Section IV., 1909. [ 147 ] Trans. R. S. C. 



X. — ^Eseidin BUe Salt Media for the Isolation of B. coH and B. typhosiis. 



By F. C. Harrison and J. Vanderleck, Bacteriological Laboratories, 

 Macdonald College, P.Q., Canada. 



(Read May 27, 1909.) 



The importance of the reaction of media as a controlling factor in 

 the development of biological characters is well known, and in our 

 former papers on " iEsculin Bil3 Salt Media " nothing was mentioned 

 about the acidity of the media, because at that time the question 

 of the right acidity had not troubled us. After the reading of the 

 paper at the meeting of the American Public Health Association, 

 and its subsequent publication, we received several inquiries from 

 laboratory workers who had tried the media with only partial success; 

 about the same time we had some difficulty in the preparation of 

 the media in our own laboratory. The unsatisfactory results at 

 first ascribed to a shortage in the amount of iron citrate were found 

 to be due to the incorrect acidity. 



Our remarks in previous papers (1) as to the utility of the medium 

 for the isolation and determination of B. coli still hold good, and 

 it is the purpose of the present paper to give specific directions for 

 making sesculin media, relate our experiments on acidity, with some 

 theoretical explanations and a description of the cultural characters 

 of the typhoid group when growing in sesculin media. 



Preparation of ^Esculin-bile-salt Agar. 



The directions for making a litre of aesculin-bile-salt agar are 

 as follows: — Boil until dissolved 15 grams of agar, 2.5 grams com- 

 mercial bile salt, and 10 grams peptone (Witte) in 1000 c.c. of dis- 

 tilled water. Neutralise with a normal solution of sodium hydrate. 

 Cool below 60°C., add the whites of two eggs or a sufficient quantity 

 of a solution of albumen, bring to the boil and filter as soon as the 

 albumen has coagulated properly. Try the acidity and neutralise, 

 if necessar}^ and then add to the clear hot filtrate — 1 gram sesculin 

 (Merck) and 1 gram iron citrate scales (Merck). After these sub- 

 stances are dissolved test the acidity with decinormal soda solution. 

 It will be found to be about -[-0.6, as a solution of 1 gram iron citrate 

 scales in 1000 c.c. water gives an acidity of -|- 0.56. In case the 

 acidity is too high add alkali until the reaction is -j- 0.6, and if the 

 acidity is too low add more iron citrate until the reaction is -J- 0.6. 



