THE PHYSIOLOGY OF ALIMENTATION. 543 



deduce the explanation of the most intricate and disputed phenomena 

 of nutrition as the consequence of three simple laws. 



Examples abound of the fecundity and innate power of these ideas. 

 To illustrate by a single point, take the long-cherished error of physi- 

 ologists who believed with Beclard, in the transformation within the 

 organism of heat into mechanical work. After the establishment of the 

 doctrine of energy this error was no longer possible. Energetics teaches 

 us that the current of energy divides itself in leaving the body into two 

 divergent branches, one thermal and the other mechanical, which are 

 strangers to each other though springing from a common source, and 

 have no other relation in common except, that in summation, they rep- 

 resent the total energy of life. 



We will now clothe these simple ideas in words more or less foreign 

 to the usage of physiology; and in so doing, we are convinced, to use 

 the words of Buffon, that "the language of science is more difficult to 

 comprehend than science itself." The amount of chemical energy which 

 a unit weight of a given aliment is able to furnish to an organism, and 

 which may be evaluated according to the principles of thermo-chemis- 

 try by the aid of the numerical tables of Berthelot, Rubner, and Stoh- 

 mann, constitutes the alimentary potential, or energetic value of the 

 substance, or in still other words, its dynamogenic power. The same 

 number expresses also the thermogenic power, actual or theoretical, of 

 the alimentary substance. This energy being destined to be trans- 

 formed into vital energy (termed physiological work by Chauveau, or 

 physiological energy) the dynamogenic and thermogenic value of the 

 aliment is at the same time its biogenetic value. Two weights of dif- 

 ferent aliments for which these numerical values are the same are said 

 to be isodynamogenic, isobiogenetic, or isoenergetic weights. They are 

 equivalent from the point of view of their alimentary value. Finally if, 

 as is usually the case, the cycle of energy is finished by the production 

 of heat, the aliment which has been used for this purpose has a real 

 thermogenic value identical with its theoretical thermogenic value as 

 may be experimentally determined by direct calorimetry. 



in. 



The aliment is a source of thermal energy for the organism by which 

 it is decomposed. Physiological chemistry teaches us that whatever 

 be the method of its decomposition, it always finally reaches the same 

 condition, and with the evolution of the same quantity of heat. But 

 if the point of departure and the point of destination are the same, 

 the route followed is not necessarily identical. For example, 1 gram 

 of fat always furnishes the same quantity of heat, 9.4 calories, and is 

 always rejected in the same condition of carbonic acid and water. But 

 from the state of fat to that of a mixture of carbonic acid and water 

 there are many intermediate conditions. Various alimentary cycles 

 are therefore possible., 



