ENERGY SUPPLY OF THE CELL 133 



It is also worth noting that at 29°C. and 32.5°C., the 

 rate of fermentation remains really constant during 22 

 hours, and does not decrease as in the case of zymase 

 (p. 13^). This constancy of the optimum temperature 

 after the Tammann principle has been overcome by 

 time, differentiates the fermentation by living cells 

 from that of a mere enzyme action. 



Below the optimum, the temperature coefficient 

 is normal. From the rates at 29''C. and 32.5°C. in the 

 above table, we obtain Qio = 1.98. Rubner (1913) 

 found lower values, 1.40 and 1.58, between 23°C. and 

 38°C. because the latter temperature is already too 

 high. Aberson (1903) observed an average coefficient 

 of 2.72 between 12°C. and 30°C. Slator's data ri906) 

 have already been given in Table 20, p. 122. 



The assumption has been made above that the temp- 

 erature coefficient of fermentation is that of a normal 

 chemical reaction except for a superposition of another 

 process near the maximum and the minimum tempera- 

 tures. This assumption seems justified as far as supra- 

 optimal temperatures are concerned. 



No good explanation has as yet been given for the 

 existence of a minimum temperature. It is considered 

 an established fact that with most organisms, fermenta- 

 tion ceases at a temperature well above the freezing point. 

 This might be a wrong conclusion, however. If no 

 fermentation products can be found in a medium 

 inoculated in the ordinary way, and held at low tempera- 

 ture, it is proof only that the bacteria did not grow. 

 The number of transferred cells is too small to produce 

 sufficient fermentation products to be detected in the 

 ordinary way. 



The minimum temperature of fermentation can be 

 established only if very large numbers of cells are trans- 



