CHAPTER XVII. 



THE CHEMISTRY OF RESPIRATION AND VENTILATION. 



The Quantity of Air breathed daily. After an ordi- 

 nary expiration the chest cavity is by no means completely 

 collapsed. At this time the lungs still contain about 200 

 Qubic inches of air. In the next inspiration 30 more cubic 

 inches are taken in, about the same amount sent out at the 

 following expiration, and so on throughout the day. Du- 

 ring quiet breathing the quantity of air in the lungs varies, 

 therefore, with each inspiration and expiration between 230 

 and 200 cubic inches. At each inspiration something over 

 a pint of fresh air is taken in, and at each expiration about 

 the same amount of vitiated air is expelled. As each of 

 us breathes at least fifteen times a minute, we thus use each 

 minute, and render impure, 15 X 30=450 cubic inches (loij- 

 pints) of air. In an hour the quantity would be 450 X 60 

 =27,000 cubic inches (930 pints), and in twenty-four 

 hours 27,000X24=648,000 cubic inches (22,320 pints) of 

 air, which would weigh about 28. 7 Ibs. We have next to 



How much air do the lungs contain after an ordinary expiration? 

 How much do they receive at the next inspiration? How much is 

 sent out from them during expiration? Within what limits does the 

 quantity of air in the lungs vary during quiet breathing? What bulk 

 of air is taken in during an inspiration? 



How often do we breathe? How much air does each one of us 

 render impure every minute? How much in an hour? How many 

 pints in a day? What does this quantity of air weigh? 



