114 PHYSIOLOGY OF BACTERIA 



for any retardation by its own products. The computa- 

 tion of this constant from available data on the alcoholic 

 and lactic fermentations gave values of sufficient con- 

 stancy to consider them a proof of the general principle 

 involved. 



(d) THE INFLUENCE OF CONCENTRATION OF 

 MICROORGANISMS 



It is generally understood that the fermentation 

 produced in any medium is the sum of all fermentations 

 going on in each individual cell. This assumption is 

 the basis of the formula for the fermenting capacity 

 (see p. 404). 



A number of data are available to show such propor- 

 tionality of cells and products. Slator (1906) found by 

 his method (p. 103) the following relative rates of 

 fermentation : 



Relative yeast concentrations = 



1 : 3 : 5 : 10 : 20 : 25 



Relative rates of fermentation = 



0.99 : 3.04 : 4.94 : 10 : 19.8 : 24.7 



The same can be seen from Rubner's experiments in 

 Table 18 showing the fermentation of nitrogen-free 

 sugar solution by varying amounts of yeast. The 

 fermentation constants, computed with the formula 

 on p. 110, give the rate of fermentation corrected for 

 retardation by alcohol. These rates show good propor- 

 tionality with the quantities of yeast used. 



(e) INFLUENCE OF THE CONCENTRATION OF SUBSTRATE 



Considering that fermentation is brought about by 

 enzymes in the cells, we should expect fermentation to 



