520 APPLICATION OF METHODS OF BACTERIOLOGY 



mind in the examination of drinking-water supposed to be 

 contaminated by typhoid dejections, for the organisms which 

 most closely approach the typhoid bacillus in growth and 

 morphology are just those organisms which would appear 

 in water contaminated from cesspools i. e., the organisms 

 constantly found in the normal intestinal tract. Even in 

 the stools of typhoid-fever patients the presence of these 

 normal inhabitants of the intestinal tract renders the isola- 

 tion of the typhoid organisms somewhat troublesome. 



Methods of Isolating the Typhoid Bacillus. From the fore- 

 going it is obvious that bacillus typhosus is so variable in 

 many of its biological peculiarities, and is so closely simu- 

 lated in certain respects by a group of other organisms to 

 which it appears to be botanically related, that its identi- 

 fication, especially outside the infected body, is a matter of 

 considerable difficulty and uncertainty. For these reasons 

 many efforts have been made to discover specific cultural 

 reactions for the organism, and with this end in view many 

 methods have been devised for its isolation from water, 

 feces, sewage, and other matters believed to contain it. 

 None of them, however, have given general satisfaction, 

 and many have proved wholly untrustworthy. 



In deciding upon a suitable routine these are several points 

 that should be borne in mind : 



(a) As bacillus typhosus when present in water, feces, 

 soil, milk, etc., is always numerically in the minority, as 

 compared with other organisms, it is desirable to employ 

 a method that will encourage its multiplication without 

 at the same time favoring the same rate of multiplication 

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

 ing medium;" (6) and to possess a method that will make 

 comparatively simple the isolation or separation of the 



