164 ELEMENTS OF WATER BACTERIOLOGY 



colon bacilli in 60 per cent of the i-c.c. samples from the 

 Ohio River, while the effluent from either slow sand or 

 mechanical niters gave positive results only half the 

 time in samples of 50 c.c. The results of the examina- 

 tions carried out at Lawrence for 6 years are brought 

 together in the table below from the Annual Reports 

 of the Massachusetts State Board of Health. 



B. COLI IN MERRIMAC RIVER AND LAWRENCE FILTER 

 EFFLUENT 



* Not given. 



At Harrisburg, Pa., mechanical nitration combined 

 with chlorin disinfection has yielded the results tabulated 

 below : 



B. COLI IN RAW AND TREATED WATER AT 

 HARRISBURG, PA. 



(HARRISBURG, 1913) 



Per Cent Positive Tests in i c.c. 



