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muscles, the latter being thereby filled out as a glove when one blows into it. This tendency to regard the organism as a machine was also fostered by the rapid advances made in physics and chemistry diuing the eighteenth century and the earlier part of the nine- teenth, as well as by the progress in anatomical re- search of the Italian schools, and even by the dis- coveries of such men as Harvey, Malpighi, and Bishop Stensen. The earlier crude mechanical conceptions were, however, constantly met by criticism from men like Stahl. If the advance of science seemed to ex- plain some problems, it also showed that life-phenom- ena were not so simple as had been supposed. Thus Lyonet's work on the goat-moth revealed such a mi« croscopic complexity that it was at first received with incredulity.

Stahl (1660-1734) himself advocated an exagger- ated form of vitalism. Rejecting the mechamcal theories of the Cartesian School, he taught that life has its source in a vital force which is identical with the rational soul in man. It is conceived as constructor of the body, exerting and directing the vital processes in a subconscious but instinctively intelligent manner by what he calls X670S in contrast with \oyLffijM, whilst it rather inhabits than informs the body. Oth- ers separated the vital force from the sentient soul and adopted ''didynamism". Notwithstanding the growth of materialism, vitalism achieved considerable success during the second half of the eighteenth cen- tury. It was, however, mostlv of a vague and incon- sistent charact<5r tinged with Cartesian dualism. The entity by which the organic processes were regulated was generally conceived as a tertium quid between soul and body, or as an ensemble of the vital forces in an- tagonism and conflict with those of inanimate matter. Tms was substantially the view held by the Mont-

Ejllier school (e. g. Barthez, B^rard, Lordat) and by ichat. Even to men like Cuvier life was simply a tourbiUon, a vortex, a peculiar kind of chemical gnroscope. The Bildungstrieb or nisus fonnativus of Blumenoach (1752-1840), who judiciously profited by the work of his predecessors, exhibits an improve- ment; but succeeding vitalists still showed the same want of philosophic grasp and scientific precision. Even a physiologist of the rank of Claude Bernard was constantly wavering between une idie creatrice — whatever that may mean — and une sorte de force /<*- gislatiye mais nuUemeni exi^cutive, and the meclianical organism of Descartes. Von Baer, Treviranus, and J. Mailer favoured a mild kind of vitalism. Lotze here, as in his general philosophy, manifests a twofold tendency to t-eleological idealism and to mechanical realism. The latter, however, seems to prevail in his view as to the nature of vegetative life. The second and third quarters of the nineteenth century witnessed a strong anti-vitalist reaction: a materialistic meta- physic succeeded the idealistic Identilatfiphiloaophie, Even the crude matter-and-motion theories of Mole- schott, Vogt, and Biichner gained a wide vogue in Germany, whilst Tyndall and Huxley represented pop- ular science philosophy in England and enjoyed con- siderable success in America.

The advent of Darwinism, too, turned men's minds to " phyjpgeny ", and biologists were busy establishing genetic relationships and tracing back the infiniU varietv of living types to the lowly root of the genea* logical tree. To such men life was little better than the movements of a complicated congeries of atoms, evolved from some sort of primitive protoplasmic nebula. The continuous rapia advance both of phys- ics and chemistry flattered the hope that a complete "explanation" of vital processes was at hand. The successful syntheses of organic chemistry and the es- tablishment of the law of the conservation of energy in the first half of the nineteenth century were pro- claimed as the final triumph of mechanism. Ludwig, Helmholtz, Huxley, Hftckel, and others brought out

new and improved editions of the seventeenth-centuiy machine view of life. . All physiology was reduced to processes of filtration, osmosis, and diffusion, plus chemical reactions. But with the further advance of biological research, especially from about the third c^^uarter of the last century, there be^an to find expres- sion among many investigators an mcreaaing convic- tion that though physico-chemistiy might shed light on sundry stages and operations of vitcu processes, it always left an irreducible factor unexplamed. Phe- nomena like the healing of a wound and even regular functions like the behaviour of a secreting cell, or the ventilating of the lungs, when closely studied, did not after all prove so completely amenable to physical treatment. But the insufiSciency of physico-chem- istry became especially apparent in a new and most promising branch of biolc^cal research, — experimen- tal morphology, or as one of its most distinguished founders, W. Roux, has called it, Entwicklungsm^ chanik. The embryological problem of individualistio development had not been adequately studied by the older vitalists — ^the microscope nad not reached any- thing like its present perfection — and this was one main cause of their failure. The premature success of the evolution theory too, had led to a blind, un- questioning faith in *' heredity", "variation", and "natural selection", as the final solvents of all difiS- culties, and the full significance had not yet been realized of what Wilson styles " the key to all ultimate biological problems" — ^the lesson of the cell. Recent investigation in this field and better knowledge of morphogenesis have revealed new featiures of life which have conduced much towards a widespread neo- vitalistic reaction.

Among the chief of these has been the increased proof of the doctrine of epigenesis. Already in the eighteenth century embryologists were sharply divided as to the development of the individual organism. According to the advocates of preformation or pre- delineatwti, the growth of the embryo was merely the expansion or evolution of a miniature organism. This theory was held by ovulista like Swanunerdam, Malpighi, Bonnet, and ^allanzani, and by animalcu- lists like I^eeuwenhoek, Hartsoeker, and Leibniz. In this view the future organism pre-existed in the prim- itive germ-oviun or spernmtazoon, as the flower m the bud. Development is a mere " unfolding ", analogous to the unrolling of a compressed pocket-liandkercnief. Though not quite so crude as these early notions, the views of men like Weismann are really reducible to preformation. Indeed the logical outcome of all such theories is the "encasement" of all succeeding genera- tions within the first germ-cell of the race. The oppo- site doctrine of "epigenesis", viz., that the develop- ment of the embrj'o is real successive production of visible manifoldness, real construction of new parts, goes back to Aristotle. It was upheld by Harvey, Stahl, BuiTon, and Bliunenbach. It was also advo- cated by the distinguished Douai priest, J. Turber- ville Needham (1713-1781), who achieved distinction in so many branches of science. In its modern form 0. Hertwig and Driesch have l)een amongst its noost distinguished defenders. With some limitations J. Reinke may also l>e classed with the same school, though his system of "dominants" is not easy to reo- conrile with unity of form in the living being and leaves liim what Driesch styles a "problematic vitalist". The modern theory of epigenesis, however, in the form defended, e. k. by Driesch, is probably not incompati- ble with the hypothesis of prelocalized areas of specific cytoplasmic stuffs in the body of the germ-cells, as recently advocated by Conklin and Wilson. But anyhow the nio<lem theory of pre-delineation de- mands a regulating fonnative power in the Mnbyro just as necessarily as the epigenctic doctrine. More- over, in addition to the difficulty of epigenesis, the in- adequacy of mechanistic theories to account for the