410 APPLIED PHYSIOLOGY 



sand and holds back the impurities just as the vegetable growth does. 

 By this method one hundred and twenty million gallons of water per 

 acre can be purified daily. 



714. Street cleaning. In thickly settled places dirt 

 from the streets is often a menace to health, for it contains 

 many kinds of bacteria which cause sickness in men and 

 animals. In wet weather the dirt forms mud which may 

 be carried into houses on shoes and clothing, while in dry 

 weather the germ-filled dirt is blown into our houses in the 

 form of dust. Among the bacteria which are often found 

 in street cleanings are the germs of tuberculosis, lockjaw, 

 and grippe. It is necessary that the streets be kept clean 

 as much on account of the health of the people as for the 

 sake of good appearances. Each community may properly 

 spend large sums of money for street cleaning. 



715. Quarantine. The laws of the various states require 

 physicians to report to the Health Board all cases of infec- 

 tious or contagious diseases with which they come in contact. 

 The health officer visits the sick person's house and requires 

 all persons living there to conform to all necessary require- 

 ments in order to prevent other persons from catching the 

 disease. Smallpox, diphtheria, and scarlet fever may be 

 caught by inhaling the air from the sick room. So in cases 

 of these diseases only the physician and nurses are allowed 

 to enter the sick room; all other persons are required either 

 to leave the premises, or to live in a part of the house re- 

 mote from the sick person. This enforced isolation is 

 called quarantine. 



Cases of measles, German measles, whooping cough, 

 chicken pox, and mumps should also be quarantined, but 

 they usually are not, mainly because of the popular be- 

 lief that they are not dangerous diseases. Yet in New 

 York state during 1907 measles caused nearly as many 



