404 FOODS CIRCULATED AND USED IX THE BODY 



bronchial tubes, which divide somewhat like the small branches 

 of a tree. The bronchial tubes are lined with ciliated cells, the 

 cilia of which are constantly in motion. They lash with a 

 quick stroke toward the outer end of the tube, that is, toward 

 the mouth. Hence any foreign material in the tubes will be 

 raised first by the action of the cilia and then by coughing or 

 " clearing the throat." The bronchial tubes end in very minute 

 air sacs, little pouches having elastic walls, into which air is 

 taken when we inspire, or take a deep breath. In the walls 

 of these pouches are numerous capillaries. Through the very 

 thin walls of the air sacs a diffusion of gases takes place, which 

 results in the blood giving up carbon dioxide and taking up oxygen. 

 As a result of this process the color of the blood becomes a brighter 

 red, due to the combination of the oxygen with the haemoglobin 

 in the red corpuscle. 



Demonstration 3. To determine changes that take place in the air 

 in the lungs. 



Breathe on the bulb of a thermometer and record any changes. 

 Breathe gently on any glass or polished metal surface. Xote what 

 happens. Take a moderate breath, and force air (tidal ah) by means 

 of a glass tube through lirnewater. Xotice what occurs. Force the 

 last part of a deep expiration (reserve air) through lirnewater. Xote 

 result. 



Thrust a lighted splinter into a bottle of air. How long does it 

 burn? Xow fill a glass jar with expired air by the downward displace- 

 ment of water. Invert the jar, keeping it covered. Remove the 

 cover, and introduce into the jar a lighted wood splinter. How long 

 does it continue to burn? What does this indicate? Why? (Air 

 loses about one fourth of its oxygen while in the lungs.) 



What are the changes that take place in blood in the lungs ? What 

 does air gain in the lungs ? What does it lose ? What is one reason 

 for deep breathing? 



Composition of Fresh Am and of Am Expired from the Lungs 



Constituents 



In Outdoor Air 



Ix Air Expired 



FROM THE LUXGS 



Oxygen 



Carbon dioxide 



Xitrogen and other gases . . 

 Water vapor 



20.96 

 .04 

 79. 

 variable 



16.4 

 4.1 

 79. 

 .5 



