NUTRITION AND GROWTH 137 



albumin and casein are glycocoll-free. Gliadin from 

 wheat contains no glycocoll and only a trace of lysine. 

 Zein from maize yields no lysine nor tryptophane and 

 gelatine contains no cystine, tyrosine nor tryptophane. 

 The first appreciation that qualitative differences 

 in protein composition may be of importance in nutri- 

 tion was furnished by the classic experiments of Voit 

 and Munk, who showed that gelatin could not support 

 nitrogen equilibrium. The demonstration by Escher 

 that the addition of tyrosine improved the powers of 

 gelatin in establishing nitrogenous equilibrium gave 

 rise to a series of investigations, the results of which 

 have led to a much more complete understanding of 

 the problems intimately connected with metabolism. 

 Only a few of these, however, need be reviewed here. 

 Kaufman was able to show that when gelatin is fed 

 to man and dogs with the addition of the missing 

 amino acids, tyrosine and tryptophane, nitrogen equi- 

 librium could be maintained for short periods at least. 

 The work of Willcock and Hopkins with zein, which 

 it will be remembered is deficient in lysine and tryp^ 

 tophane, is of great interest in the present discussion 

 as it attacked the problem from new viewpoints, in 

 entire accord with the conceptions of the present. In 

 their introduction these authors point out that: "We 

 are no longer bound to Liebig's view, or to any modi- 

 fication of it which implies that the whole of the 

 protein consumed is utilized as intact protein : nor are 

 we even compelled to assume that the whole of what 

 is broken down in the gut is resynthesized before 



