686 SHIGELLA 



be larger and more opaque than those of the Shiga-Flexner types. On primary 

 cultivation from the faeces this organism forms colonies on agar that are circular, 

 convex, 2 mm. in diameter, colourless, fairly translucent, with a smooth surface 

 and entire edge ; when viewed against a dark background they appear whitish and 

 relatively opaque. Some colonies show, at one or more portions of the periphery, 

 a small tangled-hair-like projection, giving to the colony a bursting bombshell 

 appearance (Braun and Weil 1928). Sometimes on first isolation, but nearly always 

 in early subculture, a second type of colony is seen, which is larger, raised, trans- 

 lucent, with a coarsely ground-glass surface and an irregularly undulate or crenated 

 edge ; when viewed against a dark background it appears clearer and less opaque 

 than the first type. These two types of colony, which consist of organisms differing 

 antigenically and in certain other respects, have been described by several workers 

 (Mita 1921, 0rskov and Larsen 1925, Leuchs and Plochmann 1927, Fyfe 1927, 

 Large 1929, Cann and de Navasquez 1931, Thjotta and Waaler 1932, Johnston and 

 Kaake 1932, Waaler 1935, Glynn and Starkey 1939). They are generally regarded 

 as corresponding to smooth and rough forms ; though, as Bridges (see Report 

 1939) points out, the antigenic change that accompanies the colonial transition 

 resembles in some respects the specific-group rather than the smooth-rough type 

 of variation. 



Morphological and cultural variants of the dysentery bacilli have been described 

 by several workers. Differences have often been noted in the antigenic structure, 

 saline and acid agglutinability, and pathogenicity for laboratory animals of the 

 rough and smooth variants. Indeed, as in members of the Salmonella group, 

 antigenic structure is of far more imj)ortance in defining smooth and rough types 

 than the colonial appearance. (For references to variation see Arkwright 1921, 

 Carver 1921, Isabolinsky 1926, Koser and Styron 1930, Braun and Baake 1930, 

 Kobayashi et al. 1931, Johnston and Kaake 1932, Wyckoff 1933, Waaler 1935.) 



Resistance and Metabolism. — The members of this group are not specially 

 resistant. They are killed by a temperature of 55° C. in 1 hour, by 0*5 per cent, 

 phenol in 6 hours, and by 1 per cent, phenol in about 15-30 minutes. When 

 dried on linen and kept in the dark at room temperature, they survive for from 

 5 to 46 days (Vaillard and Dopter 1903, Roelcke 1938). In garden earth at room 

 temperature in the dark they survive for 9 to 12 days (Roelcke 1938). In naturally 

 infected faeces kept alkaline and prevented from drying they may remain alive 

 for some days, but in stools that are allowed to become acid through growth of 

 coliform or other bacilli, they perish often in a few hours. On the whole, Sonne's 

 bacillus is more resistant to inimical agents generally than the Shiga or Flexner 

 bacillus. 



They are aerobes and facultative anaerobes. Their optimum temperature is 

 about 37° C. According to Braun and Weil (1928) Sonne's bacillus grows as readily 

 at 45° C. as at 37° C, and more readily at 10° C. than most coliform bacilli. Shiga's 

 bacillus is characterized by its inability to form catalase. 



With the exception of some strains of Sh. alkalescens, none of the members 

 appears capable of producing a haemolysin active against sheep corpuscles. 



Biochemical Reactions. — Sh. shigse, Sh. schmitzi, and members of the para- 

 Shiga group produce acid from glucose ; the remaining members, with the exception 

 of some strains of the Newcastle bacillus, also ferment mannitol. Hence, the 

 primary classification of the group is into mannitol and non-mannitol fermenters. 

 Sh. sonnei and Sh. dispar produce acid from lactose ; the fermentation, however, 



