PATHOGENIC BACTERIA. 387 



whitish. Colonies 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 light brown. No gas is formed 

 in media containing glucose or lactose. 



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

 bacillus is best cultivated on agar plates, in the incubator. 

 Colonies of B. coli communis are often more numerous than 

 those of the dysentery bacillus. The colonies which develop 

 in twenty-four hours are likely to be colonies of B. coli com- 

 munis. 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. 



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 dissemina- 

 tion in the blood and distant organs has not been demon- 

 strated. The lesion of this form of dysentery consists of a 

 severe acute inflammation of the colon, frequently with necrosis 

 of the surface and the formation of pseudomenbrane. Ulcer- 

 ation may occur, but is usually superficial. Duval and 

 Bassett found the bacillus of dysentery in the stools of infants 

 having summer diarrhea; but Collins* failed to find B. dysen- 

 teriae or paradysenteriae in infants suffering from acute and 

 subacute diarrhea. 



The introduction of pure cultures into animals by way of 

 the alimentary canal has sometimes been followed by a cer- 

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

 tery, as it occurs in man, has been reproduced. Most labor- 



* Jo-urn. Inject. Dls. Vol. II. 1905. pp. 620-626. 



