PATHOGENIC BACTERIA. 315 



slowly than B. coli communis. The growths are whitish. 

 Coloijies on gelatin plates resemble those of the typhoid bacillus. 

 Bouillon is diffusely clouded; a precipitate may form, but no 

 pellicle. Indol is not produced. Milk becomes acid and is 

 not coagulated . On potato a thin pale layer forms which may 

 become Hght brown. No gas is formed in media containing 

 glucose or lactose. 



Neutral-red agar is not changed. From the feces the ba- 

 cillus is best cultivated on agar plates, in the incubator. Colo- 

 nies of B. coU communis are often more numerous than those 

 of the dysentery bacillus. The colonies which develop in 

 twenty-four hours are hkely to be colonies of B. coh communis. 

 The position of these may be marked on the glass with a pencil. 

 Those which appear later are to be planted' in dextrose-agar. 

 If gas develops, they are not the bacilli of dysentery; otherwise 

 they are to be studied and identified by the cultural and other 

 tests mentioned above, and by the agglutination reaction. 



The bacilH are destroyed in a few minutes by boiling, and 

 at 58° C. in half an hour. They appear not to be particu- 

 larly resistant to the influences that are harmful to bacteria in 

 general. 



They have been found in the intestine and the discharges 

 of acute and epidemic dysentery in various climates and coun- 

 tries, including the United States. Thus far their dissemination 

 in the blood and distant organs has not been demonstrated. 

 The lesion of this form of dysentery consists of a severe acute 

 inflammation of the colon, frequently with necrosis of the sur- 

 face and the formation of pseudomembrane. Ulceration may 

 occur, but is usually superficial. Duval and Bassett found 

 the bacillus of dysentery in the stools of infants having summer 

 diarrhea. 



The introduction of pure cultures into animals by way of 

 the aUmentary canal has sometimes been followed by a cer- 

 tain amount of diarrhea, but it does not appear that dysen- 



