Cultivation 587 



liquid remaining clear. In from four to six days these 

 islands become still more compact. If the vessels be dis- 

 turbed, they fall like snow and are deposited at the bottom, 

 leaving the liquid clear. 



Colonies. Upon gelatin plates at 22 C. the colonies may 

 be observed in twenty-four hours by the naked eye. They 

 are pure white or yellowish white, spheric when deep in the 

 gelatin, flat when upon the surface, and are about the size 

 of a pin's head. The gelatin is not liquefied. Upon micro- 

 scopic examination the borders of the colonies are found to 



Fig. 206. Stalactite growth of bacillus pestis in bouillon. (Repro- 

 duced from Simpson's ''A Treatise on Plague," 1905, by kind permission 

 of the Cambridge University Press.) 



be sharply defined. The contents become more granular as 

 the age increases. The superficial colonies are occasionally 

 surrounded by a fine, semi-transparent zone. 



Klein* says that the colonies develop quite readily upon 

 gelatin made from beef bouillon (not infusion), appearing 

 in twenty-four hours, at 20 C., as small, gray, irregularly 

 rounded dots. Magnification shows the colonies to be 

 serrated at the edges and made up of short, oval, some- 

 times double bacilli. Some colonies contrast markedly 

 with their neighbors in that they are large, round, or oval, 

 and consist of longer or shorter, straight or looped threads 

 of bacilli. The appearance was much like that of the young 



*"Centralbl. f. Bakt. u. Parasitenk.," July 10, 1897, xxi, Nos. 24 

 and 25. 



