20 BACTERIOLOGY. 



of the species. In anthrax the bacilli do not form spores in the 

 living body, but when the animal dies the development of spores 

 takes place, and hence the danger of contaminating the soil if the 

 body is disposed of by burial. Klein, however, has pointed out that 

 if mice and guinea-pigs which have died of anthrax are kept un- 

 opened, the bacilli simply degenerate and ultimately disappear. 

 Thus there is good reason for believing that spore-formation is 

 not due to exhaustion of the pabulum, but probably free access to 

 oxygen constitutes an important factor in inducing this condition. 

 If we inoculate a potato with anthrax, copious spore- formation 

 occurs, though we cannot consider that the nourishing soil has been 

 exhausted. But we have in this case the surface of the potato 

 freely exposed to the air in the damp chamber. In the same way, 

 in cultivations on agar-agar solidified obliquely (so as to get a large- 

 surface), spore-formation readily takes place. Contamination of 



FIG. 7. SPORE-BEARING THREADS OF BACILLUS ANTHRACIS, DOUBLE- STAINED 

 WITH FUCHSINE AND METHYLENE BLUE, X 1200. 



the ground results, therefore, from animals in which a post-morteni 

 examination has been made and the blood and organs freely exposed 

 to the air ; or from carcasses the hides of which have been soiled 

 with excretions, and with blood which issues from the mouth and 

 nostrils before death. 



When spores are introduced into a suitable medium at a favour- 

 able temperature they develop again into rods. The spore loses its 

 sharp contour, and, at one pole or on one side, a pale process bursts 

 through the membrane, gradually growing into a rod from which 

 the empty capsule is thrown off. 



Spores differ from the parent cells in their behaviour to staining 

 reagents. Like them, they can be stained with aniline dyes, but 

 not by the ordinary processes. They require to be specially treated. 

 This is probably due to the tough capsule, which must be altered 

 or softened by heat or strong acid, until it allows the stain to 

 penetrate. 



