In favour of this view is to be adduced the fact that aldehydes such as isobutyraldehyde and valeraldehyde have been found in crude spirit, whilst acetaldehyde is a regular product of alcoholic fermentation [see Ashdown and Hewitt, 1910]. Benzaldehyde, moreover, has been actually detected as a product of the alcoholic fermentation of phenylaminoacetic acid, C{6}H{5}·CH(NH{2})·COOH [Ehrlich, 1907, 1]. Further, the aldehydes so produced would readily pass by oxidation into the corresponding fatty acids, small quantities of which are invariably produced in fermentation. This view of the nature of the alcoholic fermentation of the amino-acids is undoubtedly to be preferred to that previously suggested by Ehrlich [1906, 3] according to which a hydroxy-acid is first formed and then either directly decomposed into an alcohol and carbon dioxide or into an aldehyde and formic acid, the aldehyde being reduced and the formic acid destroyed (see p. 115). R·CH(NH{2})·COOH → R·CH(OH)·COOH R·CH(OH)·COOH → R·CH{2}OH + CO{2} or R·CHO + H·CO{2}H R·CHO → R·CH{2}OH The most probable course of the decomposition by which isoamyl alcohol and succinic acid are produced from leucine and glutamic acid respectively is therefore the following:-- (/a/) /Isoamyl Alcohol./ (1) (CH{3}){2}·CH·CH{2}·CH(NH{2})·COOH (3) (CH{3}){2}CHCH{2}·CHO+CO{2} Leucine Isovaleraldehyde (2) (CH{3}){2}·CH·CH{2}·CO·COOH (4) (CH{3}){2}·CH·CH{2}·CH{2}OH α-Ketoisovalerianic acid Isoamyl alcohol (/b/) /Succinic Acid./ (1) COOH·CH{2}·CH{2}·CH(NH{2})·COOH (3) COOH·CH{2}CH{2}·CHO + CO{2} Glutamic acid Succinic semialdehyde (2) COOH·CH{2}·CH{2}·CO·COOH (4) COOH·CH{2}·CH{2}·COOH α-Keto-glutaric acid Succinic acid [p095] GLYCEROL. Of the three chief by-products of alcoholic fermentation, only glycerol remains at present referable directly to the sugar. This substance, as shown by the careful experiments of Buchner and Meisenheimer [1906], is formed by the action both of yeast-juice and zymin to the extent of 3·8 per cent. of the sugar decomposed, and no other source for its production has so far been experimentally demonstrated. If it be true that during the decomposition of sugar into alcohol and carbon dioxide, substances containing three carbon atoms are formed as intermediate compounds (see p. 100), it is obvious that these might by reduction be converted into glycerol which would thus be a true by-product of the alcoholic fermentation of sugar. [See Oppenheimer, 1914, 2.] It has, however, been suggested that it may in reality be a product of decomposition of lipoid substances or of the nuclein of the cell (Ehrlich).