630 



PHYSIOLOGY 



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 



30 



20 



CM. 



UREA 



DAY I 



FIG. 320. 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 ex- 

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

 experiment the meat was reduced to a minimum. 



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

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



Days 

 1-3 

 4-5 



6-8 



Average daily out- 

 put of nitrogen 



1 -67 grm. 

 . 1-46 

 3-21 



Average amount of 

 fat oxidised daily 



1O3 grm. 

 10-3 

 2-4 



We see therefore that during starvation, apart from the first day or two, 

 the animal derives the main portion of its necessary energy from the com- 

 bustion of fats, provided that there is a sufficient store of these substances in 

 the body. A certain consumption of protein is unavoidable. Since protein 

 comes from the working tissues of the body they are spared so far as possible, 

 and it is only when the stored fat is used up that any large call is made on 

 the tissue-protein. 



