CHAPTER IX. 

 THE BACTERIA OF THE ALIMENTARY TRACT. 



A DISCUSSION of the bacteria of the alimentary tract fol- 

 lows very naturally upon a discussion of the enzymes elab- 

 orated here, for the various bacteria contain enzymes in 

 their bodies and secrete them. Some of these bacterial en- 

 zymes are not unlike those which are secreted by the glands 

 of the alimentary tract. By virtue of these, the bacteria may 

 therefore augment, in a limited way, the activities of the 

 alimentary secretions. In large part, however, the bac- 

 terial ferments are able to bring about changes in the ali- 

 mentary contents which differ totally from those brought 

 about by the secretions of the alimentary tract proper. The 

 substances formed in this way are usually harmless in char- 

 acter, though at times, through excessive production or 

 through the formation of specific poisonous substances, they 

 assume even a pathological importance. 



The subject of the bacteria of the alimentary tract, to- 

 gether with a discussion of their physiological and patho- 

 logical role, has given rise to a literature which is simply 

 enormous. Nor do the conclusions reached by the various 

 authors at all harmonize a fact not strange when the com- 

 plexity of the problem is recognized. For under normal 

 and abnormal conditions practically every form of bacterium 

 enters the intestinal tract, and when it is remembered that 

 usually more than one kind of micro-organism is present at 

 the same time, that the medium upon which they grow (food, 

 etc.) is subject to the greatest variation, and that the agencies 



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