422 GENERAL SCIENCE 



bacteria which grow and prey upon the harmful bacteria 

 of the sewage. Columbus, Ohio, recently installed a 

 sewage disposal plant having a capacity of 20,000,000 

 gallons daily. 



Figure 372 shows the new Imhoff tanks that are in ser- 

 vice at Columbus, Ohio. In the background the sprin- 

 kling filters are shown. The sewage passes through these 

 tanks at a very low velocity, which permits the heavier 

 solids to settle and cling to the sloping sides of the tanks. 

 The clarified sewage passes through the tank and is 

 sprayed over beds of broken limestone about five and one 

 half feet deep. In the photograph these sprinkling filters 

 are shown in the background, the round building being 

 the place from which the liquor is distributed by means 

 . of gates to the sprinkling filters. 



Typhoid Fever. In 1900 there were recorded about 

 350,000 cases of typhoid fever in the United States, with 

 more than 35,000 deaths. Typhoid germs leave the body 

 in the wastes from intestines and kidneys, and in the 

 sputum when pneumonia develops with typhoid. They 

 are carried by food, water, dust, and flies ; by oysters 

 that have grown in beds near outlets to sewers ; and by 

 raw vegetables which have been watered with sewage- 

 polluted water. 



We can easily understand, then, how important a ques- 

 tion is the disposal of sewage in considering the health 

 of a community. Terrible epidemics of typhoid may be 

 caused in the following ways : by throwing body waste 

 from a patient on the ground. near a stream into which 

 it may be carried by melting snow, rain, or high water; 

 by disposing of sewage where it may enter a well by means 

 of seepage water (Figure 373) ; by turning the sewage 

 from one city directly into a lake or river from which an- 



