ISOLATION OF SPECIFIC PATHOGENES 89 



media and by its characteristic colonies on Drigalski- 

 Conradi agar, Endo medium, Hiss medium, and Hesse 

 agar. In studying its immunity reactions agglutina- 

 tion should in all important cases be supplemented 

 by the Pfeiffer reaction and the absorption test which 

 will be found described in standard text-books on 

 bacteriology. 



Of the many observers who have reported the isola- 

 tion of the typhoid bacillus from water, all but the most 

 recent are quite discredited, on account of the insuf- 

 ficiency of the confirmatory tests, and even the latest 

 results should be received with caution. Since the 

 introduction of the Widal (Widal, 1896) reaction, 

 founded on the fact that typhoid bacilli examined 

 under the microscope in the diluted blood-serum of 

 a typhoid patient lose their motility and " agglutinate " 

 or clump together, an important aid has been fur- 

 nished in the diagnosis. Yet serum tests are notably 

 erratic, and insufficient to identify an organism with- 

 out an exhaustive study of biochemical reactions. 

 Many organisms are agglutinated by typhoid serum in 

 a more or less dilute solution, and agglutinations are 

 not significant unless obtained in dilutions as great as 

 1-500 or i-iooo. The discovery of the Bacillus dysen- 

 teriae of Shiga, 1 which closely resembles the typhoid 

 bacillus, has made the identification of the latter more 

 dubious than ever. Hiss (1904) has shown that the 

 fermentation and agglutination reactions of the two 

 organisms are in many respects alike, and Park and his 



* For an account of biology of B. dysenteriae the student is 

 referred to an article by Dombrowsky ; 1903. 



