48 INTERRELATIONSHIPS AMONG MICROORGANISMS 



antagonism express themselves in the destruction by the antagonist of 

 the other organisms present in the mixed culture, with or without lysis. 

 B. mesentericusj for example, is capable not only of depressing but also 

 of killing the cells of diphtheria and pseudodiphtheria (1052). The 

 lytic form of antagonism is illustrated by the action of Ps. aeruginosa, 

 B. brev'ts, and certain other antagonists upon micrococci and various 

 spore-forming bacteria. 



In differentiating between "direct antagonism" and "passive antag- 

 onism," attention was directed (670) to the fact that the latter depends 

 not upon the direct action of the antagonist but upon the changed con- 

 ditions of culture under the influence of the antagonist's growth. This 

 may comprise a change in ^H and r¥L of medium or an impoverish- 

 ment of some of the nutrient constituents. "Direct antagonism" was 

 often distinguished (677) from "indirect antagonism," the first being 

 limited to those phenomena in which the antagonistic action is con- 

 nected with the direct action of the living cell, whereas in the second the 

 metabolic products produced by one organism are injurious to others. 

 Intestinal bacteria were found (367, 369) to repress the anthrax organ- 

 ism only when the former were in an active living state. Other investi- 

 gators (418) designated the action of the living cell itself as "true 

 antagonism." 



Bail (32) suggested that for every bacterium there is a typical 

 constant number of cells capable of living in a given space. When this 

 concentration (M) is reached, multiplication comes to a standstill, in- 

 dependently of exhaustion of the nutrients or formation of toxic sub- 

 stances. The same phenomenon was believed to hold true when two 

 bacteria live together (1013): if the limiting cell-in-space concentra- 

 tions are different for the two organisms, the one with a higher M value 

 represses the other; however, the weaker species may check the stronger 

 when planted in sufficient excess (243). It has been suggested (370) 

 that certain physiological properties of the individual organisms, desig- 

 nated as "biological activity" and "competitive capacity," must also be 

 taken into consideration in evaluating this relationship. The fact that 

 the number of yeast cells reaches a maximum independently of the ini- 

 tial number of cells added or the concentration of nutrients in a given 



