400 



PATHOGENIC MICROORGANISMS 



as small grayish colonies at first transparent, later opaque. Upon agar 

 slants growth takes place in a uniform layer. There is nothing charac- 

 teristic 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 

 Hquefy 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 gela- 

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

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



Fig. 86. — Bacillus typhosus, from twenty-four-hour culture on agar. 



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

 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 ' in his early researches for purposes of 



'■ Oaffky, loc. cit. 



