THE VENTILATING SYSTEM OF THE BODY 273 



motions of the diaphragm. Sighing is a prolonged inspiration 

 and expiration which appears to be intended to increase the 

 supply of oxygen in the lungs when for any reason we have 

 neglected to breathe deepty enough. Yawning is much like 

 sighing except that the air is inspired through the mouth. It 

 seldom occurs unless we are fatigued. Snoring occurs during 

 sleep when the mouth is open and the soft palate vibrates in 

 the divided currents of air. Hiccough is due to a strong spas- 

 modic contraction of the diaphragm. In coughing and sneez- 

 ing the diaphragm forcibly expels air through the mouth. 

 The stimulation which causes coughing originates in the throat, 

 trachea or lungs; in sneezing, it originates in the nose. Most 

 actions of this kind are reflex. 



Practical Exercises 



1. How many times do you breathe a minute while sitting? Make 

 three trials. 



2. Count the number of times you breathe a minute after running a 

 hundred feet or climbing two flights of stairs. 



3. How many times does your heart beat while you are breathing once ? 



4. Expel as much breath as possible and measure the circumference 

 of the thorax, passing the tape around it just beneath the arms. Then 

 take as long a breath as possible and measure again. How many inches 

 can you expand? 



6. Get a bottle holding three or four quarts, fill it with water and 

 invert in a large pan of water. Keeping the mouth of the bottle under 

 water, by means of a rubber tube blow into the bottle as much air as 

 possible with one breath. Try the experiment with a tight band around 

 the waist. Explain the difference. 



6. Speak the vowels. Do you make these sounds with the mouth 

 open or shut? 

 18 



