THE BIO-CHEMISTRY OF ANIMALS AND PLANTS 683 



so-called " fusel bacteria " did not increase the output of 

 fusel oil in normal fermentation, soon disposed of this idea. 



To F. Ehrlich belongs the credit of having discovered the 

 exact conditions for the production of fusel oil, and its close 

 connection with protein synthesis from amino acids in the 

 growing yeast cell. The application of the results of modern 

 researches on protein constitution, and the amino acids pro- 

 duced by its cleavage, led him to this solution. He discovered 

 iso-leucine in molasses as well as in yeast, and as a constant 

 proteolytic cleavage product of other proteins (fibrin, caseinogen), 

 and this, together with the general occurrence of amino acids 

 in plant juices and the similarity in constitution of leucine to 

 iso-amylic alcohol, led him to the view that amylic alcohol 

 and its homologues are produced from amino acids by the 

 agency of yeast itself. The conclusive proof for the correct- 

 ness of this view was the discovery that the fermentation of 

 these amino acids by means of pure yeast cultures occurs in 

 the presence of sugar. In this way Ehrlich succeeded in 

 obtaining iso-butyl alcohol from valine, iso-amylic alcohol 

 from leucine, and d-amylic alcohol, the only optically active 

 constituent of fusel oil, from iso-leucine in quantities corre- 

 sponding to the amount of amino acid which he had added. 

 Whilst the highest percentage of fusel oil of raw spirit was 

 formerly 0*5 per cent., it is now possible by these means to 

 increase it ten to twelve times. 



The formation of the higher alcohols from the amino acids 

 admits of a very simple chemical explanation. With the 

 addition of water a simultaneous splitting off of CO2 and 

 NH3 takes place, as expressed by the following formulae^: 



leucine. 



Ch'/^^ • ^^- ?^ • <^^^-^ • COOH + H,0 = 



iso-amylic alcohol. 



^^^XcH . CHo . CH.OH + NH, + CO., 



iso-leucine. 



C H5/*f ^ . CH(NH,) . COOH + H,0 



d-amylic alcohol. 



^2'^CH . CHj . OH + NH, + CO, 



During the growth of the yeast cell these reactions probably 



' C = asymmetrical carbon atom. 



