INFLUENCE OF THE FOOD ON THE TISSUES 61 



Variations during Development. 



Abderhalden and Kempe (23) carried out some experiments on the 

 composition of the egg at different periods of incubation. They found 

 that tyrosine was the only amino acid which altered in amount and 

 that this alteration was very small: 100 grms. dried fresh egg con- 

 tained 1-82 grm. tyrosine; after ten days incubation at 40 there was 

 2-1 1 per cent of tyrosine and after twenty days' 2*25 per cent (in these 

 analyses the embryo was also included). The amount of glycine and 

 glutamic acid, the other two substances estimated, hardly varied during 

 the incubation. They concluded that there was no new formation of 

 amino acids during development. 



Transmutation of Amino Acids. 



Another important question, in this connexion, is whether the 

 organism always breaks down a specific protein in the same fashion 

 does any variation ever occur in the amount of individual amino acids 

 or the compound polypeptides ? 



Supposing the ingested protein contains 10 grms. of leucine, and 

 the tissue protein contains double this amount, can only 50 grms. of 

 tissue protein be formed from the 100 grms. of the food protein, or can 



'Analysis by Abderhalden and Sasaki. " Zeit. f. physiol. Chem." 1907, 51, p. 404. 



