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BIOLOGY
AND ITS MAKERS
_With Portraits and Other Illustrations_
BY
WILLIAM A. LOCY, Ph.D., Sc.D.
_Professor in Northwestern University_
[Illustration]
NEW YORK
HENRY HOLT AND COMPANY
1908
COPYRIGHT, 1908,
BY
HENRY HOLT AND COMPANY
Published June, 1908
To
MY GRADUATE STUDENTS
Who have worked by my side in the Laboratory
Inspired by the belief that those who seek shall find
This account of the findings of some of
The great men of biological science
Is dedicated by
THE AUTHOR
PREFACE
The writer is annually in receipt of letters from students, teachers,
ministers, medical men, and others, asking for information on topics
in general biology, and for references to the best reading on that
subject. The increasing frequency of such inquiries, and the wide range
of topics covered, have created the impression that an untechnical
account of the rise and progress of biology would be of interest to
a considerable audience. As might be surmised, the references most
commonly asked for are those relating to different phases of the
Evolution Theory; but the fact is usually overlooked by the inquirers
that some knowledge of other features of biological research is
essential even to an intelligent comprehension of that theory.
In this sketch I have attempted to bring under one view the broad
features of biological progress, and to increase the human interest by
writing the story around the lives of the great Leaders. The practical
execution of the task resolved itself largely into the question of
what to omit. The number of detailed researches upon which progress in
biology rests made rigid selection necessary, and the difficulties of
separating the essential from the less important, and of distinguishing
between men of temporary notoriety and those of enduring fame, have
given rise to no small perplexities.
The aim has been kept in mind to give a picture sufficiently
diagrammatic not to confuse the general reader, and it is hoped that
the omissions which have seemed necessary will, in a measure, be
compensated for by the clearness of the picture. References to selected
books and articles have been given at the close of the volume, that
will enable readers who wish fuller information to go to the best
sources.
The book is divided into two sections. In the first are considered
the sources of the ideas--except those of organic evolution--that
dominate biology, and the steps by which they have been molded into
a unified science. The Doctrine of Organic Evolution, on account of
its importance, is reserved for special consideration in the second
section. This is, of course, merely a division of convenience, since
after its acceptance the doctrine of evolution has entered into all
phases of biological progress.
The portraits with which the text is illustrated embrace those of
nearly all the founders of biology. Some of the rarer ones are
unfamiliar even to biologists, and have been discovered only after long
search in the libraries of Europe and America.
An orderly account of the rise of biology can hardly fail to be of
service to the class of inquirers mentioned in the opening paragraph.
It is hoped that this sketch will also meet some of the needs of the
increasing body of students who are doing practical work in biological
laboratories. It is important that such students, in addition to the
usual classroom instruction, should get a perspective view of the way
in which biological science has come into its present form.
The chief purpose of the book will have been met if I have succeeded
in indicating the sources of biological ideas and the main currents
along which they have advanced, and if I have succeeded, furthermore,
in making readers acquainted with those men of noble purpose whose work
has created the epochs of biological history, and in showing that there
has been continuity of development in biological thought.
Of biologists who may examine this work with a critical purpose, I beg
that they will think of it merely as an outline sketch which does not
pretend to give a complete history of biological thought. The story has
been developed almost entirely from the side of animal life; not that
the botanical side has been underestimated, but that the story can be
told from either side, and my first-hand acquaintance with botanical
investigation is not sufficient to justify an attempt to estimate its
particular achievements.
The writer is keenly aware of the many imperfections in the book. It is
inevitable that biologists with interests in special fields will miss
familiar names and the mention of special pieces of notable work, but I
am drawn to think that such omissions will be viewed leniently, by the
consideration that those best able to judge the shortcomings of this
sketch will also best understand the difficulties involved.
The author wishes to acknowledge his indebtedness to several
publishing houses and to individuals for permission to copy cuts and
for assistance in obtaining portraits. He takes this opportunity to
express his best thanks for these courtesies. The parties referred to
are the director of the American Museum of Natural History; D. Appleton
& Co.; P. Blakiston's Sons & Co.; The Macmillan Company; The Open
Court Publishing Company; the editor of the _Popular Science Monthly_;
Charles Scribner's Sons; Professors Bateson, of Cambridge, England;
Conklin, of Philadelphia; Joubin, of Rennes, France; Nierstrasz, of
Utrecht, Holland; Newcombe, of Ann Arbor, Michigan; Wheeler and E.B.
Wilson, of New York City. The editor of the _Popular Science Monthly_
has also given permission to reprint the substance of Chapters IV and
X, which originally appeared in that publication.
W.A.L.
NORTHWESTERN UNIVERSITY,
Evanston, Ill., April, 1908.
CONTENTS
PART I
The Sources of Biological Ideas Except Those of
Organic Evolution
CHAPTER I
PAGE
An Outline of the Rise of Biology and of the Epochs in its
History, 3
Notable advances in natural science during the nineteenth century, 3.
Biology the central subject in the history of opinion regarding
life, 4. It is of commanding importance in the world of science,
5. Difficulties in making its progress clear, 5. Notwithstanding
its numerous details, there has been a relatively simple and
orderly progress in biology, 6. Many books about the facts of
biology, many excellent laboratory manuals, but scarcely any
attempt to trace the growth of biological ideas, 6. The growth
of knowledge regarding organic nature a long story full of human
interest, 7. The men of science, 7. The story of their aspirations
and struggles an inspiring history, 8. The conditions under
which science developed, 8. The ancient Greeks studied nature
by observation and experiment, but this method underwent
eclipse, 9. Aristotle the founder of natural history, 9. Science
before his day, 9, 10. Aristotle's position in the development of
science, 11. His extensive knowledge of animals, 12. His scientific
writings, 13. Personal appearance, 13. His influence, 15.
Pliny: his writings mark a decline in scientific method, 16. The
arrest of inquiry and its effects, 17. A complete change in the
mental interests of mankind, 17. Men cease to observe and indulge
in metaphysical speculation, 18. Authority declared the
source of knowledge, 18. The revolt of the intellect against these
conditions, 19. The renewal of observation, 19. The beneficent
results of this movement, 20. Enumeration of the chief epochs
in biological history: renewal of observation, 20; the overthrow
of authority in science, 20. Harvey and experimental investigation,
20; introduction of microscopes, 20; Linnæus, 20; Cuvier,
20; Bichat, 21; Von Baer, 21; the rise of physiology, 21; the
beginnings of evolutionary thought, 21; the cell-theory, 21; the
discovery of protoplasm, 21.
CHAPTER II
Vesalius and the Overthrow of Authority in Science, 22
Vesalius, in a broad sense, one of the founders of biology, 22.
A picture of the condition of anatomy before he took it up, 23.
Galen: his great influence as a scientific writer, 24. Anatomy in the
Middle Ages, 24. Predecessors of Vesalius: Mundinus, Berangarius,
Sylvius, 26. Vesalius gifted and forceful, 27. His impetuous
nature, 27. His reform in the teaching of anatomy, 28.
His physiognomy, 30. His great book (1543), 30. A description
of its illustrations, 30, 31. Curious conceits of the artist, 32.
Opposition to Vesalius: curved thigh bones due to wearing tight
trousers, the resurrection bone, 34, 35. The court physician, 35.
Close of his life, 36. Some of his successors: Eustachius and
Fallopius, 36. The especial service of Vesalius: he overthrew
dependence on authority and reëstablished the scientific method
of ascertaining truth, 37, 38.
CHAPTER III
William Harvey and Experimental Observation, 39
Harvey's work complemental to that of Vesalius, 39. Their combined
labors laid the foundations of the modern method of investigating
nature, 39. Harvey introduces experiments on living
organisms, 40. Harvey's education, 40. At Padua, comes
under the influence of Fabricius, 41. Return to England, 42.
His personal qualities, 42-45. Harvey's writings, 45. His great
classic on movement of the heart and blood (1628), 46. His
demonstration of circulation of the blood based on cogent reasoning;
he did not have ocular proof of its passage through
capillaries, 47. Views of his predecessors on the movement of
the blood, 48. Servetus, 50. Realdus Columbus, 50. Cæsalpinus,
51. The originality of Harvey's views, 51. Harvey's
argument, 51. Harvey's influence, 52. A versatile student;
work in other directions, 52. His discovery of the circulation
created modern physiology, 52. His method of inquiry became
a permanent part of biological science, 53.
CHAPTER IV
The Introduction of the Microscope and the Progress of Independent
Observation, 54
The pioneer microscopists: Hooke and Grew in England; Malpighi
in Italy and Swammerdam and Leeuwenhoek in Holland, 54.
Robert Hooke, 55. His microscope and the micrographia (1665),
56. Grew one of the founders of vegetable histology, 56. Malpighi,
1628-1694, 58. Personal qualities, 58. Education, 60.
University positions, 60, 61. Honors at home and abroad, 61.
Activity in research, 62. His principal writings: Monograph
on the silkworm, 63; anatomy of plants, 66; work in embryology,
66. Jan Swammerdam, 1637-1680, 67. His temperament,
67. Early interest in natural history, 68. Studies medicine, 68.
Important observations, 68. Devotes himself to minute anatomy,
70. Method of working, 71. Great intensity, 70. High
quality of his work, 72. The _Biblia Naturæ_, 73. Its publication
delayed until fifty-seven years after his death, 73. Illustrations
of his anatomical work, 74-76. Antony van Leeuwenhoek,
1632-1723, 77. A composed and better-balanced man, 77. Self-taught
in science, the effect of this showing in the desultory character
of his observations, 77, 87. Physiognomy, 78. New biographical
facts, 78. His love of microscopic observation, 80.
His microscopes, 81. His scientific letters, 83. Observes the
capillary circulation in 1686, 84. His other discoveries, 86.
Comparison of the three men: the two university-trained men
left coherent pieces of work, that of Leeuwenhoek was discursive,
87. The combined force of their labors marks an epoch, 88.
The new intellectual movement now well under way, 88.
CHAPTER V
The Progress of Minute Anatomy, 89
Progress in minute anatomy a feature of the eighteenth century.
Attractiveness of insect anatomy. Enthusiasm awakened by the
delicacy and perfection of minute structure, 89. Lyonet, 1707-1789,
90. Description of his remarkable monograph on the
anatomy of the willow caterpillar, 91. Selected illustrations,
92-94. Great detail--4,041 muscles, 91. Extraordinary character
of his drawings, 90. A model of detailed dissection, but lacking
in comparison and insight, 92. The work of Réaumur, Roesel,
and De Geer on a higher plane as regards knowledge of insect life,
95. Straus-Dürckheim's monograph on insect anatomy, 96. Rivals
that of Lyonet in detail and in the execution of the plates, 99.
His general considerations now antiquated, 99. He attempted
to make insect anatomy comparative, 100. Dufour endeavors to
found a broad science of insect anatomy, 100. Newport, a very
skilful dissector, with philosophical cast of mind, who recognizes
the value of embryology in anatomical work, 100. Leydig starts
a new kind of insect anatomy embracing microscopic structure
(histology), 102. This the beginning of modern work, 102.
Structural studies on other small animals, 103. The discovery
of the simplest animals, 104. Observations on the microscopic
animalcula, 105. The protozoa discovered in 1675 by Leeuwenhoek,
105. Work of O.F. Müller, 1786, 106. Of Ehrenberg
1838, 107. Recent observations on protozoa, 109.
CHAPTER VI
Linnæus and Scientific Natural History, 110
Natural history had a parallel development with comparative anatomy,
110. The Physiologus, or sacred natural history of the Middle
Ages, 110, 111. The lowest level reached by zoölogy, 111. The
return to the science of Aristotle a real advance over the Physiologus,
112. The advance due to Wotton in 1552, 112. Gesner,
1516-1565. High quality of his _Historia Animalium_, 112-114.
The scientific writings of Jonson and Aldrovandi, 114. John
Ray the forerunner of Linnæus, 115. His writings, 117. Ray's
idea of species, 117. Linnæus or Linné, 118. A unique service
to natural history. Brings the binomial nomenclature into
general use, 118. Personal history, 119. Quality of his mind,
120. His early struggles with poverty, 120. Gets his degree in
Holland, 121. Publication of the _Systema Naturæ_ in 1735, 121.
Return to Sweden, 123. Success as a university professor in Upsala,
123. Personal appearance, 125. His influence on natural
history, 125. His especial service, 126. His idea of species,
128. Summary, 129. Reform of the Linnæan system, 130-138.
The necessity of reform, 130. The scale of being, 131.
Lamarck the first to use a genealogical tree, 132. Cuvier's
four branches, 132. Alterations by Von Siebold and Leuckart,
134-137. Tabular view of classifications, 138. General biological
progress from Linnæus to Darwin. Although details were
multiplied, progress was by a series of steps, 138. Analysis
of animals proceeded from the organism to organs, from organs
to tissues, from tissues to cells, the elementary parts, and finally
to protoplasm, 139-140. The physiological side had a parallel
development, 140.
CHAPTER VII
Cuvier and the Rise of Comparative Anatomy, 141
The study of internal structure of living beings, at first merely
descriptive, becomes comparative, 141. Belon, 141. Severinus
writes the first book devoted to comparative anatomy in 1645,
143. The anatomical studies of Camper, 143. John Hunter,
144. Personal characteristics, 145. His contribution to progress,
146. Vicq d'Azyr the greatest comparative anatomist
before Cuvier, 146-148. Cuvier makes a comprehensive study
of the structure of animals, 148. His birth and early education,
149. Life at the sea shore, 150. Six years of quiet study and
contemplation lays the foundation of his scientific career, 150.
Goes to Paris, 151. His physiognomy, 152. Comprehensiveness
of his mind, 154. Founder of comparative anatomy, 155. His
domestic life, 155. Some shortcomings, 156. His break with
early friends, 156. Estimate of George Bancroft, 156. Cuvier's
successors: Milne-Edwards, 157; Lacaze-Duthiers, 157; Richard
Owen, 158; Oken, 160; J. Fr. Meckel, 162; Rathke, 163;
J. Müller, 163; Karl Gegenbaur, 164; E.D. Cope, 165. Comparative
anatomy a rich subject, 165. It is now becoming experimental,
165.
CHAPTER VIII
Bichat and the Birth of Histology, 166
Bichat one of the foremost men in biological history. He carried the
analysis of animal organization to a deeper level than Cuvier, 166.
Buckle's estimate, 166. Bichat goes to Paris, 167. Attracts attention
in Desault's classes, 167. Goes to live with Desault, 168.
His fidelity and phenomenal industry, 168. Personal appearance,
168. Begins to publish researches on tissues at the age of
thirty, 170. His untimely death at thirty-one, 170. Influence
of his writings, 170. His more notable successors: Schwann,
171; Koelliker, a striking figure in the development of biology,
171; Max Schultze, 172; Rudolph Virchow, 174; Leydig, 175;
Ramon y Cajal, 176. Modern text-books on histology, 177.
CHAPTER IX
The Rise of Physiology--Harvey. Haller. Johannes Müller, 179
Physiology had a parallel development with anatomy, 179. Physiology
of the ancients, 179. Galen, 180. Period of Harvey, 180.
His demonstration of circulation of the blood, 180. His method
of experimental investigation, 181. Period of Haller, 181. Physiology
developed as an independent science, 183. Haller's personal
characteristics, 181. His idea of vital force, 182. His book
on the Elements of Physiology a valuable work, 183. Discovery
of oxygen by Priestley in 1774, 183. Charles Bell's great discovery
on the nervous system, 183. Period of Johannes Müller, 184.
A man of unusual gifts and personal attractiveness, 185. His
personal appearance, 185. His great influence over students, 185.
His especial service was to make physiology broadly comparative,
186. His monumental Handbook of Physiology, 186. Unexampled
accuracy in observation, 186. Introduces the principles
of psychology into physiology, 186. Physiology after Müller,
188-195. Ludwig, 188. Du Bois-Reymond, 189. Claude
Bernard, 190. Two directions of growth in physiology--the
chemical and the physical, 192. Influence upon biology, 193.
Other great names in physiology, 194.
CHAPTER X
Von Baer and the Rise of Embryology, 195
Romantic nature of embryology, 195. Its importance, 195.
Rudimentary organs and their meaning, 195. The domain of embryology,
196. Five historical periods, 196. The period of
Harvey and Malpighi, 197-205. The embryological work of
these two men insufficiently recognized, 197. Harvey's pioneer
attempt critically to analyze the process of development, 198. His
teaching regarding the nature of development, 199. His treatise
on Generation, 199. The frontispiece of the edition of 1651, 201,
202. Malpighi's papers on the formation of the chick within the
egg, 202. Quality of his pictures, 202. His belief in pre-formation,
207. Malpighi's rank as embryologist, 205. The period of
Wolff, 205-214. Rise of the theory of pre-delineation, 206.
Sources of the idea that the embryo is pre-formed within the egg,
207. Malpighi's observations quoted, 207. Swammerdam's
view, 208. Leeuwenhoek and the discovery of the sperm, 208.
Bonnet's views on _emboîtement_, 208. Wolff opposes the doctrine
of pre-formation, 210. His famous Theory of Generation (1759),
210. Sketches from this treatise, 209. His views on the directing
force in development, 211. His highest grade of work, 211.
Opposition of Haller and Bonnet, 211. Restoration of Wolff's
views by Meckel, 212. Personal characteristics of Wolff, 213.
The period of Von Baer, 214-222. The greatest personality in
embryology, 215. His monumental work on the Development of
Animals a choice combination of observation and reflection, 215.
Von Baer's especial service, 217. Establishes the germ-layer
theory, 218. Consequences, 219. His influence on embryology,
220. The period from Von Baer to Balfour, 222-226. The process
of development brought into a new light by the cell-theory,
222. Rathke, Remak, Koelliker, Huxley, Kowalevsky, 223, 224.
Beginnings of the idea of germinal continuity, 225. Influence of
the doctrine of organic evolution, 226. The period of Balfour,
with an indication of present tendencies, 226-236. The great
influence of Balfour's Comparative Embryology, 226. Personality
of Balfour, 228. His tragic fate, 228. Interpretation of the
embryological record, 229. The recapitulation theory, 230.
Oskar Hertwig, 232. Wilhelm His, 232. Recent tendencies;
Experimental embryology, 232; Cell-lineage, 234; Theoretical
discussions, 235.
CHAPTER XI
The Cell-Theory--Schleiden. Schwann. Schultze, 237
Unifying power of the cell-theory, 237. Vague foreshadowings, 237.
The first pictures of cells from Robert Hooke's Micrographia, 238.
Cells as depicted by Malpighi, Grew, and Leeuwenhoek, 239, 240.
Wolff on cellular structure, 240, 241. Oken, 241. The announcement
of the cell-theory in 1838-39, 242. Schleiden and
Schwann co-founders, 243. Schleiden's work, 243. His acquaintance
with Schwann, 243. Schwann's personal appearance,
244. Influenced by Johannes Müller, 245. The cell-theory his
most important work, 246. Schleiden, his temperament and disposition,
247. Schleiden's contribution to the cell-theory, 247.
Errors in his observations and conclusions, 248. Schwann's
treatise, 248. Purpose of his researches, 249. Quotations from
his microscopical researches, 249. Schwann's part in establishing
the cell-theory more important than that of Schleiden, 250.
Modification of the cell-theory, 250. Necessity of modifications,
250. The discovery of protoplasm, and its effect on the cell-theory,
250. The cell-theory becomes harmonized with the protoplasm
doctrine of Max Schultze, 251. Further modifications of
the cell-theory, 252. Origin of cells in tissues, 252. Structure of
the nucleus, 253. Chromosomes, 254. Centrosome, 256. The
principles of heredity as related to cellular studies, 257. Verworn's
definition, 258. Vast importance of the cell-theory in
advancing biology, 258.
CHAPTER XII
Protoplasm the Physical Basis of Life, 259
Great influence of the protoplasm doctrine on biological
progress, 259. Protoplasm, 259. Its properties as discovered
by examination of the amoeba, 260. Microscopic examination of
a transparent leaf, 261. Unceasing activity of its protoplasm,
261. The wonderful energies of protoplasm, 261. Quotation from
Huxley, 262. The discovery of protoplasm and the essential steps
in recognizing the part it plays in living beings, 262-275.
Dujardin, 262. His personality, 263. Education, 263. His
contributions to science, 264. His discovery of "sarcode" in the
simplest animals, in 1835, 266. Purkinje, in 1840, uses the term
protoplasma, 267. Von Mohl, in 1846, brings the designation
protoplasm into general use, 268. Cohn, in 1850, maintains the
identity of sarcode and protoplasm, 270. Work of De Bary and
Virchow, 272. Max Schultze, in 1861, shows that there is a broad
likeness between the protoplasm of animals and plants, and
establishes the protoplasm doctrine. The university life of Schultze.
His love of music and science. Founds a famous biological periodical,
272-274. The period from 1840 to 1860 an important one for biology,
274.
CHAPTER XIII
The Work of Pasteur, Koch, and Others, 276
The bacteria discovered by Leeuwenhoek in 1687, 276. The development
of the science of bacteriology of great importance to the
human race, 276. Some general topics connected with the study
of bacteria, 277. The spontaneous origin of life, 277-293. Biogenesis
or abiogenesis, 277. Historical development of the question,
277. I. From Aristotle, 325 B.C., to Redi, 1668, 278. The
spontaneous origin of living forms universally believed in, 278.
Illustrations, 278. II. From Redi to Schwann, 278-284. Redi,
in 1668, puts the question to experimental test and overthrows
the belief in the spontaneous origin of forms visible to the unaided
eye, 279. The problem narrowed to the origin of microscopic
animalcula, 281. Needham and Buffon test the question
by the use of tightly corked vials containing boiled organic
solutions, 281. Microscopic life appears in their infusions,
282. Spallanzani, in 1775, uses hermetically sealed glass flasks
and gets opposite results, 282. The discovery of oxygen raises
another question: Does prolonged heat change its vitalizing properties?
284. Experiments of Schwann and Schulze, 1836-37,
284. The question of the spontaneous origin of microscopic life
regarded as disproved, 286. III. Pouchet reopens the question
in 1858, maintaining that he finds microscopic life produced in
sterilized and hermetically sealed solutions, 286. The question
put to rest by the brilliant researches of Pasteur and of Tyndall,
288, 289. Description of Tyndall's apparatus and his use of optically
pure air, 290. Weismann's theoretical speculations regarding
the origin of biophors, 292. The germ-theory of disease,
293-304. The idea of _contagium vivum_ revived in 1840, 293.
Work of Bassi, 294. Demonstration, in 1877, of the actual connection
between anthrax and splenic fever, 294. Veneration of
Pasteur, 294. His personal qualities, 296. Filial devotion, 297.
Steps in his intellectual development, 298. His investigation of
diseases of wine (1868), 299. Of the silkworm plague (1865-68),
299. His studies on the cause and prevention of disease constitute
his chief service to humanity, 299. Establishment of the
Pasteur Institute in Paris, 299. Recent developments, 300.
Robert Koch; his services in discovering many bacteria of disease,
300. Sir Joseph Lister and antiseptic surgery, 302. Bacteria
in their relation to agriculture, soil inoculation, etc., 303.
Knowledge of bacteria as related to the growth of general biology,
304.
CHAPTER XIV
Heredity and Germinal Continuity--Mendel. Galton. Weismann, 305
The hereditary substance and the bearers of heredity, 305. The
nature of inheritance, 305. Darwin's theory of pangenesis, 306.
The theory of pangens replaced by that of germinal continuity,
307. Exposition of the theory of germinal continuity, 308. The
law of cell-succession, 309. _Omnis cellula e cellula_, 309. The
continuity of hereditary substance, 309. Early writers, 310.
Weismann, 310. Germ-cells and body cells, 310. The hereditary
substance is the germ-plasm, 311. It embodies all the past
history of protoplasm, 311. The more precise investigation of
the material basis of inheritance, 311. The nucleus of cells, 311.
The chromosomes, 312. The fertilized ovum, the starting-point
of new organisms, 313. Behavior of the nucleus during division,
313. The mixture of parental qualities in the chromosomes, 313.
Prelocalized areas in the protoplasm of the egg, 314. The inheritance
of acquired characteristics, 314. The application of
statistical methods and experiments to the study of heredity, 314.
Mendel's important discovery of alternative inheritance, 316.
Francis Galton, 317. Carl Pearson, 318. Experiments on inheritance,
318.
CHAPTER XV
The Science of Fossil Life, 320
Extinct forms of life, 320. Strange views regarding fossils, 320.
Freaks of nature, 321. Mystical explanations, 321. Large bones
supposed to be those of giants, 322. Determination of the nature
of fossils by Steno, 322. Fossil deposits ascribed to the Flood, 323.
Mosaic deluge regarded as of universal extent, 324. The comparison
of fossil and living animals of great importance, 325.
Cuvier the founder of vertebrate palæontology, 325. Lamarck
founds invertebrate palæontology, 326. Lamarck's conception of
the meaning of fossils more scientific than Cuvier's, 327. The
arrangement of fossils in strata, 328. William Smith, 328. Summary
of the growth of the science of fossil life, 329. Fossil remains
as an index to the past history of the earth, 330. Epoch-making
work of Charles Lyell, 330. Effect of the doctrine of
organic evolution on palæontology, 332. Richard Owen's
studies on fossil animals, 332. Agassiz and the parallelism between
fossil forms of life and stages in the development of
animals, 334. Huxley's geological work, 335. Leidy, 337. Cope,
337. Marsh, 338. Carl Zittel's writings and influence, 338.
Henry F. Osborn, 339. Method of collecting fossils, 340. Fossil
remains of man, 340. Discoveries in the Fayûm district of
Africa, 341.
PART II
The Doctrine of Organic Evolution
CHAPTER XVI
What Evolution Is: The Evidence upon which it Rests, etc., 345
Great vagueness regarding the meaning of evolution, 346. Causes for
this, 346. The confusion of Darwinism with organic evolution,
347. The idea that the doctrine is losing ground, 347. Scientific
controversies on evolution relate to the factors, not to the fact, of
evolution, 347. Nature of the question: not metaphysical, not
theological, but historical, 348. The historical method applied
to the study of animal life, 349. The diversity of living forms, 349.
Are species fixed in nature? 350. Wide variation among animals,
350. Evolutionary series: The shells of Slavonia and
Steinheim, 351-353. Evolution of the horse, 354. The collection
of fossil horses at the American Museum of Natural History,
New York, 355. The genealogy of the horse traced for more
than two million years, 354. Connecting forms: the archæopteryx
and pterodactyls, 358. The embryological record and its
connection with evolution, 358. Clues to the past history of
animals, 358. Rudimentary organs, 361-363. Hereditary survivals
in the human body, 363. Remains of the scaffolding for
its building, 364. Antiquity of man, 364. Pre-human types, 365.
Virtually three links: the Java man; the Neanderthal skull; the
early neolithic man of Engis, 364-366. Evidences of man's evolution
based on palæontology, embryology, and archæology, 366.
Mental evolution, 366. Sweep of the doctrine of organic evolution,
366-367.
CHAPTER XVII
Theories of Evolution--Lamarck. Darwin, 368
The attempt to indicate the active factors of evolution is the
source of the different theories, 368. The theories of Lamarck,
Darwin, and Weismann have attracted the widest attention, 369.
Lamarck, the man, 368-374. His education, 370. Leaves priestly
studies for the army, 370. Great bravery, 371. Physical injury
makes it necessary for him to give up military life, 371. Portrait,
373. Important work in botany, 371. Pathetic poverty
and neglect, 372. Changes from botany to zoölogy at the age of
fifty years, 372. Profound influence of this change in shaping
his ideas, 374. His theory of evolution, 374-380. First public
announcement in 1800, 375. His _Philosophie Zoologique_ published
in 1809, 375. His two laws of evolution, 376. The first
law embodies the principle of use and disuse of organs, the second
that of heredity, 376. A simple exposition of his theory, 377.
His employment of the word _besoin_, 377. Lamarck's view of
heredity, 377. His belief in the inheritance of acquired characters,
377. His attempt to account for variation, 377. Time
and favorable conditions the two principal means employed by
nature, 378. Salient points in Lamarck's theory, 378. His
definition of species, 379. Neo-Lamarckism, 380. Darwin. His
theory rests on three sets of facts. The central feature of his
theory is natural selection. Variation, 380. Inheritance, 382.
Those variations will be inherited that are of advantage to the
race, 383. Illustrations of the meaning of natural selection, 383-389.
The struggle for existence and its consequences, 384. Various
aspects of natural selection, 384. It does not always operate
toward increasing the efficiency of an organ--short-winged
beetles, 385. Color of animals, 386. Mimicry, 387. Sexual
selection, 388. Inadequacy of natural selection, 389. Darwin the
first to call attention to the inadequacy of this principle, 389.
Confusion between the theories of Lamarck and Darwin, 390.
Illustrations, 391. The Origin of Species published in 1859, 391.
Other writings of Darwin, 391.
CHAPTER XVIII
Theories Continued--Weismann. De Vries, 392
Weismann's views have passed through various stages of remodeling,
392. The Evolution Theory published in 1904 is the best exposition
of his views, 392. His theory the field for much controversy.
Primarily a theory of heredity, 393. Weismann's theory
summarized, 393. Continuity of the germ-plasm the central idea
in Weismann's theory, 394. Complexity of the germ-plasm. Illustrations,
395. The origin of variations, 396. The union of
two complex germ-plasms gives rise to variations, 396. His extension
of the principle of natural selection--germinal selection,
397. The inheritance of acquired characters, 398. Weismann's
analysis of the subject the best, 398. Illustrations, 399. The
question still open to experimental observation, 399. Weismann's
personality, 400. Quotation from his autobiography, 401.
The mutation theory of De Vries, 402. An important contribution.
His application of experiments commendable, 403. The
mutation theory not a substitute for that of natural selection, 404.
Tendency toward a reconciliation of apparently conflicting views,
404. Summary of the salient features of the theories of Lamarck,
of Darwin, of Weismann, and De Vries, 405. Causes for bewilderment
in the popular mind regarding the different forms of the
evolution theory, 406.
CHAPTER XIX
The Rise of Evolutionary Thought, 407
Opinion before Lamarck, 407. Views of certain Fathers of the
Church, 408. St. Augustine, 409. St. Thomas Aquinas, 409.
The rise of the doctrine of special creation, 410. Suarez, 410.
Effect of John Milton's writings, 411. Forerunners of Lamarck:
Buffon, Erasmus Darwin, Goethe, 411. Statement of Buffon's
views on evolution, 412. Erasmus Darwin the greatest of Lamarck's
predecessors, 413. His writings, 414. Paley's Natural
Theology directed against them, 414. Goethe's connection with
evolutionary thought, 414. Causes for the neglect of Lamarck's
theoretical writings, 415. The temporary disappearance of the
doctrine of organic evolution, 415. Cuvier's opposition, 415.
The debate between Cuvier and St. Hilaire, 415. Its effect, 417.
Influence of Lyell's Principles of Geology, 418. Herbert Spencer's
analysis in 1852, 419. Darwin and Wallace, 420. Circumstances
under which their work was laid before the Linnæan
Society of London, 420. The letter of transmission signed by
Lyell and Hooker, 420-422. The personality of Darwin, 422.
Appearance, 423. His charm of manner, 423. Affectionate
consideration at home, 424. Unexampled industry and conscientiousness
in the face of ill health, 424, 426. His early
life and education, 425. Voyage of the _Beagle_, 425. The results
of his five years' voyage, 426. Life at Downs, 426.
Parallelism in the thought of Darwin and Wallace, 427.
Darwin's account of how he arrived at the conception of natural
selection, 427. Wallace's narrative, 428. The Darwin-Wallace
theory launched in 1858, 429. Darwin's book on The Origin of
Species regarded by him as merely an outline, 429. The spread
of the doctrine of organic evolution, 429. Huxley one of its great
popular exponents, 430. Haeckel, 431. After Darwin, the problem
was to explain phenomena, 433.
CHAPTER XX
Retrospect and Prospect. Present Tendencies in Biology, 434
Biological thought shows continuity of development, 434. Character
of the progress--a crusade against superstition, 434. The first
triumph of the scientific method was the overthrow of authority,
435. The three stages of progress--descriptive, comparative,
experimental, 435. The notable books of biology and their authors,
435-437. Recent tendencies in biology: higher standards, 437;
improvement in the tools of science, 438; advance in methods,
439; experimental work, 439; the growing interest in the study
of processes, 440; experiments applied to heredity and evolution,
to fertilization of the egg, and to animal behavior, 440, 441. Some
tendencies in anatomical studies, 442. Cell-lineage, 442. New
work on the nervous system, 443. The application of biological
facts to the benefit of mankind, 443. Technical biology, 443.
Soil inoculation, 444. Relation of insects to the transmission of
diseases, 444. The food of fishes, 444. The establishment and
maintenance of biological laboratories, 444. The station at
Naples, 444. Other stations, 446. The establishment and maintenance
of technical periodicals, 446. Explorations of fossil
records, 447. The reconstructive influence of biological progress,
448.
READING LIST, 449
I. General References, 449-451. II. Special References, 451-460.
Index, 461
ILLUSTRATIONS
FIG. PAGE
1. Aristotle, 384-322 B.C., 14
2. Pliny, 23-79 A.D., 16
3. Galen, 131-200, 25
4. Vesalius, 1514-1565, 29
5. Anatomical Sketch from Vesalius' _Fabrica_ (1543), 31
6. The Skeleton from Vesalius' _Fabrica_, 33
7. Initial Letters from the _Fabrica_, 34
8. Fallopius, 1523-1563, 37
9. Fabricius, Harvey's Teacher, 1537-1619, 43
10. William Harvey, 1578-1657, 44
11. Scheme of the Portal Circulation according to Vesalius
(1543), 49
12. Hooke's Microscope (1665), 55
13. Malpighi, 1628-1694, 59
14. From Malpighi's _Anatomy of the Silkworm_ (1669), 65
15. Swammerdam, 1637-1680, 69
16. From Swammerdam's _Biblia Naturæ_, 74
17. Anatomy of an Insect Dissected and Drawn by Swammerdam, 76
18. Leeuwenhoek, 1632-1723, 79
19. Leeuwenhoek's Microscope, 82
20_a_. Leeuwenhoek's Mechanism for Examining the Circulation
of the Blood, 83
20_b_. The Capillary Circulation, after Leeuwenhoek, 84
21. Plant Cells from Leeuwenhoek's _Arcana Naturæ_, 86
22. Lyonet, 1707-1789, 90
23. Larva of the Willow Moth, from Lyonet's Monograph
(1750), 92
24. Muscles of the Larva of the Willow Moth, from Lyonet's
Monograph, 93
25. Central Nervous System and Nerves of the Same Animal, 93
26. Dissection of the Head of the Larva of the Willow Moth, 94
27. The Brain and Head Nerves of the Same Animal, 95
28. Roesel von Rosenhof, 1705-1759, 97
29. Réaumur, 1683-1757, 98
30. Nervous System of the Cockchafer, from Straus-Dürckheim's
Monograph (1828), 101
31. Ehrenberg, 1795-1876, 108
32. Gesner, 1516-1565, 114
33. John Ray, 1628-1705, 116
34. Linnæus at Sixty (1707-1778), 124
35. Karl Th. von Siebold, 135
36. Rudolph Leuckart, 136
37. Severinus, 1580-1656, 142
38. Camper, 1722-1789, 144
39. John Hunter, 1728-1793, 145
40. Vicq d'Azyr, 1748-1794, 147
41. Cuvier as a Young Man, 1769-1829, 152
42. Cuvier at the Zenith of His Power, 153
43. H. Milne-Edwards, 1800-1885, 157
44. Lacaze-Duthiers, 1821-1901, 159
45. Lorenzo Oken, 1779-1851, 160
46. Richard Owen, 1804-1892, 161
47. J. Fr. Meckel, 1781-1833, 162
48. Karl Gegenbaur, 1826-1903, 164
49. Bichat, 1771-1801, 169
50. Von Koelliker, 1817-1905, 173
51. Rudolph Virchow, 1821-1903, 174
52. Franz Leydig, 1821-1908 (April), 175
53. S. Ramon y Cajal, 176
54. Albrecht Haller, 1708-1777, 182
55. Charles Bell, 1774-1842, 184
56. Johannes Müller, 1801-1858, 187
57. Ludwig, 1816-1895, 188
58. Du Bois-Reymond, 1818-1896, 189
59. Claude Bernard, 1813-1878, 191
60. Frontispiece of Harvey's _Generatione Animalium_ (1651), 201
61. Selected Sketches from Malpighi's Works, 203
62. Marcello Malpighi, 1628-1694, 204
63. Plate from Wolff's _Theoria Generationis_ (1759), 209
64. Charles Bonnet, 1720-1793, 212
65. Karl Ernst von Baer, 1792-1876, 216
66. Von Baer at about Seventy Years of Age, 217
67. Sketches from Von Baer's Embryological Treatise (1828), 221
68. A. Kowalevsky, 1840-1901, 225
69. Francis M. Balfour, 1851-1882, 227
70. Oskar Hertwig in 1890, 231
71. Wilhelm His, 1831-1904, 233
72. The Earliest Known Picture of Cells, from Hooke's _Micrographia_
(1665), 238
73. Sketch from Malpighi's Treatise on the Anatomy of Plants
(1670), 239
74. Theodor Schwann, 1810-1882, 245
75. M. Schleiden, 1804-1881, 246
76. The Egg and Early Stages in Its Development (after Gegenbaur), 253
77. An Early Stage in the Development of the Egg of a Rock
Limpet (after Conklin), 254
78. Highly Magnified Tissue-Cells from the Skin of a Salamander
(after Wilson), 255
79. Diagram of the Chief Steps in Cell-Division (after Parker), 256
80. Diagram of a Cell (modified after Wilson), 257
81. (_A_) Rotation of Protoplasm in Cells of Nitella. (_B_) Highly
Magnified Cells of a Tradescantia Plant, Showing
Circulation of Protoplasm (after Sedgwick and Wilson), 261
82. Félix Dujardin, 1801-1860, 265
83. Purkinje, 1787-1869, 267
84. Carl Nägeli, 1817-1891, 268
85. Hugo von Mohl, 1805-1872, 269
86. Ferdinand Cohn, 1828-1898, 271
87. Heinrich Anton De Bary, 1831-1888, 272
88. Max Schultze, 1825-1874, 273
89. Francesco Redi, 1626-1697, 280
90. Lazzaro Spallanzani, 1729-1799, 283
91. Apparatus of Tyndall for Experimenting on Spontaneous
Generation, 290
92. Louis Pasteur (1822-1895) and His Granddaughter, 295
93. Robert Koch, born 1843, 301
94. Sir Joseph Lister, born 1827, 302
95. Gregor Mendel, 1822-1884, 315
96. Francis Galton, born 1822, 317
97. Charles Lyell, 1797-1875, 331
98. Professor Owen and the Extinct Fossil Bird of New Zealand, 333
99. Louis Agassiz, 1807-1873, 334
100. E.D. Cope, 1840-1897, 336
101. O.C. Marsh, 1831-1899, 337
102. Karl von Zittel, 1839-1904, 339
103. Transmutations of Paludina (after Neumayer), 352
104. Planorbis Shells from Steinheim (after Hyatt), 353
105. Bones of the Foreleg of a Horse, 356
106. Bones of Fossil Ancestors of the Horse, 357
107. Representation of the Ancestor of the Horse Drawn by
Charles R. Knight under the Direction of Professor
Osborn. Permission of the American Museum of Natural
History, 359
108. Fossil Remains of a Primitive Bird (Archæopteryx), 360
109. Gill-clefts of a Shark Compared with those of the Embryonic
Chick and Rabbit, 361
110. Jaws of an Embryonic Whale, showing Rudimentary Teeth, 362
111. Profile Reconstructions of the Skulls of Living and of
Fossil Men, 365
112. Lamarck, 1744-1829, 373
113. Charles Darwin, 1809-1882, 381
114. August Weismann, born 1834, 400
115. Hugo de Vries, 403
116. Buffon, 1707-1788, 412
117. Erasmus Darwin, 1731-1802, 413
118. Geoffroy Saint Hilaire, 1772-1844, 416
119. Charles Darwin, 1809-1882, 423
120. Alfred Russel Wallace, born 1823, 428
121. Thomas Henry Huxley, 1825-1895, 430
122. Ernst Haeckel, born 1834, 432
123. The Biological Station at Naples, 445
PART I
THE SOURCES OF BIOLOGICAL
IDEAS EXCEPT THOSE OF
ORGANIC EVOLUTION
CHAPTER I
AN OUTLINE OF THE RISE OF BIOLOGY AND OF THE EPOCHS IN ITS HISTORY
"Truth is the Daughter of Time."
The nineteenth century will be for all time memorable for the great
extension of the knowledge of organic nature. It was then that the
results of the earlier efforts of mankind to interpret the mysteries
of nature began to be fruitful; observers of organic nature began
to see more deeply into the province of life, and, above all, began
to see how to direct their future studies. It was in that century
that the use of the microscope made known the similarity in cellular
construction of all organized beings; that the substance, protoplasm,
began to be recognized as the physical basis of life and the seat of
all vital activities; then, most contagious diseases were traced to
microscopic organisms, and as a consequence, medicine and surgery were
reformed; then the belief in the spontaneous origin of life under
present conditions was given up; and it was in that century that the
doctrine of organic evolution gained general acceptance. These and
other advances less generally known created an atmosphere in which
biology--the great life-science--grew rapidly.
In the same period also the remains of ancient life, long since
extinct, and for countless ages embedded in the rocks, were brought to
light, and their investigation assisted materially in understanding the
living forms and in tracing their genealogy.
As a result of these advances, animal organization began to have a
different meaning to the more discerning naturalists, those whose
discoveries began to influence the trend of thought, and finally, the
idea which had been so often previously expressed became a settled
conviction, that all the higher forms of life are derived from simpler
ones by a gradual process of modification.
Besides great progress in biology, the nineteenth century was
remarkable for similar advances in physics and chemistry. Although
these subjects purport to deal with inorganic or lifeless nature, they
touch biology in an intimate way. The vital processes which take place
in all animals and plants have been shown to be physico-chemical,
and, as a consequence, one must go to both physics and chemistry in
order to understand them. The study of organic chemistry in late
years has greatly influenced biology; not only have living products
been analyzed, but some of them have already been constructed in the
chemical laboratory. The formation of living matter through chemical
means is still far from the thought of most chemists, but very complex
organic compounds, which were formerly known only as the result of the
action of life, have been produced, and the possibilities of further
advances in that direction are very alluring. It thus appears that
the discoveries in various fields have worked together for a better
comprehension of nature.
The Domain of Biology.--The history of the transformation of opinion in
reference to living organisms is an interesting part of the story of
intellectual development. The central subject that embraces it all is
biology. This is one of the fundamental sciences, since it embraces all
questions relating to life in its different phases and manifestations.
Everything pertaining to the structure, the development, and the
evolution of living organisms, as well as to their physiology,
belongs to biology. It is now of commanding importance in the world
of science, and it is coming more and more to be recognized that it
occupies a field of compelling interest not only for medical men and
scholars, but for all intelligent people. The discoveries and conquests
of biology have wrought such a revolution in thought that they should
be known to all persons of liberal culture. In addition to making
acquaintance with the discoveries, one ought to learn something about
the history of biology; for it is essential to know how it took its
rise, in order to understand its present position and the nature of its
influence upon expanding ideas regarding the world in which we live.
In its modern sense, biology did not arise until about 1860, when the
nature of protoplasm was first clearly pointed out by Max Schultze,
but the currents that united to form it had long been flowing, and
we can never understand the subject without going back to its iatric
condition, when what is now biology was in the germ and united with
medicine. Its separation from medicine, and its rise as an independent
subject, was owing to the steady growth of that zest for exploration
into unknown fields which began with the new birth of science in the
sixteenth century, and has continued in fuller measure to the present.
It was the outcome of applying observation and experiment to the
winning of new truths.
Difficulties.--But biology is so comprehensive a field, and involves
so many details, that it is fair to inquire: can its progress be made
clear to the reader who is unacquainted with it as a laboratory study?
The matter will be simplified by two general observations--first,
that the growth of biology is owing to concurrent progress in three
fields of research, concerned, respectively, with the structure or
architecture of living beings, their development, and their physiology.
We recognize also a parallel advance in the systematic classification
of animals and plants, and we note, furthermore, that the idea of
evolution permeates the whole. It will be necessary to consider the
advances in these fields separately, and to indicate the union of the
results into the main channel of progress. Secondly, in attempting
to trace the growth of ideas in this department of learning one
sees that there has been a continuity of development. The growth of
these notions has not been that of a chaotic assemblage of ideas,
but a well-connected story in which the new is built upon the old in
orderly succession. The old ideas have not been completely superseded
by the new, but they have been molded into new forms to keep pace
with the advance of investigation. In its early phases, the growth
of biology was slow and discursive, but from the time of Linnæus to
Darwin, although the details were greatly multiplied, there has been a
relatively simple and orderly progress.
Facts and Ideas.--There are many books about biology, with directions
for laboratory observation and experiment, and also many of the leading
facts of the science have been given to the public, but an account
of the growth of the ideas, which are interpretations of the facts,
has been rarely attempted. From the books referred to, it is almost
impossible to get an idea of biology as a unit; this even the students
in our universities acquire only through a coherent presentation of the
subject in the classroom, on the basis of their work in the laboratory.
The critical training in the laboratory is most important, but, after
all, it is only a part, although an essential part, of a knowledge of
biology. In general, too little attention is paid to interpretations
and the drill is confined to a few facts. Now, the facts are related to
the ideas of the science as statistics to history--meaningless without
interpretation. In the rise of biology the facts have accumulated
constantly, through observation and experiment, but the general truths
have emerged slowly and periodically, whenever there has been granted
to some mind an insight into the meaning of the facts. The detached
facts are sometimes tedious, the interpretations always interesting.
The growth of the knowledge of organic nature is a long story, full
of human interest. Nature has been always the same, but the capacity
of man as its interpreter has varied. He has had to pass through
other forms of intellectual activity, and gradually to conquer other
phases of natural phenomena, before entering upon that most difficult
task of investigating the manifestations of life. It will be readily
understood, therefore, that biology was delayed in its development
until after considerable progress had been made in other sciences.
It is an old saying that "Truth is the daughter of Time," and no
better illustration of it can be given than the long upward struggle
to establish even the elemental truths of nature. It took centuries to
arrive at the conception of the uniformity of nature, and to reach any
of those generalizations which are vaguely spoken of as the laws of
nature.
The Men of Science.--In the progress of science there is an army of
observers and experimenters each contributing his share, but the rank
and file supply mainly isolated facts, while the ideas take birth in
the minds of a few gifted leaders, either endowed with unusual insight,
or so favored by circumstances that they reach general conclusions of
importance. These advance-guards of intellectual conquest we designate
as founders. What were they like in appearance? Under what conditions
did they work, and what was their chief aim? These are interesting
questions which will receive attention as our narrative proceeds.
A study of the lives of the founders shows that the scientific mood is
pre-eminently one of sincerity. The men who have added to the growth
of science were animated by an unselfish devotion to truth, and their
lasting influence has been in large measure a reflection of their
individual characters. Only those have produced permanent results
who have interrogated nature in the spirit of devotion to truth and
waited patiently for her replies. The work founded on selfish motives
and vanity has sooner or later fallen by the wayside. We can recognize
now that the work of scientific investigation, subjected to so much
hostile criticism as it appeared from time to time, was undertaken in
a reverent spirit, and was not iconoclastic, but remodelling in its
influence. Some of the glories of our race are exhibited in the lives
of the pioneers in scientific progress, in their struggles to establish
some great truth and to maintain intellectual integrity.
The names of some of the men of biology, such as Harvey, Linnæus,
Cuvier, Darwin, Huxley, and Pasteur, are widely known because their
work came before the people, but others equally deserving of fame on
account of their contributions to scientific progress will require an
introduction to most of our readers.
In recounting the story of the rise of biology, we shall have occasion
to make the acquaintance of this goodly company. Before beginning the
narrative in detail, however, we shall look summarily at some general
features of scientific progress and at the epochs of biology.
The Conditions under which Science Developed
In a brief sketch of biology there is relatively little in the ancient
world that requires notice except the work of Aristotle and Galen; but
with the advent of Vesalius, in 1543, our interest begins to freshen,
and, thereafter, through lean times and fat times there is always
something to command our attention.
The early conditions must be dealt with in order to appreciate what
followed. We are to recollect that in the ancient world there was no
science of biology as such; nevertheless, the germ of it was contained
in the medicine and the natural history of those times.
There is one matter upon which we should be clear: in the time of
Aristotle nature was studied by observation and experiment. This is
the foundation of all scientific advancement. Had conditions remained
unchanged, there is reason to believe that science would have developed
steadily on the basis of the Greek foundation, but circumstances, to
be spoken of later, arose which led not only to the complete arrest of
inquiry, but also, the mind of man being turned away from nature, to
the decay of science.
Aristotle the Founder of Natural History.--The Greeks represented
the fullest measure of culture in the ancient world, and, naturally,
we find among them the best-developed science. All the knowledge of
natural phenomena centered in Aristotle (384-322 B.C.), and for twenty
centuries he represented the highest level which that kind of knowledge
had attained.
It is uncertain how long it took the ancient observers to lift science
to the level which it had at the beginning of Aristotle's period, but
it is obvious that he must have had a long line of predecessors, who
had accumulated facts of observation and had molded them into a system
before he perfected and developed that system. We are reminded that all
things are relative when we find Aristotle referring to the ancients;
and well he might, for we have indubitable evidence that much of the
scientific work of antiquity has been lost. One of the most striking
discoveries pointing in that direction is the now famous papyrus which
was found by Georg Ebers in Egypt about 1860. The recent translation
of this ancient document shows that it was a treatise on medicine,
dating from the fifteenth century B.C. At this time the science of
medicine had attained an astonishingly high grade of development among
that people. And since it is safe to assume that the formulation of a
system of medicine in the early days of mankind required centuries of
observation and practice, it becomes apparent that the manuscript in
question was no vague, first attempt at reducing medicine to a system.
It is built upon much scientific knowledge, and must have been preceded
by writings both on medicine and on its allied sciences.
It is not necessary that we should attempt to picture the crude
beginnings of the observation of animated nature and the dawning of
ideas relative to animals and plants; it is suitable to our purpose to
commence with Aristotle, and to designate him, in a relative sense, as
the founder of natural history.
That he was altogether dissatisfied with the state of knowledge in his
time and that he had high ideals of the dignity of science is evidenced
in his writings. Although he refers to the views of the ancients, he
regarded himself in a sense as a pioneer. "I found no basis prepared,"
he says, "no models to copy.... Mine is the first step, and therefore
a small one, though worked out with much thought and hard labor. It
must be looked at as a first step and judged with indulgence." (From
Osborn's _From the Greeks to Darwin_.)
There is general agreement that Aristotle was a man of vast intellect
and that he was one of the greatest philosophers of the ancient world.
He has had his detractors as well as his partisan adherents. Perhaps
the just estimate of his attainments and his position in the history
of science is between the enthusiastic appreciation of Cuvier and the
critical estimate of Lewes.
This great man was born in Stagira in the year 384 B.C., and lived
until 322 B.C. He is to be remembered as the most distinguished pupil
of Plato, and as the instructor of Alexander the Great. Like other
scholars of his time, he covered a wide range of subjects; we have
mention, indeed, of about three hundred works of his composition, many
of which are lost. He wrote on philosophy, metaphysics, psychology,
politics, rhetoric, etc., but it was in the domain of natural history
that he attained absolute pre-eminence.
His Position in the Development of Science.--It is manifestly unjust
to measure Aristotle by present standards; we must keep always in mind
that he was a pioneer, and that he lived in an early day of science,
when errors and crudities were to be expected. His greatest claim to
eminence in the history of science is that he conceived the things of
importance and that he adopted the right method in trying to advance
the knowledge of the natural universe. In his program of studies he
says: "First we must understand the phenomena of animals; then assign
their causes; and, finally, speak of their generation." His position
in natural history is frequently misunderstood. One of the most recent
writers on the history of science, Henry Smith Williams, pictures
him entirely as a great classifier, and as the founder of systematic
zoölogy. While it is true that he was the founder of systematic
zoölogy, as such he did not do his greatest service to natural history,
nor does the disposition to classify represent his dominant activity.
In all his work classification is made incidental and subservient to
more important considerations. His observations upon structure and
development, and his anticipation of the idea of organic evolution, are
the ones upon which his great fame rests. He is not to be remembered as
a man of the type of Linnæus; rather is he the forerunner of those men
who looked deeper than Linnæus into the structure and development of
animal life--the morphologists.
Particular mention of his classification of animals will be found
in the chapter on Linnæus, while in what follows in this chapter
attention will be confined to his observation of their structure and
development and to the general influence of his work.
His great strength was in a philosophical treatment of the structure
and development of animals. Professor Osborn in his interesting book,
_From the Greeks to Darwin_, shows that Aristotle had thought out the
essential features of evolution as a process in nature. He believed in
a complete gradation from the lowest organisms to the highest, and that
man is the highest point of one long and continuous ascent.
His Extensive Knowledge of Animals.--He made extensive studies of
life histories. He knew that drone bees develop without previous
fertilization of the eggs (by parthenogenesis); that in the squid
the yolk sac of the embryo is carried in front of the mouth; that
some sharks develop within the egg-tube of the mother, and in some
species have a rudimentary blood-connection resembling the placenta of
mammals. He had followed day by day the changes in the chick within
the hen's egg, and observed the development of many other animals.
In embryology also, he anticipated Harvey in appreciating the true
nature of development as a process of gradual building, and not as the
mere expansion of a previously formed germ. This doctrine, which is
known under the name of epigenesis, was, as we shall see later, hotly
contested in the eighteenth century, and has a modified application at
the present time.
In reference to the structure of animals he had described the tissues,
and in a rude way analyzed the organs into their component parts. It is
known, furthermore, that he prepared plates of anatomical figures, but,
unfortunately, these have been lost.
In estimating the contributions of ancient writers to science, it must
be remembered that we have but fragments of their works to examine. It
is, moreover, doubtful whether the scientific writings ascribed to
Aristotle were all from his hand. The work is so uneven that Huxley has
suggested that, since the ancient philosophers taught _viva voce_, what
we have of his zoölogical writings may possibly be the notes of some of
his students. While this is not known to be the case, that hypothesis
enables us to understand the intimate mixture of profound observation
with trivial matter and obvious errors that occur in the writings
ascribed to him.
Hertwig says: "It is a matter for great regret that there have been
preserved only parts of his three most important zoölogical works,
'_Historia animalium_,' '_De partibus_,' and '_De generatione_,' works
in which zoölogy is founded as a universal science, since anatomy and
embryology, physiology and classification, find equal consideration."
Some Errors.--Dissections were little practised in his day, and it must
be admitted that his observations embrace many errors. He supposed
the brain to be bloodless, the arteries to carry air, etc., but he
has been cleared by Huxley of the mistake so often attributed to him
of supposing the heart of mammals to have only three chambers. It is
altogether probable that he is credited with a larger number of errors
than is justified by the facts.
He must have had unusual gifts in the exposition of these technical
subjects; indeed, he made his researches appear so important to his
royal patron, Alexander, that he was aided in the preparation of
his great Natural History by a grant of 800 talents (equivalent to
$200,000) and by numerous assistants and collectors. Thus in ancient
times was anticipated the question that is being agitated to-day--that
of the support and the endowment of research.
Personal Appearance.--Some idea of his looks may be gained from Fig.
1. This is a copy of a bas-relief found in the collection of Fulvius
Ursinus (d. 1600), and was originally published by J. Faber. Its
authenticity as a portrait is attested (1811) by Visconti, who says
that it has a perfect resemblance to the head of a small bust upon the
base of which the name of Aristotle is engraved. Portrait busts and
statues of Aristotle were common in ancient times. The picture of him
most familiar to general readers is the copy of the head and shoulders
of an ancient statue representing him with a draping over the left
shoulder. This is an attractive portrait, showing a face of strong
intellectuality. Its authenticity, however, is not as well established
as that of the picture shown here. Other pictures, believed to be those
of Aristotle, represent him later in life with receding hair, and one
exists in which his baldness is very extensive. He was described as
short in stature, with spindling legs and small, penetrating eyes, and
to have been, in his younger days, vain and showy in his dress.
He was early left an orphan with a considerable fortune; and there
are stories of early excesses after coming into his property. These
charges, however, lack trustworthy support, and are usually regarded
as due mainly to that undermining gossip which follows one holding
prominent place and enviable recognition. His habits seem to have
been those of a diligent student with a zest in his work; he was an
omnivorous reader, and Plato called him the mind of his school. His
large private library and his manner of living bespeak the conserving
of his property, rather than its waste in selfish indulgences.
[Illustration: Fig. 1.--Aristotle, 384-322 B.C.]
His Influence.--The influence of Aristotle was in the right direction.
He made a direct appeal to nature for his facts, and founded his
Natural History only on observation of the structure, physiology, and
development of animals. Unfortunately, the same cannot be said of his
successors.
Galen, who is mentioned above in connection with Aristotle, was a
medical writer and the greatest anatomist of antiquity. On account
of the relation of his work to the growth of anatomy, however, the
consideration of it is reserved for the chapter on Vesalius.
Soon after the period of Aristotle the center of scientific
investigation was transferred to Alexandria, where Ptolemy had erected
a great museum and founded a large public library. Here mathematics and
geography flourished, but natural history was little cultivated.
In order to find the next famous naturalist of antiquity, it is
necessary to look to Rome. Rome, although great in political power,
never became a true culture center, characterized by originality. All
that remains of their thought shows us that the Roman people were not
creative. In the capital of the empire, the center of its life, there
arose no great scientific investigator.
[Illustration: Fig. 2.--Pliny, 23-79 A.D.]
Pliny.--The situation is represented by Pliny the Elder (23-79
A.D.), Roman general and littérateur (Fig. 2). His works on natural
history, filling thirty-seven volumes, have been preserved with
greater completeness than those of other ancient writers. Their
overwhelming bulk seems to have produced an impression upon those who,
in the nineteenth century, heralded him as the greatest naturalist
of antiquity. But an examination of his writings shows that he did
nothing to deepen or broaden the knowledge of nature, and his Natural
History marks a distinct retrograde movement. He was, at best, merely
a compiler--"a collector of anecdotes"--who, forsaking observation,
indiscriminately mixed fable, fact, and fancy taken from the writings
of others. He emphasized the feature of classification which Aristotle
had held in proper subordination, and he replaced the classification
of Aristotle, founded on plan of organization, by a highly artificial
one, founded on the incidental circumstance of the abodes of
animals--either in air, water, or on the earth.
The Arrest of Inquiry and its Effects.--Thus, natural history,
transferred from a Greek to a Roman center, was already on the decline
in the time of Pliny; but it was destined to sink still lower. It
is an old, oft-repeated story how, with the overthrow of ancient
civilization, the torch of learning was nearly extinguished. Not only
was there a complete political revolution; there was also a complete
change in the mental interests of mankind. The situation is so complex
that it is difficult to state it with clearness. So far as science is
concerned, its extinction was due to a turning away from the external
world, and a complete arrest of inquiry into the phenomena of nature.
This was an important part of that somber change which came over all
mental life.
One of the causes that played a considerable part in the cessation of
scientific investigation was the rise of the Christian church and the
dominance of the priesthood in all intellectual as well as in spiritual
life. The world-shunning spirit, so scrupulously cultivated by the
early Christians, prompted a spirit which was hostile to observation.
The behest to shun the world was acted upon too literally. The eyes
were closed to nature and the mind was directed toward spiritual
matters, which truly seemed of higher importance. Presently, the
observation of nature came to be looked upon as proceeding from a
prying and impious curiosity.
Books were now scarcer than during the classical period; the schools
of philosophy were reduced, and the dissemination of learning
ceased. The priests who had access to the books assumed direction of
intellectual life. But they were largely employed with the analysis
of the supernatural, without the wholesome check of observation and
experiment; mystical explanations were invented for natural phenomena,
while metaphysical speculation became the dominant form of mental
activity.
Authority Declared the Source of Knowledge.--In this atmosphere
controversies over trivial points were engendered, and the ancient
writings were quoted as sustaining one side or the other. All this led
to the referring of questions as to their truth or error to authority
as the source of knowledge, and resulted in a complete eclipse of
reason. Amusing illustrations of the situation are abundant; as when,
in the Middle Ages, the question of the number of teeth in the horse
was debated with great heat in many contentious writings. Apparently
none of the contestants thought of the simple expedient of counting
them, but tried only to sustain their position by reference to
authority. Again, one who noticed spots on the sun became convinced of
the error of his eyes because Aristotle had somewhere written "The face
of the sun is immaculate."
This was a barren period not only for science, but also for
ecclesiastical advance. Notwithstanding the fact that for more than
a thousand years the only new works were written by professional
theologians, there was no substantial advance in their field, and we
cannot escape the reflection that the reciprocal action of free inquiry
is essential to the growth of theology as of other departments of
learning.
In the period from the downfall of Rome to the revival of learning, one
eminent theologian, St. Augustine, stands in relief for the openness
of his mind to new truth and for his expressions upon the relation of
revelation in the Scriptures to the observation of nature. His position
will be more clearly indicated in the chapter dealing with the rise of
evolutionary thought.
Perhaps it has been the disposition of historians to paint the
Middle Ages in too dark colors in order to provide a background on
which fitly to portray the subsequent awakening. It was a remolding
period through which it was necessary to pass after the overthrow
of ancient civilization and the mixture of the less advanced people
of the North with those of the South. The opportunities for advance
were greatly circumscribed; the scarcity of books and the lack
of facilities for travel prevented any general dissemination of
learning, while the irresponsible method of the time, of appealing
to authority on all questions, threw a barrier across the stream of
progress. Intellectuality was not, however, entirely crushed during
the prevalence of these conditions. The medieval philosophers were
masters of the metaphysical method of argument, and their mentality was
by no means dull. While some branches of learning might make a little
advance, the study of nature suffered the most, for the knowledge
of natural phenomena necessitates a mind turned outward in direct
observation of the phenomena of the natural and physical universe.
Renewal of Observation.--It was an epoch of great importance,
therefore, when men began again to observe, and to attempt, even in
an unskilful way, hampered by intellectual inheritance and habit, to
unravel the mysteries of nature and to trace the relation between
causes and effects in the universe. This new movement was a revolt of
the intellect against existing conditions. In it were locked up all the
benefits that have accrued from the development of modern science. Just
as the decline had been due to many causes, so also the general revival
was complex. The invention of printing, the voyages of mariners, the
rise of universities, and the circulation of ideas consequent upon
the Crusades, all helped to disseminate the intellectual ferment.
These generic influences aided in molding the environment, but, just
as the pause in science had been due to the turning away from nature
and to new mental interests, so the revival was a return to nature and
to the method of science. The pioneers had to be men of determined
independence; they labored against self-interest as well as opposition
from the church and the priesthood, and they withstood the terrors of
the Inquisition and the loss of recognition and support.
In this uncongenial atmosphere men like Galileo, Descartes, and
Vesalius established the new movement and overthrew the reign of
authority. With the coming of Vesalius the new era of biological
progress was opened, but its growth was a slow one; a growth of which
we are now to be concerned in tracing the main features.
The Epochs in Biological History
It will be helpful to outline the great epochs of biological progress
before taking them up for fuller consideration. The foundation of
progress was the renewal of observation in which, as already stated,
all modern science was locked up.
It was an epoch in biological history when Vesalius overthrew the
authority of Galen, and studied at first hand the organization of the
human body.
It was an epoch when William Harvey, by adding experiment to
observation, demonstrated the circulation of the blood and created a
new physiology. The two coördinate branches of biology were thus early
outlined.
The introduction of the microscope, mainly through the labors of
Grew, Hooke, Malpighi, and Leeuwenhoek, opened a new world to the
investigator, and the work of these men marks an epoch in the progress
of independent inquiry.
Linnæus, by introducing short descriptions and uniform names for
animals and plants, greatly advanced the subject of natural history.
Cuvier, by founding the school of comparative anatomy, so furthered the
knowledge of the organization of animals that he created an epoch.
Bichat, his great contemporary, created another by laying the
foundation of our knowledge of the structure of animal tissues.
Von Baer, by his studies of the development of animal life, supplied
what was lacking in the work of Cuvier and Bichat and originated modern
embryology.
Haller, in the eighteenth, and Johannes Müller in the nineteenth
century, so added to the ground work of Harvey that physiology was made
an independent subject and was established on modern lines.
With Buffon, Erasmus Darwin,, and Lamarck began an epoch in
evolutionary thought which had its culminating point in the work of
Charles Darwin.
After Cuvier and Bichat came the establishing of the cell-theory, which
created an epoch and influenced all further progress.
Finally, through the discovery of protoplasm and the recognition that
it is the seat of all vital activity, arrived the epoch which brought
us to the threshold of the biology of the present day.
Step by step naturalists have been led from the obvious and superficial
facts about living organisms to the deep-lying basis of all vital
manifestations.
CHAPTER II
VESALIUS AND THE OVERTHROW OF AUTHORITY IN SCIENCE
Vesalius, although an anatomist, is to be recognized in a broad
sense as one of the founders of biology. When one is attempting to
investigate animal and plant life, not only must he become acquainted
with the external appearance of living organisms, but also must
acquire early a knowledge of their structure, without which other
facts relating to their lives can not be disclosed. Anatomy, which
is the science of the structure of organized beings, is therefore so
fundamental that we find ourselves involved in tracing the history of
its rise as one part of the story of biology. But it is not enough
to know how animals and plants are constructed; we must also know
something about the purpose of the structures and of the life that
courses through them, and, accordingly, after considering the rise of
anatomy, we must take a similar view of its counterpart, physiology.
The great importance of Vesalius in the history of science lies in
the fact that he overthrew adherence to authority as the method of
ascertaining truth, and substituted therefor observation and reason.
Several of his forerunners had tried to accomplish the same end, but
they had failed. He was indebted to them as every man is indebted
to his forebears, but at the same time we can not fail to see that
Vesalius was worthy of the victory. He was more resolute and forceful
than any of his predecessors. He was one of those rare spirits who see
new truth with clearness, and have the bravery to force their thoughts
on an unsympathetic public.
The Beginning of Anatomy.--In order to appreciate his service it is
necessary to give a brief account of his predecessors, and of the
condition of anatomy in his time. Remembering that anatomy embraces
a knowledge of the architecture of all animals and plants, we can,
nevertheless, see why in early times its should have had more narrow
boundaries. The medical men were the first to take an interest in the
structure of the human body, because a knowledge of it is necessary for
medicine and surgery. It thus happens that the earliest observations in
anatomy were directed toward making known the structure of the human
body and that of animals somewhat closely related to man in point of
structure. Anatomical studies, therefore, began with the more complex
animals instead of the simpler ones, and, later, when comparative
anatomy began to be studied, this led to many misunderstandings; since
the structure of man became the type to which all others were referred,
while, on account of his derivation, his structure presents the
greatest modification of the vertebrate type.
It was so difficult in the early days to get an opportunity to study
the human body that the pioneer anatomists were obliged to gain their
knowledge by dissections of animals, as the dog, and occasionally the
monkey. In this way Aristotle and his forerunners learned much about
anatomy. About 300 B.C., the dissection of the human body was legalized
in the Alexandrian school, the bodies of condemned criminals being
devoted to that purpose. But this did not become general even for
medical practitioners, and anatomy continued to be studied mainly from
brute animals.
Galen.--The anatomist of antiquity who outshines all others was Galen
(Claudius Galenus, 130-200 A.D.), who lived some time in Pergamos, and
for five years in Rome, during the second century of the Christian
era. He was a man of much talent, both as an observer and as a writer.
His descriptions were clear and forceful, and for twelve centuries
his works exerted the greatest influence of those of all scientific
writers. In his writings was gathered all the anatomical knowledge of
his predecessors, to which he had added observations of his own. He was
a man of originality, but not having the human body for dissection, he
erred in expounding its structure "on the faith of observations made
on lower animals." He used the right method in arriving at his facts.
Huxley says: "No one can read Galen's works without being impressed
with the marvelous extent and diversity of his knowledge, and by his
clear grasp of those experimental methods by which alone physiology can
be advanced."
Anatomy in the Middle Ages.--But now we shall see how the arrest
of inquiry already spoken of operated in the field of anatomy. The
condition of anatomy in the Middle Ages was the condition of all
science in the same period. From its practical importance anatomy had
to be taught to medical men, while physics and chemistry, biology
and comparative anatomy remained in an undeveloped state. The way in
which this science was taught is a feature which characterizes the
intellectual life of the Middle Ages. Instead of having anatomy taught
by observations, the writings of Galen were expounded from the desk,
frequently without demonstrations of any kind. Thus his work came to
be set up as the one unfailing authority on anatomical knowledge.
This was in accord with the dominant ecclesiastical influence of the
time. Reference to authority was the method of the theologians, and
by analogy it became the method of all learning. As the Scriptures
were accepted as the unfailing guide to spiritual truth, so Galen
and other ancient writers were made the guides to scientific truth
and thought. The baneful effects of this in stifling inquiry and in
reducing knowledge to parrot-like repetition of ancient formulas are
so obvious that they need not be especially dwelt upon.
[Illustration: Fig. 3.--Galen, 131-200.
From _Acta Medicorum Berolinensium_, 1715.]
Predecessors of Vesalius.--Italy gave birth to the first anatomists who
led a revolt against this slavery to authority in scientific matters.
Of the eminent anatomists who preceded Vesalius it will be necessary to
mention only three. Mundinus, or Mondino, professor at the University
of Bologna, who, in the early part of the fourteenth century, dissected
three bodies, published in 1315 a work founded upon human dissection.
He was a man of originality whose work created a sensation in the
medical world, but did not supersede Galen's. His influence, although
exerted in the right direction, was not successful in establishing
observation as the method of teaching anatomy. His book, however, was
sometimes used as an introduction to Galen's writings or in conjunction
with them.
The next man who requires notice is Berengarius of Carpi, who was
a professor in the University of Bologna in the early part of the
sixteenth century. He is said to have dissected not less than one
hundred human bodies; and although his opportunities for practical
study were greater than those of Mondino, his attempts to place the
science of anatomy upon a higher level were also unsuccessful.
We pass now from Italy to France, where Sylvius (1478-1555), one of
the teachers of Vesalius, made his mark. His name is preserved to-day
in the _fissure of Sylvius_ in the brain, but he was not an original
investigator, and he succeeded only in "making a reputation to which
his researches do not entitle him." He was a selfish, avaricious man
whose adoption of anatomy was not due to scientific interest, but to
a love of gain. At the age of fifty he forsook the teaching of the
classics for the money to be made by teaching anatomy. He was a blind
admirer of Galen, and read his works to medical students without
dissections, except that from time to time dogs were brought into the
amphitheater and their structure exposed by unskilled barbers.
Vesalius.--Vesalius now came upon the scene; and through his efforts,
before he was thirty years of age, the idol of authority had been
shattered, and, mainly through his persistence, the method of so
great moment to future ages had been established. He was well fitted
to do battle against tradition--strong in body, in mind, and in
purpose, gifted and forceful; and, furthermore, his work was marked by
concentration and by the high moral quality of fidelity to truth.
Vesalius was born in Brussels on the last day of the year 1514, of
an ancestry of physicians and learned men, from whom he inherited
his leaning toward scientific pursuits. Early in life he exhibited
a passion for anatomy; he dissected birds, rabbits, dogs, and other
animals. Although having a strong bent in this direction, he was not a
man of single talent. He was schooled in all the learning of his time,
and his earliest publication was a translation from the Greek of the
ninth book of _Rhazes_. After his early training at Brussels and at the
University of Louvain, in 1533, at the age of 18, he went to Paris to
study medicine, where, in anatomy, he came under Sylvius and Günther.
His Force and Independence.--His impetuous nature was shown in the
amphitheatre of Sylvius, where, at the third lecture, he pushed
aside the clumsy surgeon barbers, and himself exposed the parts as
they should be. He could not be satisfied with the exposition of the
printed page; he must see with his own eyes, must grasp through his own
experience the facts of anatomical structure. This demand of his nature
shows not only how impatient he was with sham, but also how much more
he was in touch with reality than were the men of his time.
After three years at the French capital, owing to wars in Belgium,
he went back to Louvain without obtaining his medical degree. After a
short experience as surgeon on the field of battle, he went to Padua,
whither he was attracted by reports of the opportunities for practical
dissection that he so much desired to undertake. There his talents were
recognized, and just after receiving his degree of Doctor of Medicine
in 1537, he was given a post in surgery, with the care of anatomy, in
the university.
His Reform of the Teaching of Anatomy.--The sympathetic and graphic
description of this period of his career by Sir Michael Foster is so
good that I can not refrain from quoting it: "He at once began to teach
anatomy in his own new way. Not to unskilled, ignorant barbers would
he entrust the task of laying bare before the students the secrets of
the human frame; his own hand, and his own hand alone, was cunning
enough to track out the pattern of the structures which day by day
were becoming more clear to him. Following venerated customs, he began
his academic labors by 'reading' Galen, as others had done before him,
using his dissections to illustrate what Galen had said. But, time
after time, the body on the table said something different from that
which Galen had written.
"He tried to do what others had done before him--he tried to believe
Galen rather than his own eyes, but his eyes were too strong for him;
and in the end he cast Galen and his writings to the winds, and taught
only what he himself had seen and what he could make his students see,
too. Thus he brought into anatomy the new spirit of the time, and the
men of the time, the young men of the time, answered the new voice.
Students flocked to his lectures; his hearers amounted, it is said, to
some five hundred, and an enlightened senate recognized his worth by
repeatedly raising his emoluments.
[Illustration: Fig. 4.--Vesalius, 1514-1564.]
"Five years he thus spent in untiring labors at Padua. Five years
he wrought, not weaving a web of fancied thought, but patiently
disentangling the pattern of the texture of the human body, trusting to
the words of no master, admitting nothing but that which he himself had
seen; and at the end of the five years, in 1542, while he was as yet
not twenty-eight years of age, he was able to write the dedication to
Charles V of a folio work entitled the 'Structure of the Human Body,'
adorned with many plates and woodcuts which appeared at Basel in the
following year, 1543."
His Physiognomy.--This classic with the Latin title, _De Humani
Corporis Fabrica_, requires some special notice; but first let us
have a portrait of Vesalius, the master. Fig. 4 shows a reproduction
of the portrait with which his work is provided. He is represented in
academic costume, probably that which he wore at lectures, in the act
of demonstrating the muscles of the arm. The picture is reduced, and in
the reduction loses something of the force of the original. We see a
strong, independent, self-willed countenance; what his features lack in
refinement they make up in force; not an artistic or poetic face, but
the face of the man of action with scholarly training.
His Great Book.--The book of Vesalius laid the foundation of modern
biological science. It is more than a landmark in the progress
of science--it created an epoch. It is not only interesting
historically, but on account of the highly artistic plates with
which it is illustrated it is interesting to examine by one not an
anatomist. For executing the plates Vesalius secured the service
of a fellow-countryman, John Stephen de Calcar, who was one of the
most gifted pupils of Titian. The drawings are of such high artistic
quality that for a long time they were ascribed to Titian. The artist
has attempted to soften the necessarily prosaic nature of anatomical
illustrations by introducing an artistic background of landscape of
varied features, with bridges, roads, streams, buildings, etc. The
employment of a background even in portrait-painting was not uncommon
in the same century, as in Leonardo da Vinci's well-known Mona Lisa,
with its suggestive perspective of water, rocks, etc.
[Illustration: Fig. 5.--Anatomical Sketch from Vesalius's _Fabrica_.
(Photographed and reduced from the facsimile edition of 1728.)]
Fig. 5 will give an idea on a small scale of one of the plates
illustrating the work of Vesalius. The plates in the original are of
folio size, and represent a colossal figure in the foreground, with a
background showing between the limbs and at the sides of the figure.
There is considerable variety as regards the background, no two plates
being alike.
Also, in delineating the skeleton, the artist has given to it an
artistic pose, as is shown in Fig. 6, but nevertheless the bones
are well drawn. No plates of equal merit had appeared before these;
in fact, they are the earliest generally known drawings in anatomy,
although woodcuts representing anatomical figures were published as
early as 1491 by John Ketham. Ketham's figures showed only externals
and preparations for opening the body, but rude woodcuts representing
internal anatomy and the human skeleton had been published notably by
Magnus Hundt, 1501; Phrysen, 1518; and Berengarius, 1521 and 1523.
Leonardo da Vinci and other artists had also executed anatomical
drawings before the time of Vesalius.
Previous to the publication of the complete work, Vesalius, in 1538,
had published six tables of anatomy, and, in 1555, he brought out a
new edition of the _Fabrica_, with slight additions, especially in
reference to physiology, which will be adverted to in the chapter on
Harvey.
[Illustration: Fig. 6.--The Skeleton, from Vesalius's _Fabrica_.]
In the original edition of 1543 the illustrations are not collected in
the form of plates, but are distributed through the text, the larger
ones making full-page (folio) illustrations. In this edition also
the chapters are introduced with an initial letter showing curious
anatomical figures in miniature, some of which are shown in Fig. 7.
[Illustration: Fig. 7.--Initial letters from Vesalius's _Fabrica_ of
1543.]
The _Fabrica_ of Vesalius was a piece of careful, honest work, the
moral influence of which must not be overlooked. At any moment in
the world's history, work marked by sincerity exercises a wholesome
influence, but at this particular stage of intellectual development
such work was an innovation, and its significance for progress was
wider and deeper than it might have been under different circumstances.
Opposition to Vesalius.--The beneficent results of his efforts were to
unfold afterward, since, at the time, his utterances were vigorously
opposed from all sides. Not only did the ecclesiastics contend that he
was disseminating false and harmful doctrine, but the medical men from
whom he might have expected sympathy and support violently opposed his
teachings.
Many amusing arguments were brought forward to discredit Vesalius, and
to uphold the authority of Galen. Vesalius showed that in the human
body the lower jaw is a single bone--that it is not divided as it is
in the dog and other lower mammals, and, as Galen had taught, also
in the human subjects. He showed that the sternum, or breast bone,
has three parts instead of eight; he showed that the thigh bones are
straight and not curved, as they are in the dog. Sylvius, his old
teacher, was one of his bitterest opponents; he declared that the human
body had undergone changes in structure since the time of Galen, and,
with the object of defending the ancient anatomist, "he asserted that
the straight thigh bones, which, as every one saw, were not curved in
accordance with the teaching of Galen, were the result of the narrow
trousers of his contemporaries, and that they must have been curved in
their natural condition, when uninterfered with by art!"
The theologians also found other points for contention. It was a
widely accepted dogma that man should have one less rib on one side,
because from the Scriptural account Eve was formed from one of Adam's
ribs. This, of course, Vesalius did not find to be the case. It was
also generally believed at this time that there was in the body an
indestructible resurrection-bone which formed the nucleus of the
resurrection-body. Vesalius said that he would leave the question of
the existence of such a bone to be decided by the theologians, as it
did not appear to him to be an anatomical question.
The Court Physician.--The hand of the church was heavy upon him, and
the hatred shown in attacks from various quarters threw Vesalius into
a state of despondency and anger. In this frame of mind he destroyed
manuscripts upon which he had expended much labor. His disappointment
in the reception of his work probably had much to do in deciding
him to relinquish his professorship and accept the post of court
physician to Charles V of the United Kingdoms of Spain and Belgium.
After the death of Charles, he remained with Philip II, who succeeded
to the throne. Here he waxed rich and famous, but he was always under
suspicion by the clerical powers, who from time to time found means
of discrediting him. The circumstances of his leaving Spain are not
definitely known. One account has it that he made a _post-mortem_
examination of a body which showed signs of life during the operation,
and that he was required to undertake a pilgrimage to the Holy Land
to clear his soul of sacrilege. Whether or not this was the reason
is uncertain, but after nineteen years at the Spanish Court he left,
in 1563, and journeyed to Jerusalem. On his return from Palestine he
suffered shipwreck and died from the effects of exposure on Zanti, one
of the Ionian Islands. It is also said that while on this pilgrimage he
had been offered the position of professor of anatomy as successor to
Fallopius, who had died in 1563, and that, had he lived, he would have
come back honorably to his old post.
Eustachius and Fallopius.--The work of two of his contemporaries,
Eustachius and Fallopius, requires notice. Cuvier says in his _Histoire
des Sciences Naturelles_ that those three men were the founders of
modern anatomy. Vesalius was a greater man than either of the other
two, and his influence was more far-reaching. He reformed the entire
field of anatomy, while the names of Eustachius and Fallopius are
connected especially with a smaller part of the field. Eustachius
described the Eustachian tube of the ear and gave especial attention to
sense organs; Fallopius made special investigations upon the viscera,
and described the Fallopian tube.
Fallopius was a suave, polite man, who became professor of anatomy at
Padua; he opposed Vesalius, but his attacks were couched in respectful
terms.
Eustachius, the professor of anatomy at Rome, was of a different
type, a harsh, violent man, who assailed Vesalius with virulence.
He corrected some mistakes of Vesalius, and prepared new plates on
anatomy, which, however, were not published until 1754, and therefore
did not exert the influence upon anatomical studies that those of
Vesalius did.
[Illustration: Fig. 8.--Fallopius, 1523-1563.]
The Especial Service of Vesalius.--It should be remembered that both
these men had the advantage of the sketches made under the direction
of Vesalius. Pioneers and path-breakers are under special limitations
of being in a new territory, and make more errors than they would in
following another's survey of the same territory; it takes much less
creative force to correct the errors of a first survey than to make the
original discoveries. Everything considered, Vesalius is deserving of
the position assigned to him. He was great in a larger sense, and it
was his researches in particular which re-established scientific method
and made further progress possible. His errors were corrected, not by
an appeal to authority, but by the method which he founded. His great
claim to renown is, not that his work outshone all other work (that of
Galen in particular) in accuracy and brilliancy, but that he overthrew
dependence on authority and re-established the scientific method of
ascertaining truth. It was the method of Aristotle and Galen given anew
to the world.
The spirit of progress was now released from bondage, but we have still
a long way to go under its guidance to reach the gateway of modern
biology.
CHAPTER III
WILLIAM HARVEY AND EXPERIMENTAL OBSERVATION
After the splendid observations of Vesalius, revealing in a new light
the construction of the human body, Harvey took the next general step
by introducing experiment to determine the use or purpose of the
structures that Vesalius had so clearly exposed. Thus the work of
Harvey was complemental to that of Vesalius, and we may safely say
that, taken together, the work of these two men laid the foundations of
the modern method of investigating nature. The results they obtained,
and the influence of their method, are of especial interest to us in
the present connection, inasmuch as they stand at the beginning of
biological science after the Renaissance. Although the observations of
both were applied mainly to the human body, they served to open the
entire field of structural studies and of experimental observations on
living organisms.
Many of the experiments of Harvey, notably those relating to the
movements of the heart, were, of course, conducted upon the lower
animals, as the frog, the dog, etc. His experiments on the living
human body consisted mainly in applying ligatures to the arms and the
legs. Nevertheless, the results of all his experiments related to the
phenomena of the circulation in the human body, and were primarily for
the use of medical men.
In what sense the observations of the two men were complemental will be
better understood when we remember that there are two aspects in which
living organisms should always be considered in biological studies;
first, the structure, and, then, the use that the structures subserve.
One view is essential to the other, and no investigation of animals and
plants is complete in which the two ideas are not involved. Just as a
knowledge of the construction of a machine is necessary to understand
its action, so the anatomical analysis of an organ must precede a
knowledge of its office. The term "physiological anatomy of an organ,"
so commonly used in text-books on physiology, illustrates the point.
We can not appreciate the work of such an organ as the liver without
a knowledge of the arrangement of its working units. The work of the
anatomist concerns the statics of the body, that of the physiologist
the dynamics; properly combined, they give a complete picture of the
living organism.
It is to be remembered that the observations of Vesalius were not
confined exclusively to structure; he made some experiments and some
comments on the use of parts of the body, but his work was mainly
structural, while that which distinguishes Harvey's research is
inductions founded on experimental observation of the action of living
tissues.
The service of Vesalius and Harvey in opening the path to biological
advance is very conspicuous, but they were not the only pioneers;
their work was a part of the general revival of science in which
Galileo, Descartes, and others had their part. While the birth of the
experimental method was not due to the exertions of Harvey alone,
nevertheless it should stand to his credit that he established that
method in biological lines. Aristotle and Galen both had employed
experiments in their researches, and Harvey's step was in the nature of
a revival of the method of the old Greeks.
Harvey's Education.--Harvey was fitted both by native talent and by his
training for the part which he played in the intellectual awakening.
He was born at Folkestone, on the south coast of England, in 1578, the
son of a prosperous yeoman. The Harvey family was well esteemed, and
the father of William was at one time the mayor of Folkestone. Young
Harvey, after five years in the King's school at Canterbury, went to
Cambridge, and in 1593, at the age of sixteen, entered Caius College.
He had already shown a fondness for observations upon the organization
of animals, but it is unlikely that he was able to cultivate this at
the university. There his studies consisted mainly of Latin and Greek,
with some training in debate and elementary instruction in the science
of physics.
At Padua.--In 1597, at the age of nineteen, he was graduated with the
Arts degree, and the following year he turned his steps toward Italy
in search of the best medical instruction that could be found at that
time in all the world. He selected the great university of Padua as
his place of sojourn, being attracted thither by the fame of some of
its medical teachers. He was particularly fortunate in receiving his
instruction in anatomy and physiology from Fabricius, one of the most
learned and highly honored teachers in Italy. The fame of this master
of medicine, who, from his birthplace, is usually given the full name
of Fabricius _ab Aquapendente_, had spread to the intellectual centers
of the world, where his work as anatomist and surgeon was especially
recognized. A fast friendship sprang up between the young medical
student and this ripe anatomist, the influence of which must have been
very great in shaping the future work of Harvey.
Fabricius was already sixty-one years of age, and when Harvey came to
Padua was perfecting his knowledge upon the valves of the veins. The
young student was taken fully into his confidence, and here was laid
that first familiarity with the circulatory system, the knowledge of
which Harvey was destined so much to advance and amplify. But it was
the stimulus of his master's friendship, rather than what he taught
about the circulation, that was of assistance to Harvey. For the views
of Fabricius in reference to the circulation were those of Galen;
and his conception of the use of the valves of the veins was entirely
wrong. A portrait of this great teacher of Harvey is shown in Fig. 9.
At Padua young Harvey attracted notice as a student of originality and
force, and seems to have been a favorite with the student body as well
as with his teachers. His position in the university may be inferred
from the fact that he belonged to one of the aristocratic-student
organizations, and, further, that he was designated a "councilor" for
England. The practice of having student councilors was then in vogue in
Padua; the students comprising the council met for deliberations, and
very largely managed the university by their votes upon instructors and
university measures.
It is a favorable comment upon the professional education of his time
that, after graduating at the University of Cambridge, he studied four
or more years (Willis says five years) in scientific and medical lines
to reach the degree of Doctor of Physic.
On leaving Padua, in 1602, he returned to England and took the
examinations for the degree of M.D. from Cambridge, inasmuch as the
medical degree from an English university advanced his prospects of
receiving a position at home. He opened practice, was married in 1604,
and the same year began to give public lectures on anatomy.
[Illustration: Fig. 9.--Fabricius, 1537-1619, Harvey's Teacher.]
His Personal Qualities.--Harvey had marked individuality, and seems to
have produced a powerful impression upon those with whom he came in
contact as one possessing unusual intellectual powers and independence
of character. He inspired confidence in people, and it is significant
that, in reference to the circulation of the blood, he won to his way
of thinking his associates in the medical profession. This is important
testimony as to his personal force, since his ideas were opposed to the
belief of the time, and since also away from home they were vigorously
assailed.
Although described as choleric and hasty, he had also winning
qualities, so that he retained warm friendships throughout his life,
and was at all times held in high respect. It must be said also that in
his replies to his critics, he showed great moderation.
[Illustration: Fig. 10.--William Harvey, 1578-1667.]
The contemplative face of Harvey is shown in Fig. 10. This is taken
from his picture in the National Portrait Gallery in London, and
is usually regarded as the second-best portrait of Harvey, since
the one painted by Jansen, now in possession of the Royal College
of Physicians, is believed to be the best one extant. The picture
reproduced here shows a countenance of composed intellectual strength,
with a suggestion, in the forehead and outline of the face, of some of
the portraits of Shakespeare.
An idea of his personal appearance may be had from the description of
Aubrey, who says: "Harvey was not tall, but of the lowest stature;
round faced, with a complexion like the wainscot; his eyes small,
round, very black, and full of spirit; his hair black as a raven,
but quite white twenty years before he died; rapid in his utterance,
choleric, given to gesture," etc.
He was less impetuous than Vesalius, who had published his work at
twenty-eight; Harvey had demonstrated his ideas of the circulation in
public anatomies and lectures for twelve years before publishing them,
and when his great classic on the Movement of the Heart and Blood
first appeared in 1628, he was already fifty years of age. This is a
good example for young investigators of to-day who, in order to secure
priority of announcement, so frequently rush into print with imperfect
observations as preliminary communications.
Harvey's Writings.--Harvey's publications were all great; in
embryology, as in physiology, he produced a memorable treatise. But his
publications do not fully represent his activity as an investigator;
it is known that through the fortunes of war, while connected with
the sovereign Charles I as court physician, he lost manuscripts and
drawings upon the comparative anatomy and development of insects
and other animals. His position in embryology will be dealt with in
the chapter on the Development of Animals, and he will come up for
consideration again in the chapter on the Rise of Physiology. Here we
are concerned chiefly with his general influence on the development of
biology.
His Great Classic on Movement of the Heart and Blood.--Since his book
on the circulation of the blood is regarded as one of the greatest
monuments along the highroad of biology, it is time to make mention of
it in particular. Although relatively small, it has a long title out
of proportion to its size: _Exercitatio Anatomica de Motu Cordis et
Sanguinis in Animalibus_, which maybe freely translated, "An Anatomical
Disquisition on the Movement of the Heart and Blood in Animals." The
book is usually spoken of under the shorter title, _De Motu Cordis et
Sanguinis_. The full title seems somewhat repellent, but the contents
of the book will prove to be interesting to general readers. It is a
clear, logical demonstration of the subject, proceeding with directness
from one point to another until the culminating force of the argument
grows complete and convincing.
The book in its first edition was a quarto volume of seventy-eight
pages, published in Frankfort in 1628. An interesting facsimile reprint
of this work, translated into English, was privately reproduced in
1894 by Dr. Moreton and published in Canterbury. As stated above, it
is known that Harvey had presented and demonstrated his views in his
lectures since 1616. In his book he showed for the first time ever in
print, that all the blood in the body moves in a circuit, and that the
beating of the heart supplies the propelling force. Both ideas were
new, and in order to appreciate in what sense they were original with
Harvey, we must inquire into the views of his forerunners.
Question as to Harvey's Originality.--The question of how near some
of his predecessors came to anticipating his demonstration of the
circulation has been much debated. It has been often maintained that
Servetus and Realdus Columbus held the conception of the circulation
for which Harvey has become so celebrated. Of the various accounts
of the views of Harvey's predecessors, those of Willis, Huxley, and
Michael Foster are among the most judicial; that of Foster, indeed,
inasmuch as it contains ample quotations from the original sources,
is the most nearly complete and satisfactory. The discussion is too
long to enter into fully here, but a brief outline is necessary to
understand what he accomplished, and to put his discovery in the proper
light.
To say that he first discovered--or, more properly, demonstrated--the
circulation of the blood carries the impression that he knew of the
existence of capillaries connecting the arteries and the veins, and
had ocular proof of the circulation through these connecting vessels.
But he did not actually see the blood moving from veins to arteries,
and he knew not of the capillaries. He understood clearly from his
observations and experiments that all the blood passes from veins to
arteries and moves in "a kind of circle"; still, he thought that it
filters through the tissues in getting from one kind of vessel to the
other. It was reserved for Malpighi, in 1661, and Leeuwenhoek, in 1669,
to see, with the aid of lenses, the movement of the blood through the
capillaries in the transparent parts of animal tissues. (See under
Leeuwenhoek, p. 84.)
The demonstration by Harvey of the movement of the blood in a circuit
was a matter of cogent reasoning, based on experiments with ligatures,
on the exposure of the heart in animals and the analysis of its
movements. It has been commonly maintained (as by Whewell) that
he deduced the circulation from observations of the valves in the
veins, but this is not at all the case. The central point of Harvey's
reasoning is that the quantity of blood which leaves the left cavity
of the heart in a given space of time makes necessary its return to
the heart, since in a half-hour (or less) the heart, by successive
pulsations, throws into the great artery more than the total quantity
of blood in the body. Huxley points out that this is the first time
that quantitative determinations were introduced into physiology.
Views of His Predecessors on the Movement of the Blood.--Galen's view
of the movement of the blood was not completely replaced until the
establishment of Harvey's view. The Greek anatomist thought that there
was an ebb and flow of blood within both veins and arteries throughout
the system. The left side of the heart was supposed to contain blood
vitalized by a mixture of animal spirits within the lungs. The veins
were thought to contain crude blood. He supposed, further, that there
was a communication between the right and the left side of the heart
through very minute pores in the septum, and that some blood from the
right side passed through the pores into the left side and there became
charged with animal spirits. It should also be pointed out that Galen
believed in the transference of some blood through the lungs from the
right to the left side of the heart, and in this foreshadowed the views
which were later developed by Servetus and Realdus Columbus.
[Illustration: Fig. 11.--Scheme of the Portal Circulation According to
Vesalius, 1543.]
Vesalius, in the first edition of his work (1543) expressed doubts
upon the existence of pores in the partition-wall of the heart through
which blood could pass; and in the second edition (1555) of the
_Fabrica_ he became more skeptical. In taking this position he attacked
a fundamental part of the belief of Galen. The careful structural
studies of Vesalius must have led him very near to an understanding
of the connection between arteries and veins. Fig. 11 shows one of
his sketches of the arrangement of arteries and veins. He saw that
the minute terminals of arteries and veins came very close together
in the tissues of the body, but he did not grasp the meaning of the
observation, because his physiology was still that of Galen; Vesalius
continued to believe that the arteries contained blood mixed with
spirits, and the veins crude blood, and his idea of the movement
was that of an ebb and flow. In reference to the anatomy of the
blood-vessels, he goes so far as to say of the portal vein and the
vena cava in the liver that "the extreme ramifications of these veins
inosculate with each other, and in many places appear to unite and be
continuous." All who followed him had the advantage of his drawings
showing the parallel arrangement of arteries and veins, and their close
approach to each other in their minute terminal twigs, but no one
before Harvey fully grasped the idea of the movement of the blood in a
complete circuit.
Servetus, in his work on the Restoration of Christianity (_Restitutio
Christianismi_, 1553), the work for which Calvin accomplished his
burning at the stake, expressed more clearly than Galen had done the
idea of a circuit of blood through the lungs. According to his view,
some of the blood took this course, while he still admits that a part
may exude through the wall of the ventricle from the right to the
left side. This, however, was embodied in a theological treatise, and
had little direct influence in bringing about an altered view of the
circulation. Nevertheless, there is some reason to think that it may
have been the original source of the ideas of the anatomist Columbus,
as the studies into the character of that observer by Michael Foster
seem to indicate.
Realdus Columbus, professor of anatomy at Rome, expressed a conception
almost identical with that of Servetus, and as this was in an important
work on anatomy, published in 1559, and well known to the medical men
of the period, it lay in the direct line of anatomical thought and
had greater influence. Foster suggests that the devious methods of
Columbus, and his unblushing theft of intellectual property from other
sources, give ground for the suspicion that he had appropriated this
idea from Servetus without acknowledgment. Although Calvin supposed
that the complete edition of a thousand copies of the work of Servetus
had been burned with its author in 1553, a few copies escaped, and
possibly one of these had been examined by Columbus. This assumption
is strengthened by the circumstance that Columbus gives no record of
observations, but almost exactly repeats the words of Servetus.
Cæsalpinus, the botanist and medical man, expressed in 1571 and 1593
similar ideas of the movement of the blood (probably as a matter
of argument, since there is no record of either observations or
experiments by him). He also laid hold of a still more important
conception, viz., that some of the blood passes from the left side of
the heart through the arteries of the body, and returns to the right
side of the heart by the veins. But a fair consideration of the claims
of these men as forerunners of Harvey requires quotations from their
works and a critical examination of the evidence thus adduced. This has
been excellently done by Michael Foster in his _Lectures on the History
of Physiology_. Further considerations of this aspect of the question
would lie beyond the purposes of this book.
At most, before Harvey, the circuit through the lungs had been vaguely
defined by Galen, Servetus, Columbus, and Cæsalpinus, and the latter
had supposed some blood to pass from the heart by the arteries and
to return to it by the veins; but no one had arrived at an idea of a
complete circulation of all the blood through the system, and no one
had grasped the consequences involved in such a conception. Harvey's
idea of the movement of the heart (_De Motu Cordis_) was new; his
notion of the circulation (_et Sanguinis_) was new; and his method of
demonstrating these was new.
Harvey's Argument.--The gist of Harvey's arguments is indicated in the
following propositions quoted with slight modifications from Hall's
_Physiology_: (I) The heart passively dilates and actively contracts;
(II) the auricles contract before the ventricles do; (III) the
contraction of the auricles forces the blood into the ventricles; (IV)
the arteries have no "pulsific power," _i.e._, they dilate passively,
since the pulsation of the arteries is nothing else than the impulse of
the blood within them; (V) the heart is the organ of propulsion of the
blood; (VI) in passing from the right ventricle to the left auricle the
blood transudes through the parenchyma of the lungs; (VII) the quantity
and rate of passage of the blood peripherally from the heart makes
it a physical necessity that most of the blood return to the heart;
(VIII) the blood does return to the heart by way of the veins. It will
be noticed that the proposition VII is the important one; in it is
involved the idea of applying measurement to a physiological process.
Harvey's Influence.--Harvey was a versatile student. He was a
comparative anatomist as well as a physiologist and embryologist; he
had investigated the anatomy of about sixty animals and the embryology
of insects as well as of vertebrates, and his general influence in
promoting biological work was extensive.
His work on the movement of the blood was more than a record of a
series of careful investigations; it was a landmark in progress. When
we reflect on the part played in the body by the blood, we readily see
that a correct idea of how it carries nourishment to the tissues, and
how it brings away from them the products of disintegrated protoplasm
is of prime importance in physiology. It is the point from which spring
all other ideas of the action of tissues, and until this was known the
fine analysis of vital processes could not be made. The true idea of
respiration, of the secretion by glands, the chemical changes in the
tissues, in fact, of all the general activities of the body, hinge
upon this conception. It was these consequences of his demonstration,
rather than the fact that the blood moves in a circuit, which made it
so important. This discovery created modern physiology, and as that
branch of inquiry is one of the parts of general biology, the bearing
of Harvey's discovery upon biological thought can be readily surmised.
Those who wish to examine Harvey's views at first hand, without the
burden of translating them from the Latin, will find an edition of his
complete works translated into English by Willis, and published by the
Ray Society, of London.
As is always the case with new truths, there was hostility to
accepting his views. In England this hostility was slight on account
of his great personal influence, but on the Continent there was many a
sharp criticism passed upon his work. His views were so illuminating
that they were certain of triumph, and even in his lifetime were
generally accepted. Thus the new conception of vital activities,
together with his method of inquiry, became permanent parts of
biological science.
CHAPTER IV
THE INTRODUCTION OF THE MICROSCOPE AND THE PROGRESS OF INDEPENDENT
OBSERVATION
The introduction of the microscope greatly increased the ocular
powers of observers, and, in the seventeenth century, led to many new
departures. By its use the observations were carried from the plane
of gross anatomy to that of minute structure; the anatomy of small
forms of life, like insects, began to be studied, and also the smaller
microscopic animalcula were for the first time made known.
Putting aside the disputed questions as to the time of the invention
and the identity of the inventor of the microscope--whether to Fontana,
Galileo, or the Jenssens belongs the credit--we know that it was
improved by the Hollander Drebbel in the early years of the seventeenth
century, but was not seriously applied to anatomical studies till after
the middle of that century.
The Pioneer Microscopists
The names especially associated with early microscopic observations are
those of Hooke and Grew in England, Malpighi in Italy, and Swammerdam
and Leeuwenhoek, both in Holland. Their microscopes were imperfect, and
were of two kinds: simple lenses, and lenses in combination, forming
what we now know as the compound microscope. Some forms of these early
microscopes will be described and illustrated later. Although thus
early introduced, microscopic observation did not produce its great
results until the nineteenth century, just after magnifying-lenses had
been greatly improved.
[Illustration: Fig. 12.--Hooke's Microscope, 1665.
From Carpenter's _The Microscope and Its Revelations_. Permission of P.
Blakiston's Sons & Co.]
Robert Hooke (1635-1703), of London, published in 1665 a book of
observations with the microscope entitled _Micrographia_, which was
embellished with eighty-three plates of figures. Hooke was a man of
fine mental endowment, who had received a good scientific training at
the University of Cambridge, but who lacked fixedness of purpose in
the employment of his talents. He did good work in mathematics, made
many models for experimenting with flying machines, and claimed to have
discovered gravitation before Newton, and also the use of a spring
for regulating watches before Huygens, etc. He gave his attention to
microscopic study for a time and then dropped it; yet, although we can
not accord to him a prominent place in the history of biology, he must
receive mention as a pioneer worker with the microscope. His book gave
a powerful stimulus to microscopy in England, and, partly through its
influence, labor in this field was carried on more systematically by
his fellow-countryman Nehemiah Grew.
The form of the microscope used by Hooke is known through a picture and
a description which he gives of it in his _Micrographia_. Fig. 12 is a
copy of the illustration. His was a compound microscope consisting of a
combination of lenses attached to a tube, one set near the eye of the
observer and the other near the object to be examined. When we come to
describe the microscopes of Leeuwenhoek, with which so much good work
was accomplished, we shall see that they stand in marked contrast, on
account of their simplicity, to the somewhat elaborate instrument of
Hooke.
Grew (1628-1711) devoted long and continuous labor to microscopic
observation, and, although he was less versatile and brilliant than
Hooke, his patient investigations give him just claim to a higher
place in the history of natural science. Grew applied the microscope
especially to the structure of plants, and his books entitled _Idea of
a Philosophical History of Plants_ (1673) and _Anatomy of Vegetables_
(1682) helped to lay the foundations of vegetable histology. When
we come to consider the work of Malpighi, we shall see that he also
produced a work upon the microscopic structure of plants which,
although not more exact and painstaking than Grew's, showed deeper
comprehension. He is the co-founder with Grew of the science of the
microscopic anatomy of plants.
It is not necessary to dwell long upon the work of either Hooke or
Grew, since that of Malpighi, Swammerdam, and Leeuwenhoek was more
far-reaching in its influence. The publications of these three men
were so important, both in reference to microscopic study and to the
progress of independent investigation, that it will be necessary
to deal with them in more detail. In the work of these men we come
upon the first fruits of the application of the methods introduced
by Vesalius and Harvey. Of this triumvirate, one--Malpighi--was an
Italian, and the other two were Hollanders. Their great service to
intellectual progress consisted chiefly in this--that, following upon
the foundations of Vesalius and Harvey, "they broke away from the
thraldom of mere book-learning, and relying alone upon their own eyes
and their own judgment, won for man that which had been quite lost--the
blessings of independent and unbiased observation."
It is natural that, working when they did, and independently as they
did, their work overlapped in many ways. Malpighi is noteworthy for
many discoveries in anatomical science, for his monograph on the
anatomy of the silkworm, for observations of the minute structure
of plants, and of the development of the chick in the hen's egg.
Swammerdam did excellent and accurate work upon the anatomy and
metamorphosis of insects, and the internal structure of mollusks,
frogs, and other animals. Leeuwenhoek is distinguished for much general
microscopic work; he discovered various microscopic animalcula; he
established, by direct observation, the fact of a connection between
arteries and veins, and examined microscopically minerals, plants,
and animals. To him, more than to the others, the general title of
"microscopist" might be applied.
Since these men are so important in the growth of biology, let us, by
taking them individually, look a little more closely into their lives
and labors.
Marcello Malpighi, 1628-1694
Personal Qualities.--There are several portraits of Malpighi extant.
These, together with the account of his personal appearance given by
Atti, one of his biographers, enable us to tell what manner of man
he was. The portrait shown in Fig. 13 is a copy of the one painted
by Tabor and presented by Malpighi to the Royal Society of London,
in whose rooms it may still be seen. This shows him in the full
attractiveness of his early manhood, with the earnest, intellectual
look of a man of high ideals and scholarly tastes, sweet-tempered,
and endowed with the insight that belongs to a sympathetic nature.
Some of his portraits taken later are less attractive, and the lines
and wrinkles that show in his face give evidence of imperfect health.
According to Atti, he was of medium stature, with a brown skin, a
delicate complexion, a serious countenance, and a melancholy look.
Accounts of his life show that he was modest, quiet, and of a pacific
disposition, notwithstanding the fact that he lived in an atmosphere of
acrimonious criticism, of jealousy and controversy. A family dispute in
reference to the boundary-lines between his father's property and the
adjoining land of the Sbaraglia family gave rise to a feud, in which
representatives of the latter family followed him all his life with
efforts to injure both his scientific reputation and his good name.
Under all this he suffered acutely, and his removal from Bologna to
Messina was partly to escape the harshness of his critics. Some of his
best qualities showed under these persecutions; he was dignified under
abuse and considerate in his reply. In reference to the attacks upon
his scientific standing, there were published after his death replies
to his critics that were written while he was smarting under their
injustice and severity, but these replies are free from bitterness and
are written in a spirit of great moderation. The following picture,
taken from Ray's correspondence, shows the fine control of his spirit.
Under the date of April, 1684, Dr. Tancred Robinson writes: "Just as I
left Bononia I had a lamentable spectacle of Malpighi's house all in
flames, occasioned by the negligence of his old wife. All his pictures,
furniture, books, and manuscripts were burnt. I saw him in the very
heat of the calamity, and methought I never beheld so much Christian
patience and philosophy in any man before; for he comforted his wife
and condoled nothing but the loss of his papers."
[Illustration: Fig. 13.--Malpighi, 1628-1694.]
Education.--Malpighi was born at Crevalcuore, near Bologna, in 1628.
His parents were landed peasants, or farmers, enjoying an independence
in financial matters. As their resources permitted it, they designed
to give Marcellus, their eldest child, the advantage of masters and
schools. He began a life of study; and, before long, he showed a taste
for belles-lettres and for philosophy, which he studied under Natali.
Through the death of both parents, in 1649, Malpighi found himself
orphaned at the age of twenty-one, and as he was the eldest of eight
children, the management of domestic affairs devolved upon him. He
had as yet made no choice of a profession; but, through the advice of
Natali, he resolved, in 1651, to study medicine. This advice followed,
in 1653, at the age of twenty-five, he received from the University of
Bologna the degree of Doctor of Medicine.
University Positions.--In the course of a few years he married the
sister of Massari, one of his teachers in anatomy, and became a
candidate for a chair in the University of Bologna. This he did not
immediately receive, but, about 1656, he was appointed to a post in
the university, and began his career as a teacher and investigator. He
must have shown aptitude for this work, for he was soon called to the
University of Pisa, where, fortunately for his development, he became
associated with Borelli, who, as an older man, assisted him in many
ways. They united in some work, and together they discovered the spiral
character of the heart muscles. But the climate of Pisa did not agree
with him, and after three years he returned, in 1659, to teach in the
University of Bologna, and applied himself assiduously to anatomy.
Here his fame was in the ascendant, notwithstanding the machinations of
his enemies and detractors, led by Sbaraglia. He was soon (1662) called
to Messina to follow the famous Castelli. After a residence there of
four years he again returned to Bologna, and as he was now thirty-eight
years of age, he thought it time to retire to his villa near the city
in order to devote himself more fully to anatomical studies, but he
continued his lectures in the university, and also his practice of
medicine.
Honors at Home and Abroad.--Malpighi's talents were appreciated even
at home. The University of Bologna honored him in 1686 with a Latin
_eulogium_; the city erected a monument to his memory; and after
his death, in the city of Rome, his body was brought to Bologna
and interred with great pomp and ceremony. At the three hundredth
anniversary of his death, in 1894, a festival was held in Bologna, his
monument was unveiled, and a book of addresses by eminent anatomists
was published in his honor.
During his lifetime he received recognition also from abroad, but that
is less remarkable. In 1668 he was elected an honorary member of the
Royal Society of London. He was very sensible of this honor; he kept in
communication with the society; he presented them with his portrait,
and deposited in their archives the original drawings illustrating the
anatomy of the silkworm and the development of the chick.
In 1691 he was taken to Rome by the newly elected pope, Innocent XII,
as his personal physician, but under these new conditions he was not
destined to live many years. He died there, in 1694, of apoplexy. His
wife, of whom it appears that he was very fond, had died a short time
previously. Among his posthumous works is a sort of personal psychology
written down to the year 1691, in which he shows the growth of his
mind, and the way in which he came to take up the different subjects of
investigation.
In reference to his discoveries and the position he occupies in the
history of natural science, it should be observed that he was an
"original as well as a very profound observer." While the ideas of
anatomy were still vague, "he applied himself with ardor and sagacity
to the study of the fine structure of the different parts of the body,"
and he extended his investigations to the structure of plants and of
different animals, and also to their development. Entering, as he did,
a new and unexplored territory, naturally he made many discoveries, but
no man of mean talents could have done his work.
Activity in Research.--During forty years of his life he was always
busy with research. Many of his discoveries had practical bearing on
the advance of anatomy and physiology as related to medicine. In 1661
he demonstrated the structure of the lungs. Previously these organs
had been regarded as a sort of homogeneous parenchyma. He showed the
presence of air-cells, and had a tolerably correct idea of how the air
and the blood are brought together in the lungs, the two never actually
in contact, but always separated by a membrane. These discoveries were
first made on the frog, and applied by analogy to the interpretation of
the lungs of the human body. He was a comparative anatomist, and the
first to insist on analogies of structure between organs throughout
the animal kingdom, and to make extensive practical use of the idea
that discoveries on simpler animals can be utilized in interpreting the
similar structures in the higher ones.
It is very interesting to note that in connection with this work he
actually observed the passage of blood through the capillaries of the
transparent lungs of the frog, and also in the mesentery. Although this
antedates the similar observations of Leeuwenhoek (1669), nevertheless
the work of Leeuwenhoek was much more complete, and he is usually
recognized in physiology as the discoverer of the capillary connection
between arteries and veins. At this same period Malpighi also observed
the blood corpuscles.
Soon after he demonstrated the mucous layer, or pigmentary layer of
the skin, intermediate between the true and the scarf skin. He had
separated this layer by boiling and maceration, and described it
as a reticulated membrane. Even its existence was for a long time
controverted, but it remains in modern anatomy under the title of the
Malpighian layer.
His observation of glands was extensive, and while it must be confessed
that many of his conclusions in reference to glandular structure were
erroneous, he left his name connected with the Malpighian corpuscles
of the kidney and of the spleen. He was also the first to indicate the
nature of the papillæ on the tongue. The foregoing is a respectable
list of discoveries, but much more stands to his credit. Those which
follow have a bearing on comparative anatomy, zoölogy, and botany.
Monograph on the Structure and Metamorphosis of the
Silkworm.--Malpighi's work on the structure of the silkworm takes rank
among the most famous monographs on the anatomy of a single animal.
Much skill was required to give to the world this picture of minute
structure. The marvels of organic architecture were being made known in
the human body and the higher animals, but "no insect--hardly, indeed,
any animal--had then been carefully described, and all the methods of
the work had to be discovered." He labored with such enthusiasm in
this new territory as to throw himself into a fever and to set up an
inflammation in the eyes. "Nevertheless," says Malpighi, "in performing
these researches so many marvels of nature were spread before my eyes
that I experienced an internal pleasure that my pen could not describe."
He showed that the method of breathing was neither by lungs nor by
gills, but through a system of air-tubes, communicating with the
exterior through buttonhole shaped openings, and, internally, by an
infinitude of branches reaching to the minutest parts of the body.
Malpighi showed an instinct for comparison; instead of confining his
researches to the species in hand, he extended his observations to
other insects, and has given sketches of the breathing-tubes, held open
by their spiral thread, taken from several species.
The nervous system he found to be a central white cord with swellings
in each ring of the body, from which nerves are given off to all
organs and tissues. The cord, which is, of course, the central nervous
system, he found located mainly on the ventral surface of the body, but
extending by a sort of collar of nervous matter around the oesophagus,
and on the dorsal surface appearing as a more complex mass, or brain,
from which nerves are given off to the eyes and other sense organs of
the head. As illustrations from this monograph we have, in Fig. 14,
reduced sketches of the drawings of the nervous system and the food
canal in the adult silkworm. The sketch at the right hand illustrates
the central nerve cord with its ganglionic enlargement in each segment,
the segments being indicated by the rows of spiracles at the sides. The
original drawing is on a much larger scale, and reducing it takes away
some of its coarseness. All of his drawings lack the finish and detail
of Swammerdam's work.
He showed also the food canal and the tubules connected with the
intestine, which retain his name in the insect anatomy of to-day,
under the designation of Malpighian tubes. The silk-forming apparatus
was also figured and described. These structures are represented, as
Malpighi drew them, on the left of Fig. 14.
[Illustration: Fig. 14.--From Malpighi's _Anatomy of the Silkworm_,
1669.]
This monograph, which was originally published in 1669 by the Royal
Society of London, bears the Latin title, _Dissertatio Epistolica de
Bombyce_. It has been several times republished, the best edition being
that in French, which dates from Montpellier, in 1878, and which is
prefaced by an account of the life and labors of Malpighi.
Anatomy of Plants.--Malpighi's anatomy of plants constitutes one of his
best, as well as one of his most extensive works. In the folio edition
of his works, 1675-79, the _Anatome Plantarum_ occupies not less than
152 pages and is illustrated by ninety-three plates of figures. It
comprises an exposition of the structure of bark, stem, roots, seeds,
the process of germination, and includes a treatise on galls, etc., etc.
In this work the microscopic structure of plants is amply illustrated,
and he anticipated to a certain degree the ideas on the cellular
structure of plants. Burnett says: "His observations appear to have
been very accurate, and not only did he maintain the cellular structure
of plants, but also declared that it was composed of separate cells,
which he designated 'utricles.'" Thus did he foreshadow the cell
theory of plants as developed by Schleiden in the nineteenth century.
When it came to interpretations, he made several errors. Applying his
often-asserted principle of analogies, he concluded that the vessels
of plants are organs of respiration and of circulation, from a certain
resemblance that they bear to the breathing-tubes of insects. But his
observations on structure are good, and if he had accomplished nothing
more than this work on plants he would have a place in the history of
botany.
Work in Embryology.--Difficult as was his task in insect anatomy
and plant histology, a more difficult one remains to be mentioned,
_viz._, his observations of the development of animals. He had pushed
his researches into the finer structure of organisms, and now he
attempted to answer this question: How does one of these organisms
begin its life, and by what series of steps is its body built up? He
turned to the chick, as the most available form in which to get an
insight into this process, but he could not extend his observations
successfully into periods earlier than about the twenty-four-hour stage
of development. Two memoirs were written on this subject, both in 1672,
which were published by the Royal Society of England under the titles
_De Formatione Pulli in Ovo_ and _De Ovo Incubato_. Of all Malpighi's
work, this has received the least attention from reviewers, but it is,
for his time, a very remarkable achievement. No one can look over the
ten folio plates without being impressed with the extent and accuracy
of his observations. His sketches are of interest, not only to students
of embryology, but also to educated people, to see how far observations
regarding the development of animals had progressed in 1672. Further
consideration of his position in embryology will be found in the
chapter on the rise of that subject.
Little is known regarding the form of microscope employed by Malpighi.
Doubtless, much of his work was done with a simple lens, since he
speaks of examining the dried lungs with a microscope of a single lens
against the horizontal sun; but he is also known to have observed with
an instrument consisting of two lenses.
Malpighi was a naturalist, but of a new type; he began to look below
the surface, and essayed a deeper level of analysis in observing and
describing the internal and minute structure of animals and plants, and
when he took the further step of investigating their development he was
anticipating the work of the nineteenth century.
Jan Swammerdam (1637-1680)
Swammerdam was a different type of man--nervous, incisive, very
intense, stubborn, and self-willed. Much of his character shows in the
portrait by Rembrandt represented in Fig. 15. Although its authenticity
has been questioned, it is the only known portrait of Swammerdam.
Early Interest in Natural History.--He was born in 1637, nine years
after Malpighi. His father, an apothecary of Amsterdam, had a taste for
collecting, which was shared by many of his fellow-townsmen. The Dutch
people of this time sent their ships into all parts of the world, and
this vast commerce, together with their extensive colonial possessions,
fostered the formation of private museums. The elder Swammerdam had
the finest and most celebrated collection in all Amsterdam. This was
stored, not only with treasures, showing the civilization of remote
countries, but also with specimens of natural history, for which he had
a decided liking. Thus "from the earliest dawn of his understanding the
young Swammerdam was surrounded by zoölogical specimens, and from the
joint influence, doubtless, of hereditary taste and early association,
he became passionately devoted to the study of natural history."
Studies Medicine.--His father intended him for the church, but he had
no taste for theology, though he became a fanatic in religious matters
toward the close of his life; at this period, however, he could brook
no restraint in word or action. He consented to study medicine, but for
some reason he was twenty-six years old before entering the University
of Leyden. This delay was very likely owing to his precarious health,
but, in the mean time, he had not been idle; he had devoted himself
to observation and study with great ardor, and had already become an
expert in minute dissection. When he went to the University of Leyden,
therefore, he at once took high rank in anatomy. Anything demanding
fine manipulation and dexterity was directly in his line. He continued
his studies in Paris, and about 1667 took his degree of Doctor of
Medicine.
[Illustration: Fig. 15.--Swammerdam, 1637-1680.]
During this period of medical study he made some rather important
observations in human anatomy, and introduced the method of injection
that was afterward claimed by Ruysch. In 1664 he discovered the
valves of lymphatic vessels by the use of slender glass tubes,
and, three years later, first used a waxy material for injecting
blood-vessels.
It should be noted, in passing, that Swammerdam was the first to
observe and describe the blood corpuscles. As early as 1658 he
described them in the blood of the frog, but not till fifty-seven years
after his death were his observations published by Boerhaave, and,
therefore, he does not get the credit of this discovery. Publication
alone, not first observation, establishes priority, but there is
conclusive evidence that he observed the blood corpuscles before either
Malpighi or Leeuwenhoek had published his findings.
Love of Minute Anatomy.--After graduating in medicine he did not
practice, but followed his strong inclination to devote himself to
minute anatomy. This led to differences with his father, who insisted
on his going into practice, but the self-willed stubbornness and
firmness of the son now showed themselves. It was to gratify no love of
ease that Swammerdam thus held out against his father, but to be able
to follow an irresistible leading toward minute anatomy. At last his
father planned to stop supplies, in order to force him into the desired
channel, but Swammerdam made efforts, without success, to sell his own
personal collection and preserve his independence. His father died,
leaving him sufficient property to live on, and brought the controversy
to a close soon after the son had consented to yield to his wishes.
Boerhaave, his fellow-countryman, gathered Swammerdam's complete
writings after his death and published them in 1737 under the title
_Biblia Naturæ_. With them is included a life of Swammerdam, in which
a graphic account is given of his phenomenal industry, his intense
application, his methods and instruments. Most of the following
passages are selected from that work.
Intensity as a Worker.--He was a very intemperate worker, and in
finishing his treatise on bees (1673) he broke himself down.
"It was an undertaking too great for the strongest constitution to
be continually employed by day in making observations and almost
as constantly engaged by night in recording them by drawings and
suitable explanations. This being summer work, his daily labors began
at six in the morning, when the sun afforded him light enough to
enable him to survey such minute objects; and from that time till
twelve he continued without interruption, all the while exposed in
the open air to the scorching heat of the sun, bareheaded, for fear
of interrupting the light, and his head in a manner dissolving into
sweat under the irresistible ardors of that powerful luminary. And if
he desisted at noon, it was only because the strength of his eyes was
too much weakened by the extraordinary efflux of light and the use of
microscopes to continue any longer upon such small objects.
"This fatigue our author submitted to for a whole month together,
without any interruption, merely to examine, describe, and represent
the intestines of bees, besides many months more bestowed upon
the other parts; during which time he spent whole days in making
observations, as long as there was sufficient light to make any, and
whole nights in registering his observations, till at last he brought
his treatise on bees to the wished-for perfection."
Method of Work.--"For dissecting very minute objects, he had a brass
table made on purpose by that ingenious artist, Samuel Musschenbroek.
To this table were fastened two brass arms, movable at pleasure to
any part of it, and the upper portion of these arms was likewise so
contrived as to be susceptible of a very slow vertical motion, by which
means the operator could readily alter their height as he saw most
convenient to his purpose. The office of one of these arms was to hold
the little corpuscles, and that of the other to apply the microscope.
His microscopes were of various sizes and curvatures, his microscopical
glasses being of various diameters and focuses, and, from the least
to the greatest, the best that could be procured, in regard to the
exactness of the workmanship and the transparency of the substance.
"But the constructing of very fine scissors, and giving them an extreme
sharpness, seems to have been his chief secret. These he made use of to
cut very minute objects, because they dissected them equably, whereas
knives and lancets, let them be ever so fine and sharp, are apt to
disorder delicate substances. His knives, lancets, and styles were so
fine that he could not see to sharpen them without the assistance of
the microscope; but with them he could dissect the intestines of bees
with the same accuracy and distinctness that others do those of large
animals.
"He was particularly dexterous in the management of small tubes of
glass no thicker than a bristle, drawn to a very fine point at one end,
but thicker at the other."
These were used for inflating hollow structures, and also for making
fine injections. He dissolved the fat of insects in turpentine and
carried on dissections under water.
An unbiased examination of his work will show that it is of a higher
quality than Malpighi's in regard to critical observation and richness
of detail. He also worked with minuter objects and displayed a greater
skill.
The Religious Devotee.--The last part of his life was dimmed by
fanaticism. He read the works of Antoinette Bourignon and fell under
her influence; he began to subdue his warm and stubborn temper, and to
give himself up to religious contemplation. She taught him to regard
scientific research as worldly, and, following her advice, he gave
up his passionate fondness for studying the works of the Creator, to
devote himself to the love and adoration of that same Being. Always
extreme and intense in everything he undertook, he likewise overdid
this, and yielded himself to a sort of fanatical worship until the end
of his life, in 1680. Had he possessed a more vigorous constitution he
would have been greater as a man. He lived, in all, but forty-three
years; the last six or seven years were unproductive because of his
mental distractions, and before that, much of his time had been lost
through sickness.
The Biblia Naturæ.--It is time to ask, What, with all his talents and
prodigious application, did he leave to science? This is best answered
by an examination of the _Biblia Naturæ_, under which title all his
work was collected. His treatise on Bees and Mayflies and a few other
articles were published during his lifetime, but a large part of his
observations remained entirely unknown until they were published in
this book fifty-seven years after his death. In the folio edition it
embraces 410 pages of text and fifty-three plates, replete with figures
of original observations. It "contains about a dozen life-histories
of insects worked out in more or less detail. Of these, the mayfly
is the most famous; that on the honey-bee the most elaborate." The
greater amount of his work was in structural entomology. It is known
that he had a collection of about three thousand different species of
insects, which for that period was a very large one. There is, however,
a considerable amount of work on other animals; the fine anatomy of
the snail, the structure of the clam, the squid; observations on the
structure and development of the frog; observations on the contraction
of the muscles, etc., etc.
It is to be remembered that Swammerdam was extremely exact in all that
he did. His descriptions are models of accuracy and completeness.
Fig. 16 shows reduced sketches of his illustrations of the structure of
the snail. The upper sketch shows the central nervous system and the
nerve trunks connected therewith, and the lower figure shows the shell
and the principal muscles. This is an exceptionally good piece of
anatomization for that time, and is a fair sample of the fidelity with
which he worked out details in the structure of small animals. Besides
showing this, these figures also serve the purpose of pointing out that
Swammerdam's fine anatomical work was by no means confined to insects.
His determinations on the structure of the young frog were equally
noteworthy.
[Illustration: Fig. 16.--From Swammerdam's _Biblia Naturæ_.]
But we should have at least one illustration of his handling of insect
anatomy to compare more directly with that of Malpighi, already
given. Fig. 17 is a reduced sketch of the anatomy of the larva of an
ephemerus, showing, besides other structures, the central nervous
system in its natural position. When compared with the drawings of
Malpighi, we see there is a more masterly hand at the task, and a more
critical spirit back of the hand. The nervous system is very well done,
and the greater detail in other features shows a disposition to go into
the subject more deeply than Malpighi.
Besides working on the structure and life-histories of animals,
Swammerdam showed, experimentally, the irritability of nerves and the
response of muscles after their removal from the body. He not only
illustrates this quite fully, but seems to have had a pretty good
appreciation of the nature of the problem of the physiologist. He says:
"It is evident from the foregoing observations that a great number of
things concur in the contraction of the muscles, and that one should
be thoroughly acquainted with that wonderful machine, our body, and
the elements with which we are surrounded, to describe exactly one
single muscle and explain its action. On this occasion it would be
necessary for us to consider the atmosphere, the nature of our food,
the blood, the brain, marrow, and nerves, that most subtle matter which
instantaneously flows to the fibers, and many other things, before we
could expect to attain a sight of the perfect and certain truth."
In reference to the formation of animals within the egg, Swammerdam
was, as Malpighi, a believer in the pre-formation theory. The basis for
his position on this question will be set forth in the chapter on the
Rise of Embryology.
[Illustration: Fig. 17.--Anatomy of an Insect: Dissected and Drawn by
Swammerdam.]
There was another question in his time upon which philosophers and
scientific men were divided, which was in reference to the origin of
living organisms: Does lifeless matter, sometimes, when submitted to
heat and moisture, spring into life? Did the rats of Egypt come, as
the ancients believed, from the mud of the Nile, and do frogs and
toads have a similar origin? Do insects spring from the dew on plants?
etc., etc. The famous Redi performed his noteworthy experiments when
Swammerdam was twenty-eight years old, but opinion was divided upon
the question as to the possible spontaneous origin of life, especially
among the smaller animals. Upon this question Swammerdam took a
positive stand; he ranged himself on the side of the more scientific
naturalists against the spontaneous formation of life.
Antony van Leeuwenhoek (1632-1723)
In Leeuwenhoek we find a composed and better-balanced man. Blessed
with a vigorous constitution, he lived ninety-one years, and worked to
the end of his life. He was born in 1632, four years after Malpighi,
and five before Swammerdam; they were, then, strictly speaking,
contemporaries. He stands in contrast with the other men in being
self-taught; he did not have the advantage of a university training,
and apparently never had a master in scientific study. This lack of
systematic training shows in the desultory character of his extensive
observations. Impelled by the same gift of genius that drove his
confrères to study nature with such unexampled activity, he too
followed the path of an independent and enthusiastic investigator.
The portrait (Fig. 18) which forms a frontispiece to his _Arcana
Naturæ_ represents him at the age of sixty-three, and shows the
pleasing countenance of a firm man in vigorous health. Richardson
says: "In the face peering through the big wig there is the quiet
force of Cromwell and the delicate disdain of Spinoza." "It is a mixed
racial type, Semitic and Teutonic, a Jewish-Saxon; obstinate and yet
imaginative; its very obstinacy a virtue, saving it from flying too far
wild by its imagination."
Recent Additions to His Biography.--There was a singular scarcity
of facts in reference to Leeuwenhoek's life until 1885, when Dr.
Richardson published in _The Asclepiad_[1] the results of researches
made by Mr. A. Wynter Blyth in Leeuwenhoek's native town of Delft. I am
indebted to that article for much that follows.
His _Arcana Naturæ_ and other scientific letters contained a complete
record of his scientific activity, but "about his parentage, his
education, and his manner of making a living there was nothing but
conjecture to go upon." The few scraps of personal history were
contained in the Encyclopædia articles by Carpenter and others, and
these were wrong in sustaining the hypothesis that Leeuwenhoek was an
optician or manufacturer of lenses for the market. Although he ground
lenses for his own use, there was no need on his part of increasing
his financial resources by their sale. He held under the court a minor
office designated 'Chamberlain of the Sheriff.' The duties of the
office were those of a beadle, and were set forth in his commission,
a document still extant. The requirements were light, as was also the
salary, which amounted to about £26 a year. He held this post for
thirty-nine years, and the stipend was thereafter continued to him to
the end of his life.
Van Leeuwenhoek was derived from a good Delft family. His grandfather
and his great-grandfather were Delft brewers, and his grandmother a
brewer's daughter. The family were doubtless wealthy. His schooling
seems to have been brought to a close at the age of sixteen, when he
was "removed to a clothing business in Amsterdam, where he filled the
office of bookkeeper and cashier." After a few years he returned to
Delft, and at the age of twenty-two he married, and gave himself up
largely to studies in natural history. Six years after his marriage he
obtained the appointment mentioned above. He was twice married, but
left only one child, a daughter by his first wife. In the old church
at Delft is a monument erected by this daughter to the memory of her
father.
[Illustration: Fig. 18.--Leeuwenhoek, 1632-1723.]
He led an easy, prosperous, but withal a busy life. The microscope had
recently been invented, and for observation with that new instrument
Leeuwenhoek showed an avidity amounting to a passion.
"That he was in comfortable, if not affluent, circumstances is clear
from the character of his writings; that he was not troubled by any
very anxious and responsible duties is certain from the continuity of
his scientific work; that he could secure the services of persons of
influence is discernible from the circumstances that, in 1673, De Graaf
sent his first paper to the Royal Society of London; that in 1680 the
same society admitted him as fellow; that the directors of the East
India Company sent him specimens of natural history, and that, in 1698,
Peter the Great paid him a call to inspect his microscopes and their
revelations."
Leeuwenhoek seems to have been fascinated by the marvels of the
microscopic world, but the extent and quality of his work lifted him
above the level of the dilettante. He was not, like Malpighi and
Swammerdam, a skilled dissector, but turned his microscope in all
directions; to the mineral as well as to the vegetable and animal
kingdoms. Just when he began to use the microscope is not known; his
first publication in reference to microscopic objects did not appear
till 1673, when he was forty-one years old.
His Microscopes.--He gave good descriptions and drawings of his
instruments, and those still in existence have been described by
Carpenter and others, and in consequence we have a very good idea of
his working equipment. During his lifetime he sent as a present to the
Royal Society of London twenty-six microscopes, each provided with an
object to examine. Unfortunately, these were removed from the rooms of
the society and lost during the eighteenth century. His lenses were of
fine quality and were ground by himself. They were nearly all simple
lenses, of small size but considerable curvature, and needed to be
brought close to the object examined. He had different microscopes for
different purposes, giving a range of magnifying powers from 40 to 270
diameters and possibly higher. The number of his lenses is surprising;
he possessed not less than 247 complete microscopes, two of which were
provided with double lenses, and one with a triplet. In addition to
the above, he had 172 lenses set between plates of metal, which give
a total of 419 lenses used by him in his observations. Three were of
quartz, or rock crystal; the rest were of glass. More than one-half the
lenses were mounted in silver; three were in gold.
It is to be understood that all his microscopes were of simple
construction; no tubes, no mirror; simple pieces of metal to hold the
magnifying-glass and the objects to be examined, with screws to adjust
the position and the focus.
[Illustration: Fig. 19.--Leeuwenhoek's Microscope.
Natural size. From Photographs by Professor Nierstrasz, of Utrecht.]
The three aspects of one of Leeuwenhoek's microscopes shown in
Fig. 19 will give a very good idea of how they were constructed.
These pictures represent the actual size of the instrument. The
photographs were made by Professor Nierstrasz from the specimen in
possession of the University of Utrecht. The instrument consists of
a double copper plate in which the circular lens is inserted, and an
object-holder--represented in the right-hand lower figure as thrown
to one side. By a vertical screw the object could be elevated or
depressed, and by a transverse screw it could be brought nearer or
removed farther from the lens, and thus be brought into focus.
Fig. 20_a_ shows the way in which the microscope was arranged to
examine the circulation of blood in the transparent tail of a small
fish. The fish was placed in water in a slender glass tube, and the
latter was held in a metallic frame, to which a plate (marked _D_) was
joined, carrying the magnifying glass. The latter is indicated in the
circle above the letter _D_, near the tail-fin of the fish. The eye
was applied close to this circular magnifying-glass, which was brought
into position and adjusted by means of screws. In some instances,
he had a concave reflector with a hole in the center, in which his
magnifying-glass was inserted; in this form of instrument the objects
were illumined by reflected, and not by transmitted light.
[Illustration: Fig. 20_a._--Leeuwenhoek's Mechanism for Examining the
Circulation of the Blood.]
His Scientific Letters.--His microscopic observations were described
and sent to learned societies in the form of letters. "All or nearly
all that he did in a literary way was after the manner of an epistle,"
and his written communications were so numerous as to justify
the cognomen, "The man of many letters." "The French Academy of
Sciences, of which he was elected a corresponding member in 1697, got
twenty-seven; but the lion's share fell to the young Royal Society
of London, which in fifty years--1673-1723--received 375 letters and
papers." "The works themselves, except that they lie in the domain
of natural history, are disconnected and appear in no order of
systematized study. The philosopher was led by what transpired at any
moment to lead him."
[Illustration: Fig. 20_b_.--The Capillary Circulation. (After
Leeuwenhoek.)]
The Capillary Circulation.--In 1686 he observed the minute circulation
of the blood, and demonstrated the capillary connection between
arteries and veins, thus forging the final link in the chain of
observation showing the relation between these blood-vessels. This was
perhaps his most important observation for its bearing on physiology.
It must be remembered that Harvey had not actually seen the circulation
of the blood, which he announced in 1628. He assumed on entirely
sufficient grounds the existence of a complete circulation, but there
was wanting in his scheme the direct ocular proof of the passage of
blood from arteries to veins. This was supplied by Leeuwenhoek. Fig.
20_b_ shows one of his sketches of the capillary circulation. In his
efforts to see the circulation he tried various animals; the comb of
the young cock, the ears of white rabbits, the membraneous wing of
the bat were progressively examined. The next advance came when he
directed his microscope to the tail of the tadpole. Upon examining this
he exclaims:
"A sight presented itself more delightful than any mine eyes had ever
beheld; for here I discovered more than fifty circulations of the blood
in different places, while the animal lay quiet in the water, and I
could bring it before my microscope to my wish. For I saw not only
that in many places the blood was conveyed through exceedingly minute
vessels, from the middle of the tail toward the edges, but that each of
the vessels had a curve or turning, and carried the blood back toward
the middle of the tail, in order to be again conveyed to the heart.
Hereby it plainly appeared to me that the blood-vessels which I now saw
in the animal, and which bear the names of arteries and veins are, in
fact, one and the same; that is to say, that they are properly termed
arteries so long as they convey the blood to the furtherest extremities
of its vessels, and veins when they bring it back to the heart. And
thus it appears that an artery and a vein are one and the same vessel
prolonged or extended."
This description shows that he fully appreciated the course of the
minute vascular circulation and the nature of the communication between
arteries and veins. He afterward extended his observations to the web
of the frog's foot, the tail of young fishes and eels.
In connection with this it should be remembered that Malpighi, in
1661, observed the flow of blood in the lungs and in the mesentery of
the frog, but he made little of the discovery. Leeuwenhoek did more
with his, and gave the first clear idea of the capillary circulation.
Leeuwenhoek was anticipated also by Malpighi in reference to the
microscopic structure of the blood. (See also under Swammerdam.)
To Malpighi the corpuscles appeared to be globules of fat, while
Leeuwenhoek noted that the blood disks of birds, frogs, and fishes were
oval in outline, and those of mammals circular. He reserved the term
'globule' for those of the human body, erroneously believing them to be
spheroidal.
Other Discoveries.--Among his other discoveries bearing on physiology
and medicine may be mentioned: the branched character of heart muscles,
the stripe in voluntary muscles, the structure of the crystalline
lens, the description of spermatozoa after they had been pointed out
to him in 1674 by Hamen, a medical student in Leyden, etc. Richardson
dignified him with the title 'the founder of histology,' but this, in
view of the work of his great contemporary, Malpighi, seems to me an
overestimate.
[Illustration: Fig. 21.--Plant Cells. (From Leeuwenhoek's _Arcana
Naturæ_.)]
Turning his microscope in all directions, he examined water and found
it peopled with minute animalcules, those simple forms of animal life
propelled through the water by innumerable hair-like cilia extending
from the body like banks of oars from a galley, except that in many
cases they extend from all surfaces. He saw not only the animalcules,
but also the cilia that move their bodies.
He also discovered the Rotifers, those favorites of the amateur
microscopists, made so familiar to the general public in works like
Gosse's _Evenings at the Microscope_. He observed that when water
containing these animalcules evaporated they were reduced to fine dust,
but became alive again, after great lapses of time, by the introduction
of water.
He made many observations on the microscopic structure of plants. Fig.
21 gives a fair sample of the extent to which he observed the cellular
construction of vegetables and anticipated the cell theory. While
Malpighi's research in that field was more extensive, these sketches
from Leeuwenhoek represent very well the character of the work of the
period on the minute structures of plants.
His Theoretical Views.--It remains to say that on the two biological
questions of the day he took a decisive stand. He was a believer in
pre-formation or pre-delineation of the embryo in an extreme degree,
seeing in fancy the complete outline of both maternal and paternal
individuals in the spermatozoa, and going so far as to make sketches of
the same. But on the question of the spontaneous origin of life he took
the side that has been supported with such triumphant demonstration in
this century; namely, the side opposing the theory of the occurrence of
spontaneous generation under present conditions of life.
Comparison of the Three Men.--We see in these three gifted
contemporaries different personal characteristics. Leeuwenhoek, the
composed and strong, attaining an age of ninety-one; Malpighi, always
in feeble health, but directing his energies with rare capacity,
reaching the age of sixty-seven; while the great intensity of
Swammerdam stopped his scientific career at thirty-six and burned out
his life at the age of forty-three.
They were all original and accurate observers, but there is variation
in the kind and quality of their intellectual product. The two
university-trained men showed capacity for coherent observation; they
were both better able to direct their efforts toward some definite end;
Leeuwenhoek, with the advantages of vigorous health and long working
period, lacked the systematic training of the schools, and all his life
wrought in discursive fashion; he left no coherent piece of work of
any extent like Malpighi's _Anatome Plantarum_ or Swammerdam's _Anatomy
and Metamorphosis of Insects_.
Swammerdam was the most critical observer of the three, if we may
judge by his labors in the same field as Malpighi's on the silkworm.
His descriptions are models of accuracy and completeness, and his
anatomical work shows a higher grade of finish and completeness than
Malpighi's. Malpighi, it seems to me, did more in the sum total than
either of the others to advance the sciences of anatomy and physiology,
and through them the interests of mankind. Leeuwenhoek had larger
opportunity; he devoted himself to microscopic observations, but
he wandered over the whole field. While his observations lose all
monographic character, nevertheless they were important in opening new
fields and advancing the sciences of anatomy, physiology, botany, and
zoölogy.
The combined force of their labors marks an epoch characterized by the
acceptance of the scientific method and the establishment of a new
grade of intellectual life. Through their efforts and that of their
contemporaries of lesser note the new intellectual movement was now
well under way.
FOOTNOTES:
[Footnote 1: _Leeuwenhoek and the Rise of Histology._ The Asclepiad,
Vol. II, 1885.]
CHAPTER V
THE PROGRESS OF MINUTE ANATOMY.
The work of Malpighi, Swammerdam, and Leeuwenhoek stimulated
investigations into the structure of minute animals, and researches
in that field became a feature of the advance in the next century.
Considerable progress was made in the province of minute anatomy before
comparative anatomy grew into an independent subject.
The attractiveness of observations upon the life-histories and the
structure of insects, as shown particularly in the publications of
Malpighi and Swammerdam, made those animals the favorite objects
of study. The observers were not long in recognizing that some of
the greatest beauties of organic architecture are displayed in the
internal structure of insects. The delicate tracery of the organs,
their minuteness and perfection are well calculated to awaken surprise.
Well might those early anatomists be moved to enthusiasm over their
researches. Every excursion into this domain gave only beautiful
pictures of a mechanism of exquisite delicacy, and their wonder grew
into amazement. Here began a new train of ideas, in the unexpected
revelation that within the small compass of the body of an insect was
embraced such a complex set of organs; a complete nervous system, fine
breathing-tubes, organs of circulation, of digestion, etc., etc.
Lyonet.--The first piece of structural work after Swammerdam's to which
we must give attention is that of Lyonet, who produced in the middle
of the eighteenth century one of the most noteworthy monographs in
the field of minute anatomy. This was a work like that of Malpighi,
upon the anatomy of a single form, but it was carried out in much
greater detail. The 137 figures on the 18 plates are models of close
observation and fine execution of drawings.
[Illustration: Fig. 22.--Lyonet, 1707-1789.]
Lyonet (also written Lyonnet) was a Hollander, born in The Hague
in 1707. He was a man of varied talents, a painter, a sculptor,
an engraver, and a very gifted linguist. It is said that he was
skilled in at least eight languages; and at one time he was the
cipher secretary and confidential translator for the United Provinces
of Holland. He was educated as a lawyer, but, from interest in the
subject, devoted most of his time to engraving objects of natural
history. Among his earliest published drawings were the figures for
Lesser's _Theology of Insects_ (1742) and for Trembley's famous
treatise on _Hydra_ (1744).
His Great Monograph.--Finally Lyonet decided to branch out for himself,
and produce a monograph on insect anatomy. After some preliminary work
on the sheep-tick, he settled upon the caterpillar of the goat moth,
which lives upon the willow-tree. His work, first published in 1750,
bore the title _Traité Anatomique de la Chenille qui ronge le bois de
Saule_. In exploring the anatomy of the form chosen, he displayed not
only patience, but great skill as a dissector, while his superiority
as a draughtsman was continually shown in his sketches. He engraved
his own figures on copper. The drawings are very remarkable for the
amount of detail that they show. He dissected this form with the same
thoroughness with which medical men have dissected the human body.
The superficial muscles were carefully drawn and were then cut away
in order to expose the next underlying layer which, in turn, was
sketched and then removed. The amount of detail involved in this work
may be in part realized from the circumstance that he distinguished
4,041 separate muscles. His sketches show these muscles accurately
drawn, and the principal ones are lettered. When he came to expose the
nerves, he followed the minute branches to individual small muscles
and sketched them, not in a diagrammatic way, but as accurate drawings
from the natural object. The breathing-tubes were followed in the same
manner, and the other organs of the body were all dissected and drawn
with remarkable thoroughness. Lyonet was not trained in anatomy like
Malpighi and Swammerdam, but being a man of unusual patience and manual
dexterity, he accomplished notable results. His great quarto volume is,
however, merely a description of the figures, and lacks the insight
of a trained anatomist. His skill as a dissector is far ahead of his
knowledge of anatomy, and he becomes lost in the details of his subject.
Extraordinary Quality of the Drawings.--A few figures will serve to
illustrate the character of his work, but the reduced reproductions
which follow can not do justice to the copper plates of the original.
Fig. 23 gives a view of the external appearance of the caterpillar
which was dissected. When the skin was removed from the outside the
muscles came into view, as shown in Fig. 24. This is a view from the
ventral side of the animal. On the left side the more superficial
muscles show, and on the right the next deeper layer.
Fig. 25 shows his dissection of the nerves. In this figure the muscles
are indicated in outline, and the distribution of nerves to particular
muscles is shown.
[Illustration: Fig. 23.--Larva of the Willow Moth. (From Lyonet's
Monograph, 1750.)]
Lyonet's dissection of the head is an extraordinary feat. The entire
head is not more than a quarter of an inch in diameter, but in a series
of seven dissections he shows all of the internal organs in the head.
Fig. 26 shows two sketches exhibiting the nervous ganglia, the air
tubes, and muscles of the head in their natural position.
Fig. 27 shows the nervous system of the head, including the extremely
fine nervous masses which are designated the sympathetic nervous system.
[Illustration: Fig. 24.
Fig. 24.--Muscles of the Larva of the Willow Moth. (From Lyonet's
Monograph.)]
[Illustration: Fig. 25.
Fig. 25.--Central Nervous System and Nerves of the Same.]
The extraordinary character of the drawings in Lyonet's monograph
created a sensation. The existence of such complicated structures
within the body of an insect was discredited, and, furthermore, some
of his critics declared that even if such a fine organization existed,
it would be beyond human possibilities to expose the details as shown
in his sketches. Accordingly, Lyonet was accused of drawing on his
imagination. In order to silence his critics he published in the
second edition of his work, in 1752, drawings of his instruments and a
description of his methods.
[Illustration: Fig. 26.--Dissection of the Head of the Larva of the
Willow Moth.]
Lyonet intended to work out the anatomy of the chrysalis and the adult
form of the same animal. In pursuance of this plan, he made many
dissections and drawings, but, at the age of sixty, on account of the
condition of his eyes, he was obliged to stop all close work, and his
project remained unfinished. The sketches which he had accumulated were
published later, but they fall far short of those illustrating the
_Traité Anatomique_. Lyonet died in 1789, at the age of eighty-one.
[Illustration: Fig. 27.--The Brain and Head Nerves of the Same Animal.]
Roesel, Réaumur, and De Geer on Insect Life.--We must also take note
of the fact that, running parallel with this work on the anatomy of
insects, observations and publications had gone forward on form,
habits, and metamorphosis of insects, that did more to advance the
knowledge of insect life than Lyonet's researches. Roesel, in Germany,
Réaumur, in France, and De Geer, in Sweden, were all distinguished
observers in this line. Their works are voluminous and are well
illustrated. Those of Réaumur and De Geer took the current French title
of _Mémoires pour servir à l'Histoire des Insectes_. The plates with
which the collected publications of each of the three men are provided
show many sketches of external form and details of external anatomy,
but very few illustrations of internal anatomy occur. The sketches of
Roesel in particular are worthy of examination at the present time.
Some of his masterly figures in color are fine examples of the art
of painting in miniature. The name of Roesel (Fig. 28) is connected
also with the earliest observations of protoplasm and with a notable
publication on the Batrachians.
Réaumur (Fig. 29), who was distinguished for kindly and amiable
personal qualities, was also an important man in his influence upon
the progress of science. He was both physician and naturalist; he
made experiments upon the physiology of digestion, which aided in the
understanding of that process; he invented the thermometer which bears
his name, and did other services for the advancement of science.
[Illustration: Fig. 28.--Roesel von Rosenhof, 1705-1759.]
Straus-Dürckheim's Monograph on Insect Anatomy.--Insect anatomy
continued to attract a number of observers, but we must go forward
into the nineteenth century before we find the subject taking a new
direction and merging into its modern phase. The remarkable monograph
of Straus-Dürckheim represents the next step in the development of
insect anatomy toward the position that it occupies to-day. His aim
is clearly indicated in the opening sentence of his preface: "Having
been for a long time occupied with the study of articulated animals, I
propose to publish a general work upon the comparative anatomy of that
branch of the animal kingdom." He was working under the influence of
Cuvier, who, some years earlier, had founded the science of comparative
anatomy and whom he recognized as his great exemplar. His work is
dedicated to Cuvier, and is accompanied by a letter to that great
anatomist expressing his thanks for encouragement and assistance.
[Illustration: Fig 29.--Réaumur, 1683-1757.]
Straus-Dürckheim (1790-1865) intended that the general considerations
should be the chief feature of his monograph, but they failed in this
particular because, with the further developments in anatomy, including
embryology and the cell-theory, his general discussions regarding the
articulated animals became obsolete. The chief value of his work now
lies in what he considered its secondary feature, _viz._, that of
the detailed anatomy of the cockchafer, one of the common beetles of
Europe. Owing to changed conditions, therefore, it takes rank with
the work of Malpighi and Lyonet, as a monograph on a single form.
Originally he had intended to publish a series of monographs on the
structure of insects typical of the different families, but that upon
the cockchafer was the only one completed.
Comparison with the Sketches of Lyonet.--The quality of this work
upon the anatomy of the cockchafer was excellent, and in 1824 it was
accepted and crowned by the Royal Institute of France. The finely
lithographed plates were prepared at the expense of the Institute, and
the book was published in 1828 with the following cumbersome title:
_Considérations Générales sur l'Anatomie comparée des Animaux Articulés
auxquelles on a joint l'Anatomie Descriptive du Melolontha Vulgaris
(Hanneton) donnée comme example de l'Organisation des Coléoptères_.
The 109 sketches with which the plates are adorned are very beautiful,
but one who compares his drawings, figure by figure, with those of
Lyonet can not fail to see that those of the latter are more detailed
and represent a more careful dissection. One illustration from
Straus-Dürckheim will suffice to bring the achievements of the two men
into comparison.
Fig. 30 shows his sketch of the anatomy of the central nervous system.
He undertakes to show only the main branches of the nerves going to
the different segments of the body, while Lyonet brings to view the
distribution of the minute terminals to particular muscles. Comparison
of other figures--notably that of the dissection of the head--will
bring out the same point, _viz._, that Lyonet was more detailed than
Straus-Dürckheim in his explorations of the anatomy of insects, and
fully as accurate in drawing what he had seen.
Nevertheless, the work of Straus-Dürckheim is conceived in a different
spirit, and is the first serious attempt to make insect anatomy broadly
comparative.
Comment.--Such researches as those of Swammerdam, Lyonet, and
Straus-Dürckheim represent a phase in the progress of the study of
nature. Perhaps their chief value lies in the fact that they embody
the idea of critical observation. As examples of faithful, accurate
observations the researches helped to bring about that close study
which is our only means of getting at basal facts. These men were all
enlisted in the crusade against superficial observation. This had to
have its beginning, and when we witness it in its early stages, before
the researches have become illuminated by great ideas, the prodigious
effort involved in the detailed researches may seem to be poorly
expended labor. Nevertheless, though the writings of these pioneers
have become obsolete, their work was of importance in helping to lift
observations upon nature to a higher level.
Dufour.--Léon Dufour extended the work of Straus-Dürckheim by
publishing, between 1831 and 1834, researches upon the anatomy and
physiology of different families of insects. His aim was to found
a general science of insect anatomy. That he was unsuccessful in
accomplishing this was owing partly to the absence of embryology and
histology from his method of study.
Newport.--The thing most needed now was not greater devotion to details
and a willingness to work, but a broadening of the horizon of ideas.
This arrived in the Englishman Newport, who was remarkable not only for
his skill as a dissector, but for his recognition of the importance
of embryology in elucidating the problems of structure. His article
"Insecta" in Todd's _Cyclopædia of Anatomy and Physiology_, in 1841,
and his papers in the _Philosophical Transactions_ of the Royal Society
contain this new kind of research. Von Baer had founded embryology
by his great work on the development of animals in 1828, before the
investigations of Dufour, but it was reserved for Newport to recognize
its great importance and to apply it to insect anatomy. He saw clearly
that, in order to comprehend his problems, the anatomist must take into
account the process of building the body, as well as the completed
architecture of the adult. The introduction of this important idea made
his achievement a distinct advance beyond that of his predecessors.
[Illustration: Fig. 30.--Nervous System of the Cockchafer. (From
Straus-Dürckheim's Monograph, 1828.)]
Leydig.--Just as Newport was publishing his conclusions the cell-theory
was established (in 1838-39); and this was destined to furnish the
basis for a new advance. The influence of the doctrine that all tissues
are composed of similar vital units, called cells, was far-reaching.
Investigators began to apply the idea in all directions, and there
resulted a new department of anatomy, called histology. The subject
of insect histology was an unworked field, but manifestly one of
importance. Franz Leydig (for portrait see p. 175) entered the new
territory with enthusiasm, and through his extensive investigations
all structural studies upon insects assumed a new aspect. In 1864
appeared his _Vom Bau des Thierchen Körpers_, which, together with
his special articles, created a new kind of insect anatomy based upon
the microscopic study of tissues. The application of this method of
investigation is easy to see; just as it is impossible to understand
the working of a machine without a knowledge of its construction, so a
knowledge of the working units of an organ is necessary to comprehend
its action. For illustration, it is perfectly evident that we can not
understand what is taking place in an organ for receiving sensory
impressions without first understanding its mechanism and the nature
of the connections between it and the central part of the nervous
system. The sensory organ is on the surface in order more readily to
receive impressions from the outside world. The sensory cells are
also modifications of surface cells, and, as a preliminary step to
understanding their particular office, we must know the line along
which they have become modified to fit them to receive stimulation.
Then, if we attempt to follow in the imagination the way by which the
surface stimulations reach the central nervous system and affect it,
we must investigate all the connections. It thus appears that we must
know the intimate structure of an organ in order to understand its
physiology. Leydig supplied this kind of information for many organs of
insects. In his investigations we see the foundation of that delicate
work upon the microscopic structure of insects which is still going
forward.
Summary.--In this brief sketch we have seen that the study of insect
anatomy, beginning with that of Malpighi and Swammerdam, was lifted to
a plane of greater exactitude by Lyonet and Straus-Dürckheim. It was
further broadened by the researches of Dufour, and began to take on its
modern aspects, first, through the labors of Newport, who introduced
embryology as a feature of investigation, and, finally, through
Leydig's step in introducing histology. In the combination of the work
of these two observers, the subject for the first time reached its
proper position.
The studies of minute structure in the seventeenth and eighteenth
centuries were by no means confined to insects; investigations were
made upon a number of other forms. Trembley, in the time of Lyonet,
produced his noteworthy memoirs upon the small fresh-water hydra
(_Mémoires pour servir à l'histoire des polypes d'eau douce_, 1744);
the illustrations for which, as already stated, were prepared by
Lyonet. The structure of snails and other mollusks, of tadpoles,
frogs, and other batrachia, was also investigated. We have seen that
Swammerdam, in the seventeenth century, had begun observations upon
the anatomy of tadpoles, frogs, and snails, and also upon the minute
crustacea commonly called water-fleas, which are just large enough
to be distinguished by the unaided eye. We should remember also that
in the same period the microscopic structure of plants began to be
investigated, notably by Grew, Malpighi, and Leeuwenhoek (see Chapter
IV).
In addition to those essays into minute anatomy, in which scalpel
and scissors were employed, an endeavor of more subtle difficulty
made its appeal; there were forms of animal life of still smaller
size and simpler organization that began to engage the attention
of microscopists. A brief account of the discovery and subsequent
observation of these microscopic animalcula will now occupy our
attention.
The Discovery of the Simplest Animals and the Progress of Observations
upon Them
These single-celled animals, since 1845 called protozoa, have become
of unusual interest to biologists, because in them the processes of
life are reduced to their simplest expression. The vital activities
taking place in the bodies of higher animals are too complicated and
too intricately mixed to admit of clear analysis, and, long ago,
physiologists learned that the quest for explanations of living
activities lay along the line of investigating them in their most
rudimentary expression. The practical recognition of this is seen in
our recent text-books upon human physiology, which commonly begin with
discussions of the life of these simplest organisms. That greatest
of all text-books on general physiology, written by Max Verworn, is
devoted largely to experimental studies upon these simple organisms as
containing the key to the similar activities (carried on in a higher
degree) in higher animals. This group of animals is so important as
a field of experimental observation that a brief account of their
discovery and the progress of knowledge in reference to them will be in
place in this chapter.
Discovery of the Protozoa.--Leeuwenhoek left so little unnoticed in the
microscopic world that we are prepared to find that he made the first
recorded observations upon these animalcula. His earliest observations
were communicated by letter to the Royal Society of London, and were
published in their _Transactions_ in 1677. It is very interesting to
read his descriptions expressed in the archaic language of the time.
The following quotation from a Dutch letter turned into English will
suffice to give the flavor of his writing:
"In the year 1675 I discovered living creatures in rainwater which had
stood but four days in a new earthen pot, glazed blew within. This
invited me to view the water with great attention, especially those
little animals appearing to me ten thousand times less than those
represented by Mons. Swammerdam, and by him called water-fleas or
water-lice, which may be perceived in the water with the naked eye.
The first sorte by me discovered in the said water, I divers times
observed to consist of five, six, seven or eight clear globules,
without being able to discover any film that held them together or
contained them. When these _animalcula_, or living atoms, did move
they put forth two little horns, continually moving themselves; the
place between these two horns was flat, though the rest of the body was
roundish, sharpening a little towards the end, where they had a tayle,
near four times the length of the whole body, of the thickness (by my
microscope) of a spider's web; at the end of which appeared a globule,
of the bigness of one of those which made up the body; which tayle I
could not perceive even in very clear water to be mov'd by them. These
little creatures, if they chanced to light upon the least filament or
string, or other such particle, of which there are many in the water,
especially after it has stood some days, they stook entangled therein,
extending their body in a long round, and striving to dis-entangle
their tayle; whereby it came to pass, that their whole body lept
back towards the globule of the tayle, which then rolled together
serpent-like, and after the manner of copper or iron wire, that having
been wound around a stick, and unwound again, retains those windings
and turnings," etc.[2]
Any one who has examined under the microscope the well-known
bell-animalcule will recognize in this first description of it, the
stalk, and its form after contraction under the designation of a 'tayle
which retains those windings and turnings.'
There are many other descriptions, but the one given is typical of
the others. He found the little animals in water, in infusions of
pepper, and other vegetable substances, and on that account they came
soon to be designated infusoria. His observations were not at first
accompanied by sketches, but in 1711 he sent some drawings with further
descriptions.
O. Fr. Müller.--These animalcula became favorite objects of microscopic
study. Descriptions began to accumulate and drawings to be made
until it became evident that there were many different kinds. It
was, however, more than one hundred years after their discovery by
Leeuwenhoek that the first standard work devoted exclusively to these
animalcula was published. This treatise by O. Fr. Müller was published
in 1786 under the title of _Animalcula Infusoria_. The circumstance
that this volume of quarto size had 367 pages of description with 50
plates of sketches will give some indication of the number of protozoa
known at that time.
Ehrenberg.--Observations in this domain kept accumulating, but the next
publication necessary to mention is that of Ehrenberg (1795-1876). This
scientific traveler and eminent observer was the author of several
works. He was one of the early observers of nerve fibres and of
many other structures of the animal frame. His book of the protozoa
is a beautifully illustrated monograph consisting of 532 pages of
letterpress and 69 plates of folio size. It was published in 1836
under the German title of _Die Infusionsthierchen als Vollkommene
Organismen_, or "The Infusoria as Perfect Organisms." The animalcula
which he so faithfully represented in his sketches have the habit,
when feeding, of taking into the body collections of food-particles,
aggregated into spherical globules or food vacuoles. These are
distinctly separated, and slowly circulate around the single-celled
body while they are undergoing digestion. In a fully fed animal these
food-vacuoles occupy different positions, and are enclosed in globular
spaces in the protoplasm, an adjustment that gave Ehrenberg the notion
that the animals possessed many stomachs. Accordingly he gave to them
the name "Polygastrica," and assigned to them a much higher grade of
organization than they really possess. These conclusions, based on
the general arrangement of food globules, seem very curious to us
to-day. His publication was almost simultaneous with the announcement
of the cell-theory (1838-39), the acceptance of which was destined to
overthrow his conception of the protozoa, and to make it clear that
tissues and organs can belong only to multicellular organisms.
Ehrenberg (Fig. 31) was a man of great scientific attainments, and
notwithstanding the grotesqueness of some of his conclusions, was held
in high esteem as a scientific investigator. His observations were
accurate, and the beautiful figures with which his work on the protozoa
is embellished were executed with such fidelity regarding fine points
of microscopic detail that they are of value to-day.
Dujardin, whom we shall soon come to know as the discoverer of
protoplasm, successfully combated the conclusions of Ehrenberg
regarding the organization of the protozoa. For a time the great
German scientist tried to maintain his point, that the infusoria have
many stomachs, but this was completely swept away, and finally the
contention of Von Siebold was adopted to the effect that these animals
are each composed of a single cell.
[Illustration: Fig. 31.--Ehrenberg, 1795-1876.]
In 1845 Stein is engrossed in proposing names for the suborders of
infusoria based upon the distribution of cilia upon their bodies. This
simple method of classification, as well as the names introduced by
Stein, is still in use.
From Stein to Bütschli, one of the present authorities on the group,
there were many workers, but with the studies of Bütschli on protozoa
we enter the modern epoch.
The importance of these animals in affording a field for
experimentation on the simplest expressions of life has already
been indicated. Many interesting problems have arisen in connection
with recent studies of them. The group embraces the very simplest
manifestations of animal life, and the experiments upon the different
forms light the way for studies of the vital activities of the higher
animals. Some of the protozoa are disease-producing; as the microbe
of malaria, of the sleeping sickness, etc., while, as is well known,
most diseases that have been traced to specific germs are caused by
plants--the bacteria. Many experiments of Maupas, Caulkins and others
have a bearing upon the discussions regarding the immortality of the
protozoa, an idea which was at one time a feature of Weissmann's theory
of heredity. Binet and others have discussed the evidences of psychic
life in these micro-organisms, and the daily activity of a protozoan
became the field for observation and record in an American laboratory
of psychology. The extensive studies of Jennings on the nature of their
responses to stimulations form a basis for some of the discussions on
animal behavior.
FOOTNOTES:
[Footnote 2: Kent's Manual of the Infusoria, Vol. I, p. 3. Quotation
from the _Philosophical Transactions_ for the year 1677.]
CHAPTER VI
LINNÆUS AND SCIENTIFIC NATURAL HISTORY
We turn now from the purely anatomical side to consider the parallel
development of the classification of animals and of plants. Descriptive
natural history reached a very low level in the early Christian
centuries, and remained there throughout the Middle Ages. The return to
the writings of Aristotle was the first influence tending to lift it
to the position from which it had fallen. After the decline of ancient
civilization there was a period in which the writers of classical
antiquity were not read. Not only were the writings of the ancient
philosophers neglected, but so also were those of the literary men as
well, the poets, the story-tellers, and the historians. As related
in Chapter I, there were no observations of animated nature, and the
growing tendency of the educated classes to envelop themselves in
metaphysical speculations was a feature of intellectual life.
The Physiologus or Sacred Natural History.--During this period of crude
fancy, with a fog of mysticism obscuring all phenomena of nature,
there existed a peculiar kind of natural history that was produced
under theological influence. The manuscripts in which this sacred
natural history was embodied exist in various forms and in about a
dozen languages of Eastern and Western Europe. The writings are known
under the general title of the Physiologus, or the Bestiarius. This
served for nearly a thousand years as the principal source of thought
regarding natural history. It contains accounts of animals mentioned
in the Bible and others of a purely mythical character. These are
made to be symbolical of religious beliefs, and are often accompanied
by quotations of texts and by moral reflections. The phoenix rising
from its ashes typifies the resurrection of Christ. In reference to
young lions, the _Physiologus_ says: "The lioness giveth birth to cubs
which remain three days without life. Then cometh the lion, breatheth
upon them, and bringeth them to life.... Thus it is that Jesus Christ
during three days was deprived of life, but God the Father raised
him gloriously." (Quoted from White, p. 35.) Besides forty or fifty
common animals, the unicorn and the dragon of the Scriptures, and the
fabled basilisk and phoenix of secular writings are described, and
morals are drawn from the stories about them. Some of the accounts of
animals, as the lion, the panther, the serpent, the weasel, etc., etc.,
are so curious that, if space permitted, it would be interesting to
quote them; but that would keep us too long from following the rise of
scientific natural history from this basis.
For a long time the religious character of the contemplations of nature
was emphasized and the prevalence of theological influence in natural
history is shown in various titles, as Lesser's _Theology of Insects_,
Swammerdam's _Biblia Naturæ_, Spallanzani's _Tracts_, etc.
The zoölogy of the _Physiologus_ was of a much lower grade than any we
know about among the ancients, and it is a curious fact that progress
was made by returning to the natural history of fifteen centuries in
the past. The translation of Aristotle's writings upon animals, and
the disposition to read them, mark this advance. When, in the Middle
Ages, the boundaries of interest began to be extended, it came like
an entirely new discovery, to find in the writings of the ancients a
storehouse of philosophic thought and a higher grade of learning than
that of the period. The translation and recopying of the writers of
classical antiquity was, therefore, an important step in the revival
of learning. These writings were so much above the thought of the time
that the belief was naturally created that the ancients had digested
all learning, and they were pointed to as unfailing authorities in
matters of science.
The Return to the Science of the Ancients.--The return to Aristotle
was wholesome, and under its influence men turned their attention once
more to real animals. Comments upon Aristotle began to be made, and in
course of time independent treatises upon animals began to appear. One
of the first to modify Aristotle to any purpose was Edward Wotton, the
English physician, who published in 1552 a book on the distinguishing
characteristics of animals (_De Differentiis Animalium_). This was a
complete treatise on the zoölogy of the period, including an account of
the different races of mankind. It was beautifully printed in Paris,
and was dedicated to Edward VI. Although embracing ten books, it was
by no means so ponderous as were some of the treatises that followed
it. The work was based upon Aristotle, but the author introduced new
matter, and also added the group of zoöphytes, or plant-like animals of
the sea.
Gesner.--The next to reach a distinctly higher plane was Conrad Gesner
(1516-1565), the Swiss, who was a contemporary of Vesalius. He was
a practising physician who, in 1553, was made professor of natural
history in Zurich. A man of extraordinary talent and learning, he
turned out an astonishing quantity of work. Besides accomplishing much
in scientific lines, he translated from Greek, Arabic, and Hebrew, and
published in twenty volumes a universal catalogue of all works known
in Latin, Greek, and Hebrew, either printed or in manuscript form. In
the domain of natural history he began to look critically at animals
with a view to describing them, and to collect with zealous care new
observations upon their habits. His great work on natural history
(_Historia Animalium_) began to appear in 1551, when he was thirty-five
years of age, and four of the five volumes were published by 1556.
The fifth volume was not published until 1587, twenty-two years after
his death. The complete work consists of about "4,500 folio pages,"
profusely illustrated with good figures. The edition which the writer
has before him--that of 1585-1604--embraces 3,200 pages of text and 953
figures.
Brooks says: "One of Gesner's greatest services to natural science is
the introduction of good illustrations, which he gives his reader by
hundreds." He was so exacting about the quality of his illustrations
that his critical supervision of the work of artists and engravers had
its influence upon contemporary art. Some of the best woodcuts of the
period are found in his work. His friend Albrecht Dürer supplied one of
the originals--the drawing of the rhinoceros--and it is interesting to
note that it is by no means the best, a circumstance which indicates
how effectively Gesner held his engraver and draughtsman up to fine
work. He was also careful to mold his writing into graceful form, and
this, combined with the illustrations, "made science attractive without
sacrificing its dignity, and thus became a great educational influence."
In preparing his work he sifted the writings of about two hundred
and fifty authors, and while his book is largely a compilation, it
is enriched with many observations of his own. His descriptions are
verbose, but discriminating in separating facts and observations
from fables and speculations. He could not entirely escape from old
traditions. There are retained in his book pictures of the sea-serpent,
the mermaids, and a few other fanciful and grotesque sketches, but
for the most part the drawings are made from the natural objects. The
descriptions are in several parts of his work alphabetically arranged,
for convenience of reference, and thus animals that were closely
related are often widely separated.
Gesner (Fig. 32) sacrificed his life to professional zeal during the
prevalence of the plague in Zurich in 1564. Having greatly overworked
in the care of the sick, he was seized with the disease, and died at
the age of forty-nine.
Considered from the standpoint of descriptions and illustrations,
Gesner's _Historia Animalium_ remained for a long time the best work in
zoölogy. He was the best zoölogist between Aristotle and John Ray, the
immediate predecessor of Linnæus.
[Illustration: Fig. 32.--Gesner 1516-1565.]
Jonston and Aldrovandi.--At about the same period as Gesner's work
there appeared two other voluminous publications, which are well
known--those of Jonston, the Scot (_Historia Animalium_, 1549-1553),
and Aldrovandi, the Italian (_Opera_, 1599-1606). The former consisted
of four folio volumes, and the latter of thirteen, of ponderous size,
to which was added a fourteenth on plants. Jonston's works were
translated, and were better known in England than those of Gesner and
Aldrovandi. The wood-engravings in Aldrovandi's volume are coarser than
those of Gesner, and are by no means so lifelike. In the Institute at
Bologna are preserved twenty volumes of figures of animals in color,
which were the originals from which the engravings were made. These are
said to be much superior to the reproductions. The encyclopædic nature
of the writings of Gesner, Aldrovandi, and Jonston has given rise to
the convenient and expressive title of the encyclopædists.
Ray.--John Ray, the forerunner of Linnæus, built upon the foundations
of Gesner and others, and raised the natural-history edifice a tier
higher. He greatly reduced the bulk of publications on natural history,
sifting from Gesner and Aldrovandi their irrelevancies, and thereby
giving a more modern tone to scientific writings. He was the son of
a blacksmith, and was born in southern England in 1628. The original
form of the family name was Wray. He was graduated at the University
of Cambridge, and became a fellow of Trinity College. Here he formed a
friendship with Francis Willughby, a young man of wealth whose tastes
for natural history were like his own. This association proved a happy
one for both parties. Ray had taken orders in the Church of England,
and held his university position as a cleric; but, from conscientious
scruples, he resigned his fellowship in 1662. Thereafter he received
financial assistance from Willughby, and the two men traveled
extensively in Great Britain and on the Continent, with the view of
investigating the natural history of the places that they visited. On
these excursions Willughby gave particular attention to animals and
Ray to plants. Of Ray's several publications in botany, his _Historia
Plantarum_ in three volumes (1686-1704) is the most extensive. In
another work, as early as 1682, he had proposed a new classification
of plants, which in the next century was adopted by Jussieu, and which
gives Ray a place in the history of botany.
[Illustration: Fig. 33.--John Ray, 1628-1705.]
Willughby died in 1662, at the age of thirty-eight, leaving an annuity
to Ray, and charging him with the education of his two sons, and the
editing of his manuscripts. Ray performed these duties as a faithful
friend and in a generous spirit. He edited and published Willughby's
book on birds (1678) and fishes (1686) with important additions of his
own, for which he sought no credit.
After completing his tasks as the literary executor of Willughby,
he returned in 1678 to his birthplace and continued his studies in
natural history. In 1691 he published "The Wisdom of God manifested in
the Works of the Creation," which was often reprinted, and became the
forerunner of the works on natural theology like Paley's, etc. This was
an amplification of ideas he had embodied in a sermon thirty-one years
earlier, and which at that time attracted much notice. He now devoted
himself largely to the study of animals, and in 1693 published a work
on the quadrupeds and serpents, a work which gave him high rank in the
history of the classification of animals. He died in 1705, but he had
accomplished much good work, and was not forgotten. In 1844 there was
founded, in London, in his memory, the Ray Society for the publication
of rare books on botany and zoölogy.
Ray's Idea of Species.--One of the features of Ray's work, in the
light of subsequent development, is of special interest, and that is
his limiting of species. He was the first to introduce into natural
history an exact conception of species. Before his time the word had
been used in an indefinite sense to embrace groups of greater or less
extent, but Ray applied it to individuals derived from similar parents,
thus making the term species stand for a particular kind of animal or
plant. He noted some variations among species, and did not assign to
them that unvarying and constant character ascribed to them by Linnæus
and his followers. Ray also made use of anatomy as the foundation
for zoölogical classification, and introduced great precision and
clearness into his definitions of groups of animals and plants. In the
particulars indicated above he represents a great advance beyond any of
his precursors, and marks the parting of the ways between mediæval and
modern natural history.
In Germany Klein (1685-1759) elaborated a system of classification
embracing the entire animal kingdom. His studies were numerous, and
his system would have been of much wider influence in molding natural
history had it not been overshadowed by that of Linnæus.
Linnæus or Linné.--The service of Linnæus to natural history was
unique. The large number of specimens of animals and plants, ever
increasing through the collections of travelers and naturalists, were
in a confused state, and there was great ambiguity arising from the
lack of a methodical way of arranging and naming them. They were known
by verbose descriptions and local names. No scheme had as yet been
devised for securing uniformity in applying names to them. The same
animal and plant had different names in the different sections of a
country, and often different plants and animals had the same name.
In different countries, also, their names were greatly diversified.
What was especially needed was some great organizing mind to catalogue
the animals and plants in a systematic way, and to give to natural
science a common language. Linnæus possessed this methodizing mind and
supplied the need. While he did little to deepen the knowledge of the
organization of animal and plant life, he did much to extend the number
of known forms; he simplified the problem of cataloguing them, and he
invented a simple method of naming them which was adopted throughout
the world. By a happy stroke he gave to biology a new language that
remains in use to-day. The tremendous influence of this may be realized
when we remember that naturalists everywhere use identical names for
the same animals and plants. The residents of Japan, of Italy, of
Spain, of all the world, in fact, as was just said, employ the same
Latin names in classifying organic forms.
He also inspired many students with a love for natural history and gave
an impulse to the advance of that science which was long felt. We can
not gainsay that a higher class of service has been rendered by those
of philosophic mind devoted to the pursuit of comparative anatomy,
but the step of Linnæus was a necessary one, and aided greatly in the
progress of natural history. Without this step the discoveries and
observations of others would not have been so readily understood, and
had it not been for his organizing force all natural science would
have been held back for want of a common language. A close scrutiny of
the practice among naturalists in the time of Linnæus shows that he
did not actually invent the binomial nomenclature, but by adopting the
suggestions of others he elaborated the system of classification and
brought the new language into common use.
Personal History.--Leaving for the present the system of Linnæus, we
shall give attention to the personal history of the man. The great
Swedish naturalist was born in Rashult in 1707. His father was the
pastor of the village, and intended his eldest son, Carl, for the same
high calling. The original family name was Ignomarsen, but it had been
changed to Lindelius, from a tall linden-tree growing in that part of
the country. In 1761 a patent of nobility was granted by the crown to
Linnæus, and thereafter he was styled Carl von Linné.
His father's resources were very limited, but he managed to send his
son to school, though it must be confessed that young Linnæus showed
little liking for the ordinary branches of instruction. His time
was spent in collecting natural-history specimens, and his mind was
engaged in thinking about them. The reports of his low scholarship
and the statement of one of his teachers that he showed no aptitude
for learning were so disappointing to his father that, in 1726, he
prepared to apprentice Carl to a shoemaker, but was prevented from
doing so through the encouragement of a doctor who, being able to
appreciate the quality of mind possessed by the young Linnæus, advised
allowing him to study medicine instead of preparing for theology.
Accordingly, with a sum amounting to about $40, all his father could
spare, he set off for the University of Lund, to pursue the study of
medicine. He soon transferred to the University of Upsala, where the
advantages were greater. His poverty placed him under the greatest
straits for the necessities of life, and he enjoyed no luxuries. While
in the university he mended his shoes, and the shoes which were given
to him by some of his companions, with paper and birch-bark, to keep
his feet from the damp earth. But his means did not permit of his
taking his degree at Upsala, and it was not until eight years later, in
1735, that he received his degree in Holland.
At Upsala he was relieved from his extreme poverty by obtaining an
assistant's position, and so great was his knowledge of plants that he
was delegated to read the lectures of the aged professor of botany,
Rudbeck.
In 1732 he was chosen by the Royal Society of Upsala to visit Lapland
as a collector and observer, and left the university without his
degree. On returning to Upsala, his lack of funds made itself again
painfully felt, and he undertook to support himself by giving public
lectures on botany, chemistry, and mineralogy. He secured hearers, but
the continuance of his lectures was prevented by one of his rivals
on the ground that Linnæus had no degree, and was therefore legally
disqualified from taking pay for instruction. Presently he became
tutor and traveling companion of a wealthy baron, the governor of the
province of Dalecarlia, but this employment was temporary.
Helped by His Fiancée.--His friends advised him to secure his medical
degree and settle as a practitioner. Although he lacked the necessary
funds, one circumstance contributed to bring about this end: he had
formed an attachment for the daughter of a wealthy physician, named
Moré or Moræus, and on applying for her hand in marriage, her father
made it a condition of his consent that Linnæus should take his
medical degree and establish himself in the practice of medicine. The
young lady, who was thrifty as well as handsome, offered her savings,
amounting to one hundred dollars (Swedish), to her lover. He succeeded
in adding to this sum by his own exertions, and with thirty-six
Swedish ducats set off for Holland to qualify for his degree. He had
practically met the requirements for the medical degree by his previous
studies, and after a month's residence at the University of Hardewyk,
his thesis was accepted and he was granted the degree in June, 1735, in
the twenty-eighth year of his age.
Instead of returning at once to Sweden, he went to Leyden, and made the
acquaintance of several well-known scientific men. He continued his
botanical studies with great energy, and now began to reap the benefits
of his earlier devotion to natural history. His heart-breaking and
harassing struggles were now over.
The Systema Naturæ.--He had in his possession the manuscript of his
_Systema Naturæ_, and with the encouragement of his new friends
it was published in the same year. The first edition (1735) of
that notable work, which was afterward to bring him so much fame,
consisted of twelve printed folio pages. It was merely an outline of
the arrangements of plants, animals, and minerals in a methodical
catalogue. This work passed through twelve editions during his
lifetime, the last one appearing in 1768. After the first edition,
the books were printed in octavo form, and in the later editions were
greatly enlarged. A copy of the first edition was sent to Boerhaave,
the most distinguished professor in the University of Leyden, and
secured for Linnæus an interview with that distinguished physician,
who treated him with consideration and encouraged him in his work.
Boerhaave was already old, and had not long to live; and when Linnæus
was about to leave Holland in 1738, he admitted him to his sick-chamber
and bade him a most affectionate adieu, and encouraged him to further
work by most kindly and appreciative expressions.
Through the influence of Boerhaave, Linnæus became the medical
attendant of Cliffort, the burgomaster at Amsterdam, who had a large
botanic garden. Cliffort, being desirous of extending his collections,
sent Linnæus to England, where he met Sir Hans Sloane and other eminent
scientific men of Great Britain. After a short period he returned
to Holland, and in 1737 brought out the _Genera Plantarum_, a very
original work, containing an analysis of all the genera of plants. He
had previously published, besides the _Systema Naturæ_, his _Fundamenta
Botanica_, 1735, and _Bibliotheca Botanica_, 1736, and these works
served to spread his fame as a botanist throughout Europe.
His Wide Recognition.--An illustration of his wide recognition is
afforded by an anecdote of his first visit to Paris in 1738. "On his
arrival he went first to the Garden of Plants, where Bernard de Jussieu
was describing some exotics in Latin. He entered without opportunity to
introduce himself. There was one plant which the demonstrator had not
yet determined, and which seemed to puzzle him. The Swede looked on in
silence, but observing the hesitation of the learned professor, cried
out '_Hæc planta faciem Americanam habet_.' 'It has the appearance
of an American plant.' Jussieu, surprised, turned about quickly and
exclaimed 'You are Linnæus.' 'I am, sir,' was the reply. The lecture
was stopped, and Bernard gave the learned stranger an affectionate
welcome."
Return to Sweden.--After an absence of three and one-half years,
Linnæus returned to his native country in 1738, and soon after was
married to the young woman who had assisted him and had waited for him
so loyally. He settled in Stockholm and began the practice of medicine.
In the period of his absence he had accomplished much: visited
Holland, England, and France, formed the acquaintance of many eminent
naturalists, obtained his medical degree, published numerous works on
botany, and extended his fame over all Europe. In Stockholm, however,
he was for a time neglected, and he would have left his native country
in disgust had it not been for the dissuasion of his wife.
Professor in Upsala.--In 1741 he was elected professor of anatomy in
the University of Upsala, but by a happy stroke was able to exchange
that position for the professorship of botany, materia medica, and
natural history that had fallen to his former rival, Rosen. Linnæus
was now in his proper element; he had opportunity to lecture on those
subjects to which he had been devotedly attached all his life, and he
entered upon the work with enthusiasm.
He attracted numerous students by the power of his personal qualities
and the excellence of his lectures. He became the most popular
professor in the University of Upsala, and, owing to his drawing power,
the attendance at the university was greatly increased. In 1749 he
had 140 students devoted to studies in natural history. The number of
students at the university had been about 500; "whilst he occupied
the chair of botany there it rose to 1,500." A part of this increase
was due to other causes, but Linnæus was the greatest single drawing
force in the university. He was an eloquent as well as an enthusiastic
lecturer, and he aroused great interest among his students, and he gave
an astonishing impulse to the study of natural history in general, and
to botany in particular. Thus Linnæus, after having passed through
great privations in his earlier years, found himself, at the age of
thirty-four, established in a position which brought him recognition,
honor, and large emolument.
[Illustration: Fig. 34.--Linnæus at Sixty, 1707-1778.]
In May, 1907, the University of Upsala celebrated the two hundredth
anniversary of his birth with appropriate ceremonies. Delegations of
scientific men from all over the world were in attendance to do honor
to the memory of the great founder of biological nomenclature.
Personal Appearance.--The portrait of Linnæus at the age of sixty is
shown in Fig. 34. He was described as of "medium height, with large
limbs, brown, piercing eyes, and acute vision." His hair in early youth
was nearly white, and changed in his manhood to brown, and became gray
with the advance of age. Although quick-tempered, he was naturally of
a kindly disposition, and secured the affection of his students, with
whom he associated and worked in the most informal way. His love of
approbation was very marked, and he was so much praised that his desire
for fame became his dominant passion. The criticism to which his work
was subjected from time to time accordingly threw him into fits of
despondency and rage.
His Influence upon Natural History.--However much we may admire the
industry and force of Linnæus, we must admit that he gave to natural
history a one-sided development, in which the more essential parts
of the science received scant recognition. His students, like their
master, were mainly collectors and classifiers. "In their zeal for
naming and classifying, the higher goal of investigation, knowledge of
the nature of animals and plants, was lost sight of and the interest in
anatomy, physiology, and embryology lagged."
R. Hertwig says of him: "For while he in his _Systema Naturæ_ treated
of an extraordinarily larger number of animals than any earlier
naturalist, he brought about no deepening of our knowledge. The
manner in which he divided the animal kingdom, in comparison with the
Aristotelian system, is to be called rather a retrogression than an
advance. Linnæus divided the animal kingdom into six classes--Mammalia,
Aves, Amphibia, Pisces, Insecta, Vermes. The first four classes
correspond to Aristotle's four groups of animals with blood. In the
division of the invertebrated animals into Insecta and Vermes Linnæus
stands undoubtedly behind Aristotle, who attempted, and in part indeed
successfully, to set up a larger number of groups.
"But in his successors even more than in Linnæus himself we see the
damage wrought by the purely systematic method of consideration. The
diagnoses of Linnæus were for the most part models, which, _mutatis
mutandis_, could be employed for new species with little trouble.
There was needed only some exchanging of adjectives to express the
differences. With the hundreds of thousands of different species of
animals, there was no lack of material, and so the arena was opened
for that spiritless zoölogy of species-making, which in the first
half of the nineteenth century brought zoölogy into such discredit.
Zoölogy would have been in danger of growing into a Tower of Babel
of species-description if a counterpoise had not been created in the
strengthening of the physiologico-anatomical method of consideration."
His Especial Service.--Nevertheless, the work of Linnæus made a lasting
impression upon natural history, and we shall do well to get clearly
in mind the nature of his particular service. In the first place, he
brought into use the method of naming animals and plants which is
employed to-day. In his _Systema Naturæ_ and in other publications he
employed a means of naming every natural production in two words, and
it is therefore called the binomial nomenclature. An illustration will
make this clearer. Those animals which had close resemblance, like the
lion, tiger, leopard, the lynx, and the cat, he united under the common
generic name of _Felis_, and gave to each a particular trivial name,
or specific name. Thus the name of the lion became _Felis leo_, of the
tiger _Felis tigris_, of the leopard _Felis pardus_, of the cat Felis
catus; and to these the modern zoölogists have added, making the Canada
lynx _Felis Canadensis_, the domestic cat _Felis domesticata_, etc. In
a similar way, the dog-like animals were united into a genus designated
_Canis_, and the particular kinds or species became _Canis lupus_,
the wolf, _Canis vulpes_, the fox, _Canis familiaris_, the common dog.
This simple method took the place of the varying names applied to the
same animal in different countries and local names in the same country.
It recognized at once their generic likeness and their specific
individuality.
All animals, plants, and minerals were named according to this method.
Thus there were introduced into nomenclature two groups, the genus and
the species. The name of the genus was a noun, and that of the species
an adjective agreeing with it. In the choice of these names Linnæus
sought to express some distinguishing feature that would be suggestive
of the particular animal, plant, or mineral. The trivial, or specific,
names were first employed by Linnæus in 1749, and were introduced into
his _Species Plantarum_ in 1753, and into the tenth edition of his
_Systema Naturæ_ in 1758.
We recognize Linnæus as the founder of nomenclature in natural history,
and by the common consent of naturalists the date 1758 has come to be
accepted as the starting-point for determining the generic and specific
names of animals. The much vexed question of priority of names for
animals is settled by going back to the tenth edition of his _Systema
Naturæ_, while the botanists have adopted his _Species Plantarum_,
1753, as their base-line for names. As to his larger divisions of
animals and plants, he recognized classes and orders. Then came genera
and species. Linnæus did not use the term family in his formulæ; this
convenient designation was first used and introduced in 1780 by Batch.
The _Systema Naturæ_ is not a treatise on the organization of
animals and plants; it is rather a catalogue of the productions of
nature methodically arranged. His aim in fact was not to give full
descriptions, but to make a methodical arrangement.
To do justice, however, to the discernment of Linnæus, it should
be added that he was fully aware of the artificial nature of his
classification. As Kerner has said: "It is not the fault of this
accomplished and renowned naturalist if a greater importance were
attached to his system than he himself ever intended. Linnæus never
regarded his twenty-four classes as real and natural divisions of the
vegetable kingdom, and specifically says so; it was constructed for
convenience of reference and identification of species. A real natural
system, founded on the true affinities of plants as indicated by the
structural characters, he regarded as the highest aim of botanical
endeavor. He never completed a natural system, leaving only a fragment
(published in 1738)."
Terseness of Descriptions.--His descriptions were marked by extreme
brevity, but by great clearness. This is a second feature of his work.
In giving the diagnosis of a form he was very terse. He did not employ
fully formed sentences containing a verb, but words concisely put
together so as to bring out the chief things he wished to emphasize. As
an illustration of this, we may take his characterization of the forest
rose, "_Rosa sylvestris vulgaris, flore odorata incarnato_." The common
rose of the forest with a flesh-colored, sweet-smelling flower. In thus
fixing the attention upon essential points he got rid of verbiage, a
step that was of very great importance.
His Idea of Species.--A third feature of his work was that of
emphasizing the idea of species. In this he built upon the work of
Ray. We have already seen that Ray was the first to define species
and to bring the conception into natural history. Ray had spoken of
the variability of species, but Linnæus, in his earlier publications,
declared that they were constant and invariable. His conception of
a species was that of individuals born from similar parents. It was
assumed that at the original stocking of the earth, one pair of each
kind of animals was created, and that existing species were the direct
descendants without change of form or habit from the original pair.
As to their number, he said: "_Species tot sunt, quot formæ ab initio
creatæ sunt_"--there are just so many species as there were forms
created in the beginning; and his oft-quoted remark, "_Nulla species
nova_," indicates in terse language his position as to the formation
of new species. Linnæus took up this idea as expressing the current
thought, without analysis of what was involved in it. He readily might
have seen that if there were but a single pair of each kind, some of
them must have been sacrificed to the hunger of the carnivorous kinds:
but, better than making any theories, he might have looked for evidence
in nature as to the fixity of species.
While Linnæus first pronounced upon the fixity of species, it is
interesting to note that his extended observations upon nature led him
to see that variation among animals and plants is common and extensive,
and accordingly in the later editions of his _Systema Naturæ_ we find
him receding from the position that species are fixed and constant.
Nevertheless, it was owing to his influence, more than to that of any
other writer of the period, that the dogma of fixity of species was
established. His great contemporary Buffon looked upon species as
not having a fixed reality in nature, but as being figments of the
imagination; and we shall see in a later section of this book how the
idea of Linnæus in reference to the fixity of species gave way to
accumulating evidence on the matter.
Summary.--The chief services of Linnæus to natural science consisted
of these three things: bringing into current use the binomial
nomenclature, the introduction of terse formulæ for description, and
fixing attention upon species. The first two were necessary steps;
they introduced clearness and order into the management of the immense
number of details, and they made it possible for the observations
and discoveries of others to be understood and to take their place in
the great system of which he was the originator. The effect of the
last step was to direct the attention of naturalists to species, and
thereby to pave the way for the coming consideration of their origin, a
consideration which became such a burning question in the last half of
the nineteenth century.
Reform of the Linnæan System
Necessity of Reform.--As indicated above, the classification
established by Linnæus had grave defects; it was not founded on a
knowledge of the comparative structure of animals and plants, but in
many instances upon superficial features that were not distinctive
in determining their position and relationships. His system was
essentially an artificial one, a convenient key for finding the names
of animals and plants, but doing violence to the natural arrangement of
those organisms. An illustration of this is seen in his classification
of plants into classes, mainly on the basis of the number of stamens
in the flower, and into orders according to the number of pistils.
Moreover, the true object of investigation was obscured by the Linnæan
system. The chief aim of biological study being to extend our knowledge
of the structure, development, and physiology of animals and plants
as a means of understanding more about their life, the arrangement of
animals and plants into groups should be the outcome of such studies
rather than an end in itself.
It was necessary to follow different methods to bring natural history
back into the line of true progress. The first modification of
importance to the Linnæan system was that of Cuvier, who proposed
a grouping of animals based upon a knowledge of their comparative
anatomy. He declared that animals exhibit four types of organization,
and his types were substituted for the primary groups of Linnæus.
The Scale of Being.--In order to understand the bearing of Cuvier's
conclusions we must take note of certain views regarding the animal
kingdom that were generally accepted at the time of his writing.
Between Linnæus and Cuvier there had emerged the idea that all animals,
from the lowest to the highest, form a graduated series. This grouping
of animals into a linear arrangement was called exposing the Scale of
Being, or the Scale of Nature (_Scala Naturæ_). Buffon, Lamarck, and
Bonnet were among the chief exponents of this idea.
That Lamarck's connection with it was temporary has been generally
overlooked. It is the usual statement in the histories of natural
science, as in the _Encyclopædia Britannica_, in the History of Carus,
and in Thomson's _Science of Life_, that the idea of the scale of
nature found its fullest expression in Lamarck. Thomson says: "His
classification (1801-1812) represents the climax of the attempt to
arrange the groups of animals in linear order from lower to higher, in
what was called a _scala naturæ_" (p. 14). Even so careful a writer as
Richard Hertwig has expressed the matter in a similar form. Now, while
Lamarck at first adopted a linear classification, it is only a partial
reading of his works that will support the conclusion that he held to
it. In his _Système des Animaux sans Vertèbres_, published in 1801, he
arranged animals in this way; but to do credit to his discernment, it
should be observed that he was the first to employ a genealogical tree
and to break up the serial arrangement of animal forms. In 1809, in the
second volume of his _Philosophie Zoologique_, as Packard has pointed
out, he arranged animals according to their relationships, in the form
of a trunk with divergent branches. This was no vague suggestion on
his part, but an actual pictorial representation of the relationship
between different groups of animals, as conceived by him. Although a
crude attempt, it is interesting as being the first of its kind. This
is so directly opposed to the idea of scale of being that we make note
of the fact that Lamarck forsook that view at least twenty years before
the close of his life and substituted for it that of the genealogical
tree.
Lamarck's Position in Science.--Lamarck is coming into full recognition
for his part in founding the evolution theory, but he is not generally,
as yet, given due credit for his work in zoölogy. He was the most
philosophical thinker engaged with zoölogy at the close of the
eighteenth and the beginning of the nineteenth century. He was greater
than Cuvier in his reach of intellect and in his discernment of the
true relationships among living organisms. We are to recollect that
he forsook the dogma of fixity of species, to which Cuvier held, and
founded the first comprehensive theory of organic evolution. To-day we
can recognize the superiority of his mental grasp over that of Cuvier,
but, owing to the personal magnetism of the latter and to his position,
the ideas of Lamarck, which Cuvier combated, received but little
attention when they were promulgated. We shall have occasion in a later
chapter to speak more fully of Lamarck's contribution to the progress
of biological thought.
Cuvier's Four Branches.--We now return to the type-theory of Cuvier.
By extended studies in comparative anatomy, he came to the conclusion
that animals are constructed upon four distinct plans or types: the
vertebrate type; the molluscan type; the articulated type, embracing
animals with joints or segments; and the radiated type, the latter with
a radial arrangement of parts, like the starfish; etc. These types
are distinct, but their representatives, instead of forming a linear
series, overlap so that the lowest forms of one of the higher groups
are simpler in organization than the higher forms of a lower group.
This was very illuminating, and, being founded upon an analysis of
structure, was important. It was directly at variance with the idea of
scale of being, and overthrew that doctrine.
Cuvier first expressed these views in a pamphlet published in 1795,
and later in a better-known paper read before the French Academy in
1812, but for the full development of his type-theory we look to his
great volume on the animal kingdom published in 1816. The central idea
of his arrangement is contained in the secondary title of his book,
"The Animal Kingdom Arranged According to its Organization" (_Le Règne
Animal Distribué d'après son Organisation_, 1816). The expression
"arranged according to its organization" embraces the feature in which
this analysis of animals differs from all previous attempts.
Correlation of Parts.--An important idea, first clearly expressed
by Cuvier, was that of correlation of parts. The view that the
different parts of an animal are so correlated that a change in one,
brought about through changes in use, involves a change in another.
For illustration, the cleft hoof is always associated with certain
forms of teeth and with the stomach of a ruminant. The sharp claws
of flesh-eating animals are associated with sharp, cutting teeth for
tearing the flesh of the victims, and with an alimentary tube adapted
to the digestion of a fleshy diet. Further account of Cuvier is
reserved for the chapter on the Rise of Comparative Anatomy, of which
he was the founder.
Von Baer.--The next notable advance affecting natural history came
through the work of Von Baer, who, in 1828, founded the science of
development of animal forms. He arrived at substantially the same
conclusions as Cuvier. Thus the system founded upon comparative anatomy
by Cuvier came to have the support of Von Baer's studies in embryology.
The contributions of these men proved to be a turning-point in natural
history, and subsequent progress in systematic botany and zoölogy
resulted from the application of the methods of Cuvier and Von Baer,
rather than from following that of Linnæus. His nomenclature remained
a permanent contribution of value, but the knowledge of the nature
of living forms has been advanced chiefly by studies in comparative
anatomy and embryology, and, also, in the application of experiments.
The most significant advances in reference to the classification of
animals was to come as a result of the acceptance of the doctrine
of organic evolution, subsequent to 1859. Then the relationships
between animals were made to depend upon community of descent, and a
distinction was drawn between superficial or apparent relationships
and those deep-seated characteristics that depend upon close genetic
affinities.
Alterations by Von Siebold and Leuckart.--But, in the mean time,
naturalists were not long in discovering that the primary divisions
established by Cuvier were not well balanced, and, indeed, that they
were not natural divisions of the animal kingdom. The group Radiata was
the least sharply defined, since Cuvier had included in it not only
those animals which exhibit a radial arrangement of parts, but also
unicellular organisms that were asymmetrical, and some of the worms
that showed bilateral symmetry. Accordingly, Karl Th. von Siebold, in
1845, separated these animals and redistributed them. For the simplest
unicellular animals he adopted the name Protozoa, which they still
retain, and the truly radiated forms, as starfish, sea-urchins, hydroid
polyps, coral animals, etc., were united in the group Zoöphyta. Von
Siebold also changed Cuvier's branch, Articulata, separating those
forms as crustacea, insects, spiders, and myriopods, which have jointed
appendages, into a natural group called Arthropoda, and uniting the
segmented worms with those worms that Cuvier has included in the
radiate group, into another branch called Vermes. This separation
of the four original branches of Cuvier was a movement in the right
direction, and was destined to be carried still farther.
[Illustration: Fig. 35.--Karl Th. von Siebold, 1804-1885.]
Von Siebold (Fig. 35) was an important man in the progress of zoölogy,
especially in reference to the comparative anatomy of the invertebrates.
Leuckart (Fig. 36), whose fame as a lecturer and teacher attracted
many young men to the University of Leipsic, is another conspicuous
personality in zoölogical progress.
This distinguished zoölogist, following the lead of Von Siebold, made
further modifications. He split Von Siebold's group of Zoöphytes into
two distinct kinds of radiated animals; the star-fishes, sea-urchins,
sea-cucumbers, etc., having a spiny skin, he designated Echinoderma;
the jelly-fishes, polyps, coral animals, etc., not possessing a true
body cavity, were also united into a natural group, for which he
proposed the name Coelenterata.
[Illustration: Fig. 36.--Rudolph Leuckart, 1823-1898.]
From all these changes there resulted the seven primary
divisions--branches, subkingdoms, or phyla--which, with small
modifications, are still in use. These are Protozoa, Coelenterata,
Echinoderma, Vermes, Arthropoda, Mollusca, Vertebrata. These seven
phyla are not entirely satisfactory, and there is being carried on
a redistribution of forms, as in the case of the brachiopods, the
sponges, the tunicates, etc. While all this makes toward progress, the
changes are of more narrow compass than those alterations due to Von
Siebold and Leuckart.
Summary.--In reviewing the rise of scientific natural history, we
observe a steady development from the time of the _Physiologus_, first
through a return to Aristotle, and through gradual additions to his
observations, notably by Gesner, and then the striking improvements
due to Ray and Linnæus. We may speak of the latter two as the founders
of systematic botany and zoölogy. But the system left by Linnæus was
artificial, and the greatest obvious need was to convert it into a
natural system founded upon a knowledge of the structure and the
development of living organisms. This was begun by Cuvier and Von Baer,
and was continued especially by Von Siebold and Leuckart. To this has
been added the study of habits, breeding, and adaptations of organisms,
a study which has given to natural history much greater importance than
if it stood merely for the systematic classification of animals and
plants.
Tabular View of Classifications.--A table showing the primary groups of
Linnæus, Cuvier, Von Siebold, and Leuckart will be helpful in picturing
to the mind the modifications made in the classification of animals.
Such a table is given on the following page.
L. Agassiz, in his famous essay on Classification, reviews in the most
scholarly way the various systems of classification. One peculiar
feature of Agassiz's philosophy was his adherence to the dogma of
the fixity of species. The same year that his essay referred to was
published (1859) appeared Darwin's _Origin of Species_. Agassiz,
however, was never able to accept the idea, of the transformations of
species.
Linnæus Cuvier Von Siebold Leuckart
Mammalia Vertebrata Vertebrata Vertebrata
(Embracing five (Embracing five (Five classes.)
Aves classes: Mammalia, classes.)
Aves, Reptilia,
Amphibia Batrachia, Pisces.)
Pisces
Insecta Mollusca Mollusca Mollusca
(Including
Crustacea, {Arthropoda
etc.) Articulata {Vermes Arthropoda
Vermes Vermes
{Zoöphyta {Echinoderma
(Including Radiata {Coelenterata
Mollusca
and all {Protozoa Protozoa
lower forms.)
Steps in Biological Progress from Linnæus to Darwin
The period from Linnæus to Darwin is one full of important advances
for biology in general. We have considered in this chapter only those
features that related to changes in the system of classification, but
in the mean time the morphological and the physiological sides of
biology were being advanced not only by an accumulation of facts, but
by their better analysis. It is an interesting fact that, although
during this period the details of the subject were greatly multiplied,
progress was relatively straightforward and by a series of steps that
can be clearly indicated.
It will be of advantage before the subject is taken up in its parts to
give a brief forecast in which the steps of progress can be represented
in outline without the confusion arising from the consideration of
details. Geddes, in 1898, pointed out the steps in progress, and the
account that follows is based upon his lucid analysis.
The Organism.--In the time of Linnæus the attention of naturalists
was mainly given to the organism as a whole. Plants and animals were
considered from the standpoint of the organism--the external features
were largely dealt with, the habitat, the color, and the general
appearance--features which characterize the organism as a whole.
Linnæus and Jussieu represent this phase of the work, and Buffon the
higher type of it. Modern studies in this line are like addition to the
_Systema Naturæ_.
Organs.--The first distinct advance came in investigating animals and
plants according to their structure. Instead of the complete organism,
the organs of which it is composed became the chief subject of
analysis. The organism was dissected, the organs were examined broadly,
and those of one kind of animal and plant compared with another. This
kind of comparative study centered in Cuvier, who, in the early part of
the nineteenth century, founded the science of comparative anatomy of
animals, and in Hofmeister, who examined the structure of plants on a
basis of broad comparison.
Tissues.--Bichat, the famous contemporary of Cuvier, essayed a deeper
level of analysis in directing attention to the tissues that are
combined to make up the organs. He distinguished twenty-one kinds of
tissues by combinations of which the organs are composed. This step
laid the foundation for the science of histology, or minute anatomy.
Bichat called it general anatomy (_Anatomie Générale_, 1801).
Cells.--Before long it was shown that tissues are not the real units of
structure, but that they are composed of microscopic elements called
cells. This level of analysis was not reached until magnifying-lenses
were greatly improved--it was a product of a closer scrutiny of nature
with improved instruments. The foundation of the work, especially for
plants, had been laid by Leeuwenhoek, Malpighi, and Grew. But when the
broad generalization, that all the tissues of animals and plants are
composed of cells, was given to the world by Schleiden and Schwann, in
1838-39, the entire organization of living forms took on a new aspect.
This was progress in understanding the morphology of animals and plants.
Protoplasm.--With improved microscopes and attention directed to cells,
it was not long before the discovery was made that the cells as units
of structure contain protoplasm. That this substance is similar in
plants and animals and is the seat of all vital activity was determined
chiefly by the researches of Max Schultze, published in 1861. Thus
step by step, from 1758, the date of the tenth edition of the _Systema
Naturæ_, to 1861, there was a progress on the morphological side,
passing from the organism as a whole to organs, to tissues, to cells,
and finally to protoplasm, the study of which in all its phases is the
chief pursuit of biologists.
The physiological side had a parallel development. In the period of
Linnæus, the physiology of the organism was investigated by Haller and
his school; following him the physiology of organs and tissues was
advanced by J. Müller, Bichat, and others. Later, Virchow investigated
the physiology of cells, and Claude Bernard the chemical activities of
protoplasm.
This set forth in outline will be amplified in the following chapters.
CHAPTER VII
CUVIER AND THE RISE OF COMPARATIVE ANATOMY
After observers like Linnæus and his followers had attained a knowledge
of the externals, it was natural that men should turn their attention
to the organization or internal structure of living beings, and
when the latter kind of investigation became broadly comparative,
it blossomed into comparative anatomy. The materials out of which
the science of comparative anatomy was constructed had been long
accumulating before the advent of Cuvier, but the mass of details had
not been organized into a compact science.
As indicated in previous chapters, there had been an increasing number
of studies upon the structure of organisms, both plant and animal,
and there had resulted some noteworthy monographs. All this work,
however, was mainly descriptive, and not comparative. Now and then, the
comparing tendency had been shown in isolated writings such as those of
Harvey, Malpighi, and others. As early as 1555, Belon had compared the
skeleton of the bird with that of the human body "in the same posture
and as nearly as possible bone for bone"; but this was merely a faint
foreshadowing of what was to be done later in comparing the systems of
the more important organs.
We must keep in mind that the study of anatomy embraces not merely the
bony framework of animals, but also the muscles, the nervous system,
the sense organs, and all the other structures of both animals and
plants. In the rise of comparative anatomy there gradually emerged
naturalists who compared the structure of the higher animals with that
of the simpler ones. These comparisons brought out so many resemblances
and so many remarkable facts that anatomy, which seems at first a dry
subject, became endued with great interest.
[Illustration: Fig. 37.--Severinus, 1580-1656.]
Severinus.--The first book expressly devoted to comparative anatomy
was that of Severinus (1580-1656), designated _Zootomia Democritæ_.
The title was derived from the Roman naturalist Democritæus, and the
date of its publication, 1645, places the treatise earlier than the
works of Malpighi, Leeuwenhoek, and Swammerdam. The book is illustrated
by numerous coarse woodcuts, showing the internal organs of fishes,
birds, and some mammals. There are also a few illustrations of stages
in the development of these animals. The comparisons were superficial
and incidental; nevertheless, as the first attempt, after the revival
of anatomy, to make the subject comparative, it has some especial
interest. Severinus (Fig. 37) should be recognized as beginning the
line of comparative anatomists which led up to Cuvier.
Forerunners of Cuvier.--Anatomical studies began to take on broad
features with the work of Camper, John Hunter, and Vicq d'Azyr. These
three men paved the way for Cuvier, but it must be said of the two
former that their comparisons were limited and unsystematic.
Camper, whose portrait is shown in Fig. 38, was born in Leyden, in
1722. He was a versatile man, having a taste for drawing, painting,
and sculpture, as well as for scientific studies. He received his
scientific training under Boerhaave and other eminent men in Leyden,
and became a professor and, later, rector in the University of
Groningen. Possessing an ample fortune, and also having married a
rich wife, he was in position to follow his own tastes. He travelled
extensively and gathered a large collection of skeletons. He showed
considerable talent as an anatomist, and he made several discoveries,
which, however, he did not develop, but left to others. Perhaps the
possession of riches was one of his limitations; at any rate, he lacked
fixity of purpose.
Among his discoveries may be mentioned the semicircular canals in the
ear of fishes, the fact that the bones of flying birds are permeated
by air, the determination of some fossil bones, with the suggestion
that they belonged to extinct forms. The latter point is of interest,
as antedating the conclusions of Cuvier regarding the nature of fossil
bones. Camper also made observations upon the facial angle as an
index of intelligence in the different races of mankind, and in lower
animals. He studied the anatomy of the elephant, the whale, the orang,
etc.
[Illustration: Fig. 38.--Camper, 1722-1789.]
John Hunter (1728-1793), the gifted Scotchman whose museum in London
has been so justly celebrated, was a man of extraordinary originality,
who read few books but went directly to nature for his facts; and,
although he made errors from which he would have been saved by a wider
acquaintance with the writings of naturalists, his neglect of reading
left his mind unprejudiced by the views of others. He was a wild,
unruly spirit, who would not be forced into the conventional mold as
regards either education or manners. His older brother, William, a
man of more elegance and refinement, who well understood the value
of polish in reference to worldly success, tried to improve John by
arranging for him to go to the University of Oxford, but John rebelled
and would not have the classical education of the university, nor would
he take on the refinements of taste and manner of which his brother was
a good example. "Why," the doughty John is reported to have said, "they
wanted to make me study Greek! They tried to make an old woman of me!"
However much lack of appreciation this attitude indicated, it shows
also the Philistine independence of his spirit. This independence of
mind is one of his striking characteristics.
[Illustration: Fig. 39.--John Hunter, 1728-1793.]
This is not the place to dwell upon the unfortunate controversy that
arose between these two illustrious brothers regarding scientific
discoveries claimed by each. The position of both is secure in the
historical development of medicine and surgery. Although the work of
John Hunter was largely medical and surgical, he also made extensive
studies on the comparative anatomy of animals, and has a place as one
of the most conspicuous predecessors of Cuvier. He was very energetic
both in making discoveries and in adding to his great museum.
The original collections made by Hunter are still open to inspection
in the rooms of the Royal College of Surgeons, London. It was his
object to preserve specimens to illustrate the phenomena of life in all
organisms, whether in health or disease, and the extent of his museum
may be divined from the circumstance that he expended upon it about
three hundred and seventy-five thousand dollars. Although he described
and compared many types of animals, it was as much in bringing this
collection together and leaving it to posterity that he advanced
comparative anatomy as in what he wrote. After his death the House of
Commons purchased his museum for fifteen thousand pounds, and placed
it under the care of the corporation of Surgeons. Hunter's portrait is
shown in Fig. 39.
Vicq d'Azyr (Fig. 40), more than any other man, holds the chief rank
as a comparative anatomist before the advent of Cuvier into the same
field. He was born in 1748, the son of a physician, and went to Paris
at the age of seventeen to study medicine, remaining in the metropolis
to the time of his death in 1794. He was celebrated as a physician,
became permanent secretary of the newly founded Academy of Medicine,
consulting physician to the queen, and occupied other positions of
trust and responsibility. He married the niece of Daubenton, and,
largely through his influence, was advanced to social place and
recognition. On the death of Buffon, in 1788, he took the seat of that
distinguished naturalist as a member of the French Academy.
[Illustration: Fig. 40.--Vicq d'Azyr, 1748-1794.]
He made extensive studies upon the organization particularly of
birds and quadrupeds, making comparisons between their structure,
and bringing out new points that were superior to anything yet
published. His comparisons of the limbs of man and animals, showing
a correspondence between the flexor and extensor muscles of the legs
and arms, were made with great exactness, and they served to mark the
beginning of a new kind of precise comparison. These were not merely
fanciful comparisons, but exact ones--part for part; and his general
considerations based upon these comparisons were of a brilliant
character.
As Huxley has said, "he may be considered as the founder of the modern
science of anatomy." His work on the structure of the brain was the
most exact which had appeared up to that time, and in his studies on
the brain he entered into broad comparisons as he had done in the study
of the other parts of the animal organization.
He died at the age of forty-six, without being able to complete a
large work on human anatomy, illustrated with colored figures. This
work had been announced and entered upon, but only that part relating
to the brain had appeared at the time of his death. Besides drawings
of the exterior of the brain, he made sections; but he was not able
to determine with any particular degree of accuracy the course of
fiber tracks in the brain. This was left for other workers. He added
many new facts to those of his predecessors, and by introducing exact
comparisons in anatomy he opened the field for Cuvier.
Cuvier.--When Cuvier, near the close of the eighteenth century,
committed himself definitely to the progress of natural science, he
found vast accumulations of separate monographs to build upon, but he
undertook to dissect representatives of all the groups of animals, and
to found his comparative anatomy on personal observations. The work of
Vicq d'Azyr marked the highest level of attainment, and afforded a good
model of what comparisons should be; but Cuvier had even larger ideas
in reference to the scope of comparative anatomy than had his great
predecessor.
The particular feature of Cuvier's service was that in his
investigations he covered the whole field of animal organization
from the lowest to the highest, and uniting his results with what
had already been accomplished, he established comparative anatomy on
broad lines as an independent branch of natural science. Almost at the
outset he conceived the idea of making a comprehensive study of the
structure of the animal kingdom. It was fortunate that he began his
investigations with thorough work upon the invertebrated animals; for
from this view-point there was gradually unfolded to his great mind
the plan of organization of the entire series of animals. Not only is
a knowledge of the structure of the simplest animals an essential in
understanding that of the more modified ones, but the more delicate
work required in dissecting them gives invaluable training for
anatomizing those of more complex construction. The value attached
to this part of his training by Cuvier is illustrated by the advice
that he gave to a young medical student who brought to his attention
a supposed discovery in anatomy. "Are you an entomologist?" inquired
Cuvier. "No," said the young man. "Then," replied Cuvier, "go first and
anatomize an insect, and return to me; and if you still believe that
your observations are discoveries I will then believe you."
Birth and Early Education.--Cuvier was born in 1769, at Montbéliard, a
village at that time belonging to Württemberg, but now a part of the
French Jura. His father was a retired military officer of the Swiss
army, and the family, being Protestants, had moved to Montbéliard
for freedom from religious persecution. Cuvier was christened
Léopold-Christian-Frédéric-Dagobert Cuvier, but early in youth took the
name of Georges at the wish of his mother, who had lost an infant son
by that name.
He gave an early promise of intellectual leadership, and his mother,
although not well educated, took the greatest pains in seeing that he
formed habits of industry and continuous work, hearing him recite his
lessons in Latin and other branches, although she did not possess a
knowledge of Latin. He early showed a leaning toward natural history;
having access to the works of Gesner and Buffon, he profited by reading
these two writers. So great was his interest that he colored the
plates in Buffon's _Natural History_ from descriptions in the text.
It was at first contemplated by his family that he should prepare for
theology, but failing, through the unfairness of one of his teachers,
to get an appointment to the theological seminary, his education was
continued in other directions. He was befriended by the sister of
the Duke of Württemberg, who sent him as a pensioner to the famous
Carolinian academy at Stuttgart. There he showed great application,
and with the wonderful memory with which he was endowed, he took high
rank as a student. Here he met Kielmeyer, a young instructor only four
years older than himself, who shared his taste for natural history
and, besides this, introduced him to anatomy. In after-years Cuvier
acknowledged the assistance of Kielmeyer in determining his future work
and in teaching him to dissect.
Life at the Seashore.--In 1788 the resources of his family, which had
always been slender, became further reduced by the inability of the
government to pay his father's retiring stipend. As the way did not
open for employment in other directions, young Cuvier took the post
of instructor of the only son in the family of Count d'Héricy, and
went with the family to the sea-coast in Normandy, near Caen. For
six years (1788-1794) he lived in this noble family, with much time
at his disposal. For Cuvier this period, from the age of nineteen to
twenty-five, was one of constant research and reflection.
While Paris was disrupted by the reign of terror, Cuvier, who, although
of French descent, regarded himself as a German, was quietly carrying
on his researches into the structure of the life at the seaside.
These years of diligent study and freedom from distractions fixed his
destiny. Here at the sea-coast, without the assistance of books and the
stimulus of intercourse with other naturalists, he was drawn directly
to nature, and through his great industry he became an independent
observer. Here he laid the foundation of his extensive knowledge
of comparative anatomy, and from this quiet spot he sent forth his
earliest scientific writings, which served to carry his name to Paris,
the great center of scientific research in France.
Goes to Paris.--His removal from these provincial surroundings was
mainly owing to the warm support of Tessier, who was spending the time
of the reign of terror in retirement in an adjacent village, under
an assumed name. He and Cuvier met in a scientific society, where
the identity of Tessier was discovered by Cuvier on account of his
ease of speech and his great familiarity with the topics discussed.
A friendship sprung up between them, and Tessier addressed some of
his scientific friends in Paris in the interest of Cuvier. By this
powerful introduction, and also through the intervention of Geoffroy
Saint-Hilaire, he came to Paris in 1795 and was welcomed into the group
of working naturalists at the Jardin des Plantes, little dreaming at
the time that he should be the leader of the group of men gathered
around this scientific institution. He was modest, and so uncertain of
his future that for a year he held to his post of instructor, bringing
his young charge with him to Paris.
Notwithstanding the doubt which he entertained regarding his abilities,
his career proved successful from the beginning. In Paris he entered
upon a brilliant career, which was a succession of triumphs. His
unmistakable talent, combined with industry and unusual opportunities,
brought him rapidly to the front. The large amount of material already
collected, and the stimulating companionship of other scientific
workers, afforded an environment in which he grew rapidly. He responded
to the stimulus, and developed not only into a great naturalist, but
expanded into a finished gentleman of the world. Circumstances shaped
themselves so that he was called to occupy prominent offices under
the government, and he came ultimately to be the head of the group of
scientific men into which he had been welcomed as a young man from the
provinces.
[Illustration: Fig. 41.--Cuvier as a Young Man, 1769-1832.]
His Physiognomy.--It is very interesting to note in his portraits the
change in his physiognomy accompanying his transformation from a young
man of provincial appearance into an elegant personage. Fig. 41 shows
his portrait in the early days when he was less mindful of his personal
appearance. It is the face of an eager, strong, young man, still
retaining traces of his provincial life. His long, light-colored hair
is unkempt, but does not hide the magnificent proportions of his head.
Fig. 42 shows the growing refinement of features which came with his
advancement, and the aristocratic look of supremacy which set upon his
countenance after his wide recognition passing by a gradation of steps
from the position of head of the educational system, to that of baron
and peer of France.
[Illustration: Fig. 42.--Cuvier at the Zenith of His Power.]
Cuvier was a man of commanding power and colossal attainments; he was a
favorite of Napoleon Bonaparte, who elevated him to office and made him
director of the higher educational institutions of the Empire. But to
whatever place of prominence he attained in the government, he never
lost his love for natural science. With him this was an absorbing
passion, and it may be said that he ranks higher as a zoölogist than as
a legislator.
Comprehensiveness of Mind.--Soon after his arrival in Paris he began
to lecture upon comparative anatomy and to continue work in a most
comprehensive way upon the subjects which he had cultivated at Caen.
He saw everything on a large scale. This led to his making extensive
studies of whatever problems engaged his mind, and his studies were
combined in such a manner as to give a broad view of the subject.
Indeed, comprehensiveness of mind seems to have been the characteristic
which most impressed those who were acquainted with him. Flourens says
of him: "_Ce qui caractérise partout M. Cuvier, c'est l'esprit vaste._"
His broad and comprehensive mind enabled him to map out on great lines
the subject of comparative anatomy. His breadth was at times his
undoing, for it must be confessed that when the details of the subject
are considered, he was often inaccurate. This was possibly owing to the
conditions under which he worked; having his mind diverted into many
other channels, never neglecting his state duties, it is reasonable to
suppose that he lacked the necessary time to prove his observations in
anatomy, and we may in this way account for some of his inaccuracies.
Besides being at fault in some of his comparative anatomy, he adhered
to a number of ideas that served to retard the progress of science.
He was opposed to the ideas of his contemporary Lamarck, on the
evolution of animals. He is remembered as the author of the dogma
of catastrophism in geology. He adhered to the old notion of the
pre-formation of the embryo, and also to the theory of the spontaneous
origin of life.
Founds Comparative Anatomy.--Regardless of this qualification, he was a
great and distinguished student, and founded comparative anatomy. From
1801 to 1805 appeared his _Leçons d' Anatomie Comparée_, a systematic
treatise on the comparative anatomy of animals, embracing both the
invertebrates and the vertebrates. In 1812 was published his great
work on the fossil bones about Paris, an achievement which founded the
science of vertebrate palæontology. His extensive examination of the
structure of fishes also added to his already great reputation. His
book on the animal kingdom (_Le Règne Animal distribué d'après son
Organisation_, 1816), in which he expounded his type-theory, has been
considered in a previous chapter.
He was also deeply interested in the historical development of science,
and his volumes on the rise of the natural sciences give us almost the
best historical estimate of the progress of science that we have at the
present day.
His Domestic Life.--Mrs. Lee, in a chatty account of Cuvier, shows one
of his methods of work. He had the faculty of making others assist
him in various ways. Not only members of his family, but also guests
in his household were pressed into service. They were invited to
examine different editions of works and to indicate the differences
in the plates and in the text. This practice resulted in saving much
time for Cuvier, since in the preparation of his historical lectures
he undertook to examine all the original sources of the history with
which he was engaged. In his lectures he summarized facts relating to
different editions of books, etc.
Mrs. Lee also gives a picture of his family life, which was, to all
accounts, very beautiful. He was devoted to his wife and children, and
in the midst of exacting cares he found time to bind his family in love
and devotion. Cuvier was called upon to suffer poignant grief in the
loss of his children, and his direct family was not continued. He was
especially broken by the death of his daughter who had grown to young
womanhood and was about to be married.
From the standpoint of a sincere admirer, Mrs. Lee writes of his
generosity and nobility of temperament, declaring that his career
demonstrated that his mind was great and free from both envy and
smallness.
Some Shortcomings.--Nevertheless, there are certain things in the
life of Cuvier that we wish might not have been. His break with his
old friends Lamarck and Saint-Hilaire seems to show a domination of
qualities that were not generous and kindly; those observations of
Lamarck showing a much profounder insight than any of which he himself
was the author were laughed to scorn. His famous controversy with
Saint-Hilaire marks a historical moment that will be dealt with in the
chapter on Evolution.
George Bancroft, the American historian, met him during a visit
to Paris in 1827. He speaks of his magnificent eyes and his fine
appearance, but on the whole Cuvier seems to have impressed Bancroft as
a disagreeable man.
Some of his shortcomings that served to retard the progress of
science have been mentioned. Still, with all his faults, he dominated
zoölogical science at the beginning of the nineteenth century, and so
powerful was his influence and so undisputed was his authority among
the French people that the rising young men in natural science sided
with Cuvier even when he was wrong. It is a noteworthy fact that
France, under the influence of the traditions of Cuvier, was the last
country slowly and reluctantly to harbor as true the ideas regarding
the evolution of animal life.
Cuvier's Successors
While Cuvier's theoretical conclusions exercised a retarding influence
upon the progress of biology, his practical studies more than
compensated for this. It has been pointed out how his type-theory led
to the reform of the Linnæan system, but, besides this, the stimulus
which his investigations gave to studies in comparative anatomy was
even of more beneficent influence. As time passed the importance of
comparative anatomy as one division of biological science impressed
itself more and more upon naturalists. A large number of investigators
in France, England, and Germany entered the field and took up the work
where Cuvier had left it. The more notable of these successors of
Cuvier should come under consideration.
[Illustration: Fig. 43.--H. Milne-Edwards, 1800-1885.]
His intellectual heirs in France were Milne-Edwards and Lacaze-Duthiers.
Milne-Edwards.--H. Milne-Edwards (1800-1885) was a man of great
industry and fine attainments; prominent alike in comparative anatomy,
comparative physiology, and general zoölogy, professor for many years
at the Sorbonne in Paris. In 1827 he introduced into biology the
fruitful idea of the division of physiological labor. He completed and
published excellent researches upon the structure and development of
many animals, notably crustacea, corals, etc. His work on comparative
anatomy took the form of explanations of the activities of animals,
or comparative physiology. His comprehensive treatise _Leçons sur la
Physiologie et l'Anatomie Comparée_, in fourteen volumes, 1857-1881,
is a mine of information regarding comparative anatomy as well as the
physiology of organisms.
[Illustration: Fig. 44.--Lacaze-Duthiers, 1821-1901.]
Lacaze-Duthiers.--Henri de Lacaze-Duthiers (1821-1901), the man
of comprehensive mind, stimulating as an instructor of young men,
inspiring other workers, and producing a large amount of original
research on his own account, director of the Seaside Stations at
Roscoff and Banyuls, the founder of a noteworthy periodical of
experimental zoölogy--this great man, whose portrait is shown in Fig.
44, was one of the leading comparative anatomists in France.
[Illustration: Fig. 45.--Lorenzo Oken, 1779-1851.]
R. Owen.--In England Richard Owen (1804-1892) carried on the influence
of Cuvier. At the age of twenty-seven he went to Paris and renewed
acquaintance with the great Cuvier, whom he had met the previous year
in England. He spent some time at the Jardin des Plantes examining
the extensive collections in the museum. Although the idea was
repudiated by Owen and some of his friends, it is not unlikely that
the collections of fossil animals and the researches upon them which
engaged Cuvier at that time had great influence upon the subsequent
studies of Owen. Although he never studied under Cuvier, in a sense
he may be regarded as his disciple. Owen introduced into anatomy the
important conceptions of analogy and homology, the former being a
likeness based upon the use to which organs are put, as the wing of a
butterfly and the wing of a bat; while homology is a true relationship
founded on likeness in structure and development, as the wing of a
bat and the foreleg of a dog. Analogy is a superficial, and often a
deceiving relationship; homology is a true genetic relationship. It
is obvious that this distinction is of great importance in comparing
the different parts of animals. He made a large number of independent
discoveries, and published a monumental work on the comparative
anatomy of vertebrates (1866-68). In much of his thought he was
singular, and many of his general conclusions have not stood the
test of time. He undertook to establish the idea of an archtype in
vertebrate anatomy. He clung to the vertebral theory of the skull long
after Huxley had shown such a theory to be untenable. The idea that the
skull is made up of modified vertebrae was propounded by Goethe and
Oken. In the hands of Oken it became one of the anatomical conclusions
of the school of _Naturphilosophie_. This school of transcendental
philosophy was founded by Schelling, and Oken (Fig. 45) was one
of its typical representatives. The vertebral theory of the skull
was, therefore, not original with Owen, but he adopted it, greatly
elaborated it, and clung to it blindly long after the foundations upon
which it rested were removed.
[Illustration: Fig. 46.--Richard Owen, 1804-1892.]
Richard Owen (Fig. 46) was succeeded by Huxley (1825-1895), whose
exactness of observation and rare judgment as to the main facts of
comparative anatomy mark him as one of the leaders in this field of
research. The influence of Huxley as a popular exponent of science is
dealt with in a later chapter.
Meckel.--Just as Cuvier stands at the beginning of the school of
comparative anatomy in France, so does J. Fr. Meckel in Germany.
Meckel (1781-1833) was a man of rare talent, descended from a family
of distinguished anatomists. From 1804 to 1806 he studied in Paris
under Cuvier, and when he came to leave the French capital to become
professor of anatomy at Halle, he carried into Germany the teachings
and methods of his master. He was a strong force in the university,
attracting students to his department by his excellent lectures and his
ability to arouse enthusiasm. Some of these students were stimulated to
undertake researches in anatomy, and there came from his laboratory a
number of investigations that were published in a periodical which he
founded. Meckel himself produced many scientific papers and works on
comparative anatomy, which assisted materially in the advancement of
that science. His portrait, which is rare, is shown in Fig. 47.
[Illustration: Fig. 47.--J. Fr. Meckel, 1781-1833.]
Rathke.--Martin Henry Rathke (1793-1860) greatly advanced the science
of comparative anatomy by insisting upon the importance of elucidating
anatomy with researches in development. This is such an important
consideration that his influence upon the progress of comparative
anatomy can not be overlooked. After being a professor in Dorpat, he
came, in 1835, to occupy the position of professor of anatomy and
zoölogy at Königsberg, which had been vacated by Von Baer on the
removal of the latter to St. Petersburg. His writings are composed with
great intelligence, and his facts are carefully coördinated. Rathke
belonged to the good old school of German writers whose researches were
profound and extensive, and whose expression was clear, being based
upon matured thought. His papers on the aortic arches and the Wolffian
body are those most commonly referred to at the present time.
Müller.--Johannes Müller (1801-1858), that phenomenal man, besides
securing recognition as the greatest physiologist of the nineteenth
century, also gave attention to comparative anatomy, and earned the
title of the greatest morphologist of his time. His researches were
so accurate, so complete, so discerning, that his influence upon
the development of comparative anatomy was profound. Although he is
accorded, in history, the double distinction of being a great anatomist
and a great physiologist, his teaching tended to physiology; and most
of his distinguished students were physiologists of the broadest type,
uniting comparative anatomy with their researches upon functional
activities. (For Müller's portrait see p. 187.)
Gegenbaur.--In Karl Gegenbaur (1826-1903) scientific anatomy reached
its highest expression. His work was characterized by broad and
masterly analysis of the facts of structure, to which were added the
ideas derived from the study of the development of organs. He was
endowed with an intensely keen insight, an insight which enabled him
to separate from the vast mass of facts the important and essential
features, so that they yielded results of great interest and of lasting
importance. This gifted anatomist attracted many young men from the
United States and from other countries to pursue under his direction
the study of comparative anatomy. He died in Heidelberg in 1903, where
he had been for many years professor of anatomy in the university.
[Illustration: Fig. 48.--Karl Gegenbaur, 1826-1903.]
In the group of living German anatomists the names of Fürbringer,
Waldeyer, and Wiedersheim can not go unmentioned.
E.D. Cope.--In America the greatest comparative anatomist was E.D. Cope
(1840-1897), a man of the highest order of attainment, who dealt with
the comparative anatomy not only of living forms, but of fossil life,
and made contributions of a permanent character to this great science;
a man whose title to distinction in the field of comparative anatomy
will become clearer to later students with the passage of time. For
Cope's portrait see p. 336.
Of the successors of Cuvier, we would designate Meckel, Owen,
Gegenbaur, and Cope as the greatest.
Comparative anatomy is a very rich subject, and when elucidated by
embryology, is one of the firm foundations of biology. If we regard
anatomy as a science of statics, we recognize that it should be
united with physiology, which represents the dynamical side of life.
Comparative anatomy and comparative physiology should go hand in
hand in the attempt to interpret living forms. Advances in these
two subjects embrace nearly all our knowledge of living organisms.
It is a cause for congratulation that comparative anatomy has now
become experimental, and that gratifying progress is being made along
the line of research designated as experimental morphology. Already
valuable results have been attained in this field, and the outlook of
experimental morphology is most promising.
CHAPTER VIII
BICHAT AND THE BIRTH OF HISTOLOGY
We must recognize Bichat as one of the foremost men in biological
history, although his name is not well known to the general public,
nor constantly referred to by biologists as that of one of the chief
luminaries of their science. In him was combined extraordinary talent
with powers of intense and prolonged application; a combination which
has always produced notable results in the world. He died at the age
of thirty-one, but, within a productive period of not more than seven
years, he made observations and published work that created an epoch
and made a lasting impression on biological history.
His researches supplemented those of Cuvier, and carried the analysis
of animal organization to a deeper level. Cuvier laid the foundations
of comparative anatomy by dissecting and arranging in a comprehensive
system the organs of animals, but Bichat went a step further and made a
profound study of the tissues that unite to make up the organs. As we
have already noted in a previous chapter, this was a step in reaching
the conception of the real organization of living beings.
Buckle's Estimate of Bichat.--It is interesting to note the impression
made by Bichat upon one of the greatest students of the history of
civilization. Buckle says of him: "Great, however, as is the name of
Cuvier, a greater still remains behind. I allude, of course, to Bichat,
whose reputation is steadily advancing as our knowledge advances; who,
if we compare the shortness of his life with the reach and depth of
his views, must be pronounced the most profound thinker and consummate
observer by whom the organization of the animal frame has yet been
studied.
"We may except Aristotle, but between Aristotle and Bichat I find no
middle man."
Whether or not we agree fully with this panegyric of Buckle, we must,
I think, place Bichat among the most illustrious men of biological
history, as Vesalius, J. Müller, Von Baer, and Balfour.
Marie François Xavier Bichat was born in 1771 at Thoirette, department
of the Ain. His father, who was a physician, directed the early
education of his son and had the satisfaction of seeing him take kindly
to intellectual pursuits. The young student was distinguished in Latin
and mathematics, and showed early a fondness for natural history.
Having elected to follow the calling of his father, he went to Lyons to
study medicine, and came under the instruction of Petit in surgery.
Bichat in Paris.--It was, on the whole, a fortunate circumstance
for Bichat that the turbulent events of the French Revolution drove
him from Lyons to Paris, where he could have the best training, the
greatest stimulus for his growth, and at the same time the widest field
for the exercise of his talents. We find him in Paris in 1793, studying
under the great surgeon Desault.
He attracted attention to himself in the class of this distinguished
teacher and operator by an extemporaneous report on one of the
lectures. It was the custom in Desault's classes to have the lectures
of the professor reported upon before an assistant by some student
especially appointed for the purpose. On one occasion the student who
had been appointed to prepare and deliver the review was absent, and
Bichat, who was gifted with a powerful memory, volunteered without
previous notice to take his place. The lecture was a long and difficult
one on the fractures of the clavicle, but Bichat's abstract was so
clear, forceful, and complete that its delivery in well-chosen language
produced a great sensation both upon the instructor and the students.
This notable performance served to bring him directly to the attention
of Desault, who invited him to become his assistant and to live in
his family. The association of Bichat with the great surgeon was most
happy. Desault treated him as a son, and when he suddenly died in 1795,
the care of preparing his works for the printer was left to Bichat.
The fidelity with which Bichat executed this trust was characteristic
of his noble nature. He laid aside his own personal interests, and his
researches in which he was already immersed, and by almost superhuman
labor completed the fourth volume of Desault's _Journal of Surgery_ and
at the same time collected and published his scattered papers. To these
he added observations of his own, making alterations to bring the work
up to the highest plane. Thus he paid the debt of gratitude which he
felt he owed to Desault for his friendship and assistance.
In 1797 he was appointed professor of anatomy, at the age of
twenty-six, and from then to the end of his life, in 1801, he continued
in his career of remarkable industry.
The portrait of this very attractive man is shown in Fig. 49. His face
shows strong intellectuality. He is described as of "middling stature,
with an agreeable face lighted by piercing and expressive eyes." He was
much beloved by his students and associates, being "in all relations of
life most amiable, a stranger to envy or other hateful passions, modest
in demeanor and lively in his manners, which were open and free."
His Phenomenal Industry.--His industry was phenomenal; besides doing
the work of a professor, he attended to a considerable practice, and
during a single winter he is said to have examined with care six
hundred bodies in the pursuance of his researches upon pathological
anatomy.
[Illustration: Fig. 49.--Bichat, 1771-1801.]
In the year 1800, when he was thirty years old, began to appear the
results of his matured researches. We speak of these as being matured,
not on account of his age or the great number of years he had labored
upon them, but from the intensity and completeness with which he had
pursued his investigations, thus giving to his work a lasting quality.
First came his treatise on the membranes (_Traité des Membranes_);
followed quickly by his Physiological Researches into the Phenomena of
Life and Death (_Recherches Physiologiques sur la Vie et la Mort_);
then appeared his General Anatomy (_Anatomie Générale_) in 1801, and
his treatise upon Descriptive Anatomy, upon which he was working at the
time of his death.
His death occurred in 1801, and was due partly to an accident. He
slipped upon the stairs of the dissecting-room, and his fall was
followed by gastric derangement, from which he died.
Results of His Work.--The new science of the anatomy of the tissues
which he founded is now known as histology, and the general anatomy,
as he called it, has now become the study of minute anatomy of the
tissues. Bichat studied the membranes or tissues very profoundly, but
he did not employ the microscope and make sketches of their cellular
construction. The result of his work was to set the world studying the
minute structure of the tissues, a consequence of which led to the
modern study of histology. Since this science was constructed directly
upon his foundation, it is proper to recognize him as the founder of
histology.
Carpenter says of him: "Altogether Bichat left an impress upon the
science of life, the depth of which can scarcely be overrated; and this
not so much by the facts which he collected and generalized, as by
the method of inquiry which he developed, and by the systematic form
which he gave to the study of general anatomy in its relations both to
physiology and pathology."
Bichat's More Notable Successors.--His influence extended far, and
after the establishment of the cell-theory took on a new phase.
Microscopic study of the tissues has now become a separate division
of the science of anatomy, and engages the attention of a very large
number of workers. While the men who built upon Bichat's foundation are
numerous, we shall select for especial mention only a few of the more
notable, as Schwann, Koelliker, Schultze, Virchow, Leydig, and Ramon y
Cajal, whose researches stand in the direct line of development of the
ideas promulgated by Bichat.
Schwann.--Schwann's cell-theory was the result of close attention
to the microscopic structure of the tissues of animals. It was an
extension of the knowledge of the tissues which Bichat distinguished
and so thoroughly investigated from other points of view. The
cell-theory, which took rise in 1839, was itself epoch-making, and the
science of general anatomy was influenced by it as deeply as was the
science of embryology. The leading founder of this theory was Theodor
Schwann, whose portrait is shown on page 245, where there is also a
more extended account of his labors in connection with the cell-theory.
Had not the life of Bichat been cut off in his early manhood, he might
well have lived to see this great discovery added to his own.
Koelliker.--Albrecht von Koelliker (1817-1905) was one of the greatest
histologists of the nineteenth century. He is a striking figure in
the development of biology in a general way, distinguished as an
embryologist, as a histologist, and in other connections. During his
long life, from 1817 to 1905, he made an astounding number of additions
to our knowledge of microscopic anatomy. In the early years of his
scientific activity, "he helped in establishing the cell-theory, he
traced the origin of tissues from the segmenting ovum through the
developing embryo, he demonstrated the continuity between nerve-fibers
and nerve-cells of vertebrates (1845), ... and much more." He is
mentioned further, in connection with the rise of embryology, in
Chapter X.
The strong features of this veteran of research are shown in the
portrait, Fig. 50, which represents him at the age of seventy.
In 1847 he was called to the University of Würzburg, where he remained
to the time of his death. From 1850 to 1900, scarcely a year passed
without some important contribution from Von Koelliker extending the
knowledge of histology. His famous text-book on the structure of the
tissues (_Handbuch der Gewebelehre_) passed through six editions from
1852 to 1893, the final edition of it being worked over and brought
up to date by this extraordinary man after he had passed the age of
seventy-five. By workers in biology this will be recognized as a
colossal task. In the second volume of the last edition of this work,
which appeared in 1893, he went completely over the ground of the vast
accumulation of information regarding the nervous system which an army
of gifted and energetic workers had produced. This was all thoroughly
digested, and his histological work brought down to date.
Schultze.--The fine observations of Max Schultze (1825-1874) may also
be grouped with those of the histologists. We shall have occasion to
speak of him more particularly in the chapter on Protoplasm. He did
memorable service for general biology in establishing the protoplasm
doctrine, but many of his scientific memoirs are in the line of normal
histology; as, those on the structure of the olfactory membrane, on the
retina of the eye, the muscle elements, the nerves, etc., etc.
[Illustration: Fig. 50.--Von Koelliker, 1817-1905.]
Normal Histology and Pathology.--But histology has two phases: the
investigation of the tissues in health, which is called normal
histology; and the study of the tissues in disease and under abnormal
conditions of development, which is designated pathological histology.
The latter division, on account of its importance to the medical man,
has been extensively cultivated, and the development of pathological
study has greatly extended the knowledge of the tissues and has had its
influence upon the progress of normal histology. Goodsir, in England,
and Henle, in Germany, entered the field of pathological histology,
both doing work of historical importance. They were soon followed by
Virchow, whose eminence as a man and a scientist has made his name
familiar to people in general.
[Illustration: Fig. 51.--Rudolph Virchow, 1821-1903.]
Virchow.--Rudolph Virchow (1821-1903), for many years a professor in
the University of Berlin, was a notable man in biological science and
also as a member of the German parliament. He assisted in molding the
cell-theory into better form, and in 1858 published a work on _Cellular
Pathology_, which applied the cell-theory to diseased tissues. It is to
be remembered that Bichat was a medical man, intensely interested in
pathological, or diseased, tissues, and we see in Virchow the one who
especially extended Bichat's work on the side of abnormal histology.
Virchow's name is associated also with the beginning of the idea of
germinal continuity, which is the basis of biological ideas regarding
heredity (see, further, Chapter XV).
[Illustration: Fig. 52.--Franz Leydig, 1821-1908 (April).
Courtesy of Dr. Wm. M. Wheeler.]
Leydig.--Franz Leydig (Fig. 52) was early in the field as a histologist
with his handbook (_Lehrbuch der Histologie des Menschen und der
Thiere_) published in 1857. He applied histology especially to the
tissues of insects in 1864 and subsequent years, an account of which
has already been given in Chapter V.
[Illustration: Fig. 53.--S. Ramon y Cajal, 1850-]
Cajal as Histologist.--Ramon y Cajal, professor in the University of
Madrid, is a histologist whose work in a special field of research is
of world-wide renown. His investigations into the microscopic texture
of the nervous system and sense-organs have in large part cleared
up the questions of the complicated relations between the nervous
elements. In company with other European investigators he visited the
United States in 1899 on the invitation of Clark University, where his
lectures were a feature of the celebration of the tenth anniversary of
that university. Besides receiving many honors in previous years, in
1906 he was awarded, in conjunction with the Italian histologist Golgi,
one of the Nobel prizes in recognition of his notable investigations.
Golgi invented the staining methods that Ramon y Cajal has applied so
extensively and so successfully to the histology of the nervous system.
These men in particular may be remembered as the investigators who
expanded the work of Bichat on the tissues: Schwann, for disclosing the
microscopic elements of animal tissues and founding the cell-theory;
Koelliker, as the typical histologist after the analysis of tissues
into their elementary parts; Virchow, as extending the cell-idea
to abnormal histology; Leydig, for applying histology to the lower
animals; and Ramon y Cajal, for investigations into the histology of
the nervous system.
Text-Books of Histology.--Besides the works mentioned, the text-books
of Frey, Stricker, Ranvier, Klein, Schäfer, and others represent a
period in the general introduction of histology to students between
1859 and 1885. But these excellent text-books have been largely
superseded by the more recent ones of Stöhr, Boem-Davidoff, Piersol,
Szymonowicz, and others. The number of living investigators in
histology is enormous; and their work in the subject of cell-structure
and in the department of embryology now overlaps.
In pathological histology may be observed an illustration of the
application of biological studies to medicine. While no attempt is
made to give an account of these practical applications, they are of
too great importance to go unmentioned. Histological methods are in
constant use in clinical diagnosis, as in blood counts, the study
of inflammations, of the action of phagocytes, and of all manner of
abnormal growths.
In attempting to trace the beginning of a definite foundation for the
work on the structure of tissues, we go back to Bichat rather than to
Leeuwenhoek, as Richardson has proposed. Bichat was the first to give a
scientific basis for histology founded on extensive observations, since
all earlier observers gave only separated accounts of the structure of
particular tissues.
CHAPTER IX
THE RISE OF PHYSIOLOGY
Harvey Haller Johannes Müller
Physiology had a parallel development with anatomy, but for convenience
it will be considered separately. Anatomy shows us that animals and
plants are wonderfully constructed, but after we understand their
architecture and even their minute structure, the questions remain,
What are all the organs and tissues for? and what takes place within
the parts that are actually alive? Physiology attempts to answer
questions of this nature. It stands, therefore, in contrast with
anatomy, and is supplementary to it. The activities of living organisms
are varied, and depend on life for their manifestations. These
manifestations may be called vital activities. Physiology embraces a
study of them all.
Physiology of the Ancients.--This subject began to attract the
attention of ancient medical men who wished to fathom the activities
of the body in order to heal its diseases, but it is such a difficult
thing to begin to comprehend the activities of life that even the
simpler relationships were imperfectly understood, and they resorted to
mythical explanations. They spoke of spirits and humors in the body as
causes of various changes; the arteries were supposed to carry air, the
veins only blood; and nothing was known of the circulation. There arose
among these early medical men the idea that the body was dominated by a
subtle spirit. This went under the name _pneuma_, and the pneuma-theory
held sway until the period of the Revival of Learning.
Among the ancient physiologists the great Roman physician Galen is the
most noteworthy figure. As he was the greatest anatomist, so he was
also the greatest physiologist of ancient times. All physiological
knowledge of the time centered in his writings, and these were the
standards of physiology for many centuries, as they were also for
anatomy. In the early days anatomy, physiology, and medicine were all
united into a poorly digested mass of facts and fancies. This state
of affairs lasted until the sixteenth century, and then the awakening
came, through the efforts of gifted men, endued with the spirit of
independent investigation. The advances made depended upon the work
or leadership of these men, and there are certain periods of especial
importance for the advance of physiology that must be pointed out.
Period of Harvey.--The first of these epochs to be especially noted
here is the period of Harvey (1578-1657). In his time the old idea of
spirits and humors was giving way, but there was still much vagueness
regarding the activities of the body. He helped to illuminate the
subject by showing a connection between arteries and veins, and by
demonstrating the circulation of the blood. As we have seen in an
earlier chapter, Harvey did not observe the blood passing through the
capillaries from arteries to veins, but his reasoning was unassailable
that such a connection must exist, and that the blood made a complete
circulation. He gave his conclusions in his medical lectures as early
as 1619, but did not publish his views until 1628. It was reserved
for Malpighi, in 1661, actually to see the circulation through the
capillaries under the microscope, and for Leeuwenhoek, in 1669 and
later years, to extend these observations.
It was during Harvey's life that the microscope was brought into
use and was of such great assistance in advancing knowledge. Harvey
himself, however, made little use of this instrument. It was during
his life also that the knowledge of development was greatly promoted,
first through his own efforts, and later through those of Malpighi.
Harvey is to be recognized, then, as the father of modern physiology.
Indeed, before his time physiology as such can hardly be spoken of
as having come into existence. He introduced experimental work into
physiology, and thus laid the foundation of modern investigation. It
was the method of Harvey that made definite progress in this line
possible, and accordingly we honor him as one of the greatest as well
as the earliest of physiologists.
Period of Haller.--From Harvey's time we pass to the period of
Haller (1708-1777), at the beginning of which physiology was still
wrapped up with medicine and anatomy. The great work of Haller was
to create an independent science of physiology. He made it a subject
to be studied for its own sake, and not merely as an adjunct to
medicine. Haller was a man of vast and varied learning, and to him
was applied by unsympathetic critics the title of "that abyss of
learning." His portrait, as shown in Fig. 54, gives the impression of
a somewhat pompous and overbearing personality. He was egotistical,
self-complacent, and possessed of great self-esteem. The assurance
in the inerrancy of his own conclusions was a marked characteristic
of Haller's mind. While he was a good observer, his own work showing
conscientious care in observation, he was not a good interpreter, and
we are to recollect that he vigorously opposed the idea of development
set forth by Wolff, and we must also recognize that his researches
formed the chief starting-point of an erroneous conception of vitality.
As Verworn points out, Haller's own experiments upon the phenomena of
irritability were exact, but they were misinterpreted by his followers,
and through the molding influence of others the attempted explanation
of their meaning grew into the conception of a special vital force
belonging to living organisms only. In its most complete form, this
idea provided for a distinct dualism between living and lifeless
matter, making all vital actions dependent upon the operation of a
mystical supernatural agency. This assumption removed vital phenomena
from the domain of clear scientific analysis, and for a long time
exercised a retarding influence upon the progress of physiology.
His chief service of permanent value was that he brought into one work
all the facts and the chief theories of physiology carefully arranged
and digested. This, as has been said, made physiology an independent
branch of science, to be pursued for itself and not merely as an
adjunct to the study of medicine. The work referred to is his Elements
of Physiology (_Elementa Physiologiæ Corporis Humani_, 1758), one
of the noteworthy books marking a distinct epoch in the progress of
science.
[Illustration: Fig. 54.--Albrecht Haller, 1708-1777.]
To the period of Haller also belongs the discovery of oxygen, in 1774,
by Priestley, a discovery which was destined to have profound influence
upon the subsequent development of physiology, so that even now
physiology consists largely in tracing the way in which oxygen enters
the body, the manner in which it is distributed to the tissues, and the
various phases of vital activity that it brings about within the living
tissues.
Charles Bell.--The period of Haller may be considered as extending
beyond his lifetime and as terminating when the influence of Müller
began to be felt. Another discovery coming in the closing years of
Haller's period marks a capital advance in physiology. I refer to the
discovery of Charles Bell (1774-1842) showing that the nerve fibers of
the anterior roots of the spinal cord belong to the motor type, while
those of the posterior roots belong to the sensory type.
This great truth was arrived at theoretically, rather than as the
result of experimental demonstration. It was first expounded by Bell
in 1811 in a small essay entitled _Idea of a New Anatomy of the
Brain_, which was printed for private distribution. It was expanded
in his papers, beginning in 1821, and published in the Philosophical
Transactions of the Royal Society of London, and finally embodied in
his work on the nervous system, published in 1830. At this latter date
Johannes Müller had reached the age of twenty-nine, and had already
entered upon his career as the leading physiologist of Germany. What
Bell had divined he demonstrated by experiments.
Charles Bell (Fig. 55) was a surgeon of eminence; in private life he
was distinguished by "unpretending amenity, and simplicity of manners
and deportment."
[Illustration: Fig. 55.--Charles Bell, 1774-1842.]
Period of Johannes Müller.--The period that marks the beginning of
modern physiology came next, and was due to the genius and force of
Johannes Müller (1801-1858). Verworn says of him: "He is one of those
monumental figures that the history of every science brings forth but
once. They change the whole aspect of the field in which they work,
and all later growth is influenced by their labors." Johannes Müller
was a man of very unusual talent and attainments, the possessor of
a master mind. Some have said, and not without reason, that there
was something supernatural about Müller, for his whole appearance
bore the stamp of the uncommon. His portrait, with its massive head
above the broad shoulders, is shown in Fig. 56. In his lectures his
manner and his gestures reminded one of a Catholic priest. Early in
his life, before the disposition to devote himself to science became
so overwhelming, he thought of entering the priesthood, and there
clung to him all his life some marks of the holy profession. In his
highly intellectual face we find "a trace of severity in his mouth and
compressed lips, with the expression of most earnest thought on his
brow and eyes, and with the remembrance of a finished work in every
wrinkle of his countenance."
This extraordinary man exercised a profound influence upon those who
came into contact with him. He excited almost unbounded enthusiasm and
great veneration among his students. They were allowed to work close by
his side, and so magnetic was his personality that he stimulated them
powerfully and succeeded in transmitting to them some of his own mental
qualities. As professor of physiology in Berlin, Müller trained many
gifted young men, among whom were Ludwig (1816-1895), Du Bois-Reymond
(1818-1896), and Helmholtz (1821-1894), who became distinguished
scholars and professors in German universities. Helmholtz, speaking of
Müller's influence on students, paid this tribute to the grandeur of
his teacher: "Whoever comes into contact with men of the first rank has
an altered scale of values in life. Such intellectual contact is the
most interesting event that life can offer."
The particular service of Johannes Müller to science was to make
physiology broadly comparative. So comprehensive was his grasp upon
the subject that he gained for himself the title of the greatest
physiologist of modern times. He brought together in his great work on
the physiology of man not only all that had been previously made known,
carefully sifted and digested, but a great mass of new information,
which was the result of his own investigations and of those of his
students. So rigorous were his scientific standards that he did not
admit into this treatise anything which had been untested either by
himself or by some of his assistants or students. Verworn says of this
monumental work, which appeared in 1833, under the title _Handbuch der
Physiologie des Menschen_: "This work stands to-day unsurpassed in the
genuinely philosophical manner in which the material, swollen to vast
proportions by innumerable special researches, was for the first time
sifted and elaborated into a unitary picture of the mechanism within
the living organism. In this respect the _Handbuch_ is to-day not only
unsurpassed, but unequalled."
Müller was the most accurate of observers; indeed, he is the most
conspicuous example in the nineteenth century of a man who accomplished
a prodigious amount of work all of which was of the highest quality. In
physiology he stood on broader lines than had ever been used before.
He employed every means at his command--experimenting, the observation
of simple animals, the microscope, the discoveries in physics, in
chemistry, and in psychology.
He also introduced into physiology the principles of psychology, and
it is from the period of Johannes Müller that we are to associate
recognition of the close connection between the operations of the
mind and the physiology of the brain that has come to occupy such a
conspicuous position at the present time.
[Illustration: Fig. 56.--Johannes Müller, 1801-1858.]
Müller died in 1858, having reached the age of fifty-seven, but his
influence was prolonged through the teachings of his students.
Physiology after Müller
[Illustration: Fig. 57.--Ludwig, 1816-1895.]
Ludwig.--Among the men who handed on the torch of Müller there has
already been mentioned Ludwig (Fig. 57). For many years he lectured in
the University of Leipsic, attracting to that university high-minded,
eager, and gifted young men, who received from this great luminary of
physiology by expression what he himself had derived from contact with
Müller. There are to-day distributed through the universities a number
of young physiologists who stand only one generation removed from
Johannes Müller, and who still labor in the spirit that was introduced
into this department of study by that great master.
[Illustration: Fig. 58.--Du Bois-Reymond, 1818-1896.]
Du Bois-Reymond.--Du Bois-Reymond (Fig. 58), another of his
distinguished pupils, came to occupy the chair which Müller himself
had filled in the University of Berlin, and during the period of his
vigor was in physiology one of the lights of the world. It is no
uncommon thing to find recently published physiologies dedicated either
to the memory of Johannes Müller, as in the case of that remarkable
_General Physiology_ by Verworn; or to Ludwig, or to Du Bois-Reymond,
who were in part his intellectual product. From this disposition among
physiologists to do homage to Müller, we are able to estimate somewhat
more closely the tremendous reach of his influence.
Bernard.--When Müller was twelve years old there was born in
Saint-Julien, department of the Rhône, Claude Bernard, who attained
an eminence as a physiologist, of which the French nation are justly
proud. Although he was little thought of as a student, nevertheless
after he came under the influence of Magendie, at the age of
twenty-six, he developed rapidly and showed his true metal. He
exhibited great manual dexterity in performing experiments, and also a
luminous quality of mind in interpreting his observations. One of his
greatest achievements in physiology was the discovery of the formation
within the liver of glycogen, a substance chemically related to sugar.
Later he discovered the system of vaso-motor nerves that control and
regulate the caliber of the blood-vessels. Both of these discoveries
assisted materially in understanding the wonderful changes that are
going on within the human body. But besides his technical researches,
any special consideration of which lies quite beyond the purpose of
this book, he published in 1878-1879 a work upon the phenomena of
life in animals and vegetables, a work that had general influence
in extending the knowledge of vital activities. I refer to his now
classic _Leçons sur les Phénomènes de la vie communs aux animaux et aux
végétaux_.
The thoughtful face of Bernard is shown in his portrait, Fig. 59. He
was one of those retiring, silent men whose natures are difficult to
fathom, and who are so frequently misunderstood. A domestic infelicity,
that led to the separation of himself from his family, added to his
isolation and loneliness. When touched by the social spirit he charmed
people by his personality. He was admired by the Emperor Napoleon
Third, through whose influence Bernard acquired two fine laboratories.
In 1868 he was elected to the French Academy, and became thereby one of
the "Forty Immortals."
[Illustration: Fig. 59.--Claude Bernard, 1813-1878.]
Foster describes him thus: "Tall in stature, with a fine presence,
with a noble head, the eyes full at once of thought and kindness, he
drew the look of observers upon him wherever he appeared. As he walked
in the streets passers-by might be heard to say 'I wonder who that is;
he must be some distinguished man.'"
Two Directions of Growth.--Physiology, established on the broad
foundations of Müller, developed along two independent pathways, the
physical and the chemical. We find a group of physiologists, among whom
Weber, Ludwig, Du Bois-Reymond, and Helmholtz were noteworthy leaders,
devoted to the investigations of physiological facts through the
application of measurements and records made by machinery. With these
men came into use the time-markers, the myographs, and the ingenious
methods of recording blood-pressure, changes in respiration, the
responses of muscle and nerve to various forms of stimulation, the rate
of transmission of nerve-currents, etc.
The investigation of vital activities by means of measurements and
instrumental records has come to represent one especial phase of
modern physiology. As might have been predicted, the discoveries and
extensions of knowledge resulting from this kind of experimentation
have been remarkable, since it is obvious that permanent records made
by mechanical devices will rule out many errors; and, moreover, they
afford an opportunity to study at leisure phenomena that occupy a very
brief time.
The other marked line of physiological investigation has been in the
domain of chemistry, where Wöhler, Liebig, Kühne, and others have,
through the study of the chemical changes occurring in its body,
observed the various activities that take place within the organism.
They have reduced all tissues and all parts of the body to chemical
analysis, studied the chemical changes in digestion, in respiration,
etc. The more recent observers have also made a particular feature of
the study of the chemical changes going on within the living matter.
The union of these two chief tendencies into the physico-chemical
aspects of physiology has established the modern way of looking upon
vital activities. These vital activities are now regarded as being, in
their ultimate analysis, due to physical and chemical changes taking
place within the living substratum. All along, this physico-chemical
idea has been in contest with that of a duality between the body and
the life that is manifested in it. The vitalists, then, have had
many controversies with those who make their interpretations along
physico-chemical lines. We will recollect that vitalism in the hands of
the immediate successors of Haller became not only highly speculative,
but highly mystical, tending to obscure any close analysis of vital
activity and throwing explanations all back into the domain of
mysticism. Johannes Müller was also a vitalist, but his vitalism was
of a more acceptable form. He thought of changes in the body as being
due to vitality--to a living force; but he did not deny the possibility
of the transformation of this vital energy into other forms of energy;
and upon the basis of Müller's work there has been built up the
modern conception that there is found in the human body a particular
transformation-form of energy, not a mystical vital force that presides
over all manifestations of life.
The advances in physiology, beginning with those of William Harvey,
have had immense influence not only upon medicine, but upon all
biology. We find now the successful and happy union between physiology
and morphology in the work which is being so assiduously carried on
to-day under the title of experimental morphology.
The great names in physiology since Müller are numerous, and perhaps it
is invidious to mention particular ones; but, inasmuch as Ludwig and Du
Bois-Reymond have been spoken of, we may associate with them the names
of Sir Michael Foster and Burdon-Sanderson, in England; and of Brücke
(one of Müller's disciples) and Verworn, in Germany, as modern leaders
whose investigations have promoted advance, and whose clear exposition
of the facts and the theories of physiology have added much to the
dignity of the science.
CHAPTER X
VON BAER AND THE RISE OF EMBRYOLOGY
Anatomy investigates the arrangement of organic tissues; embryology, or
the science of development, shows how they are produced and arranged.
There is no more fascinating division of biological study. As Minot
says: "Indeed, the stories which embryology has to tell are the most
romantic known to us, and the wildest imaginative creations of Scott
or Dumas are less startling than the innumerable and almost incredible
shifts of rôle and change of character which embryology has to
entertain us with in her histories."
Embryology is one of the most important biological sciences in
furnishing clues to the past history of animals. Every organism
above the very lowest, no matter how complex, begins its existence
as a single microscopic cell, and between that simple state and the
fully formed condition every gradation of structure is exhibited.
Every time an animal is developed these constructive changes are
repeated in orderly sequence, and one who studies the series of steps
in development is led to recognize that the process of building an
animal's body is one of the most wonderful in all nature.
Rudimentary Organs.--But, strangely enough, the course of development
in any higher organism is not straightforward, but devious. Instead of
organs being produced in the most direct manner, unexpected by-paths
are followed, as when all higher animals acquire gill-clefts and many
other rudimentary organs not adapted to their condition of life.
Most of the rudimentary organs are transitory, and bear testimony, as
hereditary survivals, to the line of ancestry. They are clues by means
of which phases in the evolution of animal life may be deciphered.
Bearing in mind the continually shifting changes through which animals
pass in their embryonic development, one begins to see why the adult
structures of animals are so difficult to understand. They are not
only complex; they are also greatly modified. The adult condition of
any organ or tissue is the last step in a series of gradually acquired
modifications, and is, therefore, the farthest departure from that
which is ancestral and archetypal. But in the process of formation
all the simpler conditions are exhibited. If, therefore, we wish to
understand an organ or an animal, we must follow its development, and
see it in simpler conditions, before the great modifications have been
added.
The tracing of the stages whereby cells merge into tissues, tissues
into organs, and determining how the organs by combinations build
up the body, is embryology. On account of the extended applications
of this subject in biology, and the light which it throws on all
structural studies, we shall be justified in giving its history at
somewhat greater length than that adopted in treating of other topics.
Five Historical Periods.--The story of the rise of this interesting
department of biology can, for convenience, be divided into five
periods, each marked by an advance in general knowledge. These are: (1)
the period of Harvey and Malpighi; (2) the period of Wolff; (3) the
period of Von Baer; (4) the period from Von Baer to Balfour; and (5)
the period of Balfour, with an indication of present tendencies. Among
all the leaders Von Baer stands as a monumental figure at the parting
of the ways between the new and the old--the sane thinker, the great
observer.
The Period of Harvey and Malpighi
In General.--The usual account of the rise of embryology is derived
from German writers. But there is reason to depart from their
traditions, in which Wolff is heralded as its founder, and the one
central figure prior to Pander and Von Baer.
The embryological work of Wolff's great predecessors, Harvey and
Malpighi, has been passed over too lightly. Although these men have
received ample recognition in closely related fields of investigation,
their insight into those mysterious events that culminate in the
formation of a new animal has been rarely appreciated. Now and then a
few writers, as Brooks and Whitman, have pointed out the great worth
of Harvey's work in embryology, but fewer have spoken for Malpighi in
this connection. Koelliker, it is true, in his address at the unveiling
of the statue of Malpighi, in his native town of Crevalcuore, in 1894,
gives him well-merited recognition as the founder of embryology, and
the late Sir Michael Foster has written in a similar vein in his
delightful _Lectures on the History of Physiology_.
However great was Harvey's work in embryology, I venture to say that
Malpighi's was greater when considered as a piece of observation.
Harvey's work is more philosophical; he discusses the nature of
development, and shows unusual powers as an accurate reasoner. But that
part of his treatise devoted to observation is far less extensive and
exact than Malpighi's, and throughout his lengthy discussions he has
the flavor of the ancients.
Malpighi's work, on the contrary, flavors more of the moderns. In terse
descriptions, and with many sketches, he shows the changes in the hen's
egg from the close of the first day of development onward.
It is a noteworthy fact that, at the period in which he lived,
Malpighi could so successfully curb the tendency to indulge in wordy
disquisitions, and that he was satisfied to observe carefully, and tell
his story in a simple way. This quality of mind is rare. As Emerson has
said: "I am impressed with the fact that the greatest thing a human
soul ever does in this world is to see something, and tell what it saw
in a plain way. Hundreds of people can talk for one who can think, but
thousands can think for one who can see. To see clearly is poetry,
philosophy, and religion all in one." But "to see" here means, of
course, to interpret as well as to observe.
Although there were observers in the field of embryology before Harvey,
little of substantial value had been produced. The earliest attempts
were vague and uncritical, embracing only fragmentary views of the
more obvious features of body-formation. Nor, indeed, should we look
for much advance in the field of embryology even in Harvey's time. The
reason for this will become obvious when we remember that the renewal
of independent observation had just been brought about in the preceding
century by Vesalius, and that Harvey himself was one of the pioneers in
the intellectual awakening. Studies on the development of the body are
specialized, involving observations on minute structures and recondite
processes, and must, therefore, wait upon considerable advances in
anatomy and physiology. Accordingly, the science of embryology was of
late development.
Harvey.--Harvey's was the first attempt to make a critical analysis
of the process of development, and that he did not attain more was
not owing to limitations of his powers of discernment, but to the
necessity of building on the general level of the science of his time,
and, further, to his lack of instruments of observation and technique.
Nevertheless, Harvey may be considered as having made the first
independent advance in embryology.
By clearly teaching, on the basis of his own observations, the gradual
formation of the body by aggregation of its parts, he anticipated
Wolff. This doctrine came to be known under the title of "epigenesis,"
but Harvey's epigenesis[3] was not, as Wolff's was, directed against
a theory of pre-delineation of the parts of the embryo, but against
the ideas of the medical men of the time regarding the metamorphosis
of germinal elements. It lacked, therefore, the dramatic setting which
surrounded the work of Wolff in the next century. Had the doctrine of
pre-formation been current in Harvey's time, we are quite justified in
assuming that he would have assailed it as vigorously as did Wolff.
His Treatise on Generation.--Harvey's embryological work was published
in 1651 under the title _Exercitationes de Generatione Animalium_. It
embraces not only observations on the development of the chick, but
also on the deer and some other mammals. As he was the court physician
of Charles I, that sovereign had many deer killed in the park, at
intervals, in order to give Harvey the opportunity to study their
development.
As fruits of his observation on the chick, he showed the position in
which the embryo arises within the egg, _viz._, in the white opaque
spot or cicatricula; and he also corrected Aristotle, Fabricius, and
his other predecessors in many particulars.
Harvey's greatest predecessor in this field, Fabricius, was also his
teacher. When, in search of the best training in medicine, Harvey took
his way from England to Italy, as already recounted, he came under
the instruction of Fabricius in Padua. In 1600, Fabricius published
sketches showing the development of animals; and, again, in 1625,
six years after his death, appeared his illustrated treatise on the
development of the chick. Except the figures of Coiter (1573), those
of Fabricius were the earliest published illustrations of the kind.
Altogether his figures show developmental stages of the cow, sheep,
pig, galeus, serpent, rat, and chick.
Harvey's own treatise was not illustrated. With that singular
independence of mind for which he was conspicuous, the vision of the
pupil was not hampered by the authority of his teacher, and, trusting
only to his own sure observation and reason, he described the stages of
development as he saw them in the egg, and placed his own construction
on the facts.
One of the earliest activities to arrest his attention in the chick was
a pulsating point, the heart, and, from this observation, he supposed
that the heart and the blood were the first formations. He says: "But
as soon as the egg, under the influence of the gentle warmth of the
incubating hen, or of warmth derived from another source, begins to
pullulate, this spot forthwith dilates, and expands like the pupil of
the eye; and from thence, as the grand center of the egg, the latent
plastic force breaks forth and germinates. This first commencement of
the chick, however, so far as I am aware, has not yet been observed by
any one."
It is to be understood, however, that the descriptive part of his
treatise is relatively brief (about 40 pages out of 350 in Willis's
translation), and that the bulk of the 106 "exercises" into which his
work is divided is devoted to comments on the older writers and to
discussions of the nature of the process of development.
The aphorism, "_omne vivum ex ovo_," though not invented by Harvey,
was brought into general use through his writings. As used in his day,
however, it did not have its full modern significance. With Harvey it
meant simply that the embryos of all animals, the viviparous as well as
the oviparous, originate in eggs, and it was directed against certain
contrary medical theories of the time.
[Illustration: Fig. 60.--Frontispiece to Harvey's _Generatione
Animalium_ (1651).]
The first edition of his _Generatione Animalium_, London, 1651, is
provided with an allegorical frontispiece embodying this idea. As shown
in Fig. 60, it represents Jove on a pedestal, uncovering a round box,
or ovum, bearing the inscription "_ex ovo omnia_," and from the box
issue all forms of living creatures, including also man.
Malpighi.--The observer in embryology who looms into prominence
between Harvey and Wolff is Malpighi. He supplied what was greatly
needed at the time--an illustrated account of the actual stages in the
development of the chick from the end of the first day to hatching,
shorn of verbose references and speculations.
His observations on development are in two separate memoirs, both sent
to the Royal Society in 1672, and published by the Society in Latin,
under the titles _De Formatione Pulli in Ovo_ and _De Ovo Incubato_.
The two taken together are illustrated by twelve plates containing
eighty-six figures, and the twenty-two quarto pages of text are nearly
all devoted to descriptions, a marked contrast to the 350 pages of
Harvey unprovided with illustrations.
His pictures, although not correct in all particulars, represent what
he was able to see, and are very remarkable for the age in which they
were made, and considering the instruments of observation at his
command. They show successive stages from the time the embryo is first
outlined, and, taken in their entirety, they cover a wide range of
stages.
His observations on the development of the heart, comprising twenty
figures, are the most complete. He clearly illustrates the aortic
arches, those transitory structures of such great interest as showing a
phase in ancestral history.
[Illustration: Fig. 61.--Selected Sketches from Malpighi's Works.
Showing Stages in the Development of the Chick (1672).]
He was also the first to show by pictures the formation of the
head-fold and the neural groove, as well as the brain-vesicles and
eye-pockets. His delineation of heart, brain, and eye-vesicles are far
ahead of those illustrating Wolff's _Theoria Generationis_, made nearly
a hundred years later.
Fig. 61 shows a few selected sketches from the various plates of his
embryological treatises, to compare with those of Wolff. (See Fig. 63.)
[Illustration: Fig. 62.--Marcello Malpighi, 1628-1694.]
The original drawings for _De Ovo Incubato_, still in possession of the
Royal Society, are made in pencil and red chalk, and an examination
of them shows that they far surpass the reproductions in finish and
accuracy.
While Harvey taught the gradual formation of parts, Malpighi, from his
own observations, supposed the rudiments of the embryo to pre-exist
within the egg. He thought that, possibly, the blood-vessels were in
the form of tubes, closely wrapped together, which by becoming filled
with blood were distended. Nevertheless, in the treatises mentioned
above he is very temperate in his expressions on the whole matter, and
evidently believed in the new formation of many parts.
The portrait of Malpighi shown in Fig. 62 is taken from his life by
Atti. From descriptions of his personal appearance (see page 58) one
would think that this is probably a better likeness than the strikingly
handsome portrait painted by Tabor, and presented by Malpighi to the
Royal Society of London. For a reproduction of the latter see page 59.
Malpighi's Rank.--On the whole, Malpighi should rank above Harvey as an
embryologist, on account of his discoveries and fuller representation,
by drawings and descriptions, of the process of development. As Sir
Michael Foster has said: "The first adequate description of the long
series of changes by which, as they melt the one into the other,
like dissolving views, the little white opaque spot in the egg is
transformed into the feathered, living, active bird, was given by
Malpighi. And where he left it, so for the most part the matter
remained until even the present century. For this reason we may speak
of him as the founder of embryology."
The Period of Wolff
Between Harvey and Wolff, embryology had become dominated by the theory
that the embryo exists already pre-formed within the egg, and, as a
result of the rise of this new doctrine, the publications of Wolff had
a different setting from that of any of his predecessors. It is only
fair to say that to this circumstance is owing, in large part, the
prominence of his name in connection with the theory of epigenesis.
As we have already seen, Harvey, more than a century before the
publications of Wolff, had clearly taught that development is a process
of gradual becoming. Nevertheless, Wolff's work, as opposed to the new
theory, was very important.
While the facts fail to support the contention that he was the founder
of epigenesis, it is to be remembered that he has claims in other
directions to rank as the foremost student of embryology prior to Von
Baer.
As a preliminary to discussing Wolff's position, we should bring under
consideration the doctrine of pre-formation and encasement.
Rise of the Theory of Pre-delineation.--The idea of pre-formation in
its first form is easily set forth. Just as when we examine a seed we
find within an embryo plantlet, so it was supposed that the various
forms of animal life existed in miniature within the egg. The process
of development was supposed to consist of the expansion or unfolding
of this pre-formed embryo. The process was commonly illustrated by
reference to flower-buds. "Just as already in a small bud all the
parts of the flower, such as stamens and colored petals, are enveloped
by the green and still undeveloped sepals; just as the parts grow in
concealment and then suddenly expand into a blossom, so also in the
development of animals, it was thought that the already present, small
but transparent parts grow, gradually expand, and become discernible."
(Hertwig.) From the feature of unfolding this was called in the
eighteenth century the theory of _evolution_, giving to that term quite
a different meaning from that attached to it at the present time.
This theory, strange as it may seem to us now, was founded on a
basis of actual observation--not entirely on speculation. Although
it was a product of the seventeenth century, from several printed
accounts one is likely to gather the impression that it arose in the
eighteenth century, and that Bonnet, Haller, and Leibnitz were among
its founders. This implication is in part fostered by the circumstance
that Swammerdam's _Biblia Naturæ_, which contains the germ of the
theory, was not published until 1737--more than half a century
after his death--although the observations for it were completed
before Malpighi's first paper on embryology was published in 1672.
While it is well to bear in mind that date of publication, rather
than date of observation, is accepted as establishing the period of
emergence of ideas, there were other men, as Malpighi and Leeuwenhoek,
contemporaries of Swammerdam, who published in the seventeenth century
the basis for this theory.
Malpighi supposed (1672) the rudiment of the embryo to pre-exist within
the hen's egg, because he observed evidences of organization in the
unincubated egg. This was in the heat of the Italian summer (in July
and August, as he himself records), and Dareste suggests that the
developmental changes had gone forward to a considerable degree before
Malpighi opened the eggs. Be this as it may, the imperfection of his
instruments and technique would have made it very difficult to see
anything definitely in stages under twenty-four hours.
In reference to his observations, he says that in the unincubated egg
he saw a small embryo enclosed in a sac which he subjected to the rays
of the sun. "Frequently I opened the sac with the point of a needle,
so that the animals contained within might be brought to the light,
nevertheless to no purpose; for the individuals were so jelly-like and
so very small that they were lacerated by a light stroke. Therefore,
it is right to confess that the beginnings of the chick pre-exist in
the egg, and have reached a higher development in no other way than
in the eggs of plants." ("Quare _pulli stamina_ in ovo _præexistere_,
altiorémque originem nacta esse fateri convenit, haud dispari ritu, ac
in Plantarum ovis.")
Swammerdam (1637-1680) supplied a somewhat better basis. He observed
that the parts of the butterfly, and other insects as well, are
discernible in the chrysalis stage. Also, on observing caterpillars
just before going into the pupa condition, he saw in outline the organs
of the future stage, and very naturally concluded that development
consists of an expansion of already formed parts.
A new feature was introduced through the discovery, by Leeuwenhoek,
about 1677,[4] of the fertilizing filaments of eggs. Soon after,
controversies began to arise as to whether the embryo pre-existed in
the sperm or in the egg. By Leeuwenhoek, Hartsoeker, and others the egg
was looked upon as simply a _nidus_ within which the sperm developed,
and they asserted that the future animal existed in miniature in
the sperm. These controversies gave rise to the schools of the
animalculists, who believed the sperm to be the animal germ, and of the
ovulists, who contended for the ovum in that rôle.
It is interesting to follow the metaphysical speculations which led
to another aspect of the doctrine of pre-formation. There were those,
notably Swammerdam, Leibnitz, and Bonnet, who did not hesitate to
follow the idea to the logical consequence that, if the animal germ
exists pre-formed, one generation after another must be encased within
it. This gave rise to the fanciful idea of encasement or _emboîtement_,
which was so greatly elaborated by Bonnet and, by Leibnitz, applied to
the development of the soul. Even Swammerdam (who, by the way, though
a masterly observer, was always a poor generalizer) conceived of the
germs of all forthcoming generations as having been located in the
common mother Eve, all closely encased one within the other, like the
boxes of a Japanese juggler. The end of the human race was conceived
of by him as a necessity, when the last germ of this wonderful series
had been unfolded.
[Illustration: Fig. 63.--Plate from Wolff's _Theoria Generationis_
(1759), Showing Stages in the Development of the Chick.]
His successors, in efforts to compute the number of homunculi which
must have been condensed in the ovary of Eve, arrived at the amazing
result of two hundred millions.
Work of Wolff.--Friedrich Kaspar Wolff, as a young man of twenty-six
years, set himself against this grotesque doctrine of pre-formation
and encasement in his _Theoria Generationis_, published in 1759. This
consists of three parts: one devoted to the development of plants, one
to the development of animals, and one to theoretical considerations.
He contended that the organs of animals make their appearance
gradually, and that he could actually follow their successive stages of
formation.
The figures in it illustrating the development of the chick, some
of which are shown in Fig. 63, are not, on the whole, so good as
Malpighi's. Wolff gives, in all, seventeen figures, while Malpighi
published eighty-six, and his twenty figures on the development of the
heart are more detailed than any of Wolff's. When the figures represent
similar stages of development, a comparison of the two men's work is
favorable to Malpighi. The latter shows much better, in corresponding
stages, the series of cerebral vesicles and their relation to the optic
vesicles. Moreover, in the wider range of his work, he shows many
things--such as the formation of the neural groove, etc.--not included
in Wolff's observations. Wolff, on the other hand, figures for the
first time the primitive kidneys, or "Wolffian bodies," of which he was
the discoverer.
Although Wolff was able to show that development consists of a gradual
formation of parts, his theory of development was entirely mystical and
unsatisfactory. The fruitful idea of germinal continuity had not yet
emerged, and the thought that the egg has inherited an organization
from the past was yet to be expressed. Wolff was, therefore, in
the same quandary as his predecessors when he undertook to explain
development. Since he assumed a total lack of organization in the
beginning, he was obliged to make development "miraculous" through
the action on the egg of a hyperphysical agent. From a total lack of
organization, he conceived of its being lifted to the highly organized
product through the action of a "_vis essentialis corporis_."
He returned to the problem of development later, and, in 1768-1769,
published his best work in this field on the development of the
intestine.[5] This is a very original and strong piece of observational
work. While his investigations for the _Theoria Generationis_ did not
reach the level of Malpighi's, those of the paper of 1768 surpassed
them and held the position of the best piece of embryological work up
to that of Pander and Von Baer. This work was so highly appreciated by
Von Baer that he said: "It is the greatest masterpiece of scientific
observation which we possess." In it he clearly demonstrated that the
development of the intestine and its appendages is a true process
of becoming. Still later, in 1789, he published further theoretical
considerations.
Opposition to Wolff's Views.--But all Wolff's work was launched into an
uncongenial atmosphere. The great physiologist Haller could not accept
the idea of epigenesis, but opposed it energetically, and so great
was his authority that the views of Wolff gained no currency. This
retarded progress in the science of animal development for more than a
half-century.
Bonnet was also a prolific writer in opposition to the ideas of Wolff,
and we should perhaps have a portrait of him (Fig. 64) as one of
the philosophical naturalists of the time. His prominent connection
with the theory of pre-delineation in its less grotesque form, his
discovery of the development of the eggs of plant-lice without previous
fertilization, his researches on regeneration of parts in polyps
and worms, and other observations place him among the conspicuous
naturalists of the period. His system of philosophy, which has been
carefully analyzed by Whitman, is designated by that writer as a system
of negations.
[Illustration: Fig. 64.--Charles Bonnet, 1720-1793.]
In 1821, J. Fr. Meckel, recognizing the great value of Wolff's
researches on the development of the intestines, rescued the work from
neglect and obscurity by publishing a German translation of the same,
and bringing it to the attention of scholars. From that time onward
Wolff's labor was fruitful.
His _De Formatione Intestinorum_ rather than his _Theoria Generationis_
embodies his greatest contribution to embryology. Not only is it a
more fitting model of observation, but in it he foreshadows the idea
of germ-layers in the embryo, which, under Pander and Von Baer, became
the fundamental conception in structural embryology. Throughout his
researches both early and late, he likens the embryonic rudiments,
which precede the formation of organs, to leaflets. In his work of
1768 he described in detail how the leaf-like layers give rise to the
systems of organs; showing that the nervous system arises first from a
leaf-like layer, and is followed, successively, by a flesh layer, the
vascular system, and lastly, by the intestinal canal--all arising from
original leaf-like layers.
In these important generalizations, although they are verbally
incorrect, he reached the truth as nearly as it was possible at the
time, and laid the foundation of the germ-layer theory.
Wolff was a man of great power as an observer, and although his
influence was for a long time retarded, he should be recognized as the
foremost investigator in embryology before Von Baer.
Few Biographical Facts.--The little known of his life is gained through
his correspondence and a letter by his amanuensis. Through personal
neglect, and hostility to his work, he could not secure a foothold
in the universities of Germany, and, in 1764, on the invitation
of Catherine of Russia, he went to the Academy of Sciences at St.
Petersburg, where he spent the last thirty years of his life.
It has been impossible to discover a portrait of Wolff, although I have
sought one in various ways for several years. The secretary of the
Academy of Sciences at St. Petersburg writes that no portrait of Wolff
exists there, and that the Academy will gratefully receive information
from any source regarding the existence of a portrait of the great
academician.
His sincere and generous spirit is shown in his correspondence with
Haller, his great opponent. "And as to the matter of contention between
us, I think thus: For me, no more than for you, glorious man, is truth
of the very greatest concern. Whether it chance that organic bodies
emerge from an invisible into a visible condition, or form themselves
out of the air, there is no reason why I should wish the one were truer
than the other, or wish the one and not the other. And this is your
view also, glorious man. We are investigating for truth only; we seek
that which is true. Why then should I contend with you?" (Quoted from
Wheeler.)
The Period of Von Baer
What Johannes Müller was for physiology, von Baer was for embryology;
all subsequent growth was influenced by his investigations.
The greatest classic in embryology is his _Development of Animals_
(_Entwicklungsgeschichte der Tiere--Beobachtung und Reflexion_), the
first part of which was published in 1828, and the work on the second
part completed in 1834, although it was not published till 1837. This
second part was never finished according to the plan of Von Baer, but
was issued by his publisher, after vainly waiting for the finished
manuscript. The final portion, which Von Baer had withheld, in order to
perfect in some particulars, was published in 1888, after his death,
but in the form in which he left it in 1834.
The observations for the first part began in 1819, after he had
received a copy of Pander's researches, and covered a period of seven
years of close devotion to the subject; and the observations for the
last part were carried on at intervals for several years.
It is significant of the character of his _Reflexionen_ that, although
published before the announcement of the cell-theory, and before the
acceptance of the doctrine of organic evolution, they have exerted a
molding influence upon embryology to the present time. The position of
von Baer in embryology is owing as much to his sagacity in speculation
as to his powers as an observer. "Never again have observation and
thought been so successfully combined in embryological work" (Minot).
Von Baer was born in 1792, and lived on to 1876, but his enduring fame
in embryology rests on work completed more than forty years before
the end of his useful life. After his removal from Königsberg to St.
Petersburg, in 1834, he very largely devoted himself to anthropology in
its widest sense, and thereby extended his scientific reputation into
other fields.
If space permitted, it would be interesting to give the biography[6]
of this extraordinary man, but here it will be necessary to content
ourselves with an examination of his portraits and a brief account of
his work.
Portraits.--Several portraits of von Baer showing him at different
periods of his life have been published. A very attractive one, taken
in his early manhood, appeared in _Harper's Magazine_ for 1898. The
expression of the face is poetical, and the picture is interesting
to compare with the more matured, sage-like countenance forming
the frontispiece of Stieda's _Life of Von Baer_ (see Fig. 65).
This, perhaps the best of all his portraits, shows him in the full
development of his powers. An examination of it impresses one with
confidence in his balanced judgment and the thoroughness and profundity
of his mental operations.
[Illustration: Fig. 65.--Karl Ernst von Baer, 1792-1876.]
The portrait of Von Baer at about seventy years of age, reproduced in
Fig. 66, is, however, destined to be the one by which he is commonly
known to embryologists, since it forms the frontispiece of the
great cooperative _Handbook of Embryology_ just published under the
editorship of Oskar Hertwig.
[Illustration: Fig. 66.--Von Baer at about Seventy Years of Age.]
Von Baer's Especial Service.--Apart from special discoveries, Von Baer
greatly enriched embryology in three directions: In the first place, he
set a higher standard for all work in embryology, and thereby lifted
the entire science to a higher level. Activity in a great field of this
kind is, with the rank and file of workers, so largely imitative that
this feature of his influence should not be overlooked. In the second
place, he established the germ-layer theory, and, in the third, he made
embryology comparative.
In reference to the germ-layer theory, it should be recalled that
Wolff had distinctly foreshadowed the idea by showing that the
material out of which the embryo is constructed is, in an early stage
of development, arranged in the form of leaf-like layers. He showed
specifically that the alimentary canal is produced by one of these
sheet-like expansions folding and rolling together.
Pander, by observations on the chick (1817), had extended the knowledge
of these layers and elaborated the conception of Wolff. He recognized
the presence of three primary layers--an outer, a middle, and an
inner--out of which the tissues of the body are formed.
The Germ-Layers.--But it remained for Von Baer,[7] by extending his
observations into all the principal groups of animals, to raise this
conception to the rank of a general law of development. He was able to
show that in all animals except the very lowest there arise in the
course of development leaf-like layers, which become converted into the
"fundamental organs" of the body.
Now, these elementary layers are not definitive tissues of the body,
but are embryonic, and therefore may appropriately be designated
"germ-layers." The conception that these germ-layers are essentially
similar in origin and fate in all animals was a fuller and later
development of the germ-layer theory, a conception which dominated
embryological study until a recent date.
Von Baer recognized four such layers; the outer and inner ones being
formed first, and subsequently budding off a middle layer composed of
two sheets. A little later (1845) Remak recognized the double middle
layer of Von Baer as a unit, and thus arrived at the fundamental
conception of three layers--the ecto-, endo-, and mesoderm--which
has so long held sway. For a long time after Von Baer the aim of
embryologists was to trace the history of these germ-layers, and so in
a wider and much qualified sense it is to-day.
It will ever stand to his credit, as a great achievement, that Von
Baer was able to make a very complicated feature of development clear
and relatively simple. Given a leaf-like rudiment, with the layers
held out by the yolk, as is the case in the hen's egg, it was no easy
matter to conceive how they are transformed into the nervous system,
the body-wall, the alimentary canal, and other parts, but Von Baer saw
deeply and clearly that the fundamental anatomical features of the body
are assumed by the leaf-like rudiments being rolled into tubes.
Fig. 67 shows four sketches taken from the plates illustrating von
Baer's work. At _A_ is shown a stage in the formation of the embryonic
envelope, or amnion, which surrounds the embryos of all animals above
the class of amphibia. _B_, another figure of an ideal section, shows
that, long before the day of microtomes, Von Baer made use of sections
to represent the relationships of his four germ-layers. At _C_ and
_D_ is represented diagrammatically the way in which these layers are
rolled into tubes. He showed that the central nervous system arose in
the form of a tube, from the outer layer; the body-wall in the form of
a tube, composed of skin and muscle layers; and the alimentary tube
from mucous and vascular layers.
The generalization that embryos in development tend to recapitulate
their ancestral history is frequently attributed to Von Baer, but the
qualified way in which he suggests something of the sort will not
justify one in attaching this conclusion to his work.
Von Baer was the first to make embryology truly comparative, and to
point out its great value in anatomy and zoölogy. By embryological
studies he recognized four types of organization--as Cuvier had done
from the standpoint of comparative anatomy. But, since these types of
organization have been greatly changed and subdivided, the importance
of the distinction has faded away. As a distinct break, however, with
the old idea of a linear scale of being it was of moment.
Among his especially noteworthy discoveries may be mentioned that
of the egg of mammals (1827), and the notochord as occurring in all
vertebrate animals. His discovery of the mammalian egg had been
preceded by Purkinje's observations upon the germinative spot in the
bird's egg (1825).
Von Baer's Rank.--Von Baer has come to be dignified with the title of
the "father of modern embryology." No man could have done more in his
period, and it is owing to his superb intellect, and to his talents
as an observer, that he accomplished what he did. As Minot says: "He
worked out, almost as fully as was possible at this time, the genesis
of all the principal organs from the germ-layers, instinctively getting
at the truth as only a great genius could have done."
[Illustration: Fig. 67.--Sketches from Von Baer's Embryological
Treatise (1828).]
After his masterly work, the science of embryology could never return
to its former level; he had given it a new direction, and through his
influence a period of great activity was introduced.
The Period from Von Baer to Balfour
In the period between Von Baer and Balfour there were great general
advances in the knowledge of organic structure that brought the whole
process of development into a new light.
Among the most important advances are to be enumerated the announcement
of the cell-theory, the discovery of protoplasm, the beginning of
the recognition of germinal continuity, and the establishment of the
doctrine of organic evolution.
The Cell-Theory.--The generalization that the tissues of all animals
and plants are structurally composed of similar units, called cells,
was given to the world through the combined labors of Schleiden and
Schwann. The history of this doctrine, together with an account of its
being remodeled into the protoplasm doctrine, is given in Chapter XII.
The broad-reaching effects of the cell-theory may be easily imagined,
since it united all animals on the broad place of likeness in
microscopic structure. Now for the first time the tissues of the body
were analyzed into their units; now for the first time was comprehended
the nature of the germ-layers of Von Baer.
Among the first questions to emerge in the light of the new researches
were concerning the origin of cells in the organs, the tissues, and
the germ-layers. The road to the investigation of these questions was
already opened, and it was followed, step by step, until the egg and
the sperm came to be recognized as modified cells. This position was
reached, for the egg, about 1861, when Gegenbaur showed that the eggs
of all vertebrate animals, regardless of size and condition, are in
reality single cells. The sperm was put in the same category about 1865.
The rest was relatively easy: the egg, a single cell, by successive
divisions produces many cells, and the arrangement of these into
primary embryonic layers brings us to the starting-point of Wolff and
Von Baer. The cells, continuing to multiply by division, not only
increase in number, but also undergo changes through division of
physiological labor, whereby certain groups are set apart to perform a
particular part of the work of the body. In this way arise the various
tissues of the body, which are, in reality, similar cells performing a
similar function. Finally, from combinations of tissues, the organs are
formed.
But the egg, before entering on the process of development, must be
stimulated by the union of the sperm with the nucleus of the egg, and
thus the starting-point of every animal and plant, above the lowest
group, proves to be a single cell with protoplasm derived from two
parents. While questions regarding the origin of cells in the body were
being answered, the foundation for the embryological study of heredity
was also laid.
Advances were now more rapid and more sure; flashes of morphological
insight began to illuminate the way, and the facts of isolated
observations began to fit into a harmonized whole.
Apart from the general advances of this period, mentioned in other
connections, the work of a few individuals requires notice.
Rathke and Remak were engaged with the broader aspects of embryology,
as well as with special investigations. From Rathke's researches came
great advances in the knowledge of the development of insects and
other invertebrates, and Remak is notable for similar work with the
vertebrates. As already mentioned, he was the first to recognize the
middle layer as a unit, through which the three germ-layers of later
embryologists emerged into the literature of the subject.
Koelliker, 1817-1905, the veteran embryologist, for so many years a
professor in the University of Würzburg, carried on investigations on
the segmentation of the egg. Besides work on the invertebrates, later
he followed with care the development of the chick and the rabbit; he
encompassed the whole field of embryology, and published, in 1861 and
again in 1876, a general treatise on vertebrate embryology, of high
merit. The portrait of this distinguished man is shown in Chapter VIII,
where also his services as a histologist are recorded.
Huxley took a great step toward unifying the idea of germ-layers
throughout the animal kingdom, when he maintained, in 1849, that
the two cell-layers in animals like the hydra and oceanic hydrozoa
correspond to the ectoderm and endoderm of higher animals.
Kowalevsky (Fig. 68) made interesting discoveries of a general
bearing. In 1866 he showed the practical identity, in the early stages
of development, between one of the lowest vertebrates (amphioxus)
and a tunicate. The latter up to that time had been considered an
invertebrate, and the effect of Kowalevsky's observations was to
break down the sharply limited line supposed to exist between the
invertebrates and the vertebrates. This was of great influence in
subsequent work. Kowalevsky also founded the generalization that all
animals in development pass through a gastrula stage--a doctrine
associated, since 1874, with the name of Haeckel under the title of the
gastræa theory.
Beginning of the Doctrine of Germinal Continuity.--The conception
that there is unbroken continuity of germinal substance between all
living organisms, and that the egg and the sperm are endowed with
an inherited organization of great complexity, has become the basis
for all current theories of heredity and development. So much is
involved in this conception that, in the present decade, it has been
designated (Whitman) "the central fact of modern biology." The first
clear expression of it is found in Virchow's _Cellular Pathology_,
published in 1858. It was not, however, until the period of Balfour,
and through the work of Fol, Van Beneden (chromosomes, 1883), Boveri,
Hertwig, and others, that the great importance of this conception began
to be appreciated, and came to be woven into the fundamental ideas of
development.
[Illustration: Fig. 68.--A. Kowalevsky, 1840-1901.]
Influence of the Doctrine of Organic Evolution.--This doctrine,
although founded in its modern sense by Lamarck in the early part of
the nineteenth century, lay dormant until Darwin, in 1859, brought a
new feature into its discussion by emphasizing the factor of natural
selection. The general acceptance of the doctrine, which followed after
fierce opposition, had, of course, a profound influence on embryology.
The latter science is so intimately concerned with the genealogy of
animals and plants, that the newly accepted doctrine, as affording an
explanation of this genealogy, was the thing most needed.
The development of organisms was now seen in the light of ancestral
history, rudimentary organs began to have meaning as hereditary
survivals, and the whole process of development assumed a different
aspect. This doctrine supplied a new impulse to the interpretation
of nature at large, and of the embryological record in particular.
The meaning of the embryological record was so greatly emphasized in
the period of Balfour that it will be commented upon under the next
division of our subject.
The period between Von Baer and Balfour proved to be one of great
importance on account of the general advances in knowledge of all
organic nature. Observations were moving toward a better and more
consistent conception of the structure of animals and plants. A new
comparative anatomy, more profound and richer in meaning than Cuvier's,
was arising. The edifice on the foundation of Von Baer's work was now
emerging into recognizable outlines.
The Period of Balfour, with an Indication of Present Tendencies
Balfour's Masterly Work.--The workers of this period inherited all
the accumulations of previous efforts, and the time was ripe for
a new step. Observations on the development of different animals,
vertebrates and invertebrates, had accumulated in great number, but
they were scattered through technical periodicals, transactions of
learned societies, monographs, etc., and there was no compact science
of embryology with definite outlines. Balfour reviewed all this mass
of information, digested it, and molded it into an organized whole.
The results were published in the form of two volumes with the title
of _Comparative Embryology_. This book of "almost priceless value" was
given to the world in 1880-1881. It was a colossal undertaking, but
Balfour was a phenomenal worker. Before his untimely death at the age
of thirty-one, he had been able to complete this work and to produce,
besides, a large number of technical researches. The period of Balfour
is taken arbitrarily in this volume as beginning about 1874, when he
published, with Michael Foster, _The Elements of Embryology_.
[Illustration: Fig. 69.--Francis M. Balfour, 1851-1882.]
His University Career.--Balfour (Fig. 69) was born in 1851. During
his days of preparation for the university he was a good student,
but did not exhibit in any marked way the powers for which later he
became distinguished. At Cambridge, his distinguished teacher, the
late Sir Michael Foster, recognized his great talents, and encouraged
him to begin work in embryology. His labors in this field once begun,
he threw himself into it with great intensity. He rose rapidly to
a professorship in Cambridge, and so great was his enthusiasm and
earnestness as a lecturer that in seven years "voluntary attendance
on his classes advanced from ten to ninety." He was also a stimulator
of research, and at the time of his death there were twenty students
engaged in his laboratory on problems of development.
He was distinguished for personal attractiveness, and those who met him
were impressed with his great sincerity, as well as his personal charm.
He was welcomed as an addition to the select group of distinguished
scientific men of England, and a great career was predicted for him.
Huxley, when he felt the call, at a great personal sacrifice, to lay
aside the more rigorous pursuits of scientific research, and to devote
himself to molding science into the lives of the people, said of
Balfour: "He is the only man who can carry out my work."
His Tragic Fate.--But that was not destined to be. The story of his
tragic end need be only referred to. After completing the prodigious
labor on the _Comparative Embryology_ he went to Switzerland for
recuperation, and met his death, with that of his guide, by slipping
from an Alpine height into a chasm. His death occurred in July, 1882.
The memorial edition of his works fills four quarto volumes, but the
"Comparative Embryology" is Balfour's monument, and will give him
enduring fame. It is not only a digest of the work of others, but
contains also general considerations of a far-seeing quality. He saw
developmental processes in the light of the hypothesis of organic
evolution. His speculations were sufficiently reserved, and nearly
always luminous. It is significant of the character of this work to
say that the speculations contained in the papers of the rank and file
of embryological workers for more than two decades, and often fondly
believed to be novel, were for the most part anticipated by Balfour,
and were also better expressed, with better qualifications.
The reading of ancestral history in the stages of development is such
a characteristic feature of the embryological work of Balfour's period
that some observations concerning it will now be in place.
Interpretation of the Embryological Record.--Perhaps the most
impressive feature of animal development is the series of similar
changes through which all pass in the embryo. The higher animals,
especially, exhibit all stages of organization from the unicellular
fertilized ovum to the fully formed animal so far removed from it.
The intermediate changes constitute a long record, the possibility of
interpreting which has been a stimulus to its careful examination.
Meckel, in 1821, and later Von Baer, indicated the close similarity
between embryonic stages of widely different animals; Von Baer, indeed,
confessed that he was unable to distinguish positively between a
reptile, a bird, and a mammalian embryo in certain early stages of
growth.
In addition to this similarity, which is a constant feature of the
embryological record, there is another one that may be equally
significant; _viz._, in the course of embryonic history, sets of
rudimentary organs arise and disappear. Rudimentary teeth make
their appearance in the embryo of the whalebone whale, but they are
transitory and soon disappear without having been of service to the
animal. In the embryos of all higher vertebrates, as is well known,
gill-clefts and gill-arches with an appropriate circulation, make their
appearance, but disappear long before birth. These indications, and
similar ones, must have some meaning.
Now whatever qualities an animal exhibits after birth are attributed
to heredity. May it not be that all the intermediate stages are also
inheritances, and, therefore, represent phases in ancestral history? If
they be, indeed, clues to ancestral conditions, may we not, by patching
together our observations, be able to interpret the record, just as
the history of ancient peoples has been made out from fragments in the
shape of coins, vases, implements, hieroglyphics, inscriptions, etc.?
The Recapitulation Theory.--The results of reflection in this direction
led to the foundation of the _recapitulation theory_, according to
which animals are supposed, in their individual development, to
recapitulate to a considerable degree phases of their ancestral
history. This is one of the widest generalizations of embryology.
It was suggested in the writings of Von Baer and Louis Agassiz, but
received its first clear and complete expression in 1863, in the
writings of Fritz Müller.
Although the course of events in development is a record, it is, at
best, only a fragmentary and imperfect one. Many stages have been
dropped out, others are unduly prolonged or abbreviated, or appear out
of chronological order, and, besides this, some of the structures have
arisen from adaptation of a particular organism to its conditions of
development, and are, therefore, not ancestral at all, but, as it were,
recent additions to the text. The interpretation becomes a difficult
task, which requires much balance of judgment and profound analysis.
The recapitulation theory was a dominant note in all Balfour's
speculations, and in that of his contemporary and fellow-student
Marshall. It has received its most sweeping application in the works of
Ernst Haeckel.
Widely spread throughout recent literature is to be noted a reaction
against the too wide and unreserved application of this doctrine.
This is naturally to be expected, since it is the common tendency
in all fields of scholarship to demand a more critical estimate of
results, and to undergo a reaction from the earlier crude and sweeping
conclusions.
[Illustration: Fig. 70.--Oskar Hertwig in 1890.]
Nearly all problems in anatomy and structural zoölogy are approached
from the embryological side, and, as a consequence, the work of
the great army of anatomists and zoölogists has been in a measure
embryological. Many of them have produced beautiful and important
researches, but the work is too extended to admit of review in this
connection.
Oskar Hertwig, of Berlin (Fig. 70), is one of the representative
embryologists of Europe, while, in this country, lights of the first
magnitude are Brooks, Minot, Whitman, E.B. Wilson, and others.
Although no attempt is made to review the researches of the recent
period, we cannot pass entirely without mention the discovery of
chromosomes, and of their reduction in the ripening of the egg
and in the formation of sperm. This has thrown a flood of light
on the phenomena of fertilization, and has led to the recognition
of chromosomes as probably the bearers of heredity. The nature of
fertilization, investigated by Fol, O. Hertwig, and others, formed the
starting-point for a series of brilliant discoveries.
The embryological investigations of the late Wilhelm His (Fig. 71)
are also deserving of especial notice. His luminous researches on the
development of the nervous system, the origin of nerve fibers, and his
analysis of the development of the human embryo are all very important.
Recent Tendencies. Experimental Embryology.--Soon after the publication
of Balfour's great work on "Comparative Embryology," a new tendency
in research began to appear which led onward to the establishment of
experimental embryology. All previous work in this field had been
concerned with the structure, or architecture, of organisms, but now
the physiological side began to receive attention. Whitman has stated
with great aptness the interdependence of these two lines of work,
as follows: "Morphology raises the question, How came the organic
mechanism into existence? Has it had a history, reaching its present
stage of perfection through a long series of gradations, the first
term of which was a relatively simple stage? The embryological history
is traced out, and the palæontological records are searched, until
the evidence from both sources establishes the fact that the organ
or organism under study is but the summation of modifications and
elaborations of a relatively simple primordial. This point settled,
physiology is called upon to complete the story. Have the functions
remained the same through the series? or have they undergone a series
of modifications, differentiations, and improvements more or less
parallel with the morphological series?"
[Illustration: Fig. 71.--Wilhelm His, 1831-1904. At Sixty-four Years.]
Since physiology is an experimental science, all questions of this
nature must be investigated with the help of experiments. Organisms
undergoing development have been subjected to changed conditions, and
their responses to various forms of stimuli have been noted. In the
rise of experimental embryology we have one of the most promising
of the recent departures from the older aspects of the subject. The
results already attained in this attractive and suggestive field
make too long a story to justify its telling in this volume. Roux,
Herbst, Loeb, Morgan, E.B. Wilson, and many others have contributed
to the growth of this new division of embryology. Good reasons have
been adduced for believing that qualitative changes take place in
the protoplasm as development proceeds. And a curb has been put upon
that "great fault of embryology, the tendency to explain any and
every operation of development as merely the result of inheritance."
It has been demonstrated that surrounding conditions have much to do
with individual development, and that the course of events may depend
largely upon stimuli coming from without, and not exclusively on an
inherited tendency.
Cell-Lineage.--Investigations on the structural side have reached a
high grade of perfection in studies on cell-lineage. The theoretical
conclusions in the germ-layer theory are based upon the assumption
of identity in origin of the different layers. But the lack of
agreement among observers, especially in reference to the origin
of the mesoderm, made it necessary to study more closely the early
developmental stages before the establishment of the germ-layers. It
is a great triumph of exact observation that, although continually
changing, the consecutive history of the individual cells has been
followed from the beginning of segmentation to the time when the
germ-layers are established. Some of the beautifully illustrated
memoirs in this field are highly artistic.
Blochman (1882) was a pioneer in observations of this kind, and,
following him, a number of American investigators have pursued studies
on cell-lineage with great success. The researches of Whitman, Wilson,
Conklin, Kofoid, Lillie, Mead, and Castle have given us the history of
the origin of the germ-layers, cell by cell, in a variety of animal
forms. These studies have shown that there is a lack of uniformity in
the origin of at least the middle layer, and therefore there can be no
strict homology of its derivatives. This makes it apparent that the
earlier generalizations of the germ-layer theory were too sweeping,
and, as a result, the theory is retained in a much modified form.
Theoretical Discussions.--Certain theoretical discussions, based on
embryological studies, have been rife in recent years. And it is to
be recognized without question that discussions regarding heredity,
regeneration, the nature of the developmental process, the question of
inherited organization within the egg, of germinal continuity, etc.,
have done much to advance the subject of embryology.
Embryology is one of the three great departments of biology which,
taken in combination, supply us with a knowledge of living forms along
lines of structure, function, and development. The embryological
method of study is of increasing importance to comparative anatomy
and physiology. Formerly it was entirely structural, but it is now
becoming also experimental, and it will therefore be of more service
to physiology. While it has a strictly technical side, the science
of embryology must always remain of interest to intelligent people
as embracing one of the most wonderful processes in nature--the
development of a complex organism from the single-celled condition,
with a panoramic representation of all the intermediate stages.
FOOTNOTES:
[Footnote 3: As Whitman has pointed out, Aristotle taught epigenesis as
clearly as Harvey, and is, therefore, to be regarded as the founder of
that conception.]
[Footnote 4: The discovery is also attributed to Hamm, a medical
student, and to Hartsoeker, who claimed priority in the discovery.]
[Footnote 5: _De Formatione Intestinorum, Nova Commentar, Ac. Sci.
Petrop._, St. Petersburg, XII., 1768; XIII., 1769.]
[Footnote 6: Besides biographical sketches by Stieda, Waldeyer,
and others, we have a very entertaining autobiography of Von Baer,
published in 1864, for private circulation, but afterward (1866)
reprinted and placed on sale.]
[Footnote 7: It is of more than passing interest to remember that
Pander and Von Baer were associated as friends and fellow-students,
under Döllinger at Würzburg. It was partly through the influence
of Von Baer that Pander came to study with Döllinger, and took up
investigations on development. His ample private means made it possible
for him to bear the expenses connected with the investigation, and to
secure the services of a fine artist for making the illustrations. The
result was a magnificently illustrated treatise. His unillustrated
thesis in Latin (1817) is more commonly known, but the illustrated
treatise in German is rarer. Von Baer did not take up his researches
seriously until Pander's were published. It is significant of their
continued harmonious relations that Von Baer's work is dedicated "An
meinen Jugendfreund, Dr. Christian Pander."]
CHAPTER XI
THE CELL THEORY--SCHLEIDEN, SCHWANN, SCHULTZE
The recognition, in 1838, of the fact that all the various tissues
of animals and plants are constructed on a similar plan was an
important step in the rise of biology. It was progress along the line
of microscopical observation. One can readily understand that the
structural analysis of organisms could not be completed until their
elementary parts had been discovered. When these units of structure
were discovered they were called cells--from a misconception of their
nature--and, although the misconception has long since been corrected,
they still retain this historical but misleading name.
The doctrine that all tissues of animals and plants are composed of
aggregations of these units, and the derivatives from the same, is
known as the cell-theory. It is a generalization which unites all
animals and plants on the broad plane of similitude of structure, and,
when we consider it in the light of its consequences, it stands out as
one of the great scientific achievements of the nineteenth century.
There is little danger of overestimating the importance of this
doctrine as tending to unify the knowledge of living organisms.
Vague Foreshadowings of the Cell-Theory.--In attempting to trace
the growth of this idea, as based on actual observations, we first
encounter vague foreshadowings of it in the seventeenth and the
eighteenth centuries. The cells were seen and sketched by many early
observers, but were not understood.
As long ago as 1665 Robert Hooke, the great English microscopist,
observed the cellular construction of cork, and described it as made
up of "little boxes or cells distinguished from one another." He made
sketches of the appearance of this plant tissue; and, inasmuch as the
drawings of Hooke are the earliest ones made of cells, they possess
especial interest and consequently are reproduced here. Fig. 72, taken
from the _Micrographia_, shows this earliest drawing of Hooke. He made
thin sections with a sharp penknife; "and upon examination they were
found to be all cellular or porous in the manner of a honeycomb, but
not so regular."
[Illustration: Fig. 72.--The Earliest Known Picture of Cells from
Hooke's _Micrographia_ (1665). From the edition of 1780.]
We must not completely overlook the fact that Aristotle (384-322
B.C.) and Galen (130-200 A.D.), those profound thinkers on anatomical
structure, had reached the theoretical position "that animals and
plants, complex as they may appear, are yet composed of comparatively
few elementary parts, frequently repeated"; but we are not especially
concerned with the remote history of the idea, so much as with the
principal steps in its development after the beginning of microscopical
observations.
[Illustration: Fig. 73.--Sketch from Malpighi's Treatise on the Anatomy
of Plants (1670).]
Pictures of Cells in the Seventeenth Century.--The sketches
illustrating the microscopic observations of Malpighi, Leeuwenhoek,
and Grew show so many pictures of the cellular construction of plants
that one who views them for the first time is struck with surprise, and
might readily exclaim: "Here in the seventeenth century we have the
foundation of the cell-theory." But these drawings were merely faithful
representations of the appearance of the fabric of plants; the cells
were not thought of as uniform elements of organic architecture, and
no theory resulted. It is true that Malpighi understood that the cells
were separable "utricles," and that plant tissue was the result of
their union, but this was only an initial step in the direction of the
cell-theory, which, as we shall see later, was founded on the supposed
identity in development of cells in animals and plants. Fig. 73 shows
a sketch, made by Malpighi about 1670, illustrating the microscopic
structure of a plant. This is similar to the many drawings of Grew and
Leeuwenhoek illustrating the structure of plant tissues.
Wolff.--Nearly a century after the work of Malpighi, we find Wolff,
in 1759, proposing a theory regarding the organization of animals and
plants based upon observations of their mode of development. He was one
of the most acute scientific observers of the period, and it is to be
noted that his conclusions regarding structure were all founded upon
what he was able to see; while he gives some theoretical conclusions of
a purely speculative nature, Wolff was careful to keep these separate
from his observations. The purpose of his investigations was to show
that there was no pre-formation in the embryo; but in getting at
the basis of this question, he worked out the identity of structure
of plants and animals as shown by their development. In his famous
publication on the Theory of Development (_Theoria Generationis_) he
used both plants and animals.
Huxley epitomizes Wolff's views on the development of elementary
parts as follows: "Every organ, he says, is composed at first of a
little mass of clear, viscous, nutritive fluid, which possesses no
organization of any kind, but is at most composed of globules. In this
semifluid mass cavities (_Bläschen_, _Zellen_) are now developed;
these, if they remain round or polygonal, become the subsequent cells;
if they elongate, the vessels; and the process is identically the
same, whether it is examined in the vegetating point of a plant, or in
the young budding organs of an animal."
Wolff was contending against the doctrine of pre-formation in the
embryo (see further under the chapter on Embryology), but on account
of his acute analysis he should be regarded, perhaps, as the chief
forerunner of the founders of the cell-theory. He contended for the
same method of development that was afterward emphasized by Schleiden
and Schwann. Through the opposition of the illustrious physiologist
Haller his work remained unappreciated, and was finally forgotten,
until it was revived again in 1812.
We can not show that Wolff's researches had any direct influence
in leading Schleiden and Schwann to their announcement of the
cell-theory. Nevertheless, it stands, intellectually, in the direct
line of development of that idea, while the views of Haller upon the
construction of organized beings are a side-issue. Haller declared
that "the solid parts of animals and vegetables have this fabric in
common, that their elements are either fibers or unorganized concrete."
This formed the basis of the fiber-theory, which, on account of the
great authority of Haller in physiology, occupied in the accumulating
writings of anatomists a greater place than the views of Wolff.
Bichat, although he is recognized as the founder of histology, made
no original observations on the microscopic units of the tissues. He
described very minutely the membranes in the bodies of animals, but did
not employ the microscope in his investigations.
Oken.--In the work of the dreamer Oken (1779-1851), the great
representative of the German school of "_Naturphilosophie_," we find,
about 1808, a very noteworthy statement to the effect that "animals and
plants are throughout nothing else than manifoldly divided or repeated
vesicles, as I shall prove anatomically at the proper time." This is
apparently a concise statement of the cell-idea prior to Schleiden and
Schwann; but we know that it was not founded on observation. Oken, as
was his wont, gave rein to his imagination, and, on his part, the idea
was entirely theoretical, and amounted to nothing more than a lucky
guess.
Haller's fiber-theory gave place in the last part of the eighteenth
century to the theory that animals and plants are composed of globules
and formless material, and this globular theory was in force up to the
time of the great generalization of Schleiden and Schwann. It was well
expounded by Milne-Edwards in 1823, and now we can recognize that at
least some of the globules which he described were the nucleated cells
of later writers.
The Announcement of the Cell-Theory.--We are now approaching the time
when the cell-theory was to be launched. During the first third of
the nineteenth century there had accumulated a great mass of separate
observations on the microscopic structure of both animals and plants.
For several years botanists, in particular, had been observing and
writing about cells, and interest in these structures was increasing.
"We must clearly recognize the fact that for some time prior to 1838
the cell had come to be quite universally recognized as a constantly
recurring element in vegetable and animal tissues, though little
importance was attached to it as an element of organization, nor had
its character been clearly determined" (Tyson).
Then, in 1838, came the "master-stroke in generalization" due to the
combined labors of two friends, Schleiden and Schwann. But, although
these two men are recognized as co-founders, they do not share honors
equally; the work of Schwann was much more comprehensive, and it was he
who first used the term cell-theory, and entered upon the theoretical
considerations which placed the theory before the scientific world.
Schleiden was educated as a lawyer, and began the practice of that
profession, but his taste for natural science was so pronounced that
when he was twenty-seven years old he deserted law, and went back to
the university to study medicine. After graduating in medicine, he
devoted himself mainly to botany. He saw clearly that the greatest
thing needed for the advancement of scientific botany was a study of
plant organization from the standpoint of development. Accordingly
he entered upon this work, and, in 1837, arrived at a new view
regarding the origin of plant cells. It must be confessed that this
new view was founded on erroneous observations and conclusions, but
it was revolutionary, and served to provoke discussion and to awaken
observation. This was a characteristic feature of Schleiden's influence
upon botany. His work acted as a ferment in bringing about new activity.
The discovery of the nucleus in plant cells by Robert Brown in 1831
was an important preliminary step to the work of Schleiden, since the
latter seized upon the nucleus as the starting-point of new cells. He
changed the name of the nucleus to cytoblast, and supposed that the new
cell started as a small clear bubble on one side of the nucleus, and
by continued expansion grew into the cell, the nucleus, or cytoblast,
becoming encased in the cell-wall. All this was shown by Nägeli and
other botanists to be wrong; yet, curiously enough, it was through the
help of these false observations that Schwann arrived at his general
conclusions.
Schleiden was acquainted with Schwann, and in October, 1838, while the
two were dining together, he told Schwann about his observations and
theories. He mentioned in particular the nucleus and its relationship
to the other parts of the cell. Schwann was immediately struck with the
similarity between the observations of Schleiden and certain of his
own upon _animal_ tissues. Together they went to his laboratory and
examined the sections of the dorsal cord, the particular structure upon
which Schwann had been working. Schleiden at once recognized the nuclei
in this structure as being similar to those which he had observed in
plants, and thus aided Schwann to come to the conclusion that the
elements in animal tissues were practically identical with those in
plant tissues.
Schwann.--The personalities of the co-founders of the cell-theory are
interesting. Schwann was a man of gentle, pacific disposition, who
avoided all controversies aroused by his many scientific discoveries.
In his portrait (Fig. 74) we see a man whose striking qualities are
good-will and benignity. His friend Henle gives this description of
him: "He was a man of stature below the medium, with a beardless face,
an almost infantile and always smiling expression, smooth, dark-brown
hair, wearing a fur-trimmed dressing-gown, living in a poorly lighted
room on the second floor of a restaurant which was not even of the
second class. He would pass whole days there without going out, with
a few rare books around him, and numerous glass vessels, retorts,
vials, and tubes, simple apparatus which he made himself. Or I go in
imagination to the dark and fusty halls of the Anatomical Institute
where we used to work till nightfall by the side of our excellent
chief, Johann Müller. We took our dinner in the evening, after the
English fashion, so that we might enjoy more of the advantages of
daylight."
Schwann drew part of his stimulus from his great master, Johannes
Müller. He was associated with him as a student, first in the
University of Würzburg, where Müller, with rare discernment for
recognizing genius, selected Schwann for especial favors and for close
personal friendship. The influence of his long association with Müller,
the greatest of all trainers of anatomists and physiologists of the
nineteenth century, must have been very uplifting. A few years later,
Schwann found himself at the University of Berlin, where Müller had
been called, and he became an assistant in the master's laboratory.
There he gained the powerful stimulus of constant association with a
great personality.
[Illustration: Fig. 74.--Theodor Schwann, 1810-1882.]
In 1839, just after the publication of his work on the cell-theory,
Schwann was called to a professorship in the University of Louvain, and
after remaining there nine years, was transferred to the University of
Liège. He was highly respected in the university, and led a useful
life, although after going to Belgium he published only one work--that
on the uses of the bile. He was recognized as an adept experimenter and
demonstrator, and "clearness, order, and method" are designated as the
characteristic qualities of his teaching.
[Illustration: Fig. 75.--M. Schleiden, 1804-1881.]
His announcement of the cell-theory was his most important work. Apart
from that his best-known contributions to science are: experiments upon
spontaneous generation, his discovery of the "sheath of Schwann," in
nerve fibers, and his theory of fermentation as produced by microbes.
Schleiden.--Schleiden (Fig. 75) was quite different in temperament
from Schwann. He did not have the fine self-control of Schwann, but
was quick to take up the gauntlet and enter upon controversies. In his
caustic replies to his critics, he indulged in sharp personalities,
and one is at times inclined to suspect that his early experience as a
lawyer had something to do with his method of handling opposition. With
all this he had correct ideas of the object of scientific study and of
the methods to be used in its pursuit. He insisted upon observation
and experiment, and upon the necessity of studying the development of
plants in order to understand their anatomy and physiology. He speaks
scornfully of the botany of mere species-making as follows:
"Most people of the world, even the most enlightened, are still in the
habit of regarding the botanist as a dealer in barbarous Latin names,
as a man who gathers flowers, names them, dries them, and wraps them in
paper, and all of whose wisdom consists in determining and classifying
this hay which he has collected with such great pains."
Although he insisted on correct methods, his ardent nature led him to
champion conclusions of his own before they were thoroughly tested.
His great influence in the development of scientific botany lay in
his earnestness, his application of new methods, and his fearlessness
in drawing conclusions, which, although frequently wrong, formed the
starting-point of new researches.
Let us now examine the original publications upon which the cell-theory
was founded.
Schleiden's Contribution.--Schleiden's paper was particularly directed
to the question, How does the cell originate? and was published
in Müller's _Archiv_, in 1838, under the German title of _Ueber
Phytogenesis_. As stated above, the cell had been recognized for some
years, but the question of its origin had not been investigated.
Schleiden says: "I may omit all historical introduction, for, so far
as I am acquainted, no direct observations exist at present upon the
development of the cells of plants."
He then goes on to define his view of the nucleus (cytoblast) and
of the development of the cell around it, saying: "As soon as the
cytoblasts have attained their full size, a delicate transparent
vesicle arises upon their surface. This is the young cell." As to
the position of the nucleus in the fully developed cell, he is very
explicit: "It is evident," he says, "from the foregoing that the
cytoblast can never lie free in the interior of the cell, but is always
enclosed in the cell-wall," etc.
Schleiden fastened these errors upon the cell-theory, since Schwann
relied upon his observations. On another point of prime importance
Schleiden was wrong: he regarded all new cell-formation as the
formation of "cells within cells," as distinguished from cell-division,
as we now know it to take place.
Schleiden made no attempt to elaborate his views into a comprehensive
cell-theory, and therefore his connection as a co-founder of this great
generalization is chiefly in paving the way and giving the suggestion
to Schwann, which enabled the latter to establish the theory.
Schleiden's paper occupies some thirty-two pages, and is illustrated by
two plates. He was thirty-four years old when this paper was published,
and directly afterward was called to the post of adjunct professor of
botany in the University of Jena, a position which with promotion to
the full professorship he occupied for twenty-three years.
Schwann's Treatise.--In 1838, Schwann also announced his cell-theory
in a concise form in a German scientific periodical, and, later, to
the Paris Academy of Sciences; but it was not till 1839 that the fully
illustrated account was published. This treatise with the cumbersome
title, "Microscopical Researches into the Accordance in the Structure
and Growth of Animals and Plants" (_Mikroscopische Untersuchungen über
die Uebereinstimmung in der Structur und dem Wachsthum der Thiere und
Pflanzen_) takes rank as one of the great classics in biology. It fills
215 octavo pages, and is illustrated with four plates.
"The purpose of his researches was to prove the identity of structure,
as shown by their development, between animals and plants." This is
done by direct comparisons of the elementary parts in the two kingdoms
of organic nature.
His writing in the "Microscopical Researches" is clear and
philosophical, and is divided into three sections, in the first two of
which he confines himself strictly to descriptions of observations, and
in the third part of which he enters upon a philosophical discussion
of the significance of the observations. He comes to the conclusion
that "the elementary parts of all tissues are formed of cells in an
analogous, though very diversified manner, so that it may be asserted
that there is one universal principle of development for the elementary
parts of organisms, however different, and that this principle is the
formation of cells."
It was in this treatise also that he made use of the term cell-theory,
as follows: "The development of the proposition that there exists
one general principle for the formation of all organic productions,
and that this principle is the formation of cells, as well as
the conclusions which may be drawn from this proposition, may be
comprised under the term _cell-theory_, using it in its more extended
signification, while, in a more limited sense, by the theory of cells
we understand whatever may be inferred from this proposition with
respect to the powers from which these phenomena result."
One comes from the reading of these two contributions to science with
the feeling that it is really Schwann's cell-theory, and that Schleiden
helped by lighting the way that his fellow-worker so successfully trod.
Modification of the Cell-Theory.--The form in which the cell-theory was
given to the world by Schleiden and Schwann was very imperfect, and,
as already pointed out, it contained fundamental errors. The founders
of the theory attached too much importance to the cell-wall, and they
described the cell as a hollow cavity bounded by walls that were formed
around a nucleus. They were wrong as to the mode of the development of
the cell, and as to its nature. Nevertheless, the great truth that all
parts of animals and plants are built of similar units or structures
was well substantiated. This remained a permanent part of the theory,
but all ideas regarding the nature of the units were profoundly altered.
In order to perceive the line along which the chief modifications were
made we must take account of another scientific advance of about the
same period. This was the discovery of protoplasm, an achievement which
takes rank with the advances of greatest importance in biology, and has
proved to be one of the great events of the nineteenth century.
The Discovery of Protoplasm and its Effect on the Cell-Theory.--In
1835, before the announcement of the cell-theory, living matter
had been observed by Dujardin. In lower animal forms he noticed a
semifluid, jelly-like substance, which he designated sarcode, and which
he described as being endowed with all the qualities of life. The
same semifluid substance had previously caught the attention of some
observers, but no one had as yet announced it as the actual living part
of organisms. Schleiden had seen it and called it gum. Dujardin was
far from appreciating the full importance of his discovery, and for a
long time his description of sarcode remained separate; but in 1846
Hugo von Mohl, a botanist, observed a similar jelly-like substance in
plants, which he called plant _schleim_, and to which he attached the
name protoplasma.
The scientific world was now in the position of recognizing living
substance, which had been announced as sarcode in lower animals, and
as protoplasm in plants; but there was as yet no clear indication that
these two substances were practically identical. Gradually there came
stealing into the minds of observers the suspicion that the sarcode of
the zoölogists and the protoplasm of the botanists were one and the
same thing. This proposition was definitely maintained by Cohn in 1850,
though with him it was mainly theoretical, since his observations were
not sufficiently extensive and accurate to support such a conclusion.
Eleven years later, however, as the result of extended researches, Max
Schultze promulgated, in 1861, the protoplasm doctrine, to the effect
that the units of organization consist of little masses of protoplasm
surrounding a nucleus, and that this protoplasm, or living substance,
is practically identical in both plants and animals.
The effect of this conclusion upon the cell-theory was revolutionary.
During the time protoplasm was being observed the cell had likewise
come under close scrutiny, and naturalists had now an extensive
collection of facts upon which to found a theory. It has been shown
that many animal cells have no cell-wall, and the final conclusion was
inevitable that the essential part of a cell is the semifluid living
substance that resides within the cavity when a cell-wall is present.
Moreover, when the cell-wall is absent, the protoplasm is the "cell."
The position of the nucleus was also determined to be within the living
substance, and not, as Schleiden had maintained, within the cell-wall.
The definition of Max Schultze, that a cell is a globule of protoplasm
surrounding a nucleus, marks a new era in the cell-theory, in which
the original generalization became consolidated with the protoplasm
doctrine.
Further Modifications of the Cell-Theory.--The reformed cell-theory
was, however, destined to undergo further modification, and to become
greatly extended in its application. At first the cell was regarded
merely as an element of structure; then, as a supplement to this
restricted view, came the recognition that it is also a unit of
physiology, _viz._, that all physiological activities take place within
the cell. Matters did not come to a rest, however, with the recognition
of these two fundamental aspects of the cell. The importance of the
cell in development also took firmer hold upon the minds of anatomists
after it was made clear that both the egg and its fertilizing agents
are modified cells of the parent's body. It was necessary to comprehend
this fact in order to get a clear idea of the origin of cells within
the body of a multicellular organism, and of the relation between the
primordial element and the fully developed tissues. Finally, when
observers found within the nucleus the bearers of hereditary qualities,
they began to realize that a careful study of the behavior of the cell
elements during development is necessary for the investigation of
hereditary transmissions.
A statement of the cell-theory at the present time, then, must include
these four conceptions: the cell as a unit of structure, the cell as a
unit of physiological activity, the cell as embracing all hereditary
qualities within its substance, and the cell in the historical
development of the organism.
Some of these relations may now be more fully illustrated.
Origin of Tissues.--The egg in which all organisms above the very
lowest begin, is a single cell having, under the microscope, the
appearance shown in Fig. 76. After fertilization, this divides
repeatedly, and many cohering cells result. The cells are at first
similar, but as they increase in number, and as development proceeds,
they grow different, and certain groups are set apart to perform
particular duties. The division of physiological labor which arises
at this time marks the beginning of separate tissues. It has been
demonstrated over and over that all tissues are composed of cells and
cell-products, though in some instances they are much modified. The
living cells can be seen even in bone and cartilage, in which they
are separated by a lifeless matrix, the latter being the product of
cellular activity.
[Illustration: Fig. 76.--The Egg and Early Stages in its Development.
(After Gegenbaur.)]
Fig. 77 shows a stage in the development of one of the mollusks just as
the differentiation of cells has commenced.
The Nucleus.--To the earlier observers the protoplasm appeared to be
a structureless, jelly-like mass containing granules and vacuoles;
but closer acquaintance with it has shown that it is in reality very
complex in structure as well as in chemical composition. It is by no
means homogeneous; adjacent parts are different in properties and
aptitudes. The nucleus, which is more readily seen than other cell
elements, was shown to be of great importance in cell-life--to be
a structure which takes the lead in cell division, and in general
dominates the rest of the protoplasm.
Chromosomes.--After dyes came into use for staining the protoplasm
(1868), it became evident that certain parts of it stain deeply, while
other parts stain faintly or not at all. This led to the recognition of
protoplasm as made up of a densely staining portion called _chromatin_,
and a faintly staining portion designated _achromatin_. This means
of making different parts of protoplasm visible under the microscope
led to important results, as when, in 1883, it was discovered that
the nucleus contains a definite number of small (usually rod-shaped)
bodies, which become evident during nuclear division, and play a
wonderful part in that process. These bodies take the stain more deeply
than other components of the nucleus, and are designated _chromosomes_.
[Illustration: Fig. 77.--An Early Stage in the Development of the Egg
of a Rock-Limpet. (After Conklin.)]
Attention having been directed to these little bodies, continued
observations showed that, although they vary in number--commonly from
two to twenty-four--in different parts of animals and plants, they are,
nevertheless, of the same number in all the cells of any particular
plant or animal. As a conclusion to this kind of observation, it needs
to be said that the chromosomes are regarded as the actual bearers of
hereditary qualities. The chromosomes do not show in resting-stages of
the nucleus; their substance is present, but is not aggregated into the
form of chromosomes.
[Illustration: Fig. 78.--Highly Magnified Tissue Cells from the Skin
of a Salamander in an Active State of Growth. Dividing cells with
chromosomes are shown at _a_, _b_, and _c_,. (After Wilson.)]
Fig. 78 shows tissue cells, some of which are in the dividing and
others in the resting-stage. The nuclei in process of division exhibit
the rod-like chromosomes, as shown at _a_, _b_, and _c_.
[Illustration: Fig. 79.--Diagram of the Chief Steps in Cell-division.
(After Parker as altered from Fleming.)]
Centrosome.--The discovery (1876) of a minute spot of deeply staining
protoplasm, usually just outside the nuclear membrane, is another
illustration of the complex structure of the cell. Although the
centrosome, as this spot is called, has been heralded as a dynamic
agent, there is not complete agreement as to its purpose, but its
presence makes it necessary to include it in the definition of a cell.
The Cell in Heredity.--The problems of inheritance, in so far as they
can be elucidated by structural studies, have come to be recognized as
problems of cellular life. But we cannot understand what is implied by
this conclusion without referring to the behavior of the chromosomes
during cell-division. This is a very complex process, and varies
somewhat in different tissues. We can, however, with the help of Fig.
79, describe what takes place in a typical case. The nucleus does not
divide directly, but the chromosomes congregate around the equator of
a spindle (_D_) formed from the achromatin; they then undergo division
lengthwise, and migrate to the poles (_E_, _F_, _G_), after which a
partition wall is formed dividing the cell. This manner of division
of the chromosomes secures an equable partition of the protoplasm. In
the case of fertilized eggs, one-half of the chromosomes are derived
from the sperm and one-half from the egg. Each cell thus contains
hereditary substance derived from both maternal and paternal nuclei.
This is briefly the basis for regarding inheritance as a phenomenon of
cell-life.
[Illustration: Fig. 80.--Diagram of a Cell. (Modified after Wilson.)]
A diagram of the cell as now understood (Fig. 80) will be helpful in
showing how much the conception of the cell has changed since the time
of Schleiden and Schwann.
Definition.--The definition of Verworn, made in 1895, may be combined
with this diagram: A cell is "a body consisting essentially of
protoplasm in its general form, including the unmodified cytoplasm,
and the specialized nucleus and centrosome; while as unessential
accompaniments may be enumerated: (1) the cell membrane, (2) starch
grains, (3) pigment granules, (4) oil globules, and (5) chlorophyll
granules." No definition can include all variations, but the one quoted
is excellent in directing attention to the essentials--to protoplasm in
its general form, and the modified protoplasmic parts as distinguished
from the unessential accompaniments, as cell membrane and cell contents.
The definition of Verworn was reached by a series of steps representing
the historical advance of knowledge regarding the cell. Schleiden and
Schwann looked upon the cell as a hollow chamber having a cell-wall
which had been formed around the nucleus; it was a great step when
Schultze defined the cell in terms of living substance as "a globule
of protoplasm surrounding a nucleus," and it is a still deeper level
of analysis which gives us a discriminating definition like that of
Verworn.
When we are brought to realize that, in large part, the questions that
engage the mind of the biologist have their basis in the study of
cells, we are ready to appreciate the force of the statement that the
establishment of the cell-theory was one of the great events of the
nineteenth century, and, further, that it stands second to no theory,
with the single exception of that of organic evolution, in advancing
biological science.
CHAPTER XII
PROTOPLASM, THE PHYSICAL BASIS OF LIFE
The recognition of the rôle that protoplasm plays in the living world
was so far-reaching in its results that we take up for separate
consideration the history of its discovery. Although it is not yet
fifty years since Max Schultze established the protoplasm doctrine, it
has already had the greatest influence upon the progress of biology. To
the consideration of protoplasm in the previous chapter should be added
an account of the conditions of its discovery, and of the personality
and views of the men whose privilege it was to bring the protoplasm
idea to its logical conclusion. Before doing so, however, we shall look
at the nature of protoplasm itself.
Protoplasm.--This substance, which is the seat of all vital activity,
was designated by Huxley "the physical basis of life," a graphic
expression which brings before the mind the central fact that life is
manifested in a material substratum by which it is conditioned. All
that biologists have been able to discover regarding life has been
derived from the observation of that material substratum. It is not
difficult, with the help of a microscope, to get a view of protoplasmic
activity, and that which was so laboriously made known about 1860 is
now shown annually to students beginning biology.
Inasmuch as all living organisms contain protoplasm, one has a wide
range of choice in selecting the plant or the animal upon which to make
observations.
We may, for illustration, take one of the simplest of animal organisms,
the amoeba, and place it under the high powers of the microscope.
This little animal consists almost entirely of a lump of living jelly.
Within the living substance of which its body is composed all the vital
activities characteristic of higher animals are going on, but they are
manifested in simpler form. These manifestations differ only in degree
of development, not in kind, from those we see in bodies of higher
organisms.
We can watch the movements in this amoeba, determine at first hand
its inherent qualities, and then draw up a sort of catalogue of its
vital properties. We notice an almost continual flux of the viscid
substance, by means of which it is able to alter its form and to
change its position. This quality is called that of contractility. In
its essential nature it is like the protoplasmic movement that takes
place in a contracting muscle. We find also that the substance of the
amoeba responds to stimulations--such as touching it with a bristle, or
heating it, or sending through it a light electric shock. This response
is quite independent of the contractility, and by physiologists is
designated the property of being irritable.
By further observations one may determine that the substance of
the amoeba is receptive and assimilative, that it is respiratory,
taking in oxygen and giving off carbonic dioxide, and that it is also
secretory. If the amoeba be watched long enough, it may be seen to
undergo division, thus producing another individual of its kind. We
say, therefore, that it exhibits the power of reproduction. All these
properties manifested in close association in the amoeba are exhibited
in the bodies of higher organisms in a greater degree of perfection,
and also in separation, particular organs often being set apart for the
performance of one of these particular functions. We should, however,
bear in mind that in the simple protoplasm of the amoeba is found the
germ of all the activities of the higher animals.
It will be convenient now to turn our attention to the microscopic
examination of a plant that is sufficiently transparent to enable us to
look within its living parts and observe the behavior of protoplasm.
The first thing that strikes one is the continual activity of the
living substance within the boundaries of a particular cell. This
movement sometimes takes the form of rotation around the walls of the
cell (Fig. 81 _A_). In other instances the protoplasm marks out for
itself new paths, giving a more complicated motion, called circulation
(Fig. 81 _B_). These movements are the result of chemical changes
taking place within the protoplasm, and they are usually to be observed
in any plant or animal organism.
[Illustration: Fig. 81.--(_A_) Rotation of Protoplasm in the Cells of
Nitella. (_B_) Highly Magnified Cell of a Tradescantia Plant, Showing
Circulation of Protoplasm. (After Sedgwick and Wilson.)]
Under the most favorable conditions these movements, as seen under
the microscope, make a perfect torrent of unceasing activity, and
introduce us to one of the wonderful sights of which students of
biology have so many. Huxley (with slight verbal alterations) says:
"The spectacle afforded by the wonderful energies imprisoned within
the compass of the microscopic cell of a plant, which we commonly
regard as a merely passive organism, is not easily forgotten by one
who has watched its movement hour by hour without pause or sign of
weakening. The possible complexity of many other organisms seemingly
as simple as the protoplasm of the plant just mentioned dawns upon
one, and the comparison of such activity to that of higher animals
loses much of its startling character. Currents similar to these have
been observed in a great multitude of very different plants, and it is
quite uniformly believed that they occur in more or less perfection in
all young vegetable cells. If such be the case, the wonderful noonday
silence of a tropical forest is due, after all, only to the dullness
of our hearing, and could our ears catch the murmur of these tiny
maelstroms as they whirl in the innumerable myriads of living cells
that constitute each tree, we should be stunned as with the roar of a
great city."
The Essential Steps in Recognizing the Likeness of Protoplasm in Plants
and Animals
Dujardin.--This substance, of so much interest and importance to
biologists, was first clearly described and distinguished from other
viscid substance, as albumen, by Félix Dujardin in 1835. Both the
substance and the movements therein had been seen and recorded by
others: by Rösel von Rosenhof in 1755 in the proteus animalcule; again
in 1772 by Corti in chara; by Mayen in 1827 in Vallisnieria; and in
1831 by Robert Brown in Tradescantia. One of these records was for
the animal kingdom, and three were for plants. The observations of
Dujardin, however, were on a different plane from those of the earlier
naturalists, and he is usually credited with being the discoverer of
protoplasm. His researches, moreover, were closely connected with the
development of the ideas regarding the rôle played in nature by this
living substance.
Dujardin was a quiet modest man, whose attainments and service to the
progress of biology have usually been under-rated. He was born in 1801
at Tours, and died in 1860 at Rennes. Being descended from a race of
watchmakers, he received in his youth a training in that craft which
cultivated his natural manual dexterity, and, later, this assisted
him in his manipulations of the microscope. He had a fondness for
sketching, and produced some miniatures and other works of art that
showed great merit. His use of colors was very effective, and in 1818
he went to Paris for the purpose of perfecting himself in painting,
and with the intention of becoming an artist. The small financial
returns, however, "led him to accept work as an engineer directing the
construction of hydraulic work in Sédan." He had already shown a love
for natural science, and this led him from engineering into work as a
librarian and then as a teacher. He made field observations in geology
and botany, and commenced publication in those departments of science.
About 1834 he began to devote his chief efforts to microscopic work,
toward which he had a strong inclination, and from that time on he
became a zoölogist, with a steadily growing recognition for high-class
observation. Besides his technical scientific papers, he wrote in a
popular vein to increase his income. Among his writings of this type
may be mentioned as occupying high rank his charmingly written "Rambles
of a Naturalist" (_Promenades d'un Naturaliste_, 1838).
By 1840 he had established such a good record as a scientific
investigator that he was called to the newly founded University of
Rennes as dean of the faculty. He found himself in an atmosphere of
jealous criticism, largely on account of his being elevated to the
station of dean, and after two years of discomfort he resigned the
deanship, but retained his position as a professor in the university.
He secured a residence in a retired spot near a church, and lived there
simply. In his leisure moments he talked frequently with the priests,
and became a devout Catholic.
His contributions to science cover a wide range of subjects. In his
microscopic work he discovered the rhizopods in 1834, and the study
of their structure gave him the key to that of the other protozoa.
In 1835 he visited the Mediterranean, where he studied the oceanic
foraminifera, and demonstrated that they should be grouped with the
protozoa, and not, as had been maintained up to that time, with the
mollusca. It was during the prosecution of these researches that he
made the observations upon sarcode that are of particular interest to
us.
His natural history of the infusoria (1841) makes a volume of 700
pages, full of original observations and sketches. He also invented
a means of illumination for the microscope, and wrote a manual of
microscopic observation. Among the ninety-six publications of Dujardin
listed by Professor Joubin there are seven general works, twenty
relating to the protozoa, twenty-four to geology, three to botany,
four to physics, twenty-five to arthropods, eight to worms, etc., etc.
But as Joubin says: "The great modesty of Dujardin allowed him to see
published by others, without credit to himself, numerous facts and
observations which he had established." This failure to assert his
claims accounts in part for the inadequate recognition that his work
has received.
[Illustration: Fig. 82.--Félix Dujardin, 1801-1860.]
No portrait of Dujardin was obtainable prior to 1898. Somewhat earlier
Professor Joubin, who succeeded other occupants of the chair which
Dujardin held in the University of Rennes, found in the possession
of his descendants a portrait, which he was permitted to copy. The
earliest reproduction of this picture to reach this country came to the
writer through the courtesy of Professor Joubin, and a copy of it is
represented in Fig. 82. His picture bespeaks his personality. The quiet
refinement and sincerity of his face are evident. Professor Joubin
published, in 1901 (_Archives de Parasitologie_), a biographical sketch
of Dujardin, with several illustrations, including this portrait and
another one which is very interesting, showing him in academic costume.
Thanks to the spread of information of the kind contained in that
article, Dujardin is coming into wider recognition, and will occupy the
historical position to which his researches entitle him.
It was while studying the protozoa that he began to take particular
notice of the substance of which their bodies are composed; and in
1835 he described it as a living jelly endowed with all the qualities
of life. He had seen the same jelly-like substance exuding from the
injured parts of worms, and recognized it as the same material that
makes the body of protozoa. He observed it very carefully in the
ciliated infusoria--in Paramoecium, in Vorticella, and other forms,
but he was not satisfied with mere microscopic observation of its
structure. He tested its solubility, he subjected it to the action
of alcohol, nitric acid, potash, and other chemical substances, and
thereby distinguished it from albumen, mucus, gelatin, etc.
Inasmuch as this substance manifestly was soft, Dujardin proposed
for it the name of sarcode, from the Greek, meaning _soft_. Thus we
see that the substance protoplasm was for the first time brought
very definitely to the attention of naturalists through the study
of animal forms. For some time it occupied a position of isolation,
but ultimately became recognized as being identical with a similar
substance that occurs in plants. At the time of Dujardin's discovery,
sarcode was supposed to be peculiar to lower animals; it was not known
that the same substance made the living part of all animals, and it
was owing mainly to this circumstance that the full recognition of its
importance in nature was delayed.
The fact remains that the first careful studies upon sarcode were due
to Dujardin, and, therefore, we must include him among the founders of
modern biology.
[Illustration: Fig. 83.-Purkinje, 1787-1869.]
Purkinje.--The observations of the Bohemian investigator Purkinje
(1787-1869) form a link in the chain of events leading up to the
recognition of protoplasm. Although Purkinje is especially remembered
for other scientific contributions, he was the first to make use
of the name protoplasm for living matter, by applying it to the
formative substance within the eggs of animals and within the cells
of the embryo. His portrait is not frequently seen, and, therefore,
is included here (Fig. 83), to give a more complete series of
pictures of the men who were directly connected with the development
of the protoplasm idea. Purkinje was successively a professor in
the universities of Breslau and Prague. His anatomical laboratory
at Breslau is notable as being one of the earliest (1825) open to
students. He went to Prague in 1850 as professor of physiology.
[Illustration: Fig. 84.--Carl Nägeli, 1817-1891.]
Von Mohl.--In 1846, eleven years after the discovery of Dujardin, the
eminent botanist Hugo von Mohl (1805-1872) designated a particular part
of the living contents of the vegetable cell by the term protoplasma.
The viscid, jelly-like substance in plants had in the mean time
come to be known under the expressive term of plant "_schleim_." He
distinguished the firmer mucilaginous and granular constituent, found
just under the cell membrane, from the watery cell-sap that occupies
the interior of the cell. It was to the former part that he gave the
name protoplasma. Previous to this, the botanist Nägeli had studied
this living substance, and perceived that it was nitrogenous matter.
This was a distinct step in advance of the vague and indefinite idea of
Schleiden, who had in reality noticed protoplasm in 1838, but thought
of it merely as gum. The highly accomplished investigator Nägeli (Fig.
84) made a great place for himself in botanical investigation, and his
name is connected with several fundamental ideas of biology. To Von
Mohl, however, belongs the credit of having brought the word protoplasm
into general use. He stands in the direct line of development, while
Purkinje, who first employed the word protoplasm, stands somewhat
aside, but his name, nevertheless, should be connected with the
establishment of the protoplasm doctrine.
[Illustration: Fig. 85.--Hugo von Mohl, 1805-1872.]
Von Mohl (Fig. 85) was an important man in botany. Early in life he
showed a great love for natural science, and as in his day medical
instruction afforded the best opportunities for a man with scientific
tastes, he entered upon that course of study in Tübingen at the age of
eighteen. He took his degree of doctor of medicine in 1823, and spent
several years in Munich. He became professor of physiology in Bern in
1832, and three years later was transferred to Tübingen as professor of
botany. Here he remained to the end of his life, refusing invitations
to institutions elsewhere. He never married, and, without the cares
and joys of a family, led a solitary and uneventful life, devoted to
botanical investigation.
Cohn.--After Von Mohl's studies on "plant schleim" there was a general
movement toward the conclusion that the sarcode of the zoölogists and
the protoplasm of the botanists were one and the same substance. This
notion was in the minds of more than one worker, but it is perhaps to
Ferdinand Cohn (1828-1898) that the credit should be given for bringing
the question to a head. After a study of the remarkable movements of
the active spores of one of the simplest plants (protococcus), he said
that vegetable protoplasm and animal sarcode, "if not identical, must
be, at any rate, in the highest degree analogous substances" (Geddes).
Cohn (Fig. 86) was for nearly forty years professor of botany in the
University of Breslau, and during his long life as an investigator
greatly advanced the knowledge of bacteria. His statement referred
to above was made when he was twenty-two years of age, and ran too
far ahead of the evidence then accumulated; it merely anticipated
the coming period of the acceptance of the conclusion in its full
significance.
[Illustration: Fig. 86.--Ferdinand Cohn, 1828-1898.]
De Bary.--We find, then, in the middle years of the nineteenth century
the idea launched that sarcode and protoplasm are identical, but it
was not yet definitely established that the sarcode of lower animals
is the same as the living substance of the higher ones, and there was,
therefore, lacking an essential factor to the conclusion that there
is only one general form of living matter in all organisms. It took
another ten years of investigation to reach this end.
The most important contributions from the botanical side during this
period were the splendid researches of De Bary (Fig. 87) on the
myxomycetes, published in 1859. Here the resemblance between sarcode
and protoplasm was brought out with great clearness. The myxomycetes
are, in one condition, masses of vegetable protoplasm, the movements
and other characteristics of which were shown to resemble strongly
those of the protozoa. De Bary's great fame as a botanist has made his
name widely known.
[Illustration: Fig. 87.--Heinrich A. de Bary, 1831-1888.]
In 1858 Virchow also, by his extensive studies in the pathology of
living cells, added one more link to the chain that was soon to be
recognized as encircling the new domain of modern biology.
[Illustration: Fig. 88.--Max Schultze, 1825-1874.]
Schultze.--As the culmination of a long period of work, Max
Schultze, in 1861, placed the conception of the identity between
animal sarcode and vegetable protoplasm upon an unassailable basis,
and therefore he has received the title of "the father of modern
biology." He showed that sarcode, which was supposed to be confined
to the lower invertebrates, is also present in the tissues of higher
animals, and there exhibits the same properties. The qualities of
contractility and irritability were especially indicated. It was on
physiological likeness, rather than on structural grounds, that he
formed his sweeping conclusions. He showed also that sarcode agreed
in physiological properties with protoplasm in plants, and that the
two living substances were practically identical. His paper of 1861
considers the living substance in muscles (_Ueber Muskelkörperchen und
das was man eine Zelle zu nennen habe_), but in this he had been partly
anticipated by Ecker who, in 1849, compared the "formed contractile
substance" of muscles with the "unformed contractile substance" of the
lower types of animal life (Geddes).
The clear-cut, intellectual face of Schultze (Fig. 88) is that of an
admirable man with a combination of the artistic and the scientific
temperaments. He was greatly interested in music from his youth up, and
by the side of his microscope was his well-beloved violin. He was some
time professor in the University of Halle, and in 1859 went to Bonn
as professor of anatomy and director of the Anatomical Institute. His
service to histology has already been spoken of (Chapter VIII).
This astute observer will have an enduring fame in biological science,
not only for the part he played in the development of the protoplasm
idea, but also on account of other extensive labors. In 1866 he
founded the leading periodical in microscopic anatomy, the _Archiv
für Mikroscopische Anatomie_. This periodical was continued after the
untimely death of Schultze in 1874, and to-day is one of the leading
biological periodicals.
It is easy, looking backward, to observe that the period between
1840 and 1860 was a very important one for modern biology. Many new
ideas were coming into existence, but through this period we can
trace distinctly, step by step, the gradual approach to the idea that
protoplasm, the living substance of organism, is practically the same
in plants and in animals. Let us picture to ourselves the consequences
of the acceptance of this idea. Now for the first time physiologists
began to have their attention directed to the actually living
substance; now for the first time they saw clearly that all future
progress was to be made by studying this living substance--the seat of
vital activity. This was the beginning of modern biology.
Protoplasm is the particular object of study for the biologist. To
observe its properties, to determine how it behaves under different
conditions, how it responds to stimuli and natural agencies, to
discover the relation of the internal changes to the outside agencies:
these, which constitute the fundamental ideas of biology, were for the
first time brought directly to the attention of the naturalist, about
the year 1860--that epoch-making time when appeared Darwin's _Origin of
Species_ and Spencer's _First Principles_.
CHAPTER XIII
THE WORK OF PASTEUR, KOCH, AND OTHERS
The knowledge of bacteria, those minutest forms of life, has exerted
a profound influence upon the development of general biology. There
are many questions relating to bacteria that are strictly medical, but
other phases of their life and activities are broadly biological, and
some of those broader aspects will next be brought under consideration.
The bacteria were first described by Leeuwenhoek in 1687, twelve
years after his discovery of the microscopic animalcula now called
protozoa. They are so infinitesimal in size that under his microscope
they appeared as mere specks, and, naturally, observation of these
minute organisms was suspended until nearly the middle of the
nineteenth century, after the improvement of microscope lenses. It is
characteristic of the little knowledge of bacteria in Linnæus's period
that he grouped them into an order, with other microscopic forms, under
the name _chaos_.
At first sight, the bacteria appear too minute to figure
largely in human affairs, but a great department of natural
science--bacteriology--has been opened by the study of their
activities, and it must be admitted that the development of the science
of bacteriology has been of great practical importance. The knowledge
derived from experimental studies of the bacteria has been the chief
source of light in an obscure domain which profoundly affects the
well-being of mankind. To the advance of such knowledge we owe the
germ-theory of disease and the ability of medical men to cope with
contagious diseases. The three greatest names connected with the rise
of bacteriology are those of Pasteur, Koch, and Lister, the results of
whose labors will be considered later.
Among the general topics which have been clustered around the study of
bacteria we take up, first, the question of the spontaneous origin of
life.
The Spontaneous Origin of Life
It will be readily understood that the question of the spontaneous
generation of life is a fundamental one for the biologist. Does life
always arise from previously existing life, or under certain conditions
is it developed spontaneously? Is there, in the inorganic world, a
happy concourse of atoms that become chained together through the
action of the sun's rays and other natural forces, so that a molecule
of living matter is constructed in nature's laboratory without contact
or close association with living substance? This is a question of
_biogenesis_--life from previous life--or of _abiogenesis_--life
without preëxisting life or from inorganic matter alone.
It is a question with a long history. Its earliest phases do not
involve any consideration of microscopic forms, since they were
unknown, but its middle and its modern aspect are concerned especially
with bacteria and other microscopic organisms. The historical
development of the problem may be conveniently considered under three
divisions: I. The period from Aristotle, 325 B.C., to the experiments
of Redi, in 1668; II. From the experiments of Redi to those of Schulze
and Schwann in 1836 and 1837; III. The modern phase, extending from
Pouchet's observations in 1859 to the present.
I. From Aristotle to Redi.--During the first period, the notion of
spontaneous generation was universally accepted, and the whole question
of spontaneous origin of life was in a crude and grotesque condition.
It was thought that frogs and toads and other animals arose from the
mud of ponds and streams through the vivifying action of the sun's
rays. Rats were supposed to come from the river Nile, the dew was
supposed to give origin to insects, etc.
The scientific writers of this period had little openness of mind,
and they indulged in scornful and sarcastic comments at the expense
of those who doubted the occurrence of spontaneous generation. In the
seventeenth century Alexander Ross, commenting on Sir Thomas Brown's
doubt as to whether mice may be bred by putrefaction, flays his
antagonist in the following words: "So may we doubt whether in cheese
and timber worms are generated, or if beetles and wasps in cow-dung,
or if butterflies, locusts, shell-fish, snails, eels, and such life be
procreated of putrefied matter, which is to receive the form of that
creature to which it is by formative power disposed. To question this
is to question reason, sense, and experience. If he doubts this, let
him go to Egypt, and there he will find the fields swarming with mice
begot of the mud of Nylus, to the great calamity of the inhabitants."
II. From Redi to Schwann.--The second period embraces the experimental
tests of Redi (1668), Spallanzani (1775), and Schwann (1837)--notable
achievements that resulted in a verdict for the adherents to the
doctrine of biogenesis. Here the question might have rested had it not
been opened upon theoretical ground by Pouchet in 1859.
The First Experiments.--The belief in spontaneous generation, which
was so firmly implanted in the minds of naturalists, was subjected
to an experimental test in 1668 by the Italian Redi. It is a curious
circumstance, but one that throws great light upon the condition
of intellectual development of the period, that no one previous
to Redi had attempted to test the truth or falsity of the theory
of spontaneous generation. To approach this question from the
experimental side was to do a great service to science.
The experiments of Redi were simple and homely. He exposed meat in
jars, some of which were left uncovered, some covered with parchment,
and others with fine wire gauze. The meat in all these vessels became
spoiled, and flies, being attracted by the smell of decaying meat,
laid eggs in that which was exposed, and there came from it a large
crop of maggots. The meat which was covered by parchment also decayed
in a similar manner, without the appearance of maggots within it; and
in those vessels covered by wire netting the flies laid their eggs
upon the wire netting. There they hatched, and the maggots, instead
of appearing in the meat, appeared on the surface of the wire gauze.
From this Redi concluded that maggots arise in decaying meat from the
hatching of the eggs of insects, but inasmuch as these animals had
been supposed to arise spontaneously within the decaying meat, the
experiment took the ground from under that hypothesis.
He made other observations on the generation of insects, but with acute
scientific analysis never allowed his conclusions to run ahead of his
observations. He suggested, however, the probability that all cases
of the supposed production of life from dead matter were due to the
introduction of living germs from without. The good work begun by Redi
was confirmed and extended by Swammerdam (1637-1681) and Vallisnieri
(1661-1730), until the notion of the spontaneous origin of any forms
of life visible to the unaided eye was banished from the minds of
scientific men.
[Illustration: Fig. 89.--Francesco Redi, 1626-1697.]
Redi (Fig. 89) was an Italian physician living in Arentino,
distinguished alike for his attainments in literature and for his
achievements in natural science. He was medical adviser to two of
the grand dukes of Tuscany, and a member of the Academy of Crusca.
Poetry as well as other literary compositions shared his time with
scientific occupations. His collected works, literary, scientific, and
medical, were published in nine octavo volumes in Milan, 1809-1811.
This collection includes his life and letters, and embraces one
volume of sonnets. The book that has been referred to as containing
his experiments was entitled _Esperienze Intorno Alla Generazione
Degl'Insetti_, and first saw the light in quarto form in Florence
in 1668. It went through five editions in twenty years. Some of the
volumes were translated into Latin, and were published in miniature,
making books not more than four inches high. Huxley says: "The extreme
simplicity of his experiments, and the clearness of his arguments,
gained for his views and for their consequences almost universal
acceptance."
New Form of the Question.--The question of the spontaneous generation
of life was soon to take on a new aspect. Seven years after the
experiments of Redi, Leeuwenhoek made known a new world of microscopic
organisms--the infusoria--and, as we have seen, he discovered, in
1687, those still minuter forms, the bacteria. Strictly speaking, the
bacteria, on account of their extreme minuteness, were lost sight of,
but spontaneous generation was evoked to account for the birth of all
microscopic organisms, and the question circled mainly around the
infusorial animalcula. While the belief in the spontaneous generation
of life among forms visible to the unaided eye had been surrendered,
nevertheless doubts were entertained as to the origin of microscopic
organisms, and it was now asserted that here were found the beginnings
of life--the place where inorganic material was changed through natural
agencies into organized beings microscopic in size.
More than seventy years elapsed before the matter was again subjected
to experimental tests. Then Needham, using the method of Redi, began
to experiment on the production of microscopic animalcula. In many
of his experiments he was associated with Buffon, the great French
naturalist, who had a theory of organic molecules that he wished to
sustain. Needham (1713-1784), a priest of the Catholic faith, was an
Englishman living on the Continent; he was for many years director of
the Academy of Maria Theresa at Brussels. He engaged in scientific
investigations in connection with his work of teaching. The results of
Needham's first experiments were published in 1748. These experiments
were conducted by extracting the juices of meat by boiling; by then
enclosing the juices in vials, the latter being carefully corked and
sealed with mastic; by subjecting the sealed bottles, finally, to heat,
and setting them away to cool. In due course of time, the fluids thus
treated became infected with microscopic life, and, inasmuch as Needham
believed that he had killed all living germs by repeated heating,
he concluded that the living forms had been produced by spontaneous
generation.
Spallanzani.--The epoch-making researches of Spallanzani, a
fellow-countryman of Redi, were needed to point out the error in
Needham's conclusions. Spallanzani (Fig. 90) was one of the most
eminent men of his time. He was educated for the church, and,
therefore, he is usually known under the title of Abbé Spallanzani.
He did not, however, actively engage in his churchly offices, but,
following an innate love of natural science and of investigation,
devoted himself to experiments and researches and to teaching. He
was first a professor at Bologna, and afterward at the University of
Pavia. He made many additions to knowledge of the development and the
physiology of organisms, and he was the first to make use of glass
flasks in the experimental study of the question of the spontaneous
generation of life.
Spallanzani thought that the experiments of Needham had not been
conducted with sufficient care and precision; accordingly, he made use
of glass flasks with slender necks which could be hermetically sealed
after the nutrient fluids had been introduced. The vials which Needham
used as containers were simply corked and sealed with mastic, and it
was by no means certain that the entrance of air after heating had been
prevented; moreover, no record was made by Needham of the temperature
and the time of heating to which his bottles and fluids had been
subjected.
[Illustration: Fig. 90.--Lazzaro Spallanzani, 1729-1799.]
Spallanzani took nutrient fluids, such as the juices of vegetables
and meats which had been extracted by boiling, placed them in clear
flasks, the necks of which were hermetically sealed in flame, and
afterward immersed them in boiling water for three-quarters of an
hour, in order to destroy all germs that might be contained in them.
The organic infusions of Spallanzani remained free from change. It
was then, as now, a well-known fact that organic fluids, when exposed
to air, quickly decompose and acquire a bad smell; they soon become
turbid, and in a little time a scum is formed upon their surface. The
fluids in the flasks of Spallanzani remained of the same appearance and
consistency as when they were first introduced into the vessel, and the
obvious conclusion was drawn that microscopic life is not spontaneously
formed within nutrient fluids.
"But Needham was not satisfied with these results, and with a show of
reason maintained that such a prolonged boiling would destroy not only
germs, but the germinative, or, as he called it, the 'vegetative force'
of the infusion itself. Spallanzani easily disposed of this objection
by showing that when the infusions were again exposed to the air, no
matter how severe or prolonged the boiling to which they had been
subjected, the infusoria reappeared. His experiments were made in great
numbers, with different infusions, and were conducted with the utmost
care and precision" (Dunster). It must be confessed, however, that
the success of his experiments was owing largely to the purity of the
air in which he worked, the more resistant atmospheric germs were not
present: as Wyman showed, long afterward, that germs may retain their
vitality after being subjected for several hours to the temperature of
boiling water.
Schulze and Schwann.--The results of Spallanzani's experiments were
published in 1775, and were generally regarded by the naturalists
of that period as answering in the negative the question of the
spontaneous generation of life. Doubts began to arise as to the
conclusive nature of Spallanzani's experiments, on account of the
discovery of the part which oxygen plays in reference to life. The
discovery of oxygen, one of the greatest scientific events of the
eighteenth century, was made by Priestley in 1774. It was soon shown
that oxygen is necessary to all forms of life, and the question was
raised: Had not the boiling of the closed flasks changed the oxygen
so that through the heating process it had lost its life-giving
properties? This doubt grew until a reëxamination of the question of
spontaneous generation became necessary under conditions in which the
nutrient fluids were made accessible to the outside air.
In 1836 Franz Schulze, and, in the following year, Theodor Schwann,
devised experiments to test the question on this new basis. Schwann is
known to us as the founder of the cell-theory, but we must not confuse
Schulze with Max Schultze, who established the protoplasm doctrine. In
the experiments of Schulze, a flask was arranged containing nutrient
fluids, with a large cork perforated and closely fitted with bent glass
tubes connected on one side with a series of bulbs in which were placed
sulphuric acid and other chemical substances. An aspirator was attached
to the other end of this system, and air from the outside was sucked
into the flask, passing on its way through the bulbs containing the
chemical substances. The purpose of this was to remove the floating
germs that exist in the air, while the air itself was shown, through
other experiments by Schwann, to remain unchanged.
Tyndall says in reference to these experiments: "Here again the success
of Schulze was due to his working in comparatively pure air, but even
in such air his experiment is a risky one. Germs will pass unwetted
and unscathed through sulphuric acid unless the most special care is
taken to detain them. I have repeatedly failed, by repeating Schulze's
experiments, to obtain his results. Others have failed likewise. The
air passes in bubbles through the bulbs, and to render the method
secure, the passage of the air must be so slow as to cause the whole of
its floating matter, even to the very core of each bubble, to touch the
surrounding fluid. But if this precaution be observed _water will be
found quite as effectual as sulphuric acid_."
Schwann's apparatus was similar in construction, except that the bent
tube on one side was surrounded by a jacket of metal and was subjected
to a very high temperature while the air was being drawn through it,
the effect being to kill any floating germs that might exist in the
air. Great care was taken by both experimenters to have their flasks
and fluids thoroughly sterilized, and the results of their experiments
were to show that the nutrient fluids remained uncontaminated.
These experiments proved that there is something in the atmosphere
which, unless it be removed or rendered inactive, produces life within
nutrient fluids, but whether this something is solid, fluid, or gaseous
did not appear from the experiments. It remained for Helmholtz to
show, as he did in 1843, that this something will not pass through a
moist animal membrane, and is therefore a solid. The results so far
reached satisfied the minds of scientific men, and the question of the
spontaneous origin of life was regarded as having been finally set at
rest.
III. The Third Period. Pouchet.--We come now to consider the third
historical phase of this question. Although it had apparently been
set at rest, the question was unexpectedly opened again in 1859
by the Frenchman Pouchet, the director of the Natural History
Museum of Rouen. The frame of mind which Pouchet brought to his
experimental investigations was fatal to unbiased conclusions: "When,
_by meditation_," he says, in the opening paragraph of his book on
_Heterogenesis_, "it was evident to me that spontaneous generation
was one of the means employed by nature for the production of living
beings, I applied myself to discover by what means one could place
these phenomena in evidence." Although he experimented, his case was
prejudiced by metaphysical considerations. He repeated the experiments
of previous observers with opposite results, and therefore he declared
his belief in the falsity of the conclusions of Spallanzani, Schulze,
and Schwann.
He planned and executed one experiment which he supposed was
conclusive. In introducing it he said: "The opponents of spontaneous
generation assert that the germs of microscopic organisms exist
in the air, which transports them to a distance. What, then, will
these opponents say if I succeed in introducing the generation of
living organisms, while substituting artificial air for that of the
atmosphere?"
He filled a flask with boiling water and sealed it with great care.
This he inverted over a bath of mercury, thrusting the neck of the
bottle into the mercury. When the water was cooled, he opened the
neck of the bottle, still under the mercury, and connected it with
a chemical retort containing the constituents for the liberation of
oxygen. By heating the retort, oxygen was driven off from the chemical
salts contained in it, and being a gas, the oxygen passed through
the connecting tube and bubbled up through the water of the bottle,
accumulating at the upper surface, and by pressure forcing water out
of the bottle. After the bottle was about half filled with oxygen
imprisoned above the water, Pouchet took a pinch of hay that had been
heated to a high temperature in an oven, and with a pair of sterilized
forceps pushed it underneath the mercury and into the mouth of the
bottle, where the hay floated into the water and distributed itself.
He thus produced a hay infusion in contact with pure oxygen, and after
a few days this hay infusion was seen to be cloudy and turbid. It was,
in fact, swarming with micro-organisms. Pouchet pointed with triumphant
spirit to the apparently rigorous way in which his experiment had been
carried on: "Where," said he, "does this life come from? It can not
come from the water which had been boiled, destroying all living germs
that may have existed in it. It can not come from the oxygen which was
produced at the temperature of incandescence. It can not have been
carried in the hay, which had been heated for a long period before
being introduced into the water." He declared that this life was,
therefore, of spontaneous origin.
The controversy now revived, and waxed warm under the insistence of
Pouchet and his adherents. Finally the Academy of Sciences, in the hope
of bringing it to a conclusion, appointed a committee to decide upon
conflicting claims.
Pasteur.--Pasteur had entered into the investigation of the subject
about 1860, and, with wonderful skill and acumen, was removing all
possible grounds for the conclusions of Pouchet and his followers. In
1864, before a brilliant audience at the Sorbonne, he repeated the
experiment outlined above and showed the source of error. In a darkened
room he directed a bright beam of light upon the apparatus, and his
auditors could see in the intense illumination that the surface of the
mercury was covered with dust particles. Pasteur then showed that when
a body was plunged beneath the mercury, some of these surface granules
were carried with it. In this striking manner Pasteur demonstrated
that particles from the outside had been introduced into the bottle of
water by Pouchet. This, however, is probably not the only source of
the organisms which were developed in Pouchet's infusions. It is now
known that a hay infusion is very difficult to sterilize by heat, and
it is altogether likely that the infusions used by Pouchet were not
completely sterilized.
The investigation of the question requires more critical methods than
was at first supposed, and more factors enter into its solution than
were realized by Spallanzani and Schwann.
Pasteur demonstrated that the floating particles of the air contained
living germs, by catching them in the meshes of gun cotton, and then
dissolving the cotton with ether and examining the residue. He also
showed that sterilized organic fluids could be protected by a plug of
cotton sufficiently porous to admit of exchange of air, but matted
closely enough to entangle the floating particles. He showed also that
many of the minute organisms do not require free oxygen for their life
processes, but are able to take the oxygen by chemical decomposition
which they themselves produce from the nutrient fluids.
Jeffries Wyman, of Harvard College, demonstrated that some germs are
so resistant to heat that they retain their vitality after several
hours of boiling. This fact probably accounts for the difference in
the results that have been obtained by experimenters. The germs in a
resting-stage are surrounded by a thick protective coat of cellulose,
which becomes softened and broken when they germinate. On this account
more recent experimenters have adopted a method of discontinuous
heating of the nutrient fluid that is being tested. The fluids are
boiled at intervals, so that the unusually resistant germs are killed
after the coating has been rendered soft, and when they are about to
germinate.
After the brilliant researches of Pasteur, the question of spontaneous
germination was once again regarded as having been answered in the
negative; and so it is regarded to-day by the scientific world.
Nevertheless, attempts have been made from time to time, as by Bastian,
of England, in 1872, to revive it on the old lines.
[Illustration: Fig. 91.--Apparatus of Tyndall for Experimenting on
Spontaneous Generation.]
Tyndall.--John Tyndall (1820-1893), the distinguished physicist,
of London, published, in 1876, the results of his experiments on
this question, which, for clearness and ingenuity, have never been
surpassed. For some time he had been experimenting in the domain of
physics with what he called optically pure air. It was necessary for
him to have air from which the floating particles had been sifted,
and it occurred to him that he might expose nutrient fluids to this
optically pure air, and thus very nicely test the question of the
spontaneous origin of life within them.
He devised a box, or chamber, as shown in Fig. 91, having in front a
large glass window, two small glass windows on the ends, and in the
back a little air-tight trap-door. Through the bottom of this box
he had fitted ordinary test tubes of the chemist, with an air-tight
surrounding, and on the top he had inserted some coiled glass tubes,
which were open at both ends and allowed the passage of air in and out
of the box through the tortuous passage. In the middle of the top of
the box was a round piece of rubber. When he perforated this with a
pinhole the elasticity of the rubber would close the hole again, but
it would also admit of the passage through it of a small glass tube,
such as is called by chemists a "thistle tube." The interior of this
box was painted with a sticky substance like glycerin, in order to
retain the floating particles of the air when they had once settled
upon its sides and bottom. The apparatus having been prepared in this
way, was allowed to stand, and the floating particles settled by their
own weight upon the bottom and sides of the box, so that day by day the
number of floating particles became reduced, and finally all of them
came to rest.
The air now differed from the outside air in having been purified
of all of its floating particles. In order to test the complete
disappearance of all particles. Tyndall threw a beam of light into the
air chamber. He kept his eye in the darkness for some time in order
to increase its sensitiveness; then, looking from the front through
the glass into the box, he was able to see any particles that might be
floating there. The floating particles would be brightly illuminated by
the condensed light that he directed into the chamber, and would become
visible. When there was complete darkness within the chamber, the
course of the beam of light was apparent in the room as it came up to
the box and as it left the box, being seen on account of the reflection
from the floating particles in the air, but it could not be seen at
all within the box. When this condition was reached, Tyndall had what
he called optically pure air, and he was now ready to introduce the
nutrient fluids into his test tubes. Through a thistle tube, thrust
into the rubber diaphragm above, he was able to bring the mouth of
the tube successively over the different test tubes, and, by pouring
different kinds of fluids from above, he was able to introduce these
into different test tubes. These fluids consisted of mutton broth, of
turnip-broth, and other decoctions of animal and vegetable matter. It
is to be noted that the test tubes were not corked and consequently
that the fluids contained within them were freely exposed to the
optically pure air within the chamber.
The box was now lifted, and the ends of the tubes extending below it
were thrust into a bath of boiling oil. This set the fluids into a
state of boiling, the purpose being to kill any germs of life that
might be accidentally introduced into them in the course of their
conveyance to the test tubes. These fluids, exposed freely to the
optically pure air within this chamber, then remained indefinitely free
from micro-organisms, thus demonstrating that putrescible fluids may
be freely exposed to air from which the floating particles have been
removed, and not show a trace either of spoiling or of organic life
within them.
It might be objected that the continued boiling of the fluids had
produced chemical changes inimical to life, or in some way destroyed
their life-supporting properties; but after they had remained for
months in a perfectly clear state, Tyndall opened the little door in
the back of the box and closed it at once, thereby admitting some of
the floating particles from the outside air. Within a few days' time
the fluids which previously had remained uncontaminated were spoiling
and teeming with living organisms.
These experiments showed that under the conditions of the experiments
no spontaneous origin of life takes place. But while we must regard
the hypothesis of spontaneous generation as thus having been disproved
on an experimental basis, it is still adhered to from the theoretical
standpoint by many naturalists; and there are also many who think that
life arises spontaneously at the present time in ultra-microscopic
particles. Weismann's hypothetical "biophors," too minute for
microscopic observation, are supposed to arise by spontaneous
generation. This phase of the question, however, not being amenable to
scientific tests, is theoretical, and therefore, so far as the evidence
goes, we may safely say that the spontaneous origin of life under
present conditions is unknown.
Practical Applications.--There are, of course, numerous practical
applications of the discovery that the spoiling of putrescible fluids
is due to floating germs that have been introduced from the air. One
illustration is the canning of meats and fruits, where the object
is, by heating, to destroy all living germs that are distributed
through the substance, and then, by canning, to keep them out. When
this is entirely successful, the preserved vegetables and meats go
uncontaminated. One of the most important and practical applications
came in the recognition (1867) by the English surgeon Lister that
wounds during surgical operations are poisoned by floating particles
in the air or by germs clinging to instruments or the skin of the
operator, and that to render all appliances sterile and, by antiseptic
dressings, completely to prevent the entrance of these bacteria into
surgical wounds, insures their being clean and healthy. This led to
antiseptic surgery, with which the name of Lister is indissolubly
connected.
The Germ-Theory of Disease
The germ-theory of disease is another question of general bearing, and
it will be dealt with briefly here.
After the discovery of bacteria by Leeuwenhoek, in 1687, some medical
men of the time suggested the theory that contagious diseases were due
to microscopic forms of life that passed from the sick to the well.
This doctrine of _contagium vivum_, when first promulgated, took no
firm root, and gradually disappeared. It was not revived until about
1840. If we attempt briefly to sketch the rise of the germ-theory of
disease, we come, then, first to the year 1837, when the Italian Bassi
investigated the disease of silkworms, and showed that the transmission
of that disease was the result of the passing of minute glittering
particles from the sick to the healthy. Upon the basis of Bassi's
observation, the distinguished anatomist Henle, in 1840, expounded the
theory that all contagious diseases are due to microscopic germs.
The matter, however, did not receive experimental proof until 1877,
when Pasteur and Robert Koch showed the direct connection between
certain microscopic filaments and the disease of splenic fever, which
attacks sheep and other cattle. Koch was able to get some of these
minute filaments under the microscope, and to trace upon a warm stage
the different steps in their germination. He saw the spores bud and
produce filamentous forms. He was able to cultivate these upon a
nutrient substance, gelatin, and in this way to obtain a pure culture
of the organism, which is designated under the term anthrax. He
inoculated mice with the pure culture of anthrax germs, and produced
splenic fever in the inoculated forms. He was able to do this through
several generations of mice. In the same year Pasteur showed a similar
connection between splenic fever and the anthrax.
This demonstration of the actual connection between anthrax and splenic
fever formed the first secure foundation of the germ-theory of disease,
and this department of investigation became an important one in general
biology. The pioneer workers who reached the highest position in the
development of this knowledge are Pasteur, Koch, and Lister.
[Illustration: Fig. 92.--Louis Pasteur (1822-1895) and his
Granddaughter.]
Veneration of Pasteur.--Pasteur is one of the most conspicuous figures
of the nineteenth century. The veneration in which he is held by the
French people is shown in the result of a popular vote, taken in 1907,
by which he was placed at the head of all their notable men. One
of the most widely circulated of the French journals--the _Petit
Parisien_--appealed to its readers all over the country to vote upon
the relative prominence of great Frenchmen of the last century. Pasteur
was the winner of this interesting contest, having received 1,338,425
votes of the fifteen millions cast, and ranking above Victor Hugo,
who stood second in popular estimation, by more than one hundred
thousand votes. This enviable recognition was won, not by spectacular
achievements in arms or in politics, but by indefatigable industry in
the quiet pursuit of those scientific researches that have resulted in
so much good to the human race.
Personal Qualities.--He should be known also from the side of his human
qualities. He was devotedly attached to his family, enjoying the close
sympathy and assistance of his wife and his daughter in his scientific
struggles, a circumstance that aided much in ameliorating the severity
of his labors. His labors, indeed, overstrained his powers, so that
he was smitten by paralysis in 1868, at the age of forty-six, but
with splendid courage he overcame this handicap, and continued his
unremitting work until his death in 1895.
The portrait of Pasteur with his granddaughter (Fig. 92) gives a touch
of personal interest to the investigator and the contestant upon the
field of science. His strong face shows dignity of purpose and the grim
determination which led to colossal attainments; at the same time it is
mellowed by gentle affection, and contrasts finely with the trusting
expression of the younger face.
Pasteur was born of humble parents in Dôle in the Jura, on December
the 27th, 1822. His father was a tanner, but withal, a man of fine
character and stern experience, as is "shown by the fact that he had
fought in the legions of the First Empire and been decorated on the
field of battle by Napoleon." The filial devotion of Pasteur and his
justifiable pride in his father's military service are shown in the
dedication of his book, _Studies on Fermentation_, published in 1876:
"To the memory of my Father,
Formerly a soldier under the First Empire, and Knight of the Legion of
Honor.
The longer I live, the better do I understand the kindness of thy
heart and the superiority of thy judgment.
The efforts which I have devoted to these studies and to those which
have preceded them are the fruits of thy example and of thy counsel.
Desiring to honor these precious recollections, I dedicate this book
to thy memory."
When Pasteur was an infant of two years his parents removed to the
town of Arbois, and here he spent his youth and received his early
education. After a period of indifference to study, during which he
employed his time chiefly in fishing and sketching, he settled down to
work, and, thereafter, showed boundless energy and enthusiasm.
Pasteur, whom we are to consider as a biologist, won his first
scientific recognition at the age of twenty-five, in chemistry and
molecular physics. He showed that crystals of certain tartrates,
identical in chemical composition, acted differently upon polarized
light transmitted through them. He concluded that the differences
in optical properties depended upon a different arrangement of the
molecules; and these studies opened the fascinating field of molecular
physics and physical chemistry.
Pasteur might have remained in this field of investigation, but his
destiny was different. As Tyndall remarked, "In the investigation of
microscopic organisms--the 'infinitely little,' as Pasteur loved to
call them--and their doings in this, our world, Pasteur found his true
vocation. In this broad field it has been his good fortune to alight
upon a crowd of connected problems of the highest public and scientific
interest, ripe for solution, and requiring for their successful
treatment the precise culture and capacities which he has brought to
bear upon them."
In 1857 Pasteur went to Paris as director of scientific studies in the
École Normale, having previously been a professor in Strasburg and in
Lille. From this time on his energies became more and more absorbed
in problems of a biological nature. It was a momentous year (1857) in
the annals of bacteriology when Pasteur brought convincing proof that
fermentation (then considered chemical in its nature) was due to the
growth of organic life. Again in 1860 he demonstrated that both lactic
(the souring of milk) and alcoholic fermentation are due to the growth
of microscopic organisms, and by these researches he developed the
province of biology that has expanded into the science of bacteriology.
After Pasteur entered the path of investigation of microbes his
progress was by ascending steps; each new problem the solution of which
he undertook seemed of greater importance than the one just conquered.
He was led from the discovery of microbe action to the application
of his knowledge to the production of antitoxins. In all this he did
not follow his own inclinations so much as his sense of a call to
service. In fact, he always retained a regret that he was not permitted
to perfect his researches on crystallography. At the age of seventy
he said of himself: "If I have a regret, it is that I did not follow
that route, less rude it seems to me, and which would have led, I am
convinced, to wonderful discoveries. A sudden turn threw me into the
study of fermentation, fermentations set me at diseases, but I am still
inconsolable to think that I have never had the time to go back to my
old subject" (Tarbell).
Although the results of his combined researches form a succession
of triumphs, every point of his doctrines was the subject of fierce
controversy; no investigations ever met with more determined
opposition, no investigator ever fought more strenuously for the
establishment of each new truth.
He went from the study of the diseases of wines (1865) to the
investigation (1865-1868) of the silkworm plague which had well-nigh
crushed the silk industry of his country. The result was the saving of
millions of francs annually to the people of France.
His Supreme Service.--He then entered upon his chief services
to humanity--the application of his discoveries to the cure and
prevention of diseases. By making a succession of pure cultures of a
disease-producing virus, he was able to attenuate it to any desired
degree, and thereby to create a vaccinating form of the virus capable
of causing a mild affection of the disease. The injection of this
attenuated virus secured immunity from future attacks. The efficacy
of this form of inoculation was first proved for the disease of fowl
cholera, and then came the clear demonstration (1881) that the vaccine
was effective against the splenic fever of cattle. Crowning this series
of discoveries came the use of inoculation (1885) to prevent the
development of hydrophobia in one bitten by a mad dog.
The Pasteur Institute.--The time had now come for the establishment
of an institute, not alone for the treatment of hydrophobia, but
also for the scientific study of means to control other diseases, as
diphtheria, typhoid, tuberculosis, etc. A movement was set on foot for
a popular subscription to meet this need. The response to this call
on the part of the common people was gratifying. "The extraordinary
enthusiasm which accompanied the foundation of this great institution
has certainly not been equaled in our time. Considerable sums of money
were subscribed in foreign countries, while contributions poured in
from every part of France. Even the inhabitants of obscure little
towns and villages organized fêtes, and clubbed together to send their
small gifts" (Franckland). The total sum subscribed on the date of the
opening ceremony amounted to 3,586,680 francs.
The institute was formally opened on November 14th, 1888, with
impressive ceremonies presided over by the President of the Republic
of France. The establishment of this institute was an event of
great scientific importance. Here, within the first decade of its
existence, were successfully treated more than twenty thousand cases
of hydrophobia. Here has been discovered by Roux the antitoxin
for diphtheria, and here have been established the principles of
inoculation against the bubonic plague, against lockjaw, against
tuberculosis and other maladies, and of the recent microbe inoculations
of Wright of London. More than thirty "Pasteur institutes," with aims
similar to the parent institution, have been established in different
parts of the civilized world.
Pasteur died in 1895, greatly honored by the whole world. On Saturday,
October 5th of that year, a national funeral was conducted in the
Church of Notre-Dame, which was attended by the representatives of the
state and of numerous scientific bodies and learned societies.
Koch.--Robert Koch (Fig. 93) was born in 1843, and is still living,
engaged actively in work in the University of Berlin. His studies
have been mainly those of a medical man, and have been crowned with
remarkable success. In 1881 he discovered the germ of tuberculosis, in
1883 the germ that produces Asiatic cholera, and since that time his
name has been connected with a number of remarkable discoveries that
are of continuous practical application in the science of medicine.
[Illustration: Fig. 93.--Robert Koch, Born 1843.]
Koch, with the rigorous scientific spirit for which he is noteworthy,
established four necessary links in the chain of evidence to show that
a particular organism is connected with a particular disease. These
four postulates of Koch are: First, that a microscopic organism of a
particular type should be found in great abundance in the blood and
the tissue of the sick animal; second, that a pure culture should be
made of the suspected organism; third, that this pure culture, when
introduced into the body of another animal, should produce the disease;
and, fourth, that in the blood and tissues of that animal there should
be found quantities of the particular organism that is suspected of
producing the disease. In the case of some diseases this entire chain
of evidence has been established; but in others, such as cholera and
typhoid fever, the last steps have not been completed, for the reason
that the animals experimented upon, namely, guinea-pigs, rabbits, and
mice, are not susceptible to these diseases.
[Illustration: Fig. 94.--Sir Joseph Lister, Born 1827.]
Lister.--The other member of the great triumvirate of bacteriology is
Sir Joseph Lister (Fig. 94); born in 1827, he has been successively
professor of surgery in the universities of Glasgow (1860) and of
Edinburgh (1869), and in King's College, London (1877). His practical
application of the germ-theory introduced aseptic methods into surgery
and completely revolutionized that field. This was in 1867. In an
address given that year before the British Medical Association in
Dublin, he said: "When it had been shown by the researches of Pasteur
that the septic property of the atmosphere depended, not on oxygen
or any gaseous constituent, but on minute organisms suspended in it,
which owed their energy to their vitality, it occurred to me that
decomposition in the injured part might be avoided without excluding
the air, by applying as a dressing some material capable of destroying
the life of the floating particles." At first he used carbolic acid
for this purpose. "The wards of which he had charge in the Glasgow
Infirmary were especially affected by gangrene, but in a short time
became the healthiest in the world; while other wards separated by a
passageway retained their infection." The method of Lister has been
universally adopted, and at the same time has been greatly extended and
improved.
The question of immunity, _i.e._, the reason why after having had
certain contagious diseases one is rendered immune, is of very great
interest, but is of medical bearing, and therefore is not dealt with
here.
Bacteria and Nitrates.--One further illustration of the connection
between bacteria and practical affairs may be mentioned. It is well
known that animals are dependent upon plants, and that plants in the
manufacture of protoplasm make use of certain nitrites and nitrates
which they obtain from the soil. Now, the source of these nitrites
and nitrates is very interesting. In animals the final products of
broken-down protoplasm are carbon dioxide, water, and a nitrogenous
substance called urea. These products are called excretory products.
The animal machine is unable to utilize the energy which exists in the
form of potential energy in these substances, and they are removed from
the body.
The history of nitrogenous substance is the one which at present
interests us the most. Entering the soil, it is there acted upon by
bacteria residing in the soil, these bacteria possessing the power of
making use of the lowest residuum of energy left in the nitrogenous
substance. They cause the nitrogen and the hydrogen to unite with
oxygen in such a way that there are produced nitrous and nitric
acids, and from these two acids, through chemical action, result the
nitrites and the nitrates. These substances are then utilized by the
plant in the manufacture of protoplasm, and the plant is fed upon by
animal organisms, so that a direct relationship is established between
these lower forms of life and the higher plant and animal series; a
relationship that is not only interesting, but that helps to throw an
important side-light upon the general nature of vital activities, their
kind and their reach. In addition to the soil bacteria mentioned above,
there are others that form association with the rootlets of certain
plants and possess the power of fixing free nitrogen from the air.
The nitrifying bacteria, are, of course, of great importance to the
farmer and the agriculturist.
It is not our purpose, however, to trace the different phases of the
subject of bacteriology to their conclusions, but rather to give a
picture of the historical development of this subject as related to the
broader one of general biology.
CHAPTER XIV
HEREDITY AND GERMINAL CONTINUITY--MENDEL, GALTON, WEISMANN
It is a matter of common observation that in the living world like
tends to produce like. The offspring of plants, as well as of animals,
resembles the parent, and among all organisms endowed with mind, the
mental as well as the physical qualities are inherited. This is a
simple statement of the fact of heredity, but the scientific study of
inheritance involves deep-seated biological questions that emerged late
in the nineteenth century, and the subject is still in its infancy.
In investigating this question, we need first, if possible, to locate
the bearers of hereditary qualities within the physical substance that
connects one generation with the next; then, to study their behavior
during the transmission of life in order to account for the inheritance
of both maternal and paternal qualities; and, lastly, to determine
whether or not transiently acquired characteristics are inherited.
Hereditary Qualities in the Germinal Elements.--When we take into
consideration the fact established for all animals and plants (setting
aside cases of budding and the division of unicellular organisms),
that the only substance that passes from one generation to another is
the egg and the sperm in animals, and their representatives in plants,
we see that the first question is narrowed to these bodies. If all
hereditary qualities are carried in the egg and the sperm--as it seems
they must be--then it follows that these germinal elements, although
microscopic in size, have a very complex organization. The discovery
of this organization must depend upon microscopic examination.
Knowledge regarding the physical basis of heredity has been greatly
advanced by critical studies of cells under the microscope and by the
application of experimental methods, while other phases of the problems
of inheritance have been elucidated by the analysis of statistics
regarding hereditary transmissions. The whole question, however,
is so recent that a clear formulation of the direction of the main
currents of progress will be more helpful than any attempt to estimate
critically the underlying principles.
Early Theories.--There were speculations regarding the nature of
inheritance in ancient and mediæval times. To mention any of them
prior to the eighteenth century would serve no useful purpose, since
they were vague and did not form the foundation upon which the
modern theories were built. The controversies over pre-formation and
epigenesis (see Chapter X) of the eighteenth century embodied some
ideas that have been revived. The recent conclusion that there is in
the germinal elements an inherited organization of great complexity
which conditions inheritance seems, at first, to be a return to the
doctrine of pre-formation, but closer examination shows that there is
merely a general resemblance between the ideas expressed by Haller,
Bonnet, and philosophers of their time and those current at the present
time. Inherited organization, as now understood, is founded on the idea
of germinal continuity and is vastly different from the old theory of
pre-formation. The meaning of epigenesis, as expressed by Wolff, has
also been modified to include the conception of pre-localization of
hereditary qualities within particular parts of the egg. It has come
now to mean that development is a process of differentiation of certain
qualities already laid down in the germinal elements.
Darwin's Theory of Pangenesis.--In attempting to account for heredity,
Darwin saw clearly the necessity of providing some means of getting all
hereditary qualities combined within the egg and the sperm. Accordingly
he originated his provisional theory of pangenesis. Keeping in mind the
fact that all organisms begin their lives in the condition of single
cells, the idea of inheritance through these microscopic particles
becomes difficult to understand. How is it possible to conceive of all
the hereditary qualities being contained within the microscopic germ of
the future being? Darwin supposed that very minute particles, which he
called gemmules, were set free from all the cells in the body, those of
the muscular system, of the nervous system, of the bony tissues, and
of all other tissues contributing their part. These liberated gemmules
were supposed to be carried by the circulation and ultimately to be
aggregated within the germinal elements (ovum and sperm). Thus the
germinal elements would be a composite of substances derived from all
organs and all tissues.
With this conception of the blending of the parental qualities
within the germinal elements we can conceive how inheritance would
be possible and how there might be included in the egg and the sperm
a representative in material substance of all the qualities of the
parents. Since development begins in a fertilized ovum, this complex
would contain minute particles derived from every part of the bodies of
both parents, which by growth would give rise to new tissues, all of
them containing representatives of the tissues of the parent form.
Theory of Pangenesis Replaced by that of Germinal Continuity.--This
theory of Darwin served as the basis for other theories founded
upon the conception of the existence of pangens; and although the
modifications of Spencer, Brooks, and others were important, it is not
necessary to indicate them in detail in order to understand what is to
follow. The various theories founded upon the idea of pangens were
destined to be replaced by others founded on the conception of germinal
continuity--the central idea in nineteenth-century biology.
The four chief steps which have led to the advancement of the knowledge
of heredity, as suggested by Thomson, are as follows: "(a) The
exposition of the doctrine of germinal continuity, (b) More precise
investigation of the material basis of inheritance, (c) Suspicions
regarding the inheritance of acquired characteristics, (d) Application
of statistical methods which have led to the formulation of the law of
ancestral heredity." We shall take these up in order.
Exposition of the Doctrine of Germinal Continuity.--From parent to
offspring there passes some hereditary substance; although small in
amount, it is the only living thread that connects one generation with
another. It thus appears that there enters into the building of the
body of a new organism some of the actual substance of both parents,
and that this transmitted substance must be the bearer of hereditary
qualities. Does it also contain some characteristics inherited from
grandparents and previous generations? If so, how far back in the
history of the race does unbroken continuity extend?
Briefly stated, genetic continuity means that the ovum and its
fertilizing agent are derived by continuous cell-lineage from the
fertilized ovum of previous generations, extending back to the
beginning of life. The first clear exposition of this theory occurs
in the classical work of Virchow on _Cellular Pathology_, published
in 1858. Virchow (1821-1902), the distinguished professor of the
University of Berlin, has already been spoken of in connection with
the development of histology. He took the step of overthrowing the
theory of free cell-formation, and replacing it by the doctrine of
cell-succession. According to the theory of Schleiden and Schwann,
cells arose from a blastema by a condensation of matter around
a nucleus, and the medical men prior to 1858 believed in free
cell-formation within a matrix of secreted or excreted substance. This
doctrine was held with tenacity especially for pathological growths.
Virchow demonstrated, however, that there is a continuity of living
substance in all growths--that cells, both in health and in disease,
arise only by the growth and division of previously existing living
cells; and to express this truth he coined the formula "_omnis cellula
e cellula_." Manifestly it was necessary to establish this law of
cell-succession before any idea of germinal continuity could prevail.
Virchow's work in this connection is of undying value.
When applied to inheritance the idea of the continuity of living
substance leads to making a distinction between germ-cells and
body-cells. This had been done before the observations of Virchow
made their separation of great theoretical value. Richard Owen, in
1849, pointed out certain differences between the body-cells and the
germinal elements, but he did not follow up the distinction which he
made. Haeckel's _General Morphology_, published in 1866, forecasts the
idea also, and in 1878 Jaeger made use of the phrase "continuity of the
germ protoplasm." Other suggestions and modifications led to the clear
expression by Nussbaum, about 1875, that the germinal substance was
continued by unbroken generations from the past, and is the particular
substance in which all hereditary qualities are included. But the
conception finds its fullest expression in the work of Weismann.
Weismann's explanation of heredity is at first sight relatively simple.
In reply to the question, "Why is the offspring like the parent?" he
says, "Because it is composed of some of the same stuff." In other
words, there has been unbroken germinal continuity between generations.
His idea of germinal continuity, _i.e._, unbroken continuity, through
all time, of the germinal substance, is a conception of very great
extent, and now underlies all discussion of heredity.
In order to comprehend it, we must first distinguish between the
germ-cells and the body-cells. Weismann regards the body, composed of
its many cells, as a derivative that becomes simply a vehicle for the
germ-cells. Owen's distinction between germ-cells and body-cells, made
in 1849, was not of much importance, but in the theory of Weismann it
is of vital significance. The germ-cells are the particular ones which
carry forward from generation to generation the life of the individual.
The body-cells are not inherited directly, but in the transmission of
life the germ-cells pass to the succeeding generation, and they in
turn have been inherited from the previous generation, and, therefore,
we have the phenomenon of an unbroken connection with all previous
generations.
When the full significance of this conception comes to us, we see
why the germ-cells have an inherited organization of remarkable
complexity. This germinal substance embodies all the past history of
the living, impressionable protoplasm, which has had an unbroken series
of generations. During all time it has been subjected to the molding
influence of external circumstances to which it has responded, so that
the summation of its experiences becomes in some way embedded within
its material substance. Thus we have the germinal elements possessing
an inherited organization made up of all the previous experiences of
the protoplasm, some of which naturally are much more dominant than the
others.
We have seen that this idea was not first expressed by Weismann; it
was a modification of the views of Nussbaum and Hertwig. While it
was not his individually, his conclusions were apparently reached
independently. This idea was in the intellectual atmosphere of the
times. Several investigators reached their conclusions independently,
although there is great similarity between them. Although the credit
for the first formulation of the law of germinal continuity does not
belong to Weismann, that of the greatest elaboration of it does. This
doctrine of germinal continuity is now so firmly embedded in biological
ideas of inheritance and the evolution of animal life that we may say
it has become the corner-stone of modern biology.
The conclusion reached--that the hereditary substance is the
germ-plasm--is merely preliminary; the question remains, Is the
germ-plasm homogeneous and endowed equally in all parts with a mixture
of hereditary qualities? This leads to the second step.
The More Precise Investigation of the Material Basis of
Inheritance.--The application of the microscope to critical studies of
the structure of the germ-plasm has brought important results which
merge with the development of the idea of germinal continuity. Can we
by actual observation determine the particular part of the protoplasmic
substance that carries the hereditary qualities? The earliest answer
to this question was that the protoplasm, being the living substance,
was the bearer of heredity. But close analysis of the behavior of
the nucleus during development led, about 1875, to the idea that the
hereditary qualities are located within the nucleus of the cell.
This idea, promulgated by Fol, Koelliker, and Oskar Hertwig, narrowed
the attention of students of heredity from the general protoplasmic
contents of the cell to the nucleus. Later investigations show that
this restriction was, in a measure, right. The nucleus takes an active
part during cell-division, and it was very natural to reach the
conclusion that it is the particular bearer of hereditary substance.
But, in 1883, Van Beneden and Boveri made the discovery that within
the nucleus are certain distinct little rod-like bodies which make
their appearance during cell-division. These little bodies, inasmuch
as they stain very deeply with the dyes used in microscopic research,
are called chromosomes. And continued investigation brought out the
astounding fact that, although the number of chromosomes vary in
different animals (commonly from two to twenty-four), they are of the
same number in all the cells of any particular animal or plant. These
chromosomes are regarded as the bearers of heredity, and their behavior
during fertilization and development has been followed with great care.
Brilliant studies of the formation of the egg have shown that the
egg nucleus, in the process of becoming mature, surrenders one-half
its number of chromosomes; it approaches the surface of the egg and
undergoes division, squeezing out one-half of its substance in the
form of a polar globule; and this process is once repeated.[8] The
formation of polar globules is accompanied by a noteworthy process of
reduction in the number of chromosomes, so that when the egg nucleus
has reached its mature condition it contains only one-half the number
of chromosomes characteristic of the species, and will not ordinarily
undergo development without fertilization.
The precise steps in the formation of the sperm have also been studied,
and it has been determined that a parallel series of changes occur. The
sperm, when it is fully formed, contains also one-half the number of
chromosomes characteristic of the species. Now, egg and sperm are the
two germinal elements which unite in development. Fertilization takes
place by the union of sperm and egg, and inasmuch as the nuclei of
each of these structures contain one-half of the number of chromosomes
characteristic of the species, their union in fertilization results in
the restoration of the original number of chromosomes. The fertilized
ovum is the starting-point of a new organism, and from the method of
its fertilization it appears that the parental qualities are passed
along to the cells of every tissue.
The complex mechanism exhibited in the nucleus during segmentation
is very wonderful. The fertilized ovum begins to divide, the nucleus
passing through a series of complicated changes whereby its chromosomes
undergo a lengthwise division--a division that secures an equable
partition of the substance of which they are composed. With each
successive division, this complicated process is repeated, and the
many cells, arising from continued segmentation of the original cell,
contain nuclei in which are embedded descendants of the chromosomes in
unbroken succession. Moreover, since these chromosomes are bi-parental,
we can readily understand that every cell in the body carries both
maternal and paternal qualities.
The careful analysis of the various changes within the nuclei of the
egg proves to be the key to some of the central questions of heredity.
We see the force of the point which was made in a previous chapter,
that inheritance is in the long run a cellular study, and we see in a
new light the importance of the doctrine of germinal continuity. This
conception, in fact, elucidates the general problem of inheritance in a
way in which it has never been elucidated by any other means.
For some time the attention of investigators was concentrated
upon the nucleus and the chromosomes, but it is now necessary to
admit that the basis of some structures is discoverable within the
cytoplasm that surrounds the nucleus. Experimental observations
(Conklin, Lillie, Wilson) have shown the existence of particular areas
within the apparently simple substance of the egg, areas which are
definitely related to the development of particular parts of the
embryo. The removal of any one of these pre-localized areas prevents
the development of the part with which it is genetically related.
Researches of this kind, necessitating great ingenuity in method and
great talents in the observers, are widening the field of observation
upon the phenomena of heredity.
The Inheritance of Acquired Characteristics.--The belief in the
inheritance of acquired characteristics was generally accepted up to
the middle of the nineteenth century, but the reaction against it
started by Galton and others has assumed great proportions. Discussions
in this line have been carried on extensively, and frequently in the
spirit of great partizanship. These discussions cluster very much about
the name and the work of Weismann, the man who has consistently stood
against the idea of acquired characteristics. More in reference to this
phase of the question is given in the chapter dealing with Weismann's
theory of evolution (see p. 398). Wherever the truth may lie, the
discussions regarding the inheritance of acquired characteristics
provoked by Weismann's theoretical considerations, have resulted
in stimulating experiment and research, and have, therefore, been
beneficial to the advance of science.
The Application of Statistical Methods and Experiments to the Ideas
of Heredity. Mendel.--This feature of investigating questions of
heredity is of growing importance. The first to complete experiments
and to investigate heredity to any purpose was the Austrian monk Mendel
(1822-1884) (Fig. 95), the abbot of a monastery at Brünn. In his garden
he made many experiments upon the inheritance, particularly in peas,
of color and of form; and through these experiments he demonstrated a
law of inheritance which bids fair to be one of the great biological
discoveries of the nineteenth century. He published his papers in 1866
and 1867, but since the minds of naturalists at that time were very
much occupied with the questions of organic evolution, raised through
the publications of Darwin, the ideas of Mendel attracted very little
attention. The principles that he established were re-discovered in
1900 by De Vries and other botanists, and thus naturalists were led to
look up the work of Mendel.
[Illustration: Fig. 95.--Gregor Mendel, 1822-1884.
Permission of Professor Bateson.]
The great discovery of Mendel may be called that of the purity of
the germ-cells. By cross-fertilization of pure breeds of peas of
different colors and shapes he obtained hybrids. The hybrid embodied
the characteristics of the crossed peas; one of the characteristics
appearing, and the other being held in abeyance--present within the
organization of the pea, but not visible. When peas of different
color were cross-fertilized, one color would be stronger apparently
than the other, and would stand out in the hybrids. This was called
the dominant color. The other, which was held in abeyance, was called
recessive; for, though unseen, it was still present within the young
seeds. That the recessive color was not blotted out was clearly shown
by raising a crop from the hybrid, a condition under which they would
produce seeds like those of the two original forms, and in equal
number; and thereafter the descendants of these peas would breed true.
This so-called purity of the germ-cells, then, may be expressed in this
way: "The hybrid, whatever its own character, produces ripe germ-cells,
which produce only the pure character of one parent or of the other"
(Castle).
Although Mendel's discovery was for a long time overlooked, happily
the facts were re-discovered, and at the present time extensive
experiments are being made with animals to test this law: experiments
in the inheritance of poultry, the inheritance of fur in guinea-pigs,
of erectness in the ears of rabbits, etc., etc. In this country the
experiments of Castle, Davenport, and others with animals tend to
support Mendel's conclusion and lift it to the position of a law.
Rank of Mendel's Discovery.--The discovery by Mendel of alternative
inheritance will rank as one of the greatest discoveries in the study
of heredity. The fact that in cross-breeding the parental qualities are
not blended, but that they retain their individuality in the offspring,
has many possible practical applications both in horticulture and
in the breeding of animals. The germ-cells of the hybrids have the
dominant and the recessive characters about equally divided; this will
appear in the progeny of the second generation, and the races, when
once separated, may be made to breed true.
Mendel's name was not recognized as a prominent one in the annals of
biological history until the re-discovery of his law in 1900; but now
he is accorded high rank. It may be remarked in passing that the three
leading names in the development of the theories of heredity are those
of Mendel, Galton, and Weismann.
[Illustration: Fig. 96.--Francis Galton, Born 1822.]
Galton.--The application of statistical methods is well illustrated in
the theories of Francis Galton (Fig. 96). This distinguished English
statistician was born in 1822, and is still living. He is the grandson
of Dr. Erasmus Darwin and the cousin of Charles. After publishing books
on his travels in Africa, he began the experimental study of heredity
and, in 1871, he read before the Royal Society of London a paper on
Pangenesis, in which he departed from that theory as developed by
Darwin. The observations upon which he based his conclusions were made
upon the transfusion of blood in rabbits and their after-breeding. He
studied the inheritance of stature, and other characteristics, in human
families, and the inheritance of spots on the coat of certain hounds,
and was led to formulate a law of ancestral inheritance which received
its clearest expression in his book, _Natural Inheritance_, published
in 1889.
He undertook to determine the proportion of heritage that is, on the
average, contributed by each parent, grandparent, etc., and arrived at
the following conclusions: "The parents together contribute one-half
the total heritage, the four grandparents together one-fourth, the
eight great-grandparents one-sixteenth, and all the remainder of the
ancestry one-sixteenth."
Carl Pearson has investigated this law of ancestral inheritance. He
substantiates the law in its principle, but modifies slightly the
mathematical expression of it.
This field of research, which involves measurements and mathematics
and the handling of large bodies of statistics, has been considerably
cultivated, so that there is in existence in England a journal devoted
exclusively to biometrics, which is edited by Carl Pearson, and is
entitled _Biometrika_.
The whole subject of heredity is undergoing a thorough revision.
What seems to be most needed at the present time is more exact
experimentation, carried through several generations, together with
more searching investigations into the microscopical constitution
of egg and sperm, and close analysis of just what takes place
during fertilization and the early stages of the development of the
individual. Experiments are being conducted on an extended scale in
endowed institutions. There is notably in this country, established
under the Carnegie Institution, a station for experimental evolution,
at Cold Spring Harbor, New York, of which C.B. Davenport is director.
Other experimental stations in England and on the Continent have been
established, and we are to expect as the result of coördinated and
continuous experimental work many substantial contributions to the
knowledge of inheritance.
FOOTNOTES:
[Footnote 8: There are a few exceptions to this rule, as in the eggs of
plant-lice, etc., in which a single polar globule is produced.]
CHAPTER XV
THE SCIENCE OF FOSSIL LIFE
It gradually dawned on the minds of men that the crust of the earth is
like a gigantic mausoleum, containing within it the remains of numerous
and varied forms of life that formerly existed upon the surface of the
earth. The evidence is clear that untold generations of living forms,
now preserved as fossils, inhabited the earth, disported themselves,
and passed away long before the advent of man. The knowledge of this
fossil life, on account of its great diversity, is an essential part
of biology, and all the more so from the circumstance that many forms
of life, remains of which are exhibited in the rocks, have long since
become extinct. No history of biology would be complete without an
account of the rise and progress of that department of biology which
deals with fossil life.
It has been determined by collecting and systematically studying the
remains of this ancient life that they bear testimony to a long,
unbroken history in which the forms of both animals and plants have
been greatly altered. The more ancient remains are simple in structure,
and form with the later ones, a series that exhibits a gradually
increasing complexity of structure. The study of the fossil series has
brought about a very great extension of our knowledge regarding the age
of the world and of the conditions under which life was evolved.
Strange Views Regarding Fossils.--But this state of our knowledge
was a long time coming, and in the development of the subject we
can recognize several distinct epochs, "well-marked by prominent
features, but like all stages of intellectual growth, without definite
boundaries." Fossils were known to the ancients, and by some of the
foremost philosophers of Greece were understood to be the remains of
animals and plants. After the revival of learning, however, lively
controversies arose as to their nature and their meaning.
Some of the fantastic ideas that were entertained regarding the nature
of fossil remains may be indicated. The fossils were declared by many
to be freaks of nature; others maintained that they were the results
of spontaneous generation, and were produced by the plastic forces of
nature within the rocks in which they were found embedded. Another
opinion expressed was that they were generated by fermentations. As the
history of intellectual development shows, the mind has ever seemed
benumbed in the face of phenomena that are completely misconceived;
mystical explanations have accordingly been devised to account for
them. Some of the pious persons of that period declared that fossils
had been made and distributed by the Creator in pursuance of a plan
beyond our comprehension. Another droll opinion expressed was that
the Creator in His wisdom had introduced fossil forms into the rocks
in order that they should be a source of confusion to the race of
geologists that was later to arise.
And still another fantastic conception suggested that the fossils
were the original molds used by the Creator in forming different
varieties of animals and plants, some of which had been used and others
discarded. It was supposed that in preparing for the creation of life
He experimented and discarded some of His earliest attempts; and that
fossils represented these discarded molds and also, perhaps, some that
had been used in fashioning the created forms.
When large bones, as of fossil elephants, began to be exhumed, they
became for the most part the objects of stupid wonder. The passage in
the Scriptures was pointed out, that "there were giants in those days,"
and the bones were taken to be evidences of the former existence of
giants. The opinions expressed regarding the fossil bones were varied
and fantastic, "some saying that they were rained from Heaven, others
saying that they were the gigantic limbs of the ancient patriarchs,
men who were believed to be tall because they were known to be old."
Following out this idea, "Henrion in 1718 published a work in which
he assigned to Adam a height of 123 feet 9 inches, Noah being 20 feet
shorter, and so on."
Determination of the Nature of Fossils.--In due course it came to
be recognized that fossils were the remains of forms that had been
alive during earlier periods of time; but in reaching this position
there was continual controversy. Objections were especially vigorous
from theological quarters, since such a conclusion was deemed to be
contradictory to the Scriptures. The true nature of fossils had been
clearly perceived by Leonardo da Vinci (1452-1519) and certain others
in the sixteenth century.
The work, however, that approached more nearly to scientific
demonstration was that of Steno (1638-1686), a Dane who migrated to
Italy and became the court physician to the dukes of Tuscany. He was a
versatile man who had laid fast hold upon the new learning of his day.
Eminent as anatomist, physiologist, and physician, with his ever active
mind he undertook to encompass all learning. It is interesting that
Steno--or Stensen--after being passionately devoted to science, became
equally devoted to religion and theology, and, forsaking all scientific
pursuits, took orders and returned to his native country with the title
of bishop. Here he worked in the service of humanity and religion to
the end of his life.
In reference to his work in geology, his conclusions regarding fossils
(1669) were based on the dissection of the head of a shark, by which
means he showed an almost exact correspondence between certain glossy
fossils and the teeth of living sharks. He applied his reasoning, that
like effects imply like causes, to all manner of fossils, and clearly
established the point that they should be regarded as the remains of
animals and plants. The method of investigation practiced by Steno was
that "which has consciously or unconsciously guided the researches of
palæontologists ever since."
Although his conclusions were well supported, they did not completely
overthrow the opposing views, and become a fixed basis in geology.
When, at the close of the eighteenth century and the beginning of the
nineteenth, fossil remains were being exhumed in great quantities in
the Paris basin, Cuvier, the great French naturalist, reëstablished the
doctrine that fossils are the remains of ancient life. An account of
this will be given presently, and in the mean time we shall go on with
the consideration of a question raised by the conclusions of Steno.
Fossil Deposits Ascribed to the Flood.--After it began to be
reluctantly conceded that fossils might possibly be the remains of
former generations of animals and plants, there followed a period
characterized by the general belief that these entombed forms had been
deposited at the time of the Mosaic deluge. This was the prevailing
view in the eighteenth century. As observation increased and the extent
and variety of fossil life became known, as well as the positions in
which fossils were found, it became more difficult to hold this view
with any appearance of reason. Large forms were found on the tops of
mountains, and also lighter forms were found near the bottom. Miles
upon miles of superimposed rocks were discovered, all of them bearing
quantities of animal forms, and the interpretation that these had been
killed and distributed by a deluge became very strained. But to the
reasoners who gave free play to their fancies the facts of observation
afforded little difficulty. Some declared that the entire surface of
the earth had been reduced to the condition of a pasty mass, and that
the animals drowned by the Deluge had been deposited within this pasty
mass which, on the receding of the waters, hardened into rocks.
The belief that fossil deposits were due to the Deluge sensibly
declined, however, near the close of the eighteenth century, but was
still warmly debated in the early part of the nineteenth century.
Fossil bones of large tropical animals having been discovered
about 1821, embedded in the stalagmite-covered floor of a cavern
in Yorkshire, England, some of the ingenious supporters of the
flood-theory maintained that caves were produced by gases proceeding
from the bodies of decaying animals of large size; that they were like
large bubbles in the crust of the earth, and, furthermore, that bones
found in caverns were either those from the decayed carcasses or others
that had been deposited during the occurrence of the Flood.
Even the utterances of Cuvier, in his theory of catastrophism to which
we shall presently return, gave countenance to the conclusion that the
Deluge was of universal extent. As late as 1823, William Buckland,
reader in geology in Oxford, and later canon (1825) of Christ Church,
and dean (1845) of Westminster, published his _Reliquiæ Diluvianæ_,
or _Observations on the Organic Remains Attesting the Action of a
Universal Deluge_.
The theory that the Mosaic deluge had any part in the deposit of
organic fossils was finally surrendered through the advance of
knowledge, owing mainly to the labors of Lyell and his followers.
The Comparison of Fossil and Living Animals.--The very great interest
connected with the reëstablishment of the conclusion of Steno, that
fossils were once alive, leads us to speak more at length of the
discoveries upon which Cuvier passed his opinion. In the gypsum rocks
about Paris the workmen had been turning up to the light bones of
enormous size. While the workmen could recognize that they were bones
of some monsters, they were entirely at loss to imagine to what kind
of animals they had belonged, but the opinion was frequently expressed
that they were the bones of human giants.
Cuvier, with his extensive preparation in comparative anatomy, was the
best fitted man perhaps in all the world to pass judgment upon these
particular bones. He went to the quarries and, after observing the
remains, he saw very clearly that they were different from the bones of
any animals now existing. His great knowledge of comparative anatomy
was founded on a comprehensive study of the bony system as well as the
other structures of all classes of living animals. He was familiar with
the anatomy of elephants, and when he examined the large bones brought
to light in the quarries of Montmartre, he saw that he was confronted
with the bones of elephant-like animals, but animals differing in their
anatomy from those at present living on the earth.
The great feature of Cuvier's investigations was that he instituted
comparisons on a broad scale between fossil remains and living animals.
It was not merely that he followed the method of investigation employed
by Steno; he went much further and reached a new conclusion of great
importance. Not only was the nature of fossil remains determined, but
by comparing their structure with that of living animals the astounding
inference was drawn that the fossil remains examined belonged to
forms that were truly extinct. This discovery marks an epoch in the
development of the knowledge of extinct animals.
Cuvier the Founder of Vertebrate Palæontology.--The interesting
discovery that the fossil relics in the Eocene rocks about Paris
embraced extinct species was announced to the Institute by Cuvier in
January, 1796; and thereafter he continued for a quarter of a century
to devote much attention to the systematic study of collections made
in that district. These observations were, however, shared with other
labors upon comparative anatomy and zoölogy, which indicates the
prodigious industry for which he was notable. In 1812-1813 he published
a monumental work, profusely illustrated, under the title _Ossemens
Fossiles_. This standard publication entitles him to recognition as the
founder of vertebrate palæontology.
In examining the records of fossil life, Cuvier and others saw that
the evidence indicated a succession of animal populations that had
become extinct, and also that myriads of new forms of life appeared in
the rocks of succeeding ages. Here Cuvier, who believed that species
were fixed and unalterable, was confronted with a puzzling problem. In
attempting to account for the extinction of life, and what seemed to
him the creation of new forms, he could see no way out consistent with
his theoretical views except to assume that the earth had periodically
been the scene of great catastrophes, of which the Mosaic deluge was
the most recent, but possibly not the last. He supposed that these
cataclysms of nature resulted in the extinction of all life, and
that after each catastrophe the salubrious condition of the earth
was restored, and that it was re-peopled by a new creation of living
beings. This conception, known as the theory of catastrophism, was
an obstacle to the progress of science. It is to be regretted that
Cuvier was not able to accept the views of his illustrious contemporary
Lamarck, who believed that the variations in fossil life, as well as
those of living forms, were owing to gradual transformations.
Lamarck Founds Invertebrate Palæontology.--The credit of founding
the science of palæontology does not belong exclusively to Cuvier.
Associated with his name as co-founders are those of Lamarck and
William Smith. Lamarck, that quiet, forceful thinker who for so many
years worked by the side of Cuvier, founded the science of invertebrate
palæontology. The large bones with which Cuvier worked were more easy
to be recognized as unique or as belonging to extinct animals than
the shells which occurred in abundance in the rocks about Paris. The
latter were more difficult to place in their true position because
the number of forms of life in the sea is very extended and very
diverse. Just as Cuvier was a complete master of knowledge regarding
vertebrate organization, so Lamarck was equally a master of that vast
domain of animal forms which are of a lower grade of organization--the
invertebrates. From his study of the collections of shells and other
invertebrate forms from the rocks, Lamarck created invertebrate
palæontology and this, coupled with the work of Cuvier, formed the
foundations of the entire field.
Lamarck's study of the extinct invertebrates led him to conclusions
widely at variance with those of Cuvier. Instead of thinking of a
series of catastrophes, he saw that not all of the forms of life
belonging to one geological period became extinct, but that some of
them were continued into the succeeding period. He saw, therefore, that
the succession of life in the rocks bore testimony to a long series
of gradual changes upon the earth's surface, and did not in any way
indicate the occurrence of catastrophes. The changes, according to the
views of Lamarck, were all knit together into a continuous process, and
his conception of the origin of life upon the earth grew and expanded
until it culminated in the elaboration of the first consistent theory
of evolution.
These two men, Lamarck and Cuvier, form a contrast as to the favors
distributed by fortune: Cuvier, picturesque, highly honored, the
favorite of princes, advanced to the highest places of recognition
in the government, acclaimed as the Jove of natural science; Lamarck,
hard-working, harassed by poverty, insufficiently recognized, and,
although more gifted than his confrère, overlooked by the scientific
men of the time. The judgment of the relative position of these two
men in natural science is now being reversed, and on the basis of
intellectual supremacy Lamarck is coming into general recognition
as the better man of the two. In the chapters dealing with organic
evolution some events in the life of this remarkable man will be given.
The Arrangement of Fossils in Strata.--The other name associated with
Lamarck and Cuvier is that of William Smith, the English surveyor.
Both Lamarck and Cuvier were men of extended scientific training, but
William Smith had a moderate education as a surveyor. While the two
former were able to express scientific opinions upon the nature of the
fossil forms discovered, William Smith went at his task as an observer
with a clear and unprejudiced mind, an observer who walked about over
the fields, noticing the conditions of rocks and of fossil forms
embedded therein. He noted that the organic remains were distributed
in strata, and that particular forms of fossil life characterized
particular strata and occupied the same relative position to one
another. He found, for illustration, that certain particular forms
would be found underlying certain other forms in one mass of rocks
in a certain part of the country. Wherever he traveled, and whatever
rocks he examined, he found these forms occupying the same relative
positions, and thus he came to the conclusion that the living forms
within the rocks constitute a stratified series, having definite and
unvarying arrangement with reference to one another.
In short, the work of these three men--Cuvier, Lamarck, and William
Smith--placed the new science of palæontology upon a secure basis at
the beginning of the nineteenth century.
Summary.--The chief steps up to this time in the growth of the
science of fossil life may now be set forth in categories, though we
must remember that the advances proceeded concurrently and were much
intermingled, so that, whatever arrangement we may adopt, it does not
represent a strict chronological order of events:
I. The determination of the nature of fossils. Owing to the labors of
Da Vinci, Steno, and Cuvier, the truth was established that fossils are
the remains of former generations of animals and plants.
II. The comparison of organic fossils with living forms that was
instituted on a broad scale by Cuvier resulted in the conclusion that
some of the fossils belong to extinct races. The belief of Cuvier that
entire populations became extinct simultaneously, led him to the theory
of catastrophism. The observations of Lamarck, that, while some species
disappear, others are continued and pass through transmutations, were
contrary to that theory.
III. The recognition that the stratified rocks in which fossils are
distributed are sedimentary deposits of gradual formation. This
observation and the following took the ground from under the theory
that fossils had been deposited during the Mosaic deluge.
IV. The discovery by William Smith that the arrangement of fossils
within rocks is always the same, and the relative age of rocks may be
determined by an examination of their fossil contents.
Upon the basis of the foregoing, we come to the next advance, _viz._:
V. The application of this knowledge to the determination of the
history of the earth.
Fossil Remains as an Index to the Past History of the Earth.--The most
advanced and enlightened position that had been taken in reference to
the fossil series during the first third of the nineteenth century was
that taken by Lamarck, he being the first to read in the series the
history of life upon the globe, weaving it into a connected story, and
establishing thereon a doctrine of organic evolution. It was not until
after 1859, however, that the truth of this conclusion was generally
admitted, and when it was accepted it was not through the earlier
publications of Lamarck, but through the arguments of later observers,
founded primarily upon the hypothesis set forth by Darwin. There were
several gradations of scientific opinion in the period, short as it
was, between the time of Cuvier and of Darwin; and this intermediate
period was one of contention and warfare between the theologians and
the geologists. Cuvier had championed the theory of a succession of
catastrophes, and since this hypothesis did not come into such marked
conflict with the prevailing theological opinion as did the views of
Lamarck, the theologians were ready to accept the notion of Cuvier, and
to point with considerable satisfaction to his unique position as an
authority.
Lyell.--In 1830 there was published an epoch-making work in geology
by Charles Lyell (Fig. 97), afterward Sir Charles, one of the
most brilliant geologists of all the world. This British leader
of scientific thought showed the prevalence of a uniform law of
development in reference to the earth's surface. He pointed out the
fact that had been maintained by Hutton, that changes in the past were
to be interpreted in the light of what is occurring in the present. By
making a careful study of the work performed by the waters in cutting
down the continents and in transferring the eroded material to other
places, and distributing it in the form of deltas; by observing also
the action of frost and wind and wave; by noting, furthermore, the
conditions under which animals die and are subsequently covered up in
the matrix of detritus--by all this he showed evidences of a series of
slow, continuous changes that have occurred in the past and have molded
the earth's crust into its present condition.
[Illustration: Fig. 97.--Charles Lyell, 1797-1875.]
He showed, further, that organic fossils are no exception to this law
of uniform change. He pointed to the evidences that ages of time had
been required for the formation of the rocks bearing fossils; and that
the regular succession of animal forms indicates a continual process of
development of animal life; and that the disappearance of some forms,
that is, their becoming extinct, was not owing to sudden changes, but
to gradual changes. When this view was accepted, it overthrew the
theory of catastrophism and replaced it by one designated uniformatism,
based on the prevalence of uniform natural laws.
This new conception, with all of its logical inferences, was scouted
by those of theological bias, but it won its way in the scientific
world and became an important feature in preparing for the reception of
Darwin's great book upon the descent of animal life.
We step forward now to the year 1859, to consider the effect upon
the science of palæontology of the publication of Darwin's _Origin
of Species_. Its influence was tremendous. The geological theories
that had provoked so much controversy were concerned not merely with
the disappearance of organic forms, but also with the introduction
of new species. The _Origin of Species_ made it clear that the only
rational point of view in reference to fossil life was that it had been
gradually developed, that it gave us a picture of the conditions of
life upon the globe in past ages, that the succession of forms within
the rocks represented in outline the successive steps in the formation
of different kinds of animals and plants.
Owen.--Both before and after Darwin's hypothesis was given to science,
notable anatomists, a few of whom must be mentioned, gave attention to
fossil remains. Richard Owen (1804-1892) had his interest in fossil
life stimulated by a visit to Cuvier in 1831, and for more than forty
years thereafter he published studies on the structure of fossil
animals. His studies on the fossil remains of Australia and New Zealand
brought to light some interesting forms. The extinct giant bird of New
Zealand (Fig. 98) was a spectacular demonstration of the enormous size
to which birds had attained during the Eocene period. Owen's monograph
(1879) on the oldest known bird--the archæopteryx--described an
interesting form uniting both bird-like and reptilian characteristics.
[Illustration: Fig. 98.--Professor Owen and the Extinct Fossil Bird
(Dinornis) of New Zealand.
Permission of D. Appleton & Co.]
Agassiz.--Louis Agassiz (1807-1873) (Fig. 99) also came into close
personal contact with Cuvier, and produced his first great work partly
under the stimulus of the latter. When Agassiz visited Paris, Cuvier
placed his collections at Agassiz's disposal, together with numerous
drawings of fossil fishes. The profusely illustrated monograph of
Agassiz on the fossil fishes (1833-1844) began to appear in 1833, the
year after Cuvier's death, and was carried on eleven years before it
was completed.
[Illustration: Fig. 99.--Louis Agassiz, 1807-1873.]
Agassiz, with his extensive knowledge of the developmental stages
of animals, came to see a marked parallelism between the stages in
development of the embryo and the successive forms in the geological
series. This remarkable parallelism between the fossil forms of life
and the stages in the development of higher forms of recent animals
is very interesting and very significant, and helps materially in
elucidating the idea that the fossil series represent roughly the
successive stages through which animal forms have passed in their
upward course of development from the simplest to the highest, through
long ages of time. Curiously enough, however, Agassiz failed to grasp
the meaning of the principle that he had worked out. After illustrating
so nicely the process of organic evolution, he remained to the end of
his life an opponent of that theory.
Huxley.--Thomas Henry Huxley (1825-1895) was led to study fossil life
on an extended scale, and he shed light in this province as in others
upon which he touched. With critical analysis and impartial mind he
applied the principles of evolution to the study of fossil remains.
His first conclusion was that the evidence of evolution derived from
palæontology was negative, but with the advances in discovery he grew
gradually to recognize that palæontologists, in bringing to light
complete evolutionary series, had supplied some of the strongest
supporting evidence of organic evolution. By many geologists fossils
have been used as time-markers for the determination of the age of
various deposits; but, with Huxley, the study of them was always
biological. It is to the latter point of view that palæontology owes
its great importance and its great development. The statement of
Huxley, that the only difference between a fossil and a recent animal
is that one has been dead longer than the other, represents the spirit
in which the study is being carried forward.
[Illustration: Fig. 100.--E.D. Cope, 1840-1897.]
With the establishment of the doctrine of organic evolution
palæontology entered upon its modern phase of growth; upon this basis
there is being reared a worthy structure through the efforts of the
recent votaries to the science. It is neither essential nor desirable
that the present history of the subject should be followed here in
detail. The collections of material upon which palæontologists are
working have been enormously increased, and there is perhaps no place
where activity has been greater than in the United States. The rocks
of the Western States and Territories embrace a very rich collection
of fossil forms, and, through the generosity of several wealthy men,
exploring parties have been provided for and immense collections have
been brought back to be preserved in the museums, especially of New
Haven, Conn., and in the American Museum of Natural History in New York
City.
Leidy, Cope, and Marsh.--Among the early explorers of the fossils of
the West must be named Joseph Leidy, E.D. Cope (Fig. 100), and O.C.
Marsh. These gentlemen all had access to rich material, and all of
them made notable contributions to the science of palæontology. The
work of Cope (1840-1897) is very noteworthy. He was a comparative
anatomist equal to Cuvier in the extent of his knowledge, and of larger
philosophical views. His extended publications under the direction of
the United States Government have very greatly extended the knowledge
of fossil vertebrate life in America.
O.C. Marsh (Fig. 101) is noteworthy for similar explorations; his
discovery of toothed birds in the Western rocks and his collection
of fossil horses, until recently the most complete one in existence,
are all very well known. Throughout his long life he contributed from
his own private fortune, and intellectually through his indefatigable
labors, to the progress of palæontology.
[Illustration: Fig. 101.--O.C. Marsh, 1831-1899.]
Zittel.--The name most widely known in palæontology is that of the
late Karl von Zittel (1839-1904), who devoted all his working life
to the advancement of the science of fossils. In his great work,
_Handbuch der Palaeontologie_ (1876-1893), he brought under one view
the entire range of fossils from the protozoa up to the mammals. Osborn
says: "It is probably not an exaggeration to say that he did more for
the promotion and diffusion of palæontology than any other single
man who lived during the nineteenth century. While not gifted with
genius, he possessed extraordinary judgment, critical capacity, and
untiring industry." His portrait (Fig. 102) shows a face "full of keen
intelligence and enthusiasm."
Zittel's influence was exerted not only through his writings, but also
through his lectures and the stimulus imparted to the large number of
young men who were attracted to Munich to study under his direction.
These disciples are now distributed in various universities in Europe
and the United States, and are there carrying forward the work begun
by Zittel. The great collection of fossils which he left at Munich
contains illustrations of the whole story of the evolution of life
through geological ages.
Recent Developments.--The greatest advance now being made in the
study of fossil vertebrate life consists in establishing the lineage
of families, orders, and classes. Investigators have been especially
fortunate in working out the direct line of descent of a number of
living mammals. Fossils have been collected which supply a panoramic
view of the line of descent of horses, of camels, of rhinoceroses, and
of other animals. The most fruitful worker in this field at the present
time is perhaps Henry F. Osborn, of the American Museum of Natural
History, New York City. His profound and important investigations
in the ancestry of animal life are now nearing the time of their
publication in elaborated form.
Palæontology, by treating fossil life and recent life in the same
category, has come to be one of the important lines of investigation
in biology. It is, of course, especially rich in giving us a knowledge
of the hard parts of animals, but by ingenious methods we can arrive
at an idea of some of the soft parts that have completely disappeared.
Molds of the interior of the cranium can be made, and thus one may form
a notion of the relative size and development of the brain in different
vertebrated animals. This method of making molds and studying them has
shown that one characteristic of the geological time of the tertiary
period was a marked development in regard to the brain size of the
different animals. There was apparently, just prior to the quaternary
epoch, a need on the part of animals to have an increased brain-growth;
and one can not doubt that this feature which is demonstrated by fossil
life had a great influence in the development of higher animal forms.
[Illustration: Fig. 102.--Karl von Zittel, 1839-1904.]
The methods of collecting fossils in the field have been greatly
developed. By means of spreading mucilage and tissue paper over
delicate bones that crumble on exposure to the air, and of wrapping
fossils in plaster casts for transportation, it has been made possible
to uncover and preserve many structures which with a rougher method of
handling would have been lost to science.
Fossil Man.--One extremely interesting section of palæontology deals
with the fossil remains of the supposed ancestors of the present human
race. Geological evidence establishes the great antiquity of man, but
up to the present time little systematic exploration has been carried
on with a view to discover all possible traces of fossil man. From
time to time since 1840 there have been discovered in caverns and
river-gravels bones which, taken together, constitute an interesting
series. The parts of the skull are of especial importance in this kind
of study, and there now exists in different collections a series
containing the Neanderthal skull, the skulls of Spy and Engis, and
the Java skull described in 1894 by Dubois. There have also been
found recently (November, 1906) in deposits near Lincoln, Neb., some
fossil human remains that occupy an intermediate position between the
Neanderthal skull and the skulls of the lower representatives of living
races of mankind. We shall have occasion to revert to this question in
considering the evidences of organic evolution. (See page 364.)
The name palæontology was brought into use about 1830. The science
affords, in some particulars, the most interesting field for biological
research, and the feature of the reconstruction of ancient life and the
determination of the lineage of living forms has taken a strong hold
on the popular imagination. According to Osborn, the most important
palæontological event of recent times was the discovery, in 1900, of
fossil beds of mammals in the Fayûm lake-province of Egypt, about
forty-seven miles south of Cairo. Here are embedded fossil forms, some
of which have been already described in a volume by Charles W. Andrews,
which Osborn says "marks a turning-point in the history of mammalia of
the world." It is now established that "Africa was a very important
center in the evolution of mammalian life." It is expected that the
lineage of several orders of mammalia will be cleared up through the
further study of fossils from this district.
PART II
THE DOCTRINE OF ORGANIC EVOLUTION
CHAPTER XVI
WHAT EVOLUTION IS: THE EVIDENCE UPON WHICH IT RESTS, ETC.
The preceding pages have been devoted mainly to an account of the
shaping of ideas in reference to the architecture, the physiology, and
the development of animal life.
We come now to consider a central theme into which all these ideas
have been merged in a unified system; _viz._, the process by which the
diverse forms of animals and plants have been produced.
Crude speculations regarding the derivation of living forms are
very ancient, and we may say that the doctrine of organic evolution
was foreshadowed in Greek thought. The serious discussion of the
question, however, was reserved for the nineteenth century. The
earlier naturalists accepted animated nature as they found it, and
for a long time were engaged in becoming acquainted merely, with the
different kinds of animals and plants, in working out their anatomy and
development; but after some progress had been made in this direction
there came swinging into their horizon deeper questions, such as that
of the derivation of living forms. The idea that the higher forms of
life are derived from simpler ones by a process of gradual evolution
received general acceptance, as we have said before, only in the last
part of the nineteenth century, after the work of Charles Darwin;
but we shall presently see how the theory of organic development was
thought out in completeness by Lamarck in the last years of the
eighteenth century, and was further molded by others before Darwin
touched it.
Vagueness Regarding Evolution.--Although "evolution" is to-day a word
in constant use, there is still great vagueness in the minds of most
people as to what it stands for; and, what is more, there is very
little general information disseminated regarding the evidence by which
it is supported, and regarding the present status of the doctrine in
the scientific world.
In its broad sense, evolution has come to mean the development of all
nature from the past. We may, if we wish, think of the long train of
events in the formation of the world, and in supplying it with life
as a story inscribed upon a scroll that is being gradually unrolled.
Everything which has come to pass is on that part so far exposed, and
everything in the future is still covered, but will appear in due
course of time; thus the designation of evolution as "the unrolling of
the scroll of the universe" becomes picturesquely suggestive. In its
wide meaning, it includes the formation of the stars, solar systems,
the elements of the inorganic world, as well as all living nature--this
is general evolution; but the word as commonly employed is limited to
organic evolution, or the formation of life upon our planet. It will be
used hereafter in this restricted sense.
The vagueness regarding the theory of organic evolution arises chiefly
from not understanding the points at issue. One of the commonest
mistakes is to confuse Darwinism with organic evolution. It is known,
for illustration, that controversies are current among scientific
workers regarding Darwinism and certain phases of evolution, and
from this circumstance it is assumed that the doctrine of organic
evolution as a whole is losing ground. The discussions of De Vries and
others--all believers in organic evolution--at the Scientific Congress
in St. Louis in 1904, led to the statement in the public press that the
scientific world was haggling over the evolution-theory, and that it
was beginning to surrender it. Such statements are misleading and tend
to perpetuate the confusion regarding its present status. Furthermore,
the matter as set forth in writings like the grotesque little book, _At
the Deathbed of Darwinism_ tends to becloud rather than to clear the
atmosphere.
The theory of organic evolution relates to the history of animal and
plant life, while Darwin's theory of natural selection is only one of
the various attempts to point out the causes for that history's being
what it is. An attack upon Darwinism is not, in itself, an attack
upon the general theory, but upon the adequacy of his explanation of
the way in which nature has brought about the diversity of animal and
plant life. Natural selection is the particular factor which Darwin
has emphasized, and the discussion of the part played by other factors
tends only to extend the knowledge of the evolutionary process, without
detracting from it as a general theory.
While the controversies among scientific men relate for the most part
to the influences that have been operative in bringing about organic
evolution, nevertheless there are a few in the scientific camp who
repudiate the doctrine. Fleischmann, of Erlangen, is perhaps the most
conspicuous of those who are directing criticism against the general
doctrine, maintaining that it is untenable. Working biologists will be
the first to admit that it is not demonstrated by indubitable evidence,
but the weight of evidence is so compelling that scientific men as a
body regard the doctrine of organic evolution as merely expressing
a fact of nature, and we can not in truth speak of any considerable
opposition to it. Since Fleischmann speaks as an anatomist, his
suppression of anatomical facts with which he is acquainted and his
form of special pleading have impressed the biological world as lacking
in sincerity.
This is not the place, however, to deal with the technical aspects
of the discussion of the factors of organic evolution; it is rather
our purpose here to give a descriptive account of the theory and its
various explanations. First we should aim to arrive at a clear idea
of what the doctrine of evolution is, and the basis upon which it
rests; then of the factors which have been emphasized in attempted
explanations of it; and, finally, of the rise of evolutionary thought,
especially in the nineteenth century. The bringing forward of these
points will be the aim of the following pages.
Nature of the Question.--It is essential at the outset to perceive
the nature of the question involved in the theories of organic
evolution. It is not a metaphysical question, capable of solution
by reflection and reasoning with symbols; the data for it must rest
upon observation of what has taken place in the past in so far as
the records are accessible. It is not a theological question, as so
many have been disposed to argue, depending upon theological methods
of interpretation. It is not a question of creation through divine
agencies, or of non-creation, but a question of method of creation.
Evolution as used in biology is merely a history of the steps by which
animals and plants came to be what they are. It is, therefore, a
historical question, and must be investigated by historical methods.
Fragments of the story of creation are found in the strata of the
earth's crust and in the stages of embryonic development. These clues
must be brought together; and the reconstruction of the story is mainly
a matter of getting at the records. Drummond says that evolution is
"the story of creation as told by those who know it best."
The Historical Method.--The historical method as applied to searching
out the early history of mankind finds a parallel in the investigations
into the question of organic evolution. In the buried cities of
Palestine explorers have uncovered traces of ancient races and have in
a measure reconstructed their history from fragments, such as coins,
various objects of art and of household use, together with inscriptions
on tombs and columns and on those curious little bricks which were used
for public records and correspondence. One city having been uncovered,
it is found by lifting the floors of temples and other buildings, and
the pavement of public squares, that this city, although very ancient,
is built upon the ruins of a more ancient one, which in turn covers
the ruins of one still older. In this way, as many as seven successive
cities have been found, built one on top of the other, and new and
unexpected facts regarding ancient civilization have been brought to
light. We must admit that this gives us an imperfect history, with many
gaps; but it is one that commands our confidence, as being based on
facts of observation, and not on speculation.
In like manner the knowledge of the past history of animal life is the
result of explorations by trained scholars into the records of the
past. We have remains of ancient life in the rocks, and also traces
of past conditions in the developing stages of animals. These are all
more ancient than the inscriptions left by the hand of man upon his
tombs, his temples, and his columns, but nevertheless full of meaning
if we can only understand them. This historical method of investigation
applied to the organic world has brought new and unexpected views
regarding the antiquity of life.
The Diversity of Living Forms.--Sooner or later the question of the
derivation of the animals and plants is bound to come to the mind of
the observer of nature. There exist at present more than a million
different kinds of animals. The waters, the earth, the air teem with
life. The fishes of the sea are almost innumerable, and in a single
order of the insect-world, the beetles, more than 50,000 species
are known and described. In addition to living animals, there is
entombed in the rocks a great multitude of fossil forms which lived
centuries ago, and many of which have become entirely extinct. How
shall this great diversity of life be accounted for? Has the great
variety of forms existed unchanged from the days of their creation to
the present? Or have they, perchance, undergone modifications so that
one original form, or at least a few original types, may have through
transformations merged into different kinds? This is not merely an
idle question, insoluble from the very nature of the case; for the
present races of animals have a lineage reaching far into the past,
and the question of fixity of form as against alteration of type is a
historical question, to be answered by getting evidence as to their
line of descent.
Are Species Fixed in Nature?--The aspect of the matter which presses
first upon our attention is this: Are the species (or different kinds
of animals and plants) fixed, and, within narrow limits, permanent, as
Linnæus supposed? Have they preserved their identity through all time,
or have they undergone changes? This is the heart of the question of
organic evolution. If observation shows species to be constant at the
present time, and also to have been continuous so far as we can trace
their parentage, we must conclude that they have not been formed by
evolution; but if we find evidence of their transmutation into other
species, then there has been evolution.
It is well established that there are wide ranges of variation among
animals and plants, both in a wild state and under domestication.
Great changes in flowers and vegetables are brought about through
cultivation, while breeders produce different kinds of pigeons, fowls,
and stock. We know, therefore, that living beings may change through
modification of the circumstances and conditions that affect their
lives. But general observations extending over a few decades are not
sufficient. We must, if possible, bring the history of past ages to
bear upon the matter, and determine whether or not there had been, with
the lapse of time, any considerable alteration in living forms.
Evolutionary Series.--Fortunately, there are preserved in the rocks the
petrified remains of animals, showing their history for many thousands
of years, and we may use them to test the question. It is plain that
rocks of a lower level were deposited before those that cover them,
and we may safely assume that the fossils have been preserved in their
proper chronological order. Now, we have in Slavonia some fresh-water
lakes that have been drying up from the tertiary period. Throughout the
ages, these waters were inhabited by snails, and naturally the more
ancient ones were the parents of the later broods. As the animals died
their shells sank to the bottom and were covered by mud and débris,
and held there like currants in a pudding. In the course of ages, by
successive accumulations, these layers thickened and were changed into
rock, and by this means shells have been preserved in their proper
order of birth and life, the most ancient at the bottom and the newest
at the top. We can sink a shaft or dig a trench, and collect the shells
and arrange them in proper order.
Although the shells in the upper strata are descended from those
near the bottom, they are very different in appearance. No one would
hesitate to name them different species; in fact, when collections
were first made, naturalists classified these shells into six or eight
different species. If, however, a collection embracing shells from all
levels is arranged in a long row in proper order, a different light
is thrown on the matter; while those at the ends are unlike, yet if
we begin at one end and pass to the other we observe that the shells
all grade into one another by such slight changes that there is no
line showing where one kind leaves off and another begins. Thus their
history for thousands of years bears testimony to the fact that the
species have not remained constant, but have changed into other species.
Fig. 103 will give an idea of the varieties and gradations. It
represents shells of a genus, Paludina, which is still abundant in most
of the fresh waters of our globe.
[Illustration: Fig. 103.--Transmutations of Paludina. (After Neumayer.)]
A similar series of shells has been brought to light in Württemberg
in which the variations pass through wider limits, so that not only
different species may be observed, but different genera connected by
almost insensible gradations. These transformations are found in a
little flattened pond-shell similar to the planorbis, which is so
common at the present time.
[Illustration: Fig. 104.--Planorbis Shells from Steinheim. (After
Hyatt.)]
Fig. 104 shows some of these transformations, the finer gradations
being omitted. The shells from these two sources bear directly upon the
question of whether or not species have held rigidly to their original
form.
After this kind of revelation in reference to lower animals, we turn
with awakened interest to the fossil bones of the higher animals.
Evolution of the Horse.--When we take into account the way in which
fossils have been produced we see clearly that it is the hard parts,
such as the shells and the bones, that will be preserved, while the
soft parts of animals will disappear. Is it not possible that we may
find the fossil bones of higher animals arranged in chronological order
and in sufficient number to supplement the testimony of the shells?
There has been preserved in the rocks of our Western States a very
complete history of the evolution of the horse family, written, as it
were, on tablets of stone, and extending over a period of more than
two million years, as the geologists estimate time. Geologists can, of
course, measure the thickness of rocks and form some estimate of the
rate at which they were deposited by observing the character of the
material and comparing the formation with similar water deposits of
the present time. Near the surface, in the deposits of the quarternary
period, are found remains of the immediate ancestors of the horse,
which are recognized as belonging to the same genus, Equus, but to a
different species; thence, back to the lowest beds of the tertiary
period we come upon the successive ancestral forms, embracing several
distinct genera and exhibiting an interesting series of transformations.
If in this way we go into the past a half-million years, we find the
ancestors of the horse reduced in size and with three toes each on the
fore and hind feet. The living horse now has only a single toe on each
foot, but it has small splint-like bones that represent the rudiments
of two more. If we go back a million years, we find three toes and the
rudiments of a fourth; and going back two million years, we find four
fully developed toes, and bones in the feet to support them. It is
believed that in still older rocks a five-toed form will be discovered,
which was the parent of the four-toed form.
In the collections at Yale College there are preserved upward of thirty
steps or stages in the history of the horse family, showing that it
arose by evolution or gradual change from a four-or five-toed ancestor
of about the size of a fox, and that it passed through many changes,
besides increase in size, in the two million years in which we can get
facts as to its history.
Remarkable as is this feature of the Marsh collection at New Haven, it
is now surpassed by that in the Museum of Natural History in New York
City. Here, through the munificent gifts of the late W.C. Whitney,
there has been accumulated the most complete and extensive collection
of fossil horses in the world. This embraced, in 1904, some portions
of 710 fossil horses, 146 having been derived from explorations under
the Whitney fund. The extraordinary character of the collection is
shown from the fact that it contains five complete skeletons of fossil
horses--more than existed at that time in all other museums of the
world.
The specimens in this remarkable collection show phases in the parallel
development of three or four distinct races of horse-like animals, and
this opens a fine problem in comparative anatomy; _viz._, to separate
those in the direct line of ancestry of our modern horse from all the
others. This has been accomplished by Osborn, and through his critical
analysis we have become aware of the fact that the races of fossil
horses had not been distinguished in any earlier studies. As a result
of these studies, a new ancestry of the horse, differing in details
from that given by Huxley and Marsh, is forthcoming.
Fig. 105 shows the bones of the foreleg of the modern horse, and Fig.
106 some of the modifications through which it has passed. Fig. 107
shows a reconstruction of the ancestor of the horse made by Charles R.
Knight, the animal painter, under the direction of Professor Osborn.
[Illustration: Fig. 105.--Bones of the Foreleg of a Horse.]
While the limbs were undergoing the changes indicated, other parts of
the organism were also being transformed and adapted to the changing
conditions of its life. The evolution of the grinding teeth of the
horse is fully exhibited in the fossil remains. All the facts bear
testimony that the horse was not originally created as known to-day,
but that his ancestors existed in different forms, and in evolution
have transcended several genera and a considerable number of species.
The highly specialized limb of the horse adapted for speed was the
product of a long series of changes, of which the record is fairly
well preserved. Moreover, the records show that the atavus of the horse
began in North America, and that by migration the primitive horses
spread from this continent to Europe, Asia, and Africa.
[Illustration: Fig. 106.--Bones of the Foreleg and Molar Teeth of
Fossil Ancestors of the Horse. European Forms. (After Kayser.)]
So far we have treated the question of fixity of species as a
historical one, and have gone searching for clues of past conditions
just as an archæologist explores the past in buried cities. The facts
we have encountered, taken in connection with a multitude of others
pointing in the same direction, begin to answer the initial question,
Were the immense numbers of living forms created just as we find them,
or were they evolved by a process of transformation?
The geological record of other families of mammals has also been made
out, but none so completely as that of the horse family. The records
show that the camels were native in North America, and that they spread
by migration from the land of their birth to Asia and Africa, probably
crossing by means of land-connections which have long since become
submerged.
The geological record, considered as a whole, shows that the earlier
formed animals were representatives of the lower groups, and that when
vertebrate animals were formed, for a very long time only fishes were
living, then amphibians, reptiles, birds, and finally, after immense
reaches of time, mammals began to appear.
Connecting Forms.--Interesting connecting forms between large groups
sometimes are found, or, if not connecting forms, generalized ones
embracing the structural characteristics of two separate groups. Such
a form is the archæopteryx (Fig. 108), a primitive bird with reptilian
anatomy, with teeth in its jaws, and a long, lizard-like tail covered
with feathers, which seems to show connection between birds and
reptiles. The wing also shows the supernumerary fingers, which have
been suppressed in modern birds. Another suggestive type of this kind
is the flying reptile or pterodactyl, of which a considerable number
have been discovered. Illustrations indicating that animals have had a
common line of descent might be greatly multiplied.
[Illustration: Fig. 107.--Reconstruction of the Ancestor of the Horse
by Charles R. Knight, under the direction of Professor Osborn. Permission
American Museum Natural History.]
The Embryological Record and its Connection with Evolution.--The most
interesting, as well as the most comprehensive clues bearing on the
evolution of animal life are found in the various stages through which
animals pass on their way from the egg to the fully formed animal.
All animals above the protozoa begin their lives as single cells,
and between that rudimentary condition and the adult stage every
gradation of structure is exhibited. As animals develop they become
successively more and more complex, and in their shifting history many
rudimentary organs arise and disappear. For illustration, in the young
chick, developing within the hen's egg, there appear, after three or
four days of incubation, gill-slits, or openings into the throat, like
the gill-openings of lower fishes. These organs belong primarily to
water life, and are not of direct use to the chick. The heart and the
blood-vessels at this stage are also of the fish-like type, but this
condition does not last long; the gill-slits, or gill-clefts, fade away
within a few days, and the arteries of the head and the neck undergo
great changes long before the chick is hatched. Similar gill-clefts
and similar arrangements of blood-vessels appear also very early in
the development of the young rabbit, and in the development of all
higher life. Except for the theory of descent, such things would remain
a lasting enigma. The universal presence of gill-clefts is not to be
looked on as a haphazard occurrence. They must have some meaning, and
the best suggestion so far offered is that they are survivals inherited
from remote ancestors. The higher animals have sprung from simpler
ones, and the gill-slits, along with other rudimentary organs, have
been retained in their history. It is not necessary to assume that they
are inherited from adult ancestors; they are, more likely, embryonic
structures still retained in the developmental history of higher
animals. Such traces are like inscriptions on ancient columns--they
are clues to former conditions, and, occurring in the animal series,
they weigh heavily on the side of evolution.
[Illustration: Fig. 108.--Fossil Remains of a Primitive Bird
(Archeopteryx). From the specimen in the Berlin Museum. (After Kayser.)]
An idea of the appearance of gill-clefts may be obtained from Fig. 109
showing the gill-clefts in a shark and those in the embryo of a chick
and a rabbit.
[Illustration: Fig. 109.--The Gill-clefts of a Shark (upper fig.)
Compared with Those of the Embryonic Chick (to the left) and Rabbit.]
Of a similar nature are the rudimentary teeth in the jaws of the embryo
of the whalebone whale (Fig. 110). The adults have no teeth, these
appearing only as transitory rudiments in the embryo. It is to be
assumed that the teeth are inheritances, and that the toothless baleen
whale is derived from toothed ancestors.
[Illustration: Fig. 110.--The Jaws of an Embryonic Whale, Showing
Rudimentary Teeth.]
If we now turn to comparative anatomy, to classification, and to the
geographical distribution of animals, we find that it is necessary to
assume the doctrine of descent in order to explain the observed facts;
the evidence for evolution, indeed, becomes cumulative. But it is not
necessary, nor will space permit, to give extended illustrations from
these various departments of biological researches.
The Human Body.--Although the broad doctrine of evolution rests largely
upon the observation of animals and plants, there is naturally unusual
interest as to its teaching in reference to the development of the
human body. That the human body belongs to the animal series has long
been admitted, and that it has arisen through a long series of changes
is shown from a study of its structure and development. It retains
marks of the scaffolding in its building. The human body has the same
devious course of embryonic development as that of other mammals.
In the course of its formation gill-clefts make their appearance;
the circulation is successively that of a single-, a double-, and a
four-chambered heart, with blood-vessels for the gill-clefts. Time and
energy are consumed in building up rudimentary structures which are
evanescent and whose presence can be best explained on the assumption
that they are, as in other animals, hereditary survivals.
Wiedersheim has pointed out more than one hundred and eighty
rudimentary or vestigial structures belonging to the human body,
which indicate an evolutionary relationship with lower vertebrates.
It would require a considerable treatise to present the discoveries
in reference to man's organization, as Wiedersheim has done in his
_Structure of Man_. As passing illustrations of the nature of some of
these suggestive things bearing on the question of man's origin may be
mentioned: the strange grasping power of the newly born human infant,
retained for a short time, and enabling the babe to sustain its weight;
the presence of a tail and rudimentary tail muscles; of rudimentary ear
muscles; of gill-clefts, etc.
Antiquity of Man.--The geological history of man is imperfectly known,
although sporadic explorations have already accumulated an interesting
series, especially as regards the shape and capacity of skulls. The
remains of early quarternary man have been unearthed in various parts
of Europe, and the probable existence of man in the tertiary period is
generally admitted. As Osborn says, "Virtually three links have been
found in the chain of human ancestry." The most primitive pre-human
species is represented by portions of the skull and of the leg bones
found in Java by the Dutch surgeon Dubois in the year 1890. These
remains were found in tertiary deposits, and were baptized under the
name of _Pithecanthropus erectus_. The structural position of this
fossil is between the chimpanzee, the highest of anthropoid apes, and
the "Neanderthal man." With characteristic scientific caution Osborn
says that the _Pithecanthropus_ "belongs in the line of none of the
existing anthropoid apes, and falls very near, but not directly, in the
line of human ancestry."
The second link is supplied by the famous Neanderthal skull found in
the valley of the Neander, near Düsseldorf, in 1856. The discovery
of this skull, with its receding forehead and prominent ridges above
the orbits of the eyes, and its small cranial capacity, created a
sensation, for it was soon seen that it was intermediate between the
skulls of the lowest human races and those of the anthropoid apes.
Virchow declared that if the skull was pre-human its structural
characteristics were abnormal. This conclusion, however, was rendered
untenable by the discovery in 1886 of similar skulls and the skeletons
of two persons, in a cave near Spy in Belgium. The "Spy man" and the
"Neanderthal man" belong to the same type and are estimated to have
been living in the middle of the palæolithic age.
[Illustration: Fig. 111.--Profile Reconstructions of the Skulls of
Living and Fossil Men: 1. Brachycephalic European; 2. The more ancient
of the Nebraska skulls; 3. The Neanderthal man; 4. One of the Spy
skulls; 5. Skull of the Java man. (Altered from Schwalbe and Osborn.)]
The third link is in the early Neolithic man of Engis.
And now to this interesting series of gradations has been added
another by the discovery in 1906 of a supposed primitive race of men
in Nebraska. The two skulls unearthed in Douglass County in that State
indicate a cranial capacity falling below that of the "Australian
negro, the lowest existing type of mankind known at present."
Fig. 111 shows in outline profile reconstructions of the skulls of some
of the fossil types as compared with the short-headed type of Europe.
Palæontological discoveries are thus coming to support the evidences of
man's evolution derived from embryology and archæology. While we must
admit that the geological evidences are at present fragmentary, there
is, nevertheless, reasonable ground for the expectation that they will
be extended by more systematic explorations of caverns and deposits of
the quarternary and late tertiary periods.
Mental Evolution.--Already the horizon is being widened, and new
problems in human evolution have been opened. The evidences in
reference to the evolution of the human body are so compelling as to be
already generally accepted, and we have now the question of evolution
of mentality to deal with. The progressive intelligence of animals is
shown to depend upon the structure of the brain and the nervous system,
and there exists such a finely graded series in this respect that there
is strong evidence of the derivation of human faculties from brute
faculties.
Sweep of the Doctrine of Evolution.--The great sweep of the doctrine
of evolution makes it "one of the greatest acquisitions of human
knowledge." There has been no point of intellectual vantage reached
which is more inspiring. It is so comprehensive that it enters into
all realms of thought. Weismann expresses the opinion that "the theory
of descent is the most progressive step that has been taken in the
development of human knowledge," and says that this position "is
justified, it seems to me, even by this fact alone: that the evolution
idea is not merely a new light on the special region of biological
sciences, zoölogy and botany, but is of quite general importance. The
conception of an evolution of life upon the earth reaches far beyond
the bounds of any single science, and influences our whole realm of
thought. It means nothing less than the elimination of the miraculous
from our knowledge of nature, and the placing of the phenomena of life
on the same plane as the other natural processes, that is, as having
been brought about by the same forces and being subject to the same
laws."
One feature of the doctrine is very interesting; it has enabled
anatomists to predict that traces of certain structures not present
in the adult will be found in the embryonic condition of higher
animals, and by the verification of these predictions, it receives a
high degree of plausibility. The presence of an _os centrale_ in the
human wrist was predicted, and afterward found, as also the presence
of a rudimentary thirteenth rib in early stages of the human body. The
predictions, of course, are chiefly technical, but they are based on
the idea of common descent and adaptation.
It took a long time even for scientific men to arrive at a belief in
the continuity of nature, and having arrived there, it is not easy to
surrender it. There is no reason to think that the continuity is broken
in the case of man's development. Naturalists have now come to accept
as a mere statement of a fact of nature that the vast variety of forms
of life upon our globe has been produced by a process of evolution. If
this position be admitted, the next question would be, What are the
factors which have been operative to bring this about? This brings us
naturally to discuss the theories of evolution.
CHAPTER XVII
THEORIES OF EVOLUTION: LAMARCK, DARWIN
The impression so generally entertained that the doctrine of organic
evolution is a vague hypothesis, requiring for its support great
stretches of the imagination, gives way to an examination of the facts,
and we come to recognize that it is a well-founded theory, resting
upon great accumulations of evidence. If the matter could rest here,
it would be relatively simple; but it is necessary to examine into
the causes of the evolutionary process. While scientific observation
has shown that species are not fixed, but undergo transformations of
considerable extent, there still remains to be accounted for the way in
which these changes have been produced.
One may assume that the changes in animal life are the result of
the interaction of protoplasm and certain natural agencies in its
surroundings, but it is evidently a very difficult matter to designate
the particular agencies or factors of evolution that have operated to
bring about changes in species. The attempts to indicate these factors
give rise to different theories of evolution, and it is just here that
the controversies concerning the subject come in. We must remember,
however, that to-day the controversies about evolution are not as
to whether it was or was not the method of creation, but as to the
factors by which the evolution of different forms was accomplished.
Says Packard: "We are all evolutionists, though we may differ as to the
nature of the efficient causes."
Of the various theories which had been advanced to account for
evolution, up to the announcement of the mutation-theory of De Vries
in 1900, three in particular had commanded the greatest amount of
attention and been the field for varied and extensive discussion.
These are the theories of Lamarck, Darwin, and Weismann. They are
comprehensive theories, dealing with the process as a whole. Most of
the others are concerned with details, and emphasize certain phases of
the process.
Doubtless the factors that have played a part in molding the forms
that have appeared in the procession of life upon our globe have
been numerous, and, in addition to those that have been indicated,
Osborn very aptly suggests that there may be undiscovered factors of
evolution. Within a few years De Vries has brought into prominence
the idea of sudden transformations leading to new species, and has
accounted for organic evolution on that basis. Further consideration of
this theory, however, will be postponed, while in the present chapter
we shall endeavor to bring out the salient features of the theories of
Lamarck and Darwin, without going into much detail regarding them.
Lamarck
Lamarck was the first to give a theory of evolution that has retained
a place in the intellectual world up to the present time, and he may
justly be regarded as the founder of that doctrine in the modern sense.
The earlier theories were more restricted in their reach than that of
Lamarck. Erasmus Darwin, his greatest predecessor in this field of
thought, announced a comprehensive theory, which, while suggestive and
forceful in originality, was diffuse, and is now only of historical
importance. The more prominent writers on evolution in the period
prior to Lamarck will be dealt with in the chapter on the Rise of
Evolutionary Thought.
Lamarck was born in 1744, and led a quiet, monotonous life, almost
pathetic on account of his struggles with poverty, and the lack of
encouragement and proper recognition by his contemporaries. His life
was rendered more bearable, however, even after he was overtaken by
complete blindness, by the intellectual atmosphere that he created for
himself, and by the superb confidence and affection of his devoted
daughter Cornélie, who sustained him and made the truthful prediction
that he would be recognized by posterity ("_La postérité vous
honorera_").
His Family.--He came of a military family possessing some claims to
distinction. The older name of the family had been de Monet, but in
the branch to which Lamarck belonged the name had been changed to
de Lamarque, and in the days of the first Republic was signed plain
Lamarck by the subject of this sketch. Jean Baptiste Lamarck was the
eleventh and last child of his parents. The other male members of
the family having been provided with military occupations, Jean was
selected by his father, although against the lad's own wish, for the
clerical profession, and accordingly was placed in the college of the
Jesuits at Amiens. He did not, however, develop a taste for theological
studies, and after the death of his father in 1760 "nothing could
induce the incipient abbé, then seventeen years of age, longer to wear
his bands."
His ancestry asserted itself, and he forsook the college to follow
the French army that was then campaigning in Germany. Mounted on a
broken-down horse which he had succeeded in buying with his scanty
means, he arrived on the scene of action, a veritable raw recruit,
appearing before Colonel Lastic, to whom he had brought a letter of
recommendation.
Military Experience.--The Colonel would have liked to be rid of him,
but owing to Lamarck's persistence, assigned him to a company; and,
being mounted, Lamarck took rank as a sergeant. During his first
engagement his company was exposed to the direct fire of the enemy,
and the officers one after another were shot until Lamarck by order
of succession was in command of the fourteen remaining grenadiers.
Although the French army retreated, Lamarck refused to move with his
squad until he received directions from headquarters to retire. In
this his first battle he showed the courage and the independence that
characterized him in later years.
Adopts Natural Science.--An injury to the glands of the neck, resulting
from being lifted by the head in sport by one of his comrades,
unfitted him for military life, and he went to Paris and began the
study of medicine, supporting himself in the mean time by working
as a bank clerk. It was in his medical course of four years' severe
study that Lamarck received the exact training that was needed to
convert his enthusiastic love for science into the working powers of
an investigator. He became especially interested in botany, and, after
a chance interview with Rousseau, he determined to follow the ruling
passion of his nature and devote himself to natural science. After
about nine years' work he published, in 1778, his _Flora of France_,
and in due course was appointed to a post in botany in the Academy of
Sciences. He did not hold this position long, but left it to travel
with the sons of Buffon as their instructor. This agreeable occupation
extended over two years, and he then returned to Paris, and soon after
was made keeper of the herbarium in the Royal Garden, a subordinate
position entirely beneath his merits. Lamarck held this poorly paid
position for several years, and was finally relieved by being appointed
a professor in the newly established _Jardin des Plantes_.
He took an active part in the reorganization of the Royal Garden
(_Jardin du Roi_) into the _Jardin des Plantes_. When, during the
French Revolution, everything that was suggestive of royalty became
obnoxious to the people, it was Lamarck who suggested in 1790 that the
name of the King's Garden be changed to that of the Botanical Garden
(_Jardin des Plantes_). The Royal Garden and the Cabinet of Natural
History were combined, and in 1793 the name Jardin des Plantes proposed
by Lamarck was adopted for the institution.
It was through the endorsements of Lamarck and Geoffroy Saint-Hilaire
that Cuvier was brought into this great scientific institution; Cuvier,
who was later to be advanced above him in the Jardin and in public
favor, and who was to break friendship with Lamarck and become the
opponent of his views, and who also was to engage in a memorable debate
with his other supporter, Saint-Hilaire.
The portrait of Lamarck shown in Fig. 112 is one not generally known.
Its date is undetermined, but since it was published in Thornton's
_British Plants_ in 1805, we know that it was painted before the
publication of Lamarck's _Philosophie Zoologique_, and before the full
force of the coldness and heartless neglect of the world had been
experienced. In his features we read supremacy of the intellect, and
the unflinching moral courage for which he was notable. Lamarck has a
more hopeful expression in this portrait than in those of his later
years.
[Illustration: Fig. 112.--Lamarck, 1774-1829.
From Thornton's _British Plants_, 1805.]
Lamarck Changes from Botany to Zoölogy.--Until 1794, when he was fifty
years of age, Lamarck was devoted to botany, but on being urged, after
the reorganization of the _Jardin du Roi_, to take charge of the
department of invertebrates, he finally consented and changed from the
study of plants to that of animals. This change had profound influence
in shaping his ideas. He found the invertebrates in great confusion,
and set about to bring order out of chaos, an undertaking in which, to
his credit be it acknowledged, he succeeded. The fruit of his labors,
the Natural History of Invertebrated Animals (_Historie naturelle des
Animaux sans Vertèbres_, 1815-1822), became a work of great importance.
He took hold of this work, it should be remembered, as an expert
observer, trained to rigid analysis by his previous critical studies
in botany. In the progress of the work he was impressed with the
differences in animals and the difficulty of separating one species
from another. He had occasion to observe the variations produced in
animals through the influence of climate, temperature, moisture,
elevation above the sea-level, etc.
He observed also the effects of use and disuse upon the development of
organs: the exercise of an organ leading to its greater development,
and the disuse to its degeneration. Numerous illustrations are cited
by Lamarck which serve to make his meaning clear. The long legs of
wading birds are produced and extended by stretching to keep above the
water; the long neck and bill of storks are produced by their habit of
life; the long neck of the giraffe is due to reaching for foliage on
trees; the web-footed birds, by spreading the toes when they strike the
water, have stimulated the development of a membrane between the toes,
etc. In the reverse direction, the loss of the power of flight in the
"wingless" bird of New Zealand is due to disuse of the wings; while the
loss of sight in the mole and in blind cave animals has arisen from
lack of use of eyes.
The changes produced in animal organization in this way were believed
to be continued by direct inheritance and improved in succeeding
generations.
He believed also in a perfecting principle, tending to improve
animals--a sort of conscious endeavor on the part of the animal playing
a part in its better development. Finally, he came to believe that the
agencies indicated above were the factors of the evolution of life.
His Theory of Evolution.--All that Lamarck had written before he
changed from botany to zoölogy (1794) indicates his belief in the
fixity of species, which was the prevailing notion among naturalists
of the period. Then, in 1800, we find him apparently all at once
expressing a contrary opinion, and an opinion to which he held
unwaveringly to the close of his life. It would be of great interest to
determine when Lamarck changed his views, and upon what this radical
reversal of opinion was based; but we have no sure record to depend
upon. Since his theory is developed chiefly upon considerations of
animal life, it is reasonable to assume that his evolutionary ideas
took form in his mind after he began the serious study of animals.
Doubtless, his mind having been prepared and his insight sharpened by
his earlier studies, his observations in a new field supplied the data
which led him directly to the conviction that species are unstable.
As Packard, one of his recent biographers, points out, the first
expression of his new views of which we have any record occurred in the
spring of 1800, on the occasion of his opening lecture to his course on
the invertebrates. This avowal of belief in the extensive alteration
of species was published in 1801 as the preface to his _Système des
Animaux sans Vertèbres_. Here also he foreshadowed his theory of
evolution, saying that nature, having formed the simplest organisms,
"then with the aid of much time and favorable circumstances ... formed
all the others." It has been generally believed that Lamarck's first
public expression of his views on evolution was published in 1802
in his _Recherches sur l'Organisation des Corps Vivans_, but the
researches of Packard and others have established the earlier date.
Lamarck continued for several years to modify and amplify the
expression of his views. It is not necessary, however, to follow the
molding of his ideas on evolution as expressed in the opening lectures
to his course in the years 1800, 1802, 1803, and 1806, since we find
them fully elaborated in his _Philosophie Zoologique_, published in
1809, and this may be accepted as the standard source for the study of
his theory. In this work he states two propositions under the name of
laws, which have been translated by Packard as follows:
"_First Law_: In every animal which has not exceeded the term of its
development, the more frequent and sustained use of any organ gradually
strengthens this organ, develops and enlarges it, and gives it a
strength proportioned to the length of time of such use; while the
constant lack of use of such an organ imperceptibly weakens it, causing
it to become reduced, progressively diminishes its faculties, and ends
in its disappearance.
"_Second Law_: Everything which nature has caused individuals to
acquire or lose by the influence of the circumstances to which their
race may be for a long time exposed, and consequently by the influence
of the predominant use of such an organ, or by that of the constant
lack of use of such part, it preserves by heredity and passes on to the
new individuals which descend from it, provided that the changes thus
acquired are common to both sexes, or to those which have given origin
to these new individuals.
"These are the two fundamental truths which can be misunderstood only
by those who have never observed or followed nature in its operations,"
etc. The first law embodies the principle of use and disuse, the second
law that of heredity.
In 1815 his theory received some extensions of minor importance. The
only points to which attention need be called are that he gives four
laws instead of two, and that a new feature occurs in the second law in
the statement that the production of a new organ is the result of a new
need (_besoin_) which continues to make itself felt.
Simplified Statement of Lamarck's Views.--For practical exposition the
theory maybe simplified into two sets of facts: First, those to be
classed under variation; and, second, those under heredity. Variations
of organs, according to Lamarck, arise in animals mainly through
use and disuse, and new organs have their origin in a physiological
need. A new need felt by the animal expresses itself on the organism,
stimulating growth and adaptations in a particular direction. This part
of Lamarck's theory has been subjected to much ridicule. The sense in
which he employs the word _besoin_ has been much misunderstood; when,
however, we take into account that he uses it, not merely as expressing
a wish or desire on the part of the animal, but as the reflex
action arising from new conditions, his statement loses its alleged
grotesqueness and seems to be founded on sound physiology.
Inheritance.--Lamarck's view of heredity was uncritical; according
to his conception, inheritance was a simple, direct transmission of
those superficial changes that arise in organs within the lifetime
of an individual owing to use and disuse. It is on this question of
the direct inheritance of variations acquired in the lifetime of an
individual that his theory has been the most assailed. The belief in
the inheritance of acquired characteristics has been so undermined by
experimental evidence that at the present time we can not point to a
single unchallenged instance of such inheritance. But, while Lamarck's
theory has shown weakness on that side, his ideas regarding the
production of variations have been revived and extended.
Variation.--The more commendable part of his theory is the attempt to
account for variation. Darwin assumed variation, but Lamarck attempted
to account for it, and in this feature many discerning students
maintain that the theory of Lamarck is more philosophical in its
foundation than that of Darwin.
In any theory of evolution we must deal with the variation of organisms
and heredity, and thus we observe that the two factors discussed by
Lamarck are basal. Although it must be admitted that even to-day we
know little about either variation or heredity, they remain basal
factors in any theory of evolution.
Time and Favorable Conditions.--Lamarck supposed a very long time was
necessary to bring about the changes which have taken place in animals.
The central thought of time and favorable conditions occurs again and
again in his writings. The following quotation is interesting as coming
from the first announcement of his views in 1800:
"It appears, as I have already said, that _time_ and _favorable
conditions_ are the two principal means which nature has employed in
giving existence to all her productions. We know that for her time has
no limit, and that consequently she has it always at her disposal.
"As to the circumstances of which she has had need and of which she
makes use every day in order to cause her productions to vary, we can
say that in a manner they are inexhaustible.
"The essential ones arising from the influence and from all the
environing media, from the diversity of local causes, of habits,
of movements, of action, finally of means of living, of preserving
their lives, of defending themselves, of multiplying themselves, etc.
Moreover, as the result of these different influences, the faculties,
developed and strengthened by use, become diversified by the new habits
maintained for long ages, and by slow degrees the structure, the
consistence--in a word, the nature, the condition of the parts and of
the organs consequently participating in all these influences, became
preserved and were propagated by heredity (génération)." (Packard's
translation.)
Salient Points.--The salient points in Lamarck's theory may be
compacted into a single sentence: It is a theory of the evolution of
animal life, depending upon variations brought about mainly through use
and disuse of parts, and also by responses to external stimuli, and the
direct inheritance of the same. His theory is comprehensive, so much
so that he includes mankind in his general conclusions.
Lamarck supposed that an animal having become adapted to its
surroundings would remain relatively stable as to its structure. To
the objection raised by Cuvier that animals from Egypt had not changed
since the days when they were preserved as mummies, he replied that the
climate of Egypt had remained constant for centuries, and therefore no
change in its fauna was to be expected.
Species.--Since the question of the fixity of species is the central
one in theories of evolution, it will be worth while to quote Lamarck's
definition of species: "All those who have had much to do with the
study of natural history know that naturalists at the present day
are extremely embarrassed in defining what they mean by the word
species.... We call _species_ every collection of individuals which
are alike or almost so, and we remark that the regeneration of these
individuals conserves the species and propagates it in continuing
successively to reproduce similar individuals." He then goes on with
a long discussion to show that large collections of animals exhibit a
great variation in species, and that they have no absolute stability,
but "enjoy only a relative stability."
Herbert Spencer adopted and elaborated the theory of Lamarck. He
freed it from some of its chief crudities, such as the idea of an
innate tendency toward perfection. In many controversies Mr. Spencer
defended the idea of the transmission of acquired characters. The
ideas of Lamarck have, therefore, been transmitted to us largely in
the Spencerian mold and in the characteristic language of that great
philosopher. There has been but little tendency to go to Lamarck's
original writings. Packard, whose biography of Lamarck appeared
in 1901, has made a thorough analysis of his, writings and had
incidentally corrected several erroneous conception.
Neo-Lamarckism.--The ideas of Lamarck regarding the beginning of
variations have been revived and accorded much respect under the
designation of Neo-Lamarckism. The revival of Lamarckism is especially
owing to the palæontological investigations of Cope and Hyatt. The work
of E.D. Cope in particular led him to attach importance to the effect
of mechanical and other external causes in producing variation, and
he points out many instances of use-inheritance. Neo-Lamarckism has a
considerable following; it is a revival of the fundamental ideas of
Lamarck.
Darwin's Theory
While Lamarck's theory rests upon two sets of facts, Darwin's is
founded on three: _viz._, the facts of variation, of inheritance, and
of natural selection. The central feature of his theory is the idea
of natural selection. No one else save Wallace had seized upon this
feature when Darwin made it the center of his system. On account of the
part taken by Wallace simultaneously with Darwin in announcing natural
selection as the chief factor of evolution, it is appropriate to
designate this contribution as the Darwin-Wallace principle of natural
selection. The interesting connection between the original conclusions
of Darwin and Wallace is set forth in Chapter XIX.
Variation.--It will be noticed that two of the causes assigned by
Darwin are the same as those designated by Lamarck, but their treatment
is quite different. Darwin (Fig. 113) assumed variation among animals
and plants without attempting to account for it, while Lamarck
undertook to state the particular influences which produce variation,
and although we must admit that Lamarck was not entirely successful
in this attempt, the fact that he undertook the task places his
contribution at the outset on a very high plane.
[Illustration: Fig. 113.--Charles Darwin, 1809-1882.]
The existence of variation as established by observation is
unquestioned. No two living organisms are exactly alike at the time of
their birth, and even if they are brought up together under identical
surroundings they vary. The variation of plants and animals under
domestication is so conspicuous and well known that this kind of
variation was the first to attract attention. It was asserted that
these variations were perpetuated because the forms had been protected
by man, and it was doubted that animals varied to any considerable
extent in a state of nature. Extended collections and observations in
field and forest have, however, set this question at rest.
If crows or robins or other birds are collected on an extensive scale,
the variability of the same species will be evident. Many examples
show that the so-called species differ greatly in widely separated
geographical areas, but collections from the intermediate territory
demonstrate that the variations are connected by a series of fine
gradations. If, for illustration, one should pass across the United
States from the Atlantic to the Pacific coast, collecting one species
of bird, the entire collection would exhibit wide variations, but the
extremes would be connected by intermediate forms.
The amount of variation in a state of nature is much greater than was
at first supposed, because extensive collections were lacking, but
the existence of wide variation is now established on the basis of
observation. This fact of variation among animals and plants in the
state of nature is unchallenged, and affords a good point to start from
in considering Darwinism.
Inheritance.--The idea that these variations are inherited is the
second point. But what particular variations will be preserved and
fostered by inheritance, and on what principle they will be selected,
is another question--and a notable one. Darwin's reply was that
those variations which are of advantage to the individual will be
the particular ones selected by nature for inheritance. While Darwin
implies the inheritance of acquired characteristics, his theory of
heredity was widely different from that of Lamarck. Darwin's theory of
heredity, designated the provisional theory of pangenesis, has been
already considered (see Chapter XIV).
Natural Selection.--Since natural selection is the main feature of
Darwin's doctrine, we must devote more time to it. Darwin frequently
complained that very few of his critics took the trouble to find out
what he meant by the term natural selection. A few illustrations will
make his meaning clear. Let us first think of artificial selection as
it is applied by breeders of cattle, fanciers of pigeons and of other
fowls, etc. It is well known that by selecting particular variations in
animals and plants, even when the variations are slight, the breeder
or the horticulturalist will be able in a short time to produce new
races of organic forms. This artificial selection on the part of man
has given rise to the various breeds of dogs, the 150 different kinds
of pigeons, etc., all of which breed true. The critical question is,
Have these all an individual ancestral form in nature? Observation
shows that many different kinds--as pigeons--may be traced back to a
single ancestral form, and thus the doctrine of the fixity of species
is overthrown.
Now, since it is demonstrated by observation that variations occur, if
there be a selective principle at work in nature, effects similar to
those caused by artificial selection will be produced. The selection by
nature of the forms fittest to survive is what Darwin meant by natural
selection. We can never understand the application, however, unless
we take into account the fact that while animals tend to multiply in
geometrical progression, as a matter of fact the number of any one
kind remains practically constant. Although the face of nature seems
undisturbed, there is nevertheless a struggle for existence among all
animals.
This is easily illustrated when we take into account the breeding
of fishes. The trout, for illustration, lays from 60,000 to 100,000
eggs. If the majority of these arrived at maturity and gave rise to
progeny, the next generation would represent a prodigious number, and
the numbers in the succeeding generations would increase so rapidly
that soon there would not be room in the fresh waters of the earth to
contain their descendants. What becomes of the immense number of fishes
that die? They fall a prey to others, or they are not able to get food
in competition with other more hardy relatives, so that it is not a
matter of chance that determines which ones shall survive; those which
are the strongest, the better fitted to their surroundings, are the
ones which will be perpetuated.
The recognition of this struggle for existence in nature, and the
consequent survival of the fittest, shows us more clearly what is meant
by natural selection. Instead of man making the selection of those
particular forms that are to survive, it is accomplished in the course
of nature. This is natural selection.
Various Aspects of Natural Selection.--Further illustrations are needed
to give some idea of the various phases of natural selection. Speed
in such animals as antelopes may be the particular thing which leads
to their protection. It stands to reason that those with the greatest
speed would escape more readily from their enemies, and would be the
particular ones to survive, while the weaker and slower ones would fall
victims to their prey. In all kinds of strain due to scarcity of food,
inclemency of weather, and other untoward circumstances, the forms
which are the strongest, physiologically speaking, will have the best
chance to weather the strain and to survive. As another illustration,
Darwin pointed out that natural selection had produced a long-legged
race of prairie wolves, while the timber wolves, which have less
occasion for running, are short-legged.
We can also see the operation of natural selection in the production of
the sharp eyes of birds of prey. Let us consider the way in which the
eyes of the hawk have been perfected by evolution. Natural selection
compels the eye to come up to a certain standard. Those hawks that are
born with weak or defective vision cannot cope with the conditions
under which they get their food. The sharp-eyed forms would be the
first to discern their prey, and the most sure in seizing upon it.
Therefore, those with defective vision or with vision that falls below
the standard will be at a very great disadvantage. The sharp-eyed
forms will be preserved by a selective process. Nature selects, we may
say, the keener-eyed birds of prey for survival, and it is easy to see
that this process of natural selection would establish and maintain a
standard of vision.
But natural selection tends merely to adapt animals to their
surroundings, and does not always operate in the direction of
increasing the efficiency of the organ. We take another illustration to
show how Darwin explains the origin of races of short-winged beetles on
certain oceanic islands. Madeira and other islands, as Kerguelen island
of the Indian Ocean, are among the most windy places in the world.
The strong-winged beetles, being accustomed to disport themselves in
the air, would be carried out to sea by the sudden and violent gales
which sweep over those islands, while the weaker-winged forms would
be left to perpetuate their kind. Thus, generation after generation,
the strong-winged beetles would be eliminated by a process of natural
selection, and there would be left a race of short-winged beetles
derived from long-winged ancestors. In this case the organs are
reduced in their development, rather than increased; but manifestly
the short-winged race of beetles is better adapted to live under the
particular conditions that surround their life in these islands.
While this is not a case of increase in the particular organ, it
illustrates a progressive series of steps whereby the organism becomes
better adapted to its surroundings. A similar instance is found in
the suppression of certain sets of organs in internal parasites. For
illustration, the tapeworm loses particular organs of digestion for
which it does not have continued use; but the reproductive organs, upon
which the continuance of its life depends, are greatly increased. Such
cases as the formation of short-winged beetles show us that the action
of natural selection is not always to preserve what we should call
the best, but simply to preserve the fittest. Development, therefore,
under the guidance of natural selection is not always progressive.
Selection by nature does not mean the formation and preservation of the
ideally perfect, but merely the survival of those best fitted to their
environment.
Color.--The various ways in which natural selection acts are
exceedingly diversified. The colors of animals may be a factor in
their preservation, as the stripes on the zebra tending to make it
inconspicuous in its surroundings. The stripes upon the sides of
tigers simulate the shadows cast by the jungle grass in which the
animals live, and serves to conceal them from their prey as well as
from enemies. Those animals that assume a white color in winter become
thereby less conspicuous, and they are protected by their coloration.
As further illustrating color as a factor in the preservation of
animals, we may cite a story originally told by Professor E.S. Morse.
When he was collecting shells on the white sand of the Japanese coast,
he noticed numerous white tiger-beetles, which could scarcely be seen
against the white background. They could be detected chiefly by their
shadows when the sun was shining. As he walked along the coast he
came to a wide band of lava which had flowed from a crater across the
intervening country and plunged into the sea, leaving a broad dark
band some miles in breadth across the white sandy beach. As he passed
from the white sand to the dark lava, his attention was attracted to a
tiger-beetle almost identical with the white one except as to color.
Instead of being white, it was black. He found this broad, black band
of lava inhabited by the black tiger beetle, and found very few, if
any, of the white kind. This is a striking illustration of what has
occurred in nature. These two beetles are of the same species, and in
examining the conditions under which they grow, it is discovered that
out of the eggs laid by the original white forms, there now and then
appears one of a dusky or black color. Consider how conspicuous this
dark object would be against the white background of sand. It would be
an easy mark for the birds of prey that fly about, and therefore on the
white surface the black beetles would be destroyed, while the white
ones would be left. But on the black background of lava the conditions
are reversed. There the white forms would be the conspicuous ones; as
they wandered upon the black surface, they would be picked up by birds
of prey and the black ones would be left. Thus we see another instance
of the operation of natural selection.
Mimicry.--We have, likewise, in nature a great number of cases that are
designated mimicry. For illustration, certain caterpillars assume a
stiff position, resembling a twig from a branch. We have also leaf-like
butterflies. The Kallima of India is a conspicuous illustration of a
butterfly having the upper surface of its wings bright-colored, and the
lower surface dull. When it settles upon a twig the wings are closed
and the under-sides have a mark across them resembling the mid-rib of
a leaf, so that the whole butterfly in the resting position becomes
inconspicuous, being protected by mimicry.
One can readily see how natural selection would be evoked in order
to explain this condition of affairs. Those forms that varied in the
direction of looking like a leaf would be the most perfectly protected,
and this feature being fostered by natural selection, would, in the
course of time, produce a race of butterflies the resemblance of whose
folded wings to a leaf would serve as a protection from enemies.
It may not be out of place to remind the reader that the illustrations
cited are introduced merely to elucidate Darwin's theory and the writer
is not committed to accepting them as explanations of the phenomena
involved. He is not unmindful of the force of the criticisms against
the adequacy of natural selection to explain the evolution of all kinds
of organic structures.
Many other instances of the action of color might be added, such as the
wearing of warning colors, those colors which belong to butterflies,
grubs, and other animals that have a noxious taste. These warning
colors have taught birds to leave alone the forms possessing those
colors. Sometimes forms which do not possess a disagreeable taste
secure protection by mimicking the colors of the noxious varieties.
Sexual Selection.--There is an entirely different set of cases which
at first sight would seem difficult to explain on the principle of
selection. How, for instance, could we explain the feathers in the
tails of the birds of paradise, or that peculiar arrangement of
feathers in the tail of the lyre-bird, or the gorgeous display of
tail-feathers of the male peacock? Here Mr. Darwin seized upon a
selective principle arising from the influence of mating. The male
birds in becoming suitors for a particular female have been accustomed
to display their tail-feathers; the one with the most attractive
display excites the pairing instinct in the highest degree, and becomes
the selected suitor. In this way, through the operation of a form of
selection which Darwin designates sexual selection, possibly such
curious adaptations as the peacock's tail may be accounted for.
It should be pointed out that this part of the theory is almost wholly
discredited by biologists. Experimental evidence is against it.
Nevertheless in a descriptive account of Darwin's theory it may be
allowed to stand without critical comment.
Inadequacy of Natural Selection.--In nature, under the struggle for
existence, the fittest will be preserved; and natural selection will
operate toward the elaboration or the suppression of certain organs
or certain characteristics when the elaboration or the suppression
is of advantage to the animal form. Much has been said of late as to
the inadequacy of natural selection. Herbert Spencer and Huxley, both
accepting natural selection as one of the factors, doubted its complete
adequacy.
One point is often overlooked, and should be brought out with
clearness; _viz._, that Darwin himself was the first to point out
clearly the inadequacy of natural selection as a universal law for the
production of the great variety of animals and plants. In the second
edition of the _Origin of Species_ he says: "But, as my conclusions
have lately been much misrepresented, and it has been stated that I
attribute the modification of species exclusively to natural selection,
I may be permitted to remark that in the first edition of this work and
subsequently I placed in a most conspicuous position,--namely, at the
close of the introduction--the following words: 'I am convinced that
natural selection has been the main, but not the exclusive means of
modification.' This has been of no avail. Great is the power of steady
misrepresentation. But the history of science shows that fortunately
this power does not long endure."
The reaction against the all-sufficiency of natural selection,
therefore, is something which was anticipated by Darwin, and the
quotation made above will be a novelty to many of our readers who
supposed that they understood Darwin's position.
Confusion between Lamarck's and Darwin's Theories.--Besides the failure
to understand what Darwin has written, there is great confusion,
both in pictures and in writings, in reference to the theories of
Darwin and Lamarck. Poulton illustrated a state of confusion in one
of his lectures on the theory of organic evolution, and the following
instances are quoted from memory.
We are most of us familiar with such pictures as the following: A
man standing and waving his arms; in the next picture these arms and
hands become enlarged, and in the successive pictures they undergo
transformations into wings, and the transference is made into a flying
animal.
Such pictures are designated "The origin of flight after Darwin." The
interesting circumstance is this, that the illustration does not apply
to Darwin's idea of natural selection at all, but is pure Lamarckism.
Lamarck contended for the production of new organs through the
influence of use and disuse, and this particular illustration refers to
that, and not to natural selection at all.
Among the examples of ridicule to which Darwin's ideas have been
exposed, we cite one verse from the song of Lord Neaves. His lordship
wrote a song with a large number of verses hitting off in jocular vein
many of the claims and foibles of his time. In attempting to make fun
of Darwin's idea he misses completely the idea of natural selection,
but hits upon the principle enunciated by Lamarck, instead. He says:
"A deer with a neck which was longer by half
Than the rest of his family's--try not to laugh--
By stretching and stretching became a giraffe,
Which nobody can deny."
The clever young woman, Miss Kendall, however, in her _Song of the
Ichthyosaurus_, showed clearness in grasping Darwin's idea when she
wrote:
"Ere man was developed, our brother,
We swam, we ducked, and we dived,
And we dined, as a rule, on each other.
What matter? The toughest survived."
This hits the idea of natural selection. The other two illustrations
miss it, but strike the principle which was enunciated by Lamarck. This
confusion between Lamarckism and Darwinism is very wide-spread.
Darwin's book on the _Origin of Species_, published in 1859, was
epoch-making. If a group of scholars were asked to designate the
greatest book of the nineteenth century--that is, the book which
created the greatest intellectual stir--it is likely that a large
proportion of them would reply that it is Darwin's _Origin of Species_.
Its influence was so great in the different domains of thought that
we may observe a natural cleavage between the thought in reference to
nature between 1859 and all preceding time. His other less widely known
books on _Animals and Plants Under Domestication_, the _Descent of
Man_, etc., etc., are also important contributions to the discussion
of his theory. A brief account of Darwin, the man, will be found in
Chapter XIX.
CHAPTER XVIII
THEORIES OF EVOLUTION CONTINUED: WEISMANN, DE VRIES
Weismann's views have passed through various stages of remodeling since
his first public championship of the Theory of Descent on assuming,
in 1867, the position of professor of zoölogy in the University of
Freiburg. Some time after that date he originated his now famous theory
of heredity, which has been retouched, from time to time, as the result
of aggressive criticism from others, and the expansion of his own
mental horizon. As he said in 1904, regarding his lectures on evolution
which have been delivered almost regularly every year since 1880, they
"were gradually modified in accordance with the state of my knowledge
at the time, so that they have been, I may say, a mirror of my own
intellectual evolution."
Passing over his book, _The Germ Plasm_, published in English in 1893,
we may fairly take his last book, _The Evolution Theory_, 1904, as the
best exposition of his conclusions. The theoretical views of Weismann
have been the field of so much strenuous controversy that it will
be well perhaps to take note of the spirit in which they have been
presented. In the preface of his book just mentioned, he says: "I make
this attempt to sum up and present as a harmonious whole the theories
which for forty years I have been gradually building up on the basis
of the legacy of the great workers of the past, and on the results of
my own investigations and those of my fellow-workers, not because
I regard the picture as incomplete or incapable of improvement, but
because I believe its essential features to be correct, and because
an eye-trouble which has hindered my work for many years makes it
uncertain whether I shall have much more time and strength granted to
me for its further elaboration."
The germ-plasm theory is primarily a theory of heredity, and only when
connected with other considerations does it become the full-fledged
theory of evolution known as Weismannism. The theory as a whole
involves so many intricate details that it is difficult to make a clear
statement of it for general readers. If in considering the theories of
Lamarck and Darwin it was found advantageous to confine attention to
salient points and to omit details, it is all the more essential to do
so in the discussion of Weismann's theory.
In his prefatory note to the English edition of _The Evolution Theory_
Thomson, the translator, summarizes Weismann's especial contributions
as: "(1) the illumination of the evolution process with a wealth of
fresh illustrations; (2) the vindication of the 'germ-plasm' concept
as a valuable working hypothesis; (3) the final abandonment of any
assumption of transmissible acquired characters; (4) a further analysis
of the nature and origin of variations; and (5), above all, an
extension of the selection principle of Darwin and Wallace, which finds
its logical outcome in the suggestive theory of germinal selection."
Continuity of the Germ-Plasm.--Weismann's theory is designated that
of continuity of the germ-plasm, and in considering it we must first
give attention to his conception of the germ-plasm. As is well known,
animals and plants spring from germinal elements of microscopic size;
these are, in plants, the spores, the seeds, and their fertilizing
agents; and, in animals, the eggs and the sperms. Now, since all
animals, even the highest developed, begin in a fertilized egg, that
structure, minute as it is, must contain all hereditary qualities,
since it is the only material substance that passes from one generation
to another. This hereditary substance is the germ-plasm. It is the
living, vital substance of organisms that takes part in the development
of new generations.
Naturalists are agreed on this point, that the more complex animals
and plants have been derived from the simpler ones; and, this being
accepted, the attention should be fixed on the nature of the connection
between generations during their long line of descent. In the
reproduction of single-celled organisms, the substance of the entire
body is divided during the transmission of life, and the problem both
of heredity and origin is relatively simple. It is clear that in these
single-celled creatures there is unbroken continuity of body-substance
from generation to generation. But in the higher animals only a minute
portion of the organism is passed along.
Weismann points out that the many-celled body was gradually produced by
evolution; and that in the transmission of life by the higher animals
the continuity is not between body-cells and their like, but only
between germinal elements around which in due course new body-cells are
developed. Thus he regards the body-cells as constituting a sort of
vehicle within which the germ-cells are carried. The germinal elements
represent the primordial substance around which the body has been
developed, and since in all the long process of evolution the germinal
elements have been the only form of connection between different
generations, they have an unbroken continuity.
This conception of the continuity of the germ-plasm is the foundation
of Weismann's doctrine. As indicated before, the general way in which
he accounts for heredity is that the offspring is like the parent
because it is composed of some of the same stuff. The rise of the idea
of germinal continuity has been indicated in Chapter XIV, where it was
pointed out that Weismann was not the originator of the idea, but he is
nevertheless the one who has developed it the most extensively.
Complexity of the Germ-Plasm.--The germ-plasm has been molded for
so many centuries by external circumstances that it has acquired an
organization of great complexity. This appears from the following
considerations: Protoplasm is impressionable; in fact, its most
characteristic feature is that it responds to stimulation and
modifies itself accordingly. These subtle changes occurring within
the protoplasm affect its organization, and in the long run it is the
summation of experiences that determines what the protoplasm shall be
and how it will behave in development. Two masses of protoplasm differ
in capabilities and potentialities according to the experiences through
which they have passed, and no two will be absolutely identical. All
the time the body was being evolved the protoplasm of the germinal
elements was being molded and changed, and these elements therefore
possess an inherited organization of great complexity.
When the body is built anew from the germinal elements, the derived
qualities come into play, and the whole process is a succession of
responses to stimulation. This is in a sense, on the part of the
protoplasm, a repeating of its historical experience. In building the
organism it does not go over the ground for the first time, but repeats
the activities which it took centuries to acquire.
The evident complexity of the germ-plasm made it necessary for
Weismann, in attempting to explain inheritance in detail, to assume the
existence of distinct vital units within the protoplasm of the germinal
elements. He has invented names for these particular units as biophors,
the elementary vital units, and their combination into determinants,
the latter being united into ids, idants, etc. The way in which he
assumes the interactions of these units gives to his theory a highly
speculative character. The conception of the complex organization of
the germ-plasm which Weismann reached on theoretical grounds is now
being established on the basis of observation (see Chapter XIV, p. 313).
The Origin of Variations.--The way in which Weismann accounts for
the origin of variation among higher animals is both ingenious and
interesting. In all higher organisms the sexes are separate, and the
reproduction of their kind is a sexual process. The germinal elements
involved are seeds and pollen, eggs and sperms. In animals the egg
bears all the hereditary qualities from the maternal side, and the
sperm those from the paternal side. The intimate mixture of these in
fertilization gives great possibilities of variations arising from the
different combinations and permutations of the vital units within the
germ-plasm.
This union of two germ-plasms Weismann calls amphimixis, and for a long
time he maintained that the purpose of sexual reproduction in nature is
to give origin to variations. Later he extended his idea to include a
selection, mainly on the basis of nutrition, among the vital elements
composing the germ-plasm. This is germinal selection, which aids in the
production of variations.
In _The Evolution Theory_, volume II, page 196, he says: "Now that I
understand these processes more clearly, my opinion is that the roots
of all heritable variation lie in the germ-plasm; and, furthermore,
that the determinants are continually oscillating hither and thither
in response to very minute nutritive changes and are readily compelled
to _variation in a definite direction_, which may ultimately lead to
considerable variations in the structure of the species, if they are
favored by personal selection, or at least if they are not suppressed
by it as prejudicial."
But while sexual reproduction may be evoked to explain the origin of
variation in higher animals, Weismann thought it was not applicable to
the lower ones, and he found himself driven to assume that variation in
single-celled organisms is owing to the direct influence of environment
upon them, and thus he had an awkward assumption of variations arising
in a different manner in the higher and in the simplest organisms. If I
correctly understand his present position, the conception of variation
as due to the direct influence of environment is being surrendered in
favor of the action of germinal selection among the simplest organisms.
Extension of the Principle of Natural Selection.--These variations,
once started, will be fostered by natural selection provided they are
of advantage to the organism in its struggle for existence. It should
be pointed out that Weismann is a consistent Darwinian; he not only
adopts the principle of natural selection, but he extends the field
of its operation from externals to the internal parts of the germinal
elements.
"Roux and others have elaborated the idea of a struggle of the parts
within the organism, and of a corresponding intra-selection; ... but
Weismann, after his manner, has carried the selection-idea a step
farther, and has pictured the struggle among the determining elements
of the germ-cell's organization. It is at least conceivable that the
stronger 'determinants,' _i.e._, the particles embodying the rudiments
of certain qualities, will make more of the food-supply than those
which are weaker, and that a selective process will ensue" (Thomson).
This is the conception of germinal selection.
He has also extended the application of the general doctrine of natural
selection by supplying a great number of new illustrations.
The whole theory of Weismann is so well constructed that it is very
alluring. Each successive position is worked out with such detail and
apt illustration that if one follows him step by step without dissent
on some fundamental principle, his conclusion seems justified. As a
system it has been elaborated until it makes a coherent appeal to the
intellect.
Inheritance of Acquired Characters.--Another fundamental point
in Weismann's theory is the denial that acquired characters are
transmitted from parent to offspring. Probably the best single
discussion of this subject is contained in his book on _The Evolution
Theory_, 1904, to which readers are referred.
A few illustrations will be in place. Acquired characters are
any acquisitions made by the body-cells during the lifetime of
an individual. They may be obvious, as skill in piano-playing,
bicycle-riding, etc.; or they may be very recondite, as turns of the
intellect, acquired beliefs, etc. Acquired bodily characters may
be forcibly impressed upon the organism, as the facial mutilations
practiced by certain savage tribes, the docking of the tails of horses,
of dogs, etc. The question is, Are any acquired characters, physical or
mental, transmitted by inheritance?
Manifestly, it will be difficult to determine on a scientific basis
whether or not such qualities are inheritable. One would naturally
think first of applying the test of experiment to supposed cases of
such inheritances, and this is the best ground to proceed on.
It has been maintained on the basis of the classical experiments of
Brown-Séquard on guinea-pigs that induced epilepsy is transmitted
to offspring; and, also, on the basis of general observations, that
certain bodily mutilations are inherited. Weismann's analysis of the
whole situation is very incisive. He experimented by cutting off the
tails of both parents of breeding mice. The experiments were carried
through twenty-two generations, both parents being deprived of
their tails, without yielding any evidence that the mutilations were
inheritable.
To take one other case that is less superficial, it is generally
believed that the thirst for alcoholic liquors has been transmitted to
the children of drunkards, and while Weismann admits the possibility
of this, he maintains that it is owing to the germinal elements being
exposed to the influence of the alcohol circulating in the blood of
the parent or parents; and if this be the case it would not be the
inheritance of an acquired character, but the response of the organism
to a drug producing directly a variation in the germ-plasm.
Notwithstanding the well-defined opposition of Weismann, the
inheritance of acquired characters is still a mooted question. Herbert
Spencer argued in favor of it, and during his lifetime had many a
pointed controversy with Weismann. Eimer stands unalterably against
Weismann's position, and the Neo-Lamarckians stand for the direct
inheritance of useful variations in bodily structure. The question is
still undetermined and is open to experimental observation. In its
present state there are competent observers maintaining both sides,
but it must be confessed that there is not a single case in which the
supposed inheritance of an acquired character has stood the test of
critical examination.
The basis of Weismann's argument is not difficult to understand.
Acquired characters affect the body-cells, and according to his view
the latter are simply a vehicle for the germinal elements, which
are the only things concerned in the transmission of hereditary
qualities. Inheritance, therefore, must come through alterations in the
germ-plasm, and not directly through changes in the body-cells.
[Illustration: Fig. 114.--August Weismann, Born 1834.
Permission of Charles Scribner's Sons.]
Weismann, the Man.--The man who for more than forty years has been
elaborating this theory (Fig. 114) is still living and actively at
work in the University of Freiburg. August Weismann was born at
Frankfort-on-the-Main in 1834. He was graduated at Göttingen in 1856,
and for a short time thereafter engaged in the practice of medicine.
This line of activity did not, however, satisfy his nature, and he
turned to the pursuit of microscopic investigations in embryology and
morphology, being encouraged in this work by Leuckart, whose name we
have already met in this history. In 1863 he settled in Freiburg as
_privat-docent_, and has remained connected with the university ever
since. From 1867 onward he has occupied the chair of zoölogy in that
institution. He has made his department famous, especially by his
lectures on the theory of descent.
He is a forceful and interesting lecturer. One of his hearers in 1896
wrote: "His lecture-room is always full, and his popularity among his
students fully equals his fame among scientists."
It is quite generally known that Weismann since he reached the age
of thirty has been afflicted with an eye-trouble, but the inference
sometimes made by those unacquainted with his work as an investigator,
that he has been obliged to forego practical work in the field in which
he has speculated, is wrong. At intervals his eyes have strengthened
so that he has been able to apply himself to microscopic observations,
and he has a distinguished record as an observer. In embryology his
studies on the development of the diptera, and of the eggs of daphnid
crustacea, are well known, as are also his observations on variations
in butterflies and other arthropods.
He is an accomplished musician, and during the period of his enforced
inactivity in scientific work he found much solace in playing "a good
deal of music." "His continuous eye trouble must have been a terrible
obstacle, but may have been the prime cause of turning him to the
theories with which his name is connected."
In a short autobiography published in _The Lamp_ in 1903, although
written several years earlier, he gives a glimpse of his family life.
"During the ten years (1864-1874) of my enforced inactivity and rest
occurred my marriage with Fräulein Marie Gruber, who became the mother
of my children and was my true companion for twenty years, until
her death. Of her now I think only with love and gratitude. She was
the one who, more than any one else, helped me through the gloom of
this period. She read much to me at this time, for she read aloud
excellently, and she not only took an interest in my theoretical and
experimental work, but she also gave practical assistance in it."
In 1893 he published _The Germ-Plasm, A Theory of Heredity_, a treatise
which elicited much discussion. From that time on he has been actively
engaged in replying to his critics and in perfecting his system of
thought.
The Mutation-Theory of De Vries.--Hugo de Vries (Fig. 115), director
of the Botanical Garden in Amsterdam, has experimented widely with the
growth of plants, especially the evening primrose, and has shown that
different species appear to rise suddenly. The sudden variations that
breed true, and thus give rise to new forms, he calls mutations, and
this indicates the source of the name applied to his theory.
In his _Die Mutationstheorie_, published in 1901, he argues for the
recognition of mutations as the universal source of the origin of
species. Although he evokes natural selection for the perpetuation
and improvement of variations, and points out that his theory is
not antagonistic to that of natural selection, it is nevertheless
directly at variance with Darwin's fundamental conception--that slight
individual variations "are probably the sole differences which are
effective in the production of new species" and that "as natural
selection acts solely by accumulating slight, successive, favorable
variations, it can produce no great or sudden modifications." The
foundation of De Vries's theory is that "species have not arisen
through gradual selection, continued for hundreds or thousands of
years, but by jumps through sudden, through small transformations."
(Whitman's translation.)
The work of De Vries is a most important contribution to the study of
the origin of species, and is indicative of the fact that many factors
must be taken into consideration when one attempts to analyze the
process of organic evolution. One great value of his work is that it
is based on experiments, and that it has given a great stimulus to
experimental studies. Experiment was likewise a dominant feature in
Darwin's work, but that seems to have been almost overlooked in the
discussions aroused by his conclusions; De Vries, by building upon
experimental evidence, has led naturalists to realize that the method
of evolution is not a subject for argumentative discussion, but for
experimental investigation. This is most commendable.
[Illustration: Fig. 115.--Hugo de Vries.]
De Vries's theory tends also to widen the field of exploration.
Davenport, Tower, and others have made it clear that species may
arise by slow accumulations of trivial variations, and that, while
the formation of species by mutation may be admitted, there is still
abundant evidence of evolution without mutation.
Reconciliation of Different Theories.--All this is leading to a clearer
appreciation of the points involved in the discussion of the theories
of evolution; the tendency is not for the breach between the different
theories to be widened, but for evolutionists to realize more fully
the great complexity of the process they are trying to explain, and
to see that no single factor can carry the burden of an explanation.
Mutation is not a substitute for natural selection, but a coöperating
factor; and neither mutation nor natural selection is a substitute for
the doctrine of the continuity of the germ-plasm. Thus we may look
forward to a reconciliation between apparently conflicting views, when
naturalists by sifting shall have determined the truth embodied in
the various theories. One conviction that is looming into prominence
is that this will be promoted by less argument and more experimental
observation.
That the solution of the underlying question in evolution will still
require a long time is evident; as Whitman said in his address before
the Congress of Arts and Science in St. Louis in 1904: "The problem of
problems in biology to-day, the problem which promises to sweep through
the present century as it has the past one, with cumulative interest
and correspondingly important results, is the one which became the
life-work of Charles Darwin, and which can not be better or more simply
expressed than in the title of his epoch-making book, _The Origin of
Species_."
Summary.--The number of points involved in the four theories considered
above is likely to be rather confusing, and we may now bring them into
close juxtaposition. The salient features of these theories are as
follows:
I. Lamarck's Theory of Evolution.
1. Variation is explained on the principle of use and disuse.
2. Heredity: The variations are inherited directly and improved in
succeeding generations.
A long time and favorable conditions are required for the production
of new species.
II. Darwin's Theory of Natural Selection.
1. Variations assumed.
2. Heredity: Those slight variations which are of use to the organism
will be perpetuated by inheritance.
3. Natural selection is the distinguishing feature of the theory.
Through the struggle for existence nature selects those best fitted to
survive. The selection of trivial variations that are of advantage to
the organism, and their gradual improvement, leads to the production
of new species.
III. Weismann's Theory of Continuity of the Germ-plasm.
1. The germ-plasm has had unbroken continuity from the beginning
of life. Owing to its impressionable nature, it has an inherited
organization of great complexity.
2. Heredity is accounted for on the principle that the offspring is
composed of some of the same stuff as its parents. The body-cells are
not inherited, _i.e._,
3. There is no inheritance of acquired characters.
4. Variations arise from the union of the germinal elements, giving
rise to varied combinations and permutations of the qualities of the
germ-plasm. The purpose of amphimixis is to give rise to variations.
The direct influence of environment has produced variations in
unicellular organisms.
5. Weismann adopts and extends the principle of natural selection.
Germinal selection is exhibited in the germ-plasm.
IV. De Vries's Theory of Mutations.
1. The formation of species is due not to gradual changes, but to
sudden mutations.
2. Natural selection presides over and improves variations arising
from mutation.
Among the other theories of evolution that of Eimer is the most
notable. He maintains that variations in organisms take place not
fortuitously or accidentally, but follow a perfectly determinate
direction. This definitely directed evolution is called orthogenesis.
He insists that there is continuous inheritance of acquired characters,
and he is radically opposed to the belief that natural selection plays
an important part in evolution. The title of his pamphlet published
in 1898, _On Orthogenesis and the Impotence of Natural Selection in
Species-Formation_, gives an indication of his position in reference to
natural selection. A consideration of Eimer's argument would be beyond
the purpose of this book.
The cause for the general confusion in the popular mind regarding
any distinction between organic evolution and Darwinism is not far
to seek. As has been shown, Lamarck launched the doctrine of organic
evolution, but his views did not even get a public hearing. Then, after
a period of temporary disappearance, the doctrine of evolution emerged
again in 1859. And this time the discussion of the general theory
centered around Darwin's hypothesis of natural selection. It is quite
natural, therefore, that people should think that Darwinism and organic
evolution are synonymous terms. The distinction between the general
theory and any particular explanation of it has, I trust, been made
sufficiently clear in the preceding pages.
CHAPTER XIX
THE RISE OF EVOLUTIONARY THOUGHT
A current of evolutionary thought can be traced through the literature
dealing with organic nature from ancient times. It began as a small
rill among the Greek philosophers and dwindles to a mere thread in the
Middle Ages, sometimes almost disappearing, but is never completely
broken off. Near the close of the eighteenth century it suddenly
expands, and becomes a broad and prevailing influence in the nineteenth
century. Osborn, in his book, _From the Greeks to Darwin_, traces
the continuity of evolutionary thought from the time of the Greek
philosophers to Darwin. The ancient phase, although interesting, was
vague and general, and may be dismissed without much consideration.
After the Renaissance naturalists were occupied with other aspects
of nature-study. They were at first attempting to get a knowledge of
animals and plants as a whole, and later of their structure, their
developments, and their physiology, before questions of their origin
were brought under consideration.
Opinion before Lamarck.--The period just prior to Lamarck is
of particular interest. Since Lamarck was the first to give a
comprehensive and consistent theory of evolution, it will be
interesting to determine what was the state of opinion just prior to
the appearance of his writings. Studies of nature were in such shape
at that time that the question of the origin of species arose, and
thereafter it would not recede. This was owing mainly to the fact that
Ray and Linnæus by defining a species had fixed the attention of
naturalists upon the distinguishing features of the particular kinds of
animals and plants. Are species realities in nature? The consideration
of this apparently simple question soon led to divergent views, and
then to warm controversies that extended over several decades of time.
The view first adopted without much thought and as a matter of course
was that species are fixed and constant; _i.e._, that the existing
forms of animals and plants are the descendants of entirely similar
parents that were originally created in pairs. This idea of the fixity
of species was elevated to the position of a dogma in science as well
as in theology. The opposing view, that species are changeable, arose
in the minds of a few independent observers and thinkers, and, as has
already been pointed out, the discussion of this question resulted
ultimately in a complete change of view regarding nature and man's
relation to it. When the conception of evolution came upon the scene,
it was violently combated. It came into conflict with the theory
designated special creation.
Views of Certain Fathers of the Church.--And now it is essential that
we should be clear as to the sources of this dogma of special creation.
It is perhaps natural to assume that there was a conflict existing
between natural science and the views of the theologians from the
earliest times; that is, between the scientific method and the method
of the theologians, the latter being based on authority, and the former
upon observation and experiment. Although there is a conflict between
these two methods, there nevertheless was a long period in which many
of the leading theological thinkers were in harmony with the men of
science with reference to their general conclusions regarding creation.
Some of the early Fathers of the Church exhibited a broader and more
scientific spirit than their successors.
St. Augustine (353-430), in the fifth century, was the first of the
great theologians to discuss specifically the question of creation.
His position is an enlightened one. He says: "It very often happens
that there is some question as to the earth or the sky, or the other
elements of this world ... respecting which one who is not a Christian
has knowledge derived from most certain reasoning or observation" (that
is, a scientific man); "and it is very disgraceful and mischievous and
of all things to be carefully avoided, that a Christian speaking of
such matters as being according to the Christian Scriptures, should
be heard by an unbeliever talking such nonsense that the unbeliever,
perceiving him to be as wide from the mark as east from west, can
hardly restrain himself from laughing." (Quoted from Osborn.)
Augustine's view of the method of creation was that of derivative
creation or creation _causaliter_. His was a naturalistic
interpretation of the Mosaic record, and a theory of gradual creation.
He held that in the beginning the earth and the waters of the earth
were endowed with power to produce plants and animals, and that it
was not necessary to assume that all creation was formed at once. He
cautions his readers against looking to the Scriptures for scientific
truths. He said in reference to the creation that the days spoken of
in the first chapter of Genesis could not be solar days of twenty-four
hours each, but that they must stand for longer periods of time.
This view of St. Augustine is interesting as being less narrow
and dogmatic than the position assumed by many theologians of the
nineteenth century.
The next theologian to take up the question of creation was St.
Thomas Aquinas (1225-1274) in the thirteenth century. He quotes St.
Augustine's view with approval, but does not contribute anything of
his own. One should not hastily conclude, however, because these
views were held by leaders of theological thought, that they were
universally accepted. "The truth is that all classes of theologians
departed from the original philosophical and scientific standards of
some of the Fathers of the Church, and that special creation became the
universal teaching from the middle of the sixteenth to the middle of
the nineteenth centuries."
The Doctrine of Special Creation.--About the seventeenth century a
change came about which was largely owing to the writings and influence
of a Spanish theologian named Suarez (1548-1617). Although Suarez is
not the sole founder of this conception, it is certain, as Huxley
has shown, that he engaged himself with the questions raised by the
Biblical account of creation; and, furthermore, that he opposed the
views that had been expressed by Augustine. In his tract upon the work
of the six days (_Tractatus de opere sex dierum_) he takes exception
to the views expressed by St. Augustine; he insisted that in the
Scriptural account of creation a day of twenty-four hours was meant,
and in all other cases he insists upon a literal interpretation of the
Scriptures. Thus he introduced into theological thought the doctrine
which goes under the name of special creation. The interesting feature
in all this is that from the time of St. Augustine, in the fifth
century, to the time when the ideas of Suarez began to prevail, in the
seventeenth, there had been a harmonious relation between some of the
leading theologians and scientific men in their outlook upon creation.
The opinion of Augustine and other theologians was largely owing to the
influence of Aristotle. "We know," says Osborn, "that Greek philosophy
tinctured early Christian theology; what is not so generally realized
is that the Aristotelian notion of the development of life led to the
true interpretation of the Mosaic account of the creation.
"There was in fact a long Greek period in the history of the
evolutionary idea extending among the Fathers of the Church and later
among some of the schoolmen, in their commentaries upon creation,
which accord very closely with the modern theistic conception of
evolution. If the orthodoxy of Augustine had remained the teaching of
the Church, the final establishment of evolution would have come far
earlier than it did, certainly during the eighteenth century instead of
the nineteenth century, and the bitter controversy over this truth of
nature would never have arisen."
The conception of special creation brought into especial prominence
upon the Continent by Suarez was taken up by John Milton in his great
epic _Paradise Lost_, in which he gave a picture of creation that
molded into specific form the opinion of the English-speaking clergy
and of the masses who read his book. When the doctrine of organic
evolution was announced, it came into conflict with this particular
idea; and, as Huxley has very pointedly remarked, the new theory of
organic evolution found itself in conflict with the Miltonic, rather
than the Mosaic cosmology. All this represents an interesting phase in
intellectual development.
Forerunners of Lamarck.--We now take up the immediate predecessors of
Lamarck. Those to be mentioned are Buffon, Erasmus Darwin, and Goethe.
Buffon (1707-1788) (Fig. 116), although of a more philosophical mind
than many of his contemporaries, was not a true investigator. That is,
he left no technical papers or contributions to science. From 1739
to the time of his death he was the superintendent of the _Jardin du
Roi_. He was a man of elegance, with an assured position in society.
He was a delightful writer, a circumstance that enabled him to make
natural history popular. It is said that the advance sheets of Buffon's
_Histoire Naturelle_ were to be found on the tables of the boudoirs
of ladies of fashion. In that work he suggested the idea that the
different forms of life were gradually produced, but his timidity and
his prudence led him to be obscure in what he said.
[Illustration: Fig. 116.--Buffon, 1707-1788.]
Packard, who has studied his writings with care, says that he was an
evolutionist through all periods of his life, not, as is commonly
maintained, believing first in the fixity of species, later in their
changeability, and lastly returning to his earlier position. "The
impression left on the mind after reading Buffon is that even if he
threw out these suggestions and then retracted them, from fear of
annoyance or even persecution from the bigots of his time, he did not
himself always take them seriously, but rather jotted them down as
passing thoughts. Certainly he did not present them in the formal,
forcible, and scientific way that Erasmus Darwin did. The result is
that the tentative views of Buffon, which have to be with much research
extracted from the forty-four volumes of his works, would now be
regarded as in a degree superficial and valueless. But they appeared
thirty-four years before Lamarck's theory, and though not epoch-making,
they are such as will render the name of Buffon memorable for all
time." (Packard.)
[Illustration: Fig. 117.--Erasmus Darwin, 1731-1802.]
Erasmus Darwin (Fig. 117) was the greatest of Lamarck's predecessors.
In 1794 he published the _Zoönomia_. In this work he stated ten
principles; among them he vaguely suggested the transmission of
acquired characteristics, the law of sexual selection--or the law
of battle, as he called it--protective coloration, etc. His work
received some notice from scholars. Paley's _Natural Theology_, for
illustration, was written against it, although Paley is careful not to
mention Darwin or his work. The success of Paley's book is probably one
of the chief causes for the neglect into which the views of Buffon and
Erasmus Darwin fell.
Inasmuch as Darwin's conclusions were published before Lamarck's
book, it would be interesting to determine whether or not Lamarck was
influenced by him. The careful consideration of this matter leads to
the conclusion that Lamarck drew his inspiration directly from nature,
and that points of similarity between his views and those of Erasmus
Darwin are to be looked upon as an example of parallelism in thought.
It is altogether likely that Lamarck was wholly unacquainted with
Darwin's work, which had been published in England.
Goethe's connection with the rise of evolutionary thought is in
a measure incidental. In 1790 he published his _Metamorphosis of
Plants_, showing that flowers are modified leaves. This doctrine of
metamorphosis of parts he presently applied to the animal kingdom, and
brought forward his famous, but erroneous, vertebrate theory of the
skull. As he meditated on the extent of modifications there arose in
his mind the conviction that all plants and animals have been evolved
from the modification of a few parental types. Accordingly he should be
accorded a place in the history of evolutionary thought.
Opposition to Lamarck's Views.--Lamarck's doctrine, which was published
in definite form in 1809, has been already outlined. We may well
inquire, Why did not his views take hold? In the first place, they were
not accepted by Cuvier. Cuvier's opposition was strong and vigorous,
and succeeded in causing the theory of Lamarck to be completely
neglected by the French people. Again, we must recognize that the
time was not ripe for the acceptance of such truths; and, finally,
that there was no great principle enunciated by Lamarck which could be
readily understood as there was in Darwin's book on the doctrine of
natural selection.
The temporary disappearance of the doctrine of organic evolution which
occurred after Lamarck expounded his theory was also owing to the
reaction against the speculations of the school of _Natur-Philosophie_.
The extravagant speculation of Oken and the other representatives of
this school completely disgusted men who were engaged in research by
observation and experiment. The reaction against that school was so
strong that it was difficult to get a hearing for any theoretical
speculation; but Cuvier's influence must be looked upon as the chief
one in causing disregard for Lamarck's writings.
The work of Cuvier has been already considered in connection both with
comparative anatomy and zoölogy, but a few points must still be held
under consideration. Cuvier brought forward the idea of catastrophism
in order to explain the disappearance of the groups of fossil animals.
He believed in the doctrine of spontaneous generation. He held to the
doctrine of pre-delineation, so that it must be admitted that whenever
he forsook observation for speculation he was singularly unhappy, and
it is undeniable that his position of hostility in reference to the
speculation of Lamarck retarded the progress of science for nearly half
a century.
Cuvier and Saint-Hilaire.--In 1830 there occurred a memorable
controversy between Cuvier and Saint-Hilaire. The latter (Fig. 118) was
in early life closely associated with Lamarck, and shared his views
in reference to the origin of animals and plants; though in certain
points Saint-Hilaire was more a follower of Buffon than of Lamarck.
Strangely enough, Saint-Hilaire was regarded as the stronger man of
the two. He was more in the public eye, but was not a man of such deep
intellectuality as Lamarck. His scientific reputation rests mainly upon
his _Philosophie Anatomique_. The controversy between him and Cuvier
was on the subject of unity of type; but it involved the question of
the fixity or mutability of species, and therefore it involved the
foundation of the question of organic evolution.
Fig. 118.--Geoffroy Saint-Hilaire, 1772-1844.
This debate stirred all intellectual Europe. Cuvier won as being
the better debater and the better manager of his case. He pointed
triumphantly to the four branches of the animal kingdom which he
had established, maintaining that these four branches represented
four distinct types of organization; and, furthermore, that fixity
of species and fixity of type were necessary for the existence of a
scientific natural history. We can see now that his contention was
wrong, but at the time he won the debate. The young men of the period,
that is, the rising biologists of France, were nearly all adherents of
Cuvier, so that the effect of the debate was, as previously stated,
to retard the progress of science. This noteworthy debate occurred in
February, 1830. The wide and lively interest with which the debate was
followed may be inferred from the excitement manifested by Goethe. Of
the great poet-naturalist, who was then in his eighty-first year, the
following incident is told by Soret:
"Monday, Aug. 2d, 1830.--The news of the outbreak of the revolution of
July arrived in Weimar to-day, and has caused general excitement. In
the course of the afternoon I went to Goethe. 'Well,' he exclaimed as I
entered, 'what do you think of this great event? The volcano has burst
forth, all is in flames, and there are no more negotiations behind
closed doors.' 'A dreadful affair,' I answered; 'but what else could
be expected under the circumstances, and with such a ministry, except
that it would end in the expulsion of the present royal family?' 'We do
not seem to understand each other, my dear friend,' replied Goethe. 'I
am not speaking of those people at all; I am interested in something
very different. I mean the dispute between Cuvier and Geoffroy de
Saint-Hilaire, which has broken out in the Academy, and which is of
such great importance to science.' This remark of Goethe came upon me
so unexpectedly that I did not know what to say, and my thoughts for
some minutes seemed to have come to a complete standstill. 'The affair
is of the utmost importance,' he continued, 'and you can not form any
idea of what I felt on receiving the news of the meeting on the 19th.
In Geoffroy de Saint-Hilaire we have now a mighty ally for a long time
to come. But I see also how great the sympathy of the French scientific
world must be in this affair, for, in spite of the terrible political
excitement, the meeting on the 19th was attended by a full house.
The best of it is, however, that the synthetic treatment of nature,
introduced into France by Geoffroy, can now no longer be stopped. This
matter has now become public through the discussions in the Academy,
carried on in the presence of a large audience; it can no longer be
referred to secret committees, or be settled or suppressed behind
closed doors.'"
Influence of Lyell's Principles of Geology.--But just as Cuvier was
triumphing over Saint-Hilaire a work was being published in England
which was destined to overthrow the position of Cuvier and to bring
again a sufficient foundation for the basis of mutability of species.
I refer to Lyell's _Principles of Geology_, the influence of which has
already been spoken of in Chapter XV. Lyell laid down the principle
that we are to interpret occurrences in the past in the terms of what
is occurring in the present. He demonstrated that observations upon the
present show that the surface of the earth is undergoing gradually slow
changes through the action of various agents, and he pointed out that
we must view the occurrences in the past in the light of occurrences in
the present. Once this was applied to animal forms it became evident
that the observations upon animals and plants in the present must be
applied to the life of the fossil series.
These ideas, then, paved the way for the conception of changes in
nature as being one continuous series.
H. Spencer.--In 1852 came the publication of Herbert Spencer in the
_Leader_, in which he came very near anticipating the doctrine of
natural selection. He advanced the developmental hypothesis, saying
that even if its supporters could "merely show that the production
of species by the process of modification is conceivable, they would
be in a better position than their opponents. But they can do much
more than this; they can show that the process of modification has
affected and is affecting great changes in all organisms subject to
modifying influences.... They can show that any existing species,
animal or vegetable, when placed under conditions different from
its previous ones, immediately begins to undergo certain changes of
structure fitting it for the new conditions. They can show that in
successive generations these changes continue, until ultimately the new
conditions become the natural ones. They can show that in cultivated
plants and domesticated animals, and in the several races of men, these
changes have uniformly taken place. They can show that the degrees of
difference so produced are often, as in dogs, greater than those on
which distinctions of species are in other cases founded. They can
show that it is a matter of dispute whether some of these modified
forms _are_ varieties or modified species. And thus they can show that
throughout all organic nature there is at work a modifying influence
of the kind they assign as the cause of these specific differences;
an influence which, though slow in its action, does in time, if the
circumstances demand it, produce marked changes; an influence which,
to all appearance, would produce in the millions of years, and under
the great varieties of conditions which geological records imply, any
amount of change."
"It is impossible," says Marshall, "to depict better than this the
condition prior to Darwin. In this essay there is full recognition of
the fact of transition, and of its being due to natural influences or
causes, acting now and at all times. Yet it remained comparatively
unnoticed, because Spencer, like his contemporaries and predecessors,
while advocating evolution, was unable to state explicitly what these
causes were."
Darwin and Wallace.--In 1858 we come to the crowning event in the
rise of evolutionary thought, when Alfred Russel Wallace sent a
communication to Mr. Darwin, begging him to look it over and give him
his opinion of it. Darwin, who had been working upon his theory for
more than twenty years, patiently gathering facts and testing the same
by experiment, was greatly surprised to find that Mr. Wallace had
independently hit upon the same principle of explaining the formation
of species. In his generosity, he was at first disposed to withdraw
from the field and publish the essay of Wallace without saying anything
about his own work. He decided, however, to abide by the decision of
two of his friends, to whom he had submitted the matter, and the result
was that the paper of Wallace, accompanied by earlier communications of
Darwin, were laid before the Linnæan Society of London. This was such
an important event in the history of science that its consideration is
extended by quoting the following letter:
"London, June 30th, 1858.
"My Dear Sir: The accompanying papers, which we have the honor of
communicating to the Linnæan Society, and which all relate to the same
subject; _viz_., the laws which affect the production of varieties,
races, and species, contain the results of the investigations of two
indefatigable naturalists, Mr. Charles Darwin and Mr. Alfred Wallace.
"These gentlemen having, independently and unknown to one another,
conceived the same very ingenious theory to account for the appearance
and perpetuation of varieties and of specific forms on our planet,
may both fairly claim the merit of being original thinkers in this
important line of inquiry; but neither of them having published his
views, though Mr. Darwin has for many years past been repeatedly
urged by us to do so, and both authors having now unreservedly
placed their papers in our hands, we think it would best promote the
interests of science that a selection from them should be laid before
the Linnæan Society.
"Taken in the order of their dates, they consist of:
"1. Extracts from a MS. work on species, by Mr. Darwin, which was
sketched in 1839 and copied in 1844, when the copy was read by Dr.
Hooker, and its contents afterward communicated to Sir Charles Lyell.
The first part is devoted to _The Variation of Organic Beings under
Domestication and in their Natural State_; and the second chapter of
that part, from which we propose to read to the Society the extracts
referred to, is headed _On the Variation of Organic Beings in a State
of Nature; on the Natural Means of Selection; on the Comparison of
Domestic Races and True Species_.
"2. An abstract of a private letter addressed to Professor Asa Gray,
of Boston, U.S., in October, 1857, by Mr. Darwin, in which he repeats
his views, and which shows that these remained unaltered from 1839 to
1857.
"3. An essay by Mr. Wallace, entitled _On the Tendency of Varieties
to Depart Indefinitely from the Original Type_. This was written
at Ternate in February, 1858, for the perusal of his friend and
correspondent, Mr. Darwin, and sent to him with the expressed wish
that it should be forwarded to Sir Charles Lyell, if Mr. Darwin
thought it sufficiently novel and interesting. So highly did Mr.
Darwin appreciate the value of the views therein set forth that he
proposed, in a letter to Sir Charles Lyell, to obtain Mr. Wallace's
consent to allow the essay to be published as soon as possible. Of
this step we highly approved, provided Mr. Darwin did not withhold
from the public, as he was strongly inclined to do (in favor of Mr.
Wallace), the memoir which he had himself written on the same subject,
and which, as before stated, one of us had perused in 1844, and the
contents of which we had both of us been privy to for many years.
"On representing this to Mr. Darwin, he gave us permission to make
what use we thought proper of his memoir, etc.; and in adopting our
present course, of presenting it to the Linnæan Society, we have
explained to him that we are not solely considering the relative
claims to priority of himself and his friend, but the interests of
science generally; for we feel it to be desirable that views founded
on a wide deduction from facts, and matured by years of reflecting,
should constitute at once a goal from which others may start; and
that, while the scientific world is waiting for the appearance of Mr.
Darwin's complete work, some of the leading results of his labours,
as well as those of his able correspondent, should together be laid
before the public.
"We have the honour to be yours very obediently,
Charles Lyell,
Jos. D. Hooker."
Personality of Darwin.--The personality of Darwin is extremely
interesting. Of his numerous portraits, the one shown in Fig. 119 is
less commonly known than those showing him with a beard and a much
furrowed forehead. This portrait represents him in middle life, about
the time of the publication of his _Origin of Species_. It shows a
rather typical British face, of marked individuality. Steadiness,
sincerity, and urbanity are all depicted here. His bluish-gray
eyes were overshadowed by a projecting ridge and very prominent,
bushy eyebrows that make his portrait, once seen, easily recognized
thereafter. In the full-length portraits representing him seated, every
line in his body shows the quiet, philosophical temper for which he
was notable. An intimate account of his life is contained in the _Life
and Letters of Charles Darwin_ (1887) and in _More Letters of Darwin_
(1903), both of which are illustrated by portraits and other pictures.
The books about Darwin and his work are numerous, but the reader
is referred in particular to the two mentioned as giving the best
conception of the great naturalist and of his personal characteristics.
[Illustration: Fig. 119.--Charles Darwin, 1809-1882.]
He is described as being about six feet high, but with a stoop of the
shoulders which diminished his apparent height; "of active habits,
but with no natural grace or neatness of movement." "In manner he was
bright, animated, and cheerful; a delightfully considerate host, a man
of never-failing courtesy, leading him to reply at length to letters
from anybody, and sometimes of a most foolish kind."
His Home Life.--"Darwin was a man greatly loved and respected by
all who knew him. There was a peculiar charm about his manner, a
constant deference to others, and a faculty for seeing the best side of
everything and everybody."
He was most affectionate and considerate at home. The picture of
Darwin's life with his children gives a glimpse of the tenderness and
deep affection of his nature, and the reverent regard with which he
was held in the family circle is very touching. One of his daughters
writes: "My first remembrances of my father are of the delights of his
playing with us. He was passionately attached to his own children,
although he was not an indiscriminate child-lover. To all of us he
was the most delightful playfellow, and the most perfect sympathizer.
Indeed, it is impossible adequately to describe how delightful a
relation his was to his family, whether as children or in their later
life.
"It is a proof of the terms on which we were, and also of how much he
was valued as a playfellow, that one of his sons, when about four years
old, tried to bribe him with a sixpence to come and play in working
hours. We all knew the sacredness of working time, but that any one
should resist sixpence seemed an impossibility."
Method of Work.--Darwin's life, as might be inferred from the enduring
quality of his researches, shows an unswerving purpose. His theory was
not the result of a sudden flash of insight, nor was it struck out
in the heat of inspiration, but was the product of almost unexampled
industry and conscientious endeavor in the face of unfavorable
circumstances. Although strikingly original and independent as a
thinker, he was slow to arrive at conclusions, examining with the
most minute and scrupulous care the ground for every conclusion. "One
quality of mind that seemed to be of especial advantage in leading him
to make discoveries was the habit of never letting exceptions pass
unnoticed." He enjoyed experimenting much more than work which only
entailed reasoning. Of course, he was a great reader, but for books as
books he had no respect, often cutting large ones in two in order to
make them easier to hold while in use.
Darwin's Early Life.--Charles Darwin was born in 1809 at Shrewsbury,
England, of distinguished ancestry, his grandfather being the famous
Dr. Erasmus Darwin, the founder, as we have seen, of a theory of
evolution. In his youth he gave no indication of future greatness.
He was sent to Edinburgh to study medicine, but left there after two
sessions, at the suggestion of his father, to study for the Church.
He then went to the University of Cambridge, where he remained three
years, listening to "incredibly dull lectures." After taking his
baccalaureate degree, came the event which proved, as Darwin says, "the
turning-point of my life." This was his appointment as naturalist on
the surveying expedition about to be entered upon by the ship _Beagle_.
In Cambridge he had manifested an interest in scientific study, and had
been encouraged by Professor Henslow, to whom he was also indebted for
the recommendation to the post on the _Beagle_. An amusing circumstance
connected with his appointment is that he was nearly rejected by
Captain Fitz-Roy, who doubted "whether a man with such a shaped nose
could possess sufficient energy and determination for the voyage."
Voyage of the Beagle.--The voyage of the _Beagle_ extended over five
years (1831-1836), mainly along the west coast of South America. It was
on this voyage that Darwin acquired the habit of constant industry.
He had also opportunity to take long trips on shore, engaged in
observation and in making extensive collections. He observed nature
in the field under exceptional circumstances. As he traveled he noted
fossil forms in rocks as well as the living forms in field and forest.
He observed the correspondence in type between certain extinct forms
and recent animals in South America. He noticed in the Galapagos
Islands a fauna similar in general characteristics to that of the
mainland, five or six hundred miles distant, and yet totally different
as to species. Moreover, certain species were found to be confined to
particular islands. These observations awakened in his mind, a mind
naturally given to inquiring into the causes of things, questions that
led to the formulation of his theory. It was not, however, until 1837
that he commenced his first note-book for containing his observations
upon the transmutations of animals. He started as a firm believer
in the fixity of species, and spent several years collecting and
considering data before he changed his views.
At Downs.--On his return to England, after spending some time in
London, he purchased a country-place at Downs, and, as his inheritance
made it possible, he devoted himself entirely to his researches.
But, as is well known, he found in his illness a great obstacle to
steady work. He had been a vigorous youth and young man, fond of
outdoor sports, as fishing, shooting, and the like. After returning
from his long voyage, he was affected by a form of constant illness,
involving a giddiness in the head, and "for nearly forty years he never
knew one day of the health of an ordinary man, and thus his life was
one long struggle against the weariness and strain of sickness." Gould
in his _Biographical Clinics_ attributes his illness to eye-strain.
"Under such conditions absolute regularity of routine was essential,
and the day's work was carefully planned out. At his best, he had three
periods of work: from 8.00 to 9.30; from 10.30 to 12.15; and from 4.30
to 6.00, each period being under two hours' duration."
The patient thoroughness of his experimental work and of his
observation is shown by the fact that he did not publish his book on
the _Origin of Species_ until he had worked on his theory twenty-two
years. The circumstances that led to his publishing it when he did have
already been indicated.
Parallelism in the Thought of Darwin and Wallace.--No one can read the
letters of Darwin and Wallace explaining how they arrived at their idea
of natural selection without marveling at the remarkable parallelism
in the thought of the two. It is a noteworthy circumstance that the
idea of natural selection came to both by the reading of the same book,
_Malthus on Population_.
Darwin's statement of how he arrived at the conception of natural
selection is as follows: "In October, 1838, that is, fifteen months
after I had begun my systematic inquiry, I happened to read for
amusement _Malthus on Population_, and being well prepared to
appreciate the struggle for existence which everywhere goes on from
long-continued observations of the habits of animals and plants, it at
once struck me that under these circumstances favourable variations
would tend to be preserved and unfavourable ones to be destroyed.
_The result of this would be the formation of new species._ Here then
I had at last got a theory by which to work, but I was so anxious to
avoid prejudice that I determined not for some time to write even
the briefest sketch of it. In June, 1842, I first allowed myself the
satisfaction of writing a very brief abstract of my theory in pencil,
in thirty-five pages, and this was enlarged during the summer of 1844
into one of 230 pages."
[Illustration: Fig. 120.--Alfred Russel Wallace, Born 1823.]
And Wallace gives this account: "In February, 1858, I was suffering
from a rather severe attack of intermittent fever at Ternate, in the
Moluccas; and one day, while lying on my bed during the cold fit,
wrapped in blankets, though the thermometer was at 88° Fahr., the
problem again presented itself to me, and something led me to think
of the 'positive checks' described by Malthus in his _Essay on
Population_, a work I had read several years before, and which had
made a deep and permanent impression on my mind. These checks--war,
disease, famine, and the like--must, it occurred to me, act on animals
as well as man. Then I thought of the enormously rapid multiplication
of animals, causing these checks to be much more effective in them
than in the case of man; and while pondering vaguely on this fact,
there suddenly flashed upon me the _idea_ of the survival of the
fittest--that the individuals removed by these checks must be on the
whole inferior to those that survived. In the two hours that elapsed
before my ague fit was over, I had thought out almost the whole of the
theory; and the same evening I sketched the draught of my paper, and in
the two succeeding evenings wrote it out in full, and sent it by the
next post to Mr. Darwin."
It thus appears that the announcement of the Darwin-Wallace theory
of natural selection was made in 1858, and in the following year was
published the book, the famous _Origin of Species_, upon which Darwin
had been working when he received Mr. Wallace's essay. Darwin spoke of
this work as an outline, a sort of introduction to other works that
were in the course of preparation. His subsequent works upon _Animals
and Plants under Domestication_, _The Descent of Man_, etc., etc.,
expanded his theory, but none of them effected so much stir in the
intellectual world as the _Origin of Species_.
This skeleton outline should be filled out by reading _Darwin's
Life and Letters_, by his son, and the complete papers of Darwin
and Wallace, as originally published in the _Journal of the Linnæan
Society_. The original papers are reproduced in the _Popular Science
Monthly_ for November, 1901.
Wallace was born in 1823, and is still living. He shares with Darwin
the credit of propounding the theory of natural selection, and he is
notable also for the publication of important books, as the _Malay
Archipelago_, _The Geographical Distribution of Animals_, _The
Wonderful Century_, etc.
The Spread of the Doctrine of Organic Evolution. Huxley.--Darwin was
of a quiet habit, not aggressive in the defense of his views. His
theory provoked so much opposition that it needed some defenders of
the pugnacious type. In England such a man was found in Thomas Henry
Huxley (1825-1895). He was one of the greatest popular exponents of
science of the nineteenth century; a man of most thorough and exact
scholarship, with a keen, analytical mind that went directly to the
center of questions under consideration, and powers as a writer that
gave him a wide circle of readers. He was magnificently sincere in his
fight for the prevalence of intellectual honesty. Doubtless he will be
longer remembered for this service than for anything else.
[Illustration: Fig. 121.--Thomas Henry Huxley, 1825-1895.]
He defended the doctrine of evolution, not only against oratorical
attacks like that of Bishop Wilberforce, but against well-considered
arguments and more worthy opponents. He advanced the standing of the
theory in a less direct way by urging the pursuit of scientific studies
by high-school and university students, and by bringing science closer
to the people. He was a pioneer in the laboratory teaching of biology,
and his _Manual_ has been, ever since its publication in 1874, the
inspiration and the model for writers of directions for practical work
in that field.
It is not so generally known that he was also a great investigator,
producing a large amount of purely technical researches. After his
death a memorial edition of his scientific memoirs was published in
four large quarto volumes. The extent of his scientific output when
thus assembled was a surprise to many of his co-workers in the field
of science. His other writings of a more general character have
been collected in fourteen quarto volumes. Some of the essays in
this collection are models of clear and vigorous English style. Mr.
Huxley did an astonishing amount of scientific work, especially in
morphology and palæontology. Those who have been privileged to look
over his manuscripts and unpublished drawings in his old room at South
Kensington could not fail to have been impressed, not only with the
extent, but also with the accuracy of his work. Taking Johannes Müller
as his exemplar, he investigated animal organisms with a completeness
and an exactness that have rarely been equaled.
An intimate account of his life will be found in _The Life and Letters
of Thomas Henry Huxley_, by his son.
Haeckel.--Ernst Haeckel, of Jena, born in 1834 (Fig. 122), was one of
the earliest in Germany to take up the defense of Darwin's hypothesis.
As early as 1866 he applied the doctrine of evolution to all organisms
in his _Generelle Morphologie_. This work, which has been long out
of print, represents his best contribution to evolutionary thought.
He has written widely for general readers, and although his writings
are popularly believed to represent the best scientific thought on
the matter, those written for the general public are not regarded by
most biologists as strictly representative. As a thinker he is more
careless than Huxley, and as a result less critical and exact as a
writer.
[Illustration: Fig. 122.--Ernst Haeckel, Born 1834.]
There can be no doubt that the germs of evolutionary thought existed
in Greek philosophy, and that they were retained in a state of low
vitality among the mediæval thinkers who reflected upon the problem of
creation. It was not, however, until the beginning of the nineteenth
century that, under the nurture of Lamarck, they grew into what we may
speak of as the modern theory of evolution. After various vicissitudes
this doctrine was made fertile by Darwin, who supplied it with a new
principle, that of natural selection.
The fruits of this long growth are now being gathered. After Darwin
the problem of biology became not merely to describe phenomena, but to
explain them. This is the outcome of the rise and progress of biology:
first, crude and uncritical observations of the forms of animated
nature; then descriptive analysis of their structure and development;
and, finally, experimental studies, the effort to explain vital
phenomena, an effort in which biologists are at present engaged.
CHAPTER XX
RETROSPECT AND PROSPECT. RECENT TENDENCIES IN BIOLOGY
When one views the progress of biology in retrospect, the broad
truth stands out that there has been a continuity of development in
biological thought and interpretation. The new proceeds out of the
old, but is genetically related to it. A good illustration of this
is seen in the modified sense in which the theories of epigenesis
and pre-formation have been retained in the biological philosophy of
the nineteenth century. The same kind of question that divided the
philosophers of the seventeenth and eighteenth centuries has remained
to vex those of the nineteenth; and, although both processes have
assumed a different aspect in the light of germinal continuity, the
theorists of the last part of the nineteenth century were divided in
their outlook upon biological processes into those of the epigenetic
school and those who are persuaded of a pre-organization in the
germinal elements of organisms. Leading biological questions were
warmly discussed from these different points of view.
In its general character the progress of natural science has been,
and still is, a crusade against superstition; and it may be remarked
in passing that "the nature of superstition consists in a gross
misunderstanding of the causes of natural phenomena." The struggle
has been more marked in biology than in other departments of science
because biology involves the consideration of living organisms and
undertakes to establish the same basis for thinking about the
organization of the human body as about the rest of the animal series.
The first triumph of the scientific method was the overthrow of
authority as a means of ascertaining truth and substituting therefor
the method of observation and experiment. This carries us back to
the days of Vesalius and Harvey, before the framework of biology was
reared. But the scientific method, once established, led on gradually
to a belief in the constancy of nature and in the prevalence of
universal laws in the production of all phenomena. In its progress
biology has exhibited three phases which more or less overlap: The
first was the descriptive phase, in which the obvious features
of animals and plants were merely described; the descriptive was
supplemented by the comparative method; this in due course by the
experimental method, or the study of the processes that take place in
organisms. Thus, description, comparison, and experiment represent the
great phases of biological development.
The Notable Books of Biology and their Authors.--The progress of
biology has been owing to the efforts of men of very human qualities,
yet each with some special distinguishing feature of eminence. Certain
of their publications are the mile-stones of the way. It may be worth
while, therefore, in a brief recapitulation to name the books of widest
general influence in the progress of biology. Only those publications
will be mentioned that have formed the starting-point of some new
movement, or have laid the foundation of some new theory.
Beginning with the revival of learning, the books of Vesalius, _De
Corporis Humani Fabrica_ (1543), and Harvey, _De Motu Cordis et
Sanguinis_ (1628), laid the foundations of scientific method in biology.
The pioneer researches of Malpighi on the minute anatomy of plants
and animals, and on the development of the chick, best represent
the progress of investigation between Harvey and Linnæus. The three
contributions referred to are those on the _Anatomy of Plants_
(_Anatome Plantarum_, 1675-1679); on the _Anatomy of the Silkworm_ (_De
Bombyce_, 1669); and on the _Development of the Chick_ (_De Formatione
Pulli in Ovo_ and _De Ovo Incubato_, both 1672).
We then pass to the _Systema Naturæ_ (twelve editions, 1735-1768) of
Linnæus, a work that had such wide influence in stimulating activity in
systematic botany and zoölogy.
Wolff's _Theoria Generationis_, 1759, and his _De Formatione
Intestinorum_, 1764, especially the latter, were pieces of observation
marking the highest level of investigation of development prior to that
of Pander and Von Baer.
Cuvier, in _Le Règne Animal_, 1816, applied the principles of
comparative anatomy to the entire animal kingdom.
The publication in 1800 of Bichat's _Traité des Membranes_ created a
new department of anatomy, called histology.
Lamarck's book, _La Philosophie Zoologique_, 1809, must have a place
among the great works in biology. Its influence was delayed for more
than fifty years after its publication.
The monumental work of Von Baer on _Development_ (_Ueber
Entwicklungsgeschichte der Thiere_), 1828, is an almost ideal
combination of observation and conclusion in embryology.
The _Microscopische Untersuchungen_, 1839, of Schwann marks the
foundation of the cell-theory.
The _Handbook_ of Johannes Müller (_Handbuch der Physiologie des
Menschen_), 1846, remains unsurpassed as to its plan and its execution.
Max Schultze in his treatise _Ueber Muskelkörperchen und das was man
eine Zelle zu nennen habe_, 1861, established one of the most important
conceptions with which biology has been enriched, viz., the protoplasm
doctrine.
Darwin's _Origin of Species_, 1859, is, from our present outlook, the
greatest classic in biology.
Pasteur's _Studies on Fermentation_, 1876, is typical of the quality
of his work, though his later investigations on inoculations for the
prevention of hydrophobia and other maladies are of greater importance
to mankind.
It is somewhat puzzling to select a man to represent the study of
fossil life, one is tempted to name E.D. Cope, whose researches were
conceived on the highest plane. Zittel, however, covered the entire
field of fossil life, and his _Handbook of Palæontology_ is designated
as a mile-post in the development of that science.
Before the Renaissance the works of Aristotle and Galen should be
included.
From the view-point suggested, the more notable figures in the
development of biology are: Aristotle, Galen, Vesalius, Harvey,
Malpighi, Linnæus, Wolff, Cuvier, Bichat, Lamarck, Von Baer, J. Müller,
Schwann, Schultze, Darwin, Pasteur, and Cope.
Such a list is, as a matter of course, arbitrary, and can serve no
useful purpose except that of bringing into combination in a single
group the names of the most illustrious founders of biological science.
The individuals mentioned are not all of the same relative rank,
and the list should be extended rather than contracted. Schwann,
when the entire output of the two is considered, would rank lower
as a scientific man than Koelliker, who is not mentioned, but the
former must stand in the list on account of his connection with the
cell-theory. Virchow, the presumptive founder of pathology, is omitted,
as are also investigators like Koch, whose line of activity has been
chiefly medical.
Recent Tendencies in Biology. Higher Standards.--In attempting to
indicate some of the more evident influences that dominate biological
investigation at the present time, nothing more than an enumeration
of tendencies with a running commentary is possible. One notes first a
wholesome influence in the establishment of higher standards, both of
research and of scientific publication. Investigations as a whole have
become more intensive and more critical. Much of the work that would
have passed muster for publication two decades ago is now regarded by
the editors of the best biological periodicals as too general and too
superficial. The requisites for the recognition of creditable work
being higher, tends to elevate the whole level of biological science.
Improvement in Tools and Methods.--This has come about partly through
improvement in the tools and in the methods of the investigators. It
can hardly be said, however, that thinking and discernment have been
advanced at the same rate as the mechanical helps to research. In
becoming more intensive, the investigation of biological problems has
lost something in comprehensiveness. That which some of the earlier
investigators lacked in technique was compensated for in the breadth of
their preliminary training and in their splendid appreciation of the
relations of the facts at their disposal.
The great improvement in the mechanical adjustments and in the optical
powers of microscopes has made it possible to see more regarding the
physical structure and the activities of organisms than ever before.
Microtomes of the best workmanship have placed in the hands of
histologists the means of making serial sections of remarkable thinness
and regularity.
The great development of micro-chemical technique also has had the
widest influence in promoting exact researches in biology. Special
staining methods, as those of Golgi and Bethe, by means of which
the wonderful fabric of the nervous system has been revealed, are
illustrations.
The separation by maceration and smear preparation of entire
histological elements so that they may be viewed as solids has come
to supplement the study of sections. Reconstruction, by carving wax
plates of known thickness into the form of magnified sections drawn
upon their surfaces to a scale, and then fitting the plates together,
has been very helpful in picturing complicated anatomical relations.
This method has made it possible to produce permanent wax models of
minute structures magnified to any desired degree. Minute dissections,
although not yet sufficiently practiced, are nevertheless better than
the wax models for making accurate drawings of minute structures as
seen in relief.
The injection of the blood-vessels of extremely small embryos has
made it possible to study advantageously the circulatory system. The
softening of bones by acid after the tissues are already embedded in
celloidin has offered a means of investigating the structure of the
internal ear by sections, and is widely applicable to other tissues.
With the advantage of the new appliances and the new methods, the
old problems of anatomy are being worked over on a higher level of
requirement. Still, it is doubtful whether even the old problems will
be solved in more than a relative way. It is characteristic of the
progress of research that as one proceeds the horizon broadens and
new questions spring up in the pathway of the investigator. He does
not solve the problems he sets out to solve, but opens a lot of new
ones. This is one of the features of scientific research that make its
votaries characteristically optimistic.
Experimental Work.--Among the recent influences tending to advance
biology, none is more important than the application of experiments to
biological studies. The experimental method is in reality applicable
to diverse fields of biological research, and its extensive use at
present indicates a movement in the right direction; that is, a growing
interest in the study of processes. One of the earliest problems of
the biologist is to investigate the architecture of living beings;
then there arise questions as to the processes that occur within
the organism, and the study of processes involves the employment of
experiments. In the pursuit of physiology experiments have been in
use since the time of Harvey, but even in that science, where they
are indispensable, experiments did not become comparative until the
nineteenth century. It now appears that various forms of experiment
give also a better insight into the structure of organisms, and the
practice of applying experiments to structural studies has given rise
to the new department of experimental morphology.
For the purpose of indicating some of the directions in which biology
has been furthered by the experimental method of investigation,
we designate the fields of heredity and evolution, changes in the
environment of organisms, studies on fertilization and on animal
behavior.
The recognition that both heredity and the process of evolution can
be subjected to experimental tests was a revelation. Darwin and
the early evolutionists thought the evolutionary changes too slow
to be appreciated, but now we know that many of the changes can be
investigated by experiment. Numerous experiments on heredity in
poultry (Davenport), in rats, in rabbits, and in guinea-pigs (Castle)
have been carried out--experiments that test the laws of ancestral
inheritance and throw great light upon the questions introduced by the
investigations of Mendel and De Vries. The investigations of De Vries
on the evolution of plant-life occupy a notable position among the
experimental studies.
A large number of experiments on the effects produced by changes in
the external conditions of life have been made. To this class of
investigations belong studies on the regulation of form and function in
organisms (Loeb, Child), the effects produced by altering mechanical
conditions of growth, by changing the chemical environment, etc.
There is some internal mechanism in living matter that is influenced
by changes in external conditions, and the study of the regulation
of the internal processes that produce form and structure have
given rise to a variety of interesting problems. The regeneration
of lost parts and regeneration after intentionally-imposed injury
has received much attention (Morgan). Marine animals are especially
amenable to manipulations of this nature, as well as to alterations in
their surroundings, on account of the ease in altering the chemical
environment in which they live. The latter may be accomplished by
dissolving harmless chemical salts in the sea-water, and observing the
changes produced by the alterations of the surrounding conditions. By
this means Herbst and others have produced very interesting results.
In the field of artificial fertilization, free swimming larvæ have
been raised from eggs artificially fertilized by changes in osmotic
pressure, and also by treating them with both organic and inorganic
acids; and these studies have greatly altered opinion regarding the
nature of fertilization, and of certain other phenomena of development.
Animal Behavior.--The study of animal behavior (Jennings) is a very
characteristic activity of the present, in which certain psychological
processes are investigated. These investigations have given rise to
a distinct line of research participated in by psychologists and
biologists. The study of the way in which animals will react toward
light of different colors, to variations in the intensity of light,
to alterations in temperature, and to various other forms of stimuli
are yielding very important results, that enable investigators to look
beneath the surface and to make important deductions regarding the
nature of psychological processes.
A line closely allied to experimentation is the application of
statistics to biological processes, such as those of growth, stature,
the law of ancestral inheritance, the statistical study of variations
in spines, markings on shells, etc., etc., (Galton, Pearson, Davenport).
Other branches of biology that have been greatly developed by the
experimental method are those of bacteriology and physiological
chemistry. The advances in the latter have greatly widened the horizon
of our view regarding the nature of vital activities, and they compose
one of the leading features of current biological investigation.
Some Tendencies in Anatomical Studies. Cell-Lineage.--While
experimental work occupies the center of the stage, at the same time
great improvements in morphological studies are evident. It will be
only possible, however, to indicate in a general way the direction
in which investigations are moving. We note, first, as in a previous
paragraph, that the improvement in morphology is generic as well as
specific. Anatomical analysis is being carried to its limits in a
number of directions. The investigations that are connected with the
study of cells afford a conspicuous illustration of this fact. Studies
in cell-lineage have led to an exact determination of cell-succession
in the development of certain animals, and such studies are still in
progress. Great progress also has been made in the study of physical
structure of living matter. The tracing of cell-lineage is a feat
of remarkably accurate and patient work. But, however much this may
command our admiration, it has been surpassed (as related in Chapter
XI) by investigations regarding the organization of the egg and the
analysis of chromosomes. Boveri, Conklin, Wilson, and others have shown
that there are recognizable areas within the protoplasm of the egg
that have a definite historical relationship to certain structures in
process of development. This is the basis upon which rests the doctrine
of pre-localization of tissue-forming substances within the protoplasm
of the egg.
Anatomy of the Nervous System.--In another direction the progress
of anatomical studies is very evident, that is, investigations of
the nervous system and the sense-organs. The wonderfully complicated
relations of nerve elements have been worked out by Ramon y Cajal. The
studies of Hodge and others upon optical changes occurring within the
cells of the nervous system owing to their functional activity have
opened a great field for investigation. The studies of Strong, Herrick,
and others upon the distribution of nerve-components in the nerves
of the head and the investigations of Harrison on the growth and the
regeneration of nerve-fibers give illustrations of current tendencies
in biological investigation. The analysis of the central nervous system
into segmental divisions on the basis of functional activity (Johnston)
is still another illustration.
The Application of Biological Facts to the Benefit of Mankind.--The
practical application of biology to the benefit of mankind is a
striking feature of present-day tendencies. The activity set on foot by
the researches of Pasteur, Koch, and others has created a department of
technical biology of the greatest importance to the human race.
Under the general heading should be included the demonstration of
the connection between insects and the propagation of yellow fever,
malaria, and other disorders; and as an illustration of activity in
1907, we think of the commission recently appointed to investigate the
terrible scourge of the sleeping-sickness which has been prevalent in
Africa. Here also we would group studies of a pathological character on
blood-immunity, toxin and antitoxin, also studies on the inoculation
for the prevention of various diseases that affect animals and mankind.
Very much benefit has already accrued from the practical application of
biological researches of this nature, which, in reality, are still in
their infancy.
We find the application of biological facts to agriculture in the form
of soil-inoculation, in the tracing of the sources of nitrates in the
soil, and studies of the insects injurious to vegetation; their further
application to practical forestry, and in sanitary sciences. This kind
of research is also applied to the study of food-supply for fishes, as
in the case of Plankton studies.
The Establishment and Maintenance of Biological Laboratories.--The
establishment of seaside biological observatories and various other
stations for research have had a great influence on the development
of biology. The most famous biological station is that founded at
Naples (Fig. 123) in 1872 by Anton Dohrn, and it is a gratification
to biologists to know that he still remains its director. This
international station for research has stimulated, and is at present
stimulating, the growth of biology by providing the best conditions for
carrying on researches and by the distribution of material which has
been put up at the sea-coast by the most skilled preservators. There
are many stations modeled after that at Naples. The Marine Biological
Laboratory at Woods Holl, Mass., is of especial prominence, and the
recently reorganized Wistar Institute of Anatomy at Philadelphia is
making a feature of the promotion of anatomical researches, especially
those connected with the anatomy of the nervous system.
Laboratories similar to those at the seaside have been established
on several fresh-water lakes. The studies carried on in those places
of the complete biology of lakes, taking into account the entire
surroundings of organisms, are very interesting and important.
[Illustration: Fig. 123.--The Biological Station at Naples.]
Under this general head should be mentioned stations under the control
of the Carnegie Institution, the various scientific surveys under the
Government, and the United States Fish Commission, which carries on
investigations in the biology of fishes as well as observations that
affect their use as articles of diet. The combined output of the
various laboratories and stations of this nature is very considerable,
and their influence upon the progress of biology is properly included
under the head of present tendencies.
The organization of laboratories in our great universities and their
product exercise a wide influence on the progress of biology, that
science having within twenty-five years come to occupy a position of
great importance among the subjects of general education.
Establishment and Maintenance of Technical Periodicals.--It is
manifestly very important to provide means for the publication of
results and, as needed, to have technical periodicals established
and properly maintained. Their maintenance can not be effected on
a purely commercial basis, and the result is that some of our best
periodicals require financial assistance in order to exist at all. The
subsidizing and support of these periodicals aid materially in the
biological advance. A typical technical periodical is Schultze's famous
_Archiv für Mikroscopische Anatomie_, founded in 1864 by Schultze and
continued to the present time. Into its pages go the highest grade of
investigations, and its continued existence has a salutary influence
upon the progress of biology. The list of technical periodicals would
be too long to name, but among others the _Morphologisches Jahrbuch_
of Gegenbaur, and Koelliker's _Zeitschrift für Wissenschaftliche
Zoologie_ have had wide influence. In England the _Quarterly Journal
of Microscopical Science_ is devoted to morphological investigations,
while physiology is provided for in other journals, as it is also in
Germany and other countries. In the United States the _Journal of
Morphology_, edited by C.O. Whitman, passed through seventeen volumes
and was maintained on the highest plane of scholarship. The fine
execution of the plates and the high grade of typographical work made
this journal conspicuous. It represents in every way an enterprise
of which Americans can be justly proud. The _American Journal of
Anatomy_ is now filling the field left unoccupied by the cessation of
the _Journal of Morphology_.[9] In the department of experimental work
many journals have sprung up, as _Biometrica_, edited by Carl Pearson,
Roux's _Archiv für Entwicklungsmechanik_, the _Journal of Experimental
Zoology_ recently established in the United States, etc., etc.
Exploration of the Fossil Records.--Explorations of the fossil records
have been recently carried out on a scale never before attempted,
involving the expenditure of large sums, but bringing results of
great importance. The American Museum of Natural History, in New York
City, has carried on an extensive survey, which has enriched it with
wonderful collections of fossil animals. Besides explorations of the
fossil-bearing rocks of the Western States and Territories, operations
in another locality of great importance are conducted in the Fayûm
district of Egypt. The result of the studies of these fossil animals is
to make us acquainted not only with the forms of ancient life, but with
the actual line of ancestry of many living animals. The advances in
this direction are most interesting and most important. This extensive
investigation of the fossil records is one of the present tendencies in
biology.
Conclusion.--In brief, the chief tendencies in current biological
researches are mainly included under the following headings:
Experimental studies in heredity, evolution, and animal behavior; more
exact anatomical investigations, especially in cytology and neurology,
the promotion and dissemination of knowledge through biological
periodicals; the provision of better facilities in specially equipped
laboratories, in the application of results to the benefit of mankind,
and in the investigation of the fossil records.
The atmosphere of thought engendered by the progress of biology is
beneficial in every way. While its progress has dealt the death-blow
to many superstitions and changed materially views regarding the
universe, it is gratifying to think that it has not been iconoclastic
in its influence, but that it has substituted something better for that
which was taken away. It has given a broader and more wholesome basis
for religion and theories of ethics; it has taught greater respect
for truth and morality. However beneficial this progress has been in
the past, who can doubt that the mission of biology to the twentieth
century will be more important than to the past, and that there will be
embraced in its progress greater benefits than any we have yet known?
FOOTNOTES:
[Footnote 9: It is a source of gratification to biologists that--thanks
to the Wistar Institute of Anatomy--the publication of the _Journal of
Morphology_ is to be continued.]
READING LIST
The books and articles relating to the history of biology are numerous.
Those designated below embrace some of the more readily accessible
ones. While some attention has been given to selecting the best
sources, no attempt has been made to give a comprehensive list.
I. GENERAL REFERENCES
Cuvier. Histoire des Sciences Naturelles. 5 vols., 1841-1845.
Excellent. Written from examination of the original documents.
Carus. Geschichte der Zoologie, 1872. Also Histoire de la Zoologie,
1880. A work of scholarship. Contains excellent account of the
Physiologus.
Sachs. History of Botany, 1890. Excellent. Articles in the _Botanical
Gazette_ for 1895 supplement his account by giving the more recent
development of botany.
White. A History of the Warfare of Science with Theology in
Christendom, 2 vols., 1900. Good account of Vesalius and the overthrow
of authority in science.
Whewell. History of the Inductive Sciences, vol. II, 1863. Lacks
insight into the nature of biology and the steps in its progress.
Mentioned because so generally known.
Williams. A History of Science, 5 vols., 1904. Finely illustrated.
Contains many defects in the biological part as to the relative rank
of the founders: Vesalius diminished, Paracelsus magnified, etc. Also,
the Story of Nineteenth Century Science, 1900. Collected articles from
_Harper's Magazine_. Good portraits. Uncritical on biological matters.
Thomson. The Science of Life, 1899. An excellent brief history of
biology.
Foster. Lectures on the History of Physiology, 1901. Fascinatingly
written. Notable for poise and correct estimates, based on the use of
the original documents.
Geddes. A Synthetic Outline of the History of Biology. _Proc. Roy. Soc.
Edinb._, 1885-1886. Good.
Richardson. Disciples of Æsculapius, 2 vols., 1901. Collected papers
from _The Asclepiad_. Sympathetic accounts of Vesalius, Malpighi, J.
Hunter, and others. Good illustrations.
Lankester. The History and Scope of Zoology, in The Advancement of
Science, 1890. Good. Same article in Ency. Brit. under the title of
Zoology.
Spencer. Principles of Biology, 2 vols., 1866.
Hertwig. The Growth of Biology in the Nineteenth Century, _Ann. Rept.
Smithson. Inst._, 1900.
Buckle. History of Civilization, vol. I, second edition, 1870.
Macgilivray. Lives of Eminent Zoölogists from Aristotle to Linnæus.
Merz. A History of European Thought in the Nineteenth Century, vol. II,
Scientific Thought, 1903.
Routledge. A Popular History of Science. General and uncritical as to
biology.
Hoefer. Histoire de la Zoologie, 1873. Not very good.
Encyclopædia Britannica. Among the more excellent articles are: Biology
by Huxley; Protoplasm by Geddes; History of Anatomy by Turner.
Chambers's Encyclopædia. New Edition. Discerning articles by Thomson on
the Cell-theory, by Geddes on Biology, Evolution.
Nouvelle Biographie Générale. Good articles on the older writers. Often
unreliable as to dates.
Haeckel. The historical chapters in The Evolution of Man, 1892, and
Anthropogenie, fifth edition, 1903. Good.
Haeckel. The History of Creation, vol. I, 1884.
Hertwig. The General Survey of the History of Zoölogy in his Manual of
Zoölogy, 1902. Brief but excellent.
Parker and Haswell. Text-book of Zoölogy, 1897. Historical chapter in
vol. II.
Nicholson. Natural History, its Rise and Progress in Britain, 1886.
Also Biology.
Pettigrew. Gallery of Medical Portraits, 5 vols. Contains many
portraits and biographical sketches of men of general influence, as
Bichat, Galen, Malpighi, etc.
Puschmann. Handbuch der Geschichte der Medizin, 3 vols. Good for topics
in anatomy and physiology.
Baas. The History of Medicine, 1889.
Radl. Geschichte der Biologischen Theorien seit dem Ende des
Siebzehnten Jahrhundert, 1905.
Janus. A Periodical devoted to the history of medicine and natural
science, founded in 1896.
Zoologische Annalen. Founded by Max Braun in 1904 in the interests of
the history of zoölogy.
Mitteilungen zur Geschichte der Medizin und Naturwissenschaften,
founded 1901.
Surgeon General's Library. The Catalogue should be consulted for its
many biographical references to biologists. The Library is especially
rich in historical documents, as old anatomies, physiologies,
zoölogies, etc.
Evolution. The bibliography of Evolution is given below under the
chapters dealing with the evolution theory.
II. SPECIAL REFERENCES
CHAPTER I
Ancient biological Science: Carus; Botany after 1530, Sachs. Aristotle:
Cuvier, a panegyric; Lewes, Aristotle--A Chapter from the History of
Science, 1864, a critical study; Huxley, On some Mistakes Attributed
to Aristotle; Macgilivray; Aristotle's History of Animals translated
in Bohn's Classical Library, 1887. Pliny: Macgilivray; Thorndike, The
Place of Magic in the Intellectual History of Europe, 1905, chap. III.
The Renaissance: Symonds. Epochs in Biological History: Geddes (see
General List).