BACILLI OF THE COLON-TYPHOID-DYSENTERY GROUP 645 



four hours as small grayish colonies at first transparent, later opaque. 

 Upon agar slants growth takes place in a uniform layer. There is 

 nothing characteristic about this growth to aid in differentiation. 



In broth, the typhoid bacillus grows rapidly, giving rise to an even 

 clouding, rarely to a pellicle. 



Upon gelatin, the typhoid bacillus grows readily and does not liquefy 

 the medium. In stabs, growth takes place along the entire extent 

 of the stab and over the surface of the gelatin in a thin layer. In gelatin 

 plates the growth may show some differences from that of other mem- 

 bers of this group, and this medium was formerly much used for isolation 

 of the bacillus from mixed cultures, Growth appears within twenty- 



FIG. 70. SURFACE COLONY OF BACILLUS TYPHOSUS ON GELATIN. (After Heim.) 



four hours as small transparent, oval, round, or occasionally leaf-shaped 

 colonies which are smaller, more delicate, and more transparent than 

 contemporary colonies of the colon bacillus. They do not, however, 

 show any reliable differential features from bacilli of the dysentery 

 group. As the colonies grow older they grow heavier, more opaque, and 

 lose much of their early differential value. 



On potato the growth of typhoid bacilli is distinctive, and this medium 

 was recommended by Gaffky 4 in his early researches for purposes of 

 identification. On it typhoid bacilli, after twenty-four to forty-eight 

 hours, produce a hardly visible growth, evident to the naked eye only 



4 Gaffky, loc. cit. 



