HEALTH AND WELL-BEING 63 



spread of certain diseases, and the logical application of this knowledge 

 to other health conditions, constitutes one of the brightest pages in 

 the history of preventive medicine. 



In the increased use of cement for building purposes lies one of the 

 chief aids in the warfare upon rats and mice. Without access to food 

 supplies, starvation will keep their numbers down. They are a menace 

 to health as carriers of disease, and their destruction of foodstuffs and 

 other property necessitates their extermination. Freedom from vermin 

 of all kinds is an indispensable sanitary measure. 



FIG. 26. A breeding place for house flies. 



Exercises 



1. Name various ways in which the waters of wells near dwellings and 

 farm buildings are likely to become contaminated. 



2. How may surface drainage into wells be prevented? 



3. Describe the action of "chain pumps" as means for the aeration of 

 cistern waters. 



4. Why are cisterns as sources of water for household uses in large towns 

 and cities quite out of question? 



5. How may the stored waters of large reservoirs in city water systems be 

 aerated? 



