THE ANTHRAX BACILLUS 307 



condition these filaments appear homogeneous, but on 

 staining are seen to be composed of a chain of bacilli 

 (Plate IV, a and c). The bacillus is one of the largest 

 of pathogenic organisms, its ends are very square, and it 

 is quite non-motile. In the blood, by certain methods 

 of staining (see p. 318), the bacilli appear encapsuled 

 (Plate IV, c). 



Under cultivation, the filaments of bacilli may be of 

 almost unlimited length, and lie parallel to one another 

 or in more or less tangled masses (Plate V). In the 

 animal body during life, and for some hours after death, 

 spores never occur ; but in cultures more than a day or 

 so old, and from which oxygen has not been excluded, 

 they are always present, almost every segment containing 

 one. The spores are ellipsoidal, measuring about 1 p, by 

 1-25 IJL, and are centrally placed in each segment, the long 

 axis corresponding with the long axis of the segment. 



Cultural reactions. The anthrax bacillus is aerobic and 

 facultatively anaerobic ; it is non-motile, and stains well 

 with the ordinary anilin dyes, and especially so by Gram's 

 method. It grows readily on all culture media at from 

 20 to 37 C., the latter being the optimum. Develop- 

 ment ceases at temperatures below about 15 and above 

 45 C. Small, cream-coloured, granular colonies develop 

 in a gelatin plate in about thirty hours, and in two to 

 three days appear as small, roundish, cream-coloured 

 pasty masses in little pits in the gelatin, due to lique- 

 faction. Microscopically the colonies are somewhat 

 characteristic ; each consists of a mass of wavy, tangled 

 filaments like a tiny wad of cotton- wool. In gelatin 

 streak-cultures development is slow, and in four or five 

 days a creamy, pasty growth forms in a trough of lique- 

 faction. In a gelatin stab-culture (preferably 5 per cent, 

 gelatin) lateral branches spread from the central growth, 

 longer in the upper layers, shorter below, so that at the 



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