142 PHYSIOLOGY OF BACTERIA 



the general laws of the endpoint of enzyme action. A 

 brief review will soon convince us, however, that the 

 material on hand is of little help. Even though, on 

 general principles, enzyme reactions are considered 

 incomplete, the endpoint of the action of most enzymes 

 is reached only when the decomposition is practically 

 complete. In the case of maltase and lipase, we have 

 true reversible action. However, in the fermentation 

 processes, there is no reversion known. It seems quite 

 impossible that streptococci produce dextrose from an 

 excess of lactic acid, or that yeast produce sugar from 

 an excess of alcohol and CO2. It is probably safe to 

 assume that the process is irreversible. 



This assumption that the mass law does not enter into 

 consideration is well substantiated by the fact that a 

 certain strain of Strept. lactis will produce 0.4% of lactic 

 acid in broth and no more, regardless of whether the 

 nutrient medium contains, 2, 5, 10 or 20% of lactose 

 (see Table 28 by Orla- Jensen, 1919). According to 

 the mass law, an increase of substrate should always 

 bring about an increase in the products, because the 



equilibrium would require the coefficient: '7 -^ — 7-^ 



or f -T — rjn to be constant. It is not necessary, there- 

 fore, to consider the inhibition of the alcoholic fermenta- 

 tion by alcohol from any different chemical view point 

 than the inhibition by phenol or other disinfectants. 



The proof that a fermentation is stopped by the 

 accumulation of its products has been given in some 

 instances by the observation that fermentation starts 

 anew if the harmful products are removed. It is 

 generally known that acid forming organisms will pro- 

 duce more acid if the medium is neutralized. 



