50 INTERRELATIONSHIPS AMONG MICROORGANISMS 



bacteria live together (983, 984): if the limiting cell-in-space concentra- 

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

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

 when planted in sufficient excess (244). It has been suggested (368) 

 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 (634, 983, 984). 

 Brown (90) explained the fact that the number of yeast cells reaches a 

 maximum independent of the initial number of cells added or the con- 

 centration of nutrients in a given volume of medium by the amount of 

 oxygen originally present. 



Garre (311) deserves the credit for having first noted that antago- 

 nism may be either one-sided or two-sided. In the first case, one organ- 

 ism represses another that is not antagonistic to itj in the second case, 

 both organisms repress each other. A one-sided antagonism may become 

 two-sided under certain conditions of culture. E. coU is antagonistic to 

 E. tyfhosa; however, if the latter is inoculated into a medium some- 

 what earlier than the former, E. tyfhosa becomes antagonistic to E. colt 



(324,915). 



Although the most common antagonisms are between organisms of 

 different species, there are numerous instances where one strain of a 

 species may be antagonistic toward another strain of the same species 

 (52, 368, 611). Certain strains may develop antagonistic properties in 

 the presence of other strains (77). Nonflagellated variants of typhoid 

 bacteria were repressed by a flagellated form, smooth variants of para- 

 typhoid bacteria by rough forms, and so on. The fact that all bacterial 

 cultures stop growing after a certain period of time has been interpreted 

 to be a result of the antagonistic action of some cells upon others. When 

 the filtrates of such cultures are added to fresh nutrient media they may 

 stop the growth of the same species as well as that of other species. 



Certain organisms produce pigments in the presence of others j these 

 pigments are believed to be in some way associated with the phenome- 

 non of antagonism. In the presence of S. lutea^ V. comma forms a 

 dark violet pigment that is accompanied by an increase in agglutination 

 and in virulence (627). The destruction of Dktyostelium muco- 

 roides by a red-pigment-forming bacterium was accompanied by an in- 



