410 



PATHOGENIC MICROORGANISMS 



from the feces by the use of the Endo fuchsin-agar. Emulsions of feces 

 are made in tubes of ordinary broth in the manner described in the Con- 

 radi-Drigalski method, and smears of this emulsion are made upon 

 plates of the fuchsin-agar by means of a glass smearing rod. The 

 colonies of Bacillus coli, after eighteen or more hours of incubation, will 

 be found to have brought back a deep red color to the medium, whereas 

 the typhoid colonies are smaller, more transparent, and have left the 

 medium uncolored. 



In all cases where plates are prepared from broth emulsions of feces, 

 it is desirable to allow the emulsion to stand at incubator temperature 

 for several hours, or, better, to centrifugalize the emulsion and then allow 

 it to stand without agitation. Subsequent removal of fluid from the 



Fig. 92. — Colon and Typhoid Colonies in Hiss Plate Medium. (Planted 

 from stool. Note the small thread-forming typhoid colonies.) 



upper layers of the medium is likely to bring away a comparatively 

 larger number of the motile organisms. 



The methods of isolating typhoid bacilli given above do not ex- 

 haust the records of work done upon this problem. Other methods have 

 been devised, but those given are the ones most generally in use. It is 

 not satisfactory to compare any two of these methods as to practical 

 value, since all of them require a considerable amount of working famil- 

 iarity with organisms and media. In fact, it may be said that all of the 

 methods given are satisfactory if consistently employed by a worker 

 who has become thoroughly accustomed to the peculiarities and 

 variations of the typhoid colonies upon the medium with which he 

 is working. 



