192 RESPIRATION 



and other small particles drawn in with the breath (Fig. 52). 

 The three diseases which more commonly affect the lungs, as 

 the result of exposure, are pneumonia, or inflammation of the 

 lungs, affecting, principally, the air-cells ; bronchitis, an inflam- 

 mation of the large bronchial tubes ; and pleurisy, an inflamma- 

 tion of the pleura, or outside wrapping of the lungs. Among 

 the young, an inflammation of the trachea takes place, known 

 as croup. 



7. The Movements of Respiration. The act of breathing has 

 two parts (1), inspiration, or drawing air into the lungs, and 

 (2), expiration, or driving it out again. In inspiration, the 



chest extends in its length, breadth, 

 and height. The motion outward and 

 upward can be observed every time 

 we draw a full breath ; and is caused 

 by a lifting .of the ribs. But the mo- 

 tion downward is not so apparent, as 

 it is caused by a muscle within the 

 PIG. 52. CILIATED CELLS HIGHLY body called the diaphragm. This is 



MAGNIFIED , . . . . 



the thin partition which separates the 



chest from the- abdomen, rising like a dome within the chest 

 (Fig. 22). 



8. With every inspiration the diaphragm contracts, and in 

 so doing, approaches more nearly a level surface, and thus 

 enlarges the capacity of the chest. Laughing, sobbing, and 

 sneezing are due to sudden action of the diaphragm. On the 

 proper acting of this muscle depends our power to breathe 

 deeply; and like other muscles, its strength is increased by 

 exercise. This gives that endurance, or " long wind," as it is 

 commonly called, which is possessed in a marked degree by 

 the mountaineer, the oarsman, and the trained singer. The 

 habit of taking frequent and deep inspirations, in the erect 

 position, with the shoulders thrown back, tends greatly to 

 increase the capacity and power of the organs of respiration. 



7. The act of breathing ? Extension of the chest by breathing ? 



8. Contraction of the diaphragm ? Power of the diaphragm ? Effects of extending the 

 walls of the chest ? The habit of taking frequent and deep inspirations ? 



