The properties which differentiate living matter from any kind of inorganic imitation may be instinctively felt, but can hardly be formulated without expert knowledge. The differences between a growing organism and a growing crystal are many and various, but it must suffice here to specify the simplest and most familiar sort of difference; and as it is convenient to take a possibly controversial statement of this kind from the writings of a physiologist, I quote here a passage from an article by Professor Fraser Harris, of Halifax, Nova Scotia, in the current number of the quarterly magazine called _Science Progress_ edited by Sir Ronald Ross-- "Living animal bioplasm has the power of growing, that is of assimilating matter in most cases chemically quite unlike that of its own constitution. Now this is a remarkable power, not in the least degree shared by non-living matter. Its very familiarity has blinded us to its uniqueness as a chemical phenomenon. The mere fact that a man eating beef, bird, fish, lobster, sugar, fat, and innumerable other things can transform these into human bioplasm, something chemically very different even from that of them which most resembles human tissue, is one of the most extraordinary facts in animal physiology. A crystal growing in a solution is not only not analogous to this process, it is in the sharpest possible contrast with it. The crystal grows only in the sense that it increases in bulk by accretions to its exterior, and only does that by being immersed in a solution of the same material as its own substance. It takes up to itself only material which is already similar to itself; this is not assimilation, it is merely incorporation. * * * * * "The term 'growth,' strictly speaking, can be applied only to metabolism in the immature or convalescent organism. The healthy adult is not 'growing' in this sense; when of constant weight he is adding neither to his stature nor his girth, and yet he is assimilating as truly as ever he did. Put more technically: in the adult of stationary weight, anabolism is quantitatively equal to katabolism, whereas in the truly growing organism anabolism is prevailing over katabolism; and reversely in the wasting of an organism or in senile decay, katabolism is prevailing over anabolism. The crystal in its solution offers no analogies with the adult or the senile states--but these are of the very essence of the life of an organism....