THE EFFECT OF FOOD ON METABOLISM 



679 



Thus nitrogenous equilibrium was attained by Siven on a diet containing 

 33 grm. of protein daily (= 5 grm. of nitrogen), but in this case the carbo- 

 hydrates and fats were increased to such an extent that the man was taking 

 in 78-5 Calories per kilo per day. These results suggest that the qualitative 

 metabolism of the body is determined by the relative amount of foodstuff 

 supplied to the body and circulating in its juices at any given time, and that 

 preponderance of one foodstuff will tend to excite the cells of the body to 

 the utilisation of this foodstuff at the expense of the other two. That such 

 is the case is shown by a study of the effect of increasing each class of food 

 on the metabolism of the body as a whole. 



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 Tables by Voit given below, representing two experi- 

 ments 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 tissues of his body in addition to the 500 grm. supplied in 

 the food. On increasing his food threefold 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 inter- 

 vening 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 practicaUy attained on the last day of the experiment. During 

 this time the animal had excreted 14'8 grm. of nitrogen more than it had 



