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VITALISM : A BRIEF HISTORICAL AND CRITICAL REVIEW. 321 of consciousness derived from a falling body differ from those arising from an equivalent amount of heat. In the physical world the states of consciousness derived from heat, light, electricity and magnetism are commonly ex- pressed in those derived from matter and motion. The same aim directs the attempts of psychology to give a like rendering to the states of consciousness derived from psychic activity. To posit several forms of activity in terms of one other form is to describe, not to give an ultimate explanation. To do this and to determine the relation between such various forms of activity are the sole aims of Natural Science. By similar arguments may be met the complaint of the vitalist that after the properties of life have been described in terms of matter and motion after the entire phenomenal world has been expressed in vast mathematical equations no nearer approach will have been made by Natural Science to a solution of the world-riddle (17). It will be interesting briefly to consider in this place a few of the attempts which have been made to span the gulf between ultimate and scientific explanation. Here as every- where the human intellect has shown its eagerness to buckle on the brilliant wings of speculation and to soar, heedless and unrestrained, beyond the restraining power of experi- ment and observation ; until, Icarus-like, it is compelled to descend to its proper level before the fierce glare of logic and verification. Various ages have seen sporadic attempts to combine under one comprehensive system the contradictions of materialism and spiritualism. Emanating from Mauper- tius and Kobinet, and elaborated within recent years by Clifford, v. Nageli, Cams and others, these efforts have cul- minated in a Monism, which essentially teaches that all matter is endowed to a varying degree with mind and that matter and mind are the two sides of some one thing, unknown and unknowable (18, 19). A similar conception has been applied to the nature of life itself. It has been urged either that inert matter is animated with something " which is not life but which may develop into life," or, as Glisson once said, " Materiam non esse tantuin naturae vitalis capacem sed et actu vivam ". The absurdity of the view that an inherent vitality is spread through the universe becomes sufficiently evident, if " life " be for the moment viewed objectively as a group of definite sense-impressions. With equal reason might the elements of the smell of ammonia be accorded to a mixture of nitrogen and hydrogen, although it is clear that neither of the constituents of ammonia can contain in itself that 21