ASSOCIATIVE INTERRELATIONSHIPS 43 



aeruginosa may be weakened when the latter is grown together with 

 other organisms. E. colt may lose the property of fermenting sugars 

 when grown in the presence of paratyphoid organisms (462). 



Some associations of microorganisms are not so simple. The complex 

 system of animal infection by more than one organism, with the result- 

 ing complex reactions in the animal body, is a case in point. 



The effect of one organism upon the activities of another can be illus- 

 trated by the results of the decomposition of complex plant material by 

 pure and mixed cultures of microbes (Table 5). Trichoderma, a fungus 



TABLE 5. DECOMPOSITION OF ALFALFA BY PURE AND MIXED 

 CULTURES OF MICROORGANISMS 



From Waksman and Hutchings (960). 



known to be an active cellulose-decomposing organism, did not attack 

 at all the cellulose of alfalfa and decomposed the hemicelluloses only to 

 a limited extent} however, the organism utilized the proteins rapidly, 

 as illustrated by the amount of ammonia liberated. RhizofuSy a non- 

 cellulose-decomposing fungus, attacked largely the hemicelluloses in 

 the alfalfa and some of the protein } a small reduction in cellulose was 

 recorded, probably because of an analytical error. When Trichoderma 

 was combined with Rhizofus y the former attacked readily both the cel- 

 lulose and the hemicelluloses. The same effect upon the activity of 

 Trichoderma was exerted by other noncellulose-decomposing organ- 



