162 ELEMENTS OF WATER BACTERIOLOGY 



to be highly contaminated, chemically. In 7 other 

 cases B. coli was found in the bottled samples alone; 

 3 of these sources were of high purity, but the bottling 

 process furnished opportunity for contamination. 



Clark and Gage (1903), in the examination of 170 

 samples of water from tubular and curb wells of good 

 quality used as sources of water-supply, found B. coli 

 only 5 times, once in i c.c. and 4 times in 100 c.c. Horton 

 (1903), from a study of ground-waters in Ohio, concluded 

 that the presence of B. coli in wells and springs was 

 indicative of serious pollution. 



Houston (1903'') makes an instructive comparison of 

 some more or less polluted shallow wells at Chichester 

 with deep ground-waters of high quality at Tunbridge 

 Wells. The following table shows the value of the 

 I cubic-centimeter sample in discriminating between 

 good and bad waters. 



DISTRIBUTION OF B. COLI IN GOOD AND BAD WELL 

 WATERS 



(Houston, 1903'') 



Percentage of Positive Tests 



In a subsequent investigation, Houston (1905) exam- 

 ined still larger samples of water from the Tunbridge 

 Wells for B. coli: 49 samples of icx) c.c. each showed no 

 B. coli, and 27 liter samples showed B. coli only once. 



