130 LIFE AND DEATH. 



two divergent branches, the one thermal and the 

 other mechanical, external the one to the other 

 although both issuing from the same common trunk, 

 and having between them no relation but this, that 

 the sum of their discharges represents the total of the 

 energy in motion. Let us now translate these very 

 simple notions into the more or less barbarous jargon 

 in use in physiology. We shall be convinced as we 

 go on of the truth of the saying of Buffon, that " the 

 language of science is more difficult to learn than the 

 science itself" We shall say, then, thfft chemical 

 energy, that the unit of weight of the food which may 

 be placed in the organism, constitutes the alimentary 

 potential, the energetic value of this substance, its 

 dynainogenic power. It is measured in units of heat, 

 in Calories, which the substance may leave in the 

 organism. The evaluation is made according to the 

 principles of thermo-chemistry, by means of the 

 numerical tables of Berthelot, Rubner, and Stohmann. 

 The same number also expresses the thermogenic 

 power, virtual or theoretical, of the alimentary sub- 

 stance. This energy being destined to be transformed 

 into vital energies (Chauveau's physiological work, 

 physiological energy), the dynamogenic or thermogenic 

 value of the food is at the same time its biogenetic 

 value. Two weights of different foods which supply 

 the organism with the same number of Calories, — i.e. 

 for which these numerical values are the same, — will be 

 called isodynamic or isodynamogenic, isobiogenetic, iso- 

 energetic weights. They will be equivalent from the 

 point of view of their alimentary value. And finally, 

 if, as is usually the case, the cycle of energy ends in 

 the production of heat, the food which has been 

 utilized for this purpose has a real thermogenic value, 



