ENERGY SUPPLY OF THE CELL 151 



present in the medium. This was the case with bread 

 yeast and with several streptococci. 



The higher acidity produced in milk by many strep- 

 tococci when peptone is added, can be explained by the 

 larger number of cells growing in peptone milk. 



With Lactoh. acidophilus, this phenomenon could not 

 be observed. 



(g) INFLUENCE OF TEMPERATURE UPON THE ENDPOINT OF 

 FERMENTATION 



The final concentration of fermentation products is, 

 to a considerable degree, influenced by the temperature. 

 A very simple explanation is usually offered for this 

 observation: the toxic effect of the product upon the 

 zymase being a chemical reaction, its effect is increased 

 by a rise of temperature and thus causes a lower endpoint. 

 Several experiments show this decrease of the final 

 concentration of products by an increase in temperature. 

 Miiller-Thurgau (1885) gave the following endpoints 

 for the fermentation by a wine yeast: 



Table 34. — Final Alcohol Concentrations by Saccharomyces 



ellipsoideus 



At 36°C 3.8% alcohol 



27°C 7.5% 



IS^C 8.8% 



rC 9.5% 



Schierbeck (1900) observed a similar difference with 

 the lactic fermentation at 20°C. and 35°C. 



The temperature relation is not quite so simple, how- 

 ever. According to a table in Marshall, Microbiology 

 (1912 p. 273), lactic streptococci do not produce the 

 maximum acidity at the lowest temperature; there is a 

 decrease in final acidity at temperatures near the 

 minimum of growth. This agrees entirely with the 



