BIOCHEMISTRY 207 



genous diet the reciprocal phenomenon occurs. Bearing in mind 



the considerable experimental errors, the ratio r — -r-^ — \ -^ — r 



^ food N absorbed 



appears to remain constant, whatever amount of nitrogen is 



taken in the form of whole wheat bread, until equilibrium is 



reached. In the case of milk the experimental errors are 



proportionately greater and the ratio may be constant, but 



with gelatin it is certainly not so ; there being no indication 



that the amount of body nitrogen saved increases beyond that 



effected by the smallest quantity of gelatin fed. On these 



grounds the authors conclude that Thomas's procedure for 



determining the biological values is justified in the case of 



bread, doubtful with milk, and impossible with gelatin. It is 



therefore necessary to determine the ratio 7 — , \.t l \ — 3 at 



•^ lood N absorbed 



a point close to but below that of equilibrium before Thomas's 



method can be regarded as justifiable. The experiments on 



the authors tended to show that the biological value of the 



proteins of the whole wheat grain is 31-35 per cent, and that 



of cow's milk 51 per cent. 



Yeast Enzymes.' — F. Hayduck and H. Haehn {Biochem. 

 Zeit., 1922, 128, 568) have found that the distribution of zymase 

 in bottom beer yeast and in distillery yeast is different. The 

 former contains free zymase and also zymase in some proto- 

 plasmic combination which prevents it showing activity after 

 treatment by Lebedev's process or with acetone. Distillery 

 yeast, which gives no active press juice or active zymase after 

 acetone fixation, contains only combined zymase. Experi- 

 ments on a torula yeast poor in zymase showed that cultiva- 

 tion in a wort with a poor air supply caused an increased 

 content of zymase and parallel with this an increased nuclei 

 acid metabolism. Willstatter and Racke (Annalen, 1922, 

 427, 111-41) have investigated the nature of the enzymatic 

 process by which invertase is set free from the yeast cell and 

 the condition in which invertase exists in the cell. The con- 

 clusion is that invertase occurs as such, but that it is protected 

 and prevented from diffusing by the membranes of the cell- 

 structure. The function of the hberating enzyme is to destroy 

 these membranes. The hberating enzyme is somewhat un- 

 stable, and experiments tend to show that it is of the type of 

 a polysaccharase rather than a proteolytic enzyme. 



Sulphur in Protein., — This interesting and curiously little 

 explored field of research has provided the subject of a paper 

 by Hoffman and Gortner (/. Amer. Chem. Soc, 1922, 44, 341). 

 Pure cystine appears to be only slowly destroyed on boiling 

 with 20 per cent, hydrochloric acid, and probably there would 

 not be any appreciable decomposition of this amino-acid during 



