BACILLUS ANTHRACI8 843 



10-25 per cent, of CO2 (Ivanovics 1937). Some variants are asporogenous ; it 

 was these which attracted Pasteur's attention, and which he considered to be aviru- 

 lent. Preisz (1911) has, however, shown that, though there is a definite correlation 

 between capsule formation and virulence, there is none between spore formation and 



Fig. 178. — B. anthracis. Fia. 179. — B. anlhmcw. 



Smooth type of colony. Agar, Rougli type of colony. Agar, 



24 hours, 37° C. ("x 8). 24 hours, 37° C. (x 8). 



virulence. Virulent strains may ha cither sporogenous or asporogenous ; similarly 

 with avirulent strains. Asporogenous varieties may appear spontaneously in 

 cultures incubated at the usual temperature (Behring 1889), or in cultures containing 

 weak antiseptics, such as 1/2,000 potassium dichromate, or 1/1,000 phenol (Roux 

 1890). Such varieties, when arising from a virulent strain, are themselves fully 

 virulent, though prolonged contact with weak antiseptics may eventually lower their 

 virulence. The normal highly virulent bacillus forms a large, rough colony of 

 frosted glass appearance with a curled edge ; morphologically it consists of bacilli 

 arranged in chains (Figs. 179, 181). The avirulent bacillus forms a smaller, smoother 

 type of colony, with a slightly crenated edge ; morphologically it consists of bacilli 

 arranged singly, in pairs end-to-end, or in small bimdles (Figs. 178, 180). 



r- ^^"> ' ^/^^ 



T ! 





)i 



\ ^ 



/ 



T 



\ 



-- / 





Fig. ISO.— B. anihrams. Fig. 181.— 7?. anthracis. 



From smooth colony on agar, 24 hours, From rough colony on agar, 24 hour 



37°C. (X 1000). 37°C. (X 1000). 



