MODIFICATIONS OP BREATHING 331 



supply of fresh air to draw upon. Deep breathing exer- 

 cises soon accustom the lungs to fuller expansions and 

 contractions under these conditions, and thus bring the 

 air to gi-eater areas of capillaries. Runners, whose lungs 

 have been so trained, can run much longer distances and use 

 their muscles to greater advantage than those who have 

 neglected such training. " Second wind" is simply the 

 automatic response of the lungs by increase of rhythmical 

 expansions and contractions. Again, since the breathing 

 depends upon the action of the chest muscles and those of 

 the diaphragm, exercise tends to develop these muscles 

 and thus directly develop lung capacity. People who 

 have well developed lungs and muscles are said to be long- 

 winded, and are usually more healthy than short-winded 

 ones. 



Modifications of breathing. — When any obstacle such as dust 

 or food enters the trachea, the abdominal muscles contract forcibly 

 and compress the lungs. The glottis opens suddenly and the air 

 forcing out the matter gives an effect called coughing. Some- 

 times inflammation of the lining of the bronchial tubes may cause 

 this action in bronchitis. In like manner irritation of the nasal 

 membranes causes the air to be forcibly expelled through the 

 nose. Such an operation is called sneezing. Blowing is a long, 

 forcible expiration through a small opening in the lips or through 

 the nose. If the object which causes coughing is of sufficient 

 size to stop the trachea, as when food slips by the epiglottis, the 

 expirations increase in frequency and force, and we call the result 

 choking. In this last, the supply of air to the lungs may be com- 

 pletely cut off if the obstacle is not soon removed, and strangula- 

 tion, or death from lack of oxygen, result. When the air supply 

 is cut off by inclosure in a room without ventilation, or by immer- 

 sion in a gas or water, the result is spoken of as suffocation. Both 

 strangulation and suffocation are the results of oxygen starvation. 



Laughing, crying, and sobbing are merely rapid successions of 



