Lvoff [1913, 1, 2, 3] has made quantitative experiments on the effect of methylene blue both on the sugar fermentation and autofermentation of dried yeast and maceration extract. In presence of sugar the methylene blue causes a decrease in the extent of fermentation, the difference during the time required for reduction of the methylene blue being represented by an amount of glucose equimolecular to the latter. In the absence of sugar on the other hand an excess of carbon dioxide equimolecular to the methylene blue is evolved but no corresponding increase in the alcohol production occurs. The effect of methylene blue is evidently complex and it is impossible at present to say whether Lvoff's contention is correct that the methylene blue actually [p113] interferes with the fermentation by taking up hydrogen (2 atoms per molecule of glucose) destined for the subsequent reduction of some intermediate product or whether the effect is one of general depression of the fermenting power which would be presumably proportional to the concentration of methylene blue and inversely proportional to that of the fermenting complex [see Harden and Norris, R. V., 1914]. In any case it will be noticed that Lvoff s interpretation of the results is at variance with the requirements of Kostytscheff's theory (p. 109) according to which 4 atoms of hydrogen should be given off by a molecule of glucose. Kostytscheff [1913, 2; Kostytscheff and Scheloumoff, 1913] has also observed a depression of the extent of fermentation by methylene blue without any serious alteration in the ratio of CO{2} to alcohol, although an increase occurs in the production of acetaldehyde. On the whole it cannot be said that the evidence gathered from experiments on the reduction of acetaldehyde and methylene blue is very convincing. All that is established beyond doubt seems to be that yeast possesses a reducing mechanism for many aldehydes [see also in this connection Lintner and Luers, 1913; Lintner and von Liebig, 1911; as well as Neuberg and Steenbock, 1913, 1914] and colouring matters. This mechanism appears to be capable of activity in the absence of sugar and it is to be supposed that in accordance with the views of Bach [1913] the necessary hydrogen is derived from water and that some acceptor for the oxygen simultaneously liberated is also present. There seems however at the moment to be no sufficient reason to suppose that this mode of reduction is in any way altered by the presence of sugar and until the production of intermediate products equivalent to the amount of substance reduced is actually demonstrated, the conclusions of these workers may be regarded as not fully justified. Neuberg and Kerb [1913, 2] themselves tentatively propose a complicated scheme possessing some novel features according to which methylglyoxal is the starting-point for the later stages of the change.