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 than those of other organs. The inadequacy of these explanations suggested the idea of completing them by the aid of the chemistry which was then springing into being. This chemistry, rudimentary as it was, longed for a share in the government of living bodies and in the explanation of their phenomena. Distillations, fermentations, and effervescences are now seen to play their rôle, a rôle which was premature and carried to excess. Iatro-chemistry from the general point of view is only an aspect of iatro-mechanics; but it is also an auxiliary. Sylvius le Boë and Willis were its most eminent representatives. This theory remained in the background until chemistry made its great advance—that is to say, in the days of Lavoisier. After that, its importance has gradually increased, particularly in the present day. Nowadays, the general tendency is to regard the organic functional activity, or even morphogeny—i.e., whatever there is that is most peculiar to and characteristic of living beings—as a consequence of the chemical composition of their substance. This is a point of capital importance, and to it we must recur.

The Physico-chemical Theory of Life.—Contemporary biological schools have made many efforts to secure themselves from any slips on the philosophical side. They have avoided in most cases the psychological problem; they have deliberately refrained from penetrating into the world of the soul. Hence, ''the physico-chemical theory'' of life has been built up free from spiritualistic difficulties and objections. But this prudence did not exclude the tendency. And there is no doubt, as Armand Gautier said, that "real science can affirm nothing, but it also can deny nothing outside observable facts;" and again, that