for receiving the human soul, which carries matter successively through the lower gradations up to its highest known structure under the actuation of successive provisional forms" (Metaphysics of the School, Vol. II, p. 551). Hence the teachings of St. Thomas are wholly repugnant to the radical doctrines of extreme evolutionism. Before proceeding to investigate the bearing upon living bodies of the theory of matter and form as the constituent essential elements of material substance, it were well to state that, far from trespassing on the ground of the chemist and physicist, it seeks to ascertain what are the constituents of the atom of the one and the element of the other. Nay, it is the only theory that accounts for the impossibility of physical division of the atom ad infinitum, "because," to quote St. Thomas, "every species postulates a determinate quantity, in regard of its increase as of its decrease"; otherwise the matter is not disposed for the reception of the form.
Although the bearings of this theory on inorganic bodies are worthy of careful consideration, yet its application to living beings furnishes a still more interesting theme. The Schoolmen, following Aristotle, have defined a soul or life principle to be "the first act of a physical organic body suitably disposed for life." It is, therefore, the substantial form of every living material substance, man included. The Angelic Doctor distinguishes various gradations of substantial forms. "We find," he says, "certain lowest forms which are capable of no operation, save that to which those qualities attain which are dispositions of matter. . . . Hence, these forms are altogether material, and totally immersed in matter. Above these we find the forms of mixed bodies, which, albeit they do not extend to any operations that cannot be effected by virtue of the aforesaid qualities, nevertheless sometimes operate these effects by a higher bodily virtue. . . . Above these, again, we discover some forms whose operations are extended to certain effects that exceed the virtue of the aforesaid qualities; though the aforesaid organic qualities assist in the operation of these forms. Such are the souls of plants. . . . Above these
