METABOLISM AND FOOD 61 



Loss ( - ) or gain ( + ) of tissue. 

 Daily Food. Flesh. Fat. 



Fasting . . - 165 gr. . . -95 gr. 

 500 gr. flesh . - 99 gr. . . - 47 gr. 

 1000 gr. flesh . 79 gr. . . 19 gr. 

 1500 gr. flesh . o gr. . . + 4 g r - 



Thus it is seen that the loss of body protein, or 

 body fat, is smaller the larger the amount of protein 

 in the food. When the daily supply of flesh reached 

 1500 gr. the body did not require to provide any 

 protein, and a condition of "protein," or "nitrogen 

 equilibrium," was established. The proteins of the 

 food are, therefore, able to protect the body proteins 

 from consumption. Exactly the same results are 

 obtained when the animal is fed with artificially 

 prepared peptone or with the products which arise 

 from artificial digestion of protein by means of gas- 

 tric juice and which contain no traces of protein or 

 peptones. Gelatine, which is usually classed along 

 with the proteins, has a much less favourable effect 

 and does not appear to contain the substances es- 

 sential for building up body proteins. Fed to dogs 

 which received no other food, gelatine was only able 

 to replace at most 37% of the protein which was 

 used up during fasting. Dogs which were in a 

 position of nitrogen equilibrium and so got enough 

 protein to make withdrawal from their own tissue 

 unnecessary, only maintained this equilibrium when 



