RESPIRATION 91 



branches end? (This large amount of branching allows the 

 air to be brought in contact with very many small blood 

 vessels, through the walls of which oxygen is absorbed by 

 the blood.) 



LIX. MECHANICS OF RESPIRATION. 



Apparatus. A glass bell jar open at the top, a glass tube with 

 a toy balloon firmly bound to one end, a stick with a knob, a piece 

 of sheet rubber, a one-holed stopper to fit top of bell jar. 



Directions. Pass the tube through the stopper and seal 

 it in place with wax. Insert the stopper in the top of the 

 bell jar with the balloon inside the jar. Tie the knob into 

 the center of the rubber sheet and fasten the latter tightly 

 across the base of the bell jar, leaving the stick outside to 

 serve as a handle. With this arrangement the tube cor- 

 responds to the trachea, the balloon to the lungs, the rubber 

 sheet to the diaphragm, and the jar to the thoracic cavity. 



Now move the handle downward so as to stretch the 

 diaphragm. What happens to the balloon? What causes 

 this action? Move the handle upward. What happens to 

 the balloon now? Why? How does the diaphragm secure 

 rhythmic inhaling and exhaling, i. e., inflow and outflow of 

 air?, 



LX. STUDY OF EXPIRED AIR. 



Apparatus. Chemical thermometer, limewater, test tube, glass 

 tube, large-mouthed bottle, pneumatic trough. 



Directions. A. Temperature. Breathe on the bulb of the 

 thermometer and determine the temperature of the expired 

 air. Place the bulb under the tongue and determine the body 



