A comparison of the conditions of action of carboxylase and zymase has revealed several interesting points of difference. Neuberg and Rosenthal [1913] have observed that the fermentation of pyruvic acid by maceration extract commences much more rapidly than that of glucose and interpret this to mean that in the fermentation of glucose a long preliminary process occurs before sufficient pyruvic acid has been produced to yield a perceptible amount of carbon dioxide. The long delay (3 hours) which they sometimes observed in the action of maceration juice on glucose is however by no means invariable (see p. 46), but in any case indicates that the sugar fermentation can be affected by conditions which are without influence on the pyruvic fermentation. A similar conclusion is to be drawn from the fact that the pyruvic acid fermentation is less affected by antiseptics than the glucose fermentation [Neuberg and Karczag, 1911, 4; Neuberg and Rosenthal, 1913], chloroform sufficient to stop the glucose fermentation brought about by yeast or dried yeast being usually without effect on the fermentation of the pyruvates either alone or in presence of boric or arsenious acid. A more important difference is that carboxylase decomposes pyruvic acid in the absence of the co-enzyme which is necessary for the fermentation of glucose [Harden, 1913; Neuberg and Rosenthal, 1913]. This can be demonstrated experimentally by washing dried yeast or zymin with water (see p. 63) until it is no longer capable of decomposing glucose (Harden), or by allowing maceration extract to autolyse or dialyse until it is free from co-enzyme (Neuberg and Rosenthal). The zymase of maceration extract is moreover inactivated in 10 minutes at 50-51°, whereas after this treatment the carboxylase is still active. [p084] The only conclusion that can be legitimately drawn from these highly interesting facts is that if the decomposition of pyruvic acid actually be a stage in the alcoholic fermentation of glucose the soluble co-enzyme is required for some change precedent to this, so that in its absence the production of pyruvic acid cannot be effected. [p085] CHAPTER VII. THE BY-PRODUCTS OF ALCOHOLIC FERMENTATION.