Forty-sixth Annual Meeting. 27 



attention of sanitarians. In carrying on their investigations 

 they tapped the main sewer of the city of Boston, which carries 

 sewage from 500,000 people, and installed pumps for lifting 

 the sewage as needed by the experimental apparatus. The 

 sewage was then treated in different kinds of tanks; sprink- 

 ling, trickling and contact filters, and the mineral, bacterial 

 and other contents of both influent and effluent sewage care- 

 fully noted. The recorded results of these experiments, which 

 were conducted by a corps of expert engineers, chemists and 

 bacteriologists, have been recognized as authoritative, and 

 their findings have been adopted in large measure by those 

 who are intrusted with the design and construction of sewage- 

 disposal works. 



At Lawrence, Mass., experimental methods have been put in 

 practice by the State Board of Health since 1886 when the 

 Lawrence experiment station was established. Experiments 

 have been conducted at this station in both sewage and water 

 purification continuously since 1887. This station, through its 

 long series of annual reports extending over a quarter of a 

 century, has gained perhaps the highest reputation of any 

 organization working in the experimental field of sanitary 

 science. Other prominent stations for the study of conditions 

 relating to sewage purification are located at Worcester, 

 Mass., Pawtucket, R. L, Berlin, Ont., Columbus, Ohio, Water- 

 bury, Conn., Reading, Pa., Baltimore, Md., Gloversville, N. Y., 

 Philadelphia, Pa., and Chicago, 111. 



The purposes to be attained in sewage purification are two- 

 fold. First, is the decomposition and oxidation of the organic 

 matters into stable forms that will not putrefy and create a 

 nuisance. Second, is the elimination of pathogenic bacteria, 

 so that streams into which the effluent is discharged may not 

 become contaminated, and thus endanger the health of the 

 people living below the outfall. Disposal plants are now being 

 built that are reasonably efl'ective as to the first object, but 

 in bacterial eflficiency much remains to be desired. 



The average bacterial efficiency of a large number of Ameri- 

 can plants which are operating without the application of a 

 germicide is 58 per cent, with a minimum of 21 per cent and a 

 maximum of about 90 per cent. Some of the other plants, 

 where the effluent is disinfected with copper sulphate, have a 

 bacterial efficiency as high as" 99.95 per cent. 



