SO ELEMENTS OF WATER BACTERIOLOGY. 



ing amounts of a solution of 4 per cent hydrochloric acid 

 and 5 per cent phenol. From tubes in which growth 

 occurs after twenty-four hours at 37 , the organisms 

 present may be isolated in pure cultures by some plating 

 method and identified by subcultures. 



The great difficulty with the enrichment processes is 

 that the conditions which favor the multiplication of the 

 typhoid bacillus are suited in an even higher degree to 

 B. coli and other intestinal organisms. Being present in 

 almost all cases in much higher numbers than B. typhi, 

 these germs develop most abundantly, and effectually 

 mask any disease germs originally present. In order to 

 obviate this difficulty, Hankin (Hankin, 1899), after 

 adding successively increasing portions of Parietti solu- 

 tion to tubes inoculated with the water to be tested, 

 selected the second highest tube of the series in which 

 growth occurs for the inoculation of a new set, finally 

 plating as above. He believed that the chance for over- 

 growth in this method is somewhat decreased; but in 

 the hands of other investigators it has not met with marked 

 success. Klein (Thomson, 1894), in his investigations, 

 made use of the Berkefeld filter to concentrate the or- 

 ganisms in the sample. Some recent observers have 

 abandoned the enrichment process altogether and recom- 

 mend direct plating upon phenolated gelatin or on the 

 Eisner (Eisner, 1896) medium made by adding 10 per 

 cent of gelatin and 1 per cent of potassium iodide to an 

 infusion of potato whose reaction has been adjusted to 

 30 on Fuller's scale. In all cases, however, the chance 



