WATER 137 



earth from place to place. The action of the sun on 

 the water of rivers, lakes, and the ocean causes the land 

 to be well supplied with moisture, which makes the pro- 

 duction of both plants and animals possible. 



91. Why Water should be Purified. The decaying 

 matter in the fields and woods such as plants, leaves of 

 trees, and animal matter on the surface permits large 

 quantities of poisonous substances and bacteria to get 

 into the water. Many of these bacteria are not harmful, 

 but there are some that are dangerous to health and are 

 called disease germs. Some of the dangerous substances 

 which get into the water from the surface of the earth 

 are chlorine compounds. When water chemists of the 

 cities find chlorine compounds in the water, they know that 

 more or less decayed animal or plant matter has entered 

 the water. There are various disease germs which can get 

 into the water from the surface of the land, and some- 

 times these germs are carried beneath the surface and 

 may flow into springs and wells. One of those that can 

 be easily carried by water is the typhoid germ, or the 

 typhoid bacillus. 



People are sometimes careless of the waste matters of 

 a patient who has typhoid fever. This waste may con- 

 taminate the water of their wells. These germs in the 

 well water, if swallowed by a person in drinking, may 

 produce the disease. Sometimes when a well is near the 

 house and the waste water is thrown on the surface of 

 the ground or poured into the sink, it may find its way 

 into the well, carrying the germs with it. The surface 

 of the ground or the soil is capable of oxidizing or destroy- 

 ing millions of germs, but the earth beneath, the subsoil, 

 will not destroy disease germs readily, and so they may 

 pass through the soil and get into the deeper parts of the 



