ctical observation when intending to ride in a cold day? 373.
Why does exercise promote health? What are good stimulants for
sluggish circulation in the indolent?

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_Illustration._ The coach-driver and teamster throw their arms around
their bodies to warm them when cold. The muscles that are called into
action in swinging the arms, force a greater quantity of blood into
the chilled parts, and consequently, more heat is produced.

374. When a number of muscles are called into energetic action, a
greater quantity of blood will be propelled to the lungs and heart in
a given time, than when the muscles are in a state of comparative
inaction. It is no uncommon occurrence, that before there is a proper
expansion of the respiratory organs to correspond with the frequency
and energy of the movements of the muscles, there is an accumulation
of blood in the lungs, attended by a painful sensation of fulness and
oppression in the chest, with violent and irregular action of the
heart. This condition of the organs of the chest, called _congestion_,
may be followed by cough, inflammation of the lungs, asthma, and a
structural disease of the heart.

375. To avoid these sensations and results, when we feel necessitated
to walk or run a considerable distance in a short time, commence the
movements in a moderate manner increasing the speed as the respiratory
movements become more frequent and their expansion more extensive, so
that a sufficient amount of air may be received into the lungs to
purify the increased quantity of blood forced into them. The same
principles should be observed when commencing labor, and in driving
horses and other animals.

_Observation._ When a large number of muscles are called into action
after repose, as when we rise from a recumbent or sitting posture,
the blood is impelled to the heart with a very strong impetus. If that
organ should be diseased, it may arrive there in larger quantities
than can be disposed of, and death may be the result. Hence the
necessity of avoiding all sudden and violent movements, on the part of
those who have either a functional or structural disease of the
heart.

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Mention the illustration. 374. What is the effect when a number of
muscles are called into energetic action? What effect has this
accumulation of blood in the lungs? 375. How can such disagreeable
sensations be avoided? Mention a practical observation.

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