CHAPTER 3 



INTERRELATIONSHIPS AMONG MICROORGAN- 

 ISMS IN MIXED POPULATIONS 



It must not be jor gotten that there are extremes in another di- 

 rectton, where one of the two associated organisms is injuring 

 the other, as exemflified by many farasites, but these cases I 

 leave out of account here. This state of affairs has been termed 

 antibiosis. — H. M. Ward. 



The antagonistic effects of one organism upon another were observed 

 by many of the early microbiologists. It is sufficient to cite here three 

 striking examples based upon totally different approaches to the sub- 

 ject. 



In 1876, Tyndall (919), on the basis of the growth of wild cultures 

 of bacteria and fungi in organic media, spoke of "the struggle for 

 existence between the Bacteria and the PenkilUum. In some tubes the 

 former were triumphant j in other tubes of the same infusion the latter 

 was triumphant. The Bacteria which manufacture a green pigment 

 appear to be uniformly victorious in their fight with the Penicillium." 



In 1877, Pasteur (710) noted that the production of anthrax in sus- 

 ceptible animals can be repressed by the simultaneous inoculation with 

 B. anthracis and various other bacteria. This led him to make the 

 foUov/ing significant suggestion: ". . . on peut introduire a profusion 

 dans un animal la bacteridie charbonneuse sans que celui-ci contracte le 

 charbon: il suffit qu'au liquide qui tient en suspension la bacteridie on 

 ait associe en meme temps des bacteries communes." 



In 1879, DeBary (172) emphasized the significance of the antag- 

 onistic interrelations among microorganisms j when two organisms 

 are grown on the same substrate, sooner or later one overcomes the 

 other and even kills it. 



These and other observations thus laid the basis for a study of mutu- 

 alistic effects of microorganisms in natural and in artificial environ- 

 ments. 



