326 BACTERIOLOGY. 



sharply circumscribed, and slightly elevated above the 

 surface. They do not cause liquefaction of the gelatin. 



If grown in slant- or stab-cultures, the surface-devel- 

 opment is very limited; along the needle-track tiny 

 whitish or bluish-white granules appear. 



On nutrient agar-agar the colonies are almost trans- 

 parent, more or less glistening, and very delicate in 

 structure. On blood-serum development is more 

 marked, though still extremely feeble, appearing as 

 a cluster of isolated fine points growing closely side by 

 side. 



Growth on potato is not usually observed. 



When grown in milk it commonly causes an acid 

 reaction with coincident coagulation of the casein. 

 Some varieties, especially non-virulent ones, do not 

 coagulate milk. 1 



It is not motile. 



It grows best at a temperature of from 35 to 38 C. 

 Below 24 C. there is usually no development, but in a 

 few cases it has been seen to grow at as low a tempera- 

 ture as 18 C. Above 42 C. development is checked. 



It grows as well without as with oxygen. It is 

 therefore one of the facultative anaerobic forms. 



Cultivation of this organism is most successful when 

 the agar-agar-gelatin mixture of Guarniari is employed. 

 (See this medium.) 



It may be stained with the ordinary aniline staining- 

 reagents. For demonstrating the capsule the method 

 of Gram and the acetic-acid method give the best re- 

 sults. (See Stainings.) 



This organism is conspicuous for the irregularity of 

 its behavior when grown under artificial conditions : 



1 Welch : loc. cit. 



