777 /: .l.\ ////,'. l.V BACILLUS 385 



urine, etc., provided the reaction be not decidedly acid, which arrests 

 development. 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, 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. 118). 



At the same time the gelatin begins to liquefy, and the colony is soon 

 surrounded by the liquefied medium, upon the surface of which it floats 



FIG. 118 



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. Fliigge.) 



as an irregular, white pellicle. In gelatin-stick cultures at first develop- 

 ment occurs along the line of puncture as a delicate white thread, from 

 which irregular, hair-like projections soon extend perpendicularly into 

 the culture medium, the growth being most luxuriant near the surface, 

 but continuing also below. At the end of two or three days liquefaction 

 of the medium commences at the surface and gradually progresses 

 downward. 



GROWTH <>\ A<;AR. The growth on (if/nr-ftlafr cultures in the incu- 

 bator at 37 0\ is similar to that on gelatin, and is still more character- 

 i>ti<- and beautiful in appearance. A grayish-white layer i> formed on 

 the surface within twenty-four hours, which ^pread- rapidly and is 

 seen to be made up of interlaced threads. 



GROWTH IN HOIII.I.ON. The growth is characterized by the forma- 

 tion of flaky masses, which sink as a sediment to the bottom of the 

 tube, leaving the supernatant liquid clear. 



25 



