704 



PHYSIOLOGY 



The total metabolism per kilo body weight very soon attains a 

 constant level. The relative part taken in the production of 

 the total energy by fats and proteins respectively may vary from 

 animal to animal according to the amount of fat available in the 

 body. If the animal has been receiving previous to the experiment 

 a diet rich in protein the excretion of nitrogen and urea in the urine 

 diminishes rapidly during the first days of starvation. During the 

 first two days therefore a considerable proportion of the necessary 



50 



GM. 

 UREA 



DAY i 



FIG. 318. Three experiments on the output of urea during starvation (dog). 



(TIGERSTEDT after VOIT.) 



In (1) (thin line), the dog received 2500 grm. meat per day before the 

 experiment ; in (2) (thick line), the diet was 1500 grm. meat ; and in the third 

 experiment the meat was reduced to a minimum. 



energy is obtained at the expense of protein. Between the third 

 and fifth day, however, the nitrogenous excretion reaches a minimum, 

 at which point it remains approximately constant to within a day 

 or two before death. If the animal has been receiving a diet very 

 poor in protein the excretion of nitrogen may be low throughout the 

 whole course of the experiment. These facts are illustrated by the 

 curves in Fig. 318, which show the output of urea in three experiments 

 on a dog under different conditions of nutrition. In the first experi- 

 ment the dog, before the experimental period, had been receiving 

 2500 grm. of meat daily; in the second it had been receiving 

 1500 grm. of meat, and in the third only a small quantity, which 

 was not accurately measured. Although there is a great difference 

 between the urea output during the first day of the experiments, 



