The laws of biological energetics are three in number. First of all, there is the fundamental principle which we have just developed, and which is, so to speak, laid down a priori; and there are two other principles, those established by experiment and summing-up, as it were, the multitude of known physiological effects. Of these two experimental laws, one refers to the origin and the other to the termination of the energies developed in living beings.
§ 3. Second Law of Biological Energetics.
The Origin of Vital Energy.—Vital energies have
their origin in one of the external or common energies—not
in any one we choose, as might be supposed,
but in one only: chemical energy. The third principle
will show us that they terminate in another energy or
a few others, also completely fixed.
It follows that the phenomena of life must appear to us to be a circulation of energy which, starting from one fixed point in the physical world, returns to that world by a few points, also fixed, after a transient passage through the animal organism.
Or more precisely, it is a transposition from the realm of matter into the world of energy, of the idea of the vital vortex of Cuvier and the biologists. They defined life by its most constant property—nutrition. Nutrition was exactly this current of matter which the organism obtains from without by alimentation, and which it throws out again by excretion; and the even momentary interruption of which, if complete, would be the signal of death. The cycle of energy is the exact counterpart of this cycle of matter.
