PUBLIC HYGIENE, OR GENERAL SANITATION 367 



No cheap and safe method has yet been discovered. All 

 are expensive, but any one is cheaper than the sacrifice of 

 life and health which is sure to result from unsanitary or 

 slipshod ways of dealing with this serious problem. Some 

 of the most satisfactory methods in use in the most pro- 

 gressive cities may be simply mentioned here. 



Where a very large body of water is at hand, which 

 is not the source of the town's water supply, the sewage 

 may, for a time at least, be safely poured into it. This is 

 the cheapest way. But such pollution of streams and 

 lakes is now forbidden by law in many countries of 

 Europe, as it should be in the United States. In some 

 cities the sewage is collected in great vats, where the solid 

 portion is separated from the liquid, and sold for use as 

 a fertilizer. The liquid is by chemical treatment freed 

 from its harmful ingredients, and poured into the water- 

 courses. Some cities own large farms, to which the sewage 

 is conveyed in close tanks, and spread upon the soil as a 

 fertilizer. In other cases the soil is simply used as a 

 niter. The sewage is spread upon it, and the liquid 

 which filters through is received by drain tiles laid below 

 the surface, and carried into a natural stream. The solid 

 portion is decomposed by the action of air, sun, and bac- 

 teria, which render it harmless. 



Garbage and the solid portion of sewage are frequently 

 consumed in great furnaces, that which remains inde- 

 structible by fire being safely used for filling up low 

 places about the city. 



