EXPERIMENTS WITH CYTOST 



103 



energy for the organism, a relatively small fraction 

 being used for the repair or replacement of tissues. 

 While for the latter purpose the nature of the ingested 

 fats and carbohydrates appears to be immaterial as 



TABLE IX (TURCK, 192 1) 



well as interchangeable, there is a definite protein 

 requirement. This is necessary, as shown in the re- 

 searches of Osburn and Mendel (see Mendel, 1924), 

 to supply certain essential amino acids which the or- 

 ganism is incapable of synthesizing from other com- 

 ponents of its diet. 



During complete starvation, such essential amino 

 acids are not available; hence the animal is forced to 

 draw upon the proteins of some of its body cells in 

 order to satisfy the nitrogen requirements of other 



