CHAPTER IX 



RESPIRATION 



144. Use of the breath. The body is an engine, and its 

 power is made by burning or oxidation. Every cell in the 

 body must breathe in oxygen from the air, but only a few 

 on the surface have access to it. So a few cells are set 

 apart for the work of carrying it to the rest. Air is always 

 going in and out of the nose or mouth. When we stop 

 breathing for only a few seconds, we feel short of breath, 

 and if we should stop for a few min- 

 utes, we should die. Air, then, is the 

 most needful thing which we take into 

 our bodies. 



145. The air passages and the lungs. 

 The nose opens into the pharynx, 

 which is just back of the mouth. From 

 the pharynx there is an opening into 

 the windpipe. The windpipe is a tube 

 about six inches long. It branches 

 into two tubes called bronchi, one for 

 each side of the body. Each bronchus 

 divides like the branches of a tree. At 

 the ends of the smallest twigs are tiny 

 bags or sacs, with very thin sides. The sacs can be 

 blown up with air. The bronchi and air sacs make up 

 the lungs. The lungs are light red flesh, much like a 

 sponge. The air in them crackles when they are squeezed. 



80 



A frog's lung (X4). 



