SIGNIFICANCE OF COLON GROUP IN WATER 173 



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 is found in such abun- 

 dance as to be isolated in a large proportion of cases 

 from i c.c. of water, it is reasonable proof of the presence 

 of serious pollution. 



