BIOLOGY OF THE B. ANTHRACIS 347 



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

 necessary to the occurrence of spores 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 temperature. In order to make them again 

 capable of sporing, it is necessary to adopt special measures, 

 such as passage through the bodies of a series of susceptible 

 animals. 



Anthrax spores have extremely high powers of resistance. 

 In a dry condition they will remain 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. For 

 this purpose an emulsion is made by scraping off a surface 

 culture and rubbing it up in a little sterile water. Into this 

 sterile silk threads are dipped, which, after being dried over 

 strong sulphuric acid in a desiccator, can be kept for long 

 periods of time in an unchanged condition. For use they are 

 placed in the germicidal solution for the desired time, then 

 washed with water to remove the last traces of the reagent and 

 laid on the surface of agar or placed in bouillon, in order that if 

 death of the bacilli has not occurred growth may be observed 

 (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 

 slight differences in the naked-eye appearance and physical 

 characters of surface growths. In those where the capsule is 

 indefinite, the growth is moister and more slimy and the edges 

 of the colonies may not present the typical wreathed appearances 

 already described. Such variations have been noted by Preisz 



