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 grape leaf (Fig. 125). The centre of 

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



FIG. 125. 



m 



1 J 



-, 



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. 



