THEORIES OF FERMENTATION. 253 



maltase, lactase, diastase consists in the hydrolysis of the 

 polysaccharides into simpler compounds, the monosaccharides, 

 an action which can also be produced by purely chemical 

 treatment. Zymase is distinguished from these enzymes by 

 bringing about the complete breaking down of the sugar 

 molecule and the formation of new compounds, exactly like 

 the alcohol enzyme of the living yeast cell. As is well known, 

 this splits up sugar into almost equal parts of alcohol and 

 carbon dioxide. This is also the case with zymase. A part 

 of the sugar, however, is not converted into these products. 



During the pressed-juice fermentation, glycerine is produced 

 to the extent of from 3 to 8 per cent, of the fermented sugar ; 

 it is derived from the sugar. On the other hand, no succinie 

 acid is produced. Acetic acid is formed in minute quantities, 

 but somewhat more than in the fermentation with the living 

 cell. This is probably due to the action of a special enzyme. 



It is of great interest to know that lactic acid is often 

 produced in the zymase fermentation, whereas in other cases 

 the lactic acid originally present or that added to the liquor 

 disappears. This observation suggests a possible solution 

 of the way in which the sugar molecule is decomposed 

 into alcohol and carbon dioxide. It is reasonable to suppose 

 that lactic acid is an intermediate product, and that the 

 zymase consists probably of two enzymes, one of which (zymase 

 in the narrower sense) converts sugar into lactic acid ; the 

 other (" lactacidase ") converts the lactic acid so formed into- 

 alcohol and carbon dioxide. The results could then be ex- 

 plained by supposing that an excess of one or other enzyme 

 in the juice causes either the production or the decomposition 

 of lactic acid. 



It has been stated that part of the sugar is not decomposed 

 into alcohol and carbon dioxide. This cannot be detected by 

 the use of Fehling's solution, and it is certainly not present 

 as reducing sugar. The experiments of Harden and Young 

 have proved that a polysaccharide is formed by a synthesising 

 enzyme present in the juice. By suitable hydrolysis this- 

 substance may be converted into reducing sugar. 



The later work of Harden and Young has carried the 

 investigation further. They found that by adding boiled 



