552 



BACTERIOLOGY. 



reaction be not decidedly acid, which arrests develop- 

 ment. It grows in cow-dung and in more or less 

 contaminated earth. It is also capable of leading a 

 saprophytic existence. The bacillus is non-motile. 



Growth in Gelatin. In gelatin plate cultures, at 

 the end of twenty-four to thirty-six hours at 24 C., 

 small, white, opaque colonies are developed, which 



FIG. 73. 



Colonies of bacillus anthracis upon gelatin plates, a, at the end of twenty- 

 four hours ; 6, at the end of forty-eight hours. X 80. (F. FLtlGGE.) 



under a low-power lens are seen to be dark gray in 

 the centre and surrounded by a greenish, irregular 

 border, made up of wavy filaments. As the colony 

 develops on the surface of the gelatin these wavy 

 filaments spread out, until finally the entire colony 

 consists of a light gray, tangled mass, which has been 

 likened to a Medusa head (Fig. 73). 



At the same time the gelatin begins to liquefy, and 

 the colony is soon surrounded by the liquefied medium, 



