The Significance of B. Coli in Water. 133 



Houston (i9O3 b ) 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 one- 

 cubic-centimeter sample in discriminating between good 

 and bad waters : 



DISTRIBUTION OF B. COLI IN GOOD AND BAD WELL 



WATERS. 



(HOUSTON, igo 3 b.) 



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 100 c.c. each showed no 

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

 Kaiser (1905) reports an interesting correlation between 

 total numbers and B. coli in a series of 38 well waters. Of 

 ii wells containing over 200 bacteria per c.c. 90 per cent 

 showed colon-like organisms in liter samples. Of 12 wells 

 containing from 50 to 200 bacteria per c.c. 67 per cent 

 gave colon-like organisms; of 26 wells with less than 50 

 bacteria per c.c., only 27 per cent showed positive results. 



One of the most important applications of the colon 



