254 MICRO-ORGANISMS AND FERMENTATION. 



.and, therefore, inactive yeast- juice to fresh juice, the activity 

 of the latter is considerably increased. It follows that the 

 juice must contain an enzyme which is stable at the boiling 

 point, and another which cannot withstand this temperature, 

 a,nd that it is only in conjunction that they can exercise fer- 

 mentative activity. 



Buchner and Meisenheimer have obtained a pressed juice 

 and also a stable preparation from yeasts fermenting lactose, 

 which are capable of carrying on the fermentation. 



It has not yet proved possible to isolate zymase, and 

 nothing is yet known regarding its composition. Its properties 

 may be summarised as follows : It is soluble in water and 

 -dilute glycerine, and is not very sensitive to chemical reagents. 

 In solution it is decomposed at 60 C. When yeast juice is 

 kept at low temperatures (down to C.), the zymase gradually 

 disappears, whilst in a frozen condition it remains unaltered 

 for some time. In a dry condition it may be stored for months 

 with unaltered activity, and withstands a temperature of 

 110 C. It is precipitated along with albuminoids by treat- 

 ment with alcohol, acetone, and ammonium sulphate. It can 

 be dialysed with difficulty or not at all, and occurs in very 

 variable quantity in the living cells according to their stage of 

 development. 



H. Fischer describes zymase as the fermenting enzyme to 

 distinguish it from the other enzymes. 



In addition to the enzymes already mentioned, the alcoholic, 

 the hydrolytic (maltose-, cane sugar-, and glycogen-splitting), 

 .and the proteolytic enzymes, yeast-juice contains an oxidising, 

 .a reducing, a fat-splitting, a hydrogen peroxide-splitting, and 

 a clotting enzyme. 



The vitalistic view of alcoholic fermentation and of the 

 other changes brought about by the yeast cell must be given 

 up in the light of Buchner 's and Fischer's discoveries, for it 

 has been established that they can take place quite independ- 

 ently of the living cell. At the moment this has no direct or 

 important bearing upon the fermentation industry. The 

 particular action of selected species of yeast on the individual 

 substrata, wort, must, etc., is undoubtedly a product of the 

 .action of the complicated forces in the cell, of which only a 



