118 



PHYSIOLOGY OF BACTERIA 



0.3 atm., it seemed nearly proportional to the oxygen 

 concentration. The results are shown graphically in 

 Fig. 12. The influence of the nitrate concentration 

 upon the rate of oxidation by Nitrobacter, measured by 

 the same author, is shown in Fig. 13. The curves are 

 nearly alike, and agree well with those from Slator's 

 experiments. 



A good verification of the same principle can also be found in Table 

 15. The sugar concentration was varied while the yeast concentra- 

 tion was constant. The amount of sugar fermented was the same 

 in all concentrations until so much had been fermented that less than 

 1.5% of sugar remained. This moment is indicated in the table by a 

 cross line. 



No corresponding data for other fermentations have been found 

 in the literature by the author. The unpublished experiments by 

 Peltier which are mentioned in more detail on p. 207 bring out the 

 same independence as regards the lactic fermentation. Peltier 

 studied the lactic fermentation in milk diluted with varying amounts 

 of water, the highest concentration being twice that of normal milk. 

 From the number of cells and the amounts of acid formed, he com- 

 puted the fermenting capacity per cell. The following data were 

 obtained: 



The result is the same as in the alcoholic fermentation: the rate 

 of fermentation is fairly constant above 1 % of lactose, but decreases 

 as the sugar concentration falls below 1%. 



SUMMARY 



The rate of fermentation depends upon the concentra- 

 tion of the substrate only if this concentration is low. 



