BACTERIUM COLI COMMUNE. 361 



from forty-eight to seventy-two hours. It stains with 

 the ordinary aniline dyes. It is decolorized when 

 treated by the method of Gram. 



By comparing what has been said of the bacillus typhi 

 abdominalis and of the bacterium coli commune it will 

 be seen that while they simulate each other in certain 

 respects they still possess individual characteristics by 

 which they may readily be differentiated. The most 

 important of the differential points are : 



1. Motility of the bacillus typhi abdominalis is much 

 more conspicuous, as a rule, than is that of the bacterium 

 coli commune. 



2. On gelatin the colonies of the typhoid bacillus 

 develop more slowly than do those of the colon bacillus. 



3. On potato the growth of the typhoid bacillus is 

 usually invisible (though not always), while that of the 

 colon bacillus is rapid, luxuriant, and always visible. 



4. The typhoid bacillus does not cause coagulation of 

 milk with acid reaction. The colon bacillus does this 

 in from thirty-six to forty-eight hours in the incubator. 



5. The typhoid bacillus never causes fermentation, 

 with liberation of gas, in media containing glucose, lac- 

 tose, or saccharose. The colon bacillus is conspicuous 

 for its power of causing fermentation in such solutions. 



6. In nutrient agar-agar or gelatin containing lactose 

 and litmus tincture, and of a slightly alkaline reaction, 

 the color of the colonies of typhoid bacillus is pale blue, 

 and there is no reddening of the surrounding medium, 

 while the colonies of the colon bacillus are pink and 

 the medium round about them becomes red. 



7. The typhoid bacillus does not, as a rule, possess the 

 property of producing indol in solutions of peptone; the 

 growth of the colon bacillus in these solutions is accom- 



