466 PATHOGENIC MICROORGANISMS 



cultivated upon the usual laboratory media, all of which are more 

 favorable after the addition of glucose, glycerin, or nutrose. In all 

 media there is active gas formation, which, owing to an admixture of 

 butyric acid, is of a foul, sour odor. The bacillus is not very delicate 

 in its requirements of a special reaction of media, growing equally well 

 on those slightly acid or slightly alkaline. 



On gelatin plates, at 20 C., colonies appear in about twenty-four 

 hours, usually round or oval, with a compact center about which fine 

 radiating filaments form an opaque halo. The gelatin is fluidified. 



X 

 X* 



! 

 FIG. 99. BACILLUS OF SYMPTOMATIC ANTHRAX. (After Zettnow.) 



Surface colonies upon agar plates are circular and made up of a 

 slightly granular compact center, from which a thinner peripheral zone 

 emanates, containing microscopically a tangle of fine threads. 



In agar stabs, at 37.5 C., growth appears within eighteen hours, 

 rapidly spreading from the line of stab as a diffuse, fine cloud. Gas 

 formation, especially near the bottom of the tube, rapidly leads to the 

 formation of bubbles and later to extensive splitting of the medium. 

 In gelatin stab cultures growth is similar to that in agar stabs, though 

 less rapid. 



Pathogenicity. Symptomatic anthrax bacilli are pathogenic for 

 cattle, sheep, and goats. By far the largest number of cases, possibly 

 the only spontaneous ones, appear among cattle. Guinea-pigs are very 

 susceptible to experimental inoculation. Horses are very little suscep- 



