770 PASTEURELLA 



have similarly encountered two variants. On first isolation from the animal body, 

 the organisms formed smooth colonies, consisting of short bacilli, which often 

 showed well-marked bipolar staining ; on plates seeded from old broth cultures, 

 rough colonies developed, with a dull wrinkled surface and a lobate or crenated 

 edge ; morphologically these colonies consisted of larger, often longer, bacilli, which 

 did not exhibit bipolar staining. These two variants likewise differed in their bio- 

 chemical and serological characters (see below). In cultures of Past, lepiseptica 

 De Kruif (1921, 1922a, b, 1923) found two different types ; Type D grew diffusely 

 in broth, formed rather opaque, fluorescent colonies on serum agar, and was highly 

 virulent for rabbits ; Type G gave a granular deposit in broth, formed translucent 

 bluish colonies with little fluorescence, and was completely avirulent. The D type 

 gave rise to Gr variants, but the G type did not revert to D. A mucoid variant of 

 intermediate virulence has been described for Past, lepiseptica by Webster and 

 Burn (1926), while colonies similar in many respects to the D and G types have 

 been recorded for Past, aviseptica by Anderson, Coombes, and Mallick (1929), 

 Morch and Krogh-Lund (1930), and Hughes (1930). 



In broth Past, pestis causes little or no turbidity, but gives rise to a deposit 

 of fine flocculi ; with Past, pseudotuberculosis there is no turbidity but a deposit 

 of coarse flocculi ; with Past, aviseptica there is a uniform turbidity with a powdery 

 deposit (ZlatogorofE 1904). These differences are not entirely constant. A 

 noteworthy feature is that whereas growth of all three organisms on an agar slope 

 reaches its maximum in 2 to 4 days, in broth growth continues for 7 to 10 days, or, 

 at room temperature, for several weeks. An old broth cul- 

 ture is almost clear ; there is a heavy deposit which is 

 difficult or impossible to disintegrate, and there may be a 

 surface pellicle and ring ; in cultures of Past, aviseptica the 

 deposit is viscous ; in cultures of the other two it is usually 

 floccular or membranous. 



If Past, pestis is seeded into broth covered with melted 



butter or oil, and the flask is allowed to remain undisturbed 



Pasteurella ^^ ^^^ incubator, growth occurs in the form of stalactites 



muriseptica. depending from the under-surface of the droplets. This 



Surface colony of property is not peculiar to the plague bacillus, nor is it 



smooth type on possessed by all strains of that species. Past, vseudotuber- 



37° C. (X 8). ' culosis may likewise give a stalactite growth in broth. 



None of the members liquefies gelatin ; in a stab cultvu-e 

 there is a surface layer, and a filiform growth extending to the bottom of the 

 tube. In the case of Past, pestis little feathery projections sometimes occur from 

 the stab into the surrounding gelatin. 



Potato is -not a suitable medium. Past, pestis and Past, aviseptica give little 

 or no growth (Kitasato 1894, Magnusson 1914, Tanaka 1926). Past, pseudo- 

 tuberculosis either gives no growth at all or else forms a thin, yellowish layer, 

 which may later turn brown (Preisz 1894). 



In bile salt media — MacConkey's liquid or solid medium — Past, pestis and Past, 

 pseudotuberculosis give a slight but definite growth, which disappears in the course 

 of 2 or 3 days, owing presumably to autolysis of the bacilli ; Past, aviseptica. fails 

 entirely to grow. 



Resistance. — None of the members is highly resistant to inimical agencies. 

 Broth cultiu-es are killed by heat at 55° C, and by 0-5 per cent, phenol, within 15 



