308 TYPHOID FEVER. 



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 of which they are made, and the 

 acidity might proceed from the fermentation of these. With 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) Productioti of Gas by the B. coli. If a liquefied 

 gelatine tube be inoculated, shaken, and allowed to 

 solidify, a so-called "shake culture" is produced. The 

 colonies develop in situ, and round each a bubble of gas 

 forms, causing a little split in the gelatine. According to 

 Klein this gas is methane. No such development of gas 

 occurs in a shake culture of typhoid. The occasional 

 formation of bubbles of gas by the B. coli in ordinary stab 

 cultures in gelatine has already been mentioned. 



(3) Formation of Indol. Indol is a body belonging to 

 the aromatic series, and related to the phenols. It occurs 

 naturally in the lower parts of the human intestinal tract, and 

 is formed by the splitting up of peptone under the influence 

 of putrefactive bacteria. Among the latter is to be classed 

 the B. coli. The B. typhosus has no such effect. Indol 

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

 to four days old by the following test : To the culture a 

 little solution of potassium nitrite (according to Kitasato 

 best i c.c. of a .02 per cent solution) is added. On now 

 dropping in a little concentrated sulphuric acid, there is 

 observed a pink coloration caused by the formation of a 

 compound of indol and nitrous acid. Instead of potassium 



