RESPIRATION 



103 



file and hold on the end of this mark a hot poker. When the glass 

 cracks, lead the crack around the bottle by heating about one half inch 

 in advance of it.) Place the bottle in a large glass jar filled two thirds 

 full of water (Fig. 52). Let the space above 

 the water represent the chest cavity and 

 the water surface represent the diaphragm. 

 Raise the bottle, noting that the water falls, 

 thereby increasing the space and causing air 

 to enter. Then lower the bottle, noting the 

 opposite effect. To show the movement of 

 the air in and out ot the bottle, hold with 

 the hand (or arrange a support for) a burn- 

 ing splinter over the mouth of the bottle. 



To estimate the Capacity of the Lungs. 

 Breathing as naturally as possible, expel the 

 air into a spirometer (lung tester) during a 

 period, say of ten respirations (Fig. 53). 



FIG. 52. Simple appa- 

 ratus for illustrating the 

 action of the diaphragm. 



Note the total amount of 

 air exhaled and the number of " breaths " and calculate the amount of 



air exhaled at each breath. This 

 is called the tidal air. 



2. After an ordinary inspira- 

 tion empty the lungs as com- 

 pletely as possible into the spi- 

 rometer, noting the quantity 

 exhaled. This amount, less the 

 tidal air, is known as the reserve 

 air. The air which is now left 

 in the lungs is called the residual 

 air. On the theory that this is 

 equal in amount to the reserve 

 air, calculate the capacity of the 

 lungs in an ordinary inspiration. 



FIG. 53. Apparatus (spirometer) for 

 measuring the capacity of the lungs. 



3. Now fill the lungs to the full expansion of the chest and empty 

 them as completely as possible into the spirometer, noting the amount 

 expelled. This, less the tidal air and the reserve air, is called the com- 

 plemental air. Now calculate the total capacity of the lungs. 



