C{6}H{4} ╱ ╲ ╱ ╲ HN C·CH{2}·CH{2}OH, ╲ ╱╱ ╲ ╱╱ CH which was also first prepared in this way [Ehrlich, 1912] and has a very faintly bitter, somewhat biting taste. The extent to which the amino-acids of a medium in which yeast is producing fermentation are decomposed in this sense depends on the amount of the available nitrogen and on the form in which it is present. Thus the addition of ammonium carbonate to a mixture of yeast and sugar was found to lower the production of fusel oil from 0·7 to 0·33 per cent. of the alcohol produced. The addition of leucine alone raised the percentage from 0·7 to 2·78, but the addition of both leucine and ammonium carbonate resulted in the formation of only 0·78 per cent. of fusel oil, The production of fusel oil therefore and the character of the constituents of the fusel oil alike depend on the composition of the medium in which fermentation occurs. This affords a ready explanation of the fact that molasses, which contains almost equal amounts of leucine and isoleucine, yields a fusel oil also containing approximately equal amounts of isoamyl alcohol and /d/-amyl alcohol [Marckwald, 1902], whilst corn and potatoes, in which leucine preponderates over isoleucine, yield fusel oils containing a relatively large amount of the inactive alcohol. The subject is, in fact, one of great interest to the technologist, for as Ehrlich points out "the great variety of the bouquets of wine and aromas of brandy, cognac, arrak, rum, etc., may be very simply referred to the manifold variety of the proteins of the raw materials (grapes, corn, rice, sugar cane, etc.) from which they are derived". Yeast can also form fusel oil at the expense of its own protein, but this only occurs to any considerable extent when the external [p089] supply of nitrogen is insufficient. Under these circumstances the amino-acids formed by autolysis may be decomposed and their nitrogen employed over again for the construction of the protein of the cell. The yield is also influenced by the condition of the yeast employed with regard to nitrogen, a yeast poor in nitrogen being more efficacious in decomposing amino-acids than one which is already well supplied with nitrogenous materials. The nature of the carbonaceous nutriment and finally the species of yeast are also of great importance [see Ehrlich, 1911, 2; Ehrlich and Jacobsen, 1911].