674 



PHYSIOLOGY 



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 neces- 

 sary 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. 332, which show the output 



50 



DAY i 



Fio. 332. Three experiments on the output of urea during starvation (dog). 



(TIQERSTEDT, after VOIT.) 



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

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

 experiment the meat was reduced to a minimum. 



of urea in three experiments on a dog under different conditions of nutrition. 

 In the first experiment 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, the urea output during 

 the sixth to eighth days is identical. In many cases for a few days before 

 death there is a rise of protein metabolism. This rise is synchronous with a 

 practically complete disappearance of fat from the body. The animal now 

 has to supply all its requirements at the expense of the protein tissues, which 

 therefore waste rapidly and account for the increased excretion of nitrogen. 

 This is shown in the following experiment of Rubner on a rabbit : 



