city of the
respiratory organs._ The necessity of voluminous lungs may he
elucidated by the following experiment: Suppose a gill of alcohol,
mixed with a gill of water, be put into a vessel having a square foot
of surface, and over the vessel a membrane be tied, and that the water
will evaporate in twenty-four hours. If the surface had been only six
inches square, only one fourth of the water would have evaporated
through the membrane in the given time. If the surface had been
extended to two square feet, the water would have evaporated in twelve
hours.

523. Apply this principle to the lungs: suppose there are two hundred
feet of carbonic acid to be carried out of the system every
twenty-four hours. This gas, in that time, will pass through a
vesicular membrane of two thousand square feet. If the lungs were
diminished in size, so that there would be only one thousand square
feet of vesicular membrane, the amount of carbonic acid would not, and
could not, be eliminated from the system. Under such circumstances,
the blood would not be purified.

524. Again; suppose the two thousand square feet of membrane would
transmit two hundred cubic feet of oxygen into the system every
twenty-four hours. If it should be diminished one half, this amount of
oxygen would not pass into the blood. From the above illustrations we
may learn the importance of well-developed chests and voluminous
lungs; for, by increasing the size of the lungs, the oxygen is more
abundantly supplied to the blood, and this fluid is more perfectly
deprived of its carbon and hydrogen.

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What does this hereditary transmission prove? 522. How is the
necessity of voluminous lungs illustrated? 525. How is this principle
applied to the interchange of products in the lungs?

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525. The chest is not only most expanded at its lower part, but the
portion of the lungs that occupies this space of the thoracic cavity
contains the greater part of the air-cells; and, from the lower two
thirds of the lungs the greatest amount of carbonic acid is abstracted
from the blood, and the greatest amount of oxygen gas is conveyed into
the circulating fluid. Hence, contracting the lower ribs is far more
injurious to the health than diminishing the size of the upper part of
the chest.

526. The question is often asked, Can the size of the chest and the
volume of the lungs be increased, when they have been injudiciously
comp