ANTAGONISTIC INTERRELATIONSHIPS 49 



certain filters, from which they can be removed by the use of special 

 solvents such as ether, alcohol, chloroform, and acetone. The concen- 

 tration of the antagonistic substance produced by many fungi and bac- 

 teria was found (240, 641 ) to be greatly influenced by the energy and 

 nitrogen sources in the medium and by environmental conditions, such 

 as temperature and aeration. 



The three important types of antagonism are (a) the repressive, in- 

 hibitive, or bacteriostatic, (b) the bactericidal, and (c) the bacteriolytic. 

 When one bacterium is inoculated into the filtrate of another, the 

 growth of the first is slower than that of the control (299). Certain 

 types of antagonism express themselves in the destruction by the an- 

 tagonist of the other organisms present in the mixed culture, with 

 or without producing a lytic effect, B. mesenterkus^ for example, is 

 capable not only of depressing but also of killing the cells of diphtheria 

 and pseudodiphtheria (1016), The lytic form of antagonism is illus- 

 trated by the action of Ps. aeruginosa^ Bacillus hrevis, and certain other 

 antagonists upon micrococci and various spore-forming bacteria. 



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

 onism," attention was directed (627) 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 rH of medium or an impoverish- 

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

 often distinguished (634) 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 (365, 367) to repress the anthrax organ- 

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

 gators (407) designated the action of the living cell itself as "true 

 antagonism." 



Bail (31) 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- 

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

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



