COMPOSITION OF INSPIKED AND BXPIEBD AIE 325 



pressed in volume per cent the following table represents 

 the composition of ordinary air: 



Inspired Air.^ 



Oxygen 20.96% 



Nitrogen' 79.00% 



Carbon dioxide 00.04% 



If we examine the air which is expelled from the lungs 

 we find certain remarkable changes in it. If we breathe 

 upon a thermometer bulb or a mirror surface, two proper- 

 ties peculiar to expired air are apparent. The first is the 

 increase in water content as shown by the film of vapor 

 that collects upon the bulb. The second is the rise of tem- 

 perature as indicated by the rise of the mercury column of 

 the thermometer. A comparison with the body tempera- 

 ture shows that the expired air has been raised to this body 

 temperature. 



Evidently then, breathing involves a loss of water and 

 heat to the body, and thus plays an important part in the 

 .regulation of the temperature and water content of the 

 body. 



If we blow expired air through a tube into a tumbler of 

 limewater, the latter soon becomes milky, indicating that 

 a large proportion of carbon dioxide is present. (See p. 16.) 

 If we collect some of the expired air over water and intro- 

 duce a hghted match into it, the flame soon goes out, indi- 

 cating the loss of a large amount of its oxygen, and hence 

 its power to support combustion. Expressed chemically, 



1 The very small per cent of argon and krypton is included in the 

 nitrogen estimate. The percentage of water is so small as to be neglected 

 in the above table. 



