540 THE PHYSIOLOGY OP ALIMENTATION. 



accumulated in tlie material of which the organism is composed. The 

 phenomenon consequent to the expenditure of vital energy is usually 

 the production of heat. Vital energy is transformed into thermal 

 energy. These three propositions relating to the nature, origin, and 

 termination of the vital phenomena are the three fundamental princi- 

 ples, the three laws, of the energetics of biology. 



The place of vital energy in the universal classification of energy is, 

 from what has been said, perfectly determined. It belongs between 

 chemical energy, from which it springs, and thermal energy, into which 

 it is resolved, and which is the " degraded form " of energy, to use the 

 expression of physicists. From this follows a deduction of immediate 

 application in the theory of the aliment. Heat is an excretum of the 

 dynamic order from the living being, quite as much as urea, carbonic 

 acid, and water are excreta of the material order. It is therefore quite 

 incorrect to speak of the transformation of heat into vital energy in 

 the animal organism, although this expression is in common use. Nor 

 is it more proper to speak of the transformation of heat into muscular 

 motion, as was held by Beclarcl, or into animal electricity, as has been 

 maintained by other writers. These are errors of doctrine as well as of 

 fact. They imply a false interpretation of the principle of the mechan- 

 ical equivalence of heat, and the misunderstanding of Carnot's principle. 

 Thermal energy does not ascend the energetic scale in the process of 

 vital phenomena. Heat never transforms itself; it is simply dissipated. 



Is this the same as saying that heat is not essential to life? Far 

 from it, for it is most necessary. But the function of heat is a peculiar 

 one which should neither be misunderstood nor exaggerated. It is not 

 transformed- by chemical or vital reactions, but merely helps to create 

 the proper conditions for such reactions. 



According to the first principles of energetics, in order that vital 

 energy should be derived from thermal energy it is necessary for the 

 latter first to be converted into chemical energy, since that is the form 

 antecedent to and productive of vital energy. Now this retrograde 

 transformation is impossible according to the received doctrines of gen- 

 eral physics. The role of heat in the act of chemical combination is 

 merely to aid the reaction, to put the reacting substances in such con- 

 dition as regards temperature that the chemical forces are at liberty to 

 exert themselves. For example, in the union of oxygen and hydrogen 

 by igniting an explosive mixture of these gases, the heat merely pro- 

 motes the phenomenon. The two gases are indifferent to each other at 

 ordinary temperatures, and require to be raised to a temperature oi 

 about 400° in order to put in play the chemical affinity between them. 

 It is in a similar way that reactions are promoted in an organism. They 

 have a most favorable temperature which it is the role of animal heat 

 to furnish. 



Thus we have shown that heat enters into the conditions of animal 

 life in two ways; First as an excretum the product of animal activity, 



