94 PHYSIOLOGY OF YEASTS 



carbohydrates (maltase, invertase). The hexoses are fermented im- 

 mediately and the fermentable Ci 2 and Cis sugars are transformed to 

 hexoses by means of these enzymes. It contains also a glycogenase 

 which allows it to induce the fermentation of glycogen upon which the 

 living yeast has no action; the glycogenase is diffusible while the 

 glycogen is not. 



On the contrary, the ordinary juice does not act on lactose, but 

 Buchner and Meisenheimer have been able to isolate from lactose- 

 fermenting yeasts a lactase. 



One is easily able to secure, by mixing some of Buchner's yeast 

 juice with a solution of glucose, a fermentation which will start at 

 the end of six minutes: 20 c.c. of yeast juice, with 8 grams of saccha- 

 rose in the presence of 0.2 c.c. of toluol will yield after 96 hours 

 from 0.7 to 1.87 grams of carbon dioxide. If these results are com- 

 pared with those obtained with living yeast, the fermenting power of 

 the juice seems feeble, for 1 gram of living yeast will produce from 

 an 8 per cent solution of sugar at 40 in about 6 hours, 1.5 grams of 

 CO2. Zymase is not extracted in a pure state and it must be admitted 

 that it makes up only a feeble part of the juice. However, in the 

 fermentation with the living yeast, new zymase is formed constantly. 



Among the secondary products, glycerol (3 to 8 per cent), traces 

 of acetic acid and amyl alcohol, have been noticed. Lactic acid is 

 often found but it may disappear and may be transitory. Further on, 

 we shall see the significance of the formation of this lactic acid. 



Mode of Action of Zymase 



For a long time the following formula has expressed alcoholic fer- 

 mentation 



C 6 Hi20 6 = 2(C 2 H 5 OH) + 2CO 2 . 



This equation has only general value. Among the two products ex- 

 pressed, there are many intermediate products. The determination of 

 these has demanded the sagacity of the biochemists. It might be 

 advisable to give some of the principal results which have been ob- 

 tained. 



After the work on oxidases and hydrogenases of yeasts Griiss l 

 has put out a theory to explain the mechanism of alcoholic fermen- 

 tation which is very interesting. This author regards glycogen as an 

 intermediate product between fermentation and respiration. The 

 polysaccharides will be decomposed into glucose by means of the 

 hydrolytic enzymes (sucrase and maltase) ; this will be split into two 

 1 Gruss, J. Zeitschr. f. ges. Brau. 27, 1904. 



