NATURE OF ANTAGONISTIC ACTION 51 



crease in intensity of the pigment (690); the blue pigment of Bac- 

 terium violaceum, however, only delayed the growth of the fungus. Ac- 

 cording to Doebelt (177), Pemc'illlum ajricanum produces a more in- 

 tense pigment in contact with other fungi such as Aspergillus niger; this 

 pigment accumulates in the mycelium of the latter, which may thereby 

 be killed. Nadson (626) demonstrated that some fungi {Penicillium 

 luteum and Spcaria furfuro genes) produce a pigment that is used not 

 only for purposes of protection, but also for attack upon other organ- 

 isms, whereby the latter are killed and stained. 



DISTRIBUTION OF ANTAGONISTIC PROPERTIES 



Numerous microbes found among the bacteria, fungi, actinomycetes, 

 and protozoa possess the capacity of bringing about injurious or de- 

 structive effects upon other microorganisms belonging to their own 

 groups or to others. In some instances, the antagonistic effects are ob- 

 tained only in the presence of the antagonizing organism; in many 

 other cases, excretion products consisting of definite chemical com- 

 pounds are produced by the antagonist. A few of these products have 

 been isolated and have been found to be effective against certain few 

 specific organisms or able to act upon a great variety of organisms 

 (920). The wide distribution of antagonistic properties among micro- 

 organisms is brought out in subsequent tables. 



THEORIES OF THE NATURE OF 

 ANTAGONISTIC ACTION 



The various theories proposed to explain the mechanism of antago- 

 nistic effects of microorganisms may be summarized under the follow- 

 ing processes : 



Exhaustion of nutrients 



Physicochemical changes in medium 



Enzyme action, either directly by the antagonist or as a result of cell 



autolysis, under the influence of the antagonist 

 Production and liberation of toxic substances 

 Pigment action 

 ' Action at a distance 

 Space antagonism 



