682 SCIENCE PROGRESS 



Czapek and by Emmerling that the food value of the a-amino 

 acids is superior to that of all other nitrogenous substances. 

 Abderhalden and Rona proved subsequently that this mould 

 builds up its protein in the same way, if grown on potassium 

 nitrate, glycine, or glutaminic acid, and that the protein thus 

 formed in the living organism remains constant in composition, 

 i.e. furnishes identical cleavage products on hydrolysis. As an 

 explanation for this interesting observation we must assume 

 that the Aspergillus starts with the amino group in the building 

 up of its protein. 



Yeasts. — A subject of considerable biological interest and 

 at the same time of practical value is the study of the nitro- 

 genous metabolism of yeast. To mention the name of " fusel 

 oil " in this connection seems to be going away from the 

 subject, but it is not really so, for the intimate association of 

 protein formation and "fusel oil" has been made clear by 

 the researches of F. Ehrlich, and these deserve to be referred 

 to in some detail. 



Of the various by-products of the alcoholic fermentation 

 of carbohydrates by yeast (such as glycerin, succinic acid, 

 ethers, aldehydes, etc.), fusel oil is the least desirable from 

 the distiller's point of view. It was discovered by Scheele 

 in 1785, and was shown by Pasteur to consist of higher 

 alcohols and especially two amylic alcohols. Its smell and 

 taste are disagreeable, and the deleterious action of certain 

 raw spirits has, although probably without justification, been 

 ascribed to it. The separation of fusel oil from ordinary 

 ethyl alcohol was one of the difficulties of alcohol manufac- 

 ture, which was finally solved by the perfection of fractional 

 distillation. With the introduction of better methods, especially 

 the use of pure yeast cultures, a distinct falling off in the 

 quantity of fusel oil formed took place, whilst on the other 

 hand the demand for this product for industrial processes 

 rose to such an extent as to produce a scarcity in the world's 

 markets. Amylic alcohol in the form of its ethers is now in 

 great demand for the manufacture of fruit essences, celluloid, 

 and smokeless powders. While investigating the conditions 

 of fusel-oil formation, the view found most general accept- 

 ance that its origin was due to a bacterial decomposition of 

 sugar. The fact, however, that the alcohols of fusel oil 

 possess a branched carbon-chain, and that the addition of the 



