Mixed Infections 93 



kinds. Therefore their operation in the body is subject to modifi- 

 cations produced in them or in the host by these associated 

 organisms. 



In experimental investigations this fact is not infrequently for- 

 gotten and it is often remarked with surprise that the results of 

 inoculation with pure cultures of a micro-organism may be clinically 

 different from those observed under natural conditions. 



The tetanus bacillus, which endures with difficulty the effects 

 of uncombined oxygen, flourishes in association with saprophytic 

 organisms by which the oxygen is absorbed. The same thing is 

 probably true of other obligatory anaerobic organisms. 



The metabolic products of one species may intensify or accelerate 

 the action of those of an associated species, or the reverse may be 

 true, and the products of different organisms, having different 

 chemical composition, may neutralize one another, or combine to 

 form some entirely new substance different from its antecedents. 

 Such conditions cannot fail to influence the type and course of 

 infection. 



