328 TYPHOID FEVER. 



Formation of Acids in Ordinary Media. If ordinary 

 litmus bouillon or gelatine 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 more quickly produced by the B. coli. 



With such media Pere 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, though present, was diminished. Ordinary media 

 contain sugars derived from the meat from which they are made, and 

 the acidity might proceed from the fermentation of these. In media 

 made with pure syntonin or peptone, though there was an initial slight 

 acid formation, especially with the B. coli, still in the case of both 

 organisms at the end of four days the reaction was alkaline. The 

 reaction is, therefore, probably a double one, but the resulting acidity 

 in ordinary cases may be due to fermentative changes in carbohydrates. 

 Here again the acid-forming capacities of the B. typhosus are inferior 

 to those of the B. coli. 



(2) Production of Gas by the B. coli. The production 

 of gas in various media by the B. coli can be demonstrated 

 by any of the methods described (p. 86). Shake cultures 

 are usually employed. According to Klein the gas pro- 

 duced is methane. We have found, however, that in a 

 shake culture in peptone solution with 10 per cent gelatine 

 added the B. coli produces no gas, but bubbles rapidly 

 form if the medium has added to it a trace of lactose. No 

 such development of gas occurs in a shake culture of 

 typhoid in any of these media. 



(3) Formation of Indol. Among the bacteria capable 

 of forming indol is to be classed the B. coli. Indol can 

 be recognised in bouillon cultures of the B. coli three to 

 four days old by the usual tests (vide p. 87). As there is 

 no evidence that it can produce nitrites, a small quantity 

 of the latter must be added. The typhoid bacillus never 

 gives this reaction when growing in ordinary conditions, 

 but on the other hand, it appears that some varieties of the 

 B. coli fail to produce it also. Peckham, however, has 

 shown that if the typhoid bacillus be grown in peptone 

 solution, after a few generations of three days each it may 



