534 THE THEOEY OF ENERGY AND THE LIVING WORLD. 



tution of a substance, the active protoplasm, which attains a higher 

 degree of complexity, and whose formation consequently requires an 

 appreciable quantity of energy. Assimilation, in order to be realized, 

 requires the absorption of energy. Now at this same moment the 

 destruction or simplification of the reserve, in consequence of activity, 

 liberates energy which might be applied to this very purpose. If the 

 protoplasm does in reality make use of it its role would be the coun- 

 terpart of that of the reserves. But if it is uncertain whether the 

 active protoplasm behaves according to the view of Le Dantec, it is 

 certain that the reserves follow the law of Claude Bernard, and the 

 essential part in the energetic changes belongs to them. 



IV. 



The third principle of the energetics of biology is similarly the result 

 of experiment. It relates not only to the point of departure in the 

 cycle of animal energy but to its terms. 



It is here that the greatest novelty of the doctrine lies, and here we 

 may say that it is less understood by physiologists themselves. Energy 

 derived from the chemical potential of the aliment, after having trav- 

 ersed the organisms (or simply the organ which is considered to be in 

 action), and having given rise to more or less diversified phenomena 

 comprising the manifestations proper to, or in some cases still irreduci- 

 ble to, vitality, finally returns to the physical world. This return is 

 made (with some well-known exceptions) under the ultimate form of 

 thermal energy. 



The truly vital phenomena are therefore to be classed between the 

 chemical energy which gives birth to them, and the thermal phenomena 

 which they engender in their turn. The place of vital activity in the 

 cycle of universal energy is thus perfectly determined. This is a con- 

 clusion of the first importance for biology. We can express this 

 deduction in concise language as follows : Vital energy is ultimately 

 the transformation of chemical energy into heat. 



This assertion requires the condition that the animal contents himself 

 with merely living without performing external work. 



The founders of animal energetics, and especially M. Ohauveau, have 

 attempted to give more precision to this very vague conception, vital 

 energy. The same is true of it as of the ordinary physical forms of 

 energy. We know how to measure it without knowing what it is. 



Vital energy is that which accompanies the phenomena of the tissues, 

 and not actually identifiable with the known types of physical, chem- 

 ical, and mechanical energies. These actions are usually silent and 

 invisible of themselves, and only to be recognized by their effects after 

 the transformation into the familiar forms of energy. Vital energy is 

 that which acts, for instance;, in the muscle prepared for contraction, in 

 the nerve which conducts the nervous impulse, and in the glands during 

 secretion. What we call here provisionally the vital property, the 



