THE RESPIRATORY ORGANS 177 



flamed. They usually take the form of small bunches, vary- 

 ing from the size of a pea to that of an almond. Sometimes 

 they are stalked, and have the appearance of tiny mushroom- 

 like elevations. They occur most frequently in children 

 between the ages of ten and fifteen years, and are, apparently, 

 not induced by any particular exposure. They are growths 

 of useless tissue, sometimes rather tough and wart-like, but 

 more serious than warts, because they grow in the delicate 

 breathing passages. Their presence may make breathing 

 through the nose difficult and so induce mouth breathing. 

 They may impair hearing by closing the passages into the 

 ears and they prevent the perfect development of the whole 

 body. They should always be removed before they become 

 numerous. The operation is a simple one, easily performed 

 by a skilful surgeon. If one finds his nose constantly "stopped 

 up " so that he cannot breath through it easily, he should have 

 it examined by a physician to see if the trouble is due to 

 adenoids. 



THE TRACHEA 



After passing through the nose and reaching the pharynx, 

 air is drawn to the lungs through the windpipe or trachea, 

 beginning with the enlarged portion, the larynx; Fig. 98. 

 The trachea is about five inches long and three-fourths of 

 an inch in diameter. It leaves the pharynx cavity just back 

 of the tongue; the opening into it, the glottis, is covered by a 

 lid called the epiglottis, made of connective tissue and muscle, 

 supported on a framework of cartilage; Fig. 40. During 

 ordinary breathing it is raised, leaving a free, open passage 

 for the entrance of air. When food is swallowed, it closes 

 down over the glottis, preventing particles from " going the 

 wrong way." If, by chance, a bit of food passes by it into 

 the windpipe, a violent spasm of coughing takes place. The 

 trachea is held open by a number of cartilaginous rings in its 

 walls, so that the air may pass freely through it; Fig. 98. 



