27 



3. Range of normal variation. 



a) Growth and pigment on ordinary culture media. 



Morphology. 



All the cultures of the Prodigios us group, except B. kilien- 

 sis and B. ruber miquel, are small, actively motile bacilli. 

 B. kiliensis is distinctly larger than B. prodigiosus, while 

 B. ruber miquel is larger still and non-motile. None have spores. 

 A gelatinous capsule is often present in B. prodigiosus and 

 B. ruber plymouthensis. All of these organisms tend to be 

 somewhat larger on solid media, especially on potato. 



B. prodigiosus and B. kiliensis showed peritrichial flagella ; 

 the others were not examined for flagella. 



Cultural features. 



Gelatin. Plate colonies vary but slightly beyond the diffe- 

 rences in appearance due to variation in the viscosity of the medium. 

 In general the colonies are all like those described for B. pro- 

 digiosus, with slight variations as to time and manner in which 

 pigment and liquefaction appear. B. ruber miquel only, does not 

 liquefy gelatin. The same variations in time and degree of lique- 

 faction are seen in gelatin tube cultures, even in parallel inocu- 

 lations made at the same time, into the same lot of gelatin and 

 from the same culture. This is, however, not an unusual variation 

 in a series of tubes inoculated from one colony, and is probably due 

 in part, as shown by W hippie 1 ), to slight physical disturbances 

 in the action of the proteolytic enzyme. 



A gar. Variation in the agar colonies, principally in contour 

 and in coloration, is due to the same causes as in the gelatin colo- 

 nies. Proteus- like colonies often occur, i.e., in B. ruber indicus, 

 B. rutilus, B. fuchsinus, and rarely in B. kiliensis, but the 

 usual Prodigiosus form is round. Pigment usually appears in 

 granular masses throughout the colony, but often the colonies show 

 fine concentric rings of pigmentation, with darker or lighter centres. 

 My attempts to make accurate colored reproductions of these proved 

 futile, since they are quite inconstant. One plate of B. prodigio- 

 sus IV may be normally and uniformly pigmented; on another all 

 colonies may become red from the edges inward, leaving at first a 

 white centre; other cultures may have violet red centres and white 

 edges. It is noticeable in such variations that they do not occur 

 on the same plate, i. e., they are regular responsive, and not sport 

 variations. 



Potato. The tendency to consider potato as a rejuvenating 

 medium for B. prodigiosus is borne out by the vigorous growth 

 and pigmentation of B. prodigiosus I VIII on this medium, 

 cf. also B. kiliensis, rutilus, amyloruber, and ruber 

 miquel. For B. ruber indicus, B. plymouthensis, and 

 B. miniaceus, however, potato cultures were unsatisfactory for 

 chromogenesis. 



Bouillon. Dense turbidity is always produced in bouillon by 



1) W hippie, G. C., On the physical properties of gelatine, etc. (Techno- 

 logy Quarterly. Vol. XV. 1903. p. 159.) 



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