ressed, or have inherited this unnatural form? The answer is in
the affirmative. The means for attaining this end are, a judicious
exercise of the lungs, by walking in the open air, reading aloud,
singing, sitting erect, and fully inflating the lungs at each act of
inspiration. If the exercise be properly managed and persevered in, it
will expand the chest, and give tone and health to the important
organs contained in it. But, if the exercise be ill-timed or carried
to excess, the beneficial results sought will probably not be
attained.

_Observation._ Scholars, and persons who sit much of the time, should
frequently, during the day, breathe full and deep, so that the
smallest air-cells may be fully filled with air. While exercising the
lungs, the shoulders should be thrown back and the head held erect.

527. _The movement of the ribs and diaphragm is modified by the
dress._ When the lungs are properly filled with air, the chest is
enlarged in every direction. If any article of apparel is worn so
tight as to prevent the full expansion of the chest and abdomen, the
lungs, in consequence, do not receive air sufficient to purify the
blood. The effect of firm, unyielding clothing, when worn tight, in
preventing a due supply of air to the lungs, may be shown by the
following illustration.

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525. Why is it more injurious to contract the lower part of the chest
than the upper? 526. How can the size of the chest be increased when
it is contracted? Give the observation. 527. How is the movement of
the ribs and diaphragm modified?

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_Illustration._ If the diameter of a circle is three feet, the
circumference will be nine feet. If the diameter is extended to four
feet, the circumference will be increased to twelve feet. Should a
tight band be thrown around a circle of nine feet, its diameter cannot
be increased, for the circumference cannot be enlarged.

528. Any inelastic band, drawn closely around the lower part of the
chest, or the abdomen, below the ribs, operates like the band in the
preceding illustration, in restricting the movement of the ribs. When
any article of dress encircles either the chest or abdomen, so as to
prevent an increase of its circumference, it has an injudicious
tendency, as it prevents the introduction of air in sufficient
quantities to purify the blood. The question is not, How much
restriction of the respiratory movements can be endured, an