842 BACILLUS 



celled species are subdivided into those that germinate (1) by shedding their spore 

 coat equatorially or at the pole or (2) by comma-shaped expansion. The large- 

 celled species all germinate by absorption of the spore coat. Unfortunately this 

 brings many of Lamanna's large-celled species, like B. mycoides, B. cereus, B. mega- 

 therium, and many of his small-celled species, like B. suhtilis, B. vulgatus, and 

 B. mesentericus into the same primary subdivision, suggested by de Soriano, of 

 species whose spores do not cause bulging of the vegetative portion of the cell. 

 Some hope is held out by the serological studies of Howie and Cruickshank (1940) 

 and Lamanna (19406), who have shown that the spore antigen is distinct from 

 the bacillary antigen, that a classification of the non-pathogenic members of the 

 group may ultimately be based on antigenic characteristics. 



To the medical and veterinary student the chief interest is in the differentiation 

 of B. anthracis from the non-pathogenic species ; this will be discussed under 

 the description of B. anthracis which is given below. 



Bacillus anthracis. 



Named B. anthracis by Cohn (18756) and Bacteridium by Davaine (1864). 

 This bacillus is non-motile, forms capsules in the animal body and sometimes on 

 artificial media, and grows on agar in characteristic long, segmented, parallel or 

 interwoven chains. The spores are ellipsoidal or oval in shape, are found equa- 

 torially, and germinate by polar rupture. It is 

 interesting to note that the anthrax bacillus was 

 the first micro-organism in which the presence of 

 resistant spores was demonstrated. Spores are 

 never found in the animal body during life, and 

 in culture appear more slowly than those of the 

 other members of the group. They seem to be 

 formed under conditions unfavourable to continued 

 growth of the vegetative bacilli. Their appear- 

 ance can be hastened by the addition of distilled 

 water, 2 per cent, sodium chloride, and other salts 

 kfus^-^se-i * 'jf ^f.*--^ ui^^A (Bongert 1903). According to Bordet and Eenaux 

 Fig. 177. — B. anthracis. (1930), sporulation is inhibited by the presence of 



Edge of colony on agar to show calcium chloride and favoured by its absence, 

 curled hair-^ock appearance Cultures grown on oxalated agar often come to 



consist mainly of spores, while those grown on 

 agar to which CaClg has been added may lose their spore-forming power com- 

 pletely. 



The curled hair-lock appearance of single colonies on agar or gelatin is char- 

 acteristic, but may be closely simulated by B. suhtilis. Microscopically this is seen 

 to be due to the growth of the bacilli in long interwoven chains. Growth, parti- 

 cularly in broth, at a temperature of 42-5° C. for some days, causes the appearance of 

 several different variants ; some have tough, well-defined capsules, give rise on 

 agar to the typical curled colonies, and are highly virulent ; some have soft 

 poorly-defined capsules, form thin, shining colonies on agar, and are slightly 

 virulent ; others are non-capsulated, give rise to smooth, round, convex, glistening, 

 mucoid colonies on agar, and are entirely avirulent (Preisz 1911, Nungester 1929a, 6, 

 Bordet and Eenaux 1930). Capsulation is favoured by growth in air containing 



