70 



LIVING IN AN OCEAN OF AIR 



air enter-s 



Demonstration 5. To Show How We Breathe. 



a. Take a bell jar, insert in the upper end a Y-shaped glass tube, 

 and fasten over the lower ends of the Y two small rubber balloons. 

 Over the lower open end of the jar tie a piece of sheet rubber. 



Pull on the rubber so that the 

 cavity inside of the jar is made 

 larger. What happens to the 

 rubber balloons? 



b. Allow the rubber to go 

 back to its former position 

 and press it upward into the 

 jar. What happens to the 



Walloons 

 fill \vlth, 



>i~rS Y> 



space s 

 mcrea-sect. 



balloons ? 



c. Cover the open tube in 

 the cork with your finger and 

 pull down the rubber as before. 

 What happens? 



Explanation. Try to explain from the movements you 

 have observed why the rubber balloons fill with air when 

 the sheet rubber is pulled down. 



In the experiment let us suppose the rubber balloons 

 represent the lungs, and the Y-tube corresponds to the 

 air passages connecting the lungs with the mouth. We 

 move our ribs outward when we take air into the lungs. 

 This action is not shown in our experiment. At the same 

 time we pull down a thin wall of muscle (called the dia- 

 phragm), which in the experiment is represented by the 

 rubber sheet. This makes the chest cavity bigger and 

 pressure of the air in the lungs becomes less than that of 

 the atmosphere outside. The lungs fill with air, because 

 it is pushed in by the greater pressure outside. The 

 higher we raise the ribs, the more the diaphragm stretches 

 and the larger the space in the chest cavity. So deep 

 breathing brings in more air than ordinary shallow breath- 

 ing does. 



When the ribs go back into place, the diaphragm is 

 curved upward into the chest cavity, which is thus made 

 smaller. The air in the lungs is now under greater than 



