494 APPLICATION OF METHODS OF BACTERIOLOGY 



by other organisms present, that is to say, to use an " enrich- 

 ing medium;" (b) and to possess a method that will make 

 comparatively simple the isolation or separation of the 

 typhoid bacilli, after "enrichment," from the other organ- 

 isms with which it is associated. With these objects in 

 mind a routine that gives very general satisfaction is as 

 follows : 



Enriching Media. — For this purpose ox bile and "brilliant 

 green" have been found to favor the growth of typhoid 

 bacilli, and to be less favorable to the growth of other 

 organisms associated with it; consequently if a bit of 

 typhoid feces or a portion of infected water or milk be 

 mixed with either of these media and kept at suitable tem- 

 perature for a time, the result will be a more conspicuous 

 growth of bacillus typhosus than of the other organisms. 



Two forms of ox bile may be employed : 



(1) Pure fresh bile direct from the gall-bladder of a freshly- 

 slaughtered ox, or (2) a solution of peptone and dried ox 

 bile of the following proportions : 



Dried ox bile . . 10 parts 



Peptone 1 part 



Water 100 parts 



In either event test-tubes or flasks are filled with con- 

 venient amounts and sterilized; after which they are ready 

 for inoculation with the mixture suspected of containing 

 the typhoid bacillus. After inoculation they are kept at 

 body temperature for about twenty-four hours, when plates 

 may be made with the differential media to be described 

 below. 



Instead of the ox bile the aniline dye known as "brilliant 

 green" may be employed. This substance suppresses to 



