BREATHING 



L95 



plain why exercise out-of-doors is better for us than that 

 taken indoors. 



All the air passages are lined with cells bearing numer- 

 ous cilia (Figure 204), and these cilia are constantly in 

 motion. Their work is to carry toward the mouth the 

 particles of dust and other 

 foreign materials brought in 

 by the air. This foreign matter 

 is removed when we cough or 

 clear our throats. Explain why 

 clean air is better for us than 

 dirty air. 



The air that enters the lungs 

 is rich in oxygen and there is 

 some oxygen in the air which is 

 expired. But the proportion of 

 carbon dioxide is greater in 

 the expired air of plants and 

 all animals. 



Ventilation. — Associated with 

 the question of breathing is the 

 problem of supplying our homes 

 with fresh, clean air. Every 

 one feels better after a walk in the open air. How to 

 have plenty of fresh air in our rooms is a diilieiilt problem. 

 One of the difficulties is to get the air down to the breath- 

 ing line and not stir up the dust on the floor. Figures 

 209 and 210 show the best plans for ventilating a room. 

 They are adapted to the two common methods of heating, 

 hot air and steam or hot water. They show the coins.' I aken 

 by the currents of fresh air entering the room at night with 

 the window open, and in the daytime with it shut. 



Exercise. — Even if the home is furnished with fresh 

 air, we should observe good habits of breathing. When 



a. -Oesophagus 



b. -Diaphragm 



Figure 208. — Diagram of 

 the Diaphragm. 



Note the position at the bot- 

 tom of the thorax. 



