BIOLOGY OF THE B. ANTHRACTS 



339 



It is generally agreed that sporulation never occurs within 

 the body of an animal suffering from anthrax. Koch attributed 

 this to the absence of free oxygen. The latter gas he found 

 necessary to the occurrence of sjjores in cultures outside the body. 

 Many, however, are inclined to assign as the cause of sporulation 

 the absence of the optimum pabulum. Besides these conditions 

 there is another factor necessary to sporulation, namely, a 

 suitable temperature. The optimum temperature for spore pro- 

 duction is 30° C. Koch found that spore-formation did not occur 

 below 18° C. Above 42° C. not only does sporulation cease, 

 but Pasteur found that 

 if bacilli were kept at 

 this temperature for eight 

 days they did not regain 

 the capacity when again 

 grown at a lower tem- 

 perature. In order to 

 make them again capable 

 of sporing, it is necessary 

 to adopt special measures, 

 such as passages through 

 the bodies of a series of 

 susceptible animals. 

 f>* Anthrax spores have 

 extremely high powers of 

 resistance. In a dry 

 condition they will re- 

 main viable for a year 

 or more. Koch found 

 they resisted boiling for 

 five minutes ; and dry 

 heat at 140° C. must be 



applied for several hours to kill them with certainty. Unlike 

 the bacilli, they can resist the action of the gastric juice, for 

 a long period of time. They are often used as test objects by 

 which the action of germicides is judged (see Chap. VI.). ■ - 



Capsulation. — This is very frequently observed in the b. 

 anthracis both in tissues and in cultures, but the appear- 

 ances vary under different biological conditions and sometimes 

 capsule formation is absent. The capsule sometimes has as 

 sharp an external contour as occurs in the pneumococcus, but in 

 other cases is not so definitely marked, and sometimes when 

 bacilli are lying together their capsules appear to blend to form 

 a somewhat ill-defined halo. Such variations are associated with 



Fig. 101. — Anthrax bacilli containing spores 

 (the darkly coloured bodies) ; from a three 

 days' culture on agar at 37° C. See also 

 Plate III. Fig. 2. 



Stained with carbol-fiiclisin and methylene- 

 blue. x 1000. 



