ABSTRACT
65. The Materials.—We have first to consider the structure of the matter which constitutes the organs of all living machines. Man and animal do not differ one from the other as to the properties of that matter. But it must be said, first of all, that animated substance or protoplasm does not possess any constant and perfectly defined property; its elementary chemical carbonic, hydrogeneous, oxygeneous, and azotic composition varies very little, its physical characteristics evolve slowly and in a determined direction. As a rule, it hardens with age, it fixes and produces solid elements, minerals, from which it forms new material or tissue.
