400 THE HUMAN BOD 7 



breathed air are those in its chemical composition. .Pure 

 air when completely dried consists in each 100 parts of 



By Volume. By Weight. 



Oxygen 20.8 23 



Nitrogen 79.2 77 



Ordinary atmospheric air contains in addition 4 volumes 

 of carbon dioxide in 10,000, or 0.04 in 100, a quantity which, 

 for practical purposes, may be neglected. When breathed 

 once, such air gains rather more than 4 volumes in 100 of 

 carbon dioxide, and loses rather more than 5 of oxygen. 

 More accurately, 100 volumes of expired air after drying give 

 98.9 volumes, which consist of 



Oxygen 15.4 



Nitrogen 79.2 



Carbon dioxide 4.3 



The expired air also contains volatile organic substances 

 in quantities too minute for chemical analysis, but readily 

 detected by the nose upon coming into a close room in which 

 a number of persons have been collected. 



Since 10,800 litres (375 cubic feet) of air are breathed in 

 twenty-four hours and lose 5.4 per cent of oxygen, the total 

 quantity of this gas taken up in the lungs daily is 10,800 X 

 5.4 ~ 100 = 583.2 litres (20.4 cubic feet). One litre of 

 oxygen measured at C. (32 F.) and under a pressure equal 

 to one atmosphere, weighs 1.43 grams, so the total weight of 

 oxygen taken up by the lungs daily is 583.2 X 1.43 = 833.9 

 grams. Or, using inches and grains as standards, 44.5 cubic 

 inches of oxygen at the above temperature and pressure 

 weigh almost exactly 16 grains, so the 20.4 cubic feet ab- 

 sorbed in the lungs daily weigh 20.4 X 1728 -f- 44.5 X 16 = 

 12,818 grains. 



The amount of carbon dioxide excreted from the lungs 

 being 4.3 per cent of the volume of the air breathed daily, is 

 10,800 X 4.3 -^ 100 = 464.4 litres (16.25 cubic feet) measured 

 at the normal temperature and pressure. This volume 

 weighs 910 grams, or 14,105 grains. 



If the expired air be measured as it leaves the Body its 

 bulk will be found greater than that of the inspired air, since 

 it not only has water vapor added to it, but is expanded in 

 consequence of its higher temperature. If, however, it be 

 dried and reduced to the same temperature as the inspired 



