386 MAN'S niPROVEMEXT OF HIS ENVIRONMENT 



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This chart shows that during a cholera epidemic in 1892 there were hundreds 

 of cases of cholera in Hamburg, which used unfiltered water from the Elbe, 

 but in adjoining Altona, where filtered water was used, the cases were 

 very few. 



Sewage Disposal. — Sewage disposal is an important sanitary 

 problem for any city. Some cities, like New York, pour their 

 sewage directly mto rivers which flow into the ocean. Conse- 

 quently much of the liquid which bathes the shores of Manhattan 

 Island is dilute sewage. Other cities, like Buffalo or Cleveland, send 

 their sewage into the lakes from which they obtain their supply of 

 drinking water. Still other cities which are on rivers are forced to 

 dispose of their sewage in various ways. Some have a system of 











Stone filter beds in a sewage disposal plant. 



