548 THE PHYSIOLOGY OF ALIMENTATION. 



seems, take the place of heating from within. Oiie could cherish the 

 ambition of substituting for rations of sugar and fat an isodynamic 

 quantity of carbon, used to nourish the man at the same time that it 

 suitably warmed his apartment. 



In reality the aliment has another office to perform than to warm the 

 body or even furnish it with energy. It should not be forgotten that 

 the organism requires a supply of matter as well as a supply of energy. 

 It must have a proper quantity of certain definite principles, both 

 organic and mineral. These principles are evidently for the purpose 

 of replacing the substances carried out in the circulation of matter, 

 and to reconstruct the organic material. Such aliments may be called 

 histogenetic (repairers of tissues) or plastic aliments. 



This was the view of alimentation taken by the ancients. Hippoc- 

 rates, Aristotle, and Galen believed in the existence of a special 

 nutritive substance existing in all the infinite variety of substances 

 employed for nourishment by men and animals. It was not until the 

 time of Lavoisier that the idea of the dynamogenic and thermal value 

 of the aliment was conceived. The combined view of these two species 

 of attributes and their accurate distinction is due to J. Liebig, who 

 designated them as plastic and dynamogenic aliments. He held also 

 that the same substance might serve in both these roles, and this he 

 thought to be the case with the albuminoids. 



The elder Magendie, in 1836, had introduced, in an interminable list 

 of aliments, a preliminary division into proteid substances (now called 

 albuminoids, nitrogenous and quarternary substances) and terniary 

 substances. 



The proteids are capable of alone sustaining life. Preponderating 

 importance should be attributed to this class of aliments. These results 

 of Magendie have been since verified. Pfliiger, of Bonn, has given a 

 convincing demonstration of them within a year. He nourished, worked, 

 and finally fattened a dog upon meat alone. The same experiment 

 showed that the organism can form fat and carbohydrates at the 

 expense of nitrogenous aliments, and can transform the one class of 

 substances into the other. Fats and carbohydrates are therefore not 

 essential, the albuminoids alone being indispensable. Theoretically 

 man and animals may sustain life exclusive of proteid aliments, but 

 practically this is not possible for man because of the enormous quan- 

 tity of meat (3 kilos per day) which he ought properly to use. 



Ordinary alimentation employs a mixture of these three kinds of 

 substances, and in this mixture the albumen contains the plastic ele- 

 ment actually necessary to repair the waste of the organism. The two 

 other kinds carry the required energy. In such mixed diets the quan- 

 tity of albumen ought never to fall below a certain minimum. The 

 efforts of physiologists in the last few years have tended to fix with 



