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[Illustration: PLATE I
ANTHONY VON LEEUWENHOEK
Who first saw bacteria]
THE FUNDAMENTALS
OF
BACTERIOLOGY
BY
CHARLES BRADFIELD MORREY, B.A., M.D.
PROFESSOR OF BACTERIOLOGY AND HEAD OF THE DEPARTMENT
IN THE OHIO STATE UNIVERSITY,
COLUMBUS, OHIO
ILLUSTRATED WITH 171 ENGRAVINGS AND 6 PLATES
_Second Edition, thoroughly Revised_
[Illustration: Publisher’s logo]
LEA & FEBIGER
PHILADELPHIA AND NEW YORK
1921
COPYRIGHT
LEA & FEBIGER
1921
TO
GRACE HAMILTON MORREY
AMERICAN PIANIST
PREFACE TO SECOND EDITION
The first edition seems to have fulfilled a need for a general
text-book on the subject of bacteriology. The original method of
presentation is preserved. The text-book idea is adhered to, so that
the individual instructor may have full liberty to expand on topics in
which he is especially interested. A number of illustrations have been
added, the text has been improved in many instances by the addition
of further explanatory matter and the most recent general advances in
the Science. Examples are the System of Classification of the Society
of American Bacteriologists, which is used throughout the text, their
Key to the Genera of Bacteria, a discussion of the H-ion concentration
method of standardization, the selective action of anilin dyes, the
mechanism of entrance of pathogenic organisms into the body, a more
detailed explanation of the origin of antibodies, the nature of
antigens and a table of antigens and antibodies.
Professor Vera McCoy Masters has assisted in the revision by aiding
in the preparation of manuscript and the reading of proof and in the
making of the index, for which services the author’s thanks are hereby
expressed.
C. B. M.
Columbus, Ohio, 1921.
PREFACE TO FIRST EDITION
An experience of nearly twenty years in the teaching of Bacteriology
has convinced the author that students of this subject need a
comprehensive grasp of the entire field and special training in
fundamental technic before specializing in any particular line of work.
Courses at the University are arranged on this basis. One semester is
devoted to General Bacteriology. During the second semester the student
has a choice of special work in Pathogenic, Dairy, Soil, Water, or
Chemical Bacteriology. A second year may be devoted to advanced work in
any of the above lines, to Immunity and Serum Therapy, or to Pathogenic
Protozoa.
This text-book is intended to cover the first or introductory
semester’s work, and requires two classroom periods per week. Each
student is compelled to take two laboratory periods of three hours per
week along with the class work. The outline of the laboratory work is
given at the end of the text. Results attained seem to justify this
plan. A text-book is but one of many pedagogical mechanisms and is not
intended to be an encyclopedia of the subject.
The author makes no claim to originality of content, since the facts
presented are well known to every bacteriologist, though the method
of presentation is somewhat different from texts in general. During
the preparation of this work he has made a thorough review of the
literature of Bacteriology, covering the standard text-books as well
as works of reference and the leading periodicals dealing with the
subject. Thus the latest information has been incorporated.
No attempt has been made to give detailed references in a work of this
character.
The photomicrographs are original except where otherwise indicated
and are all of a magnification of one thousand diameters where no
statement to the contrary appears. These photographs were made with
a Bausch & Lomb Projection Microscope fitted with a home-made camera
box. Direct current arc light was used and exposures were five to ten
seconds. Photographs of cultures are also original with a few indicated
exceptions. All temperatures are indicated in degrees centigrade.
For use of electrotypes or for prints furnished the author is indebted
to the following: A. P. Barber Creamery Supply Company, Chicago, Ill.;
Bausch & Lomb Optical Company, Rochester, N. Y.; Creamery Package
Manufacturing Company, Chicago, Ill.; Davis Milk Machinery Company,
North Chicago, Ill.; Mr. C. B. Hoover, Superintendent of Sewage
Disposal Plant, Columbus, O.; Mr. C. P. Hoover, Superintendent of Water
Filtration Plant, Columbus, O.; The Hydraulic Press Manufacturing
Company, Mt. Gilead, O.; Loew Manufacturing Company, Cleveland, O.;
Metric Metal Works, Erie, Pa.; Sprague Canning Machine Company,
Chicago, Ill.; U. S. Marine Hospital Service; Wallace and Tiernan
Company, New York City, N. Y.
For the preparation of many cultures and slides, for great assistance
in the reading of proof and in the preparation of the index, Miss Vera
M. McCoy, Instructor in Bacteriology, deserves the author’s thanks.
The author trusts that the book will find a place in College and
University courses in Bacteriology.
C. B. M.
CONTENTS
Historical Introduction--Spontaneous Generation--Causation
of Disease--Putrefaction and Fermentation--Study of
Forms--Chronological Table 17
CHAPTER I.
Position of Bacteria--Relationships to
Algæ--Yeasts--Molds--Protozoa 37
PART I.
MORPHOLOGY.
CHAPTER II.
Cell Structures--Cell Wall--Protoplasm--Plasmolysis
--Plasmoptysis--Nucleus--Vacuoles--Capsules--Metachromatic
Granules--Flagella--Spores 41
CHAPTER III.
Cell Forms--Coccus--Bacillus--Spirillum--Involution Forms 52
CHAPTER IV.
Cell Groupings 55
CHAPTER V.
Classification--Migula’s--Society of American
Bacteriologists’--Key to the Latter 59
PART II.
PHYSIOLOGY.
CHAPTER VI.
Occurrence--General Conditions for
Growth--Moisture--Temperature--Light--Oxygen--
Osmotic Pressure--Electricity--X-rays and Radium
Emanations--Pressure--Mechanical Vibration 71
CHAPTER VII.
Chemical Environment--Reaction of Medium--Chemical
Composition 81
CHAPTER VIII.
Chemical Environment (Continued)--General Food
Relationships--Metabolism of Elements 86
CHAPTER IX.
Physiological Activities--Fermentation of
Carbohydrates--Splitting of Fats 93
CHAPTER X.
Physiological Activities (Continued)--Putrefaction of
Proteins--Cycles of Nitrogen, Carbon, Sulphur, Phosphorus 102
CHAPTER XI.
Physiological Activities (Continued)--Production of
Acids, Gases, Esters, Alcohols, Aldehydes, Aromatic
Compounds--Phosphorescence--Chromogenesis--Reduction--
Oxidation--Production of Heat--Absorption of Free
Nitrogen--Nitrogen Nutrition of Green Plants 110
CHAPTER XII.
Physiological Activities (Continued)--Production of
Enzymes--Discussion on Enzymes--Toxins--Causation of
Disease 121
CHAPTER XIII.
Disinfection--Sterilization--Disinfectants--Physical
Agents--Pasteurization 130
CHAPTER XIV.
Disinfection and Sterilization (Continued)--Chemical
Agents--Anilin Dyes 156
CHAPTER XV.
Disinfection and Sterilization (Continued)--Choice
of Agent--Standardization of Disinfectants--Phenol
Coefficient--Practical Sterilization and Disinfection 164
PART III.
THE STUDY OF BACTERIA.
CHAPTER XVI.
Culture Media--Broth, Milk, Gelatin, Agar, Potatoes, Blood
Serum--Standardization of Media--H-ion Concentration
Method--Synthetic Media 171
CHAPTER XVII.
Methods of Using Culture Media--Culture Tubes--Plates--
Anaërobic Cultures--Vignal Tubes--Fermentation Tubes--
Deep Culture Tubes--Novy Jars--Inoculation of Culture Media 184
CHAPTER XVIII.
Isolation of Bacteria in Pure Culture--Dilution
--Plating--Streaking--Barber Apparatus--Aids in
Isolation--Heat--Selective Antiseptics--Selective
Food---Indicators--Animal Inoculation 194
CHAPTER XIX.
Study of the Morphology of Bacteria--Bacteriological
Microscope--Hanging Drop Slides--Staining--Gram’s
Method--Spores--Acid-fast Bacilli--Capsules--
Flagella--Metachromatic Granules 200
CHAPTER XX.
Study of the Physiology of Bacteria--Temperature
--Incubators--Thermal Death Point--Oxygen Relationships
--Study of Physiological Activities--Appearance of Growth
on Culture Media--Appearance of Molds on Plate Cultures 213
CHAPTER XXI.
Animal Inoculation--Material for Bacteriological
Examination 227
PART IV.
GENERAL PATHOGENIC BACTERIOLOGY.
CHAPTER XXII.
Introduction--Infection--Acute Infection--Chronic
Infection--Specific--Non-specific--Koch’s
Postulates--Virulence--Susceptibility 231
CHAPTER XXIII.
Pathogenic Bacteria Outside the Body--As Saprophytes--As
Facultative Saprophytes--Latent--Carriers--Universal
Carriers--Accidental Carriers--Necessary Intermediate Hosts 237
CHAPTER XXIV.
Channels of Infection--Skin--Mucosæ--Respiratory Tract
--Alimentary Tract--Mechanism of Entrance of Organisms
--Dissemination in the Body--Paths of Elimination--
Specificity of Location 243
CHAPTER XXV.
Immunity--Natural--Artificial--Active--Passive--
Production of Immunity--Vaccine--Antiserum--Practical
Applications of Immunity Reactions 250
CHAPTER XXVI.
Theories of Immunity--Pasteur--Chauveau--Baumgärtner
--Metchnikoff--Ehrlich--Principles of Ehrlich’s Theory 256
CHAPTER XXVII.
Ehrlich’s Theory (Continued)--Receptors of the First
Order--Antitoxin--Antienzyme--Preparation of Antitoxins
--Units 261
CHAPTER XXVIII.
Ehrlich’s Theory (Continued)--Receptors of the Second
Order--Agglutinins--Agglutination Reaction--Precipitins
--Precipitin Test 265
CHAPTER XXIX.
Ehrlich’s Theory (Continued)--Receptors of the Third
Order--Cytolysins--Amboceptor--Complement--Anti-amboceptors
--Antisnake Venoms--Failure of Cytolytic Serums in
Practice--Complement-fixation Test 271
CHAPTER XXX.
Phagocytosis--Opsonins--Opsonic Index--Bacterial
Vaccines--Preparation of--Use of--Lipovaccines
--Aggressins 280
CHAPTER XXXI.
Anaphylaxis--Author’s Theory--Tuberculin Test--Table of
Antigens and Antibodies--Summary of Immunity as Applied to
Protection from Disease 289
BACTERIOLOGY.
HISTORICAL INTRODUCTION.
Bacteriology as a science is a development of the latter half of the
nineteenth century. It may be said to have begun in the decade between
1870 and 1880, due largely to the wide circulation given to Koch’s
work in proving that _Bacillus anthracis_ is the cause of Anthrax in
1876, in devising new culture methods and in demonstrating that wound
infections are due to microörganisms, 1878. Associated with this
work were the great improvements in the microscope by Abbé and the
introduction of anilin dyes for staining bacteria by Weigert. These
results attracted workers throughout the world to the “new science.”
Nevertheless, this work of Koch’s was preceded by numerous observations
and experiments which led up to it. Certainly the most important
discoveries immediately responsible were those of Pasteur. He must be
considered as the greatest of the pioneer bacteriologists since he
worked in all fields of the subject. Some of the antecedent work was
done in attempting to disprove the old “spontaneous generation” theory
as to the origin of organisms; some in searching for the causes of
disease and some in the study of fermentation and putrefaction.
SPONTANEOUS GENERATION.
Speculation as to the first origin of life is as old as history and
doubtless older. Every people of antiquity had its own legends, as for
example, the account in Genesis. This question never can be definitely
settled, even though living matter should be made in the laboratory.
The doctrine of the “spontaneous origin” of particular animals or
plants from dead material under man’s own observation is a somewhat
different proposition and may be subjected to experimental test. The
old Greek philosophers believed it. Anaximander (B.C. 610-547) taught
that some animals are derived from moisture. Even Aristotle (B.C.
384-322) said that “animals sometimes arise in soil, in plants, or
in other animals,” _i.e._, spontaneously. It can be stated that this
belief was general from his day down through the Dark and Middle Ages
and later. Cardano (A.D. 1501-1576) wrote that water gives rise to
fish and animals and is also the cause of fermentation. Van Helmont
(1578-1644) gives directions for making artificial mice. Kircher
(1602-1680) describes and figures animals _produced under his own eyes_
by water on plant stems.
However, many thinkers of the seventeenth century doubted the truth
of this long-established belief. Francesco Redi (1626-1698) made a
number of experiments which tended to prove that maggots did not
arise spontaneously in meat, as was generally believed, but developed
only when flies had an opportunity to deposit their eggs on the
meat. It seems that by the latter part of this century the idea that
organisms large enough to be seen with the naked eye could originate
spontaneously was generally abandoned by learned men.
The work of Leeuwenhoek served to suspend for a time the subject of
spontaneous generation, only to have it revived more vigorously later
on. He is usually called “The Father of the Microscope,” though the
compound microscope was invented probably by Hans Zansz or his son
Zacharias, of Holland, about 1590. Leeuwenhoek used a simple lens,
but his instruments were so much more powerful that they opened up an
entirely new and unknown world. (Fig. 1.)
Anthony van Leeuwenhoek (1632-1723) was apprenticed to a linen draper
and accumulated a comfortable fortune in this business. He became
interested in the grinding of spectacle lenses, then an important
industry in Delft, Holland, where he lived, and did a great deal of
experimental work in this line, mainly for his own enjoyment. Finally
he succeeded in making a lens so powerful that he could see in water
and various infusions very minute living bodies never before observed.
Leeuwenhoek contributed 112 papers to the Royal Society of Great
Britain, the first in 1673, many of them accompanied by such accurate
descriptions and drawings, for example a paper submitted September
12, 1683, that there is no doubt that he really saw bacteria and was
the first to do so (Fig. 2). Rightly may he be styled “The Father
of Bacteriology,” if not of the microscope. He says in one paper:
“With the greatest astonishment I observed that everywhere through
the material I was examining were distributed _animalcules_ of the
most microscopic dimness which moved themselves about in a remarkably
energetic way.” Thus he considered these living objects to be animals,
from their motion, and this belief held sway for nearly two hundred
years.
[Illustration: FIG. 1.--Leeuwenhoek’s Microscope. A is the simple
bi-convex lens held firmly in place. In front of this is the small
table, B, with the support, C, on the tip of which the object to be
examined was held. This support could be brought nearer to or removed
further away from the lens and held firmly in place by the screw, D.
E is a second screw for raising or lowering the entire table. A concave
mirror that Leeuwenhoek sometimes used to focus more light on the
object under examination, is shown at the right.]
Leeuwenhoek was a pure observer of facts and made no attempt at
speculation, but his discoveries soon started the theorists to
discussing the origin of these minute organisms. Most observers, as
was probably to be expected, believed that they arose spontaneously.
Needham, in 1749, described the development of microörganisms
around grains of barley in water. Bonnet, in 1768, suggested that
probably Needham’s animalcules came from ova in the liquid. The Abbot
Spallanzani, in 1769, called attention to the crudeness of Needham’s
methods and later, in 1776, attempted to disprove spontaneous origin
by heating infusions of organic material in flasks and then _sealing_
them. His critics raised the objections that heating the liquids
destroyed their ability to support life, and that sealing prevented
the access of fresh air which was also necessary. The first objection
was disproved by the accidental cracking of some of the flasks which
thereafter showed an abundant growth. This accident seemed also to
support the second objection, and Spallanzani did not answer it. Though
Spallanzani’s experiments failed to convince his opponents, they led to
important practical results, since François Appert, in 1810, applied
them to the preserving of fruits, meats, etc., and in a sense started
the modern canning industry.
[Illustration: FIG. 2.--The first drawings of bacteria by Leeuwenhoek.
The dotted line _C-D_ indicates the movement of the organism.]
[Illustration: FIG. 3.--Schultze’s experiment. The set of bulbs next to
the face contained KOH and the other set concentrated H₂SO₄. Air was
drawn through at frequent intervals from May until August but no growth
developed in the boiled infusion.]
From Spallanzani to Schultze, there were no further experiments to
prove or disprove spontaneous generation. Schultze, in 1836, attempted
to meet the second objection to Spallanzani’s experiment, _i.e._,
the exclusion of air, by drawing air through his boiled infusions,
first causing it to bubble through concentrated sulphuric acid to
kill the “germs” (Fig. 3.). His flasks fortunately showed no growths,
but his critics claimed that the strong acid changed the properties
of the air so that it would not support life. This experiment of
Schultze’s, though devised for a different purpose, was really the
first _experiment_ in the use of _chemical disinfectants_, though
Thaer (page 31) had used chemicals in a practical way. Schwann, in
1837, modified this experiment, by drawing the air through a tube
heated to destroy the living germs (Fig. 4). His experiments were
successful but the “spontaneous generation” theorists raised the same
objection, _i.e._, the change in the air by heating. This was the first
_experiment_ in which the principle of “_dry heat_” or “_hot air_”
sterilization was used. Similar arguments were brought forward, also
to the use of _cotton plugs_ as filters by Schroeder and Dusch in 1859
(Fig. 5). This was the first use of the principle of _sterilization by
filtration_. It remained for Chevreuil and Pasteur to overcome this
objection in 1861 by the use of flasks with long necks drawn out to a
point and bent over. These permitted a full access of air by diffusion
but kept out living germs, since these cannot fly but are carried
mechanically by air currents or fall of their own weight (Fig. 6.).
Hoffman, the year before (1860), had made similar experiments but these
remained unnoticed. The Pasteur flasks convinced most scientists that
“spontaneous generation” has never been observed by man, though some
few, notably Dr. Charlton Bastian, of England, vigorously supported the
theory from the early seventies until his death in November, 1915.
[Illustration: FIG. 4.--Schwann’s experiment. After boiling, as shown
in the diagram, and cooling, air was drawn into the flask by aspiration
while the coiled tube was kept hot with the flame.]
[Illustration: FIG. 5.--Schroeder and Dusch’s experiment. The
aspirating bottle drew the air through the flask after it had been
filtered by the cotton in the tube.]
[Illustration: FIG. 6.--Pasteur’s flask.]
[Illustration: FIG. 7.--Tyndall’s box. One side is removed to show
the construction. The bent tubes at the top are to permit a free
circulation of air into the interior. The window at the back has one
corresponding in the front (removed). Through these the beam of light
sent through from the lamp at the side was observed. The three tubes
received the infusion and were then boiled in an oil bath. The pipette
was for filling the tubes. (Popular Science Monthly, April, 1877.).]
John Tyndall, in combating Bastian’s views showed that boiled infusions
left open to the air in a closed box through which air circulated
did not show any growth of organisms provided the air was so free of
particles that the path of a ray of light sent through it from side to
side could not be seen (Fig. 7). Or if such sterilized infusions were
exposed to dust-free air, as in the high Alps, the majority showed
no growth, while all infusions in dusty air did show an abundance of
organisms. Tyndall’s experiments confirmed those of Pasteur and his
predecessors and showed that the organisms developed from “germs”
present in the air falling into the liquids and not spontaneously.
While Tyndall’s experiments were of great value as indicated, they
probably were harmful in another way. These “germs in the air” were
considered by bacteriologists as well as laymen to include necessarily
many _disease germs_ and to indicate the very general, if not
universal, presence of these latter _in the air_. This idea led to many
erroneous practices in sanitation and disinfection which even to this
day are not eliminated.
CAUSATION OF DISEASE.
The transmission of disease from person to person was recognized by the
ancients of European and Asiatic countries. Inoculation of smallpox was
practiced in China and India probably several thousand years ago and
was introduced by Lady Mary Wortley Montague into England in 1721, from
Constantinople. These beliefs and practices do not seem to have been
associated with any speculations or theories as to the cause of the
disease.
Apparently the first writer on this subject was Varo, about B.C. 70,
who suggested that fevers in swampy places were due to invisible
organisms. The treatment of wounds during the thirteenth and fourteenth
centuries by hot wine fomentations and by the application of plasters
was based on the theory that the _air_ brought about conditions in the
wounds which led to suppuration. These practices were indeed primitive
antisepsis, yet were not based on a _germ theory_ of the conditions
which were partially prevented. Fracastorius (1484-1553), in a work
published in 1546, elaborated a theory of “disease germs” and “direct
and indirect contagion” very similar to modern views, though based
on no direct pathological knowledge. Nevertheless Kircher (mentioned
already) is usually given undeserved credit for the “contagium vivum”
theory. In 1657 by the use of simple lenses he observed “worms” in
decaying substances, in blood and in the pus from bubonic plague
patients (probably rouleaux of corpuscles in the blood, certainly not
bacteria in any case). Based on these observations and possibly also on
reading the work of Fracastorius, his theory of a “living cause” for
various diseases was published in 1671, but received little support.
The discoveries of Leeuwenhoek which proved the existence of
microscopic organisms soon revived the “contagium vivum” idea of
Kircher. Nicolas Andry in a work published in 1701 upheld this view.
Lancisi in 1718 advanced the idea that “animalcules” were responsible
for malaria, a view not proved until Laveran discovered the malarial
parasite in 1880.[1] Physicians ascribed the plague which visited
Southern France in 1721 to the same cause, and many even went so far as
to attribute all disease to animalcules, which brought the theory into
ridicule. Nevertheless the “contagium vivum” theory survived, and even
Linnaeus in his _Systema Naturæ_ (1753-6) recognized it by placing the
organisms of Leeuwenhoek, the contagia of diseases and the causes of
putrefaction and fermentation in one class called “Chaos.”
Plenciz, a prominent physician and professor in the Vienna Medical
School, published in 1762 a work in which he gave strong arguments for
the “living cause” theory for transmissable diseases. He taught that
the agent is evidently transmitted through the air and that there is
a certain period of incubation pointing to a multiplication within
the body. He also believed that there was a specific agent for each
disease. His writings attracted little attention at the time and the
“contagium vivum” theory seems to have been almost lost sight of for
more than fifty years. Indeed, Oznam, in 1820, said it was no use to
waste time in refuting hypotheses as to the animal nature of contagium.
Isolated observers, were, however, keeping the idea alive, each in
his own locality. In 1787 Wollstein, of Vienna, showed that the pus
from horses with glanders could infect other horses if inoculated
into the skin. Abilgaard, of Copenhagen, made similar experiments at
about the same time. In 1797 Eric Viborg, a pupil of Abilgaard’s,
published experiments in which he showed the infectious nature not
only of the pus but also of the nasal discharges, saliva, urine, etc.,
of glandered horses. Jenner in 1795-98 introduced vaccination as a
method of preventing smallpox. This epoch-making discovery attracted
world wide attention and led to the overcoming of this scourge which
had devastated Europe for centuries, but contributed little or nothing
to the question of the causation of disease. Prevost’s discovery of
the cause of grain rust (_Puccinia graminis_) in 1807 was the _first
instance of an infectious disease of plants_ shown to be _due to a
microscopic plant organism_, though not a bacterium in this case.
Doubtless one reason why the work on glanders and grain rust attracted
little attention among the practitioners of human medicine was owing to
the prevalent belief in man’s complete separation from all lower forms
of life. The evolutionists had not yet paved the way for experimental
medicine.
In 1822 Gaspard showed the poisonous nature of material from infected
wounds by injecting it into animals and causing their death. Tiedemann
(1822), Peacock (1828) described “little bodies” in the muscles of
human cadavers which Hilton (1832) considered to be parasitic in
nature. Paget (1835) showed that these bodies were round worms and
Owen (1835) described them more accurately and gave the name _Trichina
spiralis_ to them. Leidy (1846) found organisms in the muscles of
hogs which he considered to be the same as Owen’s Trichina and paved
the way for the work of Zenker (1860) in showing the pathological
relation between the Trichina of pork and human Trichinosis. Bearing
on the “contagium vivum” theory was the rediscovery of the “itch mite”
(_Sarcoptes scabiei_) by Renucci (1834), an Italian medical student.
This had been declared several hundred years before but had been lost
sight of. Chevreuil and Pasteur, in 1836, showed that putrefaction did
not occur in meat protected from contamination, and suggested that
wound infection probably resulted from entrance of germs from without.
Bassi, investigating a disease of silkworms in Italy, demonstrated
that a certain mold-like fungus (_Botrytis bassiana_) was the cause in
1837. This was the _first instance of a microscopic vegetable organism_
proved to be capable of _causing disease in an animal_.
Boehm, in 1838, observed minute organisms in the stools of cholera
patients and conjectured that they might have a causal connection
with the disease. Dubini of Milan in 1838 discovered the _Ankylostoma
duodenale_ which later was further described by Omodei in 1843 and
shown to be the cause of Egyptian chlorosis by Griesinger (1851).
The fungous nature of favus, a scalp disease, was recognized by
Schönlein in 1839, and the organism was afterward called “_Achorion
schoenleinii_.” Berg, in 1839-41, showed that thrush is likewise due to
a fungus, “_Oidium albicans_.”
These discoveries led Henle, in 1840, to publish a work in which
he maintained that all contagious diseases must be due to living
organisms, and to propound certain postulates (afterward restated
by Koch and now known as “Koch’s postulates” p. 233) which must be
demonstrated before one can be sure that a given organism is the
specific cause of a given disease. The methods then in vogue and the
instruments of that period did not enable Henle to prove his claims,
but he must be given the credit for establishing the “contagium vivum”
theory on a good basis and pointing the way for men better equipped to
prove its soundness in after years.
[Illustration: PLATE II
SIR JOSEPH LISTER]
In 1842-43 Gruby showed that Herpes tonsurans, a form of ringworm, is
due to the fungus _Trichophyton tonsurans_. Klencke, in 1843, produced
generalized tuberculosis in a rabbit by injecting tuberculous material
into a vein in the ear, but did not carry his researches further.
In 1843, Doctor Oliver Wendell Holmes wrote a paper in which he
contended that puerperal fever was contagious. Liebert identified the
_Peronospora infestans_ as the cause of one type of potato rot in 1845.
The skin disease Pityriasis (tinea) versicolor was shown to be due to
the _Microsporon furfur_ by Eichstedt in 1846. In 1847 Semmelweiss of
Vienna recommended disinfection of the hands with chloride of lime by
obstetricians because he believed with Holmes in the transmissibility
of puerperal fever through poisons carried in this way from the
dissecting room but his theories were ridiculed.
[Illustration: PLATE III
ROBERT KOCH]
Pollender, in 1849, and Davaine and Rayer, in 1850, independently
observed small rod-like bodies in the blood of sheep and cattle
which had died of splenic fever (anthrax). That Egyptian chlorosis,
afterward identified with Old World “hookworm disease,” is caused by
the _Ankylostoma duodenale_ was shown by Greisinger in 1851. In the
same year the _Schistosomum hematobium_ was shown to be the cause
of the “Bilharzia disease” by Bilharz. Küchenmeister discovered the
tapeworm, _Tænia solium_, in 1852, Cohn, an infectious disease of
flies due to a parasitic fungus (_Empusa muscæ_) in 1855, and Zenker
showed the connection between trichinosis of pork (“measly pork”)
and human trichinosis (1860) as indicated above. The organisms just
mentioned are, of course, not bacteria, but these discoveries proved
conclusively that _living things of one kind or another, some large,
most of them microscopic, could cause disease in other organisms_ and
stimulated the search for other “living contagiums.” In 1863 Davaine,
already mentioned, showed that anthrax could be transmitted from
animal to animal by inoculation of blood, but only if the blood
contained the minute rods which he believed to be the cause. Davaine
later abandoned this belief because he transmitted the disease with
old blood in which he could find no rods. It is now known that this
was because the bacilli were in the “spore” form which Davaine did not
recognize. He thus missed the definite proof of the bacterial nature
of anthrax because he was not familiar with the life history of the
organism which was worked out by Koch thirteen years later. In 1865
Villemin repeatedly caused tuberculosis in rabbits by subcutaneous
injection of tuberculous material and showed that this disease must be
infectious also. In the same year Lord Lister introduced antiseptic
methods in surgery. He believed that wound infections were due to
microörganisms getting in from the air, the surgeon’s fingers, etc.,
and without proving this, he used carbolic acid to kill these germs
and prevent the infection. His pioneer experiments made modern surgery
possible. In this year also, Pasteur was sent to investigate a disease,
Pebrine, which was destroying the silkworms in Southern France. He
showed the cause to be a protozoan which had been seen previously by
Cornalia and described by Nägeli under the name _Nosema bombycis_ and
devised preventive measures. This was the _first infectious disease_
shown to be _due to a protozoan_. In 1866 Rindfleisch observed small
pin-point-like bodies in the heart muscle of persons who had died
of wound infection. Klebs, in 1870-71, published descriptions and
names of organisms he had found in the material from similar wounds,
though he did not establish their causal relation. Bollinger, in
1872, discovered the spores of anthrax and explained the persistence
of the disease in certain districts as due to the resistant spores.
In 1873 Obermeier observed in the blood of patients suffering from
recurrent fever long, flexible spiral organisms which have been named
_Spirochæta obermeieri_. Lösch ascribed tropical dysentery to an ameba,
named by him _Amœba coli_, in 1875. Finally, Koch, in 1876, isolated
the anthrax bacillus, worked out the life history of the organism
and reproduced the disease by the injection of pure cultures and
recovered the organism from the inoculated animals, thus establishing
beyond reasonable doubt its causal relationship to the disease. This
was the _first instance of a bacterium_ proved to be the cause of a
_disease in animals_. Pasteur, working on the disease at the same time,
confirmed all of Koch’s findings, though his results were published
the next year, 1877. Bollinger determined that the _Actinomyces bovis_
(_Streptothrix bovis_) is the cause of actinomycosis in cattle in
1877. Woronin in the same year discovered a protozoan (_Plasmodiophora
brassicæ_) to be the cause of a disease in cabbage, the _first proved
instance of a unicellular animal causing a disease in a plant_. In 1878
Koch published his researches on wound infection in which he showed
beyond question that microörganisms are the cause of this condition,
though Pasteur in 1837, had suggested the same thing and Lister had
acted on the theory in preventing infection.
These discoveries, especially those of Koch, immediately attracted
world-wide attention and stimulated a host of workers, so that within
the next ten years most of the bacteria which produce disease in
men and animals were isolated and described. It is well to remember
that the first _specific_ disease of man proved to be caused by a
_bacterium_ was _tuberculosis_, by Koch in 1882.
Progress was greatly assisted by the introduction of anilin dyes as
suitable stains for organisms by Weigert in 1877, by Koch’s application
of special technic and gelatin cultures for isolation and study, 1881,
and the great improvements in the microscope by Prof. Abbé, of Jena.
Laveran’s discovery of the malarial parasite in 1880 turned attention
to protozoa as the causes of disease and led to the discovery of the
various piroplasmoses and trypanosomiases in man and the lower animals.
Pasteur’s protective inoculations in chicken cholera and anthrax
directed attention to the possibility of using bacteria or their
products as a specific protective or curative means against particular
diseases. This finally led to the discovery of diphtheria antitoxin by
Behring, and independently by Roux, in 1890, a discovery which opened
up the wide field of immunity which is so persistently cultivated at
the present time.
[Illustration: PLATE IV
LOUIS PASTEUR]
While the causation of disease by bacteria has probably attracted
most attention, especially in the popular mind, it should not be
forgotten that this is but one of the numerous ways in which these
organisms manifest their activities, and in a sense it is one of
their least-important ways, since other kinds are essential in many
industries (dairying, agriculture) and processes (sewage purification)
and are even _indispensable for the very existence of all green plants
and hence of animals, including man himself_.
PUTREFACTION AND FERMENTATION.
The idea that there is a certain resemblance between some infectious
diseases and the processes of putrefaction and fermentation seems to
have originated during the discussion on spontaneous generation and
the “contagium vivum” theory which followed Leeuwenhoek’s discoveries.
Plenciz (1762) appears to have first formulated this belief in writing.
He considered putrefaction to be due to the “animalcules” and said that
it occurred only when there was a coat of organisms on the material
and only when they increased and multiplied. Spallanzani’s experiments
tended to support this view since his infusions did not “spoil” when
boiled and sealed. Appert’s practical application of this idea has been
mentioned.
Thaer, in his _Principles of Rational Agriculture_, published in the
first quarter of the nineteenth century, expressed the belief that the
“blue milk fermentation” was probably due to a kind of fungus that
gets in from the air, and stated that he had prevented it by treating
the milk cellars and vessels, with sulphur fumes or with “oxygenated
hydrochloric acid” (hypochlorous acid).
In 1836 Chevreuil and Pasteur showed that putrefaction did not occur
in meat protected from contamination. In 1837 Caignard-Latour, in
France, and Schwann, in Germany, independently showed that alcoholic
fermentation in beer and wine is due to the growth of a microscopic
plant, the yeast, in the fermenting wort. C. J. Fuchs described the
organism which is commonly called the “blue milk bacillus” in 1841 and
conjectured that the souring of milk was probably bacterial in origin.
It remained for Pasteur to prove this in 1857. During the following
six or seven years Pasteur also proved that acetic acid fermentation,
as in vinegar making, butyric acid fermentation (odor of rancid butter
and old cheese) and the ammoniacal fermentation of urea, so noticeable
around stables, were each due to different species of bacteria. Pasteur
also, during the progress of this work, discovered the class of
organisms which can grow in the absence of free oxygen--the anaërobic
bacteria. There is no question that Pasteur from 1857 on did more to
lay the foundations of the science of bacteriology than any other
one man. Influenced by Pasteur’s work von Hesseling, in 1866, stated
his belief that the process of cheese ripening, like the souring of
milk, was associated with the growth of fungi, and Martin also, in
1867, stated that cheese ripening was a process which was akin to
alcoholic, lactic and butyric fermentations. Kette, in 1869, asserted
the probability of Pasteur’s researches furnishing a scientific basis
for many processes of change in the soil. In 1873 Schlösing and Müntz
showed that nitrification must be due to the action of microörganisms,
though the discovery of the particular ones remained for Winogradsky
in 1889. Thus the belief that fermentation and putrefaction are due to
microörganisms was as well established by the early eighties of the
last century as that similar organisms are the causes of infectious
diseases.
STUDY OF FORMS.
An important part of the scientific knowledge of living organisms is
dependent on a study of their forms and relationships. As has been
stated, Leeuwenhoek considered bacteria to be “animalcules” because
they showed independent movement. But little attention was paid to
the natural history of these animalcules for nearly a hundred years
after Leeuwenhoek. During the last quarter of the eighteenth century,
however, workers busied themselves chiefly with the discovery and
description of new forms. Among these students were Baron Gleichen,
Jablot, Lesser, Reaumur, Hill and others. Müller, of Copenhagen, in
1786 published the first attempt at classification, a most important
step in the study of these organisms. Müller introduced the terms
Monas, Proteus and Vibrio, which are still in use. Ehrenberg, in his
work on _Infusoria_, or the organisms found in infusions, published
in 1838, introduced many generic names in use at present, but still
classed the bacteria with protozoa. Joseph Leidy, the American
naturalist, considered that the “vibrios” of previous writers were
plants and not “animalcules.” He seems to have been the first to have
made this distinction (1849). Perty (1852) recognized the presence of
spores in some of his organisms. Ferdinand Cohn (1854) classed the
bacteria among plants. Nägeli (1857) proposed the name “Schizomycetes”
or “fission fungi,” which is still retained for the entire class of
bacteria. Cohn in the years 1872-1875 established classification on
a modern basis and added greatly to the knowledge of morphology and
natural history of bacteria. He described spore formation and the
development of spores into active bacteria, and showed the close
relationships as well as differences between the bacteria and the lower
algæ. Robert Koch was a pupil of Cohn.
An examination of the accompanying chronological table will show how
the investigations and discoveries in connection with “spontaneous
generation,” the “contagium vivum” theory and putrefaction and
fermentation must have been mutually suggestive:
1546. Fracastorius, disease germs theory and direct and indirect
contagion.
1671. Kircher, “contagium vivum” theory.
1675. Leeuwenhoek, first saw bacteria, “animalcules.”
1701. Andry, “animalcules” cause of diseases.
1718. Lancisi, “animalcules” cause of malaria.
1749. Needham, described development of organisms in water around
barley grains.
1762. Plenciz, arguments for “living cause” theory and that
“animalcules” cause putrefaction.
1768. Bonnet, suggested that probably Needham’s organisms came from
germs in the liquid.
1776. Spallanzani, boiled and sealed infusions.
1786. Müller, first classified “animalcules.”
1787. Wollstein, glanders pus infectious.
1795-1798. Jenner, vaccination against smallpox.
1797. Viborg, transmitted glanders repeatedly.
1807. Prevost, grain rust, _Puccinia graminis_. _The first instance
of a microscopic plant organism shown to be the cause of a disease in
a higher plant._
1810. Appert, directions for “canning.”
1822. Gaspard, infectiousness of material from wounds.
1834. Renucci, itch--itch mite (_Sarcoptes scabiei_).
1835. Paget and Owen, _Trichina spiralis_.
1836. Schultze, air through acid to kill “germs.”
1837. Chevreuil and Pasteur, protected meat did not putrefy;
suggested wound infection due to entrance of germs from without.
1837. Caignard-Latour, Schwann, alcoholic fermentation--yeast.
1837. Schwann, air through heated tubes to kill germs.
1837. Bassi, muscardine of silkworms, _Botrytis bassiana_. _The first
instance of a microscopic plant organism shown to be the cause of a
disease in an animal._
1838. Boehm, cholera, saw organisms in stools (not the cause).
1838. Dubini discovered _Ankylostoma duodenale_.
1838. Ehrenberg, study of forms.
1839. Schönlein, Favus, _Achorion schoenleinii_.
1839-41. Berg, Thrush, _Oidium albicans_.
1840. Henle, theory of contagious diseases.
1841. Fuchs, bacterial cause of blue milk.
1842-43. Gruby, Herpes tonsurans, _Trichophyton tonsurans_.
1843. Klencke, inoculations of tuberculous material into rabbit.
1843. Holmes, puerperal fever contagious.
1845. Liebert, a potato rot, _Peronospora infestans_.
1846. Leidy, Joseph (American Naturalist), _Trichina spiralis_ in
pork.
1846. Eichstedt, Pityriasis versicolor, _Microsporon furfur_.
1847. Semmelweiss, recommended disinfection to prevent puerperal
fever. Not followed.
1849. Leidy, considered “vibrios” to be plants.
1849. Pollender, Anthrax, saw rods in blood.
1850. Davaine and Rayer, Anthrax, saw rods in blood.
1851. Griesinger, Egyptian chlorosis, _Ankylostoma duodenale_.
1851. Bilharz, Bilharzia disease, _Schistosomum hematobium_.
1852. Kückenmeister, tapeworm, _Tænia solium_.
1852. Perty, saw spores in bacteria.
1854. Cohn, classed bacteria as plants.
1855. Cohn, disease of flies, _Empusa muscæ_.
1857. Nägeli, named bacteria, Schizomycetes.
1857. Pasteur, lactic, acetic, butyric acid fermentation.
1860. Zenker, Trichinosis, _Trichinella spiralis_.
1861. Pasteur, disproof of spontaneous generation.
1863. Davaine, transmitted anthrax by blood injections.
1865. Pasteur, Pebrine of silkworms, _Nosema bombycis_. _The first
instance of a protozoan shown to be the cause of a disease in a
higher animal._
1865. Villemin, repeatedly transmitted tuberculosis to rabbits.
1865. Lister, introduced antisepsis in surgery.
1860. Rindfleisch, Pyemia, organisms in the pus.
1866. Von Hesseling, cheese ripening.
1867. De Martin, cheese ripening akin to alcoholic fermentation.
1869. Kette, Pasteur’s researches scientific basis for many processes
in the soil.
1871. Klebs, Pyemia, organisms in the pus.
1872. Bollinger, spores in anthrax.
1872-75. Cohn, definite classification.
1873. Obermeier, recurrent fever, _Spirochæta obermeieri_.
1873. Schlösing and Münz, nitrification due to organisms.
1875. Lösch, amebic dysentery, _Amœba coli_.
1875-76. Tyndall, germs in the air.
1876. Robert Koch, anthrax, _Bacillus anthracis_. _The first instance
of a bacterium shown to be the cause of disease in an animal._
1877. Bollinger, actinomycosis, _Actinomyces bovis_ (_Streptothrix
bovis_).
1877. Weigert, used anilin dyes for staining.
1877. Woronin, cabbage disease, _Plasmodiophora brassicæ_. _The first
instance of a protozoan shown to be the cause of a disease in a
plant._
1878. Koch, wound infections, bacterial in origin.
1881. Koch, gelatin plate cultures, Abbé, improvements in the
microscope.
CHAPTER I.
POSITION--RELATIONSHIPS.
Bacteria are considered to belong to the plant kingdom not because of
any one character they possess, but because they most nearly resemble
organisms which are generally recognized as plants. While it is not
difficult to distinguish between the higher plants and higher animals,
it becomes almost, if not quite, impossible to separate the lowest,
forms of life. It is only by the method of resemblances above mentioned
that a decision is finally reached. It has even been proposed to make a
third class of organisms neither plants nor animals but midway between
in which the bacteria are included, but such a classification has not
as yet been adopted.
In many respects the bacteria are most nearly related to the lowest
_algæ_, since both are unicellular organisms, both reproduce by
transverse division and the forms of the cell are strikingly similar.
The bacteria differ in one important respect, that is, they do not
contain _chlorophyl_, the green coloring matter which enables all
plants possessing it to absorb and break up carbon dioxide in the
light, and hence belong among the fungi. Bacteria average much smaller
than even the smallest algæ.
Bacteria are closely connected with the _fission yeasts_ and the
_yeasts_ and _torulæ_. All are unicellular and without chlorophyl. The
bacteria, as has been stated, reproduce by division but the others
characteristically by budding or gemmation, though the fission yeasts
also by division.
There is a certain resemblance to the _molds_ in their absence
of chlorophyl. But the molds grow as branching threads and also
have special fruiting organs for producing spores as a means of
reproduction, neither of which characteristics is found among the
_true_ bacteria. The higher thread bacteria do show true branching
and rudimentary fruiting bodies (Streptothrix) and appear to be a link
connecting the true bacteria and the molds.
[Illustration: FIG. 8.--A thread of blue-green algæ.]
[Illustration: FIG. 9.--A thread of small blue-green algæ.]
[Illustration: FIG. 10.--A thread of bacteria. Compare with Figs. 8
and 9.]
[Illustration: FIG. 11.--A chain of spherical blue-green algæ.]
[Illustration: FIG. 12.--A chain of spherical bacteria.]
[Illustration: FIG. 13.--A pair of spherical blue-green algæ.]
Further the _chemical composition_ of bacteria is more like that of
other fungous plants than of any of the forms classed as animals.
[Illustration: FIG. 14.--Spherical bacteria. Several pairs are shown.]
[Illustration: FIG. 15.--Yeast cells. Some show typical budding.]
The food of bacteria is always taken up in solution by diffusion
through the outer covering of the cell as it is in all plants. Plant
cells never surround and engulf particles of solid food and digest them
within the cell as many single-celled animals do, and as the leukocytes
and similar ameboid cells in practically all multicelled animals do.[2]
[Illustration: FIG. 16.--A portion of the mycelium of a mold. Note the
large size and the branching.]
One of the most marked differences between animals and plants is with
respect to their energy relationships. Plants are characteristically
storers of energy while animals are liberators of it. Some bacteria
which have the power of swimming in a liquid certainly liberate
relatively large amounts of energy, and in the changes which bacteria
bring about in the material which they use as food considerable heat is
evolved (“heating” of manure, etc.). Nevertheless the evidence is good
that the bacteria as a class store much more of the energy contained
in the substances actually taken into the body cell as food than is
liberated in any form.
Bacteria do show some resemblance to the protozoa, or single-celled
animal forms, in that the individuals of each group consist of one cell
only and some bacteria have the power of independent motion from place
to place in a liquid as most “infusoria” do, but here the resemblance
ceases.
Bacteria are among the smallest of organisms, so small that it requires
the highest powers of the microscope for their successful study, and
the use of a special unit for their measurement. This unit is the
one-thousandth part of a millimeter and is called the micro-millimeter
or micron. Its symbol is the Greek letter _mu_ (µ).
The size varies widely among different kinds but is fairly constant in
the same kind. The smallest described form is said to be only 0.18µ
long by 0.06µ thick and is just visible with the highest power of the
microscope, though it is possible and even probable that there are
forms still smaller which cannot be seen. Some large rare forms may
measure 40µ in length, but the vast majority are from 1µ to 4µ or 5µ
long, and from one-third to one-half as wide.
From the above description a bacterium might be said to be a
_microscopic, unicellular plant, without chlorophyl, which reproduces
by dividing transversely_.
PART I.
MORPHOLOGY
CHAPTER II.
CELL STRUCTURES.
The _essential_ structures which may by appropriate means be
distinguished in the bacterial cell are _cell wall_ and _cell
contents_, technically termed _protoplasm_, cytoplasm. The cell wall is
not so dense, relatively, as that of green plants, but is thicker than
the outer covering of protozoa. It is very similar to the cell wall
of other lower fungi. Diffusion takes place readily through it with
very little selective action on substances absorbed as judged by the
comparative composition of bacteria and their surrounding medium.
=Cytoplasm.=--The cytoplasm according to Bütschli and others is
somewhat different and slightly denser in its outer portion next to the
cell wall. This layer is designated the _ectoplasm_, as distinguished
from the remainder of the cell contents, the _endoplasm_. When bacteria
are suddenly transferred from a given medium into one of decidedly
_greater_ density, there sometimes results a contraction of the
_endoplasm_, due to the rapid diffusion of water. This phenomenon is
designated _plasmolysis_ (Fig. 17), and is similar to what occurs in
the cells of higher plants when subjected to the same treatment. This
is one of the methods which may be used to show the different parts of
the cell just described.
If bacteria are suddenly transferred from a relatively dense medium
to one which is of decidedly _less_ density, it occasionally happens
that water diffuses into the cell and swells up the endoplasm so much
more rapidly than the cell wall that the latter ruptures and some of
the endoplasm exudes in the form of droplets on the surface of the cell
wall. This phenomenon is called _plasmoptysis_. Students will seldom
observe the distinction between cell wall and cell contents, except
that in examining living bacteria the outer portion appears more highly
refractive. This is chiefly due to the presence of a cell wall, but is
not a proof of its existence.
[Illustration: FIG. 17.--Cells of bacteria showing plasmolysis. The
cell substance of three of the cells in the middle of the chain has
shrunk until it appears as a round black mass. The cell wall shows as
the lighter area.]
[Illustration: FIG. 18.--Vacuoles in the bacterial cell. The lighter
areas are vacuoles.]
=Nucleus.=--Douglas and Distaso[3] summarize the various opinions with
regard to the nucleus in bacteria as follows:
1. Those who do not admit, the presence of a nucleus or of anything
equivalent to it. (Fischer, Migula, Massart).
2. Those who consider that the entire bacterial cell is the equivalent
of a nucleus and contains no protoplasm. (Ruzicka).
3. Those who admit the presence of nuclein but say that this is not
morphologically differentiated from the protoplasm as a nucleus.
(Weigert).
4. Those who consider the bacterial protoplasm to consist of a central
endoplasm throughout which the nuclein is diffused and an external
layer of ectoplasm next to the cell wall. (Bütschli, Zettnow).
5. Those who say that the bacterial cell contains a distinct nucleus,
at least in most instances. These authors base their claims on staining
with a Giemsa stain. (Feinberg, Ziemann, Neuvel, Dobell, Douglass and
Distaso).
That nucleoproteins are present in the bacterial cell in relatively
large amounts is well established. Also that there are other proteins
and that the protoplasm is not all nuclein.
Some workers as noted above have been able to demonstrate collections
of nuclein by staining, especially in very young cells. In older cells
this material is in most instances diffused throughout the protoplasm
and can not be so differentiated.
The following statement probably represents the generally accepted view
at the present time:
A nucleus _as such_ is not present in bacterial cells, except in a few
large rare forms and in very young cells. _Nuclein_, the characteristic
chemical substance in nuclei, which when aggregated forms the nucleus,
is scattered throughout the cell contents and thus intimately mingled
with the protoplasm, and cannot be differentiated by staining as in
most cells.
The close association of nuclein and protoplasm may explain the rapid
rate of division of bacteria (Chapter VIII, p. 91).
The chemical composition of the bacterial cell is discussed in Chapter
VII.
In addition to the _essential_ parts just described the bacterial cell
may show some of the following _accidental_ structures: _vacuoles_,
_capsules_, _metachromatic granules_, _flagella_, _spores_.
=Vacuoles.=--_Vacuoles_ appear as clear spaces in the protoplasm when
the organism is examined in the living condition or when stained very
slightly (Fig. 18). During life these are filled with liquid or gaseous
material which is sometimes waste, sometimes reserve food, sometimes
digestive fluids. Students are apt to confuse vacuoles with spores (p.
47). Staining is the surest way to differentiate (Chapter XIX, p. 209).
If vacuoles have any special function, it is an unimportant one.
[Illustration: FIG. 19.--Bacteria seen within capsules.]
[Illustration: FIG. 20.--Metachromatic granules in bacteria. The dark
round spots are the granules. The cells of the bacteria are scarcely
visible.]
=Capsule.=--The _capsule_ is a second covering outside the cell wall
and probably developed from it (Fig. 19). It is usually gelatinous,
so that bacteria which form capsules frequently stick together
when growing in a fluid, so that the whole mass has a jelly-like
consistency. The term _zoöglœa_ was formerly applied to such masses,
but it is a poor term and misleading (zoön = an animal) and should
be dropped. The masses of jelly-like material frequently found on
decaying wood, especially in rainy weather, are in some cases masses
of capsule-forming bacteria, though a part of the jelly is a product
of bacterial activity, a gum-like substance which lies among the
capsulated organisms. When these masses dry out, they become tough
and leathery, but it is not to be presumed that capsules are of this
consistency. On the contrary, they are soft and delicate, though they
certainly serve as an additional protection to the organism, doubtless
more by selective absorption than mechanically. Certain bacteria
which cause disease form capsules in the blood of those animals which
they kill and not in the blood of those in which they have no effect
(_Bacterium anthracis_ in guinea pig’s blood and in rat’s blood). The
presence of capsules around an organism can be proved only by staining
the capsule. Many bacteria when stained in albuminous fluids show a
clear space around them which appears like a capsule. It is due to the
contraction of the fluid away from the organism during drying.
=Metachromatic Granules.=--The term “_metachromatic_” is applied to
granules which in stained preparations take a color different from
the protoplasm as a whole (Fig. 20). They vary widely in chemical
composition. Some of them are glycogen, some fat droplets. Others are
so-called “granulose” closely related to starch but probably not true
starch. Others are probably nuclein. Of many the chemical composition
is unknown. They are called “Babes-Ernst corpuscles” in certain
bacteria (typhoid bacillus). Since they frequently occur in the ends
of cells the term “polar granules” is also applied. Their presence is
of value in the recognition of but few bacteria (“Neisser granules” in
diphtheria).
=Flagellum.=--A _flagellum_ is a very minute thread-like process
growing out from the cell wall, probably filled with a strand of
protoplasm. The vibrations of the flagella move the organism through
the liquid medium. Bacteria which are thus capable of independent
movement are spoken of as “motile bacteria.” The actual rate of
movement is very slight, though in proportion to the size of the
organism it may be considered rapid. Thus Alfred Fischer determined
that some organisms have a speed for short periods of about 40 cm. per
hour. This is equivalent to a man moving more than 200 miles in the
same time.
It is obvious that bacteria which can move about in a liquid have an
advantage in obtaining food, since they do not need to wait for it to
be brought to them. This advantage is probably slight.
[Illustration: FIG. 21.--A bacterium showing a single flagellum at the
end--monotrichic.]
[Illustration: FIG. 22.--A bacterium showing a bundle of four flagella
at the end--lophotrichic.]
An organism may have only one flagellum at the end. It is then said
to be monotrichic (Fig. 21) (μόνος = alone, single; τριχος = hair).
This is most commonly at the front end, so that the bacterium is drawn
through the liquid by its motion. Rarely it is at the rear end. Other
bacteria may possess a bundle of flagella at one end and are called
_lophotrichic_ (Fig. 22) (λοφος = tuft). Sometimes at approaching
division the flagella may be at both ends and are then _amphitrichic_
(Fig. 23) (αμφι = both). It is probable that this condition does not
persist long, but represents the development of flagella at one end
of each of a pair resulting from division of an organism which has
flagella at one end only. In many bacteria the flagella arise from
all parts of the surface of the cell. Such bacteria are _peritrichic_
(Fig. 24) (περι = around). The position and even the number of the
flagella are very constant for each kind and are of decided value in
identification.
[Illustration: FIG. 23.--A bacterium showing flagella at each
end--amphitrichic.]
[Illustration: FIG. 24.--A bacterium showing flagella all
around--peritrichic.]
Flagella are too fine and delicate to be seen on the living organism,
or even on bacteria which have been colored by the ordinary stains.
They are rendered visible only by certain methods which cause a
precipitate on both bacteria and flagella which are thereby made thick
enough to be seen (Chapter XIX, p. 210). The movement of liquid around
a bacterium caused by vibrations of flagella can sometimes be observed
with large forms and the use of “dark-field” illumination.
Flagella are very delicate and easily broken off from the cell body.
Slight changes in the density or reaction of the medium frequently
cause this breaking off, so that preparations made from actively motile
bacteria frequently show no flagella. For this reason and also on
account of their fineness the demonstration of flagella is not easy,
and it is not safe to say that a non-motile bacterium has no flagella
except after very careful study.
The motion of bacteria is characteristic and a little practice in
observing will enable the student to recognize it and distinguish
between motility and “Brownian” or molecular motion. Dead and
non-motile bacteria show the latter. In fact, any finely divided
particles suspended in a liquid which is not too viscous and in which
the particles are not soluble show Brownian motion or “pedesis.” This
latter is a dancing motion of the particle within a very small area
and without change of place, while motile bacteria move from place to
place or even out of the field of the microscope with greater or less
speed. There is a marked difference in the character of the motion of
different kinds of bacteria. Some rotate around the long axis when
moving, others vibrate from side to side.
Among the higher thread bacteria there are some which show motility
without possessing flagella. Just how they move is little understood.
=Spores.=--Under certain conditions some bacterial cells undergo
transformations which result in the formation of so-called _spores_.
If the process is followed under the microscope, the changes observed
are approximately these: A very minute point appears in the protoplasm
which seems to act somewhat like the centrosome of higher cells as a
“center of attraction” so that the protoplasm gradually collects around
it. The spot disappears or is enclosed in the collected protoplasm.
This has evidently become denser as it is more highly refractive than
before. In time all or nearly all of the protoplasm is collected. A new
cell wall is developed around it which is thicker than the cell wall of
the bacterium. This thickened cell wall is called the “spore capsule.”
Gradually the remnants of the former cell contents and the old cell
wall disappear or dissolve and the spore becomes “free” (Fig. 25).
[Illustration: FIG. 25.--The smaller oval bodies in the middle of the
field are free spores.]
If the spore is placed in favorable conditions the protoplasm absorbs
water, swells, the capsule bursts at some point, a cell wall is formed
and the bacterium grows to normal size and divides, that is, it is an
active growing cell again. This process is called “germination” of the
spore. The point at which the spore capsule bursts to permit the new
cell to emerge is characteristic for each kind of bacterium. It may be
at the end when the germination is said to be _polar_ (Fig. 26). It may
be from the middle of one side which gives _equatorial_ germination
(Fig. 27). Rarely it is diagonally from a point between the equator and
the pole, which type may be styled _oblique_ germination. In one or
two instances the entire spore swells up, lengthens and becomes a rod
without any special germination unless this type might be designated
_bi-polar_.
[Illustration: FIG. 26.--Spores showing polar germination. The lighter
part of the two organisms just below A and B is the developing
bacterium. In the original slide the spore was stained red and the
developing bacterium a faint blue.]
[Illustration: FIG. 27.--A spore showing equatorial germination.
The spore in the center of the field shows a rod growing out of it
laterally. In the original slide the spore was stained red and the
developing bacterium blue.]
[Illustration: FIG. 28.--Spores in the middle of the rod without
enlargement of the rod. The lighter areas in the rods are spores.]
[Illustration: FIG. 29.--Spores in the middle of the rod with
enlargement of the rod around them. The lighter areas in the rods are
spores.]
Spores are most commonly oval or elliptical in shape, though sometimes
spherical. A spore may be formed in the middle of the organism without
(Fig. 28) or with (Fig. 29) a change in size of the cell around it.
If the diameter through the cell is increased, then the cell with
the contained spore becomes spindle-shaped. Such a cell is termed a
“_clostridium_.” Sometimes the spore develops in the end of the cell
either without (Fig. 30) or with enlarging it (Fig. 31). In a few
forms the spore is placed at the end of the rod and shows a marked
enlargement. This is spoken of as the “_plectridium_” or more commonly
the “drumstick spore” (Fig. 32). The position and shape of the spore
are constant for each kind of bacteria. In one or two instances only,
two spores have been observed in a single organism.
[Illustration: FIG. 30.--Spores in the end of the rod with no
enlargement of the rod around them. The lighter areas in the rods are
spores.]
[Illustration: FIG. 31.--Spores in the end of the rod with enlargement
of the rod, _A_, _A_, _A_, _A_.]
[Illustration: FIG. 32.--Drumstick spores at the end of the rod.]
The fact that the protoplasm is denser and the spore capsule thicker
(the percentage of water in each is decidedly less than in the growing
cell) gives the spore the property of much greater resistance to all
destructive agencies than the active bacterium has. For example, all
actively growing cells are destroyed by boiling in a very few minutes,
while some spores require several hours’ boiling. The same relation
holds with regard to drying, the action of chemicals, light, etc. That
the coagulation temperature of a protein varies inversely with the
amount of water, it contains, is shown by the following table from
Frost and McCampbell, “General Bacteriology”:
Egg albumin plus 50 per cent. water coagulates at 56°
„ „ „ 25 per cent. „ „ „ 74-80°
„ „ „ 18 per cent. „ „ „ 88-90°
„ „ „ 6 per cent. „ „ „ 145°
„ „ dry „ „ „ 160-170°
This resistance explains why it happens that food materials boiled
and sealed in cans to prevent the entrance of organisms sometimes
spoil. The spores have not been killed by the boiling. It explains
also in part the persistence of some diseases like anthrax and black
leg in pastures for years. From the above description it follows that
the spore is to be considered as _a condensation of the bacterial
protoplasm surrounded by an especially thick cell wall_. _Its function
is the preservation of the organism under adverse conditions._ It
corresponds most closely to the encystment of certain protozoa--the
ameba for example. Possibly the spore represents a very rudimentary
beginning of a reproductive function such as is gradually evolved in
the higher thread bacteria, the fission yeasts, the yeasts, the molds,
etc. Its characteristics are so markedly different, however, that the
function of preservation is certainly the main one.
It must not be supposed that spores are formed under adverse conditions
only, because bacteria showing vigorous growth frequently form spores
rapidly. Special conditions are necessary for their formation just as
they are for the growth and other functions of bacteria (Chapters VI
and VII).
CHAPTER III.
CELL FORMS.
Though there is apparently a wide variation in the shapes of different
bacterial cells, these may all be reduced to _three_ typical _cell
forms_. These are: first and simplest, the round or _spherical_,
typified by a ball and called the _coccus_ form, or _coccus_, plural
cocci[4] (Fig. 33). The coccus may be large, that is, from 1.5µ to 2µ
in diameter. The term _macrococcus_ is sometimes applied to these large
cocci. If the _coccus_ is less than 1µ in diameter, it is sometimes
spoken of as a _micrococcus_; in fact, this term is very commonly
applied to any coccus. When cocci are growing together, many of the
cells do not appear as true spheres but are more or less distorted
from pressure of their neighbors or from failure to grow to full size
after recent division. Most cocci divide into hemispheres and then each
half grows to full size. A few cocci elongate before division and then
appear oval or elliptical.
The second cell form is that of a _cylinder_ or rod typified by a
section of a lead-pencil. The name _bacillus_, plural _bacilli_, is
applied to this type (Fig. 34). The bacillus may be short (Fig. 35),
1µ or less in length, or long, up to 40µ in rare cases. Most bacilli
are from 2µ to 5µ or 6µ long. The ends of the rod are usually rounded,
occasionally square and very rarely pointed. It is evident that a very
short rod with rounded ends approaches a coccus in form and it is not
always easy to differentiate in such cases. Most bacilli are straight,
but some are slightly curved (Fig. 36).
The third cell form is the _spiral_, typified by a section of a
cork-screw and named _spirillum_, plural _spirilla_ (Fig. 37). A very
short spiral consisting of only a portion of a turn is sometimes called
_vibrio_ (Fig. 38). Vibrios when seen under the microscope look like
short curved rods. The distinction between the two can be made only by
examining the organism alive and moving in a liquid. The vibrio shows a
characteristic spiral twisting motion. Very long, flexible spirals are
usually named _spirochetes_ (Fig. 39). The spirochetes are motile but
flagella have not been shown to be present.
[Illustration: FIG. 33.--Cocci.]
[Illustration: FIG. 34.--Bacilli.]
[Illustration: FIG. 35.--Short bacilli.]
[Illustration: FIG. 36.--Curved bacilli. Only the one in the center of
the field is in focus. The others curve out of focus.]
Besides the three typical cell forms bacteria frequently show
very great irregularities in shape. They may be pointed, bulged,
club-shaped or even slightly branched. These peculiar and bizarre
forms practically always occur when some of the necessary conditions
for normal growth, discussed in Chapters VI and VII, are not fulfilled.
They are best regarded as _involution_ or _degeneration_ forms for this
reason (Fig. 40). In a very few cases it is not possible to obtain the
organism without these forms (the diphtheria group). It is probable
that these cell forms are normal in such cases, or else conditions
suitable for the normal growth have not been obtained.
[Illustration: FIG. 37.--Spirilla.]
[Illustration: FIG. 38.--Vibrio forms of spirilla. Compare with Fig.
36.]
[Illustration: FIG. 39.--Spirochetes.]
[Illustration: FIG. 40.--Involution forms. The organisms are tapering
and branched at one end.]
CHAPTER IV.
CELL GROUPINGS.
It has been stated that bacteria reproduce by transverse division, that
is, division across the long axis. Following repeated divisions the new
cells may or may not remain attached. In the latter case the bacteria
occur as separate isolated individuals. In the former, arrangements
characteristic of the particular organism almost invariably result.
These arrangements are best described as _cell groupings_ or _growth
forms_.
[Illustration: FIG. 41.--Streptospirillum grouping.]
[Illustration: FIG. 42.--Diplobacillus grouping.]
In the case of spiral forms it is obvious that there is only one
possible grouping, that is, in chains of two or more individuals
adherent end to end. A chain of two spirilla might be called
a _diplospirillum_ (διπλός = double); of three or more, a
_streptospirillum_ (στρεπτός = necklace, chain) (Fig. 41). These terms
are rarely used, since spirilla do not ordinarily remain attached.
Likewise the bacillus can grow only in chains of two or more, and
the terms _diplobacillus_ (Fig. 42), bacilli in groups of two, and
_streptobacillus_ (Fig. 43), bacilli in chains are frequently used.
Still the terms _thread_, _filament_, or _chain_ are more common for
_streptobacillus_.
[Illustration: FIG. 43.--Streptobacillus grouping.]
[Illustration: FIG. 44.--Typical diplococcus grouping. Note that the
individual cocci are flattened on the apposing sides.]
[Illustration: FIG. 45.--Long streptococcus grouping.]
[Illustration: FIG. 46.--Short streptococcus grouping.]
Since the coccus is spherical, _transverse_ division may occur in any
direction, though in three planes only at right angles to each other.
Division might occur in _one plane only_ as in spirilla and bacilli,
or in _two planes only_ or in _all three planes_. As a matter of fact
these three methods of division are found among the cocci, but only one
method for each particular kind of coccus. As a result there may be a
variety of cell groupings among the cocci. When division occurs in one
plane only, the possible groupings are the same as among the spirilla
or bacilli. The cocci may occur in groups of two--_diplococcus_
grouping (Fig. 44), or in chains--_streptococcus_ grouping (Figs. 45
and 46). When the grouping is in _diplococci_, the individual cocci
most commonly appear as hemispheres with the plane surfaces apposed
(Fig. 44). Sometimes they appear as spheres and occasionally are even
somewhat elongated. The individuals in a streptococcus grouping are
most commonly elongated, either in the same direction as the length of
the chain, or at right angles to it. The latter appearance is probably
due to failure to enlarge completely after division. Streptococci
frequently appear as chains of diplococci, that is, the pair resulting
from the division of a single coccus remain a little closer to each
other than to neighboring cells, as a close inspection of Fig. 45 will
show.
If division occurs in _two planes only_, there may result the above
groupings and several others in addition. The four cocci which result
from a single division may remain together, giving the _tetracoccus_
or _tetrad_ grouping. Very rarely all the cocci divide evenly and the
result is a regular _rectangular flat mass_ of cells, the total number
of which is a multiple of four. The term merismopedia (from a genus of
algæ which grows the same way) is applied to such a grouping. If the
cells within a group after a few divisions do not reproduce so rapidly
(lack of food), as usually happens, the number of cells becomes uneven
or at least not necessarily a multiple of four and the resultant _flat
mass_ has an _irregular_, _uneven outline_. This grouping is termed
_staphylococcus_ (σταφυλος = a bunch of grapes) (Fig. 47). It is the
most common grouping among the cocci.
When division occurs in all three planes, there is in addition to all
the groupings possible to one- and two-plane division a third grouping
in which the cells are in _solid packets_, _multiples of eight_. The
name _sarcina_ is applied to this growth form (Fig. 48). The individual
cells in a sarcina packet never show the typical coccus form so long as
they remain together, but are always flattened on two or more sides.
The above descriptions indicate how the method of division may be
determined. If in examining a preparation the _sarcina_ grouping
appears, that shows _three-plane division_. If there are no sarcina,
but _tetrads_ or _staphylococci_ (rarely merismopedia), then the
division is in _two planes_. If none of the foregoing is observed but
only _diplo-_ or _streptococci_, these indicate _one-plane division_
only. Cocci show their _characteristic_ groupings only when grown in a
liquid medium, and such should always be used before deciding on the
plane of division.
[Illustration: FIG. 47.--Staphylococcus grouping. The large flat masses
are staphylococcus grouping. Diplococcus grouping, tetrads and short
streptococci are also evident.]
[Illustration: FIG. 48.--Sarcina grouping.]
As the above description shows, these terms which are properly
adjectives describing the cell grouping, are quite generally used as
nouns. Thus the terms a diplococcus, a tetrad, a streptococcus, etc.,
are common, meaning a bacterium of the cell form and cell grouping
indicated.
CELL FORM. CELL GROUPING.
coccus-- {diplococcus--in 2’s.
round or spherical. {streptoccus--in chains.
{tetracoccus, tetrads--in 4’s.
{staphylococcus--irregular flat masses.
{sarcina--regular, solid packets, multiples of 8.
bacillus-- {diplobacillus--in 2’s.
rod-shaped {streptobacillus--in chains.
or cylindrical.
spirillum-- {diplospirillum--in 2’s, little used.
spiral-shaped. {streptospirillum--in chains, little used.
CHAPTER V.
CLASSIFICATION.
The arrangement of living organisms in groups according to their
resemblances and the adoption of _fixed names_ is of the greatest
advantage in their scientific study. For animal forms and for the
higher plants this classification is gradually becoming standardized
through the International Congress of Zoölogists and of Botanists
respectively. Unfortunately, the naming of the bacteria has not as
yet been taken up by the latter body, though announced as one of the
subjects for the Congress of 1916 (postponed on account of the war).
Hence there is at present no system which can be regarded as either
fixed or official.
[Illustration: FIG. 49.--Illustrates the genus Streptococcus. Typical
chains, no staphylococcus grouping, no sarcina grouping, no flagella.]
[Illustration: FIG. 50.--Illustrates the genus Micrococcus.
Diplococcus, tetrads short chains and staphylococcus; no sarcina, no
flagella.]
[Illustration: FIG. 51.--Illustrates the genus Sarcina. Sarcina
grouping, no flagella.]
[Illustration: FIG. 52.--Illustrates the genus Bacillus. A bacillus
with peritrichic flagella. (Student preparation.)]
Since Müller’s first classification of “animalcules” in 1786 numerous
attempts have been made to solve the problem. Only those beginning with
Ferdinand Cohn (1872-75) are of any real value. As long as bacteria
are regarded as plants it appears that the logical method is to follow
the well-established botanical principles in any system for naming
them. Botanists depend on morphological features almost entirely in
making their distinctions. The preceding chapters have shown that
the minute plants which are discussed have very few such features.
They are, to recapitulate, _cell wall_, _protoplasm_, _vacuoles_,
_metachromatic granules_, _capsules_, _flagella_, _spores_, _cell
forms_ and _cell groupings_. Most bacteria show not more than three
or four of these features, so that it is impossible by the aid of
morphology alone to distinguish from each other the large number of
different kinds which certainly exist. In the various systems which
are conceded to be the best these characteristics do serve to classify
them down to genera, leaving the “species” to be determined from their
_physiological_ activities. One of these systems was adopted by the
laboratory section of the American Public Health Association and by the
Society of American Bacteriologists and was practically the standard
in this country until superseded by the Society’s own classification.
It is that of the German Bacteriologist Migula and is given below for
comparison. Since practically the entire discussion in this book is
concerned with the first three families the generic characteristics
in these only will be given. The full classification as well as a
thorough discussion of this subject is given in Lafar’s _Handbuch_,
whence the following is adopted:
[Illustration: FIG. 53.--Illustrates the genus Pseudomonas. A bacillus
with flagella at the end only.]
[Illustration: FIG. 54.--Illustrates the genus Microspira. It is
(though the photograph does not prove it) a short spiral with one
flagellum at the end.]
[Illustration: FIG. 55.--Illustrates the genus Spirillum. Spiral
bacteria with more than three, in this case four, flagella at the end.]
[Illustration: FIG. 56.--Illustrates the genus Spirochæta.]
[Illustration: FIG. 57.--Illustrates the genus Chlamydothrix. Fine
threads with a delicate sheath.]
[Illustration: FIG. 58.--Illustrates the genus Crenothrix. The
thickness of the cell walls is due to deposits of iron hydroxide.
(After Lafar.)]
[Illustration: FIG. 59.--Illustrates the genus Beggiatoa. The filament
_A_ is so full of sulphur granules that the individual cells are not
visible. _B_ has fewer sulphur granules. In _C_ the granules are
nearly absent and the separate cells of the filament are seen. (After
Winogradsky, from Lafar.)]
ORDER I. Eubacteria.
Cells without nuclei, free from sulphur granules and from
bacteriopurpurin (p. 112); colorless, or slightly colored.
1. Family: COCCACEÆ (Zopf) Migula, all cocci.
{Genus 1. _Streptococcus_ Billroth:
{ division in one plane only (Fig. 49).
Non-flagellated, { „ 2. _Micrococcus_ (Hallier) Cohn:
Non-motile { division in two planes only (Fig. 50).
{ „ 3. _Sarcina_ Goodsir:
{ division in three planes only (Fig. 51).
{ „ 4. _Planococcus_ Migula:
Flagellated, { division in two planes only.
motile { „ 5. _Planosarcina_ Migula:
{ division in three planes only.
2. Family: BACTERIACEÆ Migula, all bacilli.
Genus 1. _Bacterium_ (Ehrenberg) Migula: no flagella; non-motile.
„ 2. _Bacillus_ (Cohn) Migula: flagella peritrichic (Fig. 52).
„ 3. _Pseudomonas_ Migula: flagella at the end:
monotrichic, lophotrichic, amphitrichic (Fig. 53).
3. Family: SPIRILLACEÆ Migula, all spirilla.
{Genus 1. _Spirosoma_ Migula:
{ non flagellated; non-motile.
{ „ 2. _Microspira_ (Schrœter) Migula:
Cells stiff { flagella one to three at the end (Fig. 54).
{ „ 3. _Spirillum_ (Ehrenberg) Migula:
{ flagella more than three
{ at the end (Fig. 55).
Cell flexible { „ 4. _Spirochæta_ Ehrenberg:
{ motile; no flagella (Fig. 56).
4. Family: CHLAMYDOBACTERIACEÆ.
Cells cylindrical in long threads and surrounded by a sheath.
Reproduction also by gonidia formed from an entire cell.
Genus 1. _Chlamydothrix_ Migula (Fig. 57).
„ 2. _Crenothrix_ Colin (Fig. 58).
„ 3. _Pragmidiothrix_ Engler.
„ 4. _Spherotilus_ (including Cladothrix).
ORDER II. THIOBACTERIA: SULPHUR BACTERIA.
Cells without a nucleus, but containing sulphur granules, may be
colorless or contain bacteriopurpurin and be colored reddish or violet.
1. Family BEGGIATOACEÆ.
Genus 1. _Thiothrix_ Winogradsky.
„ 2. _Beggiatoa_ Trevisan. Of interest since it is without a
sheath, is motile, but without flagella (Fig. 59).
2. Family RHODOBACTERIACEÆ.
This has five subfamilies and twelve genera, most of which are due to
the Russian bacteriologist Winogradsky who did more work than anyone
else with the sulphur bacteria.
THE CLASSIFICATION OF THE SOCIETY OF AMERICAN BACTERIOLOGISTS.
The Committee on Classification of the Society of American
Bacteriologists at the meeting held in December, 1919, submitted its
final report. This report has not been formally adopted as a whole,
but in all probability will be substantially as outlined below. This
outline does not attempt to give the detailed characterizations of the
different groups as defined by the committee, but does show the names
to be applied to the commoner organisms. These organisms are included
in the 4th and 5th orders. Details of the first three orders have not
been worked out. They are listed merely for completeness.
CLASS SCHIZOMYCETES.
Unicellular, chlorophyl-free plants, reproducing by transverse division
(some forms by gonidia also).
ORDERS:
A. Myxobacteriales--Cells united during vegetative stage into
a pseudo-plasmodium which passes over into a highly developed
cyst-producing resting stage.
B. Thiobacteriales--Sulphur bacteria.
C. Chlamydobacteriales--Iron bacteria and other sheathed bacteria.
D. Actinomycetales--Actinomyces, tubercle and diphtheria bacilli.
E. Eubacteriales--All the other common bacteria.
GENERA OF ORDERS D AND E.
D. ACTINOMYCETALES--
FAMILY I. ACTINOMYCETACEÆ Buchanan, 1918.
Genus 1. _Actinobacillus_, Brampt, 1900.
Type species, _Actinobacillus lignieresi_ Brampt, 1900.
Genus 2. _Leptotrichia_ Trevisan, 1879.
Type species, _Leptotrichia buccalis_ (Robin, 1847) Trevisan.
Genus 3. _Actinomyces_ Harz, 1877.
Type species, _Actinomyces bovis_ Harz.
Genus 4. _Erysipelothrix_ Rosenbach, 1909.
Type species, _Erysipelothrix rhusiopathiæ_ (Kitt, 1893)
Rosenbach, swine erysipelas.
FAMILY II. MYCOBACTERIACEÆ Chester, 1897.
Genus 1. _Mycobacterium_ Lehmann and Neumann, 1896.
Type species, _Mycobacterium tuberculosis_ (Koch, 1882) L.
and N.
Genus 2. _Corynebacterium_ Lehmann and Neumann, 1896.
Type species, _Corynebacterium diphtheriæ_ (Loeffler, 1882)
L. and N.
Genus 3. _Fusiformis_ Hoelling, 1910.
Type species, _Fusiformis termitidis_ Hoelling. Vincent’s
angina.
Genus 4. _Pfeifferella_ Buchanan, 1918.
Type species, _Pfeifferella mallei_ (Loeffler, 1896) Buchanan.
Glanders bacillus.
E. EUBACTERIALES
FAMILY I--NITROBACTERIACEÆ--Proto- or autotrophic for N
or C and sometimes for both (except Acetobacter).
TRIBE I--NITROBACTEREÆ--autotrophic for C.
Genus 1. _Hydrogenomonas_ Jensen, 1909.
Type species, _Hydrogenomonas pantotropha_ (Kaserer, 1906)
Jensen; oxidizes free H.
Genus 2. _Methanomonas_ Jensen, 1909.
Type species, _Methanomonas methanica_ (Söhngen) Jensen;
oxidizes CH₄.
Genus 3. _Carboxydomonas_ Jensen, 1909.
Type species, _Carboxydomonas oligocarbophila_ (Beijerinck
and Van Delden, 1903) Jensen; oxidizes CO.
Genus 4. _Acetobacter_ Fuhrman, 1905.
Type species, _Acetobacter aceti_ (Thompson, 1852) Fuhrman;
oxidizes alcohol to acetic acid.
Genus 5. _Nitrosomonas_ Winogradsky, 1892.
Type species, _Nitrosomonas europoea_ Winogradsky; oxidizes
ammonia or ammonium salts to nitrous acid,
hence nitrites.
Genus 6. _Nitrobacter_ Winogradsky, 1892.
Type species, _Nitrobacter Winogradskyi_ Committee of 1917;
oxidizes nitrous acid (nitrites)
to nitric acid (nitrates).
TRIBE II--AZOTOBACTEREÆ--prototrophic for N.
Genus 7. _Azotobacter_ Beijerinck, 1901; large, free-living,
aerobic N absorbers.
Type species, _Azotobacter chroococcum_ Beijerinck.
Genus 8. _Rhizobium_ Frank, 1889.
Type species, _Rhizobium leguminosarum_ Frank; root tubercle
bacteria of legumes.
FAMILY II--PSEUDOMONADACEÆ, Committee of 1917.
Genus 1. _Pseudomonas_ Migula, 1894.
Type species, _Pseudomonas violacea_ (Schroeter, 1872) Migula.
FAMILY III--SPIRILLACEÆ Migula, 1894--all spiral bacteria.
Genus 1. _Vibrio_ Müller, 1786, emended by E. F. Smith, 1905.
Type species, _Vibrio choleræ_ (Koch, 1884) Schroeter, 1886.
Genus 2. _Spirillum_ Ehrenberg, 1830, emended Migula, 1894.
Type species, _Spirillum undula_ (Müller, 1786) Ehrenberg.
FAMILY IV--COCCACEÆ Zopf, 1884, emended Migula, 1894--all cocci.
Tribe I--NEISSEREÆ.
Genus 1. _Neisseria_ Trevisan, 1885.
Type species, _Neisseria gonorrhoeae_ Trevisan.
Tribe II--STREPTOCOCCEÆ Trevisan, 1889.
Genus 2. _Diplococcus_ Weichselbaum, 1886.
Type species, _Diplococcus pneumoniae_ Weichselbaum.
Genus 3. _Leuconostoc_ Van Tieghem, 1878.
Type species, _Leuconostoc mesenterioides_ (Cienkowski) Van
Tieghem.
Genus 4. _Streptococcus_ Rosenbach, 1884; emended Winslow
and Rogers, 1905.
Type species, _Streptococcus pyogenes_ Rosenbach.
Tribe III--MICROCOCCEÆ Trevisan, 1889.
Genus 5. _Staphylococcus_ Rosenbach, 1884; animal parasites.
Type species, _Staphylococcus aureus_ Rosenbach.
Genus 6. _Micrococcus_ Cohn, 1872, emended Winslow and Rogers,
1905. Facultative parasites or saprophytes.
Type species, _Micrococcus luteus_ (Schroeter, 1872) Cohn.
Genus 7. _Sarcina_ Goodsir, 1842, emended Winslow and
Rogers, 1905.
Type species, _Sarcina ventriculi_ Goodsir.
Genus 8. _Rhodococcus_ Zopf, 1891, emended Winslow and
Rogers, 1905; cocci with red pigment.
Type species, _Rhodococcus rhodochrous_ Zopf.
FAMILY V--BACTERIACEÆ Cohn, 1872, emended by Committee of 1917;
bacilli without spores not above included.
Tribe I--CHROMOBACTEREÆ Committee of 1919; producing red or
violet pigment, mainly water forms.
Genus 1. _Erythrobacillus_ Fortineau, 1905.
Type species, _Erythrobacillus prodigiosus_
(Ehrenberg, 1848) Fortineau.
Genus 2. _Chromobacterium_ Bergonzini, 1881.
Type species, _Chromobacterium violaceum_ Bergonzini.
Tribe II--ERWINEÆ Committee 1919; plant pathogens.
Genus 3. _Erwinia_ Committee 1917.
Type species, _Erwinia amylovora_ (Burrill, 1883) Committee
1917.
Tribe III--ZOPFEÆ Committee of 1919; Gram +, no pigment,
non-carbohydrate-fermenting.
Genus 4. _Zopfius_ Wenner and Rettger, 1919.
Type species, _Zopfius zopfii_ (Kurth) Wenner and Rettger.
Tribe IV--BACTEREÆ Committee of 1919; Gram -, carbohydrate
fermenters.
Genus 5. _Proteus_ Hauser, 1885; liquefy gelatin.
Type species, _Proteus vulgaris_ Hauser.
Genus 6. _Bacterium_ Ehrenberg, 1828, emended Jensen, 1909;
liquefy gelatin rarely.
Type species, _Bacterium coli_.
Tribe VI--LACTOBACILLEÆ Committee of 1919; Gram +, high acid,
thermophils.
Genus 7. _Lactobacillus_ Beijerinck, 1901.
Type species, _Lactobacillus caucasicus_ (Kern?) Beijerinck;
Bulgarian bacillus.
Tribe VI--PASTEURELLEÆ Committee of 1919; organisms of
hemorrhagic septicemia.
Genus 8. _Pasteurella_ Trevisan, 1888.
Type species, _Pasteurella cholerae-gallinarum_
(Flügge, 1886); Trevisan.
Tribe VII--HEMOPHILEÆ Committee of 1917; require hemoglobin for
growth.
Genus 9. _Hemophilus_ Committee of 1917.
Type species, _Hemophilus influenzae_ (Pfeiffer, 1893)
Committee of 1917.
FAMILY VI--BACILLACEÆ Fischer, 1895. Spore forming rods.
Genus 1. _Bacillus_ Cohn, 1872; aerobic, no change of form
around the spore.
Type species, _Bacillus subtilis_ Cohn.
Genus 2. _Clostridium_ Prazmowski, 1880; anaërobic, frequently
enlarged around spore.
Type species, _Clostridium butyricum_ Prazmowski.
As compared with Migula’s classification it is to be noted that there
are 38 genera listed by the Committee instead of 13 in the same general
groups.
The following list of _Genera conservanda_ submitted by the Committee
was formally adopted by the Society and these are therefore its
official names for the organisms included in these genera.
_Acetobacter_ Fuhrman
_Actinomyces_ Harz
_Bacillus_ Cohn
_Bacterium_ Ehrenberg
_Chromobacterium_ Bergonzini
_Clostridium_ Prazmowski
_Erythrobacillus_ Fortineau
_Leptotrichia_ Trevisan
_Leuconostoc_ Van Tieghem
_Micrococcus_ Cohn
_Rhizobium_ Frank
_Sarcina_ Goodsir
_Spirillum_ Ehrenberg
_Staphylococcus_ Rosenbach
_Streptococcus_ Rosenbach
_Vibrio_ Müller
_It is greatly to be desired that the Society’s Classification when
finally completed shall become the standard in the United States at
least._
_Such names as have been adopted by the Society are used throughout
this work._
The Committee also submitted the following artificial key for
determining the genera in the two orders _ACTINOMYCETALES AND
EUBACTERIALES_:
A--Typically filamentous forms _Actinomycetacae_
B--Mycelium and conidia formed _Actinomyces_
BB--No true mycelium
C--Cells show branching
D--Gram negative _Actinobacillus_
DD--Gram positive _Erysipelothrix_
CC--Cells never branch. Gram positive threads later fragmenting
into rods _Leptotrichia_
AA--Typically unicellular forms (though chains of cells may occur)
B--Cells spherical--_COCCACEÆ_
C--Parasitic forms (except Leuconostoc), cells generally grouped
in pairs or chains, never in packets, generally active
fermenters.
D--Cells in flattened coffee-bean-like pairs, gram -.
_Neisseria_
DD--Not as D
E--Saprophytes in zoögloea masses in sugar solutions.
_Leuconostoc_
EE--Not as E. Gram +.
F--Cells in lanceolate pairs or in chains. Growth on
media not abundant.
G--Cells in lanceolate pairs. Inulin generally fermented.
_Diplococcus_
GG--Cells in chains. Inulin not generally fermented.
_Streptococcus_
FF--Cells in irregular groups. Growth in media fairly
vigorous. White or orange pigment.
_Staphylococcus_
CC--Saprophytic forms. Cells in irregular groups or packets,
not in chains. Fermentative powers low.
D--Packets _Sarcina_
DD--No packets.
E--Yellow pigment _Micrococcus_
EE--Red pigment _Rhodococcus_
BB--Rods:
C--Spiral rods
D--Short, comma-like rods. One to three flagella.
_Vibrio_
DD--Long spirals. Five to twenty flagella. _Spirillum_
CC--Straight rods.
D--No endospores.
E--Rods of irregular shape or showing branched or filamentous
involution forms.
F--Cells irregular in shape. Staining unevenly. Animal
parasites.
G--Acid fast _Mycobacterium_
GG--Not acid fast.
H--Cells elongated, fusiform _Fusiformis_
HH--Cells not elongated, sometimes branching.
I--Gram positive. Slender, sometimes club-shaped.
_Corynebacterium_
II--Gram negative. Rods sometimes form threads.
Characteristic honey-like growth on potato.
_Pfeifferella_
FF--Cells staining unevenly but with branched or filamentous
forms at certain stages. Never acid fast.
Not animal parasites.
G--Metabolism simple, growth processes involving oxidation
of alcohol or fixation of free N (latter in symbiosis
with green plants).
H--Cells minute. Symbiotic in roots of legumes.
_Rhizobium_
HH--Oxidizing alcohol. Branching forms common.
_Acetobacter_
GG--Not as G. Proteus-like colonies.
H--Not attacking carbohydrates _Zopfius_
HH--Fermenting glucose and sucrose at least.
_Proteus_
EE--Regularly formed rods.
F--Metabolism simple, growth processes involving oxidation
of C, H, or their simple compounds or the fixation
of free N.--_NITROBACTERIACEÆ._
G--Fixing N or oxidizing its simple compounds.
H--Fixing N, cells large, free in soil _Azotobacter_
HH--Oxidizing N compounds.
I--Oxidizing NH₄ compounds _Nitrosomonas_
II--Oxidizing nitrites _Nitrobacter_
GG--Not as G.
H--Oxidizing free H _Hydrogenomonas_
HH--Oxidizing simple C compounds, not free H.
I--Oxidizing CO _Carboxydomonas_
II--Oxidizing CH₄ _Methanomonas_
FF--Not as F.
G--Flagella usually present, polar--_PSEUDOMONADACEÆ_
_Pseudomonas_
GG--Flagella when present peritrichic--_BACTERIACEÆ_
H--Parasitic forms showing bi-polar staining.
_Pasteurella_
HH--Not as H.
I--Strict parasites growing only in presence
of hemoglobin
_Hemophilus_
II--Not as I.
J--Water forms producing red or violet pigment.
K--Pigment red _Erythrobacillus_
KK--Pigment violet _Chromobacterium_
JJ--Not as J.
K--Plant pathogens _Erwinia_
KK--Not plant pathogens.
L--Gram +, forming large amount of acid
from carbohydrates, sometimes CO₂,
never H _Lactobacillus_
LL--Gram -, forming H as well as CO₂ if
gas is produced _Bacterium_
DD--Endospores present--_BACILLACEÆ_
E--Aerobes, rods not swollen at sporulation. _Bacillus_
EE--Anaërobes, rods swollen at sporulation. _Clostridium_
PART II.
PHYSIOLOGY.