METABOLISM 



277 



Zein lacks the tryptophan group and the diamino-acid lysin. 

 GHadin and hordein lack lysin. 



Fig. 139. — Showing typical growth of rats on diets containing a single 

 protein. (1) On casein food (devoid of glj'cin) satisfactory growth 

 is shown ; (2) on gliadin food (deficient in lysin) little more than 

 maintenance of body weight is shown ; (3) after a mixed diet with 

 satisfactory growth, zein food (devoid of glycin, Ij'sin, and trypto- 

 phan) even maintenance is impossible. (Mendel.) 



Chart 1 shows the results of feeding rats on an adequate 

 and on an inadequate protein diet. 



Fig. 140.— To show the efifect of the addition of tryptophan {A) and of 

 tryptophan and lysin (B) to the food of rats on zein diet. A gives 

 maintenance of weight alone, A and B increase of growth. 

 (Mexdel.) 



Chart 2 shows the etfect of adding the lacking amino- 



acid. 



