RESPIRATION 57 



SUMMARY OF THE MAIN POINTS 



1. The oxygen of the air is necessary to cause the slow 

 combustion or oxidation of the foods in the cells of the body. 



2. The air reaches the lungs through a number of organs 

 which form the air passages. They are all composed of plates 

 and rings of cartilage held together by connective tissue, and 

 lined with a mucous membrane. 



3. The nasal passages are large, irregular, winding passages 

 in the nose that warm the air, remove particles of dust and dirt, 

 and contain the nerves of smell. We should breathe through 

 the nose rather than through the mouth. 



4. The pharynx is a funnel-shaped organ back of the nose 

 and mouth from which there are seven different openings. 



5. The larynx is just below the back part of the mouth and 

 serves as an air passage and as the organ of voice. 



6. The trachea is about four and one half inches long, ex- 

 tending from the larynx to the two bronchi. It is usually 

 called the windpipe. 



7. The bronchial tubes extend to the lungs, where they get 

 smaller and lighter until they terminate in very small, thin- 

 walled air sacs. 



8. The lungs are the central organs of respiration. They 

 are pinkish, spongy, elastic masses completely filling the chest 

 Each lung is covered with a closed sac called the pleura. 



9. The diaphragm, intercostal muscles, and the muscles 

 of the neck work together and enlarge the chest at regular 

 intervals. 



10. The atmospheric pressure and elasticity of the lungs 

 make the lungs follow the chest in its movements. 



11. The lungs of the average adult hold about three hun- 

 dred and thirty cubic inches of air. At each ordinary inspira- 

 tion about thirty cubic inches of air is inhaled. 



