82 



THE STRUGGLE FOR EXISTENCE 



tion. Let us at present leave them aside and endeavor to calculate 

 the values of the coefficients of competition starting from the alcohol 

 production. As mentioned above, the cessation of growth is con- 

 nected with the reaching of a certain critical concentration of alcohol 

 (characteristic for the given species under given conditions) . Let us 

 now assume that it is mainly alcohol that matters and that other by- 

 products of fermentation are but of subordinate importance. Conse- 

 quently, every unit of volume in each species produces a determined 

 amount of alcohol, and when the latter reaches a certain threshold 

 concentration the growth is checked. It follows that when a unit of 

 volume of the first species produces an amount of alcohol consider- 

 ably surpassing that produced by a unit of volume of the other species 



TABLE V 



Alcohol production in Saccharomyces cerevisiae and Schizosaccharomyces kephir 



From Gause ('32b) 



«1 



0.247 

 0.113 



- 2.186 



and the threshold values of alcohol in both are somewhat near to one 

 another, the critical concentration of alcohol and the cessation of 

 growth in the first species will be reached with a lower level of accumu- 

 lated yeast volume. In Table V are given the data on the alcohol 

 production in Saccharomyces and Schizosaccharomyces under anaerobic 

 conditions. The determinations of the alcohol were made for the 

 middle stages of growth, when its accumulation was almost strictly 

 in proportion to the increase of the yeast volume. In Saccharomyces 

 the alcohol production per unit of volume averages 0.113 per cent 

 by weight, and in Schizosaccharomyces 0.247. These data show 

 clearly that the latter species utilizes the medium unproductively 

 and it occupies "a great number of places" by a comparatively small 



