180 



RESPIRATION 



cords. Here the voice is produced chiefly by the passage of the 

 respired air over these cords, causing them to vibrate (Fig. 51). 



5. Over the opening of the larynx is found the epiglottis, 

 which fits like the lid of a box at the entrance to the lungs, 

 and closes during the act of swallowing, so that food and 

 drink shall pass backward to the oesophagus, or gullet (Fig. 

 51). Occasionally it does not close in time, and some sub- 

 stance intrudes within the larynx, when we at once discover, 

 by a choking sensation, that " something has gone the wrong 



FIG. 50. SECTION OF THE LUNGS 



way," and, by coughing, we attempt to expel the unwelcome 

 intruder. The epiglottis is one of the many safeguards fur- 

 nished by nature for our security and comfort, and is planned 

 and put in place long before these organs are brought into 

 actual use in breathing and in taking food. 



6. The air-passages are lined throughout almost their whole 

 extent with mucous membrane, which keeps them in a con- 



5. The epiglottis ? When it does not close in time, what is the consequence ? 



6. Lining of the air-passages ? Ciliated cells ? Their uses ? The three diseases of the 

 lungs ? 



