Effects of Bacterial Growth on the Environment 



189 



Cooperations and antagonisms are very common among microscopic 

 plants and animals just as these relationships exist with higher 

 forms of life. Even in infections, such as a severe sore throat, more 

 than one organism is found in the affected area, but only one 

 species may be attributed as the cause of the severe symptoms. 



Fig. 31. Microbial antagonisms in an agar plate inoculated with 

 soil. Three of the colonies have produced an inhibitory substance that 

 has prevented the growth of surrounding organisms. (Courtesy of 

 A. Kelner, S.A.B. No. 143.) 



Blood poisonings, at least in the advanced stages, are usually pure 

 cultures of aggressive organisms. The various relationships exist- 

 ing between microorganisms will ultimately affect their environ- 

 ment. Therefore, a discussion of these reactions seems pertinent in 

 this chapter. 



When organisms work together for mutual benefit, we call this 



