246 ANTHRAX BACILLUS 



which do not grow as well as the surface colonies. The latter soon 

 spread out into larger spots, with a still generally spherical but more 

 irregular outline, from which bundles of filaments and cords formed 

 by the bacilli project. The whole formation then somewhat resembles 

 a tuft of wool or the serpent-covered head of the mythological Greek 

 Medusa, as can be demonstrated in stained specimens, prepared by 

 the so-called impression method (Klatsch-Praparat, German). Such 

 preparations are made by pressing a perfectly clean dry cover-glass 

 upon a surface colony on a gelatin plate and then carefully lifting it off 

 with forceps. The impression on the cover-glass is then air dried, 

 fixed, and stained in the usual manner. 



FIG. 134 



Colonies of bacillus anthracis upon gelatin plates: a, at the end of twenty-four hours; b, at the 

 end of forty-eight hours. X 80. (F. Fliigge.) 



A gelatin stick culture of anthrax is very characteristic. The growth 

 first develops on the surface and along the stab, because the bacillus 

 requires oxygen in artificial cultures. The very surface growth, for 

 this reason, is most luxuriant, and the pellicle formed is irregular 

 and uneven. Along the stab itself a radiating or arborescent effect is 

 produced, making the culture at first somewhat resemble an inverted 

 pine tree. Liquefaction of the gelatin is most pronounced at the 

 surface where the growth is most abundant. Some of the liquefied 

 material runs down into the canal of the stab and some of the fluid 

 is lost by evaporation, causing a cup-like or cone- or funnel-shaped 

 depression to form on the surface. After several days when the growth 

 has become more abundant the entire upper stratum of the gelatin 

 may be liquefied and the growth itself sinks to the bottom of the 

 fluid layer. 



Agar and Other Media. On agar plates the development is similar 

 to that on gelatin plates. There is, of course, no liquefaction, because 



