62 HUMAN PHYSIOLOGY CHAP. 



nose-breathing impossible. Air must then be taken 

 through the mouth. If these growths are not removed, 

 they may become so large as to fill the upper part of the 

 pharynx and impair the hearing by closing the tubes 

 that lead to the ears. All who find it difficult to inhale 

 enough air through the nasal passages should consult a 

 skillful physician. 



57. Sources of Impure Air. What may make the 

 atmosphere impure and dangerous to breathe ? On the 

 seashore, in the country, and on mountains the air is 

 quite fresh and invigorating, but there are many ways 

 of polluting the air in our homes and in the cities. Let 

 us see what some of them are. 



1. Burning. Whenever wood, coal, oil, coal gas, 

 etc., are burned, a large amount of impurity is produced, 

 some of which passes off into the air as carbon dioxid 

 and other gaseous substances. All smokestacks and 

 chimneys pour volumes of such impurities into the 

 atmosphere. 



2. Decaying. All animal and vegetable matter allowed 

 to decay pollutes the atmosphere with its poisonous 

 matter for a long distance. 



3. BreatJiing. Man and all other animals exhale 

 carbon dioxid and organic wastes that are poisonous to 

 rebreathe. 



4. Sewer Gas. If the plumber has not done his work 

 well, air from the sewer escapes in the house. Such air 

 contains very dangerous gaseous compounds and various 

 disease germs that are thrown into the air by the bubbles 

 which burst on the surface of the putrefying sewage. 



