It is well known that oxygen over putrid substances is absorbed, while
carbonic acid and other gases take its place; and hence all places near
or in our houses which contain impurities diminish the oxygen of the
air. The average quantity of oxygen in pure air amounts to 21 parts out
of 100. In impure places, such, for instance, as in a sleeping-room
where the windows have been shut all night, or in a lecture-theater
after a lecture, or in a close stable, the oxygen has been found to be
reduced to as little as 20 parts in 100.
That is to say, a man breathing pure air obtains, and he requires, 2,164
grains of oxygen per hour. In bad air he would, if breathing at the same
rate, get little over 2,000 grains of oxygen an hour--that is, a loss
of 5 per cent.; and this diminished quantity of oxygen is replaced with
other, and in almost all cases, pernicious matters. The oxygen is the
hard-working, active substance that keeps up the fire, cooks the food,
and purifies the blood; and, of course, as the proportion of oxygen in
the air breathed diminishes, the lungs must exert themselves more to
obtain the necessary quantity of oxygen for carrying on the functions of
life.
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