[HARRISON A vanokrleck] .ESCULIN BILIO SALT MEDIA 153 



y. Experiments re Acidify/. 



Distilled water 1.5% agar, 1% peptone, 0.25% commercial 

 bile salt, boiled, neutralised and filtered, 0.4% iron citrate (scales) 

 and 0.1% aesculin were then added. Acidity -\- 2.7. 



The media were tested with river water containing B. coli, 

 the varying degrees of acidity being obtained by the addition of 

 sodium hydrate. 



Acidify. Appearance of colonies of B. coli. 



-\- 0. Abundant growth, no fields, plate brown colour. 



-|- 0.3 " " light brown, but large fields. 



-[-0.5 A few colonies of B. coli, darker fields. 



4-0.6 Black, well formed fields. 



-j- . 75 Smaller black fields and fewer colonies 



-j- 1.0 Very small black points. 



4-1.3 No fields at all, plates cloudy. 



A repetition of this test with acidities 4-0-6 and 4-0-75 showed 

 that acidity 4~ 0.6 was by far superior. 



//. Experiments concerning the relation between acidity and the 

 amount of iron iit^the formation of black fields. The medium used was 

 the same as in Experiment I., except acidity and amount of iron 

 citrate. River water containing B. coli; B. coli and B. lactis aerogenes 

 from milk were used in the following tests: 



Acidity 0.0 0.1% Iron Light brown fields. 



" 0.2% " Better growth, light brown fields, plate 

 brown. 

 " " 0.3% " CJood growth, somewhat darker fields, plate 



brown. 

 " " 0.4% " Good growth, somewhat darker fields, plate 



brown. 

 " " 0.5%- " Poor growth, plate too dark in colour to 



see fields. 



All fields in the above experiments were too large and too faint. 

 Acidity 0.5 0.1% Iron. Good growth, dark brown fields. 

 " " " 0.2% " Better^ 

 " " 0.3% " Very good growth, dark brown fields. 



« a r\ A.C7 " " " '' " " " 



" " 0.5% " Poor growth, dark brown fields, agar in 



plate too dark for clear outUnes of the 

 fields. 



