140 PHYSIOLOGY OF BACTERIA 



A large number of experiments on stimulation of 

 alcoholic fermentation by poisons has been published by 

 Branham (1929) . These data do not show the Tammann 

 principle. Perhaps the time intervals chosen in these 

 experiments were not appropriate to bring forth this 

 effect. 



SUMMARY 



The action of enzymes, zymases and living cells can be 

 stimulated by certain poisons, i.e., by compounds which, 

 in slightly higher concentrations, would be distinctly 

 toxic. 



In some instances, a shifting of the optimum concen- 

 tration for stimulation with time is quite evident, as in 

 the Tammann principle. It seems possible to explain 

 chemical stimulation on the same basis as temperature 

 effects, assuming the poison to act as a catalyst for 

 enzyme action as well as for enzyme deterioration. 



VI. THE ENDPOINT OF FERMENTATION 

 (a) CHEMICAL CONSIDERATIONS 



All fermentation in a given volume of fermentable 

 solution will ultimately come to an end. This endpoint 

 is an important and usually quite definite property of a 

 culture. It is caused by one of two possibilities; either 

 the fermentable substrate is exhausted, or the accumula- 

 tion of products prevents any further enzyme action (or 

 possibly enzyme regeneration). In most fermentations, 

 we can bring about at will the first or second type of 

 endpoint, by varying the concentration of the ferment- 

 able material. It still remains to be shown what happens 

 in the case where all fermentation products are volatile, 

 as in complete oxidation of lactic acid by Mycoderma. 



