## The Quantity Of Air Breathed Daily

After an ordinary expiration the chest cavity is by no means completely collapsed. At this time the lungs still contain about 200 cubic 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. During 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, 15x30=450 cubic inches (15 1/2 pints) of air. In an hour the quantity would be 450x60 =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 lbs. We have next to see what it is that happens to this vast quantity of air breathed daily by each one of us; what we have taken out of it, and what we have given off to it.

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?