284 



GENEEAL SCIENCE 



together so as not to allow any cracks, thus preventing the entrance 

 of filth and other contamination. 



Toads, moles, or insects are liable to tunnel through the cool 

 moist soil by the well and fall into the water, in this way producing 

 contamination. One should be careful of the location of cesspools, 

 barnyards, hen-houses and outhouses, that no water draining from 



FIG. 181. Why is a well of this type dangerous? What diseases do you think 

 people might get from drinking the water? Where would be a better 

 place for the well? 



these places may lead toward the well without filtering through a 

 great deal of soil. Wells should be cleaned often. 



Rivers and Streams. Great care should be taken by all health 

 authorities that no impure matter is placed near streams or lakes 

 from which water is being used for drinking purposes. Epidemics 

 of typhoid fever have often been started by the draining of water 

 into such streams or lakes from places which have been polluted. 

 Lakes and ponds, which are quiet waters with large surfaces exposed 

 to the light, may become purified by the suspended matter settling, 



