446 A MANUAL OF BACTERIOLOGY 



in the East was the Shiga strain, in the West the Flexner 

 strain. 



Morphology. The B. dysenterice are small slender bacilli 

 much resembling the colon bacillus. They are non-motile, 

 but Brownian movement is often active, Gram-negative, 

 and non-sporing, and are readily destroyed by heat (58- 

 60 C.) and antiseptics. 



Cultural characters. The dysentery bacilli are aerobic 

 and facultatively anaerobic. On agar a thinnish creamy 

 growth develops ; on gelatin a white growth nearly limited 

 to the inoculation track, and without liquefaction. The 

 colonies on a gelatin plate resemble those of the typhoid 

 bacillus. On potato the growth is either thin, grey and 

 slightly visible, or thicker and yellowish or brownish. 

 The colour of neutral red media is unaltered. Litmus 

 milk first becomes faintly acid, then alkaline ; no clotting. 

 Indole is generally not formed (never by the Shiga type) ; 

 occasionally a trace may be detected. As regards fer- 

 mentation reactions, gas is never formed. All strains 

 ferment glucose with the formation of acid ; none of the 

 ordinary strains ferments lactose. Some strains (the 

 Flexner type) ferment mannitol ; other strains (the 

 Shiga-Kruse type) have no action on this alcohol. The 

 principal fermentation reactions are given in the table 

 on p. 450 ; they are somewhat variable with different 

 strains, but differentiation may be accomplished by 

 agglutination, saturation, and complement fixation tests. 

 The following four types of dysentery bacilli are 

 ordinarily distinguished by their action on sugars and 

 mannitol : 



1. Fermenting glucose alone [Shiga, Kruse, Flexner 



(Newhaven)]. The Shiga-Kruse Bacillus. 



2. Fermenting glucose and mannitol (Hiss and Russell's 



Y bacillus, Ferran, Seal Harbour bacillus). The 

 Y-Bacillus. 



