MECHANISM OF BREATHING 181 



C. Insert a glass tube in the trachea and breathe into it. 



1. What effect has this on the lungs ? 



2. When you blow into the lungs, do you find any structures that 

 might account for the texture of the lungs ? 



III. Cut out a small piece of the lung tissue where the bronchus enters it. 



A. Describe the branches of the bronchus in the lungs. 



B. Try to trace one of the tubes until it ends. How does it end ? 



Problem. Study of the mechanics of breathing. 



Place a cork, through which runs a glass rod, in the mouth of a small-sized 

 bell jar. Attach a balloon to the end of the rod inside the jar. Cover the 

 bottom of the jar with a piece of rubber sheeting in the center of which a string 

 is attached. 



I. To what structures in our bodies are the glass tube, balloon, bell 

 jar, and rubber sheeting comparable ? 



II. Pull the string gently, so that the rubber sheeting moves down. 



A. What effect has the lowering of the rubber sheeting on the balloon ? 



B. Is the balloon pressed on by air in this position of the rubber sheet- 

 ing as much as in the former position ? 



C. When the pressure on the outside of the balloon is released, what 

 effect has it on the air in the balloon ? 



D. Why, then, does air enter the balloon ? 



E. To what is this comparable in human breathing ? 



III. Push the rubber sheeting into the battery jar to form an arch. 



A. What effect has the arching of the rubber sheeting on the balloon ? 



B. In this position, is the balloon pressed on by air as much as in the 

 lowered position? 



C. When the pressure on the outside of the balloon is increased, what 

 effect has it on the air in the balloon ? 



D. Why, then, does air go out of the balloon ? 



E. To what is this comparable in human breathing? 



IV. To what is the inflation and deflation of air in the balloon due ? 



V. What is one of the reasons for inspiration and expiration in man ? 



Mechanism of breathing. Air with its oxygen is taken in, and 

 air with increased amounts of carbon dioxide is given off as a re- 

 sult of muscular activity. The floor of the chest cavity is formed 

 by the muscular diaphragm. The upper surface of the diaphragm 



