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230 CHARLES S. MYERS: Miiller, dawned the present age of patient investigation and physiological experiment. While Vitalism was still at its height, Johannes Miiller, the father of modern physiology, began his monumental work of collecting the past writings on his subject with an ability and a thoroughness the like of which had not been employed since the days of Haller. Calling to his aid, as it has been said, not one but every method of research, Miiller next endeavoured to sum up his laborious inquiries into the nature of life in a far-reaching vitalistic theory. His opinions certainly changed as years passed by ; but throughout his life Miiller seems to have argued that, since to him no difference was manifest between the elementary composition of living and recently dead bodies, a principle, having "the nature of force rather than of imponderable matter " must necessarily be introduced to explain this want of difference. By further reasoning, Miiller inferred that all matter contained in a latent state both the vital and mental principles. Nevertheless he intended to explain life by mechanical principles, for to his mind vital force followed the lines of physical and chemical forces, however different it might be from these forces themselves (4). While in England Sharpey (a pupil, like Miiller, of Eudolphi), Bowman and Goodsir were pursuing their anatomical investigations, in Germany Schleiden, followed in 1839 by Schwann, proclaimed a new biological unit the cell. Naturally carried away by the importance of his dis- covery, Schwann was led to look on growth as a kind of crystallisation-process in the cell, and to give a quasi- mechanical explanation of vital phenomena, diametrically opposed to the vitalism of his time. These views were vigorously denounced by E. H. Weber and by Virchow. But one of the most fatal blows (5) to the dying conception of the vital principle was now given in 1845 by J. Eobert Mayer, who introduced the far-reaching conception of the indestructibility of force. In 1859 the first edition of Darwin's Origin of Species was published. This rapid succession of revolutionary discoveries made a reaction towards mechanism clearly imminent. J. K. Mayer in 1845 and E. W. Weber in 1858 maintained the move- ments of a living as of a lifeless body to be dependent on forces acting on it from without. Weber's pupil, Carl Ludwig, and Miiller's school of rising physiologists in 1847 banded themselves together for an avowed " Befreiungswerk aus dem Vitalismus" . A few remained, like Liebig, Wagner and Lotze, to assert the existence of a special vital principle,