[10] The reason is to be found in the large number of indeterminates in the problem we have to solve. It will be sufficient to enumerate them: the two substances which exist in the anatomical element, protoplasm and reserve-stuff, to which are attributed contrary roles; the two conditions attributable to the protoplasm, of manifested or latent activity; the faculty possessed by both of being prolonged for an indeterminate period, and of encroaching each on its protagonist when its existence is at stake. Here are more elements than are necessary to explain the positive or negative results of all the experiments in the world. The only favourable argument (not demonstrative) is furnished by energetics. It is this. The _re-building of the protoplasm_ is not like the _organisation of reserve-stuff_, a slightly complicated or even simplified phenomenon, as happens in the case of the reserve of muscular glycogen. The glycogen, in fact, is built up at the expense of foods chemically more complex. It is, on the contrary, a clearly synthetic phenomenon, certainly of chemical complexity, since it ends in building up the active protoplasm which is, in some measure, of the highest scale of complexity. Its formation at the expense of the simplest alimentary materials requires, therefore, an appreciable quantity of energy. The assimilation which organizes the active protoplasm therefore requires energy for its realization. Now, at the moment of functional activity, and by a necessary consequence thereof, the chemical destruction or simplification of the substance of reserve takes place. Here is something that meets the case, and we may note the coincidence. It does not mean that the disposable energy is really used to increase the protoplasm, nor that the protoplasm itself is thereby increased. It merely signifies that the wherewithal exists to provide for that increase if it takes place. It is therefore _possible_ that the active protoplasm follows the law of functional assimilation; but it is _certain_ that the reserve-stuff follows the law laid down by Claude Bernard. All these considerations definitely result in the confirmation of this second law of general physiology, according to which all vital energies are borrowed from the potential chemical energy of the reserve-stuff of alimentary origin. § 4. THE THIRD LAW OF BIOLOGICAL ENERGETICS. The third law of biological energetics is also drawn from experiment. It relates no longer to the point of departure of the cycle of animal energy, but to its final position. _The energetic transformations of the animal end in thermal energy._