REACTIONS OF B. TYPHOSUS AND B. COLL 327 



may also be demonstrated by means of Petruschky's litmus-whey 

 (p. 41)- 



The fermentation of sugars is a very important effect of the 

 growth of the B. coli.^ In a culture on a medium equally rich 

 in lactose, for example, and peptone, the former will be broken 

 up and the latter be left practically unaffected. According to 

 the first results of Chantemesse and Widal, the B. typhosus did 

 not ferment lactose ; and F6r6 stated that though it cannot fer- 

 ment cane sugar or lactose, it can originate such a change in 

 arabinose, galactose, levulose, and dextrose, but with regard to 

 the last this is very doubtful. Petruschky, however, holds that 

 it can break up lactose in litmus-whey. Much seems to depend 

 upon what other constituents are present in the medium, and 

 also on its reaction. The fermentative power of the typhoid 

 bacillus is undoubtedly much less active than that of the B. coli ; 

 and as a matter of practical experience the formation of bubbles 

 of gas in Chantemesse and Widal's lactose medium is rarely 

 observed. The test may, therefore, be taken in conjunction 

 with others, as of use in diagnosing the identity of the bacillus. 



Dextrose agar and dextrose gelatin (2 per cent) are also 

 valuable media. The typhoid bacillus in all cases produces no 

 gas in these media, while with the B. coli gas production is 

 observed in from twenty-four to forty-eight hours. 



Curdling of Milk by the B. Coli. — This probably depends on 

 the fermentation of the lactose of the milk, and the throwing 

 down of the casein by the resulting lactic acid ; but the action 

 may be a more complicated one, as milk can be curdled by 

 organisms which do not possess acid-forming properties. 



Formation of Acids in Ordinary Media. — If ordinary litmus 

 bouillon or gelatin be inoculated with the B. typhosus or the B. 

 coli, a production of acid will be observed during the early period 

 of growth, but the acid reaction is mqre quickly produced by 

 the B. coH. 



With such media V6r€ found that in the case of both microbes there was 

 for forty-eight hours a production of acid. At the end of five days, however, 

 typhoid cultures were alkaline, and in cultures of B. coli the acidity, thd%h 

 present, was diminished. Ordinary media contain sugars derived from the 



^ For fuller information the student is referred to the valuable article of Pro- 

 fessor Theobald Smith on "The Fermentation-tube," in the Wilder Quarter-Century 

 Book, 1893, P- '87. 



