THE SIGNIFICANCE OF B. COLI IN WATER. 93 



i to 1,000,000 per c.c. The authors conclude that a 

 quantitative estimation of the B. coli content furnishes a 

 good measure of the fecal pollution of water and that 

 the observed differences in the extent of B. coli contam- 

 ination of surface-waters are so great that they differ 

 from each other more than a million- fold. 



Altogether the evidence is quite conclusive that the 

 absence of B. coli demonstrates the harmlessness of a 

 water as far as bacteriology can prove it. That when 

 present, its numbers form a reasonably close index of 

 the amount of pollution the authors above quoted 

 have proved beyond reasonable cavil. It may safely be 

 said that when the colon bacillus, as denned by the tests 

 above, is found in such abundance as to be isolated in a 

 large proportion of cases from i c.c. of water, it is reason- 

 able proof of the presence of serious pollution, a view 

 which is to-day accepted by most American bacteriolo- 

 gists. 



