BIOLOGY OF THE B. ANTHRACIS 



305 



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. 102). 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 cultures 

 outside the body. Many, however, are inclined to assign as the 

 cause of sporulation the 

 absence of the optimum 

 pabulum, which in the case 

 of anthrax is afforded by 

 the animal tissues. Besides 

 these conditions there is 

 another factor necessary 

 to sporulation, viz. a suit- 

 able temperature. The 

 optimum temperature for 

 spore production is 30 C. 

 Koch found that spore 

 formation did not occur 

 below 18 C. Above 42 

 C. not only does sporula- 

 tion cease, but Pasteur 

 found that if bacilli were 



kept at this temperature 



FIG. 107. Anthrax bacilli containing spores 

 (the darkly coloured bodies) ; from a 



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



tor eight days they did not stained with ca rbol-fuchsin and methylene- 

 regain the capacity when blue, x 1000. 

 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 

 20 



