GROWTH AND NUTRITION 73 



zein (prepared from maize) as the sole protein did not suffice 

 even for maintenance. If such a ration were supplemented with 

 tryptophane, maintenance could be secured for at least some 

 time. No other amino acid can take the place of tryptophane. 

 When the ration was supplemented with lysine and trypto- 

 phane, growth followed at nearly the normal rate. Since zein 

 does not contain glycocoll these observations also yield evidence 

 that glycocoll is dispensable as a dietary component. The same 

 paper also contains additional evidence that lysine is indispensa- 

 ble for growth. Rats were fed a ration in which the protein was 

 supplied as gliadin, and they noted that the gliadin rations per- 

 mitted maintenance, but no growth. If, however, lysine (3 per 

 cent of the protein) were added to the ration, normal growth 

 resulted. If the lysine were subsequently withdrawn, growth 

 promptly ceased. 



As to the indispensability of lysine for maintenance, it has 

 not been possible to obtain unequivocal evidence from the use 

 of gliadin, for it contains a small quantity of lysine. The author 

 has reported 4 data which seem to afford direct evidence that 

 lysine is also indispensable for maintenance. Rations which con- 

 tained kafirin as the sole source of protein were fed to rats, but 

 on such rations the animals slowly and continuously lost weight. 

 Similar rations supplemented with lysine, however, permitted 

 a slow rate of growth. 



Osborne and Mendel have also shown 5 that though casein con- 

 tains cystine, it contains it in less than the optimum quantity. Rats 

 grew normally on diets containing 18 to 15 per cent of casein, 

 but at less than the normal rate when the diet contained only 1 2 

 per cent of this protein. When the diet contained 9 per cent, 

 growth was checked sharply. Evidently in rations of the char- 

 acter used the minimum quantity of protein on which normal 

 growth may be secured lies somewhere between 12 and 15 per 

 cent. If, however, cystine were added to these diets, normal 

 growth could be attained at considerably lower levels. 



The Fats. When we mention the word nutrients, we at once 



