INTESTINAL BACTERIA 201 



tions. The invaders multiply, produce local lesions, and more 

 or less crowd out the normal inhabitants. 



Apart from infections abnormal conditions may result from 

 the unbalanced activities of the organisms ordinarily present in 

 the intestines. So far as at present known two distinct processes 

 may be concerned : (1) excessive bacterial proteolysis, by means 

 of which toxic substances are produced from the protein ingested 

 as food which when absorbed by the body cells give rise to the 

 condition known as " auto-intoxication," or (2) excessive carbo- 

 hydrate fermentation which may result in an overproduction of 

 acids or other irritating substances and cause a chronic diarrheal 

 condition. 



Of the many varieties of bacteria occupying the intestines of 

 man and animals a certain group, ordinarily non-pathogenic, are 

 classed together as " colon bacilli " because they live in the colon 

 and have similar characteristics. Closely related morphologically 

 and biologically to the colon bacilli are a number of other organ- 

 isms which when they gain access to the intestines give rise to 

 distinctly morbid conditions. The entire group is termed the 

 colon-typhoid group. Such members as the typhoid and para- 

 typhoid bacilli, including the types responsible for meat poisoning, 

 are specifically pathogenic ; the colon bacilli and their near rela- 

 tives are pathogenic only under certain circumstances. 



The group is usually arranged in four subdivisions : 



1. Colon Group. Normally present in the intestines, rarely 



pathogenic. 



2. Para-typhoid Group. Possessing varying degrees of patho- 



genicity. 



3. Bacillus typhosus. Pathogenic. 



4. Dysentery Group. Pathogenic. 



All members of the entire group possess certain common char- 

 acteristics. They are rather short, non-spore-bearing bacilli ; stained 

 by Gram's method they are decolorized; none of them liquefies 

 gelatin. 



Apart from these general features there appears to be a variety 



