SYMBIOSIS AND ANTIBIOSIS 39 



by Pfeffer (684), who said that "the entire world and all the friendly 

 and antagonistic relationships of different organisms are primarily 

 regulated by the necessity of obtaining food." It was soon recognized, 

 however, that this explanation does not account fully for all the com- 

 plex interrelations among microorganisms in nature. 



De Bary (165) was the first to emphasize, in 1879, the significance 

 of the antagonistic interrelations among microorganisms j when two or- 

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

 the other and even kills it. This phenomenon was designated "anti- 

 biosis" (42, 953). Symbiotic, or mutualistic, and antagonistic relation- 

 ships among microorganisms indicate whether advantages or disadvan- 

 tages will result to the organisms from the particular association; the 

 first are beneficial and the second are injurious and may even be para- 

 sitic. Kruse (508) asserted that, when two organisms are capable of 

 utilizing the same nutrients but are diflFerently affected by environ- 

 mental conditions such as reaction, air supply, and temperature, the one 

 that finds conditions more suitable for its development will grow more 

 rapidly and in time be able to suppress the other. According to Porter 

 (695), the effects produced by fungi in mixed culture are due either to 

 exhaustion of nutrients or to the formation of detrimental or beneficial 

 products. E. F. Smith (829) emphasized that when two or more or- 

 ganisms live in close proximity they may exert antagonistic, indifferent, 

 or favorable effects upon one another. These potentialities were later 

 enlarged (loii) to include stimulating, inhibiting, overgrowing, and 

 noninfluencing effects. After considerable experimentation and specula- 

 tion, Lasseur (513, 514) came to the conclusion that antagonism is a 

 very complex phenomenon and is a result of numerous and often little- 

 known activities. Antagonism influences the morphology of the organ- 

 isms, their capacity of pigment production, and other physiological 

 processes. 



No sharp lines of demarcation can be drawn between associative and 

 antagonistic effects. Well-defined effects of two symbionts may change 

 during the various stages of their life cycles or as a result of changes in 

 the environment. It is often difficult to separate strictly symbiotic phe- 

 nomena from associations of less intimate nature, frequently desig- 



