BREATHING 



231. Other Changes in the Air we breathe. The air, as 

 it leaves the lungs, is saturated with watery vapor. This is 

 seen when we breathe on the bright steel blade of a pocket- 

 knife, a mirror, or any cold, polished surface. As we all 

 know, the surface becomes covered with a thin film, or 

 minute drops of water. In cold 

 weather this moisture becomes 

 visible with each expiration. 



Air as it leaves the lungs is 

 warmer than the surrounding air. 

 It is generally about 98 F. For 

 this reaso'n, on a cold day, when 

 our breath passes off as a cloud 

 of steam, we blow on our fingers 

 to warm them. 



The air breathed out of the 

 lungs also contains a small 

 amount of decaying animal mat- 

 ter. Everybody knows the un- 

 pleasant odor of the air in rooms 

 in which many persons have been 

 closely shut up. 



FIG. 1 08. 



Showing the structure of a lobule 

 of the lung. The lobule has been 

 injected with mercury,afterwards 

 dried and cut open. A large 

 bronchial tube with its various 

 branches is well shown. 



Experiment 53. To show that the 

 air we expire is warm and moist. 

 Breathe on a thermometer for a few 

 minutes. The mercury will rise rapidly. 



Breathe on a mirror, a knife blade, or any polished metallic 

 surface, and note the deposit of moisture. 



Experiment 54. To show that the expired air contains carbon 

 dioxide. Put a glass tube into a glass of clear limewater and blow 

 through the tube. The liquid will soon become milky, because the 

 carbon dioxide of the expired air unites with the lime held in solu- 

 tion and forms the white, solid carbonate of lime. 



