RENEWAL OF AIR IN LUNGS. 



241 



bottle larger, the bag would have a larger space to fill. 

 The impediment on its outside being removed the 

 atmospheric pressure on its inside would expand it 

 still further, and the elastic bag would swell out to 

 fill the extra space. As the movable bottom was pulled 

 down, the bag would enlarge and receive fresh air 



FIG. 08. The skeleton of the thorax, a, g, vertebral column; &, first rib; c, 

 clavicle ; d, third rib ; i, glenoid fossa. 



through #. When the bottom was raised again the bag 

 would diminish, and some air be driven out of it through b. 

 It is in quite a similar way that the air is renewed in our 

 lungs by breathing. When we breathe-in, the thoracic 

 cavity is enlarged and air enters the lungs; when we 



How would the bag inside it be affected? 



What would the bag receive? What would happen when the 

 bottom was again raised? What happens when we breathe-in? 



