METABOLISM 169 



equilibrium is considerably more than the amount of proteid 

 decomposed during starvation. If an animal takes up just 

 as much proteid as it decomposes during starvation, nitroge- 

 nous equilibrium is not obtained, but the animal decomposes, 

 in addition to the food proteid, some of its body proteid. 

 The more proteid is given in its food, the less body proteid 

 will be used, and when about two and one half times as 

 much proteid is fed as is decomposed during starvation, 

 nitrogenous equilibrium is obtained. 



The facts derived from the study of metabolism during 

 pure proteid feeding establish the following laws: 



1. Within certain limits the body can maintain nitroge- 

 nous equilibrium with any amount of food proteid. 



2. Increase in food proteid also increases the consumption 

 of proteids. 



This increase in proteid consumption has been regarded as 

 " Luxus-consumption, " but it is not without beneficial effect, for 

 by it the power of the body is increased. 



2. Effect of fats and carbohydrates on metabolism. If a 

 person fed on a mixed diet (proteids, fats, carbohydrates, 

 water, and salts) and brought to a condition of nutritive 

 equilibrium is supplied with an increased amount of non- 

 nitrogenous foods (fats and carbohydrates), the amount of 

 non-nitrogenous material consumed in the body is increased, 

 but the consumption of proteids is decreased to an extent 

 expressed by the law of isodynamics (see page 117). 

 Hence, in reality, no general increase of combustion in the 

 body will take place. Fats and carbohydrates therefore 

 shield the proteids, and the proteid is stored up in the body 

 as flesh. If there is still more fat or carbohydrate present 

 in the food, these are stored up in the body, chiefly in the 

 form of fat. 



As far as their influence upon the extent of metabolism is 

 concerned, there is no real difference between fats and carbo- 

 hydrates, but the carbohydrates are more easily oxidized and 

 shield the proteids better than fats. In general, they can 

 replace each other according to the law of isodynamics. 



