RESPIRATION. 



8. With every inspiration, the diaphragm contracts, and 

 in so doing, approaches more nearly a plane, or horizontal, 

 surface, and thus enlarges the capacity of the chest. 

 Laughing, sobbing, hiccoughing, and sneezing are caused 

 by the spasmodic or sudden contraction of the diaphragm. 

 The special power of this muscle is important in securing 

 endurance, or " long wind," as it is commonly expressed; 

 which may be obtained mainly by practice. It is possessed 

 in a marked degree by the mountaineer, the oarsman, and 

 the trained singer. As the walls of the chest extend, the 

 lungs expand, and the air rushes in to fill them. This 

 constitutes an inspiration. The habit of taking frequent 

 and deep inspirations, in the erect position, with the 

 shoulders thrown back, tends greatly to increase the ca- 

 pacity and power of the organs of respiration. 



9. Expiration is a less powerful act than inspiration. 

 The diaphragm relaxes its contraction, and ascends in the 

 form of a dome; the ribs descend and contract the chest; 

 while the lungs themselves, being elastic, assist to drive 

 out the air. The latter passes out through the same chan- 

 nels by which it entered. At the end of each expiration 

 there is a pause, or period of repose, lasting about as long 

 as the period of action. 



10. Frequency of Respiration. It is usually esti- 

 mated that we breathe once during every four beats of the 

 heart, or about eighteen times in a minute. There is, of 

 course, a close relation between the heart and lungs, and 

 whatever modifies the pulse, in like manner affects the 

 breathing. When the action of the heart is hurried, a 

 larger amount of blood is sent to the lungs, and, as the 

 consequence, they must act more rapidly. Occasionally, 

 the heart beats so very forcibly that the lungs cannot keep 

 pace with it, and then we experience a peculiar sense of 



8. Contraction of the diaphragm ? Power of the diaphragm? Effects of ex- 

 tending the wails of the chest ? The habit of taking frequent and deep inspirations '( 



9. Expiration ? The mechanism of expiration ? 



1O. Frequency of respiration ? Effect of hurried action of the heart? 



6* 



