MECHANICS OF RESPIRATION. Ill 



as before are noticed, and it will further be seen, or rather 

 heard and felt, that when the balloon is inflated, some air 

 comes out of the jar around the tube, and when the balloon 

 collapses air again enters the jar. 



EXPERIMENT 3. Again inflate the balloon, and while it is 

 inflated tightly cork the jar. If all the parts fit well, the bal- 

 loon should now remain inflated. This may at first seem 

 strange, as the mouth is taken away from the tube, and the 

 tube left entirely open to the air. But it will be seen that to 

 just the extent that the balloon contracts, so much more space 

 is left in the jar outside the balloon. This means dimin- 

 ished pressure ; and the pressure of the outer air presses the 

 diaphragm up, and keeps the balloon partly distended, main- 

 taining equilibrium. 



EXPERIMENT 4. Pull the diaphragm down, using the 

 marble as a handle. This shows the expansion of the lung 

 by the pressure of the external air when more space is given 

 by the depression of the diaphragm. On releasing the dia- 

 phragm, it springs upward, and the balloon becomes reduced 

 in size, driving out part of the air that was in it. This shows 

 how expiration is accomplished, so far as the diaphragm is 

 concerned. 



If a bell jar be not at hand, a quart bottle may be used, 

 after cutting off the bottom, as follows : File a deep notch 

 across near the bottom ; heat an iron rod, and apply the end 

 of it to one end of the notch, and slowly draw the rod around 

 to the other end of the notch (the rod may need to be re- 

 heated). After cracking off the bottom of the jar, file the 

 edges so they will not cut the rubber. 



Let each pupil make a drawing, showing the position of 

 the parts in Inspiration and in Expiration. 



Action of the Walls of the Chest. To show the ac- 

 tion of the chest walls, take a pair of bellows, and stop the 



