68 Elements of Water Bacteriology. 



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 degrees, the organisms 

 present may be isolated in pure cultures by some plating 

 method and identified by subcultures. 



The great difficulty with a majority of the enrichment 

 processes is that the conditions which favor the multipli- 

 cation of the typhoid bacillus are frequently suited in an 

 even higher degree to B. coli and other intestinal organ- 

 isms. Being present in almost all cases in much higher 

 numbers than B. typhi, these germs develop 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 solution to tubes inoculated with the 

 water to be tested, selected the second highest tube of the 

 series in which growth occurred for the inoculation of a new 

 set, finally plating as above. He believed that the chance 

 for overgrowth in this method was 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 con- 

 centrate the organisms in the sample. Some observers 

 have abandoned the enrichment process altogether and 

 recommend direct plating upon phenolated gelatin or 

 on the Eisner (Eisner, 1896) medium made by adding 10 

 per cent of gelatin and i per cent of potassium iodide to 

 an infusion of potato whose reaction has been adjusted 



