116 PHYSIOLOGY OF BACTERIA 



Slater and Sand (1910) have shown it to be very unlikely 

 that conditions could be experimentally realized under 

 which diffusion becomes a controlling factor of the rate 

 of fermentation. 



The influence of the concentration of the substrate 

 upon enzyme activity is rather complex as may be seen 

 from the discussion by Waldschmidt-Leit z ( 1 929) . There 

 is no need of going into the details of this discussion 

 because it concerns largely the rate at very low concen- 

 trations of the substrate, while in experiments with rates 

 of fermentation, we are dealing mostly with fairly high 

 concentrations. Under these conditions, the rate of 

 enzyme action is almost independent of the substrate 

 concentration. The enzyme combines rapidly with the 

 substrate, and this compound decomposes but slowly; 

 therefore, the concentration of the enzyme-substrate 

 compound determines the rate of products formed. 

 As long as there is enough substrate available to combine 

 readily with any enzyme molecule that is set free, the 

 concentration of the enzyme-substrate compound will 

 be constant, and consequently the rate of enzyme action 

 is constant. 



Nelson and Vosburgh (1917) found the rate of invertase 

 action constant if the sucrose concentration was above 

 5%. Northrup (1923) found the rate of trypsin action 

 upon casein constant if the casein concentration was 

 above 2%. 



The rate of alcoholic fermentation has been found 

 to be independent of the sugar concentration by Dumas, 

 as early as 1874, and this result has been verified by a 

 number of investigators (Literature, see Slator, 1906). 

 More accurate measurements were made by Slator (1906) 

 who found the following relative rates of fermentation 

 at 30°C. by the same amount of yeast: 



