MECHANISM OF COMPETITION IN YEAST CELLS 89 



petition between our species in aerobic conditions is entirely regu- 

 lated by alcohol, and there is scarcely any interference of other 

 factors. 



(5) We can now appreciate from a more general viewpoint the 

 results of the aerobic experiments as well as those of this chapter. It 

 has been shown that under aerobic conditions the theoretical equa- 

 tion of competition between two species of yeast for a common place 

 in the microcosm given for the first time by Vito Volterra is com- 

 pletely realized. In other words, if we know the properties of two 

 species growing separately, i.e., their coefficients of geometric increase, 

 their maximal volumes, and alcohol production per unit of volume 

 when alcohol limits the growth, then connecting these values into a 

 theoretical equation of the struggle for existence we can calculate in what 

 proportion a certain limited amount of energy will be distributed between 

 the populations of two competing species. This means that we can 

 calculate theoretically the growth of species and their maximal 

 volumes in a mixed population. The equation of the struggle for 

 existence expresses the idea that a potential geometric increase of each 

 species in every infinitesimal interval of time is only realized up to 

 a certain degree depending on the unutilized opportunity for growth 

 at that moment, and that the species possesses certain coefficients of 

 seizing this unutilized opportunity. Such theoretical calculations 

 agree completely with the experimental data only under aerobic 

 conditions, where the limitation of growth in both species depends 

 almost completely on the ethyl alcohol. In the case of anaerobic 

 conditions the situation becomes more complicated as a result of the 

 influence of certain other waste products. This shows that extreme 

 care is necessary in the investigation of biological systems, because 

 various and often unexpected factors may participate in the process 

 of interaction between two species. 



