280 BACTERIOLOGICAL CHEMISTRY 



cells. He showed that leucine, (CH3)2CH.CH2.CHNH2. 

 CO OH, was converted by yeast in sugar solution to iso- 

 amyl alcohol, (CHgjgCH.CHg.CHaOH, and that ^5oleucine, 

 CH3.CH.CH.NH2.COOH, gave rise to cZ-amyl alcohol, 



C2H5 

 CH3.CH.CH2OH, by loss of carbon dioxide and ammonia. 



I 



C2H5 



Other amino -acids were found to undergo the same sort 

 of conversion giving rise to the corresponding alcohol 

 (see p. 231). 



The production of these alcohols is only brought about 

 by living cells which are actively growing in a sugar 

 medium. Yeast juice and yeast preparations, like zymin, 

 do not lead to the conversion of the amino -acid to the 

 alcohol, nor does living yeast in the absence of sugar. It 

 seems that the process is bound up with the life of the 

 cell, and is the mechanism by which the organism obtains 

 the nitrogen for its synthetic processes. All the ammonia 

 produced is assimilated by the cell, and practically none 

 accumulates in the medium. Yeast juice or zymin, 

 which do not produce new cells, do not assimilate ammonia 

 and the reaction does not occur ; living yeast in the 

 absence of sugar does not grow and reproduce, and again 

 there is no demand for ammonia for synthesis. This 

 dependence of fusel oil production on the nitrogen 

 metabolism is further illustrated by the fact that if a 

 readily available source of ammonia is present in the 

 form of salts, the production of the higher alcohols is 

 very much lowered because the requisite ammonia is 

 supplied more readily from the salts. 



It is very probable that the flavours and bouquets 

 of fermented drinks depend largely on the proportions 

 and natures of the various alcohols and esters produced 



