88 THE STRUGGLE FOR EXISTENCE 



fluence of Schizosaccharomyces upon Saccharomyces, was equal to 

 3.05-3.15, than under aerobic conditions it is equal to 1.25. In 

 other terms the influence of Schizosaccharomyces on Saccharomyces 

 is no longer 3.05, but only 1.25 times as strong as the influence of the 

 latter upon itself. 



(4) Let us now examine the production of alcohol under aerobic 

 conditions. The corresponding data are given in Table 2 (Appen- 

 dix). As was to be expected, in aerobic conditions the amount of 

 alcohol per unit of yeast volume is smaller than in anaerobic ones, 

 because a part of the available energy is furnished by oxidation. It 

 is interesting to compare the critical concentration of alcohol at which 

 growth ceases, in aerobic and anaerobic conditions. Let us multiply 

 as before the production of alcohol per unit of yeast volume by the 

 maximal volume. For the anaerobic experiments of 1932 we shall 

 obtain: Saccharomyces, 6.25 X 0.245 = 1.53; Schizosaccharomyces, 

 3.0 X 0.510 = 1.53. These threshold concentrations of alcohol 

 coincide in both species, and they are sufficiently near to those with 

 which we have had to deal in the anaerobic experiments of 1931. As 

 to the threshold concentrations of alcohol in aerobic conditions, they 

 prove to be higher than in the anaerobic ones, and in Saccharomyces 

 the threshold lies somewhat higher than in Schizosaccharomyces: 

 Saccharomyces, 9.80 X 0.207 = 2.03; Schizosaccharomyces, 

 6.9 X 0.258 = 1.78. 



If we now calculate for aerobic conditions the degree of influence 

 of Schizosaccharomyces upon Saccharomyces starting from the produc- 

 tion of alcohol per unit of yeast volume, we shall obtain : 



0.258 

 ai = O207 = L25 - 



Correspondingly the coefficient 



* = °oi-s = «■ 



Comparing these results with the data of the kinetics of growth, we 

 see (Table VII) that in aerobic conditions the degree of influence of 

 one species upon another calculated according to the system of equa- 

 tions of the struggle for existence fully coincides with the coefficients 

 of the relative alcohol production. Therefore, the process of com- 



