INFECTIONS OF THE DIGESTIVE TRACT 155 



have made on milk that the peptonizing action of these 

 bacilli is extremely slight, though not absolutely lacking. 

 On the other hand, the colon bacilli are able to cleave 

 energetically peptones prepared by other microorgan- 

 isms. Then they give rise to familiar products of pu- 

 trefaction such as ammonia, volatile fatty acids, phenol 

 and indol, and hydrogen sulphide. These facts have an 

 important bearing on the significance of these bacteria 

 within the digestive tract, which may be summarized 

 as follows. If there is good absorption of proteids above 

 the lower ileum, that is, above the level where there is 

 a predominance of colon bacilli, little proteid material 

 finds its way into the colon. Hence whatever may be the 

 nature of the bacterial inhabitants of the large intestine, 

 but little putrefactive decomposition occurs there. But 

 if, owing to a superabundance of proteid food consid- 

 erable native proteid finds its way into the colon, its 

 fate depends on the character of the flora there. In a 

 normal intestine, containing few peptonizing bacteria, 

 there will be little putrefaction, because the dominant 

 races, members of the coli group, cannot initiate active 

 putrefaction of native proteids. But if there be present 

 also putrefactive anaerobes capable of peptonizing pro- 

 teids, the colon bacilli take an active part in breaking 

 down the hydrolyzed proteids with which they are thus 

 supplied. In this way the colon bacilli frequently be- 

 come active participants in excessive intestinal putre- 

 faction. I shall recur to this subject in the discussion 

 of the putrefactive anaerobes. 

 The disappearance of typical colon bacilli from the 



