CHAPTER VIII 

 BREATHING 



220. The Act of Breathing. Night and day, without one 

 minute's rest, from the first to the last moment of our 

 lives, we are breathing. Most of the time we do not think 

 anything about it. We eat, talk, work, and sleep ; and all 

 this time our breathing goes quietly on. We can hold our 

 breath for a short time, yet after a few seconds we begin 

 to feel uncomfortable. 



221. The Object of Breathing. In studying food and 

 blood, we have learned that without food and air the burn- 

 ing, or oxidation, which is slowly going on in our bodies 

 all the time, would soon flag, and life would come to an end. 



We have learned that the dark blood is sent to the lungs 

 from the right ventricle and is returned to the left auricle 

 as blood of a bright red color. The blood has got rid of 

 part of its waste matter, and has taken up oxygen. 



Hence, in breathing we have two objects in view: first, 

 to give a fresh supply of oxygen to the blood ; second, to 

 get rid of carbon dioxide and other waste matter taken up 

 from the tissues and brought to the lungs by the blood. 



222. The Air Passages. The air is drawn into the lungs 

 through the mouth, the nostrils, and the windpipe. 



The nostrils are really the passageways for the air, and 

 warm it somewhat before it passes into the windpipe, or 

 trachea, on its way to the lungs. 



161 



