BACILLI OF DYSENTERY 383 



one another. The various strains resolve themselves into two 

 chief groups, whose differences lie in their behaviour towards 

 certain sugars, in their capacities of forming indol, and in their 

 agglutinating reactions. The relation of amoebae to dysentery 

 will be discussed in the Appendix. 



Bacilli of Dysentery. — The following are the characters 

 common to the group : — 



Morphological Characters. — The bacillus morphologically' 

 closely resembles the typhoid bacillus, but is on the whole 

 somewhat plumper, and filamentous forms are comparatively 

 rare. Involution forms sometimes occur, especially in glucose 

 agar. The organism is non-motile. Vedder and Duval have, 

 however, demonstrated in the case of one strain the presence of 

 numerous lateral flagella, which are of great fineness, but of 

 considerable length. No spore formation occurs ; the organism 

 is stained readily by the ordinary dyes, but is decolorised by 

 Gram's method. 



Cultural Characters. — In gelatin a whitish line of growth 

 occurs along the puncture, but a superficial film-like growth is 

 usually absent, or at least poorly marked. In plate cultures the 

 superficial growths have often the vine-leaf contour of typhoid 

 colonies, but they are more slimy. On agar, growth occurs as a 

 smooth film with regular margins, but after two or three days, 

 especially if the surface be moist, Vedder and Duval describe 

 an outgrowth of lateral offshoots on the surface of the medium. 

 On agar plates the colonies resemble those of the typhoid 

 drganism, being of smaller size and less opaque than those of 

 the bacillus coli. 



In peptone bouillon a uniform haziness is produced. In 

 litmus milk there is developed at first a slight degree of 

 acidity, which is followed by a phase of increased alkalinity ; 

 no coagulation of the milk ever occurs. On potato the organism 

 forms a transparent or whitish layer, which, however, in the 

 course of a few days assumes a brownish-red or dirty grey 

 colour, with some discoloration of the potato at the margin of 

 the growth. As has been indicated, different strains of the 

 bacillus behave differently towards different sugars. Without 

 going into the question of the particular strains to be placed 

 in the two groups, we may say that, roughly, these may be 

 classified into the Shiga-Kruse group and the Flexner group. 

 All produce acid in peptone-glucose and in taurocholate peptone- 

 glucose; none produce change in lactose. The Shiga group 

 ferment glucose only, while the Flexner group in addition 

 produce acid in maltose or mannite, and the former do not 



