External Respiration. 



93 



enough to cover the mouth of the jar, toy rubber balloon, cork (rubber 

 preferred), glass tube, cotton string, collar button. 



PREPARATION. Lay the collar button on the center of the sheet of 

 rubber, double the rubber over it, stretching the rubber strongly over 

 the head of the button, and tie the head firmly in its place. Stretch 

 the sheet of rubber over the base of the jar with the base of the 

 button on the outside, and fasten with string. Bore a hole in the cork, 

 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* 



CILIA 



.BRONCHIAL TUBE. 



Fig. 57. Minute Structure of the Lungs, showing Air Sacs and Capillaries. 



EXPERIMENT i. Insert the balloon and tube into the jar, inflate 

 the balloon, and while it is inflated tightly cork the jar. If all the parts 

 fit well, the balloon should now remain inflated, and the rubber which 

 represents the diaphragm will be arched upward. 



EXPERIMENT 2. Pull the diaphragm down, using the base of the 

 collar button 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 diaphragm, it springs 

 upward, and the balloon becomes smaller, 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 is 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 



