442 BACTERIOLOGY. 



The composition of the medium used is : 



Agar-agar 5 grammes. 



Gelatin 80 " 



Liebig's beef-extract 5 " 



Sodium chloride 5 " 



Glucose 5-10 " 



Water 1000 c.c. 



The gelatin should be added after the agar-agar and 

 other ingredients are dissolved ; the volume of the mass 

 is then brought to 1000 c.c., and finally the reaction is 

 corrected. This should be equivalent to a degree of 

 acidity that would require 15 c.c. of a normal sodium 

 hydroxide solution to the litre to bring it to the phenol- 

 phtalein neutral point. 



When planted as stab-cultures in this medium and 

 kept at body-temperature the growth of bacillus typho- 

 sus appears simply as a diffuse cloud, with little or no 

 tendency to appear more concentrated along the track of 

 the needle ; while the development of the colon bacillus 

 is confined to the neighborhood of the needle-track, is 

 moderately dense, is accompanied by the formation of 

 gas-bubbles, and the surrounding gelatin is more or 

 less clear. 



These distinctions were found by Hiss to be much 

 more marked with the slowly or feebly motile speci- 

 mens of the colon bacillus than when the actively motile 

 varieties were used. Many of these latter, except for 

 their power to ferment glucose with liberation of gas, 

 were almost, indistinguishable from the typhoid bacillus 

 in so far as their power to wander through and cloud 

 the medium was concerned. For the isolation and dif- 

 ferentiation of colonies of the two organisms by the 

 plate method the following medium was employed : 



