294 PATHOGENIC BACTERIA. 



The margin of the colony is sharply circumscribed ; the 

 interior is broken up. The gelatin is not liquefied. In 

 gelatin punctures there is no liquefaction observable. 



Upon agar-agar the development at the temperature 

 of the incubator, which is more rapid than that at the 

 temperature of the room, results in the production of a 

 bluish-gray layer. 



The growth upon potato has a brownish color. The 

 growth in bouillon and in peptone solutions is accompa- 

 nied by the production of indol. 



The spirillum is pathogenic for mice, guinea-pigs, and 

 canary birds. 



Spirillum Weibeli. This spirillum (Fig. 92) was found 

 in 1892 by Weibel in spring-water which had a long time 



FIG. 92. Spirillum Weibeli, from agar-agar; x 1000 (Itzerott and Niemann). 



before been infected by cholera. It is short, rather thick, 

 and distinctly bent, often forming S-shaped figures. 



The colonies before liquefaction sets in are described 

 as pale-brown, transparent, circular, and homogeneous. 

 L/iquefaction is much more rapid than in cholera, and 

 causes the borders of the colonies to become irregular. 

 In the centre of each colony a little depression is ob- 

 served. 



In gelatin puncture-cultures the growth is rapid, be- 



