BACILLUS TYPHOSUS. 407 



medium appear to be chiefly due to variations in the 

 substance, especially in the reaction, of the potato. 



Milk. The typhoid bacillus does not cause coagu- 

 lation when grown in sterilized milk. 



Fermentation. It does not produce fermentation in 

 either glucose, lactose, saccharose, or glycerin bouillon, 

 and evolves no gas as the result of fermentation. 



Lactose-litmus Agar. It grows usually as pale blue 

 colonies on lactose-litmus agar, but occasionally causes 

 slight reddening of the surrounding medium. 



Indol Reaction. It does not produce indol. This 

 test was proposed by Kitasato for differentiating the 

 typhoid bacillus from other similar bacilli, such as 

 those of the colon group, which, as a rule, give the 

 indol reaction. 



The reaction, being a very delicate one, requires 

 great care in its performance to arrive at accurate con- 

 clusions. (For test of indol, see page 77.) Instead of 

 bouillon, the simple peptone-water (which consists of 

 dried peptone, 1 part; sodium chloride, 0.5 part, and 

 distilled water, 100 parts) is to be preferred for this 

 purpose, because its pale color does not mask the reac- 

 tion*. 



Pathogenic Properties. It has been extremely diffi- 

 cult to show experimentally that the bacillus typhosus 

 is specifically pathogenic for animals. A great many 

 experiments have been made, with the view of repro- 

 ducing in the tissues of lower animals the pathological 

 lesions of typhoid fever as seen in man, but the results 

 have not been completely satisfactory ; nor is this sur- 

 prising when one considers that this disease does not 

 occur naturally, so far as is known, among animals. 

 Sickness or fatal results without the appearance of the 



