MULLER, JOHANNES, and MEDICINE, HISTORY OF.) The latter part of Miller's life was given mainly to zoological research, and there is hardly a group in the animal kingdom on the knowledge of which he has not left his mark. As a microscopist he worked out the anatomy of the glandular and cartilaginous tissues, and grouped the connective tissues. He thus prepared the way for the work of his pupil Schwann. Muller was a convinced vitalist and his "Doctrine of Specific Nerve Energy" remains one of the corner-stones of vitalistic theory.
The study of the palaeontology of plants came later than that of animals. A few fossil plants had been described by earlier naturalists. Toward the end of Cuvier's time several figures of plants from the coal measures had been published with the generic and specific names that they still bear. Not until 1831 was the technique of their examination sufficiently advanced for micro scopic study.
The study of fossil botany began to be systematic in 1858 with the work of W. C. Williamson (1816-95) who demonstrated that in coal are to be found gigantic forms similar to the higher flower less plants such as horse-tails, ferns and club moss. His results were long treated with neglect, but have at last earned more recognition. During the last 5o years the palaeontology of plants has come near to be on the same footing as that of animals.
Effects of Geographical Exploration in the Course of Biological Development.—From the end of the I5th century the western nations of Europe were sending forth expeditions east and west, and these brought home knowledge of the natural products of lands newly explored. Thus the idea that each region has its characteristic living things, implicit in ancient biology but forgotten during the middle ages, became gradually explicit. In the i8th century exploratory expeditions began the practice of carrying specially-trained naturalists and thus they enter the history of biology. The three voyages of Captain Cook (q.v.) form an era, not only in the history of geographic discovery, but also in the study of living things. Among the naturalists that Cook took with him were Joseph Banks (1743-1800, q.v.), D. C. Solander (1736-82) and the pupil of Linnaeus, Robert Brown q.v.). These three were in exploring the flora and fauna in the Pacific.
An important voyage which covered the western as well as the eastern hemisphere was that of the "Beagle," which sailed in 1831 and carried the naturalist Charles Darwin (1809-82, q.v.) with it. Quite apart from the investigations and theories with which Dar win's name is especially associated, the voyage was important as making accessible a whole multitude of new forms and as estab lishing the doctrine of zoo-geographical and regions.
By the middle of the 19th century exploration and survey had become recognized as an important duty of the British Admiralty. Many scientific expeditions were sent out by that body. Of these the most important was that of the "Challenger" which sailed in 1872. The features of this expedition were, firstly, the very care ful examination of the depth and character of the seas and sea water whereby oceanography was established as a separate science; secondly, the large number of very inaccessible places visited, and thirdly, the magnificent scale on which the scientific results of the journey were published. The reports of the "Challenger" expedition are still in current use by naturalists. The influence of this expedition, coming as a culmination of a series of previous voyages of exploration, was to modify consider ably the general view of the range and variety of living things, and to enable naturalists to form a picture of life in the ocean where the geographical regions are distributed vertically rather than horizontally.
Reproduction of Plants and Its Comparison to That of Animals.—One of the main gaps in biological thought was the great difference between the nature of animals and that of plants. Especially the mode of reproduction of plants seemed to separate them very widely from animal forms. Theophrastus, for instance, gives a list of the modes of plant reproduction without hinting at the essential nature of fertilization. It is on this account, perhaps, that there have arisen so many legends concerning the "loves of the plants" and vague ideas ascribing sex to these beings. We have already seen how the idea was adumbrated in antiquity, by Theophrastus, among others, and how in the I7th century Millington, through the mouth of Grew, actually suggested sexual characters in the parts of the flowers. The conception of sex in plants was, however, lucidly, consistently and accurately set forth, though in elementary fashion, towards the end of the 17th century by R. J. Camerarius (1665-1721). This remarkable ob server pointed out that the sex theory could not be made to apply to flowerless plants. The doctrine of the sex of flowers was accepted by Linnaeus and incorporated in a mechanical way into his system. Linnaeus found the sexual parts of plants convenient for establishing his classification.
During the course of the i8th century several botanists suc ceeded in using the pollen of one species to fertilize the flowers of another species of plant. The existence of hybridization was recognized, and one writer, J. G. Koelreuter (1733-1806) of Carlsruhe, held that the main agent in the fertilization of flowers was the wind, but that some flowers fertilized themselves, and that in others insects played a part. With great acumen, moreover, he pointed out that in some plants, e.g., the mistletoe, which did not lend themselves to pollination by the wind, and in which the flowers were of different sexes, the only way of pollination was by insects. Moreover, for this same plant he called atten tion to a matter that was later very successfully investigated by Charles Darwin, namely, the question of the distribution of seeds by birds. Thus, as he pointed out, the mistletoe depends upon two groups of animals, birds and insects, for its existence. The subject was taken up by several German workers, notably, by C. C. Sprengel (1750-1816) who, in his work The Newly Revealed Mystery of Nature in the Structure and Fertilization of Flowers, paid special attention to cases in which the sexual parts occurring on a single blossom matured at different periods (dichogamy) .
Sprengel reached the conclusion that some flowers can only be fertilized by insects, that some are so constructed as to injure and even kill insects that serve them, and that yet other flowers are fertilized by wind. He observed that flowers belonging to the last class always produced large quantities of light pollen, whereas in the flowers of the other types pollen is relatively heavy. He demonstrated the relation of the nectary to the process of fertil ization, and in general he sought to show that his principles ex plained all the course of flowers—position, size, smell, colour, form, date of flowering and the like.
The actual process of fertilization was first observed by the extremely acute and versatile Italian microscopist, G. B. Amici (1784-186o). In 1823 this remarkable naturalist, whose work has not been adequately noticed, working with the microscope which he had himself improved, saw the tube given off by the pollen grain and its contents perform streaming movements. In 183o he actually followed the pollen tubes into the ovary and observed one find its way to the micropyle of each ovule. These observations were confirmed by Robert Brown and Schleiden, and finally in 1846 the process of fertilization in flowering plants was placed upon a firm and recognized basis by Amici himself. Thus the general character of the vital processes of plants was brought into relation with that of animals.
Metamorphoses and Alternation of Generations in Ani mals and Plants.—An obstacle to the conception of living things obeying general laws has always been the observation of the extreme changes that some forms undergo. Such "meta morphoses" were observed by the ancients and were the sub ject of exact study during the i7th century by Swammerdam and other naturalists. These observations were extended by many observers during the i8th century and notably by John Turber ville Needham (1713-81) In the early '4os Johannes Steenstrup (1813-97) of Copen hagen, described how certain animals, notably jellyfish and para sitic worms, produce offspring which at no time resemble their parents, but which, on the other hand, bring forth progeny similar to the grandparents. Instances of the alternation of generations, as this process was called, were rapidly accumulated by naturalists from a number of organisms belonging to different groups in the animal kingdom. The well-known and easily observed instance of such a curious cycle is in the common aphis of roses in which there is an alternation of parthenogenetic and sexual generations.
In 185i, a short time after the appearance of Steenstrup's volume, Charles Darwin published his first important monograph on a living group. In this work on the barnacle and allied organ isms, he demonstrated that these creatures go through a very remarkable metamorphosis, being born as free-swimming forms similar to other Crustacea and subsequently settling down to fixed life in which they sometimes resemble the Mollusca, with which Cuvier had classed them.
Darwin, moreover, demonstrated the curious feature that while individuals of this group were normally hermaphrodite, yet from time to time forms appeared that were male only, and there was at such times true sexual generation.
The interpretation of these phenomena was, however, unsat isfactory and vague. The botanist, Karl Nageli (1817-91) in the '4os made some ath ance in examining the prothallia of ferns, and observed their free-swimming spermatozoa. At last in 185o Wilhelm Hofmeister (1824-77, q.v.) gave a consecutive account of the actual process of generation in the fern, having observed the whole process of development from a single cell into the prothallus. He saw how the prothallus matured specialized cells, which, after conjugation, gave rise to the more conspicuous and well known asexual form. In other words, he had demonstrated the process of alternation of generations in the fern. He went on to show that the mode of production of the embryo in the pines and their allies was in certain cases intermediate between that of flowering plants and that of the higher flowerless plants such as ferns. Thus, by the sixth- decade of the P9th century, it was established that fertilization in flowerless plants consists in the blending together of the spermatozoid and the egg-cell, and that in certain flowerless plants, e.g., the ferns, there is a definite alternation of generations.
Observations on the sexual character of plants, on the alterna tion of generations and on metamorphoses gave absorbing inter est to the investigation of generation in general, and stimulated the study of embryology both of animals and plants. Indirectly, these studies led to the firmer establishment and wider applica tion of the cell theory, and to the accumulation of data which were used by the founders of the evolutionary school.
The Establishment of the Cellular Nature of Animals and Plants.—The appearance of cell walls is to be seen in many microscopic drawings of plant tissues made in the 17th century by the great classical microscopists. In the careful analysis made by these men there is distinction between the various tissues of the higher plants, although in making this distinction they knew nothing of the cell substance dwelling within the cell wall. Not until the i9th century was the actual living substance of the cell first observed, a feat achieved by Amici.
In some of the accounts of the microscopic appearance of the tissues of animals by the classical microscopists, cells had been vaguely distinguished, though much less definitely than in plants. During the i8th century little important microscopic work was done. At the beginning of the i9th century a brilliant French investigator, M. F. X. Bichat (1771-18o2), perceiving that the different parts of the body such as bones, muscle, nerves, blood vessels, cartilages, etc., had a different microscopic appearance, succeeded in analysing the microscopical appearance into 21 "tissues." Out of this discovery arose the study of histology, a word introduced by Richard Owen, and still in current use.
Between the 17th and early i9th centuries advances were made in the knowledge of uni-cellular organisms. V orticella had been described in 1667, Bacteria in 1683, Paramecium in 1702 and Amoeba in 1755. Several monographs dealing with uni-cellular plants and animals had appeared, but no advance had been made in the proper appreciation of the real nature of these organisms. In 1833 Robert Brown in his investigations on plant fertili zation had discussed the nucleus and found it a normal accom paniment of the cell, but had no clear idea of the nature either of cell or of nucleus. The modern doctrine of the cell theory was placed upon a secure footing in the work of M. J. Schleiden of Jena (1804-81) in 1838, and of Theodore Schwann (1810-82) in the years 1838-39. Schleiden observed the process of pro toplasmic streaming in many cells, and he recognized the nucleus as an essential element. He made a, curious blunder in holding that cells originated by budding from the surges of the nucleus.
The work of Schwann, who was a pupil of Johannes Muller, has a more modern appearance than that of Schleiden. He gives admirable figures of animal cells, and especially of those of car tilage. He traces the cells of these and of other tissues from their undifferentiated origins, and he shows how the ovum is itself a cell. Finally, he passes to a general statement as to the cellular origin of animals and plants. We may note that he introduced the word "metabolic." He did not, however, shake himself free from Schleiden's theory of the cell originating from the nucleus. The investigator who was instrumental in destroying this theory was Karl Nageli (1817-91). The word "protoplasm" was introduced by Hugo von Mohl (18°5-72) of Tubingen, in 1846, and the conception of this substance as the physical basis of life was the work of Max Schultze (1822-74)• With the final establishment of the cell theory, histology be came a special science and was admirably developed by the Swiss Albrecht von Kolliker (1817-19o5), a pupil of Johannes Muller. The subject of histology was extended into the department of disease by yet another pupil of Johannes Milner, Rudolf Virchow (1821-19o2, q.v.).
Organic Evolution. The Origin of Species.—By most older writers, species are treated as fixed and definite--as though their characteristics had been made once and for all, and have never altered. Thus in the opinion of Linnaeus there are "as many species as issued in pairs from the hands of the Creator." Even Linnaeus, despite his systematic obsession, began to see that it is often very difficult to separate species one from another. He did not like to move from his original position of the fixity of species, and therefore he simply substituted the genus for the species as the original creation. He thus reached the conclusion that "all the species of one genus constituted at first one species." There are a great many early naturalists who adumbrated more or less clearly the doctrine of the evolution of organic forms. Many antiquarian writers have applied themselves to excavating this conception from writings of antiquity, of the middle ages and of modern times. The first naturalist, however, who clearly set forth the idea of evolution as applied to existing living things was Buffon 0707-78).
Buffon's great scientific work, Natural History, General and Particular, appeared in 45 volumes, and its publication occupied 55 Years, 1749 to 1804, being completed after his death by one of his assistants. It aimed at containing all scientific knowledge and was the first modern attempt of the kind. In various parts of his great work and in other works Buffon expressed himself differently on the subject of organic evolution; nevertheless, we can see that he was moving farther and farther from the position occupied by Linnaeus. He finally accepted definitely the conception that species alter in type from time to time, but that at each alteration they retain some marks of their previous type, as the pig, for instance, retains fingers now in disuse but formerly used. He thus came to the conclusion that many species are degenerate forms of others; that the ape, for instance, is a degraded man, and that the ass is a degraded horse.
Similar views were set forth even more clearly by Erasmus Darwin (1731-1802), the grandfather of Charles Darwin. Eras mus Darwin held that species change in course of time, and that these changes are due to influences that bear upon the individual from without. These changes he held to be passed on to the off spring, so that he was a believer in the inheritance of acquired characteristics, a conception which was further developed by his younger contemporary J. B. de M. Lamarck (1744-1829, q.v.), whose Zoological Philosophy appeared in 1809. Lamarck held that for living organisms there existed a "natural order." He thought that if all the species that exist were known, they would be found to form a long ladder or scale in which each would differ but little from the next. This linear view of the arrangement of species Lamarck inherited ultimately from Aristotle. The gaps that he could discern in the existing series he ascribed to the de struction of the intermediate links. These gaps he hoped would be filled in by palaeontological discovery.
Over and above such value as Lamarck gave to the conception of the evolution of species we owe to him one important step of permanent value. It was part of his scheme that the animal and the plant world must be continuous with each other at some stage or stages. He set in sharp contrast the study of living things against that of non-living things. For the scientific study of the former, he adopted from Treviranus the word biology 0802). We thus owe this word biology largely to Lamarck, but still more we owe to Lamarck the conception of biology as a comprehensive study. Since according to Lamarck species shade into each other, it seemed to him improbable that they were permanently fixed. In reaching this conclusion, he laid much stress, as did Charles Dar win after him, on the peculiar development of domesticated ani mals. There must, he thought, be some agent acting to produce variations from the original type. This agent Lamarck believed to be environment. He thus reached the conclusions, firstly, that species vary under changing external influences; secondly, that there is a fundamental unity underlying the diversity of many things and thirdly, that the diversity of living things is subject to a progressive development. The mechanism of that develop ment Lamarck held to be use and disuse of acquired characters.
Discussion of the conception of the progressive development of living things with its corollary, the inconstancy of species, was raised by many writers in the first half of the 19th century, among them the French naturalist Etienne Geoffroy Saint-Hilaire (1772 1844) , and the German poet Goethe (1749-183 2) . In England the writer who attracted the most attention was the Rev. T. R. Malthus (1766-1834), whose important Essay on Population was first published anonymously in 1798. That work appeared during the French Revolution, and its tone and argument are not un related to the social views of the time—views which had their influence upon Darwin. Indeed, it is not too much to say that the Origin of Species is one of the secondary products of the utilitarian philosophy of which the chief exponent was Jeremy Bentham.
The treatise on the Origin of Species by Charles Darwin ap peared early in 1859. For the detailed nature of the views there expressed, the reader is referred elsewhere (see DARWIN, CHARLES). It created a revolution in thought in England, and to a less extent in France and Germany. The cause of that change in opinion was not so much the doctrine of the impermanence of species, which had been voiced by many before Darwin, as the fact that Darwin displayed to his readers the details of a process which could be seen in daily operation. Moreover, in setting forth his hypothesis of the action of natural selection he placed before his public a mechanism which he believed, and they believed, was sufficient to account for the process in question. His theory appealed specially to the practical minds of the English natural ists, who required an explanation of the process before they would altogether accept it. The theory naturally had less effect upon certain more philosophic thinkers, whom the actual evidence for the existence of evolution had already convinced.
In 1852, seven years before the publication of the Origin of Species, the philosopher Herbert Spencer (1820-1902) had set forth doctrines of evolution in which that word was probably used for the first time in literature to describe the idea of a gen eral process of production of higher from lower forms. Sir Charles Lyell, of whom Darwin professed himself a disciple, and who deeply influenced his whole thought and work, used the word some 20 years earlier in a similar, though less general, sense. The word evolution was seldom used by Darwin himself, but the par ticular application that had been given to it by Spencer rapidly caught on, and Darwinism and Evolution were often treated as synonymous terms. The doctrines of Darwin, however, only ap plied and were only meant to apply to the world of life, nor even there can we regard the words Darwinism and Evolution as truly synonymous, for it is quite possible to conceive of organic evolution that is independent of such "Darwinian" factors as natural selection or sexual selection. The phrase "survival of the fittest" was also coined by Spencer, and caught on in the same way as did evolution. Evolutionary doctrines were diffused by a host of expert biologists who were rapidly converted to the Dar winian point of view. Among them T. H. Huxley q.v.) in England and Ernst Haeckel (1834-1919, q.v.) in Germany are worthy of special commemoration.
Since Darwin's time, and especially in the loth century, a great deal of doubt has been cast on the evolutionary efficacy of those factors on which Darwin himself laid most stress. The con clusion that species do in fact give rise to other species has earned almost universal acceptance, and on the general relation of living things within the larger groups there is no wide divergence of opinion. Here Darwin may be regarded as victorious all along the line. It cannot be said, however, that any general agreement has been reached as to the process by which the great variation in living things has been produced, nor can it be claimed that there is any consensus of opinion as to the relationship of the main groups of living things with each other.
Despite these reservations it cannot be gainsaid that the his tory of biology since the days of Darwin may be treated as in large part a commentary on his work. The stimulus which he gave to comparative morphology has given rise to an almost incredible mass of literature dealing with plant and animal forms. His work has acted as a less stimulating influence on those depart ments which deal with function, and comparative physiology re mains in a rudimentary state. The study of inheritance and of genetic characters, however, may be traced back directly to his example. A large part of the work of the last half century in this direction has been done in confirmation or refutation of the views which he expressed.
Biogenesis Versus Abiogenesis. The Origin of Life.—All the older naturalists, following Aristotle and his pupil Theophras tus, were willing to accept spontaneous generation at least of the lower forms of life. According to them, spontaneous generation was the normal mode of production of certain organisms. These views were universally accepted until the middle of the 17th century, and the advent of microscopic research.
The exploration of microscopic life soon revealed that many cases of apparent spontaneous generation had been falsely in terpreted. Thus, for instance, Malpighi showed that galls were not spontaneously generated, but were associated with the larvae of the insect, the egg of which was placed within the plant by the parent insect. On the other hand, the increasing power of the microscope revealed the existence of more and more minute organ isms which seemed to appear out of nothing. Thus Leeuwenhoek saw such organisms in infusions of broth and other substances. Such infusions, at first perfectly clear, became in a few days turbid with these minute actively moving bodies, which were for this reason called Infusoria.
The first scientific treatment of the question of spontaneous gen eration was made by the Italian Francesco Redi (1626-97). This remarkable naturalist's experiments were most admirably designed, and his conclusions were lucidly set forth. He exposed fresh meat in jars covered with fine gauze, using as controls meat in other jars not so covered. Soon in the open jars larvae of flies de veloped, while eggs corresponding to such larvae were deposited on the surface of the gauze above the closed jars, but no larvae ever developed within the closed jar itself. Redi traced the larvae to their parents and showed conclusively that the generation of these insects could only be through parent forms.
With the extension of microscopic observation, however, the problem was thrown farther and farther back, and during the i8th century the battle on the subject of spontaneous generation raged back and forth. On the one hand it was shown that by boiling or chemically treating a medium, organisms appeared in it slowly or not at all. On the other hand, cases were always being adduced in which microscopic organisms did so appear, despite all precautions. About the middle of the i8th century the con troversy reached an important stage in a discussion between John Turberville Needham (1713-81) and the versatile Abbe Spal lanzani (1729-99). This discussion is interesting since it was practically repeated about i oo years later between Pasteur and his opponents. In i 748 Needham published what was in effect a repetition—made in conjunction with Buffon—of the experi ments of Redi of the previous century. His experiments were, however, more refined than those of Redi, since he aimed at ex cluding even the most microscopic organisms. He came to the opposite conclusions to those of Redi, and inferred that micro scopic organisms are generated spontaneously in organic sub stances. His apparatus consisted in effect of a phial filled with broth, the mouth of which was closed with mastic after the broth had been boiled. Needham's observations were good, but his de ductions obscure, often verging on the mystical. He was effec tively answered by Spallanzani, an investigator and writer of very great ability, who made important contributions to several branches of biological science. Some of Spallanzani's experiments to test the truth of spontaneous generation were so exactly like those of Pasteur in the last century that the figures of Pasteur might be used to illustrate the memoirs of his predecessor.
The controversy concerning spontaneous generation continued in much the same state until 1859. During the previous years Pas teur had shown that putrefactive and fermentative changes in organic substances and especially in fluids were due to organisms. The question was as to the origin of the organisms. He was well aware of the controversy between Needham and Spallanzani, but took the side of Spallanzani. By 1859, the year of the publica tion of The Origin of Species, Pasteur was engaged in acute con troversy as to the origin of life. The matter was brought finally to a head by a very fine series of studies on the subject of spon taneous generation, the results of which Pasteur published in 186r.
Spallanzani, in his experiments, had heated phials, and he showed them containing putrescible substances. He was able to show that the contents of such phials remained indefinitely with out any sign of putrefaction or fermentation. These processes did not take place unless or until the phial was opened. The only effective criticism made on the experiments of Spallanzani was that by the process of heating he had altered not only the infusions themselves but also the air contained within the phial. To this Pasteur had his answer, and it was the most triumphant of his experiments. He introduced into a flask an infusion of ferment able fluid. The neck was then drawn out into a long S shape, nar rowed, but left open. The flask and its contents were then raised to boiling point repeatedly, and finally left at rest. The flask was left for days, weeks, months, undisturbed, and no fermentation took place. Finally, the neck was severed, thus exposing the fluid to the fall of atmospheric dust. In a few hours the liquid began to ferment, and organisms could be demonstrated under the microscope.
This is the critical experiment in a demonstration that there is no such thing, under present terrestrial conditions, as biogenesis. The issue has been raised in various forms at various times and by various observers, but experiments comparable to those of Pasteur have always been devised in rebuttal. So far as any biological doctrine can be said to be firmly established, it is the doctrine that all living things are the product of living things. It is manifest that this doctrine does not prejudge the question as to the first origin of life, nor does it prejudge the question as to whether life may have arisen at more than one date and in more than one place. It does, however, give to the biologist a concep tion of the nature of life comparable in its value as a standard of scientific research to the doctrine of the conservation of matter and of energy in the hands of the physicist. By a chance, the movements which led to this demonstration on the origin of life were almost exactly contemporaneous with the movement which led to the establishment of the doctrine of organic evolution. Thus the modern period of biology may be said to open in our era about the year 186°.
Change in the Biological Outlook to the Modern Stage.— The whole outlook on the nature of living things underwent a complete and profound change in the period of about 20 years following 1860. This change may be ascribed to a variety of causes, some of which we have been able to discuss. These we may now review categorically.
(a) The discovery of the essential identity in the mode of reproduction of animals and of plants.
(b) The discovery of the essential identity in the living sub stance of animals and of plants, and the emergence of the con ception of protoplasm.
(c) The examination of methods of nutrition and of respira tion, and the realization that these too are fundamentally the same for all living things.
(d) At first the differences of the food supply of animals and of plants seemed an insuperable barrier to this last step. Grad ually, however, there emerged the conception of the chlorophyll apparatus concerned with the manufacture of organic substance for nutrition of both animal and plant. The elaboration within the plant body, from atmospheric gases, of material for absorp tion into tissue came to be recognized as part of the mechanism of living nature as a whole. The view of the "balance of lite" and of organic nature as one huge mechanism came to the fore.
(e) The reduction of all living processes to terms of the cell.
(f) An evolutionary view of life gave a new conception of what may perhaps be called the "economics of nature." Thus there arose the tendency to examine the manner of life and habits of living things involving also their relations to other forms of living things.
(g) The conviction that, so far as scientific experience extends, all living things are derived from living things and are not gener ated from not-living things.
The combination of these conclusions and tendencies has intro duced so much alteration in the approach of biologists to the material with which they deal that we may speak of entering an entirely new era. During this new era much attention has been concentrated on genetics and the process of heredity. For long, under evolutionary influence, the subject of variation in animals and plants was intensively studied. It is, however, apparent that the real problem to be solved is why the offspring resembles, not why it differs from its parent. This is perhaps the main modern biological problem. It may be observed that Aristotle, the first biologist, most clearly visualized this very problem. In this con nection we may ascribe to Aristotle a most remarkable insight in his contention that the male contributes form only to the off spring and that nothing material need pass from male to female.
The study of Aristotle's expression of his views on this and allied topics will convince the investigator that throughout his writings he is in the presence of something far different from one of those cases of lucky prevision that are of frequent occurrence in the course of scientific development. A careful study of the texts of Aristotle and of the history of biology reveals him as one of the very greatest and most profound of all biologists. From his writings and from the thoughts enshrined therein, biologists will ever return with refreshment and stimulus. Biological science in its most modern dress has indeed begun to tread again the Aristotelian path. The different fragments into which biology has been rent, morphology, physiology, genetics, embryology, ecology, cannot concern themselves with living things as they are but only with abstractions and ideas of what parts of them are or might be. The great master of those who know sought in antiquity to set forth a science of life as a whole. The greatest of his modern disciples had still the same objective when he wrote The Origin of Species 2,200 years later. It may be that this aspiration toward a unified biology, a true science of life, is the real legacy of Aristotle and Darwin.
Historia animalium, translated by D'Arcy Wentworth Thompson (191o), De partibus animalium, translated by William Ogle (1912) , De generatione animalium, translated by Arthur Platt (191o) ; L. C. Miall, The Early Naturalists. Their Lives and Work (1912) ; W. A. Locy, Biology and its Makers (1908) • Julius von Sachs, History of Botany, 1530-1860, translated by H. E. F. Garnsey, revised by I. B. Balfour (1906) ; J. Reynolds Green, A History of Botany from 1830 (1914) ; Sir Michael Foster, Lectures on the History of Physiology (190I) ; Henri Daudin, Methodes de la Classification et Idee de Serie en Botanique et en Zoologie (1926), Les Classes Zoologiques (1926) ; Charles Darwin, Works and Life and Letters, also The Darwin-Wallace Celebration . . . by the Linnean Society of London (1908) also The Foundation of the Origin of Species, two Essays written in 1842 and 1844 edited by his son Francis Darwin (1909) ; Thomas Henry Huxley, Life and Letters (1900) • J. B. Lamarck, Zoological Philosophy translated, edited and expounded by Hugh Elliot (1914) ; Major General Sir Frederick Smith, The Early History of Veterinary Literature (1919-25) • E. Radl, The History of Biological Theory, translated by M. Hatfield (1928) ; C. Singer, Greek Biology and Greek Medicine (1921) , Studies in the History and Method of Science, vol. ii. (1920) . The Discovery of the Circulation of the Blood (1922), The Evolution of Anatomy (1925), Short History of Medicine (1928) ; Loins Pasteur, Oeuvres reunies (1922-27) ; William Bateson, Mendel's Principles of Hered ity (1909) ; Franz Carl Muller, Geschichte der Organischen Natur wissenschaften im Neunzehnten Jahrhundert (1902).
For full bibliography see the journals Mitteilungen zur Geschichte der Medizin and der Naturwissenschaften from 1902 and Isis from 1913. (C. Si.)