57 2 Bacilli Resembling the Typhoid Bacillus 



whitish expansions with irregular margin, which are actively motile 

 when examined in the hanging drop from young surface colonies taken 

 from gelatin plates, which coagulate milk within a few days ; grow upon 

 potato, either as a rich pale or brownish-yellow deposit, or merely 

 as a glistening, barely recognizable layer, and which give a distinct 

 indol reaction. Their behavior in the fermentation-tube must conform 

 to the following scheme: 



" Variety a: 



"One per cent, dextrose-bouillon (at 37 C.). Total gas approx- 

 imately \\ H CO-t = approximately 2:1; reaction strongly acid. 



"One per cent, lactose-bouillon: as in dextrose-bouillon (with slight 

 variations). 



"One per cent, saccharose-bouillon; gas-production slower than 

 the preceding, lasting from seven to fourteen days. Total gas about 

 ; H CO 2 = nearly 3:2. The final reaction in the bulb may be 

 slightly acid or alkaline, according to the rate of gas-production. 



" Variety 0: 



"The same in all respects, excepting as to its behavior in saccharose- 

 bouillon; neither gas nor acids are formed in it." 



DIFFERENTIAL CHARACTERISTICS. 

 TYPHOID BACILLUS. COLON BACILLUS. 



Bacilli usually slender. Bacilli a little thicker and shorter. 



Flagella numerous (10-20), long, Flagella fewer (8-10) (peritricha). 



and wavy (peritricha). 



Growth not very rapid, not par- Growth rapid and luxuriant. This 



ticularly luxuriant. character is by no means con- 

 stant. 



Upon Eisner's, Hiss', Piorkow- Upon Eisner's, Hiss', Piorkow- 



ski's, and other media gives ski's, and other media gives 



characteristic appearances. characteristic appearances. 



Upon fresh acid potato the so- Upon potato a brownish-yellow 



called "invisible growth" form- distinct pellicle. 



erly thought to be differential. 



Acid-production in whey not ex- Acid-production well marked 



ceeding 3 per cent. Sometimes throughout. 



slight in ordinary media, and 



succeeded by alkali-production. 



Grows in media containing sugars Fermentation with gas-produc- 



without producing any gas. tion well marked in solutions 



containing dextrose, lactose, or 

 saccharose, the usual formula 

 being H CO 2 = 2 : 1. 



Produces no indol. Indol-production marked. 



Growth in milk unaccompanied Milk coagulated. 



by coagulation. 



Gives the Widal reaction with the Does not react with typhoid 



serum of typhoid blood. blood. 



Colon Bacillus in Drinking Water. Much importance 

 attaches to the presence or absence of colon bacilli in judging 

 the potability of drinking waters. 



It is a speculation whether the colon bacilli were originally 

 micro-organisms of the soil that accidentally found their 

 way into the congenial environment of the intestine and 



