The Significance of B. Coli in Water. 135 



Susquehanna River water and in less than 3 per cent 

 of the samples of filtered effluent (Harrisburg, 1907). 

 At Washington the most complete slow-sand filtration 

 plant yet constructed has yielded the results tabulated 

 below, for which we are indebted to the courtesy of 

 Mr. F. F. Longley. 



B. COLI IN POTOMAC RIVER AND WASHINGTON FILTER 

 EFFLUENT. 



