PREVENTION OF COMMUNICABLE DISEASES 241 



If such food is eaten, an intestinal disturbance usually 

 results. 



In the attempts to prevent disease, more study has been 

 given to milk and water than to other foods. For discus- 

 sion of milk, see pages 347-350. 



While milk is used as a food by all mankind, water is 

 even more important, for it is absolutely necessary if we 



Figure 243. — A Poor Reservoir. 



Note the open stream that empties into the main body of water. 

 The impure water of the Erie Canal drains into this open stream. 



are to continue to live. In this respect man is like all 

 plants and all other animals, water being necessary for 

 the preservation of all life. 



Two conditions must be met before a water supply can be 

 deemed satisfactory. There must be an abundant supply; 

 but more important still, the water must be pure, that is, 

 free from disease-producing germs. Farmers and residents 

 of small towns ma} r without great trouble secure sufficient 

 pure water, but the large cities have to spend millions of 

 dollars in providing an adequate water supply. 



