8 FEEDING EXPERIMENTS WITH ISOLATED FOOD SUBSTANCES. 



Sicherheit angeben. Wir haben bereits angeflihrt, class es beiden genannten 

 Proteinen an Lysin abgeht. Dieser Mangel scheint also nicht von ent- 

 schiedener Bedeutung zu sein. Dagegen scheint der Umstand, dass das 

 Zein kein Tryptophan enthalt, eine grosse Rolle zu spielen. Ob das Nicht- 

 vorhandensein von Tryptophan, in Zein wirklich der Grund ist, weshalb 

 bei Fiitterung dieses Proteins kein Stickstoffgleichgewicht eintritt, muss 

 sich iibrigens durch eine Untersuchung entscheiden lassen, ob das Stick- 

 stoffgleichgewicht sich herstellen lasst, wenn das Futter Zein -f- Tryptophan 

 enthalt.* 



The preceding quotation has suggested that the deficiency in a 

 protein dietary need not be one of quantity ; the structural character 

 of the nitrogenous intake may determine its adequacy. Willcock 

 and Hopkinst have approached the problem from this view-point. 

 They fed mice on zein together with non-nitrogenous foods and 

 compared their length of life with that of mice which received in 

 addition some of the missing fragments of this "imperfect" protein, 

 viz., tryptophane (and tyrosine for comparison). Zein was shown to 

 be quite unable to take the place of a normal protein, like casein, in 

 maintaining growth: 



The addition of the missing tryptophane group has no power to convert 

 such loss (of weight) into equilibrium or gain a fact possibly due to other 

 deficiencies in the zein molecule, such as the absence of lysine. On the other 

 hand, on the average, the loss of weight was slower with tryptophane than 

 without it. But this result might well be expected, even if the tryptophane 

 administered undergoes utilization without directly contributing to tissue 

 formation or structural maintenance. If it serves as a basis for the elabo- 

 ration of a substance absolutely necessary to life something, for instance, 

 of an importance equal to that of adrenaline then, in starvation, or when it 

 is absent from the diet, a supply is likely to be maintained from the tissue- 

 proteids; the demand for it would become one of the factors determining 

 tissue breakdown. In the case of young animals which directly benefit 

 from the addition of a protein constituent, otherwise absent from their diet, 

 to the extent of a well-nigh doubled life and marked improvement in gen- 

 eral condition, but at the same time steadily lose, instead of gaining, weight, 

 the utilization of the constituent would appear to be of some direct and 

 specific nature, (p. 101.) 



The suggestion of a possibility of the direct formation of essen- 

 tial hormones from amino- acid derivatives of proteins is timely. 

 One can not draw any further conclusions regarding the value of the 

 proteins (zein and casein) fed by Willcock and Hopkins, because in 

 the absence of definite intake records, the question of a comparable 

 and adequate supply of energy in the various cases remains undeter- 

 mined. Special experiments showed that the prepared zein was "in 

 no sense actively deleterious." 



The same uncertainty regarding the real participation of in- 

 anition factors applies to the earlier widely quoted experiments of 



*Henriques: Zeitschrift fur physiologische Chemie, 1909, lx, p. 117. 

 tWillcock and Hopkins: Journal of Physiology, 1906-7, xxxv, p. 88. 



