SYMBIOSIS AND ANTIBIOSIS 39 



and any disturbance of this equilibrium results in a number of changes 

 in the microbial population, both qualitative and quantitative. The 

 ecological nature of this population found under certain specific con- 

 ditions, as well as the resulting activities, can be understood only 

 when the particular interrelationships among the microorganisms are 

 recognized. Because of its complexity, the soil population cannot be 

 treated as a whole, but some of the processes as well as some of the 

 interrelations of specific groups of organisms can be examined as sepa- 

 rate entities. Some have received particular attention, as the relations 

 between the nonspore-forming bacteria and the spore-formers, the ac- 

 tinomycetes and the bacteria, the bacteria and the fungi, the protozoa 

 and the bacteria, and the relations of the bacteria and the fungi to the 

 insects. 



The term "synergism" has been used to designate the living together 

 of two organisms, resulting in a change that could not be brought about 

 by either organism alone (440). Microbes living in association fre- 

 quently develop characteristics which they do not possess when living 

 in pure culture. For example, Schiller (835) found that when beer 

 yeasts are placed together with tubercle bacteria in a sugar-containing 

 but nitrogen-free medium, the yeasts develop antagonistic properties 

 toward the bacteria and use the latter as a source of nitrogen by secret- 

 ing a bacteriolytic subtance that is also active outside their cells. 

 Various bacteria are able to kill yeasts when they are inoculated into 

 suspensions of the latter in distilled water. The destruction of the 

 fungus Ofhiobolus, the causative agent of the take-all disease of cereals, 

 by soil organisms was believed to be a result of the need of a source of 

 nitrogen by the latter. 



Papacostas and Gate (706) suggested applying the term "antibiosis" 

 to interactions in mixed cultures in vitro and "antagonism" to mixed 

 infections in vivo. In order to obviate a possible concept that the two 

 types of interaction, namely in the test tube and in the living body, are 

 different, it is more appropriate to apply the term "antagonism" to the 

 unfavorable effects of one living system upon another and "antibiosis" 

 to the production by one organism of specific chemical substances which 

 have an injurious effect upon another organism. 



