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228 CHARLES S. MYERS : has formed the souls of animals which are and remain merely modi materia and therein contrast with the true substance of the human soul. A still bolder challenge to the growing iatromechanical schools was made by Gottfried Wilhelm Leibnitz (1646- 1676), who endeavoured to overthrow the strictures of Cartesian dualism by endowing every particle of matter with an active immaterial force the monad. He supposed that central monads ruled over subsidiary monads, and that in the living body the central monad was the soul. He denied that the soul knew all its actions and maintained the indestructibility and evolution of monads, ascribing the interaction of soul and matter to a pre-established harmony. This conception of pre-established harmony was actively combated by Georg Ernst Stahl (1660-1734), the last famous champion of modern Animism. His system, foreshadowed in some manner by the versatile Frenchman, Claude Perrault (1613-1688), rapidly won over many adherents. He owed his professorial chair at Halle to Friedrich Hoffmann (1660- 1742), to refute whose widely spread iatromechanical doc- trines he devoted his life. Stahl taught that the body lives only for the soul which directly shapes it for its own ends, and that the soul, ignorant of many of its purposeful and rational actions because of the limitations of consciousness and memory, is the source of all mental and bodily activity, perpetually fighting against that onrush of physical and chemical activities which betokens death. The bitter controversies which took place between the followers of Stahl and those of Borelli, Sylvius and Boer- have, brought home the conclusion that experiment alone contained the key to the mystery of life's nature. Thus physiology, which had received its first recognition at the hands of Galen and had again been prominently advocated by Harvey, at length obtained its lawful place during the first half of the last century. From Haller (1708-1777) dates the final establishment of experimental biology. The collection of isolated theories and long-forgotten discoveries within his Elementa Physiologies Corporis Humani, his own researches on the nature of irritability, and his contribution to the rival theories of epigenesis and evolution, all mark the dawn of a new epoch. Once more came about a decentralisation of the vital principle. For the researches, which first suggested by Glisson were extended by Haller, and subsequently by Cullen, John Brown, Broussais, Fleming and others, into the irritability of muscle and the sensibility of nerve, had a