XXX. LUNG-TESTING APPARATUS.
The capacity of the lungs, and their powers of inspiration and expiration,
can be tested by means of easily constructed apparatus which will interest
most people who are introduced to it. The reduction of the capabilities of
the lungs to figures affords a not unprofitable form of entertainment, as
even among adults these figures will be found to vary widely.
Air Volume Measuring.--The air which the lungs deal with is
scientifically classified under four heads:
1. Tidal air, which passes into and out of the lungs in natural breathing.
About 30 cubic inches in an adult (average).
2. Reserve air, which can be expelled after a normal expiration. About 100
cubic inches.
3. Complemental air, which can be drawn in after a normal inspiration.
About 100 cubic inches.
4. Residual air, which cannot be removed from the lungs under any
conditions by voluntary effort. About 120 cubic inches.
The first three added together give the vital capacity. This, as an
addition sum will show, is very much greater than the volume of air taken
in during a normal inspiration.
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