242 BACTERIA PATHOGENIC TO MAN 



their way through the food or from the anus upward. In the small 

 intestines the bacterium lactis aerogenes is most prevalent, while in the 

 csecum and below the colon types predominate. 



In healthy intestines a function of colon bacilli is supposed to be to- 

 prevent, through acids and other products formed, the development of 

 putrefactive bacteria. In normal intestines with intact mucous mem- 

 branes the toxic products formed by the colon bacilli are absorbed but 

 little or not at all, and the bacilli themselves are prevented from invad- 

 ing the tissues by the epithelial layer and the bactericidal properties of 

 the body fluids. Possibly there is an acquired immunity to the colon 

 varieties which have long inhabited the intestines. 



Behavior during Diarrhoea. In diarrhoea we find increased peristalsis, 

 less absorption of foodstuff, increased and changed intestinal secre- 

 tions. Tissier observed that under treatment with cathartics the colon 

 varieties increased, while the anaerobic forms are inhibited. In diarrhoea 

 the same conditions are active, inhibiting causes are lessened, and 

 increased mucus and serum are poured out into the canal. This is 

 notably seen in typhoid fever. In diarrhoea, although the common 

 colon varieties are met with, there is usually seen a difference in that 

 uncommon varieties and more typhoid-like bacteria are also found. 

 Much more investigation is needed on this complex subject of varia- 

 tion in types between health and disease. 



Passage of Colon Bacilli through the Walls of the Intestines Just Before 

 and After Death. The colon bacilli tend to pass through the intestinal 

 walls shortly after death in those who have suffered from chronic ill- 

 ness. In chronic disease the resistance of the tissues is lessened or 

 removed, and if to this is added ulceration or loss of epithelium in 

 the lining of the intestines the entrance of the bacteria is still more 

 favored. The temperature at which the body is kept after death deter- 

 mines often whether a general post-mortem invasion takes place. The 

 passage of the colon bacilli before death rarely occurs unless some 

 lesions of the intestines are present. 



Varieties of Colon Bacilli as Disease Producers. The colon bacillus 

 was at first regarded purely as a saprophyte. Later, through not realiz- 

 ing the post-mortem invasion and the great ease of growth of the 

 colon bacillus on ordinary media, the other extreme was taken of attrib- 

 uting too much to it. By means of specific sera and more careful study 

 we are now coming to a clearer view of the action of this micro-organism. 

 The colon varieties met with differ considerably, and we now speak of 

 the colon group rather than of the bacterium coli communis. 



It is best to try and separate the cases which come from varieties of 

 the colon bacillus normally present in the intestines from those derived 

 from outside infection. In this latter class the bacilli again vary from 

 the atypical varieties to those classed out of the group, such as the para- 

 colon bacilli, the dysentery bacillus, the bacilli from meat and food 

 infections, etc. These bacilli are considered under their special headings. 



The colon bacilli previously in the intestines can, either by an in- 

 crease in virulence in them or by a lowered resistance in the person, 



