524 



THE ANTHRAX BACILLUS 



(iv) Involution forms. 



In non-sporing cultures obtained by methods which will be described later, 

 involution forms are frequently seen : these are curved and the ends more 

 or less swollen (fig. 254). In attenuated cultures Chauveau described abnormal 



forms, sometimes short and sometimes thin 

 and filiform, with a spore at the end giving 

 the bacillus the appearance of a nail. 



In collodion sac cultures in dogs the anthrax 

 bacillus loses its virulence and occurs as single 

 coccal-like bacilli (Phisalix) which stain by Gram's 

 method and liquefy gelatin. These forms seem to 

 have a certain degree of stability and constitute 

 a true variety (B. anthracis brevigemmans of 

 Phisalix). 



V 



/ 



y 



2. Cultural characteristics. 



FIG. zzi Bacillus anthracis. 

 l u ar n 



invo- 

 D 



Conditions of growth. The bacillus is essen- 



an ae ' robic organism. 



Rosenthal has shown that the anthrax bacillus 

 can be converted into a facultative anaerobe by growing it in media containing smaller 

 and smaller quantities of oxygen. Having changed into an anaerobe it no longer 

 forms spores and is much less resistant to adverse conditions. 



[Parry Laws several years ago showed that when the anthrax bacillus was sown in 

 broth and incubated in a complete vacuum the organism when examined microscopi- 

 cally showed no spores, exhibited a peculiar morphology and died in ten to twenty days 

 but if sub-cultivated in broth and grown under 

 aerobic conditions the organism reassumed its 

 normal characteristics. ] 



The optimum temperature is 35 C. but 

 growth occurs at any temperature between 

 14 C. and 43 C. and spores form when the 

 cultures are incubated at temperatures be- 

 tween 18 C. and 42 C. The bacillus re- 

 quires a neutral or slightly alkaline medium. 



Characters of growth. Broth. After in- 

 cubation for a few hours at 35 C. delicate 

 flakes make their appearance in the medium 

 which subsequently increase in size and 

 adhering together fall to the bottom of the 

 tube, leaving the medium clear. 



Gelatin. The anthrax bacillus liquefies 

 gelatin. 



(a) Stab cultures. After incubating for 48 

 hours at 20 C. a whitish track appears along 

 the line of sowing and from this numerous 

 delicate, downy filaments soon grow out at 

 right angles giving an appearance similar 

 to the " tree of Saturn " (fig. 255). The 

 growth continues to increase in amount and 

 the lateral offshoots become thicker : later 

 the gelatin begins to liquefy at the upper part of the tube and the liquefaction 

 gradually extends through the medium, until in 10 or 12 days the whole is 

 liquefied. At this stage the growth has the appearance of large white flakes 

 floating in a clear liquid ; finally the flakes fall to the bottom of the tube. 



FIGS. 255, 256. Bacillus anthracis. Stab 

 cultures on gelatin at 20 C. (3 days and 



