90 PHYSIOLOGY. 



and fix the glass tube snugly in it, so that the lower end of the tube will 

 extend about half-way down the jar. Tie the balloon on the lower end 

 of the glass tube. 



EXPERIMENT i. Inflate the balloon. Consider that it requires 

 some expenditure of energy to do this. When the mouth is taken away 

 from the tube the balloon immediately collapses. 



EXPERIMENT 2. Insert the balloon and tube into the jar, but do 

 not cork, and repeat Experiment i. The same results 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 balloon 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 diminished 

 pressure, and the pressure of the outer air presses the diaphragm up, 

 and keeps the balloon partly distended, maintaining 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 dia- 

 phragm. On releasing the diaphragm, 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 lamp chimney or 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 reheated) . After cracking off the bot- 

 tom 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. 



Illustration of the Minute Anatomy of the Lung. To illustrate 

 the minute anatomy of the lung, take a rubber balloon, a glass tube, 

 two rubber tubes, one dyed red, the other blue, a bag of netting, with 

 one side dyed red and the other side blue. Tie the balloon on the end 

 of the glass tube, slip the bag of netting over the balloon and tie it, 



