218 BACTERIOLOGY FOR NURSES 



filamentous forms rarely are seen. Their staining reactions 

 are the same as those of other members of the colon-typhoid 

 group. 



Cultivation. In gelatin stab cultures a thin line of growth 

 develops, very little appearing on the surface. Colonies on agar 

 and gelatin plates are much the same as those of the typhoid bacilli 

 and are smaller and more transparent than those of B. coli. In 

 broth a uniform cloudiness is produced with sometimes a pellicle 

 or a slight deposit. As already stated the different strains behave 

 differently towards the different sugars ; they all ferment dextrose 

 and none of them are able to ferment lactose. 



Resistance. Dysentery bacilli show much the same degree 

 of resistance to heat and disinfectants as the typhoid bacilli. In 

 feces they usually die in one or two days. 



Pathogenesis. With the exception of monkeys the charac- 

 teristic disease cannot be produced in animals by feeding them 

 with cultures of the bacilli. Many animals, however, are sensi- 

 tive to subcutaneous or intravenous inoculations, and the surpris- 

 ing result of such inoculation is that the animals show all the symp- 

 toms of the disease, and on autopsy the mucous membrane of the 

 cecum and colon are found to be excessively inflamed. It is evident 

 that the cells of the intestinal mucous membrane have a strong 

 affinity for the bacterial toxin. 



In man the organism does not enter the blood stream and the 

 lesions are especially confined to the intestinal mucous membrane. 

 In mild cases the disease takes the form of a catarrhal inflamma- 

 tion only ; in severer cases necrosis of the epithelium may occur 

 and the intestines may be lined with a pseudomembrane consisting 

 of fibrin, dead cells, and bacteria. 



Since the bacilli are found only in the intestines the spread of 

 the disease is due to fecal contamination direct or indirect. Food, 

 soiled linen, carriers : all may play a part. Water may become 

 contaminated as in the case of typhoid, although comparatively 

 few water-borne epidemics of dysentery have been reported. It is 

 stated that in Japan in the rural districts the mortality due to 

 dysentery, resulting mainly from the use of human feces as a fer- 



