THE TYPHOID BACILLUS l>(jo 



Cultivation. Its growth on most sugar-free culture media is similar 

 to that of the bacillus coli communis, but it is somewhat slower and 

 not quite so luxuriant. 



GROWTH ON GELATIN PLATES (Fig. 92). The colonies growing 

 deep down in this plate medium have nothing in their appearance to 

 distinguish them; they appear as finely granular round points with a 

 sharp margin and a yellowish-brown color. The superficial colonies, 

 however, particularly when young, are often quite characteristic; they 

 are transparent, bluish-white in color, with an irregular outline, not 

 unlike a grape-leaf in shape. Slightly magnified they appear homo- 

 geneous in structure, but marked by a delicate network of furrows. 

 Surface colonies from some varieties of colon bacilli give a similar 

 picture. 



FIG. 92 



A superficial colony (1) and a deep colony (2) of typhoid bacilli in gelatin. X 20 diameters. 



In stick cultures in gelatin the growth is mostly on the surface, appear- 

 ing as a thin, scalloped extension, which gradually reaches out to the 

 sides of the tube. In the track of the needle there is but a limited 

 growth, which may be granular or uniform in structure, and of a 

 yellowish-brown color. There is no liquefaction. 



GROWTH IN BOUILLON. This medium is uniformly clouded by the 

 typhoid bacillus, but the clouding is not so intense as by the colon 

 bacillus. When the bouillon is somewhat alkaline a delicate film is 

 sometimes formed on the surface after eighteen to twenty-four hours' 

 growth. 



GROWTH ON AGAR. The streak cultures on agar are not distinctive; 

 a transparent, grayish streak is formed. 



GROWTH ON POTATO. The growth on this medium was formerly of 

 great importance in identification, but now other media, giving more 

 specific characteristics, have been discovered. When characteristic the 

 growth is almost invisible, but luxuriant, usually covering the surface of 



