A third theory has also been suggested to explain these phenomena, according to which the various sugars are fermented by different enzymes [see Slator, 1908, 1]. The uniformity of the result obtained with glucose and fructose suggests that these two sugars are fermented by the same enzyme (glucozymase), mannose and galactose by different ones (mannozymase and galactozymase). This would afford a simple explanation of the different rates of fermentation for different sugars and of different degrees of sensitiveness towards reagents. If, however, a separate and independent mechanism were present for each sugar, the rate of fermentation of mixtures should be the sum of the rates for the constituents. This, as shown above, is not found to be the case, and it is therefore necessary to suppose, either that one sugar influences the fermentation of another in some unknown way, or that only a part of the mechanism of fermentation is specific for the particular sugar. Thus the enzyme may be specific and, the co-enzyme [p135] non-specific, so that only a certain maximum rate is attainable, or again, the supply of free phosphate may be the controlling factor. In the prevailing state of ignorance as to the exact function of the co-enzyme and of the conditions upon which the velocity of fermentation in the cell depends, it is at present impossible to decide between these various theories, but they all offer points of attack which justify the hope that much further information can be obtained by experimental inquiry. It will be seen from the foregoing that Buchner's discovery of zymase has opened a chapter in the history of alcoholic fermentation which is yet far from being completed. In every direction fresh problems present themselves, and it cannot be doubted that as in the past, the investigation of the action of the yeast-cell will still prove to be of fundamental importance for our knowledge of the mode in which chemical change is brought about by living organisms. [p136] BIBLIOGRAPHY. Page of Text on which reference is made. ABELES, HANS (1898), /Zur Frage der alkoholischen Gährung ohne Hefezellen/ 19 Ber., 31, 2261-2267. ABERSON, J. H. (1903), /La fermentation alcoolique/ 128 Rec. trav. chim., 22, 78-132. AHRENS, FELIX B. (1900), /Ein Beitrag zur zellenfreien Gärung/ 19 Zeitsch. angew. Chemie, 483. AHRENS, FELIX B. (1902), /Das Gärungsproblem/ 9 (F. Enke, Stuttgart.) ALBERT, R. (1899, 1), /Ueber künstliche Anreicherung der Hefe an Zymase/ 24 Ber., 32, 2372-2374.