extremity. The eggs are oval and have a thick shell
presenting numerous depressions; the shell itself is brownish, but it
is colourless at the somewhat thickened poles; it measures 60 µ in
length by 40 µ in breadth. The larva measures 240 µ by 14 µ.
_Dioctophyme gigas_ lives in the pelvis of the kidney, more rarely in
the abdominal cavity of the seal, otter, dog, wolf, fox, horse, marten
and polecat, exceptionally also in human beings. It also occurs in
tumours of the mamma and perinæum. Most of the cases in which this
parasite has been reported as occurring in man may be traced back
to unrecognized _Ascaris lumbricoides_ or to clots of fibrin; seven
certain cases, eight more or less doubtful, however, remain.
[Illustration: FIG. 306.--_Dioctophyme gigas_, male. Natural size.
(After Railliet.)]
[Illustration: FIG. 307.--Eggs of _Dioctophyme gigas_; above seen from
the flat, below in optical section. 400/1. (After Railliet.)]
The source of infection is unknown, but according to Balbiani the
eggs develop an embryo in water or moist soil, and this embryo may
remain alive several years without hatching; the infection of dogs
with embryo-containing eggs did not succeed; an intermediate stage in
fishes is conjectured, but still the infection of cattle and horses is
unintelligible.
Family. *Strongylidæ.*
Sub-family. *Metastrongylinæ*, Leiper, 1908.
Buccal capsule absent or slightly developed, vagina elongate,
uteri convergent[307] and have a simple musculature. Parasitic in
the respiratory or circulatory system. Genera: Metastrongylus,
Synthetocaulus.
[307] Convergent: _i.e._, the uteri are parallel, converging from the
anterior part of body to the vagina, which is near the anus, this
position being associated with convergence of the uteri. Divergent:
Uteri run anterior and posterior, diverging from the vagina, which in
this case is near middle of body.
Genus. *Metastrongylus*, Molin, 1861.
Mouth with six lips, of which the two lateral are the largest. Postero-
and postero-external rays[308] of bursa thin, the rest thick. Only the
median ray double. Spicules very long and slender, striated. Vulva
immediately in front of anus. Eggs contain an embryo when laid.
[308] For nomenclature of rays _vide_ p. 449.
*Metastrongylus apri*, Gmelin, 1789.
Syn.: _Gordius pulmonalis apri_, Ebel, 1777; _Ascaris apri_, Gmelin,
1789; _Strongylus suis_, Rud., 1809; _Strongylus paradoxus_,
Mehlis, 1831; _Strongylus elongatus_, Duj., 1845; _Strongylus
longevaginatus_, Dies., 1851.
The male measures 12 to 25 mm. in length; the bursa is bilobed; there
are five rays in each lobe; the spicules are thin and up to 4 mm. in
length. The females measure 20 to 50 mm. in length, the anus is close
in front of the posterior extremity, which has a recurved, hook-like
process; the vulva is close in front of the anus. The eggs are
elliptical, 57 µ to 100 µ in length, 39 µ to 72 µ in breadth; when the
eggs are deposited the embryo is already formed, 220 µ to 350 µ by 10 µ
to 12 µ.
_Metastrongylus apri_ frequently lives in the bronchial tubes--usually
the smaller ones--of the pig[309] and wild boar; it is also found
occasionally in sheep and in man; in young pigs it is apt to set up a
bronchitis, which frequently causes death.
[309] The reports of the city inspection of meat in Berlin state that
_Strongylidæ_ in the lungs of pigs are by no means rare; therefore the
lungs of 1,941 pigs were condemned between 1885–1886, of 1,641 between
1886–1887, of 3,237 between 1887–1888, of 4,855 between 1888–1889, of
7,197 between 1889–1890, and of 5,574 pigs between 1890–1891, etc.
Ostertag found _Strongylus apri_ in 60 per cent. of the pigs examined
in the Berlin abattoir; Meyer, in Leipzig, found the parasite in 15 per
cent. of the native pigs and in 52 per cent. of the Hungarian pigs.
The first communication as to the occurrence of this species in man
was that of Diesing, who, in 1845, in Klausenburg, had the opportunity
of examining _Strongylidæ_ found by Jortsits in the lung of a little
boy, aged 6, in Transylvania; probably also the Nematodes found in the
trachea and larynx of man, and described by Rainey and Bristowe as
specimens of _Filaria trachealis_, belong to this group; according to
Chatin, _Metastrongylus apri_ may also occur in the intestine of man;
this occurrence, however, may in all probability have been due to an
accidental introduction of adult worms into the intestine, and should
not be attributed to an infection by the larval stage.
[Illustration: FIG. 308.--_Metastrongylus apri_: one side of bursa.
_a._, anterior; _a.e._, antero-external; _a.m._, antero-median; _p.m._,
postero-median; _p.e._, postero-external; _p._, one division of
posterior ray. (Stephens.)]
No experiments to induce infection have been made; it is probable,
however, that infection is direct and without the aid of an
intermediate host.
Sub-family. *Trichostrongylinæ*, Leiper, 1908.
Strongylidæ with buccal capsule absent or slightly developed, vagina
short, uteri divergent (_i.e._, anterior and posterior), ovejectors
differentiated. Parasitic in the alimentary canal. Contains the genera
Trichostrongylus, Hæmonchus, Ostertagia, Nematodirus, Cooperia,
Dictyocaulus.[310]
[310] _Dictyocaulus_ is parasitic in the bronchi.
Genus. *Trichostrongylus*, Looss, 1905.
Very small _Strongylidæ_. Mouth with three small lips and nodular or
punctiform papillæ. Cervical papillæ absent. Bursa entirely closed,
with large lateral lobes, and median lobe not distinctly defined.
Anterior[311] rays double, the branches widely divergent, one thin, the
other thick, and close to the antero-median. The postero-median ray
is thin and close to the postero-external. Posterior ray bifurcate,
each branch bifid at the tip (fig. 311). Spicules short, spoon or
spatula-like, with on the broad anterior end a lateral knob or disc
and in front of the point an angular projection. Gubernaculum of a
peculiar canoe or shoe shape in profile. Vulva in the hinder half of
the body. Tail with two minute papillæ just in front of tip. Eggs thin
shelled; when laid they show eight to thirty-two segments. Parasitic in
duodenum, seldom in the stomach of herbivora.
[311] When the anterior ray is double, the branches of it are called
antero-anterior and latero-anterior.
[Illustration: FIG. 309.--_Trichostrongylus instabilis_: left,
posterior end of male; right, spicule and gubernaculum, side view.
_Cf._ fig. 311. Magnified. (After Looss.)]
[Illustration: FIG. 310.--_Trichostrongylus instabilis_: posterior end
of female. Magnified. (After Looss.)]
*Trichostrongylus instabilis*,[312] Railliet, 1893.
[312] Identical with _T. colubriformis_ of the sheep according to
Leiper. If so, this latter name has priority.
Syn.: _Strongylus instabilis_, Railliet, 1893; _Strongylus subtilis_,
Looss, 1895.
Male 4 to 5·5 mm. long, 0·08 mm. thick in front of bursa. Spicule 0·135
to 0·145 mm. long, accessory piece (gubernaculum) 0·07 mm. thick.
Antero-external ray usually thickest of all, occasionally only as
thick as the antero-median; postero-median far more slender than the
antero-external and antero-median and nearer to the postero-external
than to the antero-median. Female 5 to 6 mm. long, vulva 1·05 to
1·2 mm. distant from the tip of the tail, placed _longitudinally_,
50 µ to 55 µ long, always shorter than the unpaired portion of the
canal formed by the union of the two ovejectors; anus 0·055 to 0·07 mm.
distant from tip of the tail; ova 73 µ to 80 µ by 40 µ to 43 µ.
This species lives in the duodenum, exceptionally also in the
stomach of _Ovis aries_, _O. laticauda_, _Antilope dorcas_, _Camelus
dromedarius_ (Egypt), _Cynocephalus hamadryas_ (North Africa), sheep
and goats (France), and has been found by Looss in bodies of fellaheen
at Alexandria and in the stomach of a Japanese female by Ijima.
*Trichostrongylus probolurus*, Railliet, 1896.
Syn.: _Strongylus probolurus_, Railliet, 1896.
Male 4·5 to 5·5 mm. long, in front of bursa 0·08 mm. thick; spicule
0·126 to 0·134 mm. long, gubernaculum 0·075 to 0·08 mm. long.
Bursa: latero-anterior rib thickest; antero-external thicker than
antero-median, postero-median and postero-external very short and close
together. Female 4·5 to 6 mm. long, vulval opening 1·08 to 1·25 mm.
from tip of tail, placed _longitudinally_, and slightly curved, 76 µ
long, always longer than the unpaired portion of the ovejector; anus
0·040 to 0·05 mm. distant from tip of tail. Posterior end thick, point
of tail short. Ova 76 µ to 80 µ by 43 µ to 46 µ.
[Illustration: FIG. 311.--_Trichostrongylus probolurus_: tail of male
from left side. _d._, posterior; _e.d._, postero-external; _p.l._,
postero-median; _m.l._, antero-median; _e.l._, antero-external;
_l.v._, latero-anterior; _v.v._, antero-anterior; _gub._, portion of
gubernaculum; _sp._, portion of spicules. × c. 300. (After Looss.)]
[Illustration: FIG. 312.--_Trichostrongylus probolurus_: spicules and
gubernaculum of male; on left, ventral view; on right, lateral view. ×
c. 300. (After Looss.)]
_Habitat._--In the duodenum of _Ovis aries_, _O. laticauda_, _Antilope
dorcas_, _Camelus dromedarius_ (Egypt) and occasionally also in man
(Egypt).
*Trichostrongylus vitrinus*, Looss, 1905.
Male 4 to 5·5 mm. long, in front of bursa 0·085 mm. thick. Bursa
larger than in the other two species, antero-external rib thickest,
antero-anterior and postero-median equally thick, straight. Spicule
0·16 to 0·17 mm. long, gubernaculum 0·085 to 0·095 mm. long. Female 5
to 6·5 mm. long, vulval opening 1·15 to 1·25 mm. distant from tip of
tail, crescent shaped, _oblique_ to body axis, and around it irregular
thickenings. Ova 84 µ to 90 µ by 46 µ to 50 µ.
In duodenum of _Ovis aries_, _O. laticauda_, occasionally in _Camelus
dromedarius_ and in man (Egypt).
[Illustration: FIG. 313.--_Trichostrongylus vitrinus_: tail of male
from left side. _d._, posterior; _e.d._, postero-external; _p.l._,
postero-median; _m.l._, antero-median; _e.l._, antero-external;
_l.v._, latero-anterior; _v.v._, antero-anterior; _gub._, portion of
gubernaculum; _sp._, portion of spicule. × c. 300. (After Looss.)]
[Illustration: FIG. 314.--_Trichostrongylus vitrinus_: spicules and
gubernaculum; on left, ventral view; on right, lateral view. × c. 300.
(After Looss.)]
Genus. *Hæmonchus*, Cobb., 1898.
Small mouth cavity contains a “tooth” or “lancet” arising from the
dorsal side. Cuticle of head and neck not inflated. Cervical papillæ
well marked. Bursa bilateral, with large lateral lobes and a small
dorsal lobe _not median_, but lateral, attached to the base of one of
the lateral lobes (fig. 316). Posterior ray bifurcate, each branch
bifid apically. Each lateral lobe six rays. Anterior rays separated
distally, curving forward. Antero-median and postero-median rays
distally curve away from the antero-external. Postero-external ray long
and slender. Spicules less than 1 mm. Gubernaculum present. Vulva in
posterior part of body covered by a prominent tongue-like flap. Eggs
ellipsoidal.
*Hæmonchus contortus*, Rudolphi, 1803; Cobb., 1898.
Dorsal “tooth” or “lancet” 10 µ to 15 µ long. Cervical papillæ 0·3 mm.
from head.
Male 20 mm. long by 400 µ thick (maximum). Asymmetrical lobe of bursa
150 µ by 125 µ attached to left lateral lobe. Posterior ray bifurcate;
each branch bifid. Stem of ray less than twice as long as its branches.
Spicules 300 µ to 500 µ with knobbed tips, and the left spicule with
a barb 20 µ from the tip, right spicule with a barb 40 µ from tip.
Gubernaculum 200 µ by 25 µ to 35 µ, fusiform with thickened edges.
Female 18 to 30 mm. by 500 µ (maximum). Vulva 3 to 4·5 mm. from tip.
Linguiform flap 0·5 mm. (a second one exists, according to Brumpt).
Anus 400 µ to 630 µ from tip. Tail acutely pointed. Eggs 75 µ to 95 µ
by 40 µ to 50 µ.
[Illustration: FIG. 315.--_Hæmonchus contortus_: vulval region of
female viewed from left side. _int._, intestine; _lab._, linguiform
process covering vulva; _ov._, ovary; _ovij._, ovejector; _ut._,
uterus; _vag._, vagina; _vul._, vulva. × 75. (After Ransom.)]
[Illustration: FIG. 316.--_Hæmonchus contortus_: tail of male,
dorsal view, _d._, posterior ray of the asymmetrically placed posterior
lobe; _e.d._, postero-external; _p.l._, postero-median; _m.l._,
antero-median; _e.l._, antero-external; _l.v._, latero-anterior;
_v.v._, antero-anterior; _gub._, gubernaculum; _sp._, spicule. × 75.
(After Ransom.)]
_Habitat._--Fourth stomach of cattle, sheep, antelope.
_Distribution._--Europe, America, Africa, Asia, Australia, New Zealand.
Once in man in South America by de Magalhães.
_Pathology._--Produces anæmia, emaciation, dropsy in sheep; and in the
human case the symptoms were mistaken for those of ancylostomiasis.
_Life-history._--Rhabditic embryos easily hatch in water, then moult
several times, becoming eventually “filariform” larvæ enclosed in the
moulted skin. These crawl up blades of grass and are swallowed by
sheep, etc.
Genus. *Nematodirus*, Ransom, 1907, emend. Railliet, 1912.
Head over 50 µ in diameter. Cuticle may be slightly inflated and often
transversely striated. Cuticle with eighteen distinct longitudinal
ridges. Cervical papillæ absent (?). Posterior lobe of bursa reduced to
short lobules each with a dorsal ray. Antero-anterior + latero-anterior
(= anterior double) rays close together, parallel; antero-external
ray diverges widely from antero- and postero-median, which are close
together and parallel. Postero-external ray slender. Spicules more
than 0·5 mm. long, at most one-twelfth of body, united by a membrane
throughout their length or only distally. Gubernaculum absent. Vulva
behind middle of body. Eggs ellipsoidal, shell rather thick.
_Habitat._--Duodenum of ruminants.
Sub-genus. *Mecistocirrus*, Railliet, 1912.
Head slightly inflated, with transverse striations. Skin with eighteen
longitudinal ridges, but little apparent; cervical papillæ distinct.
Bursa bilobed; median ray double (= postero-median + antero-median);
very large antero-external at the edge, close to the anterior. Spicules
very long, slender, one-sixth length of body (3·5 mm.); tail pointed.
Vulva immediately in front of anus.
_Habitat._--Stomach of ruminants.
*Mecistocirrus fordi*, Daniels, 1908.
Syn.: _Strongylus fordi_, Daniels, 1908; _Strongylus gibsoni_,
Stephens, 1909; _Nematodirus fordi_, Leiper, 1911.
Male 21 mm. long by 0·4 mm. thick. Cervical papillæ 0·45 mm. behind the
head. Spicules about 7 mm. long, _i.e._, one-third of the body length.
At the level of the postero-external rays of the bursa, the bursa has a
projecting lobule.
Female 25 mm. long. Anus 0·2 mm., vulva 0·5 mm. from the tip of tail.
Eggs 100 µ by 53 µ.
Sub-family. *Ancylostominæ*, Railliet, 1909.
_Strongylidæ_ with buccal capsule, well developed. Uteri divergent.
Parasitic in the alimentary canal, exceptionally in the respiratory
system.
Group. *Œsophagostomeæ*, Railliet and Henry, 1909.
Bursa with anterior and median ray cleft (not double), postero- and
postero-external arising from a common trunk, posterior bifurcated,
each limb bidigitate.
Contains at present four genera: (1) Ternidens, (2) Chabertia, (3)
Œsophagostomum, (4) Agriostomum.
[Illustration: FIG. 317.--Mecistocirrus fordi: bursa of male, dorsal
view. The rays are (1) postero-external, (2) median (= postero-median
+ antero-median), (3) antero-external, (4) latero-anterior, (5)
antero-anterior. These two latter are parallel. The posterior ray is
absent. (After Stephens.)]
Genus. *Ternidens*, Railliet, 1909.
Buccal capsule sub-globular, opening obliquely in the dorsal surface,
and having at the bottom three complex teeth resembling those of
Triodontophorus.[313] Two crowns of leaflets; peristomic collar
moderate, edge of bursa slightly toothed.
[313] Triodontophorus belongs to the group _Cylicostomeæ_, which has
the following bursal formula: (1) anterior cleft, (2) median double,
(3) postero-external and posterior arising _separately_, (4) posterior
double, each branch giving off two lateral branches.
_Type._--_T. deminutus_, Railliet and Henry.
*Ternidens deminutus*, Raill. and Henry, 1905.
Syn.: _Triodontophorus deminutus_, Raill. and Henry, 1905.
Body relatively thick. Cervical papillæ 0·5 mm. behind the head. Buccal
capsule 40 µ deep. Teeth 40 µ long.
[Illustration: FIG. 318.--_Ternidens deminutus._ *A*, head end, ventral
view: c, crown of leaflets; v.o., buccal cavity; d, pharyngeal plates;
ph., pharynx; n., valve. *B*, lateral view. *C*, tail of female. *D*,
bursa of male: a., anterior ray; a.e., antero-external; m., median;
p.e., postero-external; p., posterior. *E*, pharyngeal plate. Enlarged.
(After Railliet and Henry.)]
Male 9·5 mm. long by 560 µ thick. Œsophagus 660 µ long. Bursa broader
than long, the lateral lobes united by a small posterior lobe with
slightly sinuous margin; edge of bursa finely toothed. Spicules about
900 µ long.
Female 12 to 16 mm. long by 650 µ to 730 µ thick. Œsophagus 860 µ long.
Vulva forms a distinct projection 480 µ from tip of tail. Anus 240 µ to
270 µ from tip. Eggs 60 µ to 80 µ by 40 µ.
_Habitat._--Large intestine of a negro (Comoro Islands) and in the
natives of Nyasaland and Portuguese East Africa. Also in large
intestine of _Macacus sinensis_ and _Macacus cynomolgus_.
Genus. *Œsophagostomum*, Molin, 1861.
No teeth. Cuticle around the mouth dilated to form a narrow cuticular
“peristomic collar.” Separated by a constriction from this is a much
more extensive inflation, the “cephalic vesicle,” bounded abruptly
behind on the ventral side by a transverse groove, the “ventral cleft,”
which is always present even in absence of the vesicle. Buccal cavity
of slight depth with a short dorsal tunnel. Internal margin of the
mouth armed with chitinous leaflets (“external crown”); internal border
of the buccal capsule armed with short tongue-like leaflets (internal
crown). Lateral membranous wings may extend backwards from the
ventral cleft. Cervical papillæ present. Bursa with two lateral lobes
united by a smaller median lobe. Spicules over 5 mm. long, slender;
gubernaculum inconspicuous. Vulva in front of anus. Adults usually in
large intestine of ruminants, suidæ, tapirs, edentates and apes. Larvæ
sometimes in nodules in intestinal wall.
*Œsophagostomum brumpti*, Railliet and Henry, 1905.
Female immature, 8·5 to 10·2 mm. long, 0·295 to 0·325 mm. thick.
Cuticle transversely striated. The cephalic vesicle immediately
behind the vestibulum oris, embracing the anterior two-fifths of the
œsophagus, extending ventrally, however, towards its posterior end.
Vestibulum oris formed by a cuticular band provided with a crown of
twelve apical leaflets directed forward and inwards; six cephalic
papillæ (two lateral, four submedian); buccal capsule in front of
cervical swelling not delineated circularly behind, but provided with
three wide incisions (one dorsal, two sub-ventral). Œsophagus, 0·470
to 0·500 mm. long, two cervical papillæ at five-eighths of its length.
Vulva 0·350 to 0·475 mm., anus 0·170 to 0·200 mm., before tip of tail.
_Habitat._--Found by Brumpt in tumours of the cæcum and colon of a
native of the River Omo (Lake Rudolph), East Africa. Immature forms
only were present. Adults have been found in similar tumours in monkeys.
[Illustration: FIG. 319.--_Œsophagostomum stephanostomum_ var.
_thomasi_. 1, male, natural size; 2, female, natural size; 3, head
of female, ventral view, showing cephalic vesicle and ventral cleft
limiting it behind, × 55; 4, head of female, dorsal view, × 225; 5,
head of male, end view, showing external and internal leaf crowns,
× 225; 6, tail of male, lateral view (_cf._ fig. 318, D), × 20; 7,
tail of female, lateral view, × 20; 8, _Œs. thomasi_, posterior ray of
bursa, × 150; 9, _Œs. dentigerum_, from chimpanzee, posterior ray of
bursa, × 150; 10, _Œs. stephanostomum_, from gorilla, posterior ray of
bursa, × 150.]
_Pathology._--They occur in hæmorrhagic cysts in the submucosa or
muscularis mucosæ of the gut wall. The cysts project internally and
externally, and contain immature adults, which eventually escape into
the lumen of the gut.
[Illustration: FIG. 320.--_Œsophagostomum stephanostomum_ var.
_thomasi_: cæcum and ascending colon. Subperitoneal cysts are seen on
the top right hand, and in the lumen of the gut numerous cysts arranged
transversely. The small roundish patches are areas of necrosis in the
cyst walls. (After Thomas.)]
*Œsophagostomum stephanostomum* var. *thomasi*, Raill. and Henry, 1909.
Body thick, pointed only at the ends. Buccal capsule much reduced.
External crown of thirty-eight leaflets (the “crown” nearest the centre
of fig. 319, 5). Male 17 to 22 mm. long by 750 µ thick. Spicule 1·380
to 1·475 mm., slightly curved at the tip. Female, immature, 16 to
20 mm. long by 900 µ thick, tail ending in a little conical appendage.
Anus 230 µ, vulva 500 µ to 525 µ from tip. Ovejectors close together.
Uteri very short in form of oblong pouch.
_Œs. stephanostomum_, Stossich, 1904, in the large intestine of
gorilla. _Œs. stephanostomum_ var. _dentigera_, Raill. and Henry, 1909,
in the chimpanzee.
_Habitat._--In large and small intestine of man, Brazil.
_Pathology._--Nodules occur in the gut wall; 187 were found by Thomas
in his, the sole case. The tumours contain each a single worm.
[Illustration: FIG. 321.--_Œsophagostomum stephanostomum_ var.
_thomasi_: portion of the ileum, showing a cyst with protruding worm.
× 8. (After Thomas.)]
[Illustration: FIG. 322.--_Œsophagostomum stephanostomum_ var.
_thomasi_: colon with œsophagostome withdrawn from its cyst cavity.
× 20. (After Thomas.)]
*Œsophagostomum apiostomum*, Willach, 1891.
According to Leiper, _Œs. brumpti_ is identical with, and hence a
synonym of, this species. Parasitic in large intestines of monkeys,
producing dysentery, and in man (Northern Nigeria).
According to Walker this species is common in Philippine monkeys. Ova
are scanty in the fæces. They measure 73 µ to 84 µ by 44 µ to 57 µ and
are in the morula stage. They are easily cultivated. The rhabditiform
larva is 340 µ by 16 µ and has a long filiform tail. It moults twice,
and at the second moult becomes a filariform larva retaining the skin
of this moult, this stage being that of the mature larva. It now
measures 9 mm. long by 30 µ thick. Walker suggests that the mode of
infection is similar to that of ancylostomes.
Group. *Ancylostomeæ*, Railliet and Henry, 1909.
Bursa with anterior ray cleft, median double,[314] postero- and
postero-external arising from a common trunk, posterior bifurcate,
each limb being tridigitate. Vulva in posterior third of body. Uteri
divergent.
[314] _I.e._, with a distinct space between the limbs.
Contains the following genera: (1) Strongylus,[315] (2) Ancylostoma,
(3) Uncinaria, (4) Characostomum, etc.
[315] Strongylus (Syn.: Sclerostomum) differs slightly in its posterior
ray from the other genera of the group. Each bifurcation is trifurcate
rather than tridigitate.
Genus. *Ancylostoma*, Dubini, 1843, emend. Looss, 1905.
Ventral margin of mouth capsule armed with teeth, the “roots” of which
are continued backwards and appear on the _external_ surface of capsule
as rib-like thickenings. Terminal third of dorsal ray cleft. Genital
tubes very long, with short, closely packed diagonal convolutions.
*Ancylostoma duodenale*, Dubini, 1843.
Male 9 mm. long by 0·45 mm. thick, female 12 mm. long by 0·6 mm. thick.
Pale flesh colour, or an intense red in posterior third. Anteriorly may
be more or less black due to (blood) pigment in the cells of the chyle
intestine (= stomach + small intestine). The worm is about the same
thickness all through and is plump and rigid. Cuticle striated. The
body has a marked torsion, so that if the ventral side of the head is
upwards the anus appears to open laterally and _vice versâ_. The dorsal
curve of the head end is only slight and the œsophagus is roughly
cylindrical.
_Buccal Capsule._--The buccal capsule is bent dorsally, 0·21 mm. long,
0·19 mm. broad. If a worm is rolled under the cover-glass so that the
dorsal side is upwards, we observe the following features (fig. 325):
In the dorsal edge of the chitinous capsule there is a gap as if a
*U*-piece had been punched out. This is the “dorsal gap or incision.”
The so-called “dorsal teeth” are simply the rounded edges of the tips
of this gap. They project _beyond_ the skin which covers the capsule
externally. Below this gap is seen a curved line which, if followed
along the sides of the capsule on each side, merges into the base of
the most posterior ventral tooth. This line is the optical expression
of a very shallow groove on the _inside_ of the capsule. The skin
on the outside of the capsule, which is reflected over the edge of
and into the capsule, dips into this groove, which gives it a firm
attachment. Below the middle (dorsally) of this curved line there is
a thickening in the capsule wall, which is perforated by the opening
of the dorsal œsophageal gland. This is the “dorsal ridge”; in optical
section it has a conical appearance with a lumen (of the duct).
[Illustration: FIG. 323.--_Ancylostoma duodenale_, male. _B_, bursa;
_Bm_, bursal muscles; _Cdr_, cement gland surrounding the ejaculatory
duct; _Glc_, cervical glands; _N_, nucleus of cephalic gland; _Nr_,
nerve ring; _T_, testes; _Sp_, spicule; _Vs_, vesicula seminalis. × 15.
(After Looss.)]
[Illustration: FIG. 324.--_Ancylostoma duodenale_, female. _A_, anus;
_Gcph_, cephalic gland; _N_, nucleus of cephalic gland; _Glc_, cervical
gland; _Ov_, ovary; _Pex_, excretory pore; _Rs_, receptaculum seminis;
_Ut_, uterus; _V_, vagina. × 15. (After Looss.)]
On the ventral wall one sees the two pairs of strong teeth, their
points being directed somewhat backwards. They are covered by cuticle
above and below, but their points are free, piercing the cuticle. The
“roots” of these teeth followed backwards appear as two thickenings
or ribs on the _outside_ of the capsule wall, so that the outside
wall is not smooth--a characteristic of the genus Ancylostoma. In the
space between these ribs lies the ventral nerve papilla, and lying
against the outside of the outer root the lateral nerve papilla. The
nerve papillæ are thus, as it were, concealed by these roots, and not
conspicuous as they are in Necator. Following the ventral curve of the
capsule on the inside, posteriorly we next find two triangular ventral
lancets.[316] These stand straight up into the capsule on either side
of the longitudinal axis, converging at their summits. So that to sum
up, the cutting apparatus is entirely ventral, consisting of two pairs
of cutting teeth and a pair of lancets.
[316] The ventral lancet (of one side) of Necator is seen in fig. 335.
_Cervical Papillæ._--Two, one on each side behind the head at the level
of the excretory pore. They consist of “pulp,” _i.e._, extensions of
the substance of the lateral bands covered by cuticle and supplied with
a nerve (fig. 326).
[Illustration: FIG. 325.--_Ancylostoma duodenale_: showing ventral
teeth, dorsal cleft, and behind it the dorsal ridge with duct of dorsal
œsophageal gland. × c. 200. (After Looss.)]
_Œsophageal Glands_ (3).--The chitin of the triradiate œsophagus is
continuous with that of the buccal capsule. In its muscular walls are
three glands--one dorsal, two sub-ventral. The dorsal gland opens into
the buccal cavity through the dorsal ridge; the two others into the
lumen of the œsophagus at the nerve ring. They branch freely amidst the
muscles. They are probably digestive in function.
_Cephalic Glands_ (2).--Lie in the lateral lines or bands on either
side. They begin about the middle line of the body, and their ducts
open at the base of the outer ventral tooth on the surface of the skin
on each side. Each is 0·15 mm. thick in the middle, and has a single
nucleus about as big as an ancylostome egg (_N_, fig. 323). They
probably function as poison glands.
_Excretory System and Cervical Glands_ (2).--The excretory pore lies
in the mid line ventrally behind the œsophageal nerve ring (figs. 324
and 326). It opens into the excretory vesicle, a cavity in a large
cell with lateral appendages which fuse with the lateral lines, this
cell thus forming the “bridge” of the excretory system. Adhering to
this (bridge) cell are the spindle-shaped cervical glands (_Glc_,
fig. 324), and branches from the excretory vesicle enter the glands,
which are excretory in function; the vesicle also receives branches
from the lateral excretory canals (fig. 326) running in the lateral
lines or bands. The cervical glands are swollen anteriorly, forming the
so-called ampullæ just in front of the bridge. They extend backwards a
little beyond the anterior loop of the testis.
[Illustration: FIG. 326.--_Ancylostoma duodenale_: diagrammatic
representation of excretory system. _ex.p._, excretory pore; _e.c.g._,
excretory cervical gland; _Ex. ves._, excretory vesicle in _B.c._,
bridge cell, which is connected with _c.g._, cervical gland, and
_l.l._, lateral lines; _ceph.g._, cephalic gland; _l.ex.c._, lateral
excretory canal passing into the bridge cell; l.l., lateral line
containing excretory canal and cephalic gland; _c.p._, cervical
papilla; _n._, nuclei of bridge cell. (After a drawing of Looss.)]
_Lateral Lines._--(1) Are broad elevations of the subcuticle, in which,
here and there, a nucleus occurs. (2) Near the bursa in the male they
increase in volume, and finally divide into branches which form the
“pulp” of the different rays. (3) In addition to the lateral lines or
bands, there is also a dorsal and ventral band. (4) The ventral band
is well developed caudally, forming a large pad dorsal to the cloaca,
“pulvillus post-analis.”
The bursal rays are outgrowths of the lateral lines. Beside this “pulp”
they contain a nerve, and at their bases complex muscles.
_The Bursa_ is closed on all sides with a short median (ventral) lobe,
which may be tucked inwards. It is an outgrowth of the inner layer of
the skin pushing the outer layer before it, so that it consists of
three layers, not four, as it would be if it were a fold. The bursa
is twice as broad as long. It is supported by a variety of rays, the
arrangement of which is best followed from the figure (fig. 327).
The different terminology for these rays as used by various authors
should be noted: Ventral = anterior; externo-lateral = antero-external;
medio-lateral + postero-lateral or antero-median + postero-median
= median (doubled); externo-dorsal = postero-external; dorsal =
posterior. All the rays end in tactile papillæ, seven, on each side;
the postero-external and antero-external on the _outer_ surface of the
bursa, the five others on the _inner_ surface.[317] Of the six terminal
digitations of the _dorsal_ ray, only the external two contain tactile
papillæ.
[317] This also occurs in other _Strongylidæ_, _e.g._, in the genus
Strongylus (Syn.: Sclerostomum).
In the male there are prebursal papillæ and minute caudal papillæ in
the female.
In the female the inner layer of the cuticle projects at the posterior
end as a sharp spike, 20 µ long, which may sometimes be broken off.
[Illustration: FIG. 327.--_Ancylostoma duodenale_: bursa enlarged.
_Ca_, anterior ray cleft; _cle_, antero-external; _cls_, antero-median;
_clp_, postero-median; _Cde_, postero external; _Cd_, posterior
bifurcated, each bifurcation tridigitate. (After Railliet.)]
_Ovaries._--The anterior tube runs from the cephalic to the posterior
end and back again. The posterior tube begins anteriorly, runs to
the posterior end of the body, and then back to the cephalic end,
forming a vulval loop before ending. The ovaries on the whole run in
oblique coils. The uterus is the thicker portion of the tube, 5 mm.
long. A short tube connecting the ovary and uterus is the oviduct.
The two uteri unite to form a single duct, the vagina, opening 1 mm.
_behind_ the middle line. The portion of the uterus next to the oviduct
functions as a seminal receptacle, whereas the part next the vagina
functions as an ovejector.
_Testis._--The blind end begins a little behind the beginning of the
_cement gland_. The transverse coils occupy the middle third of the
body. About the middle of the body it passes into the spindle-shaped
seminal vesicle, which, with the spicular canal and rectum, opens
into the cloaca. An anterior longitudinal coil pushing in between the
cervical glands is characteristic of Ancylostoma. The cement gland
surrounds the ejaculatory duct for practically its whole course, and it
occupies nearly the posterior half of the body and secretes a brown or
black cement. The spermatozoa are curved rods about 2 µ long.
_Spicules_ are 2 mm. long, ending in a fine point. They are moved by
exsertor and retractor muscles. At first they lie free in the body
cavity; next in a groove in the dorsal wall of the cloaca; then in an
isolated canal, and finally in two canals. Anteriorly each has two
longitudinal crests on its inner surface. These meet the corresponding
crests of the other spicule, and so form a canal along which the sperm
passes into the female. The gubernaculum is a thickening of the dorsal
wall of the cloaca. It is not a free piece, but is moved by various
muscles.
[Illustration: FIG. 328.--_Ancylostoma duodenale_: bursa of male. The
rays from left to right are: (1) anterior cleft; (2) antero-external;
(3) and (4) median doubled, _i.e._, antero-median and postero-median;
(5) postero-external arising from a common trunk with the posterior. ×
c. 120. (After Looss.)]
_Genital Cone_ is a prominence on the floor of the bursa on the ventral
side of the body, on which the genito-anal orifice opens. The cone
is only slightly marked in _Ancylostoma duodenale_, but is much more
prominent in _Necator americanus_.
_Distribution._--Africa, Egypt, Europe, Japan, China (mainly), but in
association with _Necator americanus_ in Southern States of America,
British India, Assam, Burma, Hongkong, Liberia, Jamaica, Martinique,
Costa Rica, Colombia, Antigua, Guadeloupe.
_Habitat._--The worms live in the jejunum, less frequently in the
duodenum, of man only.
_Food._--The worms feed on the mucous membrane of the gut, attaching
themselves to the base of the villi, sucking these in; and when these
are destroyed they attack further the submucosa. As a rule the worms
have no blood in the gut, but in their attack on the submucosa a
blood-vessel may be eroded, and so the gut of the worm filled with
blood.
_Development._--The eggs are oval with broadly rounded poles, 56 µ
to 61 µ by 34 µ to 38 µ. In _fresh_ fæces they contain four granular
nucleated segmentation masses of the ovum (fig. 329) separated by a
clear space from the shell.
_Egg of Ancylostome_ appears to have a single contour. Under high
powers this appears double, but they are the outer and inner surface
of the true (chitinous) egg-shell. Internal to this is the extremely
delicate yolk-envelope, a kind of skin secreted by the egg cell around
itself for protection. The function of this is probably to absorb water
to swell and burst the outer chitinous shell. The embryos when hatched
are termed larvæ.
_Embryos_ which are ready to hatch have their bodies almost free from
granules; others, though apparently mature, that have granules will not
hatch.[318]
[318] TABLE OF DIFFERENCES BETWEEN LARVÆ OF _A. duodenale_ AND _S.
stercoralis_.
--------------+----------------------+------------------------------
| _A. duodenale_ | _S. stercoralis_
--------------+----------------------+------------------------------
(1) Vestibulum| | }
oris |1·8 µ broad |3 µ }Rhabditiform.
(2) Genital | | }
rudiment|3 µ to 5 µ long |25 µ to 33 µ }
| |
(3) Thickness |Thicker | -- }
(4) Œsophagus |One-fourth body length|Half body length}
(5) Tail |Pointed |Two fine points }Filariform.
(6) Motion |Less active than | -- }
(7) Gut |Soon fills with dark | }
| granules | -- }
--------------+----------------------+------------------------------
[Illustration: FIG. 329.--_Ancylostoma duodenale_: eggs in different
stages of development. _a_ to _c_, in fresh fæces; _d_, containing a
larva, only in old fæces. × 336. (After Looss.)]
_Larva._--_Stage I_: Average length, 25 mm. Maximum thickness in
œsophageal region, 17 µ. Head end fairly blunt, from behind the
anus (the tail) tapering in an uniform manner. Buccal cavity is
characteristic, 10 µ to 12 µ by 1 µ to 8 µ, longer and narrower than
the corresponding larvæ of _Strongyloides stercoralis_. Œsophagus
“rhabditic” in character, _i.e._, it has three sections, but they are
not so clearly marked off as in larvæ of the genus Rhabditis. The
posterior bulb has a *Y*-shaped valve, the function of which, according
to Looss, is to prevent regurgitation of food. The granules of the gut
serve as a reserve of food, and are used up if the larvæ are starved.
The _genital rudiment_ consists of two cells half-way between the end
of the œsophagus and the anus in the mid-ventral line. The larva lives
on fæcal matter and grows to about 0·4 mm., then moult[319] I takes
place in two days or more, the skin being ruptured by the activity of
the larva.
[319] Moults take place by the formation of a new skin below the old
one, the two being in close apposition at first.
[Illustration: FIG. 330.--_Ancylostoma duodenale_ larva on fourth day
of culture on right; _Strongyloides stercoralis_ larva on left. (After
Leichtenstern.)]
_Stage II_: The larva is now in this stage, which does not differ much
from the previous one. It grows to 0·5 mm. The mouth opening closes.
The œsophagus elongates, becoming cylindrical or “filariform”; a new
skin is formed underneath the old one, and in about a week moult II
takes place.
_Stage III_: The _mature larva_ remains enclosed in the old skin. Its
movements are now much more active and of a boring character. Length is
now 0·6 mm. This mature stage has been erroneously called the encysted
larva, because there is no cyst _secreted_ from its surface by the
larva, but it is simply the old skin, which is not cast off, but is
retained for purposes of protection, as the larva is free living, but
casts it as soon as it assumes parasitic life again. From the egg to
this mature stage is thus six to ten days.
[Illustration: FIG. 331.--_Ancylostoma duodenale_: left, four days
after transmission into dog, 190/1; in the centre, at the commencement
of the second stage of development (five to six days), 105/1; on the
right, fourteen to fifteen days after transmission. 42/1. (After
Looss.)]
_Bionomics of Development._--_Air_: Eggs can develop when shut off from
the air for a “comparatively long” time.
_Temperature_: Hatching takes from eight hours upwards. Eggs develop
best at 25° to 30° C., but will not develop below 8° to 10° C. The
larvæ, however, will stand freezing.
_Moisture_: Eggs and larvæ do not live long under water, because they
suffocate or starve, but _mature_ larvæ will live for months (six to
twelve) in water; they require no food--in fact, can take none in--but
live on their reserve granules, and in course of time become as clear
as glass.
_Thigmotropism_: The mature larvæ, after casting their skin, will
penetrate pith, climb up stems, stalks, etc., and creep into any pore.
It is important to recognize that this third stage of the _mature
larva_ is the only infective one.
_Mode of Entry into the Body._--Infection is effected through the mouth
(Leichtenstern and others), and also through the skin, as was first
discovered by Looss and afterwards confirmed from the most diverse
quarters, partly in the case of _Ancylostoma duodenale_, partly in
that of _A. caninum_ in dog, man, and monkey. The larvæ that gain
access to the intestine partly through contaminated food, or through
unwashed hands, or under some circumstances through water, first throw
off their “sheath”--that is, they complete moult II. Moult III takes
place four to five days after they have reached the gut, and they now
have a mouth capsule supplied with four small teeth arranged crosswise,
enabling them to fasten on to the intestinal epithelium, upon which
they feed. On this food the worms grow in four to six days to 3 to
5 mm. in length, and now moult IV. takes place, thus attaining their
definite shape and distinctive character. About eight days later the
sexual organs commence to function; at this time the first copulation
should be taking place--it will later be frequently repeated--and a few
days later the first ova are laid, first in less and later in larger
numbers, so that they appear in the fæces about four to five weeks
after the infection.[320]
[320] From the number of eggs present in a given quantity of fæces, the
number of female Ancylostomes present in the gut can be reckoned by
a formula of Leichtenstern’s (x = _a_/47, in which _a_ signifies the
number of eggs counted in a single gramme of fæces).
_Infection by the Skin._--Mature larvæ, which are placed on the skin of
man or suitable animals, cast their “sheath” and bore their way through
delicate fissures either horizontal in the superficial scales of the
epidermis, or through vertical fissures into hair follicles where these
exist, and then they invade the cutis. Now according as they migrate
further into the lymphatic vessels or the small vesicles, the final
path to the gut differs to some extent. The blood path leads to the
right heart, and from there into the lungs; here the larvæ leave the
blood stream and enter the air passages, over the mucosa of which they
travel further headwards, through the bronchi into the trachea and
larynx, and from hence through the œsophagus to the stomach; in some
cases also they are swallowed. The lymphatic path leads finally also
into the blood stream, but the lymphatic glands must first be passed,
and in these many larvæ are retained and perish. In the cutaneous
infection seven to ten weeks elapse till the time of appearance of the
first ova in the fæces.
The penetration of the skin by the larvæ also in man causes reddening
and burning at the affected points, and this is followed in a
few days by transitory swelling in the subcutaneous connective
tissue. Skin affections can also be set up by such Ancylostoma
(and Strongyloides) larvæ as do not gain access to the blood or
lymphatic vessels or gut; such larvæ apparently wander further in the
connective tissue, and, as Looss has in his own person observed, gain
access to the cutis at different points, thus causing progressive
swellings (accompanied by intense itching), which cease when the
worm again penetrates into the deep tissues. Skin affections such
as “ground-itch” or “pani-ghao” occurring in the tropics and only
attacking the feet, or other affections (_e.g._, sump bunches) are
now well recognized as being due to the invasion of Ancylostoma larvæ.
Other names for these skin affections are water-sore, sore feet of
coolies, maza-morra, bunches, botches, quaddeln, krätze, ampoules,
gourmes, taons, pitirr. Whether oral or dermal infection is the more
important one further observation must decide.
The duration of life of _Ancylostoma duodenale_, which is a specific
parasite of man and has not been observed in other mammals, amounts to
about five years, as strayed larvæ according to Looss wander for this
extent of time in the body.
_Cultivation of Larvæ._--(1) Mix the fæces (free from drugs such as
salines or thymol) with animal charcoal, adding water if necessary till
a consistence of porridge is obtained. If the stools are very fluid,
allow to sediment first and pour off the fluid. The best charcoal is
that made from bones, and should not have an acid reaction. Charcoal
is necessary in order to prevent fermentation, which kills the larvæ.
Spread in layers 2 to 3 mm. thick in Petri dishes. Incubate at room
temperature. To extract the larvæ from the culture allow the surface
thoroughly to dry, then pour on water; the larvæ wander out and are
poured off and subsequently further purified by sedimentation or
filtering through blotting paper, the larvæ passing through.
(2) A funnel is plugged with cotton wool, then filled with washed sand
to within a centimetre or two of the rim. Stand this in a jar of water
so that the level of the water is slightly below that of the sand. On
the surface of the wet sand now place layers of blotting paper, and
spread the fæces, diluted if necessary, on this in layers of a few
millimetres thick (_vide_ p. 474).
_Detection of Eggs._--_Vide_ p. 473.
_Dermal Infection of Dogs._--Infection with larvæ of _A. caninum_. In
two hours most of the larvæ are free in the cutis and in four hours in
the subcutaneous tissue. By scraping a few days later the mucosa of the
trachea large numbers of larvæ are found there.
*Ancylostoma ceylanicum*, Looss, 1911.
[Illustration: FIG. 332.--_Ancylostoma ceylanicum_: head end, two teeth
on each side, the inner almost concealed by the outer. × c. 200. (After
Looss.)]
At the anterior edge of mouth capsule one large tooth; below or behind
this towards the middle line a very small tooth, the tip only of which
is seen. Male 5 mm. average. Lobes of bursa almost as long as broad,
strongly projecting towards the ventral side. Rays short and relatively
thick. Female 7 mm.
_Habitat._--Intestine civet cat (_Viverricula malacensis_), Ceylon, and
man in Bengal according to Clayton-Lane.
Other species are: _A. caninum_ (Ercolani), in cat and dog, Europe
and Africa; _A. malayanum_ (Alessandrini), 1905, in the Malay bear
(_Helaretos malayanus_); _A. pluridentatum_ (Alessandrini), 1905, in
_Felis mitis_, Brazil.
*Ancylostoma braziliense*, Gomez de Faria, 1910.
In cats (and dog), Brazil. Female 8·5 mm., male 7·5 mm. long. Eggs 65 µ
by 32 µ. Leiper considers it to be identical with _A. ceylanicum_.
[Illustration: FIG. 333.--_Ancylostoma braziliense_: bursa of male.
(After Gomez de Faria.)]
Group. *Bunostomeæ*, Railliet and Henry, 1909.
Bursa with median double, postero- and postero-external arising from a
common trunk, posterior bifurcated, each limb bidigitate (fig. 336).
Vulva in middle of body or a little in front. Uteri divergent.
Contains the following genera: (1) Bunostomum (= Monodontus); (2)
Necator; (3) Bathmostomum; (4) Gaigeria.
Genus. *Necator*, Stiles, 1903.
Mouth capsule small, narrowed anteriorly (ventrally) by chitinous
plates, as in Uncinaria. On each side of the base of the dorsal cone
a lateral chitinous plate or lancet with smooth edge (not serrated),
ventral lancets as in Ancylostoma. No ridges on outside of ventral
wall. Aperture of dorsal œsophageal gland on tip of a cone projecting
freely into the buccal capsule. Bursa closed. Posterior ray cleft to
its root.
*Necator americanus*, Stiles, 1902.
Syn.: _N. africanus_, Harrison, 1910.
[Illustration: FIG. 334.--_Necator americanus._ Showing cutting plates
and the projecting dorsal ridge, and deep in the cavity the edges of
the ventral lancets. × c. 475. (After Looss.)]
Male 8 mm. long, female 10 mm. The head is strongly bent dorsalwards
so that almost by this character alone it can be distinguished from
_Ancylostoma duodenale_. The buccal capsule is markedly small--in
the male, 0·093 by 0·084 mm., in the female 0·11 by 0·097 mm. There
are no teeth anteriorly on the ventral side of the capsule, but
instead there are two cutting chitinous plates, the anterior portions
of which are prominent and angular, and meet in the middle line
in front. Posteriorly on each side the plate projects less, while
between the anterior and posterior parts there is a deep angle. The
inner (posterior) ventral lancets which also occur in _A. duodenale_
are large, and project far into the lumen, the tips of these, of the
lateral lancets, and of the dorsal cone almost meeting in the centre of
the lumen. As already stated in the definition of the genus Necator,
there are also lateral lancets which start from the base of the dorsal
cone. This dorsal ridge, or rather in this case cone, is a striking
object in the mouth, and projects right out into the cavity, and on
its summit opens the dorsal œsophageal gland.
[Illustration: FIG. 335.--_Necator americanus_: lateral view, showing
the dorsal ridge perforated by the duct of the dorsal œsophageal gland,
the lateral lancet and ventral lancet and the nerve papillæ. × c. 475.
(After Looss.)]
The bursa is about as long as broad, but has the lateral lobes
strikingly lengthened, giving a trilobed appearance (fig. 336), but
as in _Ancylostoma duodenale_ it is closed on the ventral side. The
distribution of the rays is best understood from the figure. The
genital aperture lies on a marked conical protuberance; the cement
gland is bilobed in transverse section. In the female the opening of
the vulva is in front of the middle line, in _A. duodenale_ it is
behind.
The spicules, 0·92 mm. long are hooked at the extremity.
[Illustration: FIG. 336.--_Necator americanus_: bursa of male. The rays
from right (top) to left are: (1) posterior, (2) postero-external,
(3) and (4) median doubled, _i.e._, postero-median and antero-median,
(5) antero-external, (6) anterior (cleft), and above it on left a
pre-bursal ray. × c. 120. (After Looss.)]
Eggs more pointed at the poles than those of _A. duodenale_, 64 µ to
72 µ by 36 µ, so that it may not be possible to distinguish single eggs
owing to individual variations, yet on comparing a number they can be
distinguished.
_Geographical Distribution._--Brazil, Porto Rico, Cuba, Central Africa,
East Africa, Victoria Nyanza, Gold Coast, Uganda, North-Western
Rhodesia, Ceylon, Mysore. For other localities where _A. duodenale_ is
also found see p. 450.
_Habitat._--In small intestine of man and gorilla (_Troglodytes
gorilla_).
*Necator exilidens*, Cummins, 1912.
Syn.: _N. africanus_, Looss, 1911.
Male 7 mm., female 9 mm. long. The edges of the cutting plates are
rounded, not angular, and do not meet in the middle line. Inner
(posterior) ventral lancets very small. Lateral lobes of bursa broader
than long. Rays thick and plump.
_Habitat._--In the chimpanzee (_Anthropopithecus troglodytes_).
ANCYLOSTOMIASIS.
_Morbid Anatomy._--Organs pale and bloodless. Abdominal organs sodden,
and there is fluid in the serous cavities. Lungs: œdema. Kidneys: fatty
changes, especially large pale kidney. Liver and heart also show fatty
changes--there is much hæmosiderin in the liver cells. Blood: early
stages, a leucocytosis 20,000 upwards, and eosinophilia 50 per cent.
Later, anæmia (hydræmia). The number of worms found varies from ten to
1,000. They are rare in the duodenum, but occur as far as 6 ft. from
the pylorus.
Group. *Syngameæ*, Railliet and Henry, 1909.
Bursa with anterior and median ray cleft; antero-external, close to
median; postero-external, arising separately from posterior; posterior
bifurcate to base, each branch bifurcate or trifurcate. Vulva in the
anterior fourth of body. Uteri divergent.
Genus. *Syngamus*, von Siebold, 1836.
Head thickened, not tapering; broad mouth with gaping buccal capsule.
Male and female often in permanent copulâ.
Parasitic in respiratory passages of birds and mammals.
_Habitat._--_S. trachealis_ in poultry; _S. bronchialis_ in goose; _S.
laryngeus_ in cattle; _S. vasicola_ in goats, etc.
*Syngamus kingi*, Leiper, 1913.
Buccal capsules of male and female on same level. In _S. trachealis_
and _S. laryngeus_, that of male in front of that of female. In
_S. dispar_, that of male behind that of female. Œsophagus of male
one-sixth, that of female one-ninth of total length. Mouth capsule
in male and female terminal; it is dorsal in _S. trachealis_ and in
mammalian species. Tail of female bluntly pointed. Ovary reaches to
anus. Excretory pore opposite the middle of the bulb of œsophagus. In
_S. trachealis_ it is opposite the œsophageal valves.
_Habitat._--Found in sputum of patient by King in St. Lucia. Normal
host probably a carnivore.
[Illustration: FIG. 337.--_Syngamus kingi_: anterior end of male.
(After Leiper.)]
[Illustration: FIG. 338.--_Syngamus kingi_: anterior end of female.
(After Leiper.)]
Family. *Physalopteridæ.*
Genus. *Physaloptera*, Rudolphi, 1819.
Mouth surrounded by _two_ large lateral lips bounded posteriorly by
a cuticular band projecting anteriorly, forming a collar. Each lip
bears anteriorly and inwardly a cuticular appendage, the external
tooth. Immediately below and internal to the external teeth the
internal teeth, one on each lip. Each lip bears two large submedian
papillæ. Tail of male with four pairs of pedunculated papillæ in a
row on each side external to the six pairs of unpedunculated papillæ.
Spicules unequal. Vulva in the anterior region of the body. Eggs with a
characteristic thick smooth shell.
Parasitic in the intestine, more especially the stomach, of mammals
(twenty species), birds (twelve species), reptiles (fourteen species).
*Physaloptera caucasica*, v. Linstow, 1902.
The male measures 14·2 mm. in length and 0·71 mm. in breadth; the bursa
is broad, rounded off in front and narrower at the back; the right
spicule measures 0·62 mm. in length, the left spicule 1·76 mm.; there
are two papillæ in front of the orifice of the cloaca, four behind
it and six unpedunculated on the tail. The female measures 27 mm. in
length, 1·14 mm. in breadth; the caudal extremity is rounded off; the
vulva is on the border of the first and second sixth of the length of
the body; the eggs have thick shells, and measure 57 µ by 39 µ. It has
hitherto only been observed once, by Ménétriés in the intestine of man
(Caucasus).
[Illustration: FIG. 339.--Bursa of _Syngamus trachealis_. _a._,
anterior ray cleft; _a.e._, antero-external; _m.a._, antero-median;
_m.l._, postero-median; _p.e._, postero-external; _p._, one branch of
posterior (trifurcate). (Stephens.)]
*Physaloptera mordens*, Leiper, 1907.
Large worms resembling an immature _Ascaris lumbricoides_.
The inner lancet-shaped teeth have a sharp cutting edge towards the
lumen. Below each is a cuticular boss projecting into the mouth
(fig. 340).
Male 30 to 50 mm., bursa with four pairs of pedunculated papillæ, the
second and third lying external to the first and fourth on each side.
Spicules unequal, one slender (4·6 mm.), the other stouter (6 mm.).
Female 40 to 55 mm. Tail sharp. Vulva opens between the anterior fourth
and fifth of the body. Eggs 43·6 µ by 35·3 µ with a thick smooth shell.
_Habitat._--Œsophagus, stomach, small intestine of man (several cases).
Nyasaland and Portuguese East Africa.
Family. *Ascaridæ*, Cobbold, 1864.
Sub-family. *Ascarinæ.*
Without œsophageal or intestinal diverticula; spicules without flanges.
Genus. *Ascaris*, L., 1758.
Intermediate lips and auricles absent. Lips edged with fine teeth.
Lips triangular in cross section. Not grooved on internal surface.
[Illustration: FIG. 340.--_Physaloptera mordens_, Leiper, 1907. (*1*)
adult male: _o.e._, œsophagus; _ch.i._, chyle intestine; _t.c._,
testicular coils; _ves. sem._, vesicula seminalis; _sp._ 1, long
spicule; _sp._ 2, short spicule; _B._, bursa. (*2*) Mouth parts:
_c._, cuticular collar embracing the two lips posteriorly; _c.b._,
cuticular bosses guarding the mouth laterally; _e.d._, external tooth;
_i.d._, internal tooth; _sm.p._, submedian papillæ. (*3*) egg of _P.
caucasica_. (*4*) egg of _P. mordens_. (*5*) bursa enlarged: _ped.p._,
pedunculated papillæ; _ses.p._, sessile papillæ. (After Leiper.)]
*Ascaris lumbricoides*, L., 1758.
The colouring, in the fresh condition, is reddish-yellow or
greyish-yellow; the body is of an elongated spindle shape. The oral
papillæ are finely toothed. The dorsal papilla carries two sensory
papillæ, the two ventral papillæ each one sensory papilla. The
male measures from 15 to 17 to 25 cm. in length, and about 3 mm.
in diameter; the posterior extremity is conical and bent hook-like
ventrally; the spicules measure 2 mm. in length, are curved, and
somewhat broadened at their free end; on each side around the orifice
of the cloaca there are seventy to seventy-five papillæ, of which
seven pairs are post-anal. The testicular tube is much folded, showing
through the body integument, and is about eight times the length of
the body. The female measures 20 to 25 to 40 cm. in length and about
5 mm. in diameter; the posterior extremity is conical and straight.
The vulva is at the junction of the anterior and middle thirds of the
body, which, at this point, has a slight ring-like constriction; the
convoluted ovaries measure ten times the length of the body.
[Illustration: FIG. 341.--_Ascaris lumbricoides._ _a_, posterior
extremity of the male with the spicules protruding from the orifice of
the cloaca (_Sp._); _b_, anterior extremity from the dorsal surface,
the two lobes of the pulp of the lip separated by the “saddle”; _c_,
anterior extremity from the ventral surface; _P._, excretory pore.
(From Claus.)]
[Illustration: FIG. 342.--Ovum of _Ascaris lumbricoides_, with shell
and albuminous envelope. 400/1.]
The ova are elliptical with a thick (4 µ) transparent shell (fig. 342)
and an external albuminous coating which forms protuberances; the ova
measure 50 µ to 70 µ in length, 40 µ to 50 µ in breadth; they are
deposited _before_ segmentation; the albuminous coating is stained
yellow by the colouring matter of the fæces, but is sometimes absent.
The egg cell is unsegmented, it almost completely fills the shell, and
its nucleus is concealed by the large amount of coarse yolk granules.
Abnormal or unfertilized eggs also occur in fæces. They are
distinguished by their elongated form (80 µ by 45 µ), irregularly
cylindrical, its contents consisting of refractive granules.
_Ascaris lumbricoides_ is one of the most frequent parasites of man; it
is distributed all over the inhabited parts of the world, and though
it is particularly frequent in the warmer regions, yet it also occurs
in Finland, Greenland, etc. In temperate climates _A. lumbricoides_
occurs most frequently in young children; it is, moreover, more common
amongst country dwellers than amongst the inhabitants of towns, but is
not lacking in infants, adults and aged persons. As a rule only a few
specimens are present in the intestine, but many cases are known in
temperate zones in which several hundreds of worms have been found in
the same patient. This species is particularly numerous in the negroes
of Africa and America. It occurs also in the monkey, dog and pig (? _A.
suilla_).
The parasite was known in ancient times; the Greeks called it ἐλμινς
στρογγύλη, Plinius termed it _Tinea rotunda_, later on it was named
_Lumbricus teres_. The ἄσκαρις of the Greeks is our Oxyuris.
The small intestine is the normal habitat of _Ascaris lumbricoides_;
the worms, however, often leave this part of the intestine and wander
into the stomach, whence they are frequently evacuated by vomiting,
or they may creep through the œsophagus into the pharynx and crawl
out through the nose or mouth; very rarely they may find their way
into the Eustachian tube or into the naso-lachrymal duct, or into
the excretory ducts of the liver and pancreas; exceptionally they
may gain the trachea, and they have also been found in the abdominal
cavity. They may bore through adhesions between the intestinal wall
and the omentum (worm abscess); they occasionally penetrate the
urinary apparatus and are passed with the urine; in febrile diseases
_A. lumbricoides_ usually leaves the intestine spontaneously. It is
obvious that these wanderings may be accompanied by the most serious
symptoms, but in sensitive persons the invasion of even only a few
intestinal Ascarides gives rise to a series of almost inexplicable
symptoms (hysterical, epileptiform attacks, cerebral congestion,
aphonia, etc.), which cease with the expulsion of the worms, so
that many authors are driven to the conclusion that these Ascarides
secrete a toxin. Fortunately, the presence of _A. lumbricoides_ in
the intestine is easily demonstrated by the microscopical examination
of the fæces.
_Development._--Several authors (Gros, Schubart, Richter, Leuckart and
Davaine) have demonstrated that the ova of Ascaris develop in water or
moist earth after a long period of incubation. Freezing and desiccation
(if not too long) do not injure their powers of development; the
duration of the development depends on the degree of the surrounding
temperature. At a medium temperature, after a varying period of
incubation, it takes from thirty to forty days for the embryo to become
formed. The spirally rolled up embryo, with its so-called “tooth,”
formed by three papillæ close together, never leaves the egg-shell
in the open, even if the eggs are kept for years under favourable
conditions. Davaine proved that the larvæ hatch out in the intestine of
the rat, but are again expelled with the fæces; he therefore concluded
that the hatching likewise takes place within the intestine of man,
but is followed by the invasion of the larvæ. In the meantime Leuckart
had sought to infect himself by swallowing embryo-containing eggs,
but without results; he therefore conjectured that there must be an
intermediary host, and v. Linstow thought he had found it in myriapods
(_Julus guttulatus_). Subsequently, Davaine’s opinion proved correct.
First of all Grassi succeeded in infecting himself by swallowing 100
embryo-containing eggs of _Ascaris lumbricoides_; five weeks after
ingestion the worms had attained maturity and their ova appeared in
the fæces. Calandruccio also sought to infect himself, but failed,
yet he succeeded in infecting a little boy aged 7. Lutz also reports
a successful experiment which must have been positive, as young worms
5·5 to 18 mm. long were expelled. Lutz proved that the eggs lost their
albuminous shell by long lying in water and then died when introduced
into the stomach; this would explain the failure of Leuckart’s
experiment; in moist earth the albuminous shell is retained. Finally,
Epstein conducted unimpeachable experiments on three children which
place direct infection with embryo-containing eggs beyond doubt; he,
moreover, proved that the development of the eggs takes place more
rapidly in the fæces when there is free admission of air, sun, and a
sufficiency of moisture.
Accordingly, infection occurs partly through water, but principally
direct from the soil.
*Ascaris*, sp.
Wellmann states that yet another species of Ascaris in man occurs in
the highlands of Angola: up to the present nothing certain is known
about it (Welland, “Critical Notes on Tropical Diseases of the Angola
Highlands,” _New York Med. Journ. and Philadelphia Med. Journ._, August
12 to September 2, 1905.)
*Ascaris texana*, Smith et Goeth, 1914.
Female alone known; 58 to 60 mm. and upwards in length; characterized
by the serration of the anterior border of the lip and by the
appearance of interlabia. Evacuated by a white settler in Texas.
Position of this worm doubtful.
*Ascaris maritima*, Leuckart, 1876.
Only one immature specimen, a female (43 mm. in length and 1 mm. in
breadth), has hitherto been described, and it was vomited by a child in
North Greenland in 1865. (R. Leuckart, “Die menschlichen Parasiten,”
1876, edition 2, i, p. 877.)
Genus. *Toxascaris* (τόξον, an arrow), Leiper, 1907.
Body anteriorly bent dorsally, cuticle finely striated. Œsophagus
without a distinct bulb. Tail of male tapers to a point. Testis in
anterior portion of posterior half of body. Vulva about middle of body.
Eggs oval and smooth.
*Toxascaris limbata*, Railliet and Henry, 1911.
Syn.: _Lumbricus canis_, Werner, 1782; _Ascaris teres_, Goeze, 1782;
_Ascaris cati_ et _caniculæ_, Schrank, 1788; _Ascaris canis_ et
_felis_, Gmelin, 1789; _Ascaris tricuspidata_ et _felis_, Bruguiere,
1791; _Ascaris werneri_, Rud., 1793; _Fusaria mystax_, Zeder, 1800;
_Ascaris marginata_ et _mystax_, Rud., 1802; _Ascaris alata_,
Bellingham, 1839.
Striations 6 µ to 12 µ apart. Cephalic wings long, narrow,
semi-lanceolate. Male, 4 to 6 cm. Spicules, 1,002 µ and 1,005 µ.
Female, 0·5 to 10 cm. Eggs, 75 µ to 85 µ, shell thick and smooth. Host:
dog, occasionally man.
[Illustration: FIG. 343.--Ovum of _Toxascaris limbata_, with thin
albuminous envelope. Magnified.]
[Illustration: FIG. 344.--Transverse section through the head part of
_Belascaris cati_ from the cat, with the lateral wings. In addition,
one may note the four fields of muscles, the longitudinal lines with
the œsophagus in the centre. Magnified. (After Leuckart.)]
Genus. *Belascaris* (Βέλος, an arrow), Leiper, 1907.
Body anteriorly bent ventrally, cuticle coarsely striated. Œsophagus
with a distinct bulb. Tail of male conical. A papillæ-bearing
protuberance behind the anus. Testis in anterior half of body. Vulva in
anterior part of body. Eggs corrugated.
*Belascaris cati*, Schrank, 1788.
Syn.: _Belascaris mystax_, Leiper, 1907; _Ascaris mystax_.
Striations 12 µ to 16 µ apart. Cephalic wings lanceolate. Male 3 to
6 cm. Spicules 17 to 1·9 mm. Female 4 to 10 cm. Eggs, 65 µ to 75 µ in
diameter, surface finely honeycombed. Host: domestic cat, and man,
eight or nine cases.
*Belascaris marginata*, Rudolphi, 1802.
Striations 16 µ to 22 µ apart. Cephalic wings long, narrow,
semi-lanceolate. Male, 5 to 10 cm. Spicules, 750 µ and 950 µ. Female, 9
to 18 cm. Eggs, 75 µ to 80 µ. Shell finely honeycombed. Host: dog.
Genus. *Lagocheilascaris*, Leiper, 1909.
Thick lips separated by a furrow from the body; between the lips
small intermediate lips without “pulp.” The cutting angle of each lip
bifurcated. Along each lateral line a cuticular wing extending the
whole length of the body. Eggs, thick shell with a mosaic pattern.
*Lagocheilascaris minor*, Leiper, 1909.
Male, 9 mm., tail sharply curved. Spicules colourless, 3·5 and 4 mm.
long. More than twenty-four pairs of pre-anal papillæ, at least five
pairs of post-anal. Female, 15 mm. Straight posteriorly. Vulva 6 mm.
from head with two lips. Eggs, 65 µ in diameter. Host: man, cutaneous
abscesses. Trinidad.
Family. *Oxyuridæ.*
Genus. *Oxyuris*, Rudolphi, 1803.
Mouth unarmed. The three labial papillæ are only slightly
protuberant, the œsophagus is long and presents two well-marked
bulbs. The vulva is in the anterior part of the body.
*Oxyuris vermicularis*, Linnæus, 1767.
Syn.: _Ascaris vermicularis_, L.; _Fusaria_, Zeder, 1803.
Colour white, the striated cuticle forms projections at the anterior
end which extend some distance back along the middle of the ventral
and dorsal surfaces; the longitudinal lateral flanges of the skin
corresponding to the lateral lines are well seen in transverse
sections; there are three small retractile labial papillæ around the
mouth. The male measures 3 to 5 mm. in length, and shortens on death;
the posterior extremity of the body is curved ventrally and presents
six papillæ. Spicule 70 µ long, hook-like. The female is 10 mm. in
length and 0·6 mm. in diameter; the anus is about 2 mm. in front of
the tip of the tail; the vulva is in the anterior third of the body;
the eggs are oval, asymmetrical, with double-contoured shells, and
measure 50 µ to 55 µ by 16 µ to 25 µ; they are deposited with clear,
non-granular tadpole-like embryos already developed.
_Habitat._--Adults in large intestine of man. Young forms in small
intestine and often in the appendix.
The worm lives in the lower part of the small intestine, cæcum and
vermiform appendix, and before becoming adult undergoes two or three
moults (Heller). According to Wagener the worms at times live in the
gut wall, giving rise to calcareous nodules. When the uterus of the
fertilized females begins to fill with eggs they leave the cæcum and
travel through the colon to the rectum. The uterus is now packed with
eggs which contain a tadpole-shaped embryo. Egg-laying now takes
place, partly in the rectum, partly outside, the mode of exit being
not only passive through defecation but also an active one on the
part of the worms when the patient is in bed. In this case the worms
crawl out of the anus, producing a most intolerable itching as they
scatter their eggs between the nates and the perinæum. From here
in the case of girls they may get occasionally into the vulva and
vagina, and even into the oviducts and so into the body cavity. The
worms also may wander through the alimentary canal in the opposite
direction, getting out occasionally through the mouth. Recently a
_rôle_ has been assigned to them, as to other gut parasites, in
appendicitis and typhlitis.
It is stated that the males die after fertilizing the females,
thus explaining why they are so rarely met with in fæces [but
it is probable that they often escape notice from their small
size.--J. W. W. S.].
[Illustration: FIG. 345.--_A_, male, and _B_, female, of _Oxyuris
vermicularis_. 5/1.]
[Illustration: FIG. 346.--On the left, female; on the right, male. _A_,
anus; _M_, mouth; _V_, vulva. Greatly enlarged. (After Claus.)]
[Illustration: FIG. 347.--_Oxyuris vermicularis_: egg freshly
deposited, with tadpole-like embryo. × 640.]
[Illustration: FIG. 348.--_Oxyuris vermicularis_: egg twelve hours
after deposition, with nematode-like embryo. × 640.]
_Development._--The eggs, which often adhere together, contain a
tadpole-like embryo, the thin tail of which is bent upwards ventrally;
the embryo in a short time, given a sufficiently high temperature,
passes into a second folded nematode-like embryonal stage, lying in the
egg-shell, either in the fæces, with which also numerous females pass
out, or in the moisture of the groove between the buttocks, and they
there await the opportunity of being reintroduced into man _per os_. It
is very improbable that infection takes place directly in the large
intestine, as is occasionally stated, because although the harbourers
of Oxyuris are frequently liable to auto-infection, this takes place
exclusively through the mouth, and is conveyed by the fingers, on which
the ova of Oxyuris, and occasionally the female worms, have clung.
The opportunity for this is afforded every evening, as naturally the
troublesome itching caused by the wandering of the worms is met by
scratching and rubbing with the fingers. It is therefore possible
that the eggs may even thus be introduced into the nose, where the
young Oxyuris are perhaps hatched out, if they get high enough up on
the moist pituitary mucous membrane. As a matter of fact, the larvæ
of Oxyuris have been found in the nose. Moreover, one can understand
that the eggs of Oxyuris are transferred from person to person by
the hand, directly or indirectly. This again explains the wholesale
infections which occur in collective dwellings, after a person
harbouring Oxyuris has been admitted into boarding-houses, etc. The
primary infection may be also caused in other ways--by foods, fruits,
vegetables and other articles that are eaten raw, and are polluted
with the ova. Perhaps also flies or their excrement play a part in
the distribution of the parasite, similar to that demonstrated by
Grassi as taking place in the spread of the ova of Trichocephalus and
Tænia.
The assumption of a _direct development_ without an intermediary host
was first substantiated by Leuckart by experiments on himself and
three of his students; about fourteen days after swallowing the eggs
the Oxyuris has attained 6 to 7 mm. in length; Grassi, and later on
Calandruccio, infected themselves by swallowing adult female Oxyuris,
with the same results. Heller found worms in the gut (appendix
vermiformis) of a male child five weeks old.
Other species are: _O. compar_ in the cat; _O. curvula_ and _O.
mastigodes_ in horse, ass, mule; _O. ambigua_ in the rabbit; _O.
poculum_ in the horse; _O. tenuicauda_ in the horse. Many species
occur in insects, especially in _Blattidæ_ and _Hydrophilidæ_
(aquatic beetles).
Family. *Mermithidæ.*
Genus. *Mermis*, Dujardin, 1845.
With characters of the family.
*Mermis hominis oris*, Leidy, 1850.
Fourteen centimetres in length, 0·16 mm. in breadth; mouth terminal;
posterior extremity obtuse and provided with a recurved hook 50 µ long.
The parasite was “obtained from the mouth of a child.” Stiles
considers it to be probably a Mermis, possibly swallowed in an apple.
*Agamomermis*, Stiles, 1903.
Group name for immature _Mermithidæ_.
*Agamomermis restiformis*, Leidy, 1880.
This worm measures 65 cm. in length, pointed anteriorly, the posterior
extremity broadened and rounded off (1·5 mm. in breadth); the mouth is
terminal, without lips. Behind the mouth six papillæ; the œsophagus
measures 1·125 mm. in length; the intestine appears to terminate
blindly.
This parasite was obtained in West Virginia from the urethra of a
young man, aged 20, who for a few days previous to expelling the worm
passed turbid and bloody urine.
TECHNIQUE.
PRESERVATION AND EXAMINATION OF FLUKES.
_Fixation._--(Method A.) (1) Place the flukes in a test tube or small
bottle a quarter full of normal saline. Shake the contents _as hard as
possible_ (the object of this is to _extend_ the flukes) for half a
minute.
(2) Add _immediately_ an equal bulk of saturated aqueous solution of
corrosive sublimate and shake again as vigorously as possible for a few
minutes.
(3) Transfer when convenient to 70 per cent. alcohol. (Before staining
and mounting remove the sublimate with tincture of iodine.)
(Method B.) In case of large flukes, _e.g._, _Fasciola hepatica_,
_Fasciolopsis buski_, compress the flukes between two glass slides with
rubber bands or thread. Fix in sublimate or in absolute alcohol, or in
10 per cent. formalin.
(Method C.) Place the flukes in 10 per cent. formalin solution.
_Staining_ is successfully effected by using quite _dilute_ solutions
of carmine or hæmatein overnight. This is far preferable to using
strong solutions, as it may be almost impossible to remove a too
intense stain. Almost any dilute carmine solution suffices. One of the
best is acetic-alum carmine (boil excess of carmine in a saturated
aqueous solution of potash-alum for about fifteen minutes; add glacial
acetic acid to the extent of 10 per cent.; let it stand for a week;
filter). For use, dilute about thirty times with water. Place the
flukes directly in the stain. Stain overnight or longer.
_Differentiation._--In order to get the sharpest picture, it is best
now to differentiate (but this may often be omitted) with acid alcohol
(70 per cent. alcohol 100 parts, HCl 5 drops). Allow to act from one
to twenty-four hours, according to the appearance of the flukes.
Similarly, in staining with _hæmatoxylin_ solution, dilute twenty
to thirty times so that the water is merely tinged with the stain.
Differentiate as before. After staining, dehydrate, clear, and mount in
balsam if required.
_Clearing and Mounting._--(1) _Carbolic acid_ (carbolic acid 94,
water 6) is a very convenient clearing agent. It may be used for
stained or unstained specimens. It will clear rapidly without previous
dehydration. If it is required to mount a specimen permanently,
transfer from carbolic to alcohol, then cedar-wood oil (or xylol,
etc.), then balsam.
(2) _Creasote._--Dehydrate the specimen, stained or unstained, transfer
to creasote. If it is desired to mount permanently, transfer back to
alcohol, then cedar-wood oil, then balsam.
(3) _Cedar-wood Oil._--Preferable to xylol or oil of cloves. Dehydrate
the specimen in alcohol. To mount permanently, transfer to balsam.
(4) _Glycerine._--_Vide_ under methods of preservation of ova; to mount
permanently, transfer to glycerine jelly; subsequently to harden the
jelly, expose to formalin vapour.
Of these media, carbolic acid has the greatest refractive index
excepting that of balsam. The latter may, in some cases, render
structures too transparent, and it may be advisable to use only
glycerine or glycerine jelly.
PRESERVATION OF OVA IN FÆCES, URINE, BILE, ETC.
Heat some 70 per cent. alcohol in a basin to about 60 to 70° C. (until
bubbles begin to appear). Add the fæces, etc., in the proportion of one
part to about nine of fixative; keep stirring. Allow the sediment to
settle. Transfer to a bottle with some fresh 70 per cent. alcohol.
_Transference to Glycerine._--Prepare 5 per cent., 10 per cent., 20
per cent. solutions of glycerine in 70 per cent. alcohol. Pour off
the alcohol in the bottle of fæces, etc., and replace by 5 per cent.
glycerine solution. Allow to stand an hour or so. Then in the same way
replace the 5 per cent. by a 10 per cent. glycerine, and finally by a
20 per cent. glycerine solution. When in this latter expose freely to
the air (protecting from dust), so as to allow the alcohol and water
to evaporate. Add a few drops of glycerine from time to time till
eventually the ova are in pure glycerine. (In a very moist climate it
may be necessary to use lime or calcium chloride to dry the air.) To
mount permanently transfer some of the sediment to glycerine jelly.
PRESERVATION AND EXAMINATION OF CESTODES.
_Fixation._--(1) _Saturated aqueous corrosive sublimate._--Add to this
glacial acetic acid to the extent of 1 per cent. (Note this fixative
will dissolve the “calcareous corpuscles”; 10 grammes of sublimate to
160 c.c. of water will give a saturated solution.) Warm the fixative
to 70° to 80° C. (Avoid the use of needles.) Use plenty of fixative.
Allow to act for a quarter of an hour or so. (_a_) Transfer to 70 per
cent. alcohol. (It is advisable to remove the sublimate by the use of
Lugol’s solution, or a solution containing tincture of iodine, adding
this until the iodine colour is permanent.) Or (_b_) transfer for
preservation to 10 per cent. formalin.
Or (2) 10 _per cent. formalin_.--In order to prevent contraction it is
advisable to extend the tapeworm and keep it fixed by glass plates, or
wind the worm around a wide glass tube or bottle, and then fix it.
Or (3) _fix in hot alcohol_.
_Staining._--As under flukes. It is necessary to sacrifice portions of
the tapeworm for this purpose, cutting out, _e.g._, mature segments, so
as to study the topography of the genitalia.
_Clearing._--As under flukes. To examine the hooks satisfactorily it is
best to cut off the head with a sharp knife and mount. A certain amount
of pressure is then advisable in order to view the hooks completely so
as to measure them.
PRESERVATION OF OVA IN FÆCES, ETC.
As under flukes.
PRESERVATION AND EXAMINATION OF NEMATODES.
_Fixation._--(1) Thoroughly wash the worms to get rid of mucus, etc.,
by shaking up in warm saline (or water) till the washings are clean.
Then transfer to 70 per cent. alcohol _heated_ to about 70° C. It is
absolutely necessary to use _hot_ fixatives in order to _extend_ the
worms. If no alcohol or spirit is immediately available, drop the worms
into _hot_ water, or saline, and transfer later to 70 per cent. alcohol.
(2) Drop into hot 10 per cent. formalin.
_Clearing._--(1) Carbolic acid, _vide_ p. 471.
(2) Creasote, _vide_ p. 471.
(3) Glycerine, _vide_ p. 472.
_Staining._--In case of quite small Nematodes, _e.g._, _Anguillulidæ_,
carmine may be used, but as a rule staining is not advantageous.
_Rolling._--In order to study the mouth parts, or bursa, etc., it is
necessary to place the worm in any desired position. This is done as
one would roll a penholder along the table by one’s finger placed on
top of it. In the case of a worm, one edge of the cover-glass is placed
over the worm, the other is supported by a strip of cardboard. By
tapping the cover-glass the worm will now revolve as much as required
provided it is _round_ and _straight_. In certain cases it may be
necessary for this purpose to cut off the head or tail. Roll these
separately.
When a suitable position is got, the worm may be fixed in this position
by pressure on the cover-glass, so as slightly to flatten it.
_Mounting the Head._--If it is required to get an end view, it is
necessary to cut off the head transversely as near the end as possible,
and then mount.
_Detection of Eggs_ (Bass and Hall).--Mix the fæces thoroughly with
ten times the volume of water. Filter through gauze. Centrifugalize
the filtrate. Wash the sediment and centrifugalize. Repeat twice.
To sediment add CaCl_{2} solution, sp. gr. 1250. The eggs float
to surface. Pour off surface fluid. Dilute to sp. gr. 1050.
Centrifugalize. Examine sediment, which contains practically all the
eggs in the stool.
_Detection of Small Nematodes._--Mix the fæces thoroughly with water.
Allow to settle for five minutes. Carefully decant off, or better,
syphon off the fluid. Mix the sediment again with water. Allow to
settle. Remove the fluid. Repeat several times. Examine the sediment
in a Petri dish. As the fluid is poured off, the worms will be seen
collected in the backwater. Remove them with a brush. Fix in hot 70 per
cent. alcohol.
CULTIVATION OF LARVAL FORMS OF ANCYLOSTOMA AND STRONGYLOIDES.
A modification of the second method of Looss (p. 455) is that of
Fülleborn. A glass filter funnel is lined with linen or with cotton
wool dyed black with iron-tannin. On this is placed a layer of sterile
sand, and on top of this the fæces. The whole is moistened. The larvæ
hatch out and wander through the meshes of the wool, appearing on the
edges of the same as white threads visible to the naked eye. With a
platinum needle these can be easily removed. The glass filter can
be placed on a glass cylinder, and this in another large stoppered
cylinder containing caustic potash solution at the bottom, so that any
larvæ escaping from the funnel are killed.
D. *ACANTHOCEPHALA*, Rud.
Gutless, nematode-like worms that carry at their anterior end a
retractile rostrum beset with hooks. In their adult condition they
only live in vertebrate animals. During their larval stage they are
often parasitic in invertebrate animals.
The _Acanthocephala_ are elongated cylindrical worms, with a
rounded posterior end. In some species an annulation is distinctly
recognizable; they are, however, not segmented. The size varies
according to the species, between about 5 to 10 mm. and 40 to 50 cm.;
in general, however, there is a preponderance of the small species.
The sexes are separate, and the males can easily be distinguished
from the females without examination of the genitalia, as the females
are both larger and thicker.
The body wall of Echinorhynchus is limited by a thin cuticle, which
is attached inwardly to the hypodermis. In only exceptional cases
a syncytium with large nuclei, even in the adult condition, is
represented by the hypodermis; and in it fibre systems, the elements
of which run in layers in various directions, appear, and it is only
towards the interior from these strata of fibres that the nuclei of
the hypodermis are found. As a rule, these fibres, at all events
the radiary fibres, are regarded as muscles. Hamann describes them
as elastic fibres, which lie in a viscid gelatinous connective
substance (transformed protoplasm?); a lacune system filled with
a granular fluid, the central part of which are two longitudinal
lacunes lying at the sides, also belongs to the cutaneous strata, as
do the so-called lemnisci, two short, flat organs suspended in the
body cavity, and the pedicles of which are attached anteriorly at the
border between the rostrum and body; their structure as well as their
origin permit them to be traced to the skin (fig. 348A).
Finally, inwardly below the skin there follows a layer of annular,
and after these a layer of longitudinal muscles, the structure
cells of which remain present in the residues, carrying nuclei. The
motor apparatus of the rostrum, the sheath of the rostrum, and the
lemnisci also belong to the muscular system. The rostrum represents a
finger-shaped hollow process of the cutaneous layer; but, according
to Hamann, it originates from the entoderm and passes through the
skin secondarily. It is covered by a thin cuticle, and as a rule
contains a large number of regularly placed chitinous hooks that
adjoin a granular formation tissue. From the base of the rostrum
springs a tubular hollow muscle extending into the body cavity; this
is the RECEPTACULUM PROBOSCIDIS, from the base of which again bundles
of longitudinal muscles originate, which pass along its axis and
that of the rostrum itself, and are inserted at the inner surface of
its anterior end (RETRACTOR PROBOSCIDIS). These muscles when they
contract invaginate the proboscis and draw it into the receptaculum;
when reversed they act again as PROTRUSOR PROBOSCIDIS. The whole of
the anterior body, however, can be invaginated, and for this purpose
there is a muscle that originates from the body wall at a variable
distance back, and which is joined to the receptaculum (RETRACTOR
RECEPTACULI); there is also a bell-shaped muscle which springs from
the body wall behind the lemnisci in rings, and passes forward to the
spot of attachment of the lemnisci.
The nervous system consists of a cluster of ganglia situated at the
base of the rostrum, from which three nerves pass towards the front
and two towards the back. No sensory organs are known.
The excretory organs, according to Kaiser, lie at the upper border of
the ductus ejaculatorius in the male and at the so-called bell in the
female. Here they represent the long-known villous tufts, placed on
disc-like cushions. In each of the cylindrical villi--which terminate
blindly towards the body cavity--there lies a cilium, which springs
from the membrane lining the villus, and which lies in a space cavity
of the villus, which ultimately proceeds as a little canal. There are
three canals discharging into the uterus that serve to conduct the
excretory materials from the body cavity; special glandular cells
corresponding to the terminal cells of the Platyhelminths, at the
commencement of the system, are not present in the Acanthocephala.
SEXUAL ORGANS.
(_a_) _Male Organs._--The greatest part of the male genital apparatus
is contained in a muscular sheath--the ligament--which originates
at the posterior end of the receptaculum proboscidis, passes along
longitudinally through the body cavity, and is inserted at the
posterior end of the worm. The two oval testicles usually lie one
behind the other; their vasa efferentia unite sooner or later into a
vas deferens which passes backwards, and finally terminates in the
penis; the terminal portion of the conducting apparatus is surrounded
by six large glandular cells (prostatic glands) the excretory ducts
of which open into the vas deferens. The penis itself is placed at
the base of a bell-shaped invagination of the posterior end, the
bursa, which is everted during copulation.
[Illustration: FIG. 348A.--The male of _Echinorhynchus augustatus_.
_L._, lemnisci; _T._, testicles; _P._, prostatic glands; _P.r._, sheath
of proboscis, with ganglion; _R.r._, retractor of sheath of proboscis.
25/1.]
[Illustration: FIG. 348B.--Anterior portion of the female apparatus of
_Echinorhynchus acus_. On the left seen from behind, on the right seen
from the front. _F_, inferior orifice of the bell; _B_, bell; _Lig_,
ligament; _M_, mouth of bell; _Ut_, uterus. Magnified. (After Wagener.)]
(_b_) _Female Organs._--There are only two ovaries present in the
ligament during the larval stage. During the course of growth they
divide into accumulations of cells (placentulæ, loose or floating
ovaries), which finally cause the ligament to burst and they thus
attain the body cavity. Thence a peculiarly constructed apparatus
finally conveys the eggs out. This apparatus consists of the uterine
bell and vagina, the latter discharging at the posterior extremity
of the body. The bell is a muscular canal provided with apertures at
both the anterior and posterior extremities. Its interior space is in
direct communication with the body cavity, and the anterior orifice
takes up all materials floating in the cavity--egg-balls, mature and
immature eggs--and pushes these further backwards. The continuation
of the bell lumen is now narrowed by a number of large cells in such
a manner that only bodies of a certain form can pass through this
tract and attain the uterus; everything else is conveyed back into
the body cavity through the posterior opening of the bell.
The eggs are already fertilized in the body cavity, and in this
position go through their development to the formation of the embryo.
Completely developed eggs are surrounded by three shells, and are
generally fusiform. The eggs agglomerate in masses in the uterus
until they are finally deposited through the vagina and vulva.
For the further development, the transmission of the eggs into an
intermediary host--usually a crustacean or an insect--is necessary;
the metamorphosis is very complicated; but this transmission may be
very easily effected artificially by feeding suitable crustaceans
(_Asellus_, _Gammarus_, etc.) with the eggs of _Acanthocephala_; this
being the only method of inducing the larva to hatch out so that
its structure may be studied. The larva appears in the form of an
elongated, somewhat bent body, at the stumpy anterior end of which
there is a crown of hooks or spines, whereas the posterior end is
pointed. Especial retractors draw in the hook-beset anterior surface,
and an elastic cushion beneath them jerks them forward again when
required. In the middle of the body a roundish heap of small cells is
seen, from which the entire body of the Echinorhynchus originates,
even to the cutaneous layer; the latter is also the larval skin in
which the small Echinorhynchus gradually grows. The development of
all the organs takes place within the intermediary host, and the
parasite only needs to be imported into the terminal host to attain
the adult stage after a certain growth. In some cases, however, a
second intermediary host is utilized.
Species of _Acanthocephala_ only occur exceptionally in human beings.
*Echinorhynchus gigas*, Goeze, 1782.
Syn.: _Tænia hirudinacea_, Pallas, 1781.
[Illustration: FIG. 348C.--Egg of _Echinorhynchus gigas_. 300/1. (After
Leuckart.)]
The body is elongated, gradually decreasing in thickness towards the
back. The rostrum is almost spherical, and is beset with five or six
rows of recurved hooks. The males measure 10 to 15 cm. in length,
the females 30 to 50 cm.; the eggs are provided with three shells,
of which the middle one is the thickest. The eggs measure 0·08 to
0.1 mm. in length. The GIANT ECHINORHYNCHUS occurs especially in the
intestinal canal of the domestic pig; it is less common in other
mammals. It bores deep into the mucous membrane with its rostrum,
and causes an annular proliferation around the perforated spot;
occasionally also it causes perforation of the intestine.
It is doubtful whether the giant Echinorhynchus occurs in man.
Leuckart admitted that there were a few positive cases. According
to Lindemann, _Ech. gigas_ occurs in human beings in South Russia,
and its presence is not rare. This statement, however, has not been
confirmed. Its presence in man is by no means impossible, as its
intermediary host, the cankerworm, or cock-chafer (_Melolontha_),
is, according to Schneider, occasionally eaten raw by human
beings. According to Kaiser, the golden beetle (_Cetonia aurata_)
and, according to Stiles, another beetle in America (_Lachnosterna
arcuata_) are also intermediary hosts.
*Echinorhynchus hominis*, Lambl, 1859.
This term is applied to an ECHINORHYNCHUS found by Lambl in the
intestine of a boy who had died of _leucæmia_; the worm was 5·6 mm.
in length, and the almost spherical head was beset with twelve
transverse rows of hooks.
*Echinorhynchus moniliformis*, Bremser, 1819.
The male is 4 cm. in length, the female 8 cm. long. This species
lives in the intestine of field-mice, rats, marmots and _Myoxus
quercinius_. A beetle (_Blaps mucronata_) is the intermediary host.
This species has also once been artificially cultivated in man
(Grassi and Calandruccio).
E. *GORDIIDAE.*
Very long thin worms similar to Filariæ, which, in their adult
condition, live free in brooks, pools and springs; the mouth and the
commencement of the intestine are obliterated; there are no lateral
ridges, and the muscular system presents a structure different to
that of the _Nematoda_. The posterior end of the male is split, and
spicules are lacking; there are two testicles. In both sexes the
genitalia discharge through the terminal gut.
The larvæ, which carry a rostrum beset with hooks, force themselves
into the larvæ of water-insects; more rarely they invade molluscs,
and they then become encysted within the body of the host. According
to Villot, at least a part of them attain the intestine of fishes,
where they again become encysted, and after a period of rest they
travel into the tissues of their hosts, and finally again reach the
exterior by way of the intestine, where they then become adult. In
most cases, however, the gordius larvæ are taken up by predacious
water insects; they live for a while in the body cavity of these
insects, undergo a metamorphosis, and finally wander into the water.
A few species invade man accidentally with water, in which case they
are usually vomited up:--
_Gordius aquaticus_, Dujardin, 30 to 90 cm. in length (Aldrovandi,
Degland, Siebold, Patruban).
_Gordius tolosanus_, Duj., 11 to 13 cm. in length (Fiori).
_Gordius varius_, Leidy, 10 to 16 cm., female, up to 30 cm. in length
(Diesing).
_Gordius chilensis_, Blanch. (Guy). _Gordius villoti_, Rosa
(Bercutti, Camerano); _Gordius tricuspidatus_, L. Def. (R.
Blanchard), _Gordius violaceus_, Baird (Topsent), and _Gordius
pustulosus_, Baird (Parona).
F. *HIRUDINEA s. DISCOPHORA* (Leech).
The _Hirudinea_, which have been appropriately included amongst the
Annelida, differ in many respects from the typical members of the
group; their body is long and flat, it lacks the parapodia that
are characteristic to all forms of Annelida; but, on the other
hand, possesses a terminal posterior sucker, and in many species
there is also an anterior sucker. The mouth is terminal at the
anterior end, the anus lies dorsally above the posterior sucker
(fig. 348D). The body is segmented, but this is less manifest in
the body covering than it is in the arrangement of the internal
organs; the segmentation, nevertheless, is also indicated exteriorly
by the appearance of the cutaneous sensory organs which correspond
to the segments. This shows what the condition of the ganglia in
the abdominal ganglion chain has taught us, that the anterior and
the most posterior segments are considerably abbreviated--a part of
the latter taking part in the formation of the suctorial organs.
In a great many species the skin is distinctly annulated, four or
five of such rings, at least in the central region of the body,
appearing on one segment of the body. The condition of their body
cavity is another peculiarity of the _Hirudinea_; it is narrowed by
the powerful development of the connective tissue and the muscular
system into four tubular sinuses, which have the appearance of
blood-vessels. There are usually one dorsal and one ventral median
trunks, as well as two lateral trunks; in addition, a particular
blood-vessel system exists.
[Illustration: FIG. 348D.--The internal organs of the leech. The
creature has been opened from the dorsal surface, and part of the
intestine has been removed. The testicles, with vas deferens, may be
seen between the blind ducts of the intestine; beyond these on either
side the segmental organs. The female genital organs are in front of
the most anterior pair of testicles. (After Kennel.)]
The skin consists of a very thin cuticle that is cast off from time
to time; it is secreted by the underlying cylindrical epithelium,
which contains numerous goblet cells. The muscular system is
strongly developed; it consists of long tubular fibres, which run
circularly, longitudinally and in the dorso-ventral direction; the
muscular system is subject to a particular expansion in the clinging
organs and at the commencement of the intestine. On the whole, the
alimentary canal represents a tube running straight from the mouth to
the anus, which possesses a number of blind sac-like protuberances
at the sides varying according to the species. The most anterior
section, the pharynx, in the leeches with maxillæ carries three
chitinous, semicircular plates furnished with teeth--the jaws--which
serve to tear up the epidermis in order to open the blood-vessels;
in the leeches with rostra a long protractile proboscis rises from
the base of the elongated pharynx. Numerous salivary glands, the
secretion from which possesses toxic properties, discharge into
the pharynx. The œsophagus, which follows the pharynx, and to the
exterior of which numerous radiary muscles are fixed, is a suctorial
organ in its entire structure. The nutriment in the larger species
consists of the blood of vertebrate animals, in smaller species and
in the young stages the food consists of small invertebrate animals.
The NERVOUS SYSTEM exhibits the typical structure of other segmented
worms; the sensory organs consist of the previously mentioned
goblet-shaped cutaneous sensory organs, of the organs of taste, and
of eyes, the latter frequently being present in large numbers.
The EXCRETORY or segmental organs exhibit many peculiarities, which
cannot, however, be detailed here. They commence with funnels in the
lacunes of the body cavity, and usually discharge on the ventral
surface.
Almost all the _Hirudinea_ are hermaphrodite and copulate
reciprocally. The two ovaries are very small, and the oviducts that
proceed from them soon unite into a common duct, which then passes
into the uterus and discharges through the short vagina in the
median line of the ventral surface behind the male organs into the
so-called clitellar region. The male sexual apparatus consists of
symmetrically arranged testicles, varying in number according to the
species, the short vasa efferentia of which, one by one, run into the
vas deferens, passing towards the front on each side. In front, at
about the level, or a little in front, of the female genitalia, the
two vessels pass into a convoluted mass of tubes to the so-called
epididymis, and then discharge into the single protractile penis
(fig. 348D).
All leeches deposit so-called COCOONS. These are small barrel-shaped
or pouch-like bodies, which are surrounded by a thicker shell and
contain a number of eggs in a large mass of albumen; the albumen
originates from glands of the generative organs, the shell substance
from cutaneous glands of the clitellar region.
Family. *Gnathobdellidæ* (Leeches with Jaws).
These are distinguished by the possession of usually three jaws in
the pharynx; the body consists of twenty-six segments. The posterior
sucker is large and flat; the anterior sucker is smaller. The
_Hirudinea_ have five pairs of eyes, the _Nephelinæ_ have four pairs.
Genus. *Hirudo*, L., 1758.
The entire body consists of 102 annulations, five appearing on one
segment in the central region of the body. The pharynx has three
semicircular jaws, the arched border of which is beset with numerous
teeth (50 to 100). The male sexual orifice lies between the thirtieth
and thirty-first rings, the female orifice between the thirty-fifth
and thirty-sixth. There are numerous species, some of which are
utilized for medicinal purposes.
*Hirudo medicinalis*, L., 1758.
[Illustration: FIG. 348E.--_Hirudo medicinalis._ _a_, anterior end,
with open buccal cavity, with the jaws, _J_, at the; _b_, one jaw
isolated. (After Claus.)]
It occurs in numerous colour varieties, one of which has been
designated _Hirudo officinalis_, Moq.-Tandon. Usually the dorsal
surface is greyish-green and is marked with six rusty-red
longitudinal stripes. The ventral surface is olive-green, more
or less spotted with black, and marked at the sides with a black
longitudinal line. The length averages 8 to 12 to 20 cm. This leech
lives in swamps, ponds and brooks, overgrown with plants and having
a muddy bed. The cocoons are deposited in the soil at the sides.
Europe, as well as North Africa, is its home. At the present day it
has been exterminated from most parts of Central Europe, but it is
still very common in Hungary. Its use for medicinal purposes is well
known. A large leech can suck about 15 grs. of blood, and about the
same amount is lost through secondary hæmorrhage.
*Hirudo troctina*, Johnston, 1816.
Syn.: _Hirudo interrupta_, Moq.-Tandon, 1826.
This species measures 8 to 10 cm. in length. The back is greenish,
with six rows of black spots surrounded by red; the lateral borders
are orange-coloured; the abdomen spotted or unspotted. Its habitat is
in North Africa and Sardinia. It is applied medicinally in England,
Spain, France, Algeria, etc.
Genus. *Limnatis*, Moq.-Tandon, 1826.
Nearly related to Hirudo, but is differentiated by a longitudinal
groove on the inner surface of the upper lip of the anterior sucker.
The jaws are furnished with over 100 very sharp toothlets.
*Limnatis nilotica*, Savigny, 1820.
Syn.: _Bdella nilotica_, Sav.; _L. nilotica_, Moq.-Tandon; _Hæmopis_
(_vorax_), Moq.-Tandon, 1826, _p. p._; _Hæmopis sanguisuga_,
Moq.-Tandon, 1846 (_nec Hir. sanguis_, Bergm., 1757).
This species measures 8 to 10 cm. in length, and becomes gradually
more pointed towards the front; the body is always soft. The back is
brown or greenish, and has usually six longitudinal rows (rarely only
two or four) of black dots. The abdomen is dark; but numerous colour
variations occur.
The native place is North Africa, especially the coastal regions; it
is also found in the Canaries, the Azores, Syria, Armenia, Turkestan,
perhaps also Southern Europe. It is taken into the mouth with
drinking water, and may settle in the pharynx, larynx, œsophagus, and
nasal cavities of human beings. This species has also been observed
in the vagina and on the conjunctiva. It is equally fond of attacking
domestic animals.
_Hirudo mysomelas_ (Senegambia) and _Hirudo granulosa_ (India) are
placed with this genus, and, like our leech, are also used for
medicinal purposes.
Genus. *Hæmadipsa*, Tennent, 1861.
These leeches live on land, and measure 2 to 3 cm. in length. About a
dozen species are known. They are a veritable scourge to persons in
the tropics (Asia, South America), as they attack them to suck their
blood. They are able to force their way even under close-fitting
garments, so that it is difficult to protect oneself from their
assaults (_Hæmadipsa ceylonica_, Bl., and other species).
Family. *Rhynchobdellidæ* (Leeches with Rostrum).
These are furnished with a proboscis in lieu of the jaws; the segment
consists of three annulations.
Genus. *Hæmentaria*, de Filippi, 1849.
*Hæmentaria officinalis*, de Fil.
Inhabit Mexico, where they are used for medicinal purposes.
Genus. *Placobdella*, R. Blanch.
*Placobdella catenigera*, Moq.-Tandon.
Indigenous to South Russia, Hungary, Italy and South France. It is a
parasite of the swamp turtle, but frequently attacks human beings.
G. *ARTHROPODA* (Jointed-limbed Animals).
BY
FRED. V. THEOBALD, M.A.
BILATERALLY symmetrical segmented animals which are covered with a
thick cuticle that is frequently calcareous (_Crustacea_), but always
thinner between the segments; they carry (primitively) a pair of
jointed appendages on every segment.[321] The segments of the body
are uniform in certain regions, but differ from those of contiguous
regions, so that it is easy to distinguish three parts (head, thorax
and abdomen), each composed of segments. The cephalic segments are
always formed into a uniform head, the segmentation being scarcely
recognizable at either end; the thoracic segments may also fuse, or
part or all of them may coalesce with the head; the abdomen, as a
rule, retains its segmentation, but this may possibly also be lost,
in which case it is [sometimes] united to the cephalothorax. The
structure of the three regions depends mostly on the varying form
and function of the appendages: those on the head are primitively
locomotive organs (and frequently are still so in the early stages),
but they become transformed into feelers and mouth-parts (mandibles,
maxillæ); the limbs of the thorax, however, usually retain their
ambulatory functions, as frequently do those of the abdomen;
sometimes, however, the abdominal limbs disappear, entirely or
partly; in the latter case they are then utilized for other purposes.
[321] [In most _Arthropoda_ the skin is hardened by a deposit of chitin
(_Hexapoda_, etc.).--F. V. T.]
In their organization the _Arthropoda_ approach the segmented worms.
The _Arthropoda_ are generally divided into five groups
(_Crustacea_,[322] _Protracheata_, _Arachnoidea_, _Myriapoda_,[323]
and _Insecta_ or _Hexapoda_), of which only the _Arachnoidea_ and the
_Hexapoda_ interest us here.
[322] Parasitic or free-living Crustaceans may now and then invade man
abnormally. Thus, according to Betten, _Caligus curtus_ invade the
cornea (Betten, R. A., “Par. Crust. as a Foreign Body on the Cornea,”
_Lancet_, 1900, i, p. 1002; and _Centralbl. f. Bakt. u. Par._, xxix,
p. 506). According to Laboulbène, also _Gammarus pulex_ (Laboulbène,
A., “Obs. d’accid. caus. par le _G. pul._ apport. avec l’eau de boison
dans l’estomac d’un homme,” _Bull. Acad. méd._, 1898, p. 21).
[323] R. Blanchard has compiled thirty-five cases in which _Myriapoda_
have been observed in the intestine as well as in the nose of human
beings (“Sur le pseudopar. d. myriap. chez l’homme,” _Arch. de Par._,
1898, i, p. 452). E. Munoz Ramos reports an additional case (_ibid._,
p. 491). A few years ago a doctor in East Prussia sent me a rain
worm out of a lady’s nose (_cf._ Hanau, A., “Wahrsch. Pseudo-paras.
v. Schmeissfliegenlarv. u. angebl. Paras. v. Regenwürmern b. einer
Hysterischen,” _Arch. de Par._, 1899, ii, p. 23).
_A._ *ARACHNOIDEA* (Spiders, Mites, etc.).
The head and thorax are always united together; the abdomen is either
segmented or without exterior segmentation, in which case it is united
with the cephalothorax.[324] The number of pairs of appendages amount
to six, of which the two front pairs, the cheliceræ and the pedipalpi,
are attached to the head region and the four remaining pairs to the
thoracic region.[325] The abdomen in the adult condition has no
appendages. The Arachnoids are air-breathers, and for this purpose
are either provided with tracheæ or with so-called lung-sacs, or they
breathe through the surface of the body. Some aquatic forms breathe by
gills.
[324] [This is only so in the _Acarina_ or mites, not in the _Araneida_
or spiders.--F. V. T.]
[325] [The true character of the _Arachnoidea_ is the presence of
four pairs of ambulatory appendages. This number is reduced to two
pairs in the gall-making _Phytoptidæ_, and they differ from all other
_Arthropoda_ in having no antennæ.--F. V. T.]
There are eight or ten orders of Arachnoids,[326] of which, however,
only two, the _Acarina_ and the _Linguatulida_, have to be considered
here.[327]
[326] Twelve orders are now recognized, as follows: _Pentastomida_
or Linguatulids; _Tardigrada_ or bear-animalcules; _Phalangidæ_ or
harvest-men; _Acarina_ or ticks and mites; _Palpigradi_; _Solifugæ_;
_Pseudoscorpionidea_ or book mites; _Pedipalpi_ or false scorpions;
_Scorpionidea_ or true scorpions; _Araneida_ or spiders; _Xiphosura_ or
king crabs; and _Pycnogonida_, marine Arachnoids.
[327] _Chelifer cancroides_ has also been observed as a pseudoparasite
in man (Arnault de Very, S., “Pseudopar. du. _Chel. cancr._ chez
l’homme,” _Compt. rend. Soc. de Biol._, 1901, liii, p. 105).
Order. *Acarina* (Mites).
Small Arachnoids, the three parts of the body of which are, as a
rule, coalesced; it is only rarely that a faint line indicates the
division between a cephalothorax and abdomen. The two appendages
on the head are designed for biting or puncturing and sucking, and
vary according to their use. The cheliceræ[328] are fang-like jaws
or puncturing bristles forming a kind of rostrum, the pedipalpi are
claw-like or shear-shaped, or form a suctorial proboscis.[329] The
four pairs of legs are usually well developed, more rarely they
are rudimentary or have partly vanished; many parasitic forms are
provided with pedunculated suckers [ambulacra--F. V. T.]. Respiratory
organs (tracheal tufts) may be present or absent. The nervous system
is reduced to a minimum, eyes are usually lacking. The intestine,
situated in the central part, generally has three blind appendages;
the anus is situated on the venter above the posterior end. Sexes
separated; nearly all the species deposit eggs, from which six-legged
larvæ hatch. The _Acarina_ live either free in the water or in moist
soil, or they are parasitic on plants and animals.[330]
[328] [The cheliceræ are sometimes regarded as modified antennæ, but it
is more natural to regard them as the morphological equivalent of the
mandibles of _Hexapoda_.--F. V. T.]
[329] [The pedipalpi, or second pair of jaws, consist of a stout
basal segment and a palp, which may have the appearance of a leg in
_Arachnida_; this may end with or without a claw, or with a chela
(scorpions); they may also form a tube enclosing the styliform
cheliceræ (mites).--F. V. T.]
[330] [_Acarina_ are also found living upon trees, feeding upon other
Arthropods and also upon spores of lichen and fungi (_Oribatidæ_ or
beetle mites); they also swarm indoors amongst stores and provisions
(_Tyroglyphidæ_ and _Glyciphagi_, household, sugar and cheese mites).
This order is very important, as many are parasites upon man, his
domestic animals and his cultivated plants, and attack his provisions
and stores. Some live on blood, and in some of the ticks distribute
various protozoal and other blood parasites and germs.--F. V. T.]
Family. *Trombidiidæ* (Running Mites).
Soft-skinned _Acarina_ with tracheæ and with two eyes, usually
pedunculated; they are often brightly coloured; cheliceræ lancet- or
claw-shaped; pedipalpi claw-like; legs composed of six segments, with
suctorial discs between the terminal ungues.[331] Larvæ six-legged.
To the latter belong the larvæ of several species of Trombidium such
as:--
[331] [Some have seven segments to the legs.--F. V. T.]
Genus. *Trombidium*, Latreille (and *Leptus*).
*Leptus autumnalis*, Shaw, 1790.
Leptus occur as parasites in the human skin and cause a cutaneous
disease known as autumn erythema, and produce a very unpleasant
sensation on account of the troublesome itching; in children it is very
often accompanied by fever.[332]
[332] [This minute parasite is especially obnoxious in barley fields.
In walking over barley stubble one is sure to be attacked by this
Acarus in many districts. Trombidium is often very prevalent in
gardens, especially along rows of peas, and in spring they may be found
on fruit trees and bushes. Nut-pickers are frequently attacked by
Leptus, and also pickers in other fruit plantations. It is often called
the harvest mite.--F. V. T.]
[Illustration: FIG. 349.--_Leptus autumnalis_, with so-called sucking
proboscis. Enlarged. (After Gudden.)]
[Illustration: FIG. 350.--_Leptus autumnalis_: the so-called proboscis
is formed around the hypopharynx sunk into the skin. 100/1. (After
Trouessart.)]
Formerly these mites were considered adult forms, but when they were
recognized as mite larvæ they were taken for those of the spider-mite
(_Tetranychus telarius_); the investigations of Hanstein, however,
showed this to be a mistake. When Henking first investigated the
development of _Trombidium fuliginosum_, parasitic in the larval
stage on vine-fretters, he demonstrated the occurrence of a form
very similar to _Leptus autumnalis_, and the “autumn, grass, or
gooseberry” louse was commonly designated the Trombidium larva. Even
before Henking’s work it had been described by Mégnin as the larva
of _Trombidium holosericeum_, a red-coloured species, frequently
occurring in spring and summer on the ground, trees, etc. This
assumption, however, as Moniez was the first to explain, is not
correct; indeed, as many as three species come under consideration:
_T. gymnopterosum_, L., _T. fuliginosum_, Herm. (according to
Brucker), and two species known hitherto only in the early stage, _T.
striaticeps_, Helm. et Oudem., and _T. poriceps_, Helm. et Oudem.,
which are not only parasitic on mammals, but on birds, on Arthropods
and especially on insects. Arthropods appear to be the normal hosts
for the larvæ.
The above-mentioned forms invade the skin of man by means of their
oral apparatus, by preference invading the orifices of the sebaceous
glands so as to suck the blood; around the point attacked there arises
a wheal about the size of a lentil, and around the inserted hypopharynx
a fibrinous secretion, the “proboscis,” which, however, is a product
of the host, just as chitinous secretions are provoked by Trombidia
parasitic on Arthropods.
Further species, analogous in habit to _Leptus autumnalis_, are
described by Riley from Central and South America as _L. americanus_
and _L. irritans_.
[_L. autumnalis_ attacks small mammals by preference, such as moles
and hares, which are often literally covered with them. Dogs are also
subject to their attack, and cats suffer similarly. This mite also
frequently appears in colonies on cows; cavalry horses after autumn
manœuvres often suffer from an erythematous affection about the hocks
and knees due to this pest.
[A number of Leptus, so far undescribed, occur abroad which attack man
in the same way as _L. autumnalis_ in Europe. Dr. Durham has brought
me specimens from British Guiana called _bête rouge_; this species
works under the skin much as does our European species, but it is very
distinct, being considerably larger.--F. V. T.]
*Trombidium tlalsahuate*, Lemaire, 1867.
_T. tlalsahuate_ occurs in Mexico under conditions similar to those of
Leptus here. It also frequently attacks men, and especially fastens
itself on to the eyelids, in the axillae, navel, or on the prepuce; it
induces itching and swelling of the parts affected, and sometimes even
causes suppuration; the symptoms, however, generally disappear after a
week and remain localized.[333]
[333] Lemaire, “Import. en France du tlalsahuate,” _Compt. rend. Acad.
Sci._, Paris, 1867, lxv, p. 215.
Other species of mites which attack man are reported, mostly by
travellers, from various other places; zoologically, however, there
is little known about them. The pou d’agouti in Guiana, niaibi in New
Granada, colorada in Cuba, mouqui in Para, and the buschmucker in New
Guinea represent a few of these.
*Akamushi* or *Kedani*.
In a few districts of Japan there occurs a serious illness, with a
mortality of 40 to 70 per cent. It is called river or flood fever, and
the Japanese doctors have connected it with a small mite (akamushi,
kedani). Baelz has opposed this opinion on the grounds that he has
repeatedly observed the same species of mite in his dwelling without
any subsequent illness occurring. According to Keïsuke Tanaka, however,
a connection certainly does exist, inasmuch as the akamushi, like
Leptus, attacks persons to suck blood. If the mite is not removed,
or if the spot attacked is injured by scratching, etc., a papule
surrounded by a red area forms, and a pustule ensues; and finally a
black scab covers the seat of injury. The lesion becomes the point of
entrance of bacteria, especially a species of _proteus_ which produces
river fever. If the mites are carefully removed no general illness
takes place.
[Illustration: FIG. 351.--The kedani mite. Enlarged. (After Tanaka.)]
The orange-red mites, which we only know in their larval condition,
measure 0·16 to 0·38 mm. in length by 0·10 to 0·24 mm. in breadth. They
have leg-like palpi with three joints, hirsute bodies, and very hairy
legs composed of five segments, terminating with three ungues.
Family. *Tetranychidæ* (Spinning Mites).
These have tracheæ and eyes; the palpi are composed of four segments,
of which the last but one has a powerful claw. The legs have six
segments with sucker discs between the claws.
[The red spiders or spinning mites (Tetranychi) are usually placed in
the family _Trombidiidæ_.--F. V. T.]
Genus. *Tetranychus*, Dufour.
*Tetranychus molestissimus*, Weyenbergh, 1886.[334]
[334] [This species is also known as _Bicho colorado_. It spins a web
under the lower surface of the leaves, and it is only from December to
February that it attacks warm-blooded animals and man.--F. V. T.]
Found in Argentine and Uruguay on the under surface of the leaves of
_Xanthium macrocarpum_; it attacks mammals and men, producing severe
itching, accompanied by fever in the latter.
It has been asserted by Haller that the CAPE AILMENT (Port Natal
sickness) is caused by mites, but this statement has been contested.
*Tetranychus telarius*, L., 1758,[335] var. *russeolus*, Koch.
[335] [There is something wrong here, probably in the identification.
_T. telarius_ is purely a plant-feeder, and it is extremely unlikely
a variety would attack man. Anyhow, it will not do so in Great
Britain.--F. V. T.]
[Illustration: FIG. 352.--_Tetranychus telarius_ var. _russeolus_,
Koch. Enlarged. (After Artault.)]
This common spinning mite likewise attacks human beings, but the
papules produced by it very soon disappear.
Family. *Tarsonemidæ.*
A family distinguished by complete sexual dimorphism, the species of
which are provided with tracheæ; the legs have five segments; the
terminal segments of the front pair of legs of both sexes possess a
claw; the terminal segment of the posterior pair of legs of the male
likewise has a claw. In the female this pair of legs, like the second
and third pairs of both sexes, is provided with two hooklets and a
sucking disc. The cuticle of the body on the back is “annulated.”
[This family of small transparent mites live normally as plant
parasites. The last two pairs of legs are widely separated from the two
front pairs.--F. V. T.]
Genus. *Pediculoides.*
*Pediculoides ventricosus*, Newport, 1850.
Syn.: _Heteropus ventricosus_, Newport, 1850; _Acarus tritici_,
Lagrèze-Fossot, 1851; _Physogaster larvarum_, Lichtenstein, 1868;
_Sphærogyna ventricosa_, Laboulbène and Mégnin, 1885.
Males are oval in shape, 0·12 mm. in length and 0·08 mm. in breadth,
flattened. There are six pairs of chitinous hairs on the dorsal surface
and a lyre-shaped lamella on the posterior part. The female in the
non-gravid state is cylindrical in form, 0·2 mm. in length and 0·07 mm.
in breadth; when gravid the posterior part of the body becomes enlarged
into a ball, which may attain 1·5 mm. in size, as in the case of _Pulex
penetrans_ and of the female Termites. On emerging the young are
already provided with four pairs of legs and copulate soon after birth.
[Illustration: FIG. 353.--_Pediculoides ventricosus._ _a_, male; _b_,
young female; _c_, gravid female. Enlarged. (After Laboulbène and
Mégnin.)]
These animals live on the stalks of cereals, and feed on vegetable
and animal juices; they are also found on corn-infesting insects.
They invade the barns and seek out the insects living in the dry
grains of corn, or wait for an opportunity of obtaining food. They
have been repeatedly observed on human beings, particularly labourers
occupied in handling grain; their bite causes severe irritation,
local elevation and reddening of the epidermis, as well as fever. It
cannot be positively asserted that all cases of the occurrence of
cereal mites on man relate to _P. ventricosus_, as the descriptions
are often insufficient. Geber states that one form is _Chrithoptes
monunguiculosus_, or _Acarus hordei_; Flemming mentions _Tarsonemus
uncinatus_; Koller _Oribates_ sp.; and Karpelles _Tarsonemus
intectus_.
[The pregnant female Pediculoides has a large round inflated abdomen,
in which the ova hatch and the young mature. Later they escape from
the parent as adults.--F. V. T.]
Genus. *Nephrophages.*
*Nephrophages sanguinarius*, Miyake and Scriba, 1893.
Males measure 0·117 mm. in length and 0·079 mm. in breadth; females up
to 0·360 mm. in length by 0·120 mm. in breadth. The head is provided
with two very large scissors-like jaws and two large round eyes. The
legs are composed of five segments and are all of equal length; the
three anterior pairs of legs have pedunculated ambulacra, the posterior
ones terminate in a claw. The cuticle on the back is thickened in
three places, shield-like; the abdominal surface without scutellum
is longitudinally striped and is beset with chitinous hairs. Colour
greenish to brownish-yellow. Eggs 0·046 to 0·040 mm.
[Illustration: FIG. 354.--_Nephrophages sanguinarius_: male, ventral
surface. Enlarged. (After Miyake and Scriba.)]
[Illustration: FIG. 355.--_Nephrophages sanguinarius_: female, dorsal
aspect. Enlarged. (After Miyake and Scriba.)]
The authors discovered these mites, but always dead, in the urine
of a Japanese suffering from fibrinuria complicated with chyluria
and hæmaturia. They surmised that they were endoparasites, probably
situated in the kidney; but this view is not convincing, though they
also report that for a week, day after day, the mites were found in
the patient’s urine, as well as in urine drawn off by means of a
catheter, and in the water used to wash out the bladder (one or two
specimens and an egg). The statement that these mites have large eyes
makes the discovery suspicious, to say the least. The significance of
the discovery is not supported by the further statement that Disse
is supposed to have found an encapsuled mite closely related to the
Tyroglyphides on the wall of the vena cava.
In the case of Marpmann, who found a dead Acarid in the urine of a
man suffering from chronic nephritis, and in whom later examinations
proved negative, the author himself was of opinion that the mite had
reached the urine from outside.
We are certainly acquainted with mites living endoparasitically,
namely, the _Cysticolæ_, _Analgesinæ_, of which _Laminosioptes
gallinarum_ live in the intramuscular and subcutaneous connective
tissue of fowls, and _Cytoleichus sarcoptoïdes_ in their air sacs.
Another kind of mite (_Halarachne halichœri_) is occasionally found
in the nasal mucous membrane of the seal (_Halichœrus grypus_), and,
quite recently, _Pneumonyssus simicola_, which is more nearly related
to Halarachne, has been found in the lung of _Cynocephalus_ sp. It is
therefore not improbable that endoparasitic mites are found in man;
but no definite discovery has yet been made.
Family. *Eupodidæ.*
Small tracheate mites, with moderately long or short pedipalpi,
composed of four segments, of which the last segments bend; cheliceræ
forceps-shaped, with serrated edges; legs with two claws, more rarely
with one, and terminating in a tuft ornamented with fine hairs;
genital orifices on the abdomen, surrounded by a circle of little
hairs. Most species live free--one lives parasitically on the bodies
of slugs.
Genus. *Tydeus*, Koch.
*Tydeus molestus*, Moniez, 1889.
[Illustration: FIG. 356.--_Tydeus molestus_: seen in profile. Enlarged.
(After Moniez.)]
Male, 0·2 mm. in length, 0·125 mm. in breadth. Females, 0·225 mm. in
length, 0·135 mm. in breadth; gravid female 0·315 to 0·360 mm. in
length and 0·180 mm. in breadth. They were observed by Moniez on an
estate in Belgium, whither the creature had apparently been imported
twenty-five years previously with Peruvian guano; they appeared
regularly in the summer and remained until the first frost set in;
they were found on grass-plots, on trees and bushes in masses; they
regularly attacked human beings, mammals and birds, tormenting their
hosts in a terrible manner.
Family. *Gamasidæ* (Coleopterous or Insect Mites).
Cheliceræ chelate or styliform; pedipalpi filiform; the legs are
composed of six segments with two terminal ungues and a bladder-like
sucking disc [caruncle--F. V. T.]. Stigmata situated between the
third and fourth pairs of legs; the cuticle thickened, leather-like;
no eyes; the larvæ have six legs.
The _Gamasidæ_ are predaceous on small insects and other mites; some
are parasitic on insects, and one is noticeable as a pest on birds,
etc.
Genus. *Dermanyssus*, Dugés.
*Dermanyssus gallinæ*, de Geer, 1778.
Syn.: _Pulex gallinæ_, Redi, 1674; _Atarus gallinæ_, de Geer, 1778;
_Dermanyssus avium_, Dugés, 1834.
The male measures 0·6 mm. in length by 0·32 mm. in breadth; the female
0·7 to 0·75 mm. in length by 0·4 mm. in breadth. The body is somewhat
pear-shaped; the colour whitish, reddish, or reddish-black, according
to the contents of the intestine. The legs are fairly short and strong.
During the day they live concealed in the nests, cracks, etc., of the
hen-house, and at night attack the inmates in order to suck their
blood; they rarely remain long on the birds. They have been repeatedly
found on persons, on whose skin they produce an itching eruption.
*Dermanyssus hirundinis*, Hermann, 1804.
Syn.: _Acarus hirundinis_, Herm., 1804.
Of a brownish colour, 1·2 or 1·4 mm. in length; lives in the nests of
swallows and is occasionally found on man.
[Illustration: FIG. 357.--_Dermanyssus gallinæ._ Enlarged. (After
Berlese.)]
[Illustration: FIG. 358.--_Dermanyssus hirundinis._ 40/1. (After
Delafond.)]
[The red hen mite (_Dermanyssus gallinæ_) not only attacks poultry
and man, as stated above, but is found on all birds and many mammals.
The _D. gallinæ_ is the same as _D. avium_. The species found in
swallows’ nests is also said to be the same. This mite can remain for
weeks without any food from its normal host. They only attack man
when entering or cleaning dirty and neglected fowl-houses; they do
not produce a true dermatosis. They chiefly attack the backs of the
hands and forearms of those who constantly attend poultry and give
rise to symptoms similar to the papular eczema of scabies. That they
may remain some time upon the human body we know from the following
cases out of many recorded: Geber observed that the Dermanyssus had
caused a diffused eczema on a woman, which lasted four weeks and then
disappeared. The _tique_ of F. V. Raspail is the bird Dermanyssus;
he records children and adults being attacked not only when handling
pigeons, but even when walking in a garden manured with pigeons’ dung.
The affection soon disappeared when the pigeons were destroyed and the
excreta buried. I have frequently heard of poultrymen being seriously
attacked by this pest.--F. V. T.]
Genus. *Holothyrus.*
*Holothyrus coccinella*, Gervais, 1842.
Measures 5 mm. in size; lives on birds in the Island of Mauritius;
ducks and geese frequently fall victims to its bite; it also attacks
human beings, on whose skin it causes severe burning and swelling, but
no reddening; it may be dangerous to children, especially by settling
in the oral cavity.
Other Gamasides occasionally occur in man, for instance, according
to Moniez, _Leignathus sylviarum_, Canestr. et Fanzago; according to
Neumann _Lælaps stabularis_. The former live normally in the nests of
various species of _Sylvia_, Lælaps on dried vegetable substances,
also in houses.
[Marchoux and Conoy (_Bull. Soc. Path. exot._, 1912, v, No. 10, pp.
796–798) found Leishman granules in _Lælaps echidninus_. It is assumed
that Leishman granules may be found in most Arachnoids, and have no
connection with Spirochæta.--F. V. T.]
Family. *Ixodidæ* (Ticks).
Comparatively large Acarines with a leathery skin; they are flattened
in form, but after sucking blood the abdomen becomes spherical;
the cheliceræ are rod-like and possess a serrated terminal joint,
bent hook-like; the median parts of the pedipalpi (maxillæ) form a
rostrum furnished with barbed hooks (fig. 359); the maxillary palpi
themselves are club-like or rounded; the legs are composed of six
segments with two terminal ungues, often also with “sucking discs”;
the stigmata are at the sides of the body, posterior to the fourth or
third pair of legs. The larvæ are six-legged.
[The true ticks (_Ixodidæ_) are all blood-suckers, and as far as
is known they do not take vegetable food at all. Not only are the
_Ixodidæ_ important as actual parasites, but they are most so on
account of the fact that they are the active agents in carrying various
diseases in animals and apparently in man. It has been conclusively
proved that the bont tick (_Amblyomma hebræum_) is the carrier of the
fatal “heart-water fever” so rife amongst sheep in South Africa, that
the dog tick (_Hæmaphysalis leachi_) is the agent by which the protozoa
that cause malignant jaundice in dogs are distributed, that Texas
fever in cattle is spread by _Rhipicephalus annulatus_, and Coast or
Rhodesian fever by _R. appendiculatus_ and _R. simus_. Their importance
as disease carriers amongst mammals is therefore considerable, and
it may prove to be so for man.[336] They frequently attack man, but
chiefly, according to my observations, in their early stages in Europe;
this is not so, however, abroad. The life-history of a number of ticks
has been clearly demonstrated. Mr. Wheler has shown that in _Ixodes
reduvius_ it is as follows: the female deposits her eggs in masses upon
the ground, gradually reducing in size as the eggs pass out, until she
finally remains a mere shrivelled empty bag and then dies. The eggs are
oval, golden brown in colour and smooth; in length they are 0·59 mm.;
as in all _Ixodidæ_ they are covered with a glutinous secretion, by
means of which they adhere together in masses. These egg masses may be
deposited anywhere on the ground, but amongst rough, coarse herbage
seems to be the favourite place. The egg stage may last as long as
twenty-two weeks, or it may only take eight weeks. In the case of the
bont tick a single female may deposit 15,000 or more eggs. The process
of egg-laying is described as follows by Mr. Wheler: “When egg-laying
is about to take place, the head is further depressed till it rests
close against the under side of the body. In this attitude the end of
the rostrum actually touches the genital orifice, the palpi being at
the same time widely opened out. Behind the head and from beneath the
shield, at what for the purposes of explanation may be described as the
back of the neck, a white, perfectly transparent, delicate gelatinous
membrane is brought down through inflation, either with air or with a
transparent fluid, above the head, which it temporarily conceals. The
end of this membrane terminates in two conical points which appear
to be covered with a glutinous secretion, and at the same time an
ovipositor of a somewhat similar character, but only semi-transparent,
is pushed forward from the genital orifice. This latter is a tube,
within which is the egg. As the ovipositor projects it turns itself
inside out, like the finger of a glove, leaving the egg protruded at
the end and lying between the two finger-like points of the membrane.
The membrane and the ovipositor are then withdrawn each from the other.
The egg adheres to the former, which collapses through the withdrawal
of its contents, dragging the head forward and depositing it on the top
of the head. Neither legs, palpi, nor the organs of the mouth take any
part in oviposition, but after the collapse of the membrane the palpi
are closed and the head is raised, by which action the egg is pushed
forward to the front edge of the shield, forming in time an adherent
mass of eggs, which are deposited in front of the tick.”
[336] This has been proved in Uganda--so-called tick fever in man.
[The egg gives rise to the larval form, the so-called “seed-tick”
stage. At first these minute specks are pallid and soft, but they soon
harden and darken in colour. These larvæ are six-legged and crawl up
grasses and various plants, and there await a passing host, waving
their two front legs in the air and becoming attached by this means.
The larval ticks feed upon the blood of the host, and when replete
fall to the ground, the body becoming inflated in the meanwhile. These
larvæ may remain on the host only two days, or they may remain much
longer. Eventually they moult on the ground and change to the nymph or
pupal stage, which has four pairs of legs. This pupa acts just as the
larva, crawls up plants and waits to regain the host. After a time the
nymphs, having gorged themselves with blood, fall off and remain on the
ground for nearly three months; they then moult and become adult males
and females. In about ten days they assume their normal colour and
regain the host afresh; the female gradually swells until she attains
that large inflated form so characteristic of ticks. The male does not
swell, but nevertheless feeds upon the host and fertilizes the female.
[The act of coitus is strange: the male tick inserts its rostrum and
other mouth organs into the sexual orifice of the female, between the
base of the posterior pair of legs. The males then die and the females
fall to the ground and deposit the ova. There are variations in the
different species, of course, from those given above, which apply
solely to _Ixodes reduvius_. The larvæ and nymphs seem to attack most
animals, but the adults mainly keep to the same host. The periods in
the life-cycle of ticks not only vary in the different species, but in
each species according to climatic conditions; for instance, in the
bont tick (_Amblyomma hebræum_, Koch), Lounsbury has shown that the
development is rapid in summer, slow in winter. The period from the
time that the female drops to the time she commences to lay eggs varied
in specimens observed by him from twelve days in summer to twelve weeks
in winter, and the complete period from the dropping of the female to
the hatching of the eggs, from eleven weeks in summer to thirty-six
weeks through the winter. Other stages vary in a similar manner.
[Ticks may live a long time away from the host provided they are
supplied with a certain amount of moisture. Mr. Wheler kept dog ticks
(_Ixodes plumbeus_) in the larval stage for ten months; the pupæ, male
and female, of _I. reduvius_ for six months.
[I have kept _Ornithodorus moubata_ alive for eighteen months without
food.
[In many species moulting takes place off the host, but in _I. bovis_,
now known as _Rhipicephalus annulatus_, Say (the carrier of Texas
fever), moulting takes place on the host, and in many other species
also.[337] Some species of ticks leave their host on its death (as the
dog tick, _Hæmaphysalis leachi_), but others die with the host (bont
tick, _Amblyomma hebræum_).
[337] Some ticks require only one (_R. decoloratus_), others two (_R.
evertsi_), and some three hosts (_R. appendiculatus_) in order to reach
maturity.
[Two species are of special importance, namely _Ornithodorus moubata_,
Murray, which may infect human beings with the spirillum of African
tick fever, and _Dermatocentor reticulatus_ var. _occidentalis_, which
is said to be the carrier of Rocky Mountain spotted fever.
CLASSIFICATION OF _Ixodidæ_.
[The ticks, or _Ixodidæ_, are divided into two groups, known as (1)
_Argantinæ_, (2) _Ixodinæ_. The _Argantinæ_ are told from the _Ixodinæ_
by the absence of dorsal or ventral shields in both sexes, and also by
the rostrum being placed beneath the cephalothorax, which covers it
over: except in the larval stage, in which it is subterminal, and in
the pupal, when it partly projects. Legs nearly equal in length. The
sexual orifice is situated between the two first pairs of legs. The
males usually smaller than the females.
[The _Ixodinæ_ have the legs unequal, of six segments with two false
segments, making them look as if composed of eight segments. The
rostrum is terminal and never hidden beneath the body. The sexual
orifice is situated between the bases of the first three pairs of
legs. In the males the orifice is obsolete or very rudimentary, sexual
intercourse being effected by the rostrum. The males are smaller
than the females. The shield in the females never covers so much as
one-half of the body even when fasting, also in the larvæ and nymphs;
but in the males, which do not distend, the shield covers the body
entirely, or all but a narrow margin. The _Ixodinæ_ are divided into
two groups: (i) the _Ixodæ_, and (ii) the _Rhipicephalæ_. The former
have a long proboscis reaching nearly to the end of the palpi or even
a little longer than the palpi. The palpi are longer than broad. The
_Rhipicephalæ_ have short palpi, nearly or quite as broad as long,
more or less conical or subtriangular. They were called _Conipalpi_ by
Canestrini.
SYNOPSIS OF GENERA.
[A. _Argantinæ_: Rostrum concealed in adult, partly
exposed in larvæ and nymphs. No dorsal and
ventral shields.
Body flat with thin edges, finely shagreened and
punctate _Argas_.
Body with numerous small round granules and with
thick sides _Ornithodorus_.
[B. _Ixodinæ_: Rostrum terminal. Body with dorsal
shield over some part of it.
I. Rostrum and palpi longer than broad (_Ixodæ_).
α. A groove around anus in front.
Palpi caniculated in both sexes _Ixodes_.
Palpi claviform, not caniculated in the
male; legs very long _Eschatocephalus_.
Palpi claviform, not caniculated in the
male; _anal groove absent in the female_ _Ceratixodes_.
β. A groove around the anus behind.
No eyes; adanal shields _Aponomma_.
Eyes present.
Males with no adanal shields _Amblyomma_.
Males with adanal shields _Hyalomma_.
II. Labium and palpi short; palpi not, or very
little, longer than broad (_Rhipicephalæ_).
α. No eyes.
Rostrum rectangular; no ventral shields in
the male _Hæmaphysalis_.
β. Eyes present.
No adanal shields, but usually with greatly
developed coxæ on fourth pair of legs.
Capitulum quadrangular _Dermacentor_.
Capitulum hexagonal _Rhipicentor_.
Adanal shields in male. Stigmata comma-
shaped _Rhipicephalus_.
Stigmata oval or round; legs normal _Boophilus_.
Segments of legs expanded _Margaropus_.
[The genus Ceratixodes of Neumann, 1902, occurs on birds.
[The genus Eschatocephalus of Frauenfeld, 1853, of which seven
species are known, is mostly parasitic on bats, and is found
in holes, caves, and church towers.
[The genus Aponomma of Neumann, 1899, is exotic, and almost
entirely confined to snakes and saurians.
[The following are synonyms of the different genera:--
_Argas_, Latreille, 1796 (_Rhynchoprion_, Hermann, 1804).
_Ixodes_, Latreille, 1795 (_Acarus_, Linnæus, 1758;
_Cynorhæstes_, Hermann, 1804; _Crotonus_, Dumeril, 1822).
_Ceratixodes_, Neumann, 1902 (_Ixodes_, Cambridge, 1879;
_Hyalomma_, Cambridge, 1879).
_Eschatocephalus_, Frauenfeld, 1853 (_Sarconyssus_, Kolenati,
1857).
_Amblyomma_, Koch, 1844 (_Ixodes_, Latreille, 1795).
_Hæmaphysalis_, Koch, 1844 (_Rhipistoma_, Koch, 1844;
_Gonixodes_, Dugès, 1888; _Opitodon_, Canestrini, 1897).
_Rhipicephalus_, Koch, 1844 (_Acarus_, Linnæus, 1758;
_Ixodes_, Latreille, 1795; _Phanloixodes_, Berlese, 1889;
_Boophilus_, Curtice, 1890).
_Dermacentor_, Koch, 1844 (_Ixodes_, Latreille, 1795;
_Pseudixodes_, Haller, 1882).--F. V. T.]
Genus. *Ixodes*, Latreille.
*Ixodes reduvius*, L., 1758.[338]
[338] _Ixodes reduvius_ and _I. ricinus_ are synonymous. [The above
should read _Ixodes ricinus_, Latreille, 1806.--F. V. T.]
Syn.: _Acarus reduvius_ and _ricinus_, L.; _Ixodes ricinus_,
Latreille, 1806.
The males are oval; their length 1·2 to 2 mm.; they are brownish-red
or black in colour; the females are yellowish-red, 4 mm. long; when
gorged they are lead-coloured, and may attain 12 mm. in length by 6 to
7 mm. in breadth.
The dog tick (fig. 360) lives in thickets on leaves, etc., and
attacks sheep and oxen, and more rarely dogs, horses, and human
beings, into the skin of which the female bores with the rostrum in
order to suck blood; the bite is not dangerous, and sometimes is
not even felt. Inflammation, however, is set up if the creatures
are forcibly removed from the wound, as the rostrum as a rule
is torn off in the process. If left alone or smeared over with
some grease--vaseline, oil, butter, etc.--the creatures drop off
spontaneously. Sometimes the entire tick bores itself into the skin;
they also appear to be permanent inmates of kennels.
[Illustration: FIG. 359.--A., the rostrum of _Ixodes ricinus_ (male);
B., the terminal joint of the maxillary palpi of the female. Enlarged.
(After Pagenstecher.)]
[Illustration: FIG. 360.--Female of _Ixodes ricinus_, gorged full,
dorsal and ventral surfaces. 2/1. (After Pagenstecher.)]
[The species _I. reduvius_ is the same as _I. ricinus_, Latreille.
The male is 2·35 to 2·80 mm. long; the body is dark brown, almost
black, with a pale, almost white, margin; there are also traces of
reddish mottling. Coxæ of the first pair of legs with a short spine.
Rostrum much shorter than that of the female; shield oval; anal shield
small, about one-third the length of ventral shield. The adult female
varies from 2·80 to 3·5 mm. when not distended, but when gorged may
reach 10 mm. long. The shield and legs are dark blackish-brown, body
deep orange-red with four dark longitudinal lines, paler beneath and
light grey in front. When distending it is pale red to grey or white;
when fully gorged olive-green, or dark red to black, with irregular
yellow streaks on the back and sides just before egg-laying. Sexual
orifice opposite fourth pair of legs. The nymph varies from 1·60 to
1·70 mm. long when fasting; the body is olive-white, opaque, with four
distinct brown posterior markings and similar anterior ones, leaving
a pale centre to the shield. When fully gorged it is 3 mm. long. As
the nymph distends, it changes from opaque white to blue-black, and
finally black. The little larva is 0·80 to 1·50 mm. long, transparent
with olive-green intestinal markings; as it becomes inflated it
changes to blue-black, and then black. There are no eyes. It is widely
distributed, and chiefly attacks sheep; sometimes it occurs on dogs and
also attacks man. Mégnin records it from horses in the nymph stage.
Amongst its other numerous hosts are goats, cattle, deer, hedgehogs,
moles, bats, birds, and lizards. It is usually known as the grass tick
and bottle-nosed tick. This species occurs in Europe, Asia, North
Africa, and North America.
[_Synonyms._--Considerable confusion exists over the name of this and
other common ticks, owing to the same species having been described
under a great many names. Observers have taken the same species on
different animals and in various stages to be distinct, and have
described them accordingly.
[The name _Ixodes reduvius_, Leach, does not stand, as Leach was
describing quite a different parasite. The name _I. ricinus_,
Latreille, 1806, is now substituted by Neumann and Wheler.
[The synonyms given by Wheler are as follow: _Reduvius_, Charleton,
1668; _Ricinus caninus_, Ray, 1710; _Acarus ricinoides_, de Geer, 1778;
_Acarus ricinus_, Linnæus, 1788; _Cynorhæstes reduvius_, Hermann, 1804;
_Cynorhæstes ricinus_, Hermann, 1804; _Ixodes megathyreus_, Leach,
1815; _Ixodes bipunctatus_, Risso, 1826; _Cynorhæstes hermanni_, Risso,
1826; _Crotonus ricinus_, Dumeril, 1829; _Ixodes trabeatus_, Audouin,
1832; _Ixodes plumbeus_, Dugés, 1834; _Ixodes reduvius_, Hahn, 1834;
_Ixodes fuscus_, Koch, 1835 (?); _Ixodes lacertæ_, Koch, 1835 (?);
_Ixodes pustularum_, Lucas, 1866; _Ixodes fodiens_, Murray, 1877;
_Ixodes rufus_, _Ixodes sulcatus_, and _Ixodes sciuri_, Koch.--F. V. T.]
*Ixodes holocyclus*, Neumann, 1899.
[Under the name _I. holocyclus_, Cleland (_Journ. Trop. Med. and Hyg._,
1913, xvi, No. 3, pp. 43–45) says that: “This tick is common in man
where there is dense scrub and tropical jungle along the east coast of
Australia at certain times of the year. It may cause severe symptoms in
children resulting in death.” He records a child being attacked in 1884
which died, and another case from which 200 ticks were removed, the
symptoms being weak heart, collapse, syncope, but the patient recovered
under treatment; again, in the same journal (pp. 188, 189), the case
of a 4-1/2-year-old girl who was bitten showed widespread muscular
paralysis, and other cases resembling conium poison.
[Taylor (_Rep. Ent. Aust. Inst. Trop. Med._, 1911, p. 21, 1913) refers
to this species as the scrub tick of New South Wales. The partially
fed female has a dark reddish-yellow scutum and is almost as broad as
long, punctations very numerous, equal and confluent in places, long
white hairs on the lower half of each coxa. He records it as attacking
man commonly, mentioning Kamerunga, Cairns district, Queensland, and
Sydney, N.S.W., as localities.--F. V. T.]
*Ixodes hexagonus*, Leach, 1815.
Syn.: _Ixodes sexpunctatus_, Koch, 1897; _I. vulpis_, Pagenstecher,
1861.
Lives in the same manner as the foregoing; especially attacks hounds,
but also other mammals and even birds. The difference consists in the
shape of the legs, the shorter rostrum, and the larger size of the
male. It also occasionally attacks man, but is usually confused with
the previously mentioned species.
[The synonyms of this species are as follow:[339] _Ixodes autumnalis_,
Leach, 1815; _I. erinacei_, Audouin, 1832; _I. reduvius_, Audouin,
1832; _I. crenulatus_, Koch; _I. erinaceus_, Murray, 1877; _I.
ricinus_, Mégnin, 1880.[339] Two other synonyms are given above by
Braun.
[339] Neumann, G. L., “Rev. de la fam. des Ixodides,” _III Mém. Soc.
Zool. France_, 1899, xii, p. 129.
[The female when fully replete is 11 mm. long, when fasting 3·86 mm.;
the shield is heart-shaped and punctate, body finely hairy; palpi short
and broad; labium shorter, and tarsi of all the legs more truncate than
in _I. ricinus_. The colour of the distended body is drab and somewhat
waxy; rostrum, shield and legs light testaceous. The male varies from
3·5 to 4·0 mm. long, and is reddish-brown in colour with lighter legs;
the shield is punctate and leaves a narrow margin around the body;
the body is elliptical, almost as large in front as behind. There is
a spine on the coxæ of the first pair of legs, which is shorter than
in the male _I. ricinus_ and longer than in the female. The genital
orifice is opposite the interval between the second and third pair of
legs. The fasting _nymph_ is 1·76 mm. long, light bluish-grey, margined
and transparent, with four large posterior intestinal marks joined
together behind the shield and smaller ones extending to the front and
sides. When fully distended it is uniformly brownish-white; shield,
legs and rostrum pale testaceous. The _larva_ varies from 0·88 mm.
when fasting to 1·76 mm. when gorged. Its body is light, but gradually
becomes darker, with similar intestinal marks to _ricinus_.
[This tick is very common, especially on ferrets, stoats and hedgehogs.
It is also found on sheep, cattle, etc. The males do not generally
occur in company with the females on the host. Pairing probably takes
place on the ground.--F. V. T.]
Genus. *Amblyomma*, Koch.
*Amblyomma cayennense*, Koch, 1844.
Syn.: _Amblyomma mixtum_, Koch, 1844; _Ixodes herreræ_, Dugés, 1887;
_Amblyomma sculptum_, Berlese, 1888.
Characterized by the possession of eyes. The male measures 3·8 mm.
in length by 3 mm. in breadth; the female 4 mm. in length by 3 mm.
in breadth, but when full of blood may become 13 mm. in length and
11 mm. in breadth. They are common in the whole of Central America
(Carrapatas), and attack mammals, amphibious animals and man.[340]
[340] Neumann, G. L., _loc. cit._, p. 205.
[This species was described by Fabricius. It occurs in Cayenne, Guiana,
in Southern Texas, Florida, California, Mexico, Guatemala, Honduras,
Nicaragua, Costa Rica, Panama, Bermuda, Cuba, Jamaica, Trinidad,
Colombia, Venezuela, French Guiana, Brazil, Paraguay and the Argentine.
It is called the silver tick. It frequently attacks man. Schwarz and
Bishopp (_Bull._ 105, U.S. Dept. Agric., p. 158) heard of one man whose
legs were well covered with suppurating sores and who was ill from
the attack of these ticks and the wounds produced by scratching, and
records other cases of their swarming on man. Newstead (_Ann. Trop.
Med. and Par._, 1909, iii, No. 4, p. 442) records it as the worst pest
to man in Jamaica.--F. V. T.J
*Amblyomma americana*, Linnæus.
The so-called long star tick, from the silvery spot on the apex of the
scutum of the female. It will attack any mammal and even birds and
also man. It occurs in North America, and also in Brazil, Guiana and
Guatemala. Its punctures frequently end in suppuration. In the Eastern
and Southern States man is more frequently attacked by this species
than any other. Moss-gatherers in Louisiana are badly attacked by
it.[341] It also attacks the milkers in dairies. Attempts to transmit
Texas fever failed with this species.
[341] Morgan, “Ticks and Texas Fever,” _Louisiana State Bull._ 55,
pp. 134, 135, pl. 59.
*Amblyomma maculatum*, Koch.
The so-called Gulf Coast tick, of the Gulf Coast, occurs on birds,
mammals and man, especially cattle, and attacks the ears.
Genus. *Hyalomma*, Koch.
*Hyalomma ægyptium*, L., 1758.
Syn.: _Acarus ægyptius_, L., 1758; _Ixodes camelinus_, Fischer, 1823.
A species frequently found in Africa, particularly in Egypt and
Algeria, and which also occurs in France and Italy, as well as in Asia.
Male 8 mm. in length, 4·5 mm. in breadth. Female up to 24 mm. in length
and 15 mm. in breadth. It infests large and small animals as well as
human beings.[342]
[342] Neumann, G. L., _loc. cit._, p. 285; Ronsisvalle, “Sui fenomeni
morb. prodotti nel uomo da un Ixodide denominato _Hyal. æg._,” _Boll.
Acc. Gioenia sci. nat._, 1891, xvii.
[This is one of the largest ticks, nearly reaching the size of the bont
tick. It is known in Africa as the bont leg-tick; all farm stock is
attacked, but sheep and goats suffer most. Only one generation appears
to occur each year. The male is almost black with a pale marginal
stripe; the replete female brown with irregular light blue stripes. It
is abundant in parts of South Africa.]
Genus. *Hæmaphysalis*, Koch.
*Hæmaphysalis punctata*, Canestrini and Fanzago, 1877–1878.
Syn.: _Hæmaphysalis sulcata_, Canestrini and Fanzago, 1877–1878;
_Rhicocephalus expositicius_, Koch, 1877; _Hæmaphysalis peregrinus_,
Cambridge, 1889; _Herpetobia sulcata_, Canestrini, 1890.
[This species does not appear to be common. It occurs on sheep, goats,
horses and cattle. I have seen a female taken from man in Britain. The
female when fasting is 3·44 mm. long, when gorged 12 mm. long. Colour,
reddish-brown, leaden-grey when gorged; dorsal shield deeply indented
in front; rostrum, shield and legs brownish; body finely punctate, both
above and below; sexual opening opposite the coxæ of the second pair
of legs in both sexes. Palpi a little longer than the labium; first
segment short and narrow, second and third widened on the dorsal face.
Coxæ with a short, broad blunt spine; tarsi short, terminated with a
spur on the first pair. The male is 3·10 mm. long. Body rather narrow,
yellowish to reddish-brown; dorsal shield nearly covers the whole body;
numerous punctures over the whole surface. Eleven indentations on the
posterior margin of the body; peritremes lighter in colour, large and
comma-shaped. The three anterior pairs of legs with a short spine on
the haunches, the fourth with a very long one directed backwards. The
nymph varies from 2·5 to 3·0 mm., is oval, and light yellow to dark
red in colour. Dorsal shield rounded with few punctations. No spur on
tarsi, and sexual orifice nearly obsolete. Larva short and oval. Length
1·20 mm.--F. V. T.]
Genus. *Dermacentor*, Koch.
*Dermacentor reticulatus*, Fabricius, 1794.
Syn.: _Acarus reticulatus_, Fabr., 1794; _Ixodes reticulatus_,
Latreille, 1806; _I. marmoratus_, Risso, 1826.
This tick is provided with eyes, but it is distinguished from Ixodes
and analogous genera by the lack of the abdominal plastron in the male,
which measures 5 to 6 mm. in length by 3·5 mm. in breadth. The female
may attain 16 mm. in length and 10 mm. in breadth. It is found in the
South of Europe, in Asia, and in America; it attacks chiefly oxen,
sheep and goats, and occasionally man.[343]
[343] Neumann, G. L., “Rev. de la fam. des Ixodides,” _Mém. Soc. Zool.
France_, 1897, x, p. 360.
[This tick sometimes causes much annoyance to human beings. It was once
most troublesome at Revelstoke. Specimens have recently been found on
fowls, turkeys and pheasants in Kent.
[Other synonyms are as follows: _Cynorhæstes pictus_, Hermann, 1804;
_Crotonus variegatus_, Dumeril, 1829; _I. pictus_, Gervais, 1844;
_Dermacentor albicollis_, Koch, 1844–1847; _D. pardalinus_, Koch,
1844–1847; _D. ferrugineus_, Koch, 1844–1847; _Ixodes holsatus_,
Kolenati, 1857; _Pseudixodes-holsatus_, Haller, 1882; _Hæmaphysalis
marmorata_, Berlese, 1887.
[The _female_ when fasting is 3·86 mm. long by 2 mm. wide. The body is
depressed, larger behind and reddish-brown in colour. The shield is
very large and extends to the level of the third pair of legs, with
a few large and many small punctations, milky white, variegated with
reddish-brown. Sexual orifice opposite the coxæ of the second pair
of legs. Coxæ of the front legs are deeply bifid, the others with a
moderate spine. When gorged light brown, and may reach 16 mm. When
depositing eggs the female is mottled with dark brown above and below.
The _male_ is like the female. The shield is reddish-brown, variegated
with a milky white pattern. Coxæ of the fourth pair of legs three times
the size of the third. There is a sharp backwardly pointing spine on
the second palpal segment, also seen (but smaller) in the female.
Length 4·20 mm.
[According to Mr. Wheler this is a very variable species both in size
and colour. It occurs in England on sheep, but not commonly. It has
probably been introduced into Britain. Besides the animals mentioned
above it is also found on deer.--F. V. T.]
*Dermacentor venustus*, Banks.
[The Rocky Mountain tick fever tick. This species has been wrongly
called _Dermatocentor reticulatus_ var. _occidentalis_. The correct
name of the carrier of Rocky Mountain tick fever is _Dermacentor
venustus_, Banks (Hooker, Bishopp and Wood, _Bull._ 106, U.S. Dept.
Agric., Div. Ent., p. 165).
[The female is from 13·8 by 10 by 6·4 mm. to 16·5 by 11·4 by 6·9 mm.
when gorged; the male from 2·1 by 1·5 mm. to 6 by 3·7 by 1·4 mm. The
male reddish-brown; scutum with an extensive pattern of white lines,
usually but little white on the mid-posterior region, legs slightly
lighter than scutum, joints tipped with white. Female with scutum
mostly covered with white, abdomen reddish-brown, legs as in male. The
nymph when unengorged reddish-brown, when gorged dark bluish-grey; the
larva is yellowish-brown when unengorged, slate blue when engorged. The
ova light brown, shiny and smooth.
[The chief wild hosts are the brown bear, coyote, woodchuck, rabbit,
wild cat, badger and mountain goat for the larvæ; practically all
small mammals act as hosts for larvæ and nymphæ, whilst the adults are
seldom found on other than large domestic animals; horses and cattle
are preferred. It occurs in British Columbia, southward to Northern
New Mexico, and from the foothills of the Rocky Mountains in Colorado
to the base of the Cascade Range in Oregon and California; abundant in
Western Montana, Idaho, Eastern Washington, Oregon, North Utah, West
Wyoming and North-west Colorado.
[Of great importance in the Bitter Root Valley of Montana, where a
number of cases of fever occur each year, with a mortality of about 70
per cent. In British Columbia this tick causes tick paralysis in man
and sheep. Only the adults seem to attack man and animals there (Hadwen
and Nuttall, _Parasitology_, 1913, vi, No. 3, pp. 288–297 and 298–301)
according to the _Canadian Medical Association Journal_, December,
1912. The symptoms are unlike spotted fever. For full details of this
tick _vide Bulls._ 105 and 106, U.S. Dept. Agric.]
*Dermacentor occidentalis*, Neumann.
This tick only occurs in the Pacific Coast region of the United States.
Owing to the fact that it frequently attacks man as well as occurring
in great abundance in Oregon and California, it is of considerable
economic importance. It is spoken of as the wood tick, and in the
regions where found is the most common tick to attack man. Hooker,
Bishopp and Wood (_Bull._ 106, U.S. Dept. Agric., Div. Ent., 1912,
p. 189) state that a number of cases have been brought to their notice
where the bite of this tick has caused considerable local inflammation,
which in some cases required physicians’ attention. It has been
supposed to be connected with Rocky Mountain spotted fever, but it is
doubtful if it is concerned in its transmission. The engorged female
is steel grey, the dorsum with an olive-green surface colour, which
covers the grey except in small spots, giving a mottled appearance. The
unengorged males and females are reddish-brown, scutum covered with a
whitish bloom, interrupted by many red punctures. The female is 9 by
6·1 by 3·3 mm. to 11·8 by 7·6 by 5·6 mm.; the male 2·8 by 1·6 mm. to
4·2 by 2·3 mm. The larvæ are bluish-grey when engorged, reddish-brown
when unengorged. The nymph is light brown, sides of scutum darker, and
the intestines dark brown. It is confined to the Coast Range and Sierra
Nevada Mountains in California and Oregon and the small mountain range
to the south-west.
*Dermacentor variabilis*, Say.
The American dog tick has also been found on man, but it is of little
economic importance as it is easily removed from its host.
Genus. *Margaropus*, Karsch.
*Margaropus annulatus australis*, Fuller.
The so-called Australian cattle tick. Newstead[344] reports this as a
great pest to man in Jamaica in its larval stage. Its chief hosts are
cattle, horses, goats, sheep, dogs and rabbits.
[344] _Ann. Trop. Med. and Par._, 1909, iii, No. 4.
*Margaropus microplus*, Canestrini.
Recorded by Aragão (_Mem. Inst. Oswaldo Cruz_, 1911, iii, fasc. 2, p.
163) as occurring in larval stage on man in Brazil.
Genus. *Rhipicephalus*, Koch.
*Rhipicephalus sanguineus*, Latreille, 1804.
Syn.: _Ixodes sanguineus_, Latr., 1804; _I. rufus_, Koch, 1844;
_Rhipicephalus limbatus_, Koch, 1844; _Rh. siculus_, Koch, 1844; _Rh.
stigmaticus_, Gerstäcker, 1873.
Spread over almost the entire tropical and sub-tropical regions,
occurring in Europe in the South of France and in Italy; it infests
dogs and more rarely sheep; oxen, cats, foxes and human beings are also
attacked.[345]
[345] Neumann, G. L., _loc. cit._, 1897, p. 385.
NEUMANN’S TABLE OF SPECIES OF ARGAS.
1 {Body elliptical (sides curved) 2.
{Body oblong (sides straight), ending anteriorly
{ in a point 7.
2 {Body transversely oval _vespertilionis_.
{Body elongate oval 3.
3 {Margin of body striated 4.
{Margin of body formed by quadrangular areolæ PERSICUS.
4 {Body flat, integument plainly wrinkled 5.
{Body tumid, elongate; integument finely
{ wrinkled; coxæ of fourth pair of legs near
{ anterior third of body _hermanii_.
5 {Body oval, narrowed anteriorly REFLEXUS.
{Body elliptical, blunt, hardly narrowed
{ anteriorly 6.
6 {Body twice as long as broad _cucumerinus_.
{Body hardly longer than broad _transgariepinus_.
7 {Dorsal integument with large polygonal
{ depressions; tarsi appearing bifid BRUMPTII.
{Dorsal integument almost smooth; tarsi not
{ appearing bifid _æqualis_.
The _Argantinæ_ are distinguished from the _Ixodinæ_ by the head,
which in the former is situated on the inferior aspect of the
cephalothorax, while in the _Ixodinæ_ it projects freely; also by
the very short proboscis, the small club-like palpi, the lack of
suckers on the legs, as well as by the scutellum, which covers
the entire back and is bent up round the borders. Two genera are
distinguished: Argas, Latreille, 1796 (Rhynchoprion, Hermann, 1804),
and Ornithodorus, Koch, 1844. The species live on mammals, but more
especially on birds.
Genus. *Argas*, Latreille.
*Argas reflexus*, Fabricius, 1794.
Syn.: _Acarus reflexus_, Fabricius, 1794; _A. marginatus_, Fabricius,
1794; _Rhynchoprion columbæ_, Hermann, 1804.
The European marginated tick, _Argas reflexus_ (length of male 4 mm.,
breadth 3 mm., length of female 6 to 8 mm., breadth 4 mm.), is of a
yellowish colour and has yellowish-white legs. The ingested blood
shows red or brown through the intestine, which is provided with
blind sacs. It lives in dovecots. It remains hidden during the day
and at night crawls on to the sleeping pigeons to suck their blood.
It has been observed in France, England, Italy, Germany, and Russia.
Persons sleeping near infected dovecots, or in apartments formed from
pigeon-lofts, are also attacked, even when the room in question has not
been used for sheltering pigeons for years, as “marginated ticks” can
live in a fasting condition for a very long time. The bite sometimes
gives rise to serious symptoms, such as general erythema and sudden
œdema.
[Illustration: FIG. 361.--_Argas reflexus_: from the dorsal surface,
the intestine showing through the integuments. (After Pagenstecher.)]
[This pest more often feeds on the blood of man than is imagined.
Blanchard states that he has received them from men’s clothes in
Strasburg. Boschulte, of Westphalia, records these parasites in a
bedroom inhabited by children and connected with a pigeon-house. The
children were bitten during sleep on the hands and feet. The result
of the bite was intense itching along the nerves, the bite only being
marked by a red spot. In a girl of 14 or 15, vesicles were formed
similar to those produced by burns, and in an old man an ulcer formed.
Others record painful punctures and persistent œdema produced by this
pigeon pest. It was once abundant in Canterbury Cathedral, and often
caused much annoyance, I am told, to the worshippers; the ticks falling
down from the roof, where they were living, derived from the numerous
pigeons that breed in the towers. This Acarus has enormous powers of
vitality, living without food for months at a time.--F. V. T.]
*Argas persicus*, Fischer de Waldheim, 1824.
Of oval form and brownish-red colour. The male measures 4 to 5 mm. in
length by 3 mm. in breadth; the female 7 to 10 mm. in length by 5 to
6 mm. in breadth. It frequents the entire north-west and north-east
of Persia (the gerib-gez or malleh of the Persians, the miana bug of
travellers). It lives concealed in houses and attacks man at night to
suck his blood. Its bite is much dreaded, but the serious results may
probably be attributed to unsuitable treatment of the wound or its
invasion by bacteria.
[This tick, sometimes called the tampan and wandlius in South Africa,
is mainly a fowl parasite. Fowls and ducks frequently die under its
attack, particularly young ones, death being due to loss of blood.
This tick remains attached to its host during its larval stage for
about five days; it then leaves and moults in concealment. In its
subsequent stages it visits its host by night and remains for about an
hour only, during which time it distends itself fully with blood. As
a nymph it moults twice, not once as do the cattle ticks. This tick
and other Argas become larger with each moult, but retain their same
general appearance. The female visits the host every now and then, and,
between, deposits eggs in sheltered crevices. About fifty to 120 are
deposited at once. Four weeks seems a necessary period to intervene
between visits to the host, and the interval may be extended to upwards
of a year according to Lounsbury.[346]
[346] “Report of Government Entomologist, Cape of Good Hope, for 1899,”
1900, p. 33.
[It is found in the Sudan, where Balfour has found granules derived
from the segmentation of spirilla in their digestive tract. Fantham
and Hindl have confirmed this. It has been assumed that these granules
carry infection.
[Illustration: FIG. 362.--_Argas persicus_: ventral aspect. 7/1. (After
Mégnin.)]
[This so-called Persian tick, the miana, which is such a scourge to
travellers in Persia, appears to infest the huts of natives in that
country. It has been sent me from Quetta, where it has invaded houses
to such an extent the natives cannot live in them. The virulence of its
bite is probably due to the tick transmitting fever germs from natives,
probably inured, to strangers, who would be susceptible.--F. V. T.]
*Argas brumpti*, Neumann.
[Found in Somaliland, by Brumpt, and in the Sudan. This tick attacks
man as well as wild animals and produces a painful swelling according
to King,[347] but as pointed out by that naturalist it probably relies
on other than human food.--F. V. T.]
[347] “Fourth Report Wellcome Res. Labs.,” 1911, p. 128.
*Argas chinche*, Gervais, 1844.
This Acarus, a native of the temperate parts of Colombia, is very
troublesome to man. It is probably identical with _A. americanus_,
Packard, which infests domestic fowls and turkeys, and occasionally
also cattle, and is differentiated from _A. reflexus_ by the
sculpturing of the cuticle.
Genus. *Ornithodorus*, Koch.
Neumann’s SYNOPSIS OF THE GENUS ORNITHODORUS is as follows:--
{ Hypostome unarmed; integument in nymph stage and
1 { partly in adult spinulose MÉGNINI.
{ Hypostome armed with recurved teeth; integument
{ not spinulose 2.
2 { Camerostome with movable lateral flaps TALAJE.
{ Camerostome without movable lateral flaps 3.
{ Anterior border of distal segments of legs with
3 { tubercles or festoons 4.
{ Anterior border of segments of legs without
{ tubercles or festoons 8.
4 { Body not much contracted anteriorly 5.
{ Body pointed anteriorly 7.
{ Tubercles of distal segments of legs higher than
{ broad, distant 6.
5 { Festoons of distal segments of legs as broad as
{ high, contiguous _pavimentosus_.
6 { Eyes present SAVIGNYI.
{ No eyes MOUBATA.
7 { Eyes present _coriaceus_.
{ No eyes TURICATA.
8 { Integument with fine radiating wrinkles _lahorensis_.
{ Integument granular 9.
9 { Tarsi appearing bifid at apex _furcosus_.
{ Tarsi not appearing bifid at apex 10.
{ Tarsi of first pair of legs with three dorsal
10 { tubercles, of other legs with one _canestrinii_.
{ Tarsi without dorsal tubercles or with only one 11.
{ Tarsi of last three pairs of legs with pronounced
11 { dorsal protuberance _tholozanii_.
{ Tarsi of legs with indistinct dorsal protuberance _erraticus_.
*Ornithodorus moubata*, Murray, 1877.
An abundant African tick which is one of the carriers of the spirillum
of African relapsing fever and can also carry _Filaria perstans_
(Christy). Its body is oval, yellowish-brown when young, greenish-brown
when mature. The integument is covered with mamillose tubercles. No
eyes and the stout legs granular above, the tibiæ and tarsi fringed
with tubercles on the upper side. Pocock[348] records it from Uganda
and German East Africa, Congo and Angola, to Namaqualand and the
Transvaal in the south. It is called _bibo_ in Uganda, _moubata_ in
Angola, and _tampan_ on the Lower Zambesi. It feeds on animals and
birds as well as man. Its bite is very painful. This tick is found in
native huts, living in cracks and crevices and in the thatch roofs.
[348] “A System of Medicine,” Allbutt and Rolleston, i, pt. 2, p. 195.
The female tick infected with the spirillum transmits the infection
to the eggs and the next generation. They appear to be able to live
without food a long time, and probably live for years. They lay their
eggs in masses on the ground or in crevices, and when they hatch they
are in the nymph stage with four pairs of legs. _O. moubata_ also
occurs in Madagascar with recurrent fever (Lamoureux, _Bull. Soc. Path,
exot._, 1913, vi, No. 3, pp. 146–149).
*Ornithodorus savignyi*, Audouin, 1827.
At one time considered the same as the preceding species, but can be
easily separated by the presence of two pairs of eyes. It is widely
spread over Africa and has been found in South India and at Aden. In
the Sudan it occurs in large numbers. King[349] records that a few
miles N.N.E. of Khartoum 370 specimens were collected in two hours
under a single tree by a well. It is found in Somaliland, where
relapsing fever occurs and no _O. moubata_, which it probably replaces
as a transmitter (Drake-Brockman, “Rep. Col. Office,” April 6 and April
16, 1913). It also occurs in Tunis, where the natives call it “tobbiah”
(Weiss, _Arch. de l’Inst. Pasteur de Tunis_, 1912, pt. 4, p. 226).
[349] “Fourth Report Wellcome Res. Labs.,” 1911, B, p. 129.
*Ornithodorus coriaceus*, Koch.
Found in Mexico, Paraguay and California. Attacks man.
*Ornithodorus talaje*, Guerin, 1849.
An eyeless species with somewhat elongate pentagonal body found in
Mexico and South America, called the “chinche.” A variety of it
(_coniceps_) is found at Venice, etc., and another variety on various
islands in the Indian Ocean and South Atlantic. Its bite is very
painful to man.
*Ornithodorus turicata*, Dugès, 1876.
Without eyes. Indigenous in Central America; attacks human beings and
pigs. The bite is painful and is often followed by serious consequences.
[So virulent is this species that pigs put in an infested sty often
die in a night. This “turicatas” of Mexico often reaches 6 mm. in
length.--F. V. T.]
*Ornithodorus tholozani*, Laboulbène and Mégnin, 1882.
Syn.: _Argas tholozani_, Lab. and Még., 1882.
Without eyes. Males 4 to 6 mm. in length and 2 to 4 mm. in breadth;
females 8 to 10 mm. in length and 4 to 5 mm. in breadth. It especially
attacks sheep. Native of Persia and Asia Minor.
[This species is reputed as being very dangerous to man. It is locally
know as the kéné, or sheep-bug. In its fully gorged state it is deep
violet.--F. V. T.]
*Ornithodorus mégnini*, Dugès, 1883.
Syn.: _Argas mégnini_, Dugès, 1883.
Length 8·5 mm., breadth 5·5 mm. Native of Mexico.
[Another synonym for this species is _Rhynchoprion spinosum_, Marx. The
adult males and females are grey to dark brown, the male somewhat the
smaller; female 5 by 3·5 by 2·5 mm. to 10 by 6 by 3·5 mm. The larvæ at
the seed tick stage are dark grey, turning to pink, then to a whitish
grey when engorged. The nymph when young is blood-red in front, rest
pearly white; later they turn reddish-brown.
[Intense pain may be caused by its presence in and around the ears.
[Two specimens in the nymphal state were taken from the ears of a
visitor to Cambridge by Dr. J. Christian Simpson. They were supposed
to have entered the ears when the gentleman was camping out in Arizona
(_Lancet_, 1901, i, No. 4,052, p. 1198, fig. 3).
[This species attacks the horse, ass, dog, cats and oxen, generally
around the ears, and also attacks man. It is well known in the United
States as infesting the ears of children (_New York Ent. Soc. Journ._,
1893, pp. 49–52).
[It occurs in Texas, Arizona, New Mexico and California as well as
Mexico, Brazil, and possibly many parts of South America; and recently
Bedford (“Sec. Report Div. Vet. Res., S. African Union,” 1912, pp. 343,
344) has shown it to occur at Vryburg and Fauresmith, in the Transvaal,
on stock. It also occurs in the Sudan.--F. V. T.]
OTHER LITERATURE ON _Ixodidæ_.
(1) “Pénétration de l’_Ixodes ricinus_ sous la peau de l’homme,”
_Compt. rend. Soc. de Biol._, 1891, xliii, ser. 9, iii, pp. 689–691,
R. Blanchard.
(2) “Notas sobre Ixodidas brazileiros,” _Mem. Inst. Oswaldo
Cruz_, 1911, iii, fasc. 2, pp. 145–195, pls. 11 and 12, Dr. H. de
Beaurepaire Aragão. Table of Brazilian Species.
(3) “Contribuicão para a sistematica e biolojia dos Ixodidas,” _Mem.
Inst. Oswaldo Cruz_, 1912, iv, fasc. 1, pp. 96–120, pls. 2 and 3, Dr.
H. de Beaurepaire Aragão.
Family. *Tyroglyphidæ.*
Very small mites without eyes and without tracheæ, with smooth skin.
The males usually have a suctorial pore on either side of the anus,
which is used during copulation, or suckers may be found in both
sexes near the sexual orifice. The mouth parts form a cone with
chelate cheliceræ, and three-jointed pedipalpi; the legs are usually
short, have five segments with a terminal claw and suckers, or either
one or other of these organs. The numerous species and genera live
free and from choice in slowly decomposing vegetable and animal
matter (cheese, cereals, flour, sugar, preserves, dried anatomical
preparations, bacon, dried fruits and fungi), also in the corners
of dwellings, etc.; they incidentally get into or on to man, or are
found in chamber utensils and in spittoons; actual parasites are
rarely found amongst them.
[The chief genera are Tyroglyphus, Rhizoglyphus, Glyciphagus,
Aleurobius and Histiogaster. The first three have typical characters
referred to, but are distinguished from each other by the two
former having the hairs on the dorsum smooth, whilst in Glyciphagus
they are hairy, plumose, or feathered. Rhizoglyphus can be told
from Tyroglyphus by having claws on the tarsi without any suckers;
Tyroglyphus has both claws and suckers. The larvæ are hexapod and
may become adult in the usual way by repeated moults, or they enter
the so-called hypopial stage. In this the eight-legged nymph becomes
quiescent, and during this stage it fixes itself to some insect or
other animal by a patch of suckers on the lower surface of the hind
end of the body, and is so carried from place to place. The hypopus
does not feed and has a hard shell and short legs. When it has
reached a new home it moults and development proceeds in the normal
way. Canestrini and Kramer treat the _Tyroglyphidæ_ as a sub-family
of the _Sarcoptidæ_, calling them sub-family _Tyroglyphinæ_,
the other sub-families being _Sarcoptinæ_, _Canestriniinæ_ and
_Analsinæ_.--F. V. T.]
Sub-family. *Tyroglyphinæ.*
Genus. *Aleurobius*, Canestrini.
*Aleurobius* (*Tyroglyphus*) *farinæ*, de Geer (part), Koch.
The male measures 0·33 mm. in length by 0·16 mm. in breadth; the female
0·6 mm. in length by 0·3 mm. in breadth. These mites possess five pairs
of suctorial organs of a light colour; the legs are reddish. Moniez
observed them in Lille on the skin of labourers who had been unloading
Russian corn. A few of the species generally mentioned under the
designation of _Tyroglyphus siro_ are probably the common flour-mite,
which also occurs on dry cheese.
[The _farinæ_ of de Geer is an Aleurobius described by him in
1778 (“Mém. Hist. Ins.,” vii, t. 5, f. 15, p. 97) as _Acarus
farinæ_.--F. V. T.]
Genus. *Tyroglyphus*, Latreille.
*Tyroglyphus siro*, L., 1756.
(Defined by Gervais, 1844.)
Male 0·5 mm. in length by 0·25 mm. in breadth; female 0·53 mm. in
length by 0·28 mm. in breadth; the males have two suckers on the tarsi
of the fourth pair of legs. Penis straight, colour whitish or reddish.
*Tyroglyphus longior*, Gervais, 1844.
White or yellowish, with two black spots on the abdomen. Male 0·55 mm.
in length, 0·28 mm. in breadth; penis bent. Female 0·61 mm. in length
and 0·28 mm. in breadth.
_T. siro_ and _T. longior_ live on dry cheese, in flour, on dried
fruits, etc., and have been occasionally observed in the stools,
urine, or pus of human beings, and also on their skin. The so-called
vanillismus is to be attributed to these species.
[_T. siro_ and _T. farinæ_ of Schrank (non Geer) are the same. They
are described under other names, such as _Acarus lactis_, Linn.; _A.
favorum_, Herm., etc.; _A. lactis_ in milk, _farinæ_ in flour, and
_siro_ in cheese; and as _A. dysenteriæ_, Linnæus (“Syst. Nat.,” ed.
12, pp. 1024–1767).]
[Illustration: FIG. 363.--_Tyroglyphus farinæ_: male. Enlarged. (After
Berlese.)]
[Illustration: FIG. 364.--_Tyroglyphus longior_, Gerv. (After Fum. and
Robin.)]
It is to these species that a case of dysentery was referred. Rolander,
who studied under Linnæus, was attacked by what was called dysentery.
The complaint soon gave way to treatment, but eight days after it
returned, soon disappeared, but again came a third time. All the time
Rolander had been living like the other inmates of the house, who
all escaped. Linnæus, aware that Bartholemy had attributed dysentery
to insects which he said he had seen, advised his student to examine
his stool. The result was that innumerable mites were found to be
present. Their presence was easily accounted for by the fact that they
were found in numbers in a cup made of juniper wood from which the
student alone drank of a night, and they were found to be of the same
species. What this species is we do not know. Linnæus called it _Acarus
dysenteriæ_, but it was the same as his _Acarus siro_. No records have
occurred since. It cannot be, as Latreille supposed, the cheese mite,
for they have been eaten by millions since, and it is strange no such
case has occurred again.
[*Tyroglyphus minor* var. *Castellani*, Hirst,
causes the copra itch in persons employed in the copra mills in Ceylon.
The skin of the hands, arms, legs and even body becomes covered with
pruriginous papules, papulo-pustules and pustules near the head.
The eruption begins as a rule on the hands. The mites live in the
copra dust. They produce dermatitis. Castellani produced the disease
experimentally by rubbing copra dust containing mites on the skin of
healthy people. Beta-naphthol ointment (5 to 10 per cent.) proved
useful in treatment (_Journ. Trop. Med. and Hyg._, December 16, 1912,
Castellani and Hirst).--F. V. T.]
Genus. *Glyciphagus*, Hering, 1838.
*Glyciphagus prunorum*, Her., and *G. domesticus*, de Geer.
The Glyciphagi are differentiated from the Tyroglyphi in that the
chitinous hairs on the body are fringed or feathered, and that they
lack a furrow dividing the cephalothorax from the abdomen. They live
under similar conditions to the Tyroglyphi and are occasionally found
on man or in fæces.
[Sugar merchants and grocers are frequently troubled by swarms of _G.
domesticus_, which leave the stores when being handled, and especially
shopmen, who handle sugar kept in small stores for some time. These
are the Acari that cause that irritating temporary affection known as
“grocer’s itch.”--F. V. T.]
*Glyciphagus cursor*, Gervais.
Under this name Signor Moriggia figures a horny excrescence of great
length growing from a woman’s hand, and containing in its cavities
quantities of Acarus. This species is really _G. domesticus_, de Geer.
_G. domesticus_ has also been described by Gervais (_Ann. Sci. Nat._,
1841, ser. 2, xv, p. 8) as _G. hippopodes_.
*Glyciphagus buski*, Murray.[350]
[350] Cooper and Busk’s _Micros. Journ._, 1842, and “Economic
Entomology,” Murray, p. 280.
[This is a mite found by Busk and named after him by Murray. It was
taken from beneath the cuticle of the sole of the foot of a negro in
the Seamen’s Hospital Ship on the Thames in 1841, in large sores of
a peculiar character confined to the soles of the feet. It appeared
that the disease was caused by its burrowing beneath the thick cuticle.
The disease was attributed to the wearing of a pair of shoes which had
been lent to another negro whose feet had been similarly affected for
nearly a year. The negro to whom the shoes were lent came from Sierra
Leone. Mr. Busk stated that some water brought by Dr. Stranger from
the River Sinoe, on the coast of Africa, contained one nearly perfect
specimen, and fragments of others very similar to if not identical with
this Acarus. Mr. Busk adds that he had been informed by Staff-Assistant
Surgeon P. D. Murray that at Sierra Leone there is a native pustular
disease called craw-craw--a species of itch breaking into open sores.
[From Busk’s original figure I see no reason to doubt that this is a
Glyciphagus.--F. V. T.]
Genus. *Rhizoglyphus*, Claparède, 1869.
*Rhizoglyphus parasiticus*, Dalgetty, 1901.
The _Rhizoglyphii_ are to be recognized by their short legs, which
are beset with spines, and by the tarsi, which terminate in a claw.
They live on plants, roots and bulbs, especially the bulbs of lilies.
[Illustration: FIG. 365.--_Rhizoglyphus parasiticus._ _a._, male; _b._,
female. Enlarged. (After Dalgetty.)]
This species has been observed on the feet of Indian coolies working
in the tea plantations; they produce a skin disease which always
commences with blebs between the toes, and which almost always extends
to the malleoli, but not beyond. The Acari have an elliptical body,
which is grey, but varies from greenish-yellow to greenish-brown when
the stomach is full. Eyes are absent. The legs are composed of five
segments and terminate with a claw. The males measure 0·18 mm. in
length by 0·08 mm. in breadth, and possess genital and anal pores;
the females measure 0·2 mm. in length by 0·09 mm. in breadth.[351]
[This is also known as coolie itch and is common in Indian tea
plantations.--F. V. T.]
[351] Dalgetty, A. B., “Water-itch; or Sore Feet of Coolies,” _Journ.
Trop. Med._, 1901, iv, p. 73.
Genus. *Histiogaster*, Berlese, 1883.
*Histiogaster* (*entomophagus?*) *spermaticus*, Trouessart, 1900.
The genus Histiogaster, which also approaches the _Tyroglyphinæ_, is
characterized by the circumstance that the males possess suctorial
pores used in copulation, as well as leaf-shaped appendages at the
posterior end of the body. They feed on vegetables, especially on
small fungi.
[Illustration: FIG. 366.--_Histiogaster_ (_entomophagus?_)
_spermaticus_: on left, male; on right, female--both from the abdominal
aspect. 200/1. (After E. Trouessart.)]
This species has been described by Trouessart,[352] who found numerous
specimens, some adult, others in the developmental stage (larvæ,
nymphs), and ova, in the fluid removed by puncture from a cyst of
the right testis. The males measure 0·25 mm., the females 0·32 mm.,
and the larvæ 0·1 mm. in length. The author is of opinion that the
animal--perhaps a fertilized female--was introduced by a catheter, and,
as a matter of fact, it was afterwards found that the patient had once
had the catheter passed in India while suffering from pernicious fever.
[352] Trouessart, E. R., _Compt. rend. Soc. Biol._, Paris, 1900, lii,
pp. 742–744, 893, 894; _Arch. de Par._, 1902, v, pp. 449–459.
It would here rather appear to be the case of a facultative parasitism
of an otherwise free-living species. _Histiogaster entomophagus_,
Laboulbène, is found occasionally in collections of insects feeding
on larger species containing much fat; the species also occurs on dry
cantharides; it appears to belong to the region of South Europe, where,
however, it is widely spread.
[Entomophagus occurs all over Europe and in America. It has been
described under the following names: _Acarus malus_, Shimer, 1868
(_Trans. Illinois Hort. Soc._); _Dermaleichus mali_, Riley, 1873 (_Rep.
Ins. Missouri_, v, p. 87); _Tyroglyphus mali_, Murray, 1877 (“Eco. Ent.
Apt.,” p. 275); _T. corticalis_, Michael, 1885 (_Trans. Roy. Micros.
Soc._, ser. 2, v, 3, p. 27, figs. 1 to 14); _Histiogaster corticalis_,
Canestrini, 1888 (_Prosp. Acarof._, iii, p. 397); _H. aleurophagus_,
Sicherin, 1894, Canestrini, _Prosp. Acarof._, vi, p. 815. Trouessart’s
species is evidently distinct.--F. V. T.]
Genus. *Cheyletus.*
*Cheyletus mericourti*, Lab.
_Acaropsis mericourti_, Moq. Tand.
[This mite has been described from three specimens found in pus which
flowed from an abscess in the ear of a naval officer, produced by
inflammation of the auditory passage. Where the mites came from we do
not know, as they were found near the Bank of Newfoundland. This genus
of Acari has enormous mandibles and a peculiar tracheal system; two
ungues and appendages to the tarsi.--F. V. T.]
Family. *Sarcoptidæ* (Itch Mites).
Small mites without eyes and tracheæ, and with delicate, transversely
striated cuticle. The mouth parts form a cone, over which the
shield-shaped upper lip protrudes; the cheliceræ are chelate; the
pedipalpi (or maxillary palpi) have three joints; the legs are short
and compact, and composed of five segments; the terminal joints have
pedunculated suckers (ambulacra) or a long bristle. The larvæ are
six-legged. They live on or under the skin of birds and mammals, on
which they produce the skin disease known as scabies, or itch.
[The _Sarcoptidæ_ attack the hairs, feathers or epidermis of birds,
animals and man, living as permanent parasites. The punctures they
produce are followed by the formation of more or less thick crusts
or scabs, beneath which the mites live and breed (so called scab,
mange and itch). Most are oviparous, some ovoviviparous. The eggs are
minute, ovoid, with a thin semi-transparent shell. They incubate in
a few days, varying from two to ten or eleven, as a rule. Generally
sarcoptic diseases lie dormant in winter and revive in spring and
summer in man; but in animals with long wool, such as sheep, they are
most active during winter, although revival of active reproduction
takes place in spring.
[Speaking generally, for the _Sarcoptidæ_ there are three distinct
stages in the development of the male, four in the female, as
follows:--
[(1) The larva. In this stage only three pairs of legs occur.
[(2) The nymph, in which a fourth pair of legs appear, and which thus
approaches the adult; but so far no sexual organs occur. Nymphs are
of two sizes--the smaller being future males, the larger females.
[(3) The next stage in the female is the age of _puberty_, the female
now being provided with a vulvo-anal slit; this so-called _pubescent
female_ is fertilized by the male. The male then dies. But the female
again casts her skin and enters another stage--
[(4) The ovigerous female--the egg-laying female--which has
differently modified legs.
[The rate at which these Acari breed is very great. Gerlach has
found that roughly, in each Sarcopt gallery, a female produces
fifteen individuals--ten females and five males--and that the
progeny reproduce again in fifteen days. The table given below thus
shows that one pair may produce the enormous number of 1,500,000
descendants in three months:--
First generation after 15 days 10 females 5 males
Second " " 30 " 100 " 50 "
Third " " 45 " 1,000 " 500 "
Fourth " " 60 " 10,000 " 5,000 "
Fifth " " 75 " 100,000 " 50,000 "
Sixth " " 90 " 1,000,000 " 500,000 "
= _1,500,000 individuals._
[These _Acarinæ_ are divided into three distinct sub-families, namely
the _Cytolichinæ_, _Sarcoptinæ_, _Canestriniinæ_.
[The _Sarcoptinæ_ alone interest us here, and of the nine genera the
three following are the most important:--
[(1) Sarcoptes, Latreille; Eusarcoptes.
[(2) Psoroptes, Gerv.; Dermatodectes, Gerlach; Dermatocoptes,
Fürstenberg.
[(3) Chorioptes, Gerv.; Symbiotes, Gerlach; Dermatophagus, Fürst.;
Sarco-dermatocedes, Del.
[The following are the main characters of these three genera:--
[_Sarcoptes_--round or slightly oval; the two posterior pairs of legs
being nearly or quite concealed beneath the body; the tarsi end in
simple long pedicles, with ambulatory suckers.
[_Psoroptes_--oval; the legs are all visible outside the margin of
the body; the ambulatory suckers are carried on long triangulated
stalks; the male has copulatory suckers and abdominal prolongations.
[_Chorioptes_--oval; legs long, thick, all visible; ambulatory
suckers very wide, carried at the end of simple, short pedicles.
[Sarcoptes make channels or furrows beneath the epidermis, and in
these the female lays her eggs. This form of acariasis is thus
difficult to cure. It is the cause of human itch (_vide Sarcoptes
scabiei_).
[Psoroptes do not make sub-epidermic galleries; they live and breed
in colonies beneath crusts or scabs formed by the changes they
produce in their host’s skin. Sheep scab is a common type of disease
produced by Psoroptes. This genus is of little importance as a
parasite to man.
[Chorioptes live as Psoroptes; they also do not affect man.
Otodectes, Can., affecting cats and dogs, and others occur, but
do not affect man as far as we know at present (“Demodicidae und
Sarcoptidae,” von Professor G. Canestrini und P. Kramer, _Das
Tierreich_, 1899).--F. V. T.]
Sub-family. *Sarcoptinæ.*
Genus. *Sarcoptes*, Latreille.
*Sarcoptes scabiei*, de Geer, 1778.
Syn.: _Acarus scabiei_, de Geer, 1778; _A. psoricus_, Pallas, 1760;
_A. siro_, L., 1778; _Sarcoptes exulcerans_,? Linn., 1758, Nitsch,
1818; _S. hominis_, Raspail, 1834, and Hering, 1838; _S. galei_,
Owen, 1853; _S. communis_, Delaf. et Bourg., 1862; _S. scabiei_ var.
_hominis_, Mégnin, 1880.
The body is oval or nearly circular and whitish in colour, with
transverse rows of striæ partly interrupted on the back. There are
transverse rows of small bristles on the dorsal surface, and groups of
trichomæ on the front, sides and back. There are chitinous hairs at the
base of the legs; the two first pairs are provided with pedunculated
ambulacra in both sexes, the two posterior pairs terminate each with
a long bristle in the female; in the male the third pair of legs
terminate in a bristle, the fourth pair with a pedunculated ambulacrum.
The anus is situated at the posterior border of the dorsal surface.
[Illustration: FIG. 367.--_Sarcoptes scabiei_: female, dorsal aspect.
200/1. (After Fürstenberg.)]
At one time numerous species were differentiated, according to the
form of the Acarus, the number, position and size of the hairs and
spines, even according to the hosts, etc. All these characteristics,
however, fluctuate so considerably that absolute differentiation is
impossible; the supposed species may be regarded in the same light as
Mégnin did, as varieties. It is also hardly possible to distinguish
the mite of human scabies (_S. hominis_) from that of a number of
domestic animals (_S. squamiferus)_. It is best, therefore, to accept
one single species (_S. scabiei_), which may give rise to different
races or castes by living in the skin of man and mammals, but can
pass from one host to the other.
[Canestrini and Kramer, in their monograph of the _Sarcoptidæ_,
enumerate eighteen distinct species of this genus, from the dog, goat,
camel, horse, ferret, lion, wolf, sheep, pig, etc., and two species
parasites of man (_scabiei_ and _scabiei-crustosæ_). There is no doubt
that they are distinct species.--F. V. T.]
The _S. scabiei_ of man (_S. scabiei_ var. _hominis_) (length of male
0·2 to 0·3 mm., and breadth 0·145 to 0·190 mm.; length of female 0·33
to 0·45 mm., and breadth 0·25 to 0·35 mm.) lives in the tunnels that
it excavates in the epidermis, and attacks by preference places with
thin skin, such as between the fingers, in the bend of the elbows and
knees, in the inguinal region, on the penis, on the mammæ, but may also
affect other parts. The tunnels, which vary from a few millimetres
to a centimetre and more long, do not run straight, but are somewhat
tortuous; the female is found at the terminal end. The tunnels contain
the excrement and oval eggs (0·14 mm. in length) of the parasite;
the males are rarely met with, as they die off after copulation; the
females die after depositing their eggs. The six-legged larvæ hatch out
after four to eight days, and after about a fortnight, during which
time they change their skins three times and undergo metamorphosis,
they begin themselves to burrow. Transmission from person to person
rarely is effected through linen, but by direct contact (as in coitus);
transmission can be artificially effected on horses, dogs and monkeys,
but not on cats.
[Illustration: FIG. 368.--_Sarcoptes scabiei_: male, ventral aspect.
200/1. (After Fürstenberg.)]
The smaller _S. scabiei-crustosæ_, Fürstenberg, is the cause of the
itch that occurs chiefly in Norway; it is not certain whether this is a
distinct species of itch mite.
[This is quite a distinct species, which is recorded from Germany and
France. Mégnin (_Parasitology_, 1880, p. 165) described this as _S.
scabiei_ var. _lupi_. The female is 140 µ long, 340 µ broad; the male
is 170 µ long by 150 µ broad. In _Science_ (March 3, 1893, p. 125) is
recorded that at the Indiana Academy of Science Dr. Robert Hessler
referred to “a case of that extremely rare and almost extinct form
of itch known as ‘Norway itch,’ the _scabies norvegica_ of Hebra,
1852.” The afflicted man was covered with thick, creamy white, leathery
scales; some of these scales measured over an inch in diameter and
1/10 in. thick. A constant shedding of scales went on, a handful being
gathered daily. They were found full of mites and eggs and riddled
with passages. Under treatment the mites were killed and the skin
became normal. Dr. Hessler made a calculation of the number of eggs
and mites, amounting to ova and shells 7,004,000, mites in all stages
2,009,000.--F. V. T.]
The following forms may be transmitted from DOMESTIC ANIMALS to MAN:--
(1) _S. scabiei_ var. _equi_. Male, 0·2 to 0·23 mm. long, 0·16 to
0·17 mm. broad. Female, 0·40 to 0·42 mm. long, 0·28 to 0·32 mm.
broad. The horse is the normal host.
(2) _S. scabiei_ var. _ovis_. Male, 0·22 mm. long, 0·16 mm. broad.
Females, 0·32 to 0·44 mm. long, 0·24 to 0·36 mm. broad. This mite
lives on sheep, and passes over to goats and human beings; it may
also be artificially transferred to horses, oxen and dogs.[353]
[353] [This mite produces the so-called “black muzzle” of
sheep.--F. V. T.]
(3) _S. scabiei_ var. _capræ_. Male, 0·24 mm. long, 0·188 mm. broad.
Female, 0·345 mm. long, 0·342 mm. broad. On goats, passing from them
to horse, ox, sheep, pig and man. On the latter, in contradistinction
to the varieties (1) and (2), it produces a severe affection.
(4) _S. scabiei_ var. _cameli_. Frequently observed in man, chiefly
in Africa. A few cases have been observed in Europe; the affection
induced by it is severe.
(5) _S. scabiei_ var. _aucheniæ_. Male, 0·245 mm. long, 0·182 mm.
broad. Female, 0·34 mm. long, 0·264 mm. broad. It lives on the llama,
and may be transmitted to man.
(6) _S. scabiei_ var. _suis_. Male, 0·25 to 0·35 mm. long, 0·19 to
0·3 mm. broad. Female, 0·4 to 0·5 mm. long, 0·3 to 0·39 mm. broad.
In the domestic pig and wild boar; occasionally also in man. The
settlement, however, is usually of short duration.
(7) _S. scabiei_ var. _canis_. Male, 0·19 to 0·23 mm. long, 0·14
to 0·17 mm. broad. Female, 0·29 to 0·38 mm. long, 0·23 to 0·28 mm.
broad. In the house-dog, and also, not unusually, in human beings.
(8) and (9) _S. scabiei_ var. _vulpis_ and _S. scabiei_ var. _leonis_
of the fox and lion have likewise been observed on man.
These are all distinct species and should read as follows: _S.
canis_, Gerl.; _S. ovis_, Mégn.; _S. equi_, Gerl.; _S. dromedarii_,
Gerv. (_cameli_, Mégn.); _S. aucheniæ_, Raill.; _S. suis_, Gerl.; _S.
vulpis_, Fürst.; _S. leonis_, Can.
*Sarcoptes minor*, Fürstenberg, 1861.
Anus situated on the back, legs short, pedunculated ambulacra broad;
living on cats (_S. minor_ var. _cati_) and rabbits (_S. minor_ var.
_cuniculi_). In cats this mite usually lives in the cervical region,
and thence spreads to the ears and head; it usually causes the death
of the infected animals; it is easily transferable from cat to cat, is
difficult to transmit to rabbits, but once settled on them can easily
infect other rabbits. On the other hand, the transmission of the itch
mite of the rabbit to the cat does not succeed. In man _S. minor_
induces an eruption that disappears after about a fortnight.
[_S. minor_, Fürstenberg, 1861 (“Krätzm.,” viii, p. 218), comes
in Railliet’s sub-genus NOTOEDRES, 1893 (“Zool.,” ed. 2, p. 660).
Canestrini raised this to generic rank in 1894 (_Prosp. Acarof._, vi,
p. 724).
[There are three species: (1) _N. notoedres_, Mégnin = _Sarcoptes
alepis_, Railliet and Lucet (_Compt. rend. Soc. de Biol._, 1893,
xlv, p. 404), and _Sarcoptes notoedres_ var. _muris_, Mégnin
(_Parasitology_, 1880, pp. 172–174). This occurs on the black and brown
rats and the water-vole.
[(2) _N. cati_, Hering, 1838 (_N. acta. ac. Leop._, ii, 18, xliv,
p. 605, figs. 9 and 10), = _Sarcoptes minor_, Fürstenberg (“Krätzm.,”
1861, viii, p. 215). Found on the cat in Germany, France, Italy, and
Britain.
[(3) _N. cuniculi_, Gerlach, 1857, “Krätzm.,” iii, figs. 20, 21. It
lives on the rabbit and is found in Germany and France.--F. V. T.]
[Illustration: FIG. 369.--_Sarcoptes minor_ var. _cati_: on the left,
female (lying on its abdomen); on the right, male (lying on its back).
(After Railliet.)]
The itch mites of domestic animals, which belong to the genera
Psoroptes (= Dermatodectes = Dermatocoptes) and Chorioptes (Symbiotes
= Dermatophagus), as a rule do not infest and live on man, even when
artificially transmitted. It is, however, possible for this to occur.
Moniez (“Traité de par.,” 1896, p. 559) mentions that a species of
Chorioptes--probably _Ch. bovis_--had been found on man, as had also
_Demodex folliculorum_. This author also includes _Dermatophagoides
scheremetewskyi_, Bogdanoff (_Bull. soc. imp. d. natural._, _Moscou_,
1864, xxxvii, p. 341), which has repeatedly been found on man in
Moscow and Leipzig (Zürn, _Ber. d. med. Ges._, _Leipzig_, 1877,
p. 38), as _Chorioptes bovis_.
OTHER REFERENCES TO _Scabies crustosæ_ AND _norvegica_, ETC.
(1) “Ein Fall von _Scabies crustosa norvegica_,” _Würzb. med.
Zeitschr._, l, pp. 134–139, pl. 3, H. Bamberger.
(2) “Ueber die Krätzmilbe (_Acarus scabiei_),” _Notiz. a. d. Geb. d.
Nat. u. Heilk._, Weimar (1913), xlii (11), Oct., pp. 161–166 (1834),
de Blainville.
(3) “Rapport sur le ciron de la gale (_Acarus scabiei_),” _Ann.
de Mus. d’Hist. nat._, 1831; _Parasitology_, iv, pp. 213–232, de
Blainville.
Family. *Demodicidæ* (Mites of the Hair-follicles).
Small _Acarina_, elongated in worm-like fashion, with annulated
abdomen, and without eyes or tracheæ. The mouth parts consist of a
suctorial proboscis and three-jointed palpi; the legs are short, and
have three segments with small terminal ungues. The anus is situated
on the anterior border of the abdomen; oviparous; the larvæ have six
stumpy legs. These mites live in the hair-follicles of mammals.
Genus. *Demodex*, Owen.
*Demodex folliculorum*, Simon, 1842.
Syn.: _Acarus folliculorum_, Sim., 1843; _Demodex folliculorum_,
Owen, 1843; _Macrogaster platypus_, Miescher, 1843; _Simonea
folliculorum_, P. Gervais, 1844; _Steatozoon folliculorum_, Wilson,
1847.
As in _Sarcoptes scabiei_, numerous varieties of this species are
known; the form parasitic on man lives in the hair-follicles, the
meibomian and sebaceous glands, and hardly ever causes inconvenience;
the male measures 0·3 mm. in length and the female about 0·4 mm. in
length. The eggs 0·06 to 0·08 mm. in length, 0·04 to 0·05 mm. in
breadth, and are thin-shelled. The creatures are always attached with
the head end downwards in the parts mentioned; they are most frequent
in the sebaceous glands of the face, by the nose, lips and forehead,
but they may be present on the abdomen and on other parts of the body.
They may occasionally obstruct the excretory gland ducts, thus causing
inflammation of the gland (comedones); their agglomeration in the
meibomian glands sets up inflammation of the margins of the eyelids.
There are generally only a few specimens in a gland. According to
some statements Demodex occurs in 50 per cent. of mankind and even in
children; they survive the death of their hosts by several days.
[Illustration: FIG. 370.--_Demodex folliculorum_ of the dog. (After
Mégnin.)]
The variety living in the dog (_D. folliculorum_ var. _canis_) is
smaller than the variety living in man, and produces a skin disease
resembling scabies in these animals. According to Zürn they may also
live on man; nevertheless, no other investigator has recorded a
similar observation, and attempts at artificial infection have proved
negative.[354]
[354] [This mite causes what we know in England as red mange in
dogs.--F. V. T.]
[Ten distinct species of Demodex are given by Canestrini and Kramer
(“Demodicidae und Sarcoptidae,” _Das Tierreich_, 1899, vii). The
species are certainly distinct.
[The species living on the dog (_D. canis_, Leydig, 1844) is
cosmopolitan. According to the _British Medical Journal_ (February 22,
1913, p. 407), dog mange may be caught by humans. Whitfield and Hobday
describe in the _Veterinary Journal_ seventeen cases which have come
under their observation.--F. V. T.]
Order. *Pentastomida.*
Family. *Linguatulidæ.*
_Arachnida_ greatly altered in consequence of their parasitic manner
of life; for a long time they were regarded as helminthes. The body
is elongated, vermiform, flattened or cylindrical, and more or less
distinctly annulated. The head, thorax, and abdomen are not defined
from each other (fig. 371). The elliptical mouth, surrounded by a
chitinous ring, is situated at the anterior end, on the ventral
surface, and the intestine leading straight through the body opens at
the posterior end. Two retractile hooks are at the sides of the mouth
(fig. 372); these are usually considered to be the terminal joints of
two pairs of legs, but it appears to be more correct to regard them
as the remains of the antennæ and palpi (Stiles). According to this
opinion, the legs in the adult state are completely degenerated.
The nervous system is reduced to an œsophageal ring. No organs of
sense are recognizable except the papillæ at the anterior end. There
are neither organs of circulation nor of respiration.[355]
[355] What are designated as stigmata in the Linguatulides are the
orifices of sebaceous glands.
The sexes are distinct. In the small male the sexual orifice is
situated ventrally in the anterior part of the body; in the female it
is placed near the anus. The _Linguatulidæ_ lay eggs, and from each
egg, after being conveyed into an intermediate host, a four-legged
larva, with rudimentary mouth parts, hatches out. It goes through
a series of metamorphoses, and passes through a second larval
condition, which, however, possesses the essential characteristics
of the fully developed form. Sooner or later it migrates during this
stage, and reaches its final host, mammal or reptile, in the nostrils
or lungs of which the adult _Linguatulidæ_ live.
[As adults they live as internal blood feeders in various birds,
reptiles and mammals, especially in the nasal and respiratory passages.
The larval stage occurs in another host in an encysted condition; this
host is usually an animal preyed upon by the species in which the
sexual forms are found. The larvæ bore through the walls of the host’s
stomach and enter liver and spleen or brain, where they encyst; here
they grow until they assume almost the appearance of the adult. These
encysted larvæ on being eaten later make their way into the nasal
passages and lungs, where they mature. Both adults and larvæ occur in
man, as mentioned later.
[Three genera are recognized in this family:--
[(1) _Linguatula._--Body flat, annulated. Adults live in the nasal
sinus.
[(2) _Porocephalus._--Body cylindrical, elongate, with often deeply
cut rings. Adult in respiratory organs of snakes, larvæ in animals
and man.
[(3) _Reighardia._--Cylindrical, but not ringed. Not found in
humans.--F. V. T.]
Genus. *Linguatula*, Fröhlich.
*Linguatula rhinaria*, Pilger, 1802.
Syn.: _Tænia rhinaria_, Pilger, 1802; _Polystoma tænioides_, Rud.,
1810; _Linguatula tænioides_, Lam., 1816; _Pentastoma tænioides_,
Rud., 1819.
The male is white in colour, 18 to 20 mm. in length, anterior portion
3 to 4 mm. in breadth, posterior part 0·5 mm. in breadth. The female
is of a yellowish colour, 8, 10, or 13 cm. long, anterior part 8 to
10 mm. and posterior part 2 mm. wide. The brownish eggs can be seen in
the median line. The body is elongated, rather flat, and exhibits about
ninety rings or segments with crenellated borders. The hooks round the
mouth are strongly curved and are articulated to a basilar support.
Eggs oval, 0·09 µ in length, 0·07 µ in breadth.
_L. rhinaria_, in the adult condition, lives in the nasal cavity and
frontal sinus of the dog, wolf, fox, horse, goat, and occasionally of
man; it causes severe catarrh, epistaxis and suppuration.
[Illustration: FIG. 371.--_Linguatula rhinaria_: female. Natural size.]
[Illustration: FIG. 372.--Larva of _Linguatula rhinaria_ (_Pentastoma
denticulatum_). Enlarged. (After Leuckart.)]
_Development._--The ova, which are found in masses in the nasal mucus,
already possess an embryo; they are expelled with the nasal secretion,
and are swallowed by herbivorous mammals with their food, mostly by
hares and rabbits, but also by sheep, goats, oxen, horses, antelopes,
fallow deer, pigs, cats, and occasionally also by human beings. The
young larvæ hatch out in the stomach; they possess a thickened anterior
body with rudimentary mouth parts and two pairs of limbs; the body
gradually tapers to a short tail.
The larvæ of the _Linguatulidæ_ bore through the intestinal wall and
reach the liver, more rarely the mesenteric glands, etc.; they here
become encysted and enter a sort of pupal stage in which they lose
their limbs; after several moultings and gradual growth the second
larval stage, having the appearance of the adult Linguatula, sets in.
About five to six months after infection the creatures have become 4 to
6 mm. long, possess eighty to ninety rings, which have a series of fine
points on their posterior border; the mouth and intestine are formed,
the sexual organs mature and the two pairs of hooks are near the mouth.
This larval stage (fig. 372) has been known for a long time, but it
was regarded as an independent species of animal, and therefore had a
separate name (_Linguatula serrata_, Fr.; _Pentastoma denticalatum_,
Rud., etc.).
[Illustration: FIG. 373.--_Linguatula rhinaria_: on left, eggs in
gelatinous covering, 110/1. On right, first larval stage. 300/1. (After
M. Koch.)]
Later these Linguatula larvæ make an attempt to escape from their
hosts, and this, of course, can only be effected by means of an active
migration; they leave the cysts, and according to their respective
positions in the abdominal or pleural cavities they reach the bronchi
or the intestine, and finally pass out; they may be again sniffed
up by dogs and settle in their nasal cavities. Still this outward
migration does not appear to be necessary for further development. A
portion of the larvæ gain access to the nasal cavities directly through
the trachea, and thus herbivorous mammals certainly become directly
infected. In most cases the infection of dogs, wolves and foxes, that
is, of carnivorous mammals, takes place through consuming the bodies
of mammals, or parts of them, such as the liver and lungs, which are
affected with the second larval form; in any case most larvæ obtain
access first to the stomach of their host, from here they make an
active migration through the œsophagus to the oral and nasal cavities,
in which they settle. It is possible also that the same larvæ which
are free in the oral cavity when the food is being eaten migrate into
the nasal cavities. After being stationary a fresh skin is formed and
the spine-bearing cuticula are thrown off. The male attains its full
size in the fourth, and the female in the sixth month. The duration of
life is stated to be from fifteen months to several years.
_L. rhinaria_ has been observed in man in the adult as well as in the
larval condition (_Pentastoma denticulatum_). Zenker first called
attention to the occurrence of the larva in man, having found it
nine times in the liver in 168 autopsies. Heschl found it twice in
Vienna in twenty autopsies, Virchow found it in Würzburg and Berlin,
Wagner in Leipzig (10 per cent.), and Frerichs in Breslau five times
in forty-seven autopsies. The parasite is much less frequent in
Switzerland. According to Klebs, one case occurs in 900 autopsies,
and according to Zaeslin two cases occurred in Basle to 1,914
autopsies. In the Seamen’s Hospital in Kronstadt _P. denticulatum_
has been found six times in 659 autopsies. It was almost always the
liver that contained one or a few specimens. The parasite was very
rarely found in the kidney or spleen, or encysted in the intestinal
wall. The adult _L. rhinaria_ is far more rarely observed in man.
A case reported by Landon that related to a blacksmith of Elbing is
particularly interesting. This man accompanied the campaign of 1870;
he soon, however, fell ill with pains in the liver, accompanied by
icterus and intestinal disorders. Soon after the war, and after the
symptoms were reduced to icterus and weakness, bleeding of the nose
set in and continued with slight intermissions for seven years;
an unpleasant sensation of pressure in the left nasal cavity set
in, with inflammatory swelling of the mucous membrane. At last, in
the summer of 1878, when the pressure in the nose had considerably
increased, a Linguatula was expelled from the nose with a violent
attack of sneezing, and lived for three days longer in water. The
bleeding of the nose then ceased and the patient soon recovered.
There can be no doubt that the first illness was connected with
the invasion in the liver of numerous larvæ of Pentastoma, and
disappeared after their encystment; one or a few of these must
subsequently have found its way to the nose and settled there.
Genus. *Porocephalus.*
*Porocephalus constrictus*, v. Siebold, 1852.
Syn.: _Nematoideum hominis_, Diesing, 1851; _Pentastomum
constrictum_, v. Sieb., 1852; _Porocephalus constrictus_, Stiles,
1893.
Porocephalus is distinguished from Linguatula by its cylindrical body
and by certain internal structures. _Porocephalus constrictus_ is at
present only known in its larval stage. It is milk white in colour with
golden-yellow hooklets. Number of rings, twenty-three. Length 13 mm.,
breadth 2·2 mm. There are no prickles on the posterior border of the
annulations of the body.
This species was first discovered by Pruner encysted in the livers
of two negroes in Cairo. Bilharz reported two further cases in which
the parasites were encysted in the liver and in the mucosa of the
intestine; a few other observations have been made by Fenger, Aitken,
Giard and Chalmas. Aitken’s report deals with soldiers of the British
Colonies in Africa. The parasites were discovered in the liver as
well as in the lung, and appear to have been the cause of death in
one case (pneumonia, peritonitis).
Pruner has found the same parasite also in the liver of the giraffe.
It has recently been assumed that _Porocephalus constrictus_ is the
larva of _Pentastoma moniliforme_, Diesing, 1835, that attains a
length of 70 mm. and lives in the lungs of African Pythonides. The
larva is known to have been ejected from monkeys (_Cercopithecus
albogularis_, _Cynocephalus maimon_), from the giraffe
(_Camelopardalis giraffa_), from a species of hyæna (_Proteles
cristatus_), and should be expected to occur frequently in smaller
mammals which have been swallowed by African serpents of enormous
size.
[The three species of _Pentastomidæ_, or tongue worms, found in man are
_Linguatula serrata_, Frölich; _Porocephalus armillatus_, Wyman; and
_Pentastoma moniliformis_, Diesing.
[(1) _Linguatula serrata_ has been referred to under a great number
of names.[356] It is a frequent parasite in dogs, oxen and sheep; as
an adult in the dog and also in the fox and wolf. The nymphal stage
is found in rats, hares, rabbits, the horse, oxen, sheep, goats,
pigs, camels, deer, the African and long-eared hedgehogs, porcupine,
guinea-pig and peccary. In man it is found in both adult and nymphal
stages. Sambon says the nymphal stage is of frequent occurrence, but
is usually overlooked. Zenker, who first found it in man, obtained it
in nine out of 160 _post-mortems_, usually encysted in the liver. It
is then said to be harmless. Landon, in 1878, found the adult in man,
the patient suffering from epistaxis for about seven years; in the end
during a fit of sneezing the living parasite was ejected through the
nostril. This case is of particular interest as it appears to suggest
that this Acarid may now and then pass its entire development in the
same host, or at any rate may actively migrate from the liver to the
nasal cavities after a period of encystment in the liver or elsewhere,
which has also been observed in herbivorous animals (_vide_ also
p. 526).
[356] Synonymy given by Sambon: Adult form, _Ténia lanceolé_, Chabert, 1787; _Ver rhinaire_,
Chabert, 1787; _Tænia rhinaris_, Pilger, 1805; _Tænia lanceolata_, Rudolphi, 1805; _Cochlus
rhinarius_, Rudolphi, 1805; _Prionoderma rhinaria_, Rudolphi, 1808; _Polystoma tænioides_,
Rudolphi, 1809; _Linguatula tænioides_, Lamark, 1816; _Prionoderma lanceolata_, Cuvier,
1817; _Pentastoma tænioides_, Rudolphi, 1819; _Linguatula lanceolata_, de Blainville, 1828;
_Linguatula rhinaris_, Railliet, 1885; _Linguatula caprina_, R. Blanchard, 1900. Nymphal
form: _Linguatula serrata_, Frölich, 1789; _Tænia capræa_, Abildgaard, 1789; _Tænia caprina_,
Gmelin, 1800; _Polystoma serrata_, Goeze, 1800; _Halysis caprina_, Zeder, 1803; _Linguatula
denticulata_, Rudolphi, 1805; _Echinorhynchus capreæ_, Braun, 1809; _Tetragulus capriæ_, Bosc,
1810; _Pentastoma denticulatum_, Rudolphi, 1819; _Pentastoma emarginatum_, Rudolphi,
1819; _Pentastoma fera_, Creplin, 1829; _Linguatula ferox_, Gros, 1849.
[It is recorded from man in Central America (Darling, _Bull. Soc. Path.
exot._, 1912, v, p. 118; and again _Arch. Int. Med._, 1912, v, p. 401),
also from Rio de Janeiro (_Mem. Inst. Oswaldo Cruz_, 1913, fasc. ii,
p. 125) by Faria and Travassos.
[(2) _Porocephalus armillatus_, Wyman, is also known under a variety
of names.[357] This species is widely spread over tropical Africa.
The adult stage is found in pythons and puff-adders, the nymphal in
the chimpanzee, Sykes monkey, mandrill and other monkeys, the lion,
leopard, banded ichneumon, Aard wolf, dog, black rat, South African
reedbuck and the giraffe. The adult has never been found in man or any
mammal. No fewer than sixteen cases of the nymphal form, Sambon tells
us, have been found in man, and it is probably much more widespread
than at present known. So far it has only been found in the African
natives. This species has sixteen to seventeen body rings in the male,
eighteen to twenty-two in the female, and the body does not taper as
much as in the next species.
[357] Adult form as _Linguatula armillata_, Wyman, 1847; _Pentastomum
polyzonum_, Hailey, 1856; _Pentastomum armillatum_, Leuckart, 1860;
_Pentastomum armillatum_, Diesing, 1864; _Porocephalus armillatus_,
Stiles, 1893; _Porocephalus polyzonus_, Stiles, 1893; _Porocephalus
moniliformis_, Neumann (in part), 1899. Nymphal form: _Linguatula
diesingii_, van Beneden, 1849; _Pentastomum euryzonum_, Diesing, 1850;
_Nematoideum hominis_, Diesing, 1851; _Pentastomum constrictum_,
von Siebold, 1852; _Linguatula constricta_, Küchenmeister, 1855;
_Pentastoma leonis_, Wedl., 1863; _Pentastoma fornatum_, Cobbold,
1879; _Pentastomum protelis_, Hoyle, 1883; _Porocephalus constrictus_,
Stiles, 1893; _Linguatula constrictor_, Galli-Valerio, 1896;
_Pentastomum diesingii_, Shipley, 1898.
[(3) _Pentastoma moniliformis_, Diesing,[358] is an Oriental species,
found in India, Indo-China and South China, and the Malay Archipelago.
The adult occurs in both the Indian and reticulated pythons. The
nymphal stage has been found in monkeys, the tiger, the civet and the
Indian otter.
[358] The synonymy is as follows:--Adult form: _Pentastoma
moniliforme_, Diesing, 1835; _Linguatule moniliforme_, Mégnin, 1880;
_Porocephalus moniliformis_, Stiles. Nymphal form: _Pentastoma
fornatum_, Creplin (in part), 1849; _Pentastoma wedlii_, Cobbold, 1866;
_Pentastoma aonycis_, Macalister, 1874; _Porocephalus armillatus_,
Stiles (in part), 1908.
[The nymph has twice been found in man; in one case in the liver of
a Filipino, the other in the serous coat of the small intestine of a
native of Sumatra.
[This species can be told by the female having twenty-nine to
thirty-three body rings, the male twenty-six, and the annulations are
more bead-like and less prominent than in the African species.
[In addition to these three, Sambon thinks it probable that others
occur in man.--F. V. T.]
OTHER REFERENCES TO _Pentastomidæ_.
(1) “Die Wanderung des _Pentastomum denticulatum_ beim Rinde,”
_Centralbl. f. Bakt. u. Parasitenk._, Jan. 2, 1889, v (1), pp. 1–5,
V. Bates.
(2) “Il _Pentastoma moniliforme_, Dies., nella pantera,” _Med.-vet.
Torino_, 1877, 4 s., vi (12), pp. 529–532, R. Bassi.
(3) “On the Organization and Development of Linguatula (Pentastoma),
accompanied with the description of a new species from the abdominal
cavity of the mandrill,” _Ann. and Mag. Nat. Hist._, 1848, 2 s. ii
(7), 2, pp. 69–70, v. Beneden.
(4) “De la _Linguatula ferox_ (_Pentastoma denticulatum_ aut
_serratum_),” _Bull. Acad. roy. d. Sci. d. Belg._, 1855, xxii, pt. 1
(1), pp. 4–10, v. Beneden.
(5) “Note sur quelques pentastomes,” _Bull. Acad. roy. d. Sci. de
Belg._, 1857, 26, 2 s., ii (5), pp. 29–30, v. Beneden.
(6) “Ueber das _Pentastoma_ in de gekrösdrusen den Schafe,” _Repert.
d. Thierh. Stuttg._, 1861, xxii, pp. 37–38, Collin.
(7) “Eine Linguatula aus der Mesenterialdrüse des Schafes und
Dromedars als zweites ungesche. Stadium von _Pent. taenioides_,”
_Notiz. u. Tagsber. u. d. Geb. d. Nat. u. Heilk._ Jena, 1862, v,
pp. 127, 128, Colin.
_B._ *INSECTA* (_Hexapoda_).
Three separate regions can always be distinguished in the body
of insects, namely, the head, thorax and abdomen. The HEAD is a
roundish unsegmented capsule and possesses four pairs of appendages.
The first pair are the various shaped feelers (antennæ), which are
placed on the superior surface of the head next to the eyes; then
more ventrally placed a pair of upper jaws (mandibles) without
palpi and without articulations; they are powerful masticatory
organs.[359] The first pair of lower jaws (maxillæ) are jointed and
bear a palpus (palpus maxillaris); the second pair of maxillæ are
soldered together and form the lower lip (labium), and likewise carry
a palpus labialis on each side. The upper lip (labrum), as well as
the other parts (which, however, are only appendages), belong to the
mouth, which is really formed of a number of closely united pieces.
The mouth parts are modified according to the functions required
of them. _Coleoptera_, _Neuroptera_, and _Orthoptera_ have biting
or masticatory mouth parts which conform with the scheme described
above. In the licking mouth parts of the _Hymenoptera_ the maxillæ
and under lip are considerably elongated, while the mandibles
retain their form and are used for triturating the food; in the
_Lepidoptera_ nearly all the mouth parts are shortened except the
maxillæ, which form a long and sometimes spirally rolled suctorial
proboscis; the _Diptera_ and _Rhynchota_ have piercing and sucking
mouth parts. The mandibles and maxillæ are metamorphosed into
needle-like structures, while the suctorial apparatus is formed by
the labrum.
[359] [The mandibles are only powerful masticatory organs in
biting-mouthed insects (_Mandibulata_); in the sucking or
piercing-mouthed insects they may be absent, or in the form of
needle-like stylets (_Haustellata_).--F. V. T.]
The thorax consists of three segments, which are frequently united;
ventrally it carries three pairs of legs, which consist of a definite
number of articulated pieces joined together. Their form also changes
according to their function, so that legs for running, walking,
digging, swimming, jumping, and preying are seen. A pair of wings are
respectively attached to the last and last but one thoracic rings,
and these may be traced back, not to metamorphosed appendages, but to
tracheal branchia. They are composed of chitinous membranes supported
by branched structures (veins or ribs). Their size and formation
vary; they are seldom of equal size and form (_Neuroptera_);
often the posterior wings are larger than the anterior wings, the
former then only serving as protective coverings for the latter
(_Coleoptera_), or the anterior wings are larger (_Lepidoptera_), or
the posterior wings are shortened or are entirely absent (_Diptera_);
and finally there are insects in which both pairs of wings are
lacking.[360]
[360] [As in the order _Aptera_, which includes the Thysanura and
Collembola, and also exceptions in other orders, as the fleas amongst
_Diptera_, the Mutillus and ants amongst _Hymenoptera_.--F. V. T.]
The abdomen retains its segmentation, but, with the exception of
a few groups related to the primitive forms of insects, has no
appendages in the imago condition; the abdomen usually consists of
ten segments, on the last of which the anus is situated.
We need only observe the following characters in considering the
anatomy of insects:--
The EPIDERMIS consists of the chitinous cuticle, which is separate
from the cellular layer beneath (hypodermis); the various appendages
are supported by the chitinous layer.
The INTESTINAL CANAL usually consists of the anterior, median and
terminal intestine, and as a rule passes straight through the body;
salivary glands discharge into the anterior part, and, in some cases,
yield a stiffening secretion which serves for spinning webs; numerous
or scanty hepatic tubes are appended to the median intestine, while
on the border between the median and terminal intestine open four
to six long tubes (vasa malpighiana), which act as urinary organs.
Finally the end portion of the intestine carries various glands (anal
and rectal glands, etc.).
The CENTRAL NERVOUS SYSTEM agrees in structure with that of the
Annelids, but is more highly developed. The pharyngeal ring surrounds
the front part of the intestine; the sensory nerves originate from
its SUPERIOR PHARYNGEAL GANGLIA and are the seat of the higher
psychical functions; the INFERIOR PHARYNGEAL GANGLIA govern the mouth
parts, and in addition appear to regulate the movements (cerebellum)
of the vertebrates.
The chain of GANGLIA lying on the ventral side of the abdomen
consists primitively of pairs of ganglia corresponding with the
twelve segments, which are connected by longitudinal and transverse
commissures. But many changes in the ganglia may be seen in insects
caused by partial or entire amalgamation of single ganglia, so that
in a few cases only one abdominal ganglion is present. In conclusion,
a definite INTESTINAL NERVOUS SYSTEM is always present.
Of the organs of sense the FACETTED EYES, situated at the sides of
the head, deserve special mention, as do also the ORGANS OF TOUCH and
SMELL, situated on the antennæ, and the ORGANS OF HEARING and taste,
or finer sensations, situated at the mouth and in the buccal cavity.
The sounds emitted by insects are, as a rule, produced by the
friction or beating of certain chitinous parts, but sounds are also
produced in breathing (flies).
The ORGANS OF RESPIRATION, the so-called tracheæ, are highly
developed; there are openings (stigmata) at the sides of the body
which draw in air by means of the active participation of the muscles
of the body. The number of stigmata varies between two and ten pairs;
the tracheæ themselves branch off from the trunks in the most varied
manner, and carry air to the internal organs.
The colourless BLOOD circulates between the tissues and organs, and
is kept circulating by the contraction of a chambered dorsal vessel
provided with ostia, and which terminates in a short aorta opening at
the anterior end.
Insects are SEXUALLY DISTINCT; their sexual glands are in pairs and
have a tubular structure, but the testicular tubules are united
together by a capsule into an oval testicle; exceptionally, also, the
excretory canals are double, as also the sexual orifices; usually the
paired canals unite into a single oviduct or spermatic duct which
terminates at the posterior end of the body after receiving the
products of various glands.
As to the HISTORY OF THE DEVELOPMENT of insects, all that is
necessary to mention here is that the young hatched from eggs only
exceptionally (as in _Apterygota_) resemble the adult parent (insecta
ametabola); as a rule they differ from them not only in the shape
of the body, but also more or less by their manner of life, and
only attain the form of the parent through METAMORPHOSIS. This is
a gradual process (insecta hemimetabola) in the _Rhynchota_ and
_Orthoptera_, or a sudden one with a stage of inanition (insecta
metabola) in the other orders. This stage of rest or inanition, the
PUPA, concludes the larval life (caterpillar, maggot, etc.); during
the pupal stage no nourishment at all is taken, but the internal
organs undergo changes; in some forms the rest is not absolute, as
voluntary local movements may take place (pupæ of gnats).
The insects are divided into numerous orders according to the form
of the mouth parts, the structure of the wings, as well as the
manner of the development; with the exception of the lowest group
(_Apterygota_), which is most nearly related to the ancestors of the
insects, and which has no wings and undergoes no metamorphosis, all
the remaining orders, which are termed _Pterygota_, have wings on the
thorax, though there are, of course, a few species and families of
this group which have lost their wings.
The _Pterygota_ include--
(1) _Orthoptera._--Biting mouth parts, anterior wings leathery,
posterior wings thin, folded longitudinally; metamorphosis incomplete
(grasshoppers, crickets, cockroaches).
(2) _Pseudoneuroptera._--Biting mouth parts, wings of equal size,
thin, not folded up (dragon-flies, hair and feather lice, termites).
(3) _Rhynchota_ or _Hemiptera_.--Mouth parts formed for puncturing
and sucking; wings alike, or the anterior wings may be thickened,
parchment-like at their base (plant lice, cicadæ, bugs and true lice).
(4) _Neuroptera._--Biting mouth parts; wings alike, thin;
metamorphosis complete (ant-lions, lace-wing flies, etc.).
(5) _Trichoptera._--Licking mouth parts; anterior wings narrow,
posterior wings longitudinally folded, both ornamented with little
hairs; the larvæ are worm-like in form, live in water, and breathe
through tracheal gills (may flies, etc.).
(6) _Lepidoptera._--Suctorial mouth parts; wings covered with scales
(butterflies).
(7) _Coleoptera._--Biting mouth parts; anterior wings thickened and
differ in colour, appearance and function from the thin, folded
posterior wings (beetles).
(8) _Hymenoptera._--Mouth parts for licking and biting; the wings
alike, membranous (ichneumon flies, ants, wasps, bees, humble bees).
(9) _Diptera._--Mouth parts formed for puncturing, sucking or
licking; posterior wings degenerated (gnats, flies, gadflies, fleas).
(10) _Strepsiptera._--Anterior wings shortened; the female without
wings and living parasitically (fan-wings).
The parasites of man occur amongst the _Rhynchota_, _Coleoptera_, and
amongst the _Diptera_.
[The most usual and recent classification of the _Hexapoda_ is the
following:--
(1) _Aptera._--Wingless insects; scarcely any metamorphosis.
(2) _Neuroptera._--Four membranous wings, frequently with much
network; the front pair not much, if at all, harder than the under
pair; the latter with but little or no fan-like action in closing;
mandibulate; metamorphosis variable, but rarely complete.
(3) _Orthoptera._--Four wings; front pair coriaceous or leather-like,
usually smaller than the other pair, which are of more delicate
texture and contract in repose like a fan; mandibulate; metamorphosis
complete.
(4) _Thysanoptera._--Four very narrow fringed wings; mouth
imperfectly suctorial; metamorphosis slight.
(5) _Hemiptera._--Four wings; the front pair either all transparent
or with the basal half leathery; mouth suctorial; metamorphosis
slight.
(6) _Diptera._--Two membranous wings only; mouth suctorial, very
varied; metamorphosis complete.
(7) _Lepidoptera._--Four large wings covered with scales; mouth
suctorial, metamorphosis great.
(8) _Hymenoptera._--Four membranous wings; front pair larger than
hind, which do not fold up in repose; mandibulate, sometimes with a
tubular proboscis; metamorphosis complete.
(9) _Coleoptera._--Four wings, the front pair hard and horny
(elytra), meeting in a line over the back and covering the delicate
hind pair; mandibulate; metamorphosis complete.
[There are two other well-known arrangements, namely, Packard’s and
Brauer’s, of recent date, but the one given here, which is based on
Linnaeus’ grouping by Dr. Sharp, is by far the simplest.--F. V. T.]
Order. *Rhyncota.*[361]
[361] [Usually known as _Hemiptera_. There are two sub-orders,
_Heteroptera_ and _Homoptera_. The former have the base of the front
wings coriaceous; the latter have all four wings membranous. The
_Homoptera_ are Aphides or plant lice and scale insects (_Coccidæ_),
none of which attack man. Recently an interesting case has been
reported to me where certain Aphides had been passed in human urine.
One species was _Rhopalosiphum dianthi_, the other found in the urine
was the hop aphis (_Phorodon humuli_). I cannot believe, however, that
they had been actually passed, in spite of the case being reported by a
medical man.--F. V. T.]
The lower lip forms a long thin tube that can be turned back
(rostrum), and within which lie the setaceous mandibles and maxillæ;
the first thoracic segment is not united with the two posterior ones;
the anterior wings are usually leathery as far as the centre.
(_a_) RHYNCOTA APTERA PARASITICA.
Family. *Pediculidæ* (Lice).
The lower lip is transformed into a projecting rostrum provided with
barbed hooklets in which the hollow extensile sucker (maxillæ and
mandibles) is situated; no wings; no metamorphosis; only simple eyes;
the antennæ are five-jointed, the feet possess hook-like terminal
structures; the barrel-shaped eggs (nits) are deposited on the hair
of the host.
[The lice or _Pediculidæ_ are also known as _Anoplura_ and
_Siphunculata_.
[They have been split up into a number of families and sub-families
and a number of genera, but as far as this work is concerned it is
best to retain the single family _Pediculidæ_.
[Only the three species mentioned here are common parasites of man,
but now and then horse and cattle and sheep lice, _Hæmatopinus_, may
cause transitory annoyance.--F. V. T.]
Genus. *Pediculus*, Linnæus.
*Pediculus capitis*, de Geer, 1778.
Male 1 to 1·5 mm. in length, female 1·8 to 2·0 mm. in length. The
colour varies from light grey to black according to the colour of the
hair of the human race upon which they are parasitic. The abdomen has
eight segments, of which the six central ones are each provided with a
pair of stigmata. The thorax is as broad as the abdomen. Eggs 0·6 mm.
in length; about fifty are deposited by a female head louse. The young
can propagate when eighteen days old.
The head louse lives especially in the hairy parts of the head
of human beings; more rarely it is found on other hairy parts of
the body. It is spread over the entire surface of the globe, and
was present in America before the arrival of Europeans. Quite
exceptionally it is said that it bores itself deep into the epidermis
and can live in ulcers.
[The eggs are pear-shaped and are attached to the hairs near the
roots by means of a clasping collar. They hatch in about seven
days. The young are like the adults and mature in a month. Its
general colour varies with that of its host. In West Africans
nearly black, in Hindoos dark and smoky, on Chinese and Japanese
yellow, on Hottentots orange, on South American Indians dark brown
(Murray).--F. V. T.]
[Illustration: FIG. 374.--Mouth parts of _Pediculus vestimenti_.
Enlarged. (After Denny.)]
[Illustration: FIG. 375.--Ovum of the head louse. 70/1.]
[Illustration: FIG. 376.--Head louse, male. 15/1.]
[Illustration: FIG. 377.--_Pediculus vestimenti_, Burm.: adult female.
15/1.]
*Pediculus vestimenti*, Nitzsch, 1818.
The head in front is somewhat rounded. Antennæ longer than in the
head louse; 2 to 3·5 to 4 mm. in length; whitish-grey; the abdomen
is broader than the thorax; stigmata as in _P. capitis_. Eggs 0·7 to
0·9 mm. in length; about seventy are deposited.
_P. vestimenti_ lives on the neck, throat and trunk of persons, and
the clothing next the body, in which also the eggs are deposited.
The louse of so-called pedicular disease (_P. tabescentium_) is,
according to Landois’ researches, only the usual _P. vestimenti_;
moreover, many cases of phthiriasis are attributable to mites or fly
maggots.
[This parasite has often been a great pest amongst soldiers during
long campaigns, especially amongst the Russians during the Crimean
War. _Vide_ also notes in Addenda (p. 615) under “Body, Head and
Clothes Lice.”--F. V. T.]
Genus. *Phthirius*, Leach.
*Phthirius inguinalis*, Redi, 1668.
Syn.: _Pediculus pubis_, L.
Male 0·8 to 1·0 mm. in length; female 1·12 mm. in length; colour
greyish-white; form subquadrate; the two posterior pairs of legs are
strong; the abdomen has nine segments and six pairs of stigmata; and
still another pair of stigmata is situated between the two anterior
limbs. Eggs pear-shaped, 0·8 to 0·9 mm. in length, 0·4 to 0·5 mm. in
breadth, and are deposited in rows of about ten on the hairs.
[Illustration: FIG. 378.--_Phthirius inguinalis_, Leach: they are
distinguished by the larger tracheal trunks originating from the
stigmata. Enlarged.]
_Pediculus pubis_, which is found almost exclusively in the Caucasian
race, lives on hairy parts of the body, but hardly ever on the skin
of the head; the pubic region is its favourite place of abode.
[This species reproduces more rapidly than other lice, and is
communicated much more freely. The eggs are often laid singly
attached to the hairs near their apex. It is known as the “crab
louse.”--F. V. T.]
(_b_) RHYNCOTA HEMIPTERA.
Family. *Acanthiadæ.*
Body flattened, antennæ four-jointed, rostrum three-jointed, wings
atrophied.
[This family, the _Cimicidæ_, includes the bed bugs; the proboscis,
which lies in a groove, is of three segments; the front wings are
shown by two small elytra, there is no trace of hind wings. Two
species are known commonly to attack man.--F. V. T.]
Genus. *Cimex*, Linnæus.
*Cimex lectularius*, Linnæus.
Syn.: _Acanthia lectularia_, Fabricius, 1794.
It measures 4 to 5 mm. in length, 3 mm. in breadth; brownish-red;
eight abdominal segments. The female deposits fifty whitish eggs at
a time (1·12 mm. in length) three or four times a year; the entire
development up to complete maturity takes about eleven months. [They
will breed all the year round, but less so in cold weather.--F. V. T.]
[Illustration: FIG. 379.--Head of the bed bug from the ventral surface.
_a_, the rostrum; _b_, the antenna; and _c_, the eye. 70/1.]
The bed bugs live in the cracks and fissures of human habitations,
under carpets, behind pictures, in furniture, bedsteads, etc.; hidden
during the day, they attack persons at night to suck their blood.
The alkaline secretion of the salivary glands dropped into the wound
around the separate bites causes the so-called “wheals.”
The bed bugs were known in bygone days by the Greeks (κάριο) and
the Romans (cimex). They were first mentioned from Strasburg in the
eleventh century, and in England about 1500.
[This is the common bed bug of northern latitudes and must not be
confused with the tropical bed bug (_C. rotundatus_). The bed bug can
migrate from one house to another; this especially takes place when a
house is uninhabited. They escape from windows and pass along walls,
water-pipes and gutters, and so reach adjoining houses. This noxious
pest accompanies man wherever he goes; ships and trains become
infested, especially the former.
[A characteristic feature in this animal is the peculiar odour it
produces, like many others in the same group of insects. This odour
comes from a clear, oily volatile liquid secreted by glands in
various parts of the body. Although the normal food is man’s blood,
the bed bug can subsist upon moist wood, dust and dirt that collects
in crevices in floors, walls, furniture, etc. The puncturing mouth
consists of a fleshy under lip, within which lie four thread-like
hard filaments which pierce the flesh, the blood being drawn up
through the beak.
[The eggs are oval, white, with a projecting rim around one end,
with a lid which is pushed off when the young hatch; they are laid
in cracks and crevices in batches of from twelve to fifty. The egg
stage lasts from seven to ten days. The larval stage so gradually
passes into the adult that one scarcely notices the change; during
its growth the skin is cast five times, and at the change the
little wing-pads are seen, showing that the adult stage is reached.
The young larva is at first pale yellowish-white. It resembles
the parent, but has no trace of elytra. Although eleven weeks is
said to be necessary for their development, the stages may be gone
through much more rapidly; Howard and Marlatt[362] give seven weeks
in some instances. It seems pretty certain that these Cimex only
take one meal of blood between each moult and another preceding egg
laying.--F. V. T.]
[362] “Household Insects,” Howard and Marlatt, _Bull._ 4 (N.S.), U.S.
Dept. Agric., 1896, p. 37.
*Cimex rotundatus*, Signoret, 1852.
[This bug is common in warm climates; it is an abundant insect in
India, and King has found it in the Sudan, where _C. lectularius_ is,
however, the common species. It is usually known as the tropical bed
bug. Signoret’s bug can be told from the other common species by the
shape of the pronotum. In _C. rotundatus_ it is uniformly convex,
whilst in _C. lectularius_ the lateral edges are flat and sometimes
even concave. The abdomen of _rotundatus_ is also rather more elongate.
[This species is of considerable importance, as according to Patton it
may act partly as the intermediary host of the piroplasma of kala-azar.
[Wenyon found at Bagdad that _Cimex_ sp. would take up Leishmania from
Oriental sore, and that the parasite developed into flagellate form.
Patton came to the conclusion that the bed bug transmitted Oriental
sore in Cambay, India, but Wenyon contests this view (_vide Journ.
Lond. School Trop. Med._, 1912, ii, pt. 1, pp. 13–26). Franchini
(_Bull. Soc. Path, exot._, 1912, v, No. 10, pp. 817–819) was unable
to connect Cimex with this disease. At present nothing seems proved.
Besides their possible connection with kala-azar, it has been shown by
Howard and Clark (_Journ. Exp. Med._, 1912, xvi, No. 6, pp. 850–859)
that they can carry the virus of poliomyelitis.
[This bed bug was originally described from the Island of Réunion in
1852 by Signoret. A similar insect was described from Burma by Fieber,
in 1861, as _C. macrocephalus_. This is the same as Signoret’s species.
[The distribution given by Patton[363] is as follows: India, Burma,
Assam, Malay, Aden, Islands of Mauritius and Réunion. Patton in this
paper refers to an erroneous statement made in a recent edition of
this book (the last English edition). As I have personally kept
_lectularius_ in moist dirt, wood and refuse for over two years, the
statement as far as I am concerned is not erroneous. Moreover, since
his doubting this fact the same experiment has been twice repeated
with the same results. What they did and do persist on I cannot
say.--F. V. T.] whilst collecting them. It is rounder and has shorter
antennæ than
[363] _Indian Med. Gaz._, February, 1907, xlii, No. 2.
*Cimex columbarius*, Jenyns.
[This is common in parts of Europe in pigeon nests, and also amongst
poultry (_vide Report Econ. Zool._ for year ending September 30, 1913,
pp. 142–144, Theobald). It occurs in Britain on the latter and will
attack man. I have personally been badly bitten _C. lectularius_.
Jenyns also described a more pubescent species from swallows as _C.
hirundinis_. I have recently received an account of the swallow bug
invading a house in Kent and causing much annoyance.--F. V. T.]
*Cimex ciliatus*, Eversmann, 1841.
3·3 mm. in length, yellowish-red, thickly covered with hair; indigenous
in Russia (Kasan).
[From a single specimen seen it is evidently distinct.--F. V. T.]
Family. *Reduviidæ.*
Head long, narrowed behind into a neck; eyes large, prominent;
rostrum thick and curved; antennæ moderately long, slender at the
tip; legs long and stiff; carnivorous.
Amongst the _Reduviidæ_ one genus is of particular importance, namely
the genus Conorhinus, which has a long head and the first segment of
the beak very much shorter than the second, and the posterior tibiæ
longer than the femora.
These large bugs have a wide distribution, the Oriental region, North
and South America, and the West Indies, Madagascar and West and Central
Africa.
These large bugs may cause very nasty wounds by their bites, but beyond
that it has recently been shown that one interposes in the life-cycle
of a trypanosome, namely--
Genus. *Conorhinus*, Lap.
*Conorhinus megistus*, Burm.
This large bug has recently been shown by Chagas to be the agent in the
development of the trypanosome (_T. cruzii_) which is the cause of the
well-known disease in many parts of Brazil called _Barbeiro_ (Barbier).
This insect is about 1 in. long, black, with four red spots on the
pronotum, and six red lateral lines on the abdomen, black legs, head
and beak. The insect is figured in a coloured plate (No. 9) in _Mem.
Inst. Oswaldo Cruz_, 1909, i, fasc. 2, pp. 158–218.
A further account is given by Neiva.[364]
[364] _Mem. Inst. Oswaldo Cruz_, 1910, 2, fasc. 2, pp. 206–212.
*Conorhinus sanguisuga*, Lec. (Blood-sucking Cone-nose).
This bug is also known as the Texas or Mexican bed bug, also as the
big bed bug. It is particularly troublesome in the Mississippi Valley
in bedrooms. The bite is very severe and results in more pronounced
swelling and inflammation than that of the Cimex. Normally this genus
feeds upon the blood of mammals and insects. Its fondness for human
blood appears to be quite a new habit, and appears limited to the
mature insect only. It is nearly an inch long, flat, head very narrow
and long, the rostrum short and thick. In colour it is dark brown
with pink markings. They are fully winged when adult, and they fly
with ease, entering houses on the wing, especially being attracted by
lights in windows; they also run swiftly. Like the bed bug they conceal
themselves during the day and come out at night and bite the sleeper.
The effect of the bite is very varied, but as a rule a sore, itching
wound, accompanied by burning pain and swellings, which may extend
over a good deal of the body, occur. A specific poison is undoubtedly
injected into the puncture; but no doubt serious results are also due
to the beak being contaminated through the insects feeding upon foul
carrion. Mr. Lembert, when bitten by a _Conorhinus_ sp. (?) on the
Pacific slope, exhibited the following symptoms: an itching sensation
extending up the leg, large blotches manifesting themselves on the
upper part of the limb and extending up to the hands and arms; his lips
swelled and the itching and swelling extended over the head; there was
also much nausea. Similar results are recorded from other regions.[365]
[365] “Household Insects,” p. 42.
The eggs of the _C. sanguisuga_ are at first white, then become yellow,
then pink; the young hatch in twenty days. There are two larval and
two pupal stages, the latter showing wing-pads. The eggs are laid and
the young feed out of doors, chiefly upon insects. It is particularly
abundant in April and May indoors.
*Conorhinus*, _sp. novum_ (Monster Bug).
Another species; acts in a very similar way in California, the bite
being very poisonous.
*Conorhinus rubrofasciatus*, de Geer[366] (Malay Bug).
[366] [_First Report Econ. Zool._, 1903, p. 130.--F. V. T.]
This large bug attacks man in Malaysia and elsewhere. It is recorded as
inflicting “a very nasty sting, which is done by the huge proboscis.”
Acute pain and inflammation follow in a few minutes. In one case the
whole leg became swollen. This species occurs over the whole Oriental
region, in Madagascar and Sierra Leone. It is dark brown in colour with
dusky yellow or brick-red markings on the pronotum and elytra. Donovan
suggests that it may be connected with the kala-azar piroplasma.
*Conorhinus renggeri*, Herr-Schäff
(Great Black Bug of Pampas).
This large black bug is mentioned by Darwin,[367] who states as
follows: “At night I experienced an attack (for it deserves no less a
name) of the benchuca, a species of Reduvius, the great black bug of
the Pampas. It is most disgusting to feel soft wingless insects, about
an inch long, crawling over one’s body. Before sucking they are quite
thin, but afterwards they become round and bloated with blood, and in
this state are easily crushed. One which I caught at Iquique (for they
are found in Chili and Peru) was very empty. When placed on a table,
and though surrounded by people, if a finger was presented the bold
insect would immediately protrude its sucker, make a charge and, if
allowed, draw blood. No pain was caused by the wound. It was curious
to watch its body during the action of sucking, as in less than ten
minutes it changed from being flat as a wafer to a globular form. This
one feast, for which the benchuca was indebted to one of the officers,
kept it fat during four whole months, but after the first fortnight it
was quite ready to have another suck.” Mr. Kirby[368] also refers to
this species.
[367] Charles Darwin, “A Naturalist’s Voyage” (Voyage of the _Beagle_),
1888, p. 330.
[368] “Text-book of Entomology,” 1885, p. 205.
*Conorhinus variegatus* (Variegated Cone-nose).
Occurs in Florida in houses, and chases bugs (Cimex) and flies; not
definitely known to bite man.
*Conorhinus nigrovarius.*
This species occurs in South America. It is one of the forms known as
bichuque. Its bite makes a troublesome swelling.
*Conorhinus protractus.*
also attacks man in Utah.[369] It has been called the “big bed bug.”
[369] “The Big Bed Bug of the Far West,” _Bull._ 18 (N.S.), _U.S. Dept.
Agric._, 1898, p. 101.
Genus. *Reduvius, etc.*
*Reduvius personatus*, Linné.
Syn.: _Reduvius personatus_, Leconte, 1855.
European, but also found in the United States. The bite causes intense
pain. It bites when caught or handled, but does not seem to do so
voluntarily. Swelling and irritation result which may last a week, and
may even cause death.[370] In 1899 it was very abundant at Washington
and elsewhere; other species occurred, and so no definite opinion
existed as to the actual biter, but some people took _R. personatus_
actually biting. It was first described as a parasite of man in America
by Walsh and Riley.[371]
[370] “Insects to which the name ‘Kissing-bug’ became applied during
the summer of 1899,” _Bull._ 22 (N.S.), _U.S. Dept. Agric._, 1900,
p. 24.
[371] _American Entomologist_, 1869, i, pp. 84–88.
A popular name for this bug is the wheel or masked bug--a black insect,
three-fourths of an inch long. The larva of this bug is carnivorous and
covers its body with dust so as to conceal itself from its prey. The
adult is active on the wing.
*Coriscus subcoleoptratus*, Kirby, 1837.
Syn.: _Nabicula subcoleoptrata_, Kirby, 1837; _Nabis
subcoleoptratus_, Reuter, 1872; _Coriscus subcoleoptratus_, Stål,
1873.
Northern United States. Howard was bitten by one between the
fingers--the pain was intense, like a needle prick, but the swelling
was small.[372] No other case known.
[372] R. Blanchard, “Sur la Piqûre de quelques Hémiptères,” _Arch, de
Par._, 1902, p. 145.
*Rasahus biguttatus*, Say, 1831.
Syn.: _Pirates biguttatus_, Stål, 1862; _Callisphodrus biguttatus_,
Stål, 1866; _Rasahus biguttatus_, Stål, 1872.
Common in southern United States, and found in Cuba, Panama and Pará,
etc. Known as the two-spotted corsair on account of the great spot on
the hemielytra. Frequently found in houses, where it chases the bed
bug. It also bites man frequently. From 1869 Walsh and Riley placed it
amongst the parasites of man. In the United States Davidson[373] is
of opinion that all cases attributed to spider bites are due to this
insect.
[373] “So-called Spider-bites and their Treatment,” _Therap. Gaz._,
February 19, 1875.
*Melanolestes morio*, Erichson, 1848 (Non-walker).
Syn.: _Pirates morio_, Erichson, 1848; _Melanolestes morio_, Stål,
1866; _Pirates picipes_, Herrich-Schäffer, 1848; _Melanolestes
picipes_, Howard, 1900.
Guiana and Mexico and eastern and southern United States. Length
20 mm., hides under stones and logs during daylight, and flies at
night. Attracted by lights into houses. Very abundant in 1899 at
Washington. Howard cites cases where it was proved to bite man.
*Melanolestes abdominalis*, Herrich-Schäffer, 1848.
Syn.: _Pirates abdominalis_, Herrich-Schäffer; _Melanolestes
abdominalis_, Uhler, 1875.
Allied to the former; some say similar, but can be told by the shorter
wings on the female. It occurs in the same localities as _M. morio_.
*Phonergates bicoloripes.*
This reduvid attacks man in Africa.
Family. *Aradidæ.*
Broad and very flat bugs, with antennæ of four segments and the beak
of three; scutellum short, no cuneus to elytra and the tarsi of two
segments. They normally live under the bark of trees, etc., and are
found in most parts of the world.
*Dysodius lunatus*, Fabr. (Pito Bug).
A large species which is found in South America, frequenting houses,
and bites very severely.
THE OCHINDUNDU.
The bug is described by Wellman (_Journ. Trop. Med._, April 2, 1906,
p. 97) as not only feeding on ticks, such as _Ornithodorus moubata_,
but as also attacking man. It is called by the Angola Bantus the
ochindundu. It is black in colour; the first two pairs of legs are of
a bright red hue. It has curious paddle-like structures on the front
four legs, which seem to be designed for securely holding the ticks.
It infects native kraals for the sake of preying on ticks. The natives
also state that it inflicts a bite which far exceeds in painfulness
that of the tick. They compare the bite with that of a poisonous snake.
Family. *Lygæidæ.*
Scutellum short; antennæ four-jointed; ocelli present; membranous
part of hemielytra with never more than five nervures. Nearly all
vegetable feeders. A few are recorded here as biting man.
*Lyctocoris campestris*, Fabricius.
Syn.: _Acanthia campestris_, Fabr. (_Lyctocoris domesticus_).
Rare in habitations, lives on human blood. Found by Blanchard in a
bed at an hotel at Liverpool. The bite is undoubtedly worse than that
of Cimex; cosmopolitan. In colour it is ferruginous, shining, legs
testaceous; hemielytra slightly shorter and narrower than the abdomen;
membranous portion transparent, the apex broadly fuscous. Length 3·8 to
4·8 mm.
*Rhodinus prolixus*, Stål, 1859.
Sometimes attacks man, and the bite is very painful. It is 25 mm. long
and 8 mm. broad, and occurs in Colombia. It is found also in Cayenne
and Venezuela. This like other species is known in South America as
bichuque or benchuca.
[A few other unimportant species are also recorded as biting man, such
as _Harpactor cruentas_, in the South of France; _Eulyes amœna_, from
Borneo and Java; _Arilus carinatus_, Forster, from Brazil. The latter
appears to be the same as the _Acanthia serratus_, Fabricius.--F. V. T.]
Order. *Orthoptera.*
[The only _Orthoptera_ recorded as doing actual harm to man are
certain wingless locusts found in Africa. The cysticercus stage of
a small tapeworm found in rats and man has been found in an earwig
(Alcock).
[The strange _Hemimeridæ_ found in West Africa, resembling wingless
cockroaches, are parasitic on rats (_Cricetomys_). _Phasmidæ_, or
stick insects, are said to be able to eject a fluid which may cause
blindness if it comes in contact with the eyes.
LOCUSTS INJURIOUS TO MAN.
[A wingless locust--_Enyaliopsis durandi_, Luc--is recorded by
Wiggins[374] as injurious to man in Uganda. “The bite of this
insect,” it is said, “gives rise to a very nasty eruption, which
may extend over the whole body, with high temperature and general
malaise. The skin at the site of the bite sloughs away, and generally
leaves a large deep cavity, which heals very slowly.”
[374] _Bull. Ent. Res._, 1910, i, pt. 3, p. 227.
[An allied species--_E. petersi_, Schaum--emits a clear yellow fluid,
but according to Marshall this does no harm.[375] Stannus writes
that “for some years I have been cognizant of the fact that among
the natives of Nyasaland an allied if not the same species is held
to cause skin lesions by the emission of a fluid on the bare skin
surface of the body. I have seen cases of ulcers on various parts of
the body, for which the ‘nantundua’ was assigned as the cause.” He
then describes the destruction of the superficial layers of the skin
which he observed after the yellow fluid had been on the skin twelve
hours.--F. V. T.]
[375] _Ibid._, 1911, ii, pt. 2, p. 180.
Order. *Coleoptera.*
The larvæ of beetles, similarly to those of some other _Arthropoda_
(myriapods and the larvæ of gnats), have sometimes been observed
in man as purely accidental guests. In one case or another, such
accounts may have originated through a mistake of the observer. Thus
English doctors report the presence of the larvæ of _Blaps mortisaga_
in the stools of human beings, Sandberg of the larva of _Agrypnus
murinus_ in his ten year old son, and Blanchard mentions the larva of
a beetle that was vomited by a child. All these cases, however, do
not represent actual parasitism, although there are beetles living
parasitically.[376]
[376] [Dr. Daniels has sent me a small coleopterous larva found in an
abscess on a man in British Guiana.--F. V. T.]
*Silvanus surinamensis*, Linnæus (Saw-toothed Grain Beetle).
[Taschenberg records this beetle as having invaded some sleeping
apartments adjoining a brewery where stores were kept, and annoying the
sleepers at night by nipping them when in their beds.
[This beetle is common in many parts of the world amongst groceries,
corn, meal, seeds, dried fruits, etc. It is about 1/10 in. long, much
flattened and chocolate-brown in colour. The thorax has two shallow
grooves and bears six minute teeth on each side. The jaws are strong,
but the bite cannot be very serious.--F. V. T.]
Order. *Diptera* or *Siphonaptera*.
*Aphaniptera* (Fleas).
Wingless, the thoracic rings distinct and free; antennæ of three
segments; legs very powerful; abdomen with nine segments. [Ten
segments are present, but only nine are visible.--F. V. T.] The
mandibles transformed into serrated puncturing organs, which are
situated in the split sheath of the rostrum; the maxillæ are
laminated and have palpi, and more or less conceal the other parts.
The importance of fleas lies mainly in the fact that they act as
plague carriers. About 150 species have already been described. The
only ones of importance for this work are those found on man and
those on rats and mice. The two families in which these are found are
known as _Pulicidæ_ and _Sarcopsyllidæ_.
The eggs of fleas are laid on the ground, on rugs, etc., and in
birds’ and rodents’ nests. They hatch rapidly in warm weather and in
warm climates, varying from two to five days; in cold countries they
may take two or three weeks to incubate.
The larva is a footless creature, pearly white in colour, the head
sometimes being darkened, composed of fourteen segments including
the head, and although apodal can move with considerable agility. It
lives amongst dust and dirt, and feeds upon any organic matter it can
find. In about two weeks it is said to become mature, and then spins
a cocoon in which pupation takes place.
The cocoons of the common human flea and the fowl flea become covered
with dust and dirt. The period of pupal life seems varied, for I have
had the fowl flea hatch out in ten days, and others in three weeks at
the same time of year.
The adults are blood suckers and cause considerable irritation as
well as acting as disease carriers, and in the _Sarcopsyllidæ_ the
females attach themselves permanently to their hosts, embedding
themselves under the skin, where they become pregnant. Some kinds
harbour the cystic stage of tapeworms, and the rat trypanosome passes
certain stages in the rat flea. Most fleas have definite hosts, but
some, like the rat and fowl fleas, attack man.
The fleas which can carry the bacillus of plague are _Xenopsylla
cheopis_, _Pulex irritans_, _Ceratophyllus fasciatus_ and
_Hoplopsyllus anomalus_.
The two families, _Pulicidæ_ and _Sarcopsyllidæ_, can be
distinguished as follows:
Thoracic segments much foreshortened, coxæ and
femora of hind legs very slightly enlarged _Sarcopsyllidæ_.
Thoracic segments normal, coxæ and femora of all
the legs much enlarged _Pulicidæ_.
Family. *Sarcopsyllidæ* (Jiggers).
The members of this family are not confined to one host.
Three genera are known and tabulate as follows:--
α. Hind coxa without a patch of spines on
the inside.
α^1. Hind femur simple 1. _Dermatophilus._
α^2. Hind femur with a large tooth-like
projection near the base 2. _Hectopsylla._
β. Hind coxa with a patch of short spines on
the inside 3. _Echidnophaga._
Genus. *Dermatophilus*, Guérin.
*Dermatophilus cæcata*, Enderl.
The eyes of the female vestigial. Taken on and behind the ears of
_Mus rattus_ in Brazil.
*Dermatophilus penetrans*, L., 1758 (Jigger, Chigoe).
Syn.: _Sarcopsylla penetrans_.
About 1 to 1·2 mm. in length; brown in colour. Eyes distinct. The males
only occasionally visit man to bite; the fertilized female, on the
other hand, bores into the skin with her head, particularly about the
toes of the host, and then attains considerable dimensions. The eggs
develop on the soil with a metamorphosis similar to that of the common
flea.
[Illustration: FIG. 380.--_Dermatophilus penetrans_: young female.
Highly magnified. (After Moniez.)]
[Illustration: FIG. 381.--_Dermatophilus penetrans_: older female.
Enlarged. (After Moniez.)]
The sand flea (nigua) particularly infests Central and South America,
and, in 1873, was carried by ships from Brazil to the West Coast of
Africa. In a comparatively short time it has become disseminated
throughout Africa and has also appeared in Madagascar; recently also
it has been reported from China.
Besides attacking man, it also settles on mammals, for instance, on
dogs, pigs, etc. According to Jullien the wound or little swelling
caused by the female has no particular significance, as children
infested with ten or eleven sand fleas quietly proceeded with their
games. It will be understood, however, that the wound easily affords
the opportunity for the setting up of inflammation or even septic
processes, as is the case in any kind of wound.
[The jigger is also well known in the West Indies.--F. V. T.]
Genus. *Echidnophaga*, Olliff.
Four species found on rats, etc.
*Echidnophaga gallinacea*, Westwood (Chigoe of Fowls).
[This flea is a native of tropical Asia and Africa. It lives on the
fowl chiefly, attacking the neck and around the eyes. Specimens
were sent me from Texas, where they not only attack poultry but also
children, the latter somewhat severely. It also occurs on cats, and is
found on rats in Africa. It has been introduced into North America.
[Three other species are found on rats, _viz._: _E. myrmecobii_,
Rothsch., from Australia; _E. murina_, Tirah, from Southern Europe; and
_E. liopus_, Rothsch., India and Western Australia.--F. V. T.]
Family. *Pulicidæ* (True Fleas).
ROTHSCHILD’S CLASSIFICATION is as follows:--
SECTION I.--Club of antennæ distinctly segmented only on the hind
side.
_Key to Genera._
_a._ No comb on head and thorax.
_a^1._ The internal incrassation, which extends from
the insertion of the mid coxa into the thorax,
joins the anterior edge of the mesosternite _Pulex_.
_b^1._ This incrassation joins the upper edge of
the mesosternite _Xenopsylla_.
_b._ With a comb on the pronotum only _Hoplopsyllus_.
_c._ With a comb on the pronotum and at the lower
edge of the head _Ctenocephalus_.