At other times, again, it is an electrical phenomenon which terminates the vital cycle, and it is, in fact, in this way that things happen in the functional activity of the nerves and muscles in all animals, and in the functional activity of the electrical organ in fish, such as the ray and the torpedo. Finally, the termination may be a photic phenomenon, and this is what happens in phosphorescent animals.
It is idle to diminish the power of these principles by proceeding to enumerate the whole of the exceptions to their validity. We know perfectly well that there are no absolute principles in nature. Let us say, then, that the energy which temporarily animates the living being is furnished to it by the external world under the exclusive form of potential chemical energy; but that, if there is only one door of entry, there are two exits. It may return to the external world in the principal form of thermal energy and in the accessory form of mechanical energy.
§ 2. MEASUREMENT OF THE SUPPLY OF
ALIMENTARY ENERGY.
Calorimetric Method.—From what has preceded it is clear that if the energetic flux which circulates through the animal emerges, in toto, in the state of heat, the measurement of this heat becomes the
- [Footnote: to do excessive work. The unit of heat, the Calorie, is equivalent
to 425 units of work—i.e., to 425 kilogrammetres. In the animal at rest, the number of kilogrammetres representing the different quantities of work done is small, the number of corresponding Calories is 425 times smaller. It becomes almost negligeable in comparison with the considerable number of Calories dissipated in the form of heat.]
