THE EFFECT OF FOOD ON METABOLISM 709 



shown by a study of the eft'ect of increasing each class of food on 

 the metabolism of the body as a whole. 



EFFECTS OF VARIATIONS IN PROTEIN 



Most of the experiments on the influence of variations in the 

 quantity of protein food have been made on carnivora, such as 

 the dog and cat. Within very wide limits the output of nitrogen 

 is proportional to the intake. This is shown in the following Tables 

 by Voit, representing two experiments on dogs : 



In Experiment I the animal had been fed for some days with 

 500 grm. of meat per diem. The fact that he was excreting nitrogen 

 corresponding to 547 grm. shows that this amount was insufficient 

 and that he was not yet in a condition of nitrogenous equilibrium. 

 Each day he was using up 47 grm. of the protein of his body in addition 

 to the 500 grm. supplied in the food. On increasing his food three- 

 fold to 1500 grm. the nitrogenous output was also increased, but a 

 state of nitrogenous equilibrium was not reached until the eighth 

 day of the experiment. During the six days intervening 778 grm. 

 of meat had been retained in the body, i.e. there had been a retention 

 of protein, probably in the form of increased muscular substance. 

 The amount is too great to be accounted for by retention of the 

 disintegration products of the protein in the body. It must have 

 been stored up in the form of protein and probably, to a large extent 

 at any rate, as actual living tissue. 



In the second experiment the diminution of the protein of the 

 food was followed by a loss of protein from the body, the output being- 

 greater than the income. The excess, however, was rapidly diminishing 

 and equilibrium had been practically attained on the last day of 

 the experiment. During this time the animal had excreted 14-8 grm. 

 of nitrogen more than it had received in its food, which would 



