



374 THE HUMAN BOD T. 



The amount of heat taken off in this way during the day is 

 about 148 calories. The total daily loss of heat from the 

 Body through the lungs is therefore 198 calories, 50 in warm- 

 ing the inspired air and 148 in the evaporation of water. 



The most important changes brought about in the 

 breathed air are those in its chemical composition. Pure 

 air when completely dried consist in 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 when dried 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 liters (346 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-H 100 =583.2 liters (20.4 cubic feet). One 

 liter of oxygen measured at 0C (32 F.) and under a pressure 

 equal to one atmosphere, weighs 1.43 grams (see Chemistry), 

 so the total weight of oxygen taken up by the lungs daily is 

 583.2 X 1.43 = 833.9 grams. 0?', using inches and grains as 

 standards, 44.5 cubic inches of oxygen at the above tem- 

 perature and pressure weigh almost exactly 16 grains, so 

 the 20.4 cubic feet absorbed in the lungs daily weigh 20.4 

 X 1728-44.5x16 = 12,818 grains. 



The amount of carbon dioxide cxcretrd from the lungs 



