BACILLUS TYPHOSUS. 417 



BOUILLON. It causes uniform clouding of the bouil- 

 lon and brings about a slightly acid reaction. 



INDOL FORMATION. It is customary to regard this 

 organism as devoid of the power of forming indol ; 

 in fact, this has hitherto been considered one of its 

 important differential peculiarities, and by the usual 

 methods of cultivation and testing the indol reaction is 

 not observed in cultures. It has been shown, however, 

 by Peckham, that by repeated transplantation, at short 

 intervals, into either Dunham's peptone solution, or, 

 preferably, a freshly prepared alkali-try ptone solution, 

 made from tryptonized beef-muscle, that the indol- 

 producing function may be induced in the genuine 

 typhoid bacillus obtained directly from the spleens of 

 typhoid cadavers. 1 



It does not produce gaseous fermentation. On lactose- 

 litmus-agar-agar it grows as pale-blue colonies, causing 

 no reddening of the surrounding medium ; though if 

 glucose be substituted for lactose, both the colonies and 

 the surrounding medium may become red. In the fer- 

 mentation-tube, in glucose or lactose bouillon, no evo- 

 lution of gas as a result of fermentation occurs. 



It grows at any temperature between 20 and 38 C., 

 though more favorably at the latter point. It is 

 very sensitive to high temperatures, being killed by 

 an exposure of ten minutes to 60 C., and in a much 

 shorter time to slightly higher temperatures. 



It does not liquefy gelatin. 



It grows both with and without oxygen. 



It does not grow rapidly. 



1 A. W. Peckham: "The Influence of Environment Upon the 

 Biological Functions of the Colon Group of Bacilli," Journal of Experi- 

 mental Medicine, 1897, vol. ii. 

 27 



