MAN'S IMPROVEMENT OF HIS ENVIRONMENT 387 



filter beds in which the solid wastes are acted upon by the bacteria 

 of decay, so that they can be collected and used as fertilizer. 

 Others precipitate or condense the solid materials in the sewage 

 and then dispose of it. Another method is to flow the sewage over 

 large areas of land, later using this land for the cultivation of crops. 

 This method is used by many small European cities. 



The Work of the Department of Street Cleaning. In any 

 city a menace to the health of its citizens exists in the refuse and 

 garbage. The city streets, when dirty, contain countless millions 

 of germs which have come from decaying material, or from people 

 ill with disease. In most 

 large cities a department 

 of street cleaning not only 

 cares for the removal of 

 dust from the streets, but 

 also has the removal of 

 garbage, ashes, and other 

 waste as a part of its 

 work. The disposal of 

 solid wastes is a tremen- 

 dous task. In Manhattan the dry wastes are estimated to be 

 1,000,000 tons a year in addition to nbout 175,000 tons of garbage. 

 Prior to 1895 in the city of New York garbage was not separated 

 from ashes ; now the law requires that garbage be placed in separate 

 receptacles from ashes. Do you see why? The street-cleaning 

 department should be aided by every citizen ; rules for the separa- 

 tion of garbage, papers, and ashes should be kept. Garbage and 

 ash cans should be covered. The practice of upsetting ash or gar- 

 bage cans is one which no young citizen should allow in his neigh- 

 borhood, for sanitary reasons. The best results in summer street 

 cleaning are obtained by washing or flushing the streets, for thus 

 the dirt containing germs is prevented from getting into the air. 

 The garbage is removed in carts, and part of it is burned in huge 

 furnaces. The animal and plant refuse is cooked in great tanks ; 

 from this material the fats are extracted, and the solid matter is 

 sold for fertilizer. Ashes are used for filling marsh land. Thus 

 the removal of waste matter may pay for itself in a large city. 



1 "Hecting ashes. 



