40 PHYSIOLOGY OF BACTERIA 



equivalent of cell juice. The acetone yeast is more 

 active, and yields about one-eighth of the amount pro- 

 duced by an equivalent amount of living yeast cells. 



For this reason, the reality of a fermenting enzyme 

 is, occasionally, questioned again. Rubner (1913) could 

 obtain no appreciable fermentation by treating living 

 yeast in sugar solution with toluol. He believes that 

 only a small portion of the enzyme is separated from the 

 living protoplasm while most of it is interlinked with 

 protoplasm and is inactivated by the death of the cell. 

 Euler and his associates have proved this in a number of 

 pubhcations. 



The essential thing, from the energy viewpoint, is the 

 endo-enzymatic nature of the fermenting agent; it must 

 work within the cell in order to make the liberated 

 energy available for cell purposes. It is doubtless a 

 complex mechanism which brings about this change of 

 sugar to alcohol and carbon dioxide. Alcoholic fermen- 

 tation occurs in several steps, with intermediate products, 

 some of which have been actually isolated (see p. 49). 

 Whether fermentation is separable from the protoplasm 

 or not, has no great bearing upon the problems treated 

 in this volume. A further discussion of the enzymatic 

 nature of fermentations will be found on p. 64. 



(d) EQUATIONS OF FERMENTATION 



If fermentation is nothing but a chemical process 

 activated by the influence of an enzyme, it is necessary 

 that it obey strictly chemical laws, and that we may 

 represent the process accurately by a chemical equa- 

 tion. A considerable amount of effort has been made 

 to prove this for a number of fermentations. Most 

 attention has been given to the alcoholic fermentation; 

 the lactic and propionic fermentations and the acid- 



