The evidence for the occurrence of reaction (1) is supplied by the experiments of Neubauer and Fromherz [1911]. Having previously found that amino-acids undergo a change of this kind in the animal body, Neubauer investigated their behaviour towards yeast. Taking /dl/-phenylaminoacetic acid, C{6}H{5}·CH(NH{2})·COOH, it was found that the changes produced were essentially the same as in the animal body. The /l/-component of the acid was partly acetylated and partly unchanged, whereas the /d/-component of the acid yielded benzyl alcohol, C{6}H{5}·CH{2}·OH, phenylglyoxylic acid, C{6}H{5}·CO·COOH, and the hydroxy-acid C{6}H{5}·CH(OH)·COOH. Since however this hydroxy-acid was produced in the /l/-form it probably arose by the asymmetric reduction of phenylglyoxylic acid, a reaction which can be effected by yeast as was also found to be the case in the animal body [see Dakin, 1912, pp. 52, 78]. Moreover it was shown that when the effects of yeast on a ketonic acid and the corresponding hydroxy-acid were compared, the alcohol was formed in much better yield from the ketonic acid (70 per cent.) than from the hydroxy-acid (3-4 per cent.), the actual example being the production of tyrosol (p-hydroxyphenylethyl alcohol), OH·C{6}H{4}·CH{2}·CH{2}OH, from p-hydroxyphenylpyruvic acid, OH·C{6}H{4}·CH{2}·CO·COOH, and p-hydroxyphenyl-lactic acid, OH·C{6}H{4}·CH{2}·CH(OH)·COOH respectively. Neubauer by these experiments established two extremely important points. 1. That the amino-acids actually yield the corresponding α-ketonic acids when treated with yeast and sugar solution. 2. That the a-ketonic acids under similar conditions give the alcohol containing one carbon atom less in good yield, whereas the corresponding hydroxy-acids only give an extremely small amount of these alcohols. It is therefore probable that at an early stage in the decomposition of the amino-acids by yeast a ketonic acid is produced, which then undergoes further change. The source of the oxygen required for this reaction and the mechanism of oxidation have not yet been definitely ascertained. It is possible [p093] OH ╱ that hydrated imino-acids of the type R·C─COOH are first formed ╲ NH{2} [Knoop, 1910], but these have not as yet been isolated.