THE METABOLISM DURING STARVATION 705 



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's 

 on a rabbit : 



j^ Average daily out- Average amount of 



put of nitrogen fat oxidised daily 



1-3 . . . 1-67 grm. .. 10-3 grm. 



4-5 . . . . 1-46 .. 10-3 



6-8 . . 3-21 .. 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 combustion 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. 



45 



