BACILLUS TYPHOSUS 353 



cauterised area, and a little of the splenic pulp is taken with 

 a sterilised platinum needle and inoculated on to tubes 

 or plates, preferably of litmus lactose, Conradi-Drigalski, 

 or malachite-green, agar. These are incubated at 37 C. 

 for twenty-four to forty-eight hours, and the growths 

 which develop are examined microscopically and are tested 

 by agglutination and by cultural methods. The Bacillus 

 typhosus has the following characters : 



Morphology. Bacilli with rounded ends averaging 3 u. 

 in length, and 0-6 //. broad. It is, however, in cultivation 

 a markedly pleomorphic organism, and very short rods, 

 long rods, and thick filaments 10 to 30 /u. in length occur ; 

 the latter are known as involution forms (Plate XII. a). 

 It does not form spores, but granulation and vacuolation 

 may be observed in the protoplasm, particularly in old 

 cultures. 



It is actively motile, and possesses a number of flagella, 

 arranged peritrichically both at the poles and sides (Plate 

 XII. c). The flagella are long and wavy, and average 

 eight to twelve in number, a point of differentiation from 

 the Bacillus coli, which usually has only three or four. It 

 stains by the ordinary anilin dyes, but not by Gram's 

 method. 



Cultural characters. The B. typhosus is aerobic and 

 facultatively anaerobic, and grows well on the ordinary 

 culture media. On agar it forms a thick, moist, greyish 

 layer. On gelatin it grows slowly, and the growth, which 

 is usually scanty and confined to the needle-track, is white 

 and shining, and somewhat irregular (Plate XII. 6). The 

 colonies in gelatin are visible in about forty-eight hours, 

 and form small roundish- white points, which are granular 

 and brownish in colour by transmitted light. In broth 

 it produces a general turbidity, without film formation. 

 The growth on potato acid in reaction is somewhat charac- 

 teristic ; it forms a moist, grey, shining layer, which is 



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