HOW DO WE BREATHE? 71 



atmospheric pressure : in other words, the air is com- 

 pressed and forced out of the lungs. The process by 

 which the lungs are enlarged and air is taken into the 

 lungs is called inspiration; and the process by which 

 the lungs are compressed into smaller space, forcing out 

 the air, is called expiration. 



SELF-TESTING EXERCISE 



Select from the following list those words which best fill the blank spaces 

 in the sentences below and arrange the words in proper numerical order. 

 A word may be used more than once. 



exhaled air compressed pulled 



inhaled oxygen upward more 



decreases hydrogen cells greater 



increases water tissues less 



liquid curved blood pressure 



dioxide organs lungs lowering 



atmospheric carbon atmosphere pushed 



Oxygen from the (1) enters the (2) in the (3) and 



is then sent to the (4) in every part of the body. Here it gives 



up (5) , takes on (6) (7) __, and is returned to the (8) 



to be (9) (10) air has more carbon dioxide and less 



(11) than normal air. Muscular action expanding the ribs 



and (12) the diaphragm (13) the chest cavity, making 



the air pressure in the lungs (14) The greater (15) 



(16) outside forces air into the lungs. When we exhale, the 



air in the lungs is (17) , and having (18) pressure than 



that of the outside (19) , it is (20) out. 



STORY TEST 



FRANK EXPLAINS BREATHING 



Read carefully and critically. List all the errors and suggest cor- 

 rections. 



The human lungs are the largest organs in the body. Together 

 they hold 31^ gallons. When we make the space in the lungs 

 larger by lowering the diaphragm and expanding the ribs, air from 

 outside is pushed in under greater than atmospheric pressure. 

 Pressure on the air in the lungs is never more than 14.7 pounds 



