270 . BACILLUS TYPHOSUS. 



On gelatin plates both deep and superficial colonies develop. 

 The deep colonies possess no particular distinguishing feature. 

 They are quite small, round, and finely granular. They 

 are light brown in color. The superficial colonies are 

 much larger, transparent, with irregular, serrated edges, and 

 bluish-white in color. The colonies are usually described as 

 having the shape of^_a^grapa ]paf C^g- 125). The centre of 

 the colony is a very light yellowish-brown ; the periphery is 



FIG. 125. 



/ 



A superficial and a deep colony of typhoid bacilli in gelatin. X 50. (Park.) 



colorless and presents a reticular arrangement. The gelatin 

 is not liquefied. 



In Eisner's medium the colonies of the colon bacillus 

 appear within twenty-four hours, whereas those of the 

 typhoid bacillus do not appear until after forty-eight 

 hours. The typhoid colonies are very small, round, and 

 finely granular. Unfortunately for purposes of differentia- 

 tion the colonies of the colon bacillus occasionally come out 

 in successive crops, so that they may be mistaken for typhoid 

 colonies. Close watching will aid in the differentiation. 



