THE PHYSIOLOGY OF ALIMENTATION. 539 



sicians who have attempted to define au aliment have, faded. Most of 

 the definitions, both common and learned, have interposed the condi- 

 tion that the substance should be introduced through the digestive 

 apparatus. These definitions summarily exclude from the class of 

 beings sustained by alimentation all vegetables and animals not pro- 

 vided with an intestinal canal; and they leave out various substances 

 which enter the body through other channels than the stomach, which, 

 like the oxygen for example, participate to a large degree in the sus- 

 taining of life. 



The distinctive feature of the aliment is the use that it maybe, when 

 rightly employed, to the living creature. It is a substance necessary 

 to the maintenance of the phenomena of living organisms, and the 

 reparation of losses to which they are subjected, says CI. Bernard — a 

 substance which carries an element essential to the constitution of the 

 organism or which diminishes its disintegration (conserving aliment), 

 according to the German physiologist Voit — a substance which con- 

 tributes to assure the good operation of any of the organs of a living 

 being, following the much too broad definition of Duclaux. All these 

 characterizations, however, give but au imperfect idea of it. 



The introduction of the idea of energy into physiology has given a 

 better understanding of the true nature of the aliment. It is neces- 

 sary to recur to the doctrine of energetics to take into account all that 

 the organism requires it to furnish. The organism demands not only 

 matter but energy. The naturalists consider only the necessity of con- 

 tributing matter, and thus look upon the problem from only one point 

 of view. The living body presents in each of these directions an unin- 

 terrupted succession of tearing down and rebuilding, the materials for 

 which are furnished by alimentation and rejected by excretion. Cuvier 

 called this incessant passage of surrounding matter into and through 

 the vital world the "vital vortex," and regarded it with reason as the 

 characteristic of nutrition, and the distinctive trait of life. 



This idea of the circulation of matter has been completed in our own 

 time by that of the circulation of energy. All the phenomena of the 

 universe, and more especially those of life, are conceived as changes of 

 energy. They are now regarded in connection with their environment 

 rather than in isolation as formerly. Each has an antecedent and a 

 consequent whose magnitude is determined by a numerical law of 

 equivalence established by the contemporary physics. Thus the suc- 

 cession of events is conceived as the circulation of a sort of indestructi- 

 ble agent, which changes only in appearance or disguise in passing on, 

 but which suffers no loss; and this is energy. 



The most general result of the study of physiological chemistry has 

 been to teach us that the antecedent of the vital phenomenon is always 

 chemical. 1 Vital energy originates in the potential chemical energy 



1 See the discussion of the subject on previous pages of this paper. 



