652 Typhoid Fever 



ox-bile can be used to which i per cent, of peptone and i per cent, 

 of lactose are added. It is filled into fermentation-tubes of 40 cc. 

 capacity and sterilized in the Arnold apparatus 10 cc. of suspected 

 water or milk are planted in the tubes of this medium. The con- 

 tained micro-organisms grow rapidly, typhoid baciUi outgrowing all 

 others, and not fermenting the sugar; rapid fermentation and 

 copious gas-formation take place if colon bacilli are present. 



An excellent medium suggested by MacConkey* has the following 

 composition : 



Agar 1.5 grams 



Sodium taurocholate 0.5 gram 



Peptone 2.0 grams 



Water 100. o cc. 



It is boiled, clarified, and filtered as usual, then receives an addition of 10. 

 gram of lactose, is tubed, and then sterilized three times on successive days. 



For determining fermentation by colon bacilli the same investiga- 

 tor advises a broth composed of: 



Sodium taurocholate (pure) 0.5 gram 



Peptone 2.0 grams 



Glucose 0.5 gram 



Water 100. o cc. 



Boil, filter, add sufficient neutral litmus, fill into fermentation-tubes, and steril- 

 ize at ioo°C. Colon colonies appear red; typhoid, blue. 



• 



In a careful study of the bile-salt media MacConkey f points out an 

 error, first discovered by Theobald Smith, that depends upon the 

 alkali production of the colon bacillus in the absence of sugar. If 

 too little sugar be added to the medium, the alkali production masks 

 the acid production unless the oxygen be removed, and red colonies 

 of the colon bacillus grown upon the medium may in time turn dis- 

 tinctly blue. It becomes obvious, therefore, that the medium 

 should be as neutral as possible to the indicator used. After trial he 

 found neutral red preferable to litmus, and makes the medium as 

 follows : 



I . A stock solution is made : 



Sodium taurocholate (commercial from ox-bile and 



neutral to neutral red) 0.5 per cent. 



Peptone (Witte's) 2.0 per cent. 



Water (distilled or tap) 100 . o cc. 



(As calcium 0.03 per cent, is favorable to the growth of the organisms, 

 it should be added if distilled water is used.) 



The ingredients should be mixed, steamed in a steam sterilizer for one to two 

 hours, filtered while hot, allowed to stand twenty-four to forty-eight hours, then 

 filtered cold through paper. A clear solution should then result, which will keep 

 indefinitely under proper conditions. The various bile-salt media are prepared 

 from this stock solution by adding glucose, 0.5 per cent.; lactose, i per cent.; 

 cane-sugar, i per cent.; dulcit, 0.5 per cent.; adonit, 0.5 per cent., or inulin, 1 

 per cent.; and neutral red (i per cent, solution), 0.25 per cent., distributing into 

 fermentation-tubes and sterilizing in the steamer for fifteen minutes on each of 

 three successive days. 



* "The Thompson- Yates Laboratory Reports," in, p. 151. 

 t "Journal of Hygiene," 1908, vui, p. 322. 



