408 LIFE ON THE EARTH 



the lungs through the mouth is not sifted as it is when it 

 passes through the nose; moreover it is not sufficiently 

 warmed because the mouth passage is much shorter than 

 the nasal passages. Thus the throat and lungs are irritated 

 by mouth-breathing and are more liable to disease. 



Sometimes abnormal spongy growths called adenoids 

 partly fill the upper part of the throat. They not only 

 obstruct nose breathing but also furnish a breeding place 

 for disease germs. It is a simple matter for a surgeon to 

 remove them; and unless they are removed, they may 

 result in disordered stomach, quarrelsome disposition, 

 stunted growth, and even stupidity. Most of the cases 

 of adenoids are found in children. Children may or may 

 not outgrow adenoids, but some or all of the evil effects 

 remain if the trouble is long neglected. In the interest 

 of mental and physical vigor as well as of attractiveness 

 of countenance, the removal of adenoids ought never to 

 be unduly postponed. 



At the back of the mouth the windpipe and the throat 

 come together. 



When food is being swallowed, the passage into the wind- 

 pipe must be closed, and this is done by the little valvelike 

 epiglottis. If, in swallowing, the epiglottis is not able to 

 close quickly enough, something may pass into the wind- 

 pipe and cause choking. The windpipe, at the upper part 

 of the chest, branches into two parts, one branch going to 

 each of the lungs. 



The lungs fill the upper part of the chest and infold 

 the heart. In them the air tubes divide again and again, 

 forming a vast network of tubes which grow smaller and 

 smaller until they end in little air sacks. Interlacing with 

 these air tubes are veins and arteries which carrv the blood. 



