110 ELEMENTS OF WATER BACTERIOLOGY 



Number of samples tested 



Number giving preliminary fermentation . 

 Per cent of latter proved to contain coli . . 



Whipple (Whipple, 1903) examined a large number 

 of surface-water supplies by this " presumptive test " 

 and obtained striking results, shown in the following 

 table. The waters are arranged in six groups according 

 to the results of sanitary inspection, group I including 

 waters collected from almost uninhabited watersheds, 

 and group VI waters too much polluted to be safely 

 used for domestic purposes. 



PERCENTAGE OF SAMPLES OF WATERS OF VARIOUS 

 SANITARY GRADES GIVING POSITIVE TESTS FOR B. 

 COLI WHEN DIFFERENT AMOUNTS WERE EXAMINED 



(Whipple, 1903) 



In view of these results Whipple suggested the fol- 

 lowing provisional scheme of interpretation: 



