98 ELEMENTS OF WATER BACTERIOLOGY. 



results from the use of this test, but according to Ameri- 

 can standards, Irons (Irons, 1902) and Gage and Phelps 

 (Gage and Phelps, 1903) conclude that the group of 

 organisms giving a positive neutral red reaction is too 

 large a one to give very valuable sanitary information. 

 In a paper read at the Washington meeting of the Ameri- 

 can Public Health Association in 1903, Stokes suggested 

 a modification of this medium in which lactose is sub- 

 stituted for dextrose, since many saprophytic organisms 

 will attack the latter and not the former sugar. 



The medium devised by MacConkey (MacConkey, 

 1900; MacConkey, 1901; MacConkey and Hill, 1901) 

 containing sodium taurocholate as its characteristic 

 ingredient has also proved successful in the hands of 

 some observers. The dextrose fermentation-tube, how- 

 ever, is the only presumptive test whose value has been 

 established by conclusive general investigations. 



