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diff --git a/58867-0.txt b/58867-0.txt new file mode 100644 index 0000000..47b1431 --- /dev/null +++ b/58867-0.txt @@ -0,0 +1,14580 @@ +*** START OF THE PROJECT GUTENBERG EBOOK 58867 *** + + + + + + + + + + + + + + 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). + + +CHAPTER II + +Vesalius: Roth, Andreas Vesalius Bruxellensis, the edition of 1892, +the standard source of knowledge of Vesalius and his times, contains +bibliography, references to his different portraits, the resurrection +bone, etc., etc.; Foster (see General List), Lecture I, excellent; +Richardson in Disciples of Æsculapius, vol. I, contains pictures, +his signature, etc.; Pettigrew; White, vol. II, pp. 51-55; The +Practitioner, 1896, vol. 56; The Asclepiad, 1885, vol. II; De Humani +Corporis Fabrica, editions of 1543 and 1555; Opera Omnia, edited by +Boerhaave, 2 vols., 1725. Galen: Pettigrew; Huxley in his essay on +William Harvey. + + +CHAPTER III + +Harvey: Foster, Lecture II, with quotations, excellent; Dalton, History +of the Circulation; Huxley, William Harvey, a critical essay; Harvey's +Works translated by Willis, with biography, Sydenham Society, 1847; +Life of Harvey by D'Arcy Power, 1898; Brooks, Harvey as Embryologist, +Bull. Johns Hop. Hospit., vol. VIII, 1897, good. An Anatomical +Dissertation upon the Movement of the Heart and Blood in Animals, a +facsimile reproduction of the first edition of the famous De Motu +Cordis et Sanguinis, 1628. Privately reproduced by Dr. Moreton in 1894. +Very interesting. + + +CHAPTER IV + +Hooke: Biography in encyclopædias, his microscope in Carpenter, The +Microscope and Its Revelations, 8th ed., 1900. + +Malpighi: Richardson, vol. II; Same article in _The Asclepiad_, vol. X, +1893; Atti, Life and Work, in Italian, 1847, portrait; Pettigrew, vol. +II; Marcello Malpighi e l'Opera Sua, 1897, a collection of addresses at +the unveiling of Malpighi's monument at Crevalcuore, that by Koelliker +excellent; Locy, Malpighi, Swammerdam, and Leeuwenhoek, _Pop. Sci. +Mo._, 1901--portrait and pictures from his works; MacCallum, _J. Hop. +Univ. Hospit. Bull_. Malpighi's Writings: Opera Omnia, difficult to +obtain, the Robt. Littlebury edition, Lond., 1687, contains posthumous +papers and biography; separate works not uncommon; Traité du Ver à +Soie, Montpellier, 1878, contains his life and works. + +Swammerdam: Life by Boerhaave in Biblia Naturæ, 1735; also Bibel +der Natur, 1752; also The Book of Nature, 1758; Von Baer, Johann +Swammerdam's Leben und Verdienste um die Wissenschaft, 1864, in +_Reden_, vol. I; Locy, _loc. cit._--portrait. + +Leeuwenhoek: New biographical facts in Richardson, vol. I, p. 108; same +article in _The Asclepiad_, vol. II, 1885, portrait, signature, and +other illustrations; Arcana Naturæ; Selected works in English, 1758; +Locy, _Pop. Sci. Mo._, April, 1901. + + +CHAPTER V + +Lyonet: _The Gentleman's Magazine_, LIX, 1789; the famous Traité +Anatomique, etc., 1750, 1752, not rare. Réaumur: Portrait and life in +_Les Savants Modernes_, p. 332. Roesel: Portrait and biography in _Der +monatlich herausgegebenen Insecten Belustigung_, part IV, 1761; Zeigler +in _Natur und Haus_, 1904--nine figs. Straus-Dürckheim: his monograph +on Anatomy of the Cockchafer, rather rare. The Minute Anatomists: +Straus-Dürckheim, Dufour, Newport, Leidig, etc., in Miall and Denney's +The Cockroach, 1886. + +Discovery of the Protozoa: Leeuwenhoek, Müller, Ehrenberg, Dujardin, +etc., Kent's Manual of the Infusoria, vol. I. Ehrenberg: Life by Laue, +1895. + + +CHAPTER VI + +The Physiologus: Carus, White (for titles see General List). Gesner: +Brooks in _Pop. Sci. Mo._, 1885--illustrations; Cuvier, _loc. cit._; +Jardine's Naturalist's Library, vol. VI; Gesner's Historia Animalium, +1551-1585. Aldrovandi: Naturalist's Library, vol. III; Macgilivray, +_loc. cit._ Jonston: Macgilivray. Ray: Macgilivray; Nicholson; Memorial +of, in the Ray Society, 1846; Correspondence of, Ray Soc., 1848. +Linnæus: Macgilivray; _Janus_, vol. 8, 1903; Cuvier, _loc. cit._; +Agassiz, Essay on Classification, 1859; Jubilee at Upsala, _Science_, +Apl. 26, 1907; Caddy, Through the Fields with Linnæus, 1887; The +Systema Naturæ, especially the tenth edition, 1758. Leuckart: Archives +de Parasit., vol. I, no. 2; _Nature_, 1898. General Biological Progress +from Linnæus to Darwin: Geddes, Proc. Roy. Soc. Edinb., vol. 13, +1884-1886. + + +CHAPTER VII + +Camper: Naturalist's Library, vol. VII; Vorlesungen, by his son, +with short sketch of his life, 1793; Cuvier, _loc. cit._; _Kleinere +Schriften_, 2 vols. with copper plates illustrating brain and ear +of fishes, etc., 1782-1785. John Hunter: The Scientific Works of, 2 +vols., 1861; The _Asclepiad_, vol. VIII, 1891; the same article with +illustrations in Richardson, _loc. cit._; Pettigrew, _loc. cit._ +Vicq d'Azyr: Cuvier, _loc. cit._; Huxley in Life of Owen, p. 289; +His works in 6 vols., 1805. Cuvier: Life by Flourens; Memoirs by +Mrs. Lee, 1833; Buckle, Hist. Civ., vol. I, p. 633 et seq.; Lettres +de Geo. Cuvier à C.M. Paff, 1788-1792, translated from the German, +1858. Cuvier's numerous writings--The Animal Kingdom, Leçons d'Anat. +Comparée, etc.--are readily accessible. H. Milne-Edwards: Biographical +sketch in _Ann. Rept. Smithson. Inst_, for 1893. Lacaze-Duthiers: Life +with portraits in _Archives de Zool. Expériment._, vol. 10, 1902. +Richard Owen: Life and Letters, 2 vols., 1894; Clark, Old Friends at +Cambridge and Elsewhere, p. 349 et seq. J. Fr. Meckel: Carus, _loc. +cit._ Gegenbaur: Erlebtes und Erstrebtes, portrait, 1901; Anat. Anz., +vol. 23, 1903; _Ann. Rept. Smithson. Inst._, 1904. Cope: Osborn in +_The Century_, vol. 33, 1897; Gill, Edward Drinker Cope, Naturalist, +A Chapter in the History of Science, _Am. Naturalist_, 1897; Obituary +notice, with portraits, _Am. Naturalist_, 1897; _Pop. Sci. Mo_., vol. +19, 1881. + + +CHAPTER VIII + +Bichat: Pettigrew; Buckle, Hist. Civ., vol. I, p. 639; The Hundred +Greatest Men; _Les Savants Modernes_, p. 394; _The Practitioner_, +vol. 56, 1896. Koelliker: His Autobiography, Erinnerungen aus Meinem +Leben, 1899, several portraits, interesting; Weldon, Life and Works in +_Nature_, vol. 58, with fine portrait; Sterling, _Ann. Rept. Smithson. +Inst._, 1905. Schultze: Portrait and Necrology by Schwalbe in _Archiv +für Mikroscop. Anat._, vol. 10, 1874; See further under chapter XII. +Virchow: _J. Hop. Univ. Circulars_, vol. XI, 1891, Celebration of +Seventieth Birthday of Virchow, Addresses by Osler, Welch, and others; +Jacobi, _Medical Record_, N.Y., vol. XX, 1881, good; Israel, in +_Ann. Rept. Smithson. Inst._, 1902. Leydig: Brief sketch in his Horæ +Zoologicæ, 1902. Ramon y Cajal: Portrait in Tenth Anniversary of Clark +University, 1899. + + +CHAPTER IX + +The best brief account of the Rise of Physiology in Verworn's General +Physiology, 1899. More recent German editions of the same work. +Historical outline in Rutherford's Text-Book of Physiology, 1880. +Galen's Physiology: Verworn. Harvey: See references under Chapter +III; The analysis of his writings by Willis in The Works of Harvey, +translated into English, Sydenham Soc., 1847; See also Dr. Moreton's +facsimile reproduction of the first edition (1628) of De Motu Cordis +et Sanguinis, 1894. Haller: Fine portrait in his Elementa Physiologiæ, +1758; English translations of the Elementa. Charles Bell: Pettigrew; +Good summary in Foster's Life of Claude Bernard, p. 38 et seq. Johannes +Müller: His life, complete list of works, etc., in Gedächtnissrede +auf Johannes Müller by Du Bois-Reymond, 1860; _Eloge_ by Virchow in +_Edinburgh Med. Journ._, vol. 4; Picture of his monument in Coblenz, +_Archiv f. Mik. Anat._, vol. 55; Briefe von J. Müller and Anders +Retzius (1830-1857), 1900; His famous Handbuch der Physiologie and +English translations should be inspected. Ludwig: Burdon-Sanderson, +Ludwig and Modern Physiology, _Sci. Progress_, vol. V, 1896; The same +article in _Ann. Rept. Smithson. Inst._, 1896. Claude Bernard: Life by +M. Foster, 1899, excellent. + + +CHAPTER X + +Good general account of the Rise of Embryology in Koelliker's +Embryologie, 1880; Minot, Embryology and Medical Progress, _Pop. Sci. +Mo._, vol. 69, 1906; Eycleshymer, A Sketch of the Past and Future of +Embryology, _St. Louis Med. Rev._, 1904. Harvey: As Embryologist, +Brooks in _J. Hop. Univ. Hospit. Bull._, vol. VIII, 1897. See above, +Chaps. III and IX for further references to Harvey. Malpighi: in +Embryology, Locy in _Pop. Sci. Mo._, 1905--portrait and selected +sketches from his embryological treatises. Wolff: Wheeler, Wolff and +the Theoria Generationis, in Woods Holl Biological Lectures, 1898; +Kirchoff in _Jenaische Zeitschr._, vol. 4, 1868; Waldeyer, Festrede in +Sitzbr. d. K. Preus. Akad. d. Wissenschaft., 1904; Haeckel in Evolution +of Man, vol. I, 1892. Bonnet and Pre-delineation: Whitman, Bonnet's +Theory of Evolution, also Evolution and Epigenesis, both in Woods +Holl Biological Lectures, 1895. Von Baer: Leben und Schriften, his +autobiography (1864), 2d edition, 1886; Life by Steida, 1886; Obituary, +_Proc. Roy. Soc._, 1878; Waldeyer in _Allg. Wien. Med. Ztg._, 1877; +_Nature_, vol. 15; Life by Stölzle, 1897; Haeckel, _loc. cit._, vol. +I; Locy, V. Baer and the Rise of Embryology, _Pop. Sci. Mo._, 1905; +Fine portrait as young man in _Harper's Mag_. for 1899; _Rev. Scient._, +1879. Kowalevsky: Lankester in _Nature_, vol. 66, 1902; Portrait and +biog. in _Ann. Mus. Hist. Nat. Marseille_, vol. 8, 1903. Balfour: M. +Foster in _Nature_, vol. 29, 1882; Also Life with portrait in the +Memorial Edition of Balfour's Works; Waldeyer in _Arch. f. Mik. Anat._, +vol. 21, 1882; Osborn Recollections, with portrait, _Science_, vol. +2, 1883. His: Mall in _Am. Journ. Anat._, vol. 4, 1905; Biography in +_Anat. Anz._, vol. 26, 1904. + + +CHAPTER XI + +The Cell-Doctrine by Tyson, 1878. The Cell-Theory, Huxley, +_Medico-chir. Review_, 1853, also in Scientific Memoirs, vol. I, 1898; +The Modern Cell-Theory, M'Kendrick, _Proc. Phil. Soc. Glasgow_, vol. +XIX, 1887; The Cell-Theory, Past and Present, Turner, _Nature_, vol. +43, 1890; The Cell-Doctrine, Burnett, _Trans. Am. Med. Assn._, vol. +VI, 1853; First illustration of cells in Rob't Hooke's Micrographia, +1665, 1780, etc.; The Cell in Development and Inheritance, Wilson, +1896; Article Cell, in Chambers's (New) Cyclopædia, by Thomson. +Schleiden: Sketch of, _Pop. Sci. Mo._, vol. 22, 1882-1883; Sachs' +Hist. of Botany 1890; Translation of his original paper of 1838 (Ueber +Phytogenesis)--illustrations--Sydenham Soc., 1874. Schwann: Life, _Pop. +Sci. Mo._, vol. 37, 1900; Sa Vie et Ses Travaux, Frédéricq, 1884; +Nachruf, Henle, _Archiv f. Mik. Anat._, vol. 21, 1882; Lankester, +_Nature_, vol. XXV, 1882; _The Practitioner_, vol. 49, 1897; _The +Catholic World_, vol. 71, 1900. Translation of his contribution of +1839 (Mikroscopische Untersuchungen ueber die Uebereinstimmung in der +Structur und dem Wachstum der Thiere und Pflanzen), Sydenham Soc., 1847. + + +CHAPTER XII + +On the Physical Basis of Life, Huxley, 1868; Reprint in Methods and +Results, 1894. Article Protoplasm in Ency. Brit, by Geddes. Dujardin: +_Notice Biographique_, with portraits and other illustrations, Joubin, +_Archives de Parasitol._, vol. 4, 1901; portrait of Dujardin hitherto +unpublished. Dujardin's original description of Sarcode, _Ann. des Sci. +Nat._ (_Botanique_), vol. 4, p. 367, 1835. Von Mohl: Sachs' History +of Botany, 1890. Translation of his researches, Sydenham Soc., 1847. +Cohn: Blätter der Erinnerung, 1898, with portrait. Schultze: Necrology, +by Schwalbe in _Archiv f. Mik. Anat._, vol. 10, 1874, with portrait. +Schultze's paper founding the protoplasm doctrine in _Archiv f. Anat. +und Phys._, 1861, entitled Ueber Muskelkörperchen und das was man eine +Zelle zu nennen habe. + + +CHAPTER XIII + +Spontaneous Generation: Tyndall, _Pop. Sci. Mo._, vol. 12, 1878; +Also in Floating Matter of the Air, 1881; J.C. Dalton in _N.Y. Med. +Journ._, 1872; Dunster, good account in _Proc. Ann Arbor Sci. Assn._, +1876; Huxley, _Rept. Brit. Assn. for Adv. Sci._, 1870, republished +in many journals, reprint in Scientif. Memoirs, vol. IV, 1901. Redi: +Works in 9 vols., 1809-1811, with life and letters and portraits; +Good biographical sketch in _Archives de Parasitol._, vol. I, 1898; +Redi's Esperienze Intorno Alla Generazione Degl'Insetti, 2 plates, +first edition, 1668, in Florence, 40; reprinted at various dates, not +uncommon. Spallanzani: Foster, Lects. on Physiol.; Huxley, _loc. cit._; +Dunster, _loc. cit._; L'Abbato Spallanzani, by Pavesi, 1901, portrait. +Pouchet: His treatise of historical importance--Hétérogénie; ou Traité +de la Génération Spontanée, basé sur des Nouvelles Expériences, 1859. +Pasteur: Life by René Vallery-Radot, 2 vols., 1902; Percy and G. +Frankland, 1901; Pasteur at Home, illustrated, Tarbell in _McClure's +Mag._, vol. I, 1893; Also _McClure's_, vol. 19, 1902, review of +Vallery-Radot's Life of Pasteur; _Nature_, vol. 52, 1895; _Les Savants +Modernes_, p. 316; Life by his son-in-law, translated by Lady Hamilton, +1886; Sketches of Pasteur, very numerous. Bacteriology: Woodhead, +Bacteria and their Products, 1891; Fraenkel, Text-Book of Bacteriology, +1891; Prudden, The Story of Bacteria, etc., 1891. Germ-Theory of +Disease: Crookshank's Bacteriology, 3d edition, 1890. Koch: _Pop. Sci. +Mo._, vol. 36, 1889; _Review of Reviews_, vol. 2, 1890; Sketches and +references to his discoveries numerous. Lister: _Pop. Sci. Mo._, vol. +52, 1898; _Review of Reviews_, vol. 14, 1896; celebration of Lister's +80th birthday, _Pop. Sci. Mo._, June, 1907; _Janus_, vol. 5, 1900. The +New Microbe Inoculation of Wright, _Harper's Mag._, July, 1907. + + +CHAPTER XIV + +The History and Theory of Heredity, J.A. Thomson, _Proc. Roy. Soc. +Edinb._, vol. XVI, 1889; Chapter on Heredity in Thomson's Science of +Life, 1899; also in his Study of Animal Life, 1892. Mendel: Mendel's +Principles of Heredity, with translations of his original papers on +hybridization, Bateson, 1902; Mendel's Versuche über Pflanzenhybriden, +two papers (1865 and 1869), edited by Tschermak, 1901; _Ann. Rept. +Smithson. Inst._, 1901-1902; _Pop. Sci. Mo._, vol. 62, 1903; vol. 63, +1904; _Science_, vol. 23, 1903. Galton: _Pop. Sci. Mo._, vol. 29, +1886; _Nature_, vol. 70, 1907; Galton's Natural Inheritance, 1889. +Weismann: Brief Autobiography, with portrait, in _The Lamp_, vol. 26, +1903; Solomonsen, Bericht über die Feier des 70 Geburtstages von August +Weismann, 1904; Weismann's The Germ-Plasm, 1893, and The Evolution +Theory, 1904. + + +CHAPTER XV + +History of Geology and Paleontology, Zittel, 1901. The Founders +of Geology, Geikie, 2d edition, 1905. History and Methods of +Paleontological Discovery, Marsh, _Proceed. Am. Adv. Sci._, 1879. Same +article in _Pop. Sci. Mo._, vol. 16, 1879-1880. The Rise and Progress +of Paleontology, Huxley, _Pop. Sci. Mo._, vol. 20, 1882. Lyell: Charles +Lyell and Modern Geology, Bonney, 1895; Sketch in _Pop. Sci. Mo._, +vol. I, 1872, also vol. 20, 1881-1882. Owen: Life of, by his grandson, +2 vols., 1894; See also above under Chapter VII. Agassiz: Life and +Correspondence, by his wife, 2 vols., 1885; Life, letters and works, +Marcou, 2 vols., 1896; What we Owe to Agassiz, Wilder, _Pop. Sci. +Mo._, July, 1907; Agassiz at Penikese, _Am. Nat._, 1898. Cope: A Great +Naturalist, Osborn in _The Century_, 1897; See above, under Chapter +VII, for further references. Marsh: _Pop. Sci. Mo._, vol. 13, 1878; +Sketches of, _Nature_, vol. 59, 1898-99; _Science_, vol. 9, 1899; _Am. +J. Sci._, vol. 157, 1899. Zittel: Biographical Sketch with portrait, +Schuchert, _Ann. Rept. Smithson. Inst._, 1903-1904. Osborn, Papers +on Paleontological Discovery in Science from 1899 onward. The Fayûm +Expedition of the Am. Museum of Nat. History, _Science_, March 29, 1907. + + * * * * * + +Note. Since the four succeeding chapters deal with the Evolution +Theory, it maybe worth while to make a few general comments on the +literature pertaining to Organic Evolution. The number of books and +articles is very extensive, and I have undertaken to sift from the +great number a limited list of the more meritorious. Owing to the +prevalent vagueness regarding evolution theories, one is likely to read +only about Darwin and Darwinism. This should be avoided by reading as a +minimum some good reference on Lamarck, Weismann, and De Vries, as well +as on Darwin. It is well enough to begin with Darwin's Theory, but it +is not best to take his Origin of Species as the first book. To do this +is to place oneself fifty years in the past. The evidences of Organic +Evolution have greatly multiplied since 1859, and a better conception +of Darwin's Theory can be obtained by reading first Romanes's Darwin +and After Darwin, vol. I. This to be followed by Wallace's Darwinism, +and, thereafter, the Origin of Species may be taken up. These will +give a good conception of Darwin's Theory, and they should be followed +by reading in the order named: Packard's Lamarck; Weismann's The +Evolution Theory; and De Vries's The Origin of Species and Varieties by +Mutation. Simultaneously one may read with great profit Osborn's From +the Greeks to Darwin. + + +CHAPTER XVI + +General: Romanes, Darwin and After Darwin, 1892, vol. I, chaps. I-V; +Same author, The Scientific Evidences of Organic Evolution; Weismann, +Introduction to the Evolution Theory, 1904; Osborn, Alte und Neue +Probleme der Phylogenese, _Ergebnisse der Anat. u. Entwickel._, vol. +III, 1893; Ziegler, Ueber den derzeitigen Stand der Descendenzlehre +in der Zoologie, 1902; Jordan and Kellogg, Evolution and Animal Life, +1907, chaps. I and XIV. Evolutionary Series--Shells: Romanes, _loc. +cit._; Hyatt, Transformations of Planorbis at Steinheim, _Proc. +Am. Ass. Adv. Sci._, vol. 29, 1880. Horse: Lucas, The Ancestry of +the Horse, _McClure's Mag._, Oct., 1900; Huxley, Three Lectures on +Evolution, in Amer. Addresses. Embryology--Recapitulation Theory: +Marshall, Biolog. Lectures and Addresses, 1897; Vertebrate Embryology, +1892; Haeckel, Evolution of Man, 1892. Primitive Man: Osborn, Discovery +of a Supposed Primitive Race of Men in Nebraska, _Century Mag._, Jan., +1907; Haeckel, The Last Link, 1898. Huxley, Man's Place in Nature, +collected essays, 1900; published in many forms. Romanes, Mental +Evolution in Man and Animals. + + +CHAPTER XVII + +Lamarck: Packard, Lamarck, the Founder of Evolution, His Life and Work, +with Translations of his Writings on Organic Evolution, 1901; Lamarck's +Philosophie Zoologique, 1809. Recherches sur l'Organisation des corps +vivans, 1802, contains an early, not however the first statement of +Lamarck's views. For the first published account of Lamarck's theory +see the introduction to his Système des Animaux sans Vertèbres, +1801. Neo-Lamarckism: Packard, _loc. cit._; also in the Introduction +to the Standard Natural History, 1885; Spencer, The Principles of +Biology, 1866--based on the Lamarckian principle. Cope, The Origin of +Genera, 1866; Origin of the Fittest, 1887; Primary Factors of Organic +Evolution, 1896, the latter a very notable book. Hyatt, Jurassic +Ammonites, _Proced. Bost. Sci. Nat. Hist._, 1874. Osborn, _Trans. +Am. Phil. Soc._, vol. 16, 1890. Eigenmann, The Eyes of the Blind +Vertebrates of North America, _Archiv f. Entwicklungsmechanik_, vol. 8, +1899. + +Darwin's Theory (For biographical references to Darwin see below under +Chapter XIX): Wallace, Darwinism, 1889; Romanes, Darwin and After +Darwin, vol. I, 1892; Metcalf, An Outline of the Theory of Organic +Evolution, 1904, good for illustrations. Color: Poulton, The Colors of +Animals; Chapters in Weismann's The Evolution Theory, 1904. Mimicry: +Weismann, _loc. cit._ Sexual Selection: Darwin, The Descent of Man, +new ed., 1892. Inadequacy of Nat. Selection: Spencer, The Inadequacy +of Natural Selection, 1893; Morgan, Evolution and Adaptation, 1903. +Kellogg, Darwinism To-day, 1907, contains a good account of criticisms +against Darwinism. + + +CHAPTER XVIII + +Weismann's The Evolution Theory, translated by J.A. and Margaret +Thomson, 2 vols., 1904, contains the best statement of Weismann's +views. It is remarkably clear in its exposition of a complicated +theory. The Germ-Plasm, 1893; Romanes's An Examination of Weismannism, +1893. Inheritance of Acquired Characters: Weismann's discussion, _loc. +cit._, vol. II, very good. Romanes's Darwin and After Darwin, vol. II. +Personality of Weismann: Sketch and brief autobiography, in _The Lamp_, +vol. 26, 1903, portrait; Solomonsen, Bericht über die Feier des 70 +Geburtstages von August Weismann, 1905, 2 portraits. + +Mutation-Theory of De Vries: Die Mutations-Theorie, 1901; Species +and Varieties, their Origin by Mutation, 1905; Morgan, Evolution and +Adaptation, 1903, gives a good statement of the Mutation Theory, +which is favored by the author; Whitman, The Problem of the Origin +of Species, _Congress of Arts and Science, Universal Exposition, St. +Louis_, 1904; Davenport, Evolution without Mutation, _Journ. Exp. +Zool._, April, 1905. + + +CHAPTER XIX + +For early phases of Evolutionary thought consult Osborn, From the +Greeks to Darwin, 1894, and Clodd, Pioneers of Evolution, 1897. Suarez +and the Doctrine of Special Creation: Huxley, in Mr. Darwin's Critics, +_Cont. Rev._, p. 187, reprinted in Critiques and Addresses, 1873. +Buffon: In Packard's Life of Lamarck, chapter 13. E. Darwin: Krause's +Life of E. Darwin translated into English, 1879; Packard, _loc. cit._ +Goethe: Die Idee der Pflanzenmetamorphose bei Wolff und bei Goethe, +Kirchoff, 1867; Goethe's Die Metamorphose der Pflanzen, 1790. Oken: His +Elements of Physiophilosophy, Ray Soc., 1847. Cuvier and St. Hilaire: +Perrier, La Philosophie Zoologique avant Darwin, 1884; Osborn, _loc. +cit._ Darwin and Wallace: The original communications of Darwin and +Wallace, with a letter of transmissal signed by Hooker and Lyell, +published in the _Trans. Linnæan Soc._ for 1858, were reprinted in the +_Pop. Sci. Mo._, vol. 60, 1901. Darwin: Personality and biography (For +references to his theory see under Chapter XVII); Life and letters by +his son, 3 vols., 1887, new ed., 1896; More Letters of Charles Darwin, +2 vols., 1903; Chapter in Marshall's Lectures on the Darwinian Theory; +Darwin, Naturalist's Voyage around the World, 1880; Gould, Biographical +Clinics, for Darwin's illness due to eye-strain; Poulton, Chas. Darwin +and the Theory of Natural Selection, 1896. Wallace: My Life, 2 vols., +1905; The Critic, Oct., 1905. Huxley: Life and Letters by his son, +1901; Numerous sketches at the time of his death, 1895, in _Nature_, +_Nineteenth Century_, _Pop. Sci. Mo._, etc., etc. Haeckel: His Life and +Work by Bölsche, 1906. + + +CHAPTER XX + +It is deemed best to omit the references to Technical papers upon which +the summaries of recent tendencies are based. Morgan's Experimental +Zoology, 1907. Jennings, Behavior of the Lower Organisms, 1906. +Mosquitoes and other insects in connection with the transmission of +disease, see Folsom, Entomology, 1906, chapter IX, p. 299. Biological +Laboratories: Dean, The Marine Biological Stations of Europe, _Ann. +Rept. Smithson. Inst._, 1894; Marine Biolog. Station at Naples, +_Harper's Mag._, 1901; The _Century_, vol. 10 (Emily Nunn Whitman); +Williams, A History of Science, vol. V, chapter V, 1904; _Am. Nat._, +vol. 31, 1897; _Pop. Sci. Mo._, vol. 54, 1899; _ibid._, vol. 59, 1901. +Woods Hole Station--A Marine University, _Ann. Rept. Smithson. Inst._, +1902. + + + + +INDEX + + + A + + Abiogenesis, 277 + + Acquired characters, inheritance of, 314; + Weismann on, 398 + + Agassiz, essay on classification, 137; + agreement of embryological stages and the fossil record, 334; + fossil fishes, 334; + portrait, 334 + + Aldrovandi, 115 + + Alternative inheritance, 316 + + Amphimixis, the source of variations, 396 + + Anatomical sketches, the earliest, 32; + from Vesalius, 31, 33 + + Anatomical studies, recent tendencies of, 442 + + Anatomy, of Aristotle, 23; + beginnings of, 23; + earliest known illustrations, 32; + of Galen, 24; + of the Middle Ages, 24; + comparative, rise of, 141-165; + of insects, Dufour, 109; + Lyonet, 91; + Malpighi, 63; + Newport, 100; + Réaumur, 96; + Roesel, 96; + Straus-Dürckheim, 96; + Swammerdam, 70, 73-77; + minute, progress of, 89-104; + of plants, Grew, 56; + Malpighi, 66 + + Ancients, return to the science of, 112 + + Animal behavior, studies of, 441 + + Animal kingdom of Cuvier, 133 + + Aquinas, St. Thomas, on creation, 409 + + Arcana Naturæ, of Leeuwenhoek, 78 + + Aristotle, 9-15; + books of, 13; + errors of, 13; + estimate of, 10; + extensive knowledge of animals, 12; + the founder of natural history, 9; + influence of, 15; + personal appearance, 13, 14; + portrait, 14; + position in the development of science, 11 + + Arrest of inquiry, effect of, 17 + + Augustine, St., on creation, 409 + + Authority declared the source of knowledge, 18 + + + B + + Bacteria, discovery of, 276; + disease-producing, 300; + and antiseptic surgery, 302; + nitrifying, of the soil, 303 + + Bacteriology, development of, 276 + + Baer, Von, and the rise of embryology, 195-236; + his great classic on development of animals, 214; + and germ-layers, 218; + makes embryology comparative, 220; + and Pander 218; + period in embryology, 214-226; + portraits, 216, 217; + his rank in embryology, 220; + his especial service, 217; + sketches from his embryological treatise, 221 + + Balfour, masterly work of, 226; + his period in embryology, 226-232; + personality, 228; + portrait, 227; + tragic fate, 228; + university career, 227 + + Bary, H.A. de, 271; + portrait, 272 + + Bassi, and the germ-theory of disease, 294 + + Bell, Charles, discoveries on the nervous system, 183; + portrait, 184 + + Berengarius, 26 + + Bernard, Claude, in physiology, 190; + personality, 191; + portrait, 191 + + Biblia Naturæ of Swammerdam, 73 + + Bichat, and the birth of histology, 166-178; + Buckle's estimate of, 166, 167; + education, 167; + in Paris, 167; + personality, 168; + phenomenal industry, 168; + portrait, 169; + results of his work, 170; + writings, 170; + successes of, 170 + + Binomial nomenclature of Linnæus, 126 + + Biological facts, application of, 443 + + Biological laboratories, establishment and maintenance of, 445; + the station at Naples, 444; + picture of, 445; + the Woods Hole station, 444 + + Biological periodicals, 446 + + Biological progress, continuity of, 434; + atmosphere engendered by, + 448; + from Linnæus to Darwin, 138-140 + + Biology, defined, 4; + domain of, 4, 5; + epochs of, 20; + progress of, 3, 5; + applied, 443 + + Boerhaave, quoted, 71, 72; + and Linnæus, 122 + + Bois-Reymond, Du, 189; + portrait, 189 + + Bones, fossil, 322, 324 + + Bonnet, and emboîtement, 208; + opposition to Wolff, 211; + portrait, 212 + + Books, the notable, of biology, 435 + + Brown, Robert, discovers the nucleus in plant-cells, 243 + + Buckland, 324 + + Buckle, on Bichat, 166, 167 + + Buffon, 129, 411; + portrait, 412; + position in evolution, 412 + + + C + + Cæsalpinus, on the circulation, 50 + + Cajal, Ramon y, 176; + portrait, 176 + + Camper, anatomical work of, 143; + portrait, 144 + + Carpenter, quoted, 170 + + Carpi, the anatomist, 26 + + Castle, experiments on inheritance, 316 + + Catastrophism, theory of, Cuvier, 326; + Lyell on, 331 + + Caulkins, on protozoa, 109 + + Cell, definition of, 258; + diagram of, 257; + earliest known pictures of, 238, 239; + in heredity, 257 + + Cell-lineage, 234, 442 + + Cell-theory, announcement of, 242; + effect on embryology, 222, 224; + founded by Schleiden and Schwann, 242; + Schleiden's contribution, 247; + Schwann's treatise, 248; + modifications of, 250; + vague foreshadowings of, 237 + + Child, studies on regulation, 440 + + Chromosomes, 254, 312 + + Circulation of the blood, Harvey, 46, 47; + Servetus, 50; + Columbus, 50; + Cæsalpinus, 50; + in the capillaries, 84; + Leeuwenhoek's sketch of, 83; + Vesalius on, with illustration, 49 + + Classification of animals, tabular view of, 137-138 + + Cohn, portrait, 271 + + Color, in evolution, 386 + + Columbus, on the circulation, 50 + + Comparative anatomy, rise of, 141-165; + becomes experimental, 165 + + Cope, in comparative anatomy, 165; + portrait, 336; + important work in palæontology, 337, 437 + + Creation, Aquinas on, 409; + St. Augustine on, 408; + special, 410; + evolution the method of, 348 + + Cuvier, birth and early education, 149; + and catastrophism, 326; + comprehensiveness of mind, 154; + correlation of parts, 133; + debate with St. Hilaire, 416; + domestic life, 155; + forerunners of, 143; + founds comparative anatomy, 154; + founder of vertebrate palæontology, 325; + his four branches of the animal kingdom, 132; + goes to Paris, 151; + life at the seashore, 150; + opposition to Lamarck, 414; + portraits, 152, 153; + physiognomy, 152; + and the rise of comparative anatomy, 141-156; + shortcomings of, 156; + successors of, 156; + type-theory of, 133 + + + D + + Darwin, Charles, his account of the way his theory arose, 427; + factors of evolution, 380; + habits of work, 426; + home life, 423; + at Downs, 426; + ill health, 426; + naturalist on the Beagle, 425; + natural selection, 383; + opens note-book on the origin of species, 426; + personality, 422; + portraits, 381, 423; + parallelism in thought with Wallace, 427; + publication of the Origin of Species, 429; + his other works, 391, 429; + theory of pangenesis, 306; + variation in nature, 382; + the original drafts of his theory sent by Hooker and Lyell to the + Linnæan Society, 420-422; + working hours, 426; + summary of his theory, 405 + + Darwin, Erasmus, 413; + portrait, 413 + + Darwinism and Lamarckism confused, 391; + not the same as organic evolution, 347 + + Davenport, experiments, 319 + + Deluge, and the deposit of fossils, 323 + + De Vries, mutation theory of, 402; + portrait, 403; + summary, 406 + + Dufour, Léon, on insect anatomy, 100 + + Dujardin, 250, 262; + discovers sarcode, 250, 266; + portrait, 265; + writings, 264 + + + E + + Edwards, H. Milne-, 157; + portrait, 157 + + Ehrenberg, 106, 107; + portrait, 108 + + Embryological record, interpretation of, 229 + + Embryology, Von Baer and the rise of, 194-236; + experimental, 232; + gill-clefts and other rudimentary organs in embryos, 361; + theoretical, 235 + + Epochs in biological history, 20 + + Evolution, doctrine of, generalities regarding, 345; + controversies regarding the factors, 346, 369; + factors of, 368; + effect on embryology, 225; + on palæontology, 332; + nature of the question regarding, 348; + a historical question, 348; + the historical method in, 348; + sweep of, 366; + one of the greatest acquisitions of human knowledge, 366; + predictions verified, 367; + theories of, 369; + Lamarck, 369; + Darwin, 386; + Weismann, 392; + De Vries, 402; + summary of evolution theories, 404; + vagueness regarding, 346 + + Evolutionary series, 351; + shells, 351; + horses, 354 + + Evolutionary thought, rise of, 407-433; + views of certain fathers of the church, 408 + + Experimental observation, introduced by Harvey, 39-53 + + Experimental work in biology, 439 + + + F + + Fabrica, of Vesalius, 30 + + Fabricius, Harvey's teacher, 41; + portrait, 43 + + Factors of evolution, 369 + + Fallopius, 36; + portrait, 37 + + Flood, fossils ascribed to, 323 + + Fossil life, the science of, 320-341; + bones, 322, 325; + horses in America, 355; + collections in New + Haven, 355; + in New York, 355; + man, 340, 364; + Neanderthal skull, 365; + ape-like man, 364 + + Fossil remains an index to past history, 329 + + Fossils, arrangement in strata, 328; + ascribed to the flood, 323; + their comparison with living animals, 324; + from the Fayûm district, 341; + method of collecting, 340; + nature of, 322; + determination of, by Cuvier, 325; + Da Vinci, 322; + Steno, 322; + strange views regarding, 320 + + + G + + Galen, 23, 180; + portrait, 25 + + Galton, law of ancestral inheritance, 318; + portrait, 317 + + Geer, De, on insects, 95 + + Gegenbaur, 163; + portrait, 164 + + Generation, Wolff's theory of, 210 + + Germ-cells, organization of, 210 + + Germ-layers, 218 + + Germ-plasm, continuity of, 393; + complexity of, 395; + the hereditary substance, 311; + union of germ-plasms the source of variations, 396 + + Germ-theory of disease, 293 + + Germinal continuity, 224, 308; + doctrine of, 224, 311, 393 + + Germinal elements, 305 + + Germinal selection, 397 + + Germinal substance, 310 + + Gesner, 112; + personality, 113; + portrait, 114; + natural history of, 113 + + Gill-clefts in embryos, 361 + + Goodsir, 174 + + Grew, work of, 56 + + + H + + Haeckel, 431; + portrait, 432 + + Haller, fiber-theory, 242; + opposition to Wolff, 211; + in physiology, 181; + portrait, 182 + + Harvey, and experimental observation, 39-53; + his argument for the circulation, 51; + discovery of the circulation, 47; + his great classic, 46; + education, 40; + in embryology, 198; + embryological treatise, 199, 200; + frontispiece from his generation of animals (1651), 201; + influence of, 52; + introduces experimental + method, 47; + at Padua, 41; + period in physiology, 180; + personal appearance and qualities, 42, 44, 45; + portrait, 44; + predecessors of, 48; + question as to his originality, 46; + his teacher, 43; + writings, 45 + + Heredity, 305; + a cellular study, 257; + according to Darwin, 307; + Weismann, 309; + application of statistics to, 314; + inheritance of acquired characters, 314; + steps in advance of knowledge of, 308 + + Hertwig, Oskar, portrait, 231; + service in embryology, 232; + Richard, quoted, 125 + + Hilaire, St., portrait, 416; + see St. Hilaire + + His, Wilhelm, 232; + portrait, 233 + + Histology, birth of, 166-178; + Bichat its founder, 170; + normal and pathological, 172; + text-books of, 177 + + Hooke, Robert, 55; + his microscope illustrated, 55 + + Hooker, letter on the work of Darwin and Wallace, 420-422 + + Horse, evolution of, 354 + + Human ancestry, links in, 364, 365 + + Human body, evolution of, 363 + + Human fossils, 340, 364 + + Hunter, John, 144; + portrait, 145 + + Huxley, in comparative anatomy, 161; + influence on biology, 430; + in palæontology, 335; + portrait, 430 + + + I + + Inheritance, alternative, Mendel, 316; + ancestral, 318; + Darwin's theory of, 306; + material basis of, 311-313; + nature of, 305 + + Inheritance of acquired characters, 314; + Lamarck on, 377; + Weismann on, 398 + + Inquiry, the arrest of, 17 + + Insects, anatomy of, Dufour, 106; + Malpighi, 63; + illustration, 65; + Newport, 100; + Leydig, 102; + Straus-Dürckheim, 96; + Swammerdam, 70, 75; + illustration, 76; + theology of, 91 + + + J + + Jardin du Roi changed to Jardin des Plantes, 372 + + Jennings, on animal behavior, 109, 441 + + Jonston, 114 + + + K + + Klein, 118 + + Koch, Robert, discoveries of, 300; + portrait, 301 + + Koelliker, in embryology, 224; + in histology, 171; + portrait, 173 + + Kowalevsky, in embryology, 224; + portrait, 225 + + + L + + Lacaze-Duthiers, 158; + portrait, 159 + + Lamarck, changes from botany to zoölogy, 372; + compared with Cuvier, 327; + education, 371; + first announcement of his evolutionary views, 375; + forerunners of, 411; + first use of a genealogical tree, 131; + founds invertebrate palæontology, 326; + on heredity, 377; + laws of evolution, 376; + military experience, 370; + opposition to, 414; + Philosophie Zoologique, 375; + portrait, 373; + position in science, 132; + salient points in his theory, 378; + his theory of evolution, 374; + compared with that of Darwin, 390, 391; + time and favorable conditions, 378; + use and disuse, 374 + + Leeuwenhoek, 77-87; + new biographical facts, 78; + capillary circulation, 84, 85; + sketch of, 83; + comparison with Malpighi and Swammerdam, 87; + discovery of the protozoa, 105; + other discoveries, 85; + and histology, 178; + his microscopes, 81; + pictures of, 82, 83; + occupation of, 78; + portrait, 79; + scientific letters, 83; + theoretical views, 86 + + Leibnitz, 208 + + Leidy in palæontology, 337 + + Lesser's theology of insects, 91 + + Leuckart, 136; + portrait, 136 + + Leydig, 102; + anatomy of insects, 102; + in histology, 175; + portrait, 175 + + Linnæan system, reform of, 130-138 + + Linnæus, 118-130; + binomial nomenclature, 127; + his especial service, 126; + features of his work, 127, 128; + his idea of species, 128, 129; + influence on natural history, 125; + personal appearance, 125; + personal history, 119; + portrait, 124; + helped by his fiancée, 120; + return to Sweden, 123; + and the rise of natural history, 100-130; + the Systema Naturæ, 121, 125, 127; + professor in Upsala, 123; + celebration of two hundredth anniversary of his birth, 124; + as university lecturer, 123; + wide recognition, 122; + summary on, 129-130 + + Lister, Sir Joseph, and antiseptic surgery, 302; + portrait, 302 + + Loeb, 234; + on artificial fertilization, 441; + on regulation, 440 + + Ludwig, in physiology, 160; + portrait, 160 + + Lyell, epoch-making work in geology, 330; + letter on Darwin and Wallace, 420-422; + portrait, 331 + + Lyonet, 89; + portrait and personality, 90; + great monograph on insect anatomy, 91; + illustrations from, 92, 93, 94, 95; + extraordinary quality of his sketches, 92 + + + M + + Malpighi, 58-67; + activity in research, 62; + anatomy of plants, 66; + anatomy of the silkworm, 63; + compared with Leeuwenhoek and Swammerdam, 87; + work in embryology, 66, 202; + rank as embryologist, 205; + honors at home and abroad, 61; + personal appearance, 58; + portraits, 59, 204; + sketches from his embryological treatises, 203; + and the theory of pre-delineation, 203 + + Man, antiquity of, 364; + evolution of, 363; + fossil, 340, 364 + + Marsh, O.C., portrait, 337 + + Meckel, J. Fr., 162; + portrait, 162 + + Men, of biology, 7, 8; + the foremost, 437; + of science, 7 + + Mendel, 315; + alternative inheritance, 316; + law of, 315; + purity of the germ-cells, 316; + portrait, 315; + rank of Mendel's discovery, 316, 317 + + Microscope, Hooke's, Fig. of, 55; + Leeuwenhoek's, 81, + Figs. of, 82, 83 + + Microscopic observation, introduction of, 54; + of Hooke, 55; + Grew, 55; + Ehrenberg, 106; + Malpighi, 66, 67; + Leeuwenhoek, 81, 84, 85, 105 + + Microscopists, the pioneer, 54 + + Middle Ages, a remolding period, 19; + anatomy in, 24 + + Milne-Edwards, portrait, 157 + + Mimicry, 387 + + Mohl, Von, 268; + portrait, 269 + + Müller, Fritz, 230; + O. Fr., 106 + + Müller, Johannes, as anatomist, 163; + general influence, 185; + influence on physiology, 185; + as a teacher, 185; + his period in physiology, 184; + personality, 185; + portrait, 187; + physiology after Müller, 188 + + + N + + Nägeli, portrait, 268 + + Naples, biological station at, 446; + picture of, 445 + + Natural history, of Gesner, 112, 113, 114; + of Ray, 115-118; + of Linnæus, 118-130; + sacred, 110; + rise of scientific, 110-130 + + Natural selection, 383; + discovery of, 427; + Darwin and Wallace on, 429; + extension of, by Weismann, 397; + illustrations of, 384; + inadequacy of, 389 + + Nature, continuity of, 367; + return to, 19; + renewal of observation, 19 + + Naturphilosophie, school of, 160 + + Neanderthal skull, 365 + + Needham, experiments on spontaneous generation, 281 + + Neo-Lamarckism, 380 + + Newport, on insect anatomy, 100 + + Nineteenth century, summary of discoveries in, 3 + + Nomenclature of biology, 126, 127 + + Nucleus, discovery of, by Brown, 243; + division of, 256, 313 + + + O + + Observation, arrest of, 17; + renewal of, 19; + in anatomy, 26; + and experiment the method of science, 22, 39 + + Oken, on cells, 241; + portrait, 160 + + Omne vivum ex ovo, 200 + + Omnis cellula e cellula, 309 + + Organic evolution, doctrine of, 345-367; + influence of, on embryology, 225; + theories of, 368-406; + rise of + evolutionary thought, 407-433; + sweep of the doctrine of, 366 + + Osborn, quoted, 10, 364, 410; + in palæontology, 339 + + + P + + Palæontology, Cuvier founds vertebrate, 325; + of the Fayûm district, 341; + Lamarck founder of invertebrate, 326; + Agassiz, 332; + Cope, 337; + Huxley, 335; + Lyell, 330; + Marsh, 337; + Osborn, 339; + Owen, 332; + William Smith, 328; + steps in the rise of, 329 + + Pander, and the germ-layer theory, 218 + + Pangenesis, Darwin's theory of, 306 + + Pasteur, on fermentation, 294; + spontaneous generation, 288; + inoculation for hydrophobia, 299; + investigation of microbes, 298; + personality, 296; + portrait, 295; + his supreme service, 299; + veneration of, 294 + + Pasteur Institute, foundation of, 299; + work of, 300 + + Pearson, Carl, and ancestral inheritance, 318 + + Philosophie Anatomique of St. Hilaire, 416 + + Philosophie Zoologique of Lamarck, 375 + + Physiologus, the sacred natural history, 110-112 + + Physiology, of the ancients, 179; + rise of, 179-194; + period of Harvey, 180; + of Haller, 181; + of J. Müller, 184; + great influence of Müller, 185; + after Müller, 188 + + Pithecanthropus erectus, 341, 360 + + Pliny, portrait, 16 + + Pouchet, on spontaneous generation, 286 + + Pre-delineation, theory of, 206; + rise of, Malpighi, 207; + Swammerdam, 208; + Wolff, 210 + + Pre-formation. See Pre-delineation + + Primitive race of men, 366 + + Protoplasm, 259; + discovery of, 250, 262; + doctrine and sarcode, 270, 273; + its movements, 261; + naming of, 269; + its powers, 260 + + Protozoa, discovery of, 104; + growth of knowledge concerning, 104-109 + + Purkinje, portrait, 267 + + + R + + Rathke, in comparative anatomy, 163; + in embryology, 223 + + Ray, John, 115; + portrait, 116; + and species, 117 + + Réaumur, 96; + portrait, 98 + + Recapitulation theory, 230 + + Recent tendencies, in biology, 437; + in embryology, 232 + + Redi, earliest experiments on the generation of life, 279; + portrait, 280 + + Remak, in embryology, 223 + + Roesel, on insects, 95; + portrait, 97 + + + S + + Sarcode and protoplasm, 273, 275 + + Scala Naturæ, 131 + + Scale of being, 131 + + Schleiden, 243; + contribution to the cell-theory, 248; + personality, 247; + portrait, 246 + + Schultze, Max, establishes the protoplasm doctrine, 272; + in histology, 172; + portrait, 273 + + Schulze, Franz, on spontaneous generation, 284 + + Schwann, and the cell-theory, 242, 244, 248, 249; + in histology, 171; + and spontaneous generation, 284 + + Science, of the ancients, return to, 112; + conditions under which it developed, 8; + biological, 4 + + Servetus, on circulation of the blood, 50 + + Severinus, in comparative anatomy, 143; + portrait, 143 + + Sexual selection, 388 + + Shells, evolution of, 352, 353 + + Siebold, Von, 134, 135; + portrait, 135 + + Silkworm, Malpighi on, 63; + Pasteur on, 299 + + Smith, Wm., in geology, 328 + + Spallanzani, experiments on generation, 282; + portrait, 283 + + Special creation, theory of, 410 + + Species, Ray, 117; + Linnæus, 129; + are they fixed in nature, 350; + origin of, 350-364 + + Spencer, 418; + his views on evolution in 1852, 419 + + Spontaneous generation, belief in, 278; + disproved, 292; + first experiments on, 278; + new form of the question, 281; + Redi, 279; + Pasteur, + 288; + Pouchet, 286; + Spallanzani, 282; + Tyndall, 290 + + Steno, on fossils, 322 + + Straus-Dürckheim, his monograph, 96; + illustrations from, 101 + + Suarez, and the theory of special creation, 410 + + Swammerdam, his Biblia Naturæ, 73; + illustrations from, 74, 76; + early interest in natural history, 68; + life and works, 67-77; + love of minute anatomy, 70; + method of work, 71; + personality, 67; + portrait, 69; + compared with Malpighi and Leeuwenhoek, 87 + + System, Linnæan, reform of, 130-138 + + Systema Naturæ, of Linnæus, 121, 127 + + + T + + Theory, the cell-, 242; + the protoplasm, 272; + of organic evolution, 345-368; + of special creation, 410 + + Tyndall, on spontaneous generation, 289; + his apparatus for getting optically pure air, 290 + + Type-theory, of Cuvier, 132 + + + U + + Uniformatism, and catastrophism, 331 + + + V + + Variation, of animals, in a state of nature, 382; + origin of, according to Weismann, 396 + + Vesalius, and the overthrow of authority, in science, 22-38; + great book of, 30; + as court physician, 35; + death, 36; + force and independence, 27; + method of teaching anatomy, 28, 29; + opposition to, + 34; + personality, 22, 27, 30; + physiognomy, 30; + portrait, 29; + predecessors of, 26; + especial service of, 37; + sketches from his works, 31, 33, 34, 49 + + Vicq d'Azyr, 146; + portrait, 147 + + Vinci, Leonardo da, and fossils, 322 + + Virchow, and germinal continuity, 225; + in histology, 174; + portrait, 174 + + Vries, Hugo de, his mutation theory, 403; + portrait, 403; + summary of theory, 406 + + + W + + Wallace, and Darwin, 420; + his account of the conditions under which his theory originated, 427; + portrait, 428; + writings, 427 + + Weismann, the man, 399; + quotation from autobiography, 401; + personal qualities, 399; + portrait, 400; + his theory of the germ-plasm, 392-399; + summary of his theory, 405 + + Whitney collection of fossil horses, 355 + + Willoughby, his connection with Ray, 115 + + Wolff, on cells, 240; + his best work, 211; + and epigenesis, 205; + and Haller, 211, 214; + opposed by Bonnet and Haller, 211; + his period in embryology, 205-214; + personality, 214; + plate from his Theory of Generation, 209; + the Theoria Generationis, 210 + + Wyman, Jeffries, on spontaneous generation, 289 + + + Z + + Zittel, in palæontology, 338; + portrait, 339 + + + + + + + + +ADVERTISEMENTS + + +DARWINISM TO-DAY + + +By Prof. Vernon L. Kellogg, of Leland Stanford University Author of +"American Insects," etc. 395 pp. and index. 8vo. $2.00 net; by mail, +$2.15. + +A simple and concise discussion for the educated layman of present-day +scientific criticism of the Darwinian selection theories, together with +concise accounts of the other more important proposed auxiliary and +alternative theories of species-forming. With special notes and exact +references to original sources and to the author's own observations and +experiments. + + "Its value cannot be overestimated. A book the student must have at + hand at all times, and it takes the place of a whole library. No other + writer has attempted to gather together the scattered literature + of this vast subject, and none has subjected this literature to + such uniformly trenchant and uniformly kindly criticism. 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THE PHILOSOPHY OF NATURE + +A Series of volumes by President Jordan, of Stanford University, and +Professors Brooks of Johns Hopkins, Lull of Yale, Thomson of Aberdeen, +Przibram of Austria, zur Strassen of Germany, and others. Edited by +Professor Kellogg of Leland Stanford. 12mo. 5-1/8 × 7-1/2 in. + + + HENRY HOLT AND COMPANY, New York + June, '08. + + + + + + +End of Project Gutenberg's Biology and its Makers, by William A. Locy + +*** END OF THE PROJECT GUTENBERG EBOOK 58867 *** |