energic contents of the original material, until finally—at least, with carbohydrates and fats—the whole amount of contained energy is released. The cell regulates its own metabolism down to the minutest details. In the proper preparation of the material to be decomposed, and in the gradual liberation of the amount of energy required, lies the real importance of those substances formed by the cell, which we at present comprise under the name of ferments.
The ferments have yet another value for the cell, in that they help it to regulate its own structure. Not every product which is taken up by the cell passes into its structure. Sometimes the decomposition must be carried on further; in other cases the particles must be synthesized suitably for the production of the necessary structural unit; after which it sets about the recombination of all the numerous constructive units, so as to form the complicated characteristic structure of the cell. Though we do not yet know the precise nature of the ferments, yet their specific activities, and their great importance in regard to cell metabolism and cell structure, are well known.
Without energy no cell can do work or produce heat, and it is in energic metabolism that we find a true picture of the functions of the cell. How the cell procures the required energy, in what manner it makes use of it, and so on, we can learn only by
