ENERGY SUPPLY OF THE CELL 155 



increasing temperature. Above the growth-optimum, 

 the drop of endpoint with rising temperature is very 

 rapid. 



At temperatures near the minimum, the final concen- 

 tration decreases with decreasing temperature. 



At temperatures below the growth-minimum, the 

 endpoints are quite low. 



SUMMARY OF THEORIES 



The decrease of the endpoint by an increase in tem- 

 perature is well accounted for by the assumption that 

 the products which inhibit further fermentation are 

 more harmful to the cells or to the enzymes in the cells 

 at higher temperatures. This is in accordance with the 

 action of disinfectants. 



The explanation of the decrease of the endpoint below 

 the minimum as due to deterioration of the enzymes 

 and lack of formation of new enzymes, is not entirely 

 satisfactory, as it leaves some facts unexplained. 



VII. CHANGES IN TYPE OF FERMENTATION 

 (a) CHANGES DUE TO CHEMICAL COMPOSITION OF MEDIUM 



Many microorganisms, perhaps all except the strictly 

 prototrophic species, can use more than one kind of 

 chemical compounds for the production of the necessary 

 energy. Quite often, an organism will produce different 

 fermentations in different foods. Yeast growing in a 

 sugar-free medium will form products different from 

 those in a sugar-containing medium. In solutions of 

 dextrose or fructose or maltose or sucrose, however, a 

 beer yeast will form the same endproducts from different 



