534 APPLICATION OF METHODS OF BACTERIOLOGY 



more or less lobulated layer of a drab, dark-cream, or 

 brownish-yellow color. 



In neutral milk containing a little litmus tincture the 

 blue color is changed to red after from eighteen to twenty- 

 four hours in the incubator, and, in addition, the majority 

 of cultures cause firm coagulation of the casein in about 

 thirty-six hours, though frequently this 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 cultivated 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. 



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 decolorized 

 when treated by the method of Gram. 



By comparing what has been said of bacillus typhosus 

 and of bacillus coll 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 differential points 

 are: 



1. Motility of bacillus typhosus is much more conspicuous, 

 as a rule, than is that of bacillus coli. 



