574 Bacilli Resembling the Typhoid Bacillus 



where blue plate. These red colonies are then fished up 

 and transplanted to appropriate media for further study. 



Kline* substitutes lactose for the glucose in this medium, 

 pointing out that by so doing one at once differentiates 

 between typical colon bacilli which ferment lactose and 

 atypical varieties which do not. 



Various media and methods useful in studying the colon 

 bacilli are also discussed in the chapter upon Typhoid Fever 



(q. *.). 



Bile salts were first employed in culture media by Lim- 

 bourgf and have been more or less popular ever since, 

 though for differentiation of typhoid and colon bacilli they 

 are cause of occasional disappointment. 



Another excellent medium was suggested by MacConkey,:f 

 and has the following composition : 



Agar 1.5 grams 



Sodium taurocholate 0.5 gram 



Peptone 2.0 grams 



Water 100.0 c.c. 



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

 of i .o gram of lactose, is tubed, and then sterilized three times on suc- 

 cessive days. 



For determining fermentation by colon bacilli the same 

 investigator advises a broth composed of: 



Soduim taurocholate (pure) 0.5 gram 



Peptone 2.0 grams 



Glucose 0.5 gram 



Water 100.0 c.c. 



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

 and sterilize at 100 C. Colon colonies appear red, typhoid, blue. 



In a careful study of the bile-salt media MacConkey 

 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 



* "British Medical Journal," Oct. 27, 1906, p. 1090. 

 t "Zeitschrift fur physiol. Chemie," 1889, m > P- 196- 

 J "The Thompson- Yates Laboratory Reports," m, p. 151. 

 ' journal of Hygiene," 1908, vm, p. 322. 



