SPORULATION OF B. ANTHRACIS. 



305 



increases in size until it forms an oval body, about the same 

 thickness as the bacillus, lying in the bacillary protoplasm (Fig. 

 no). The latter gradually loses its staining capacities and 

 finally disappears. The spore thus lies free as an oval highly 

 refractile body which does not stain by ordinary methods, but 

 which can be easily stained by the special methods described 

 for such a purpose (p. 106). When the spore is again about to 

 assume the bacillary form the capsule is apparently absorbed, 

 and the protoplasm within grows out, taking on the ordinary 

 rod-shaped form. 



According to most observers sporulation never occurs within 

 the body of an animal suffering from anthrax. Koch attributes 

 this, probably rightly, to the 

 absence of free oxygen. The 

 latter gas he found necessary to 

 the occurrence of spores in cul- 

 tures outside the body. Many, 

 however, are inclined to assign 

 as the cause of sporulation the 

 absence of the optimum pabu- 

 lum, which in the case of an- 

 thrax is afforded by the animal 

 tissues. Besides these condi- 

 tions there is another factor 

 necessary to sporulation, viz., 

 a suitable temperature. The 

 optimum temperature for spore 

 production is 32° 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 tempera- 

 ture. 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 



Fig. iio. — ABthra.x bacilli containing 

 spores (the darkly coloured bodies) ; from a 

 three days' culture on agar at 37'^ C. 



Stained with carbol-fuchsin and methy- 

 lene-blue. X 1000. 



