BACILLUS COLL 457 



takes longer. Very rarely the litmus may indicate the 

 production of acid and no coagulation occur. 



In media containing glucose it grows rapidly and 

 causes active fermentation, with liberation of carbonic 

 acid and hydrogen. If cultivated in solid media to 

 which glucose (2 per cent.) has been added, the gas- 

 formation is recognized by the appearance of numerous 

 bubbles along and about the points of growth. If cul- 

 tivated in fluid media, also containing glucose, in the 

 fermentation-tube, evidence of fermentation is given by 

 the collection of gas in the closed arm of the tube. 



On lactose-litmus-agar-agar its colonies are pink and 

 the color of the surrounding medium is changed from 

 blue to red. 



It produces indol in both bouillon and peptone solu- 

 tion. 



In Dunham's peptone solution it produces indol in 

 from forty-eight to seventy-two hours. 



It stains with the ordinary aniline dyes. It is decol- 

 orized when treated by the method of Gram. 



By comparing what has been said of bacillus typho- 

 sus and of bacillus coli it will be seen that, while they 

 simulate each other in certain respects, they nevertheless 

 possess individual characteristics by which they may 

 readily be differentiated. The least variable of the dif- 

 ferential points are : 



1. Motility of bacillus typhosus is much more con- 

 spicuous, as a rule, than is that of bacillus coli. 



2. On gelatin, colonies of the typhoid bacillus de- 

 velop 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 tvphoid bacillus does not cause coagulation of 



