CHAPTER XXXVI 

 BACILLUS ANTHRACIS 



Bacillus anthracis occurs in soil and on grasses of pasture lands traversed by 

 infected animals and land polluted by the burial of animals dying with anthrax. 

 It also occurs upon wool and hides of animals coming from districts where the 

 disease prevails. 



Morphology. Bacillus anthracis is a large, straight non-motile rod with 

 square ends, 5 to 10 /x long and i to 2 /* wide. 



Bacilli observed in tissue are arranged singly and in pairs, end to end, and do 

 not contain spores. Those obtained from cultures are arranged in long fila- 

 ments and show spore formation. The spores form in the middle of the bacilli. 



FIG. 26. BACILLUS ANTHRACIS. 

 Some showing spores. (4 X eyepiece and Ma oil immersion objective.) 



Staining. Bacillus anthracis stains readily with the usual stains and is 

 Gram positive. The spores require special methods to tint them. 



Growth. Bacillus anthracis is an aerobic and facultative anaerobic organ- 

 ism. It grows at temperatures between isC. and 45C., best at 37C. 



Bouillon incubated at 37C. shows growth in 24 hours, a whitish pellicle 

 forms on the surface and a stringy, whitish sediment collects in the bottom. 

 When at rest the medium remains clear. 



Agar. Round, irregular-edged, flat, opaque, whitish colonies appear in 18 

 to 36 hours and tend to coalesce, forming a pellicle covering the surface. 



Gelatin. On the surface of gelatin growth appears as on agar. 



Gelatin stabs show growth along and radiating from the stab described as 

 " inverted fir-tree growth." Gelatin is slowly liquefied. 



Potato. A dry, whitish pellicle forms on the surface. 



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