450 



FOODS 



running water can be supplied, cesspools and septic tanks 

 answer the purpose. In cities, however, most complicated 

 systems of sewage disposal must be employed. In the 

 most healthful cities the sewage is gathered from all parts 

 of the city by means of water flowing in underground sewers. 

 In seaboard cities the sewers usually empty into the sea and 

 the tides and currents dispose of the sewage. 



Courtesy of Department of Public Works, Columbvs, Ohio 



SEWAGE DISPOSAL, LIQUIDS 



Cities upon large rivers frequently empty their sewage 

 into the rivers, but this pollutes the water far downstream. 

 A very much better way than this has of late years been 

 devised and is being used by many inland cities. Sewage 

 disposal plants are built, where the sewage is run into large 

 tanks and the solid matter is decomposed by the action 

 of certain kinds of bacteria. The liquid is then slowly 



