PATHOGENIC BACTERIA. 383 



bacillus does not produce fermentation with gas and the colon 

 bacillus does produce gas in such media. 

 ^ 6th. The typhoid bacillus produces a very slight acid reac- 

 tion without coagulation in milk, and the colon bacillus pro- 

 duces a strong acid reaction with coagulation. 



7th. In peptone solution the typhoid bacillus, as a rule, 

 produces no indol, and the colon bacillus produces indol. 



'*'':.^- 





Fig. 99. — Bacillus coli communis with flagella, stained by Van 

 Ermengem's method. (X 1000.) 



8th. The typhoid bacillus usually produces an invisible 

 growth on potato, the colon bacillus a visible growth. 



9th. The typhoid bacillus is said not to reduce neutral 

 red in media, and the colon bacillus to change it to a yellow 

 color. 



To these may be added the growth of the two organisms 

 on special media like those of Wiirtz, of Eisner, of Hiss and 

 of Drigalsky and Conradi and the application of the serum- 

 reaction. 



Injections of cultures of the Bacillus coli communis into 



