BACILLUS TYPHOSUS 521 



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 convenient amounts are placed in test- 

 tubes and sterilized; after which they are ready for inocu- 

 lation with the mixture suspected of containing the typhoid 

 bacillus. After inoculation they are kept at body tem- 

 perature 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 

 some extent the growth of organisms other than bacillus 

 typhosus, particularly those of the colon group. It is used 

 in the following manner: To test-tubes containing a known 

 amount (8 to 10 c.c.) of peptone solution, "brilliant green" is 



