BREATHING 



363 



which two strings are tied. Thrust this down so as 

 to take up as much room as possible inside the chimney ; 

 then put the stopper in the other end and make it air- 

 tight (by means of sealing wax, grafting wax, or paraf- 

 fin). Now draw the strings down- 

 ward. This increases the space 

 inside the chimney, and air rushes 

 in to fill it. Why? The lung or 

 balloon is thus blown up. 



It is just so that the lungs are 

 blown up in breathing; but what 

 corresponds to the sheet of rubber ? 

 Breathe out as much as you can, 

 run a tape line around the chest, 

 then breathe in as much as you can. 

 How many more inches of tape 

 does it now take to go around your 

 chest? This is your chest expan- 

 sion, and you should increase it in 

 every way you can. 



At the same time place your hand on the abdomen 

 and feel how the diaphragm comes down and forces the 

 abdomen out. The motion of the chest and diaphragm 

 corresponds to the motion of the sheet of rubber. This 

 motion is brought about by the action of certain muscles. 

 The diaphragm, as is shown, forms the bottom of the 

 space in which the lungs lie; this space is called the 

 chest cavity. It contains the heart as well as the lungs ; 



FIG. 185. Apparatus 

 to illustrate inflation 

 of lungs. 



