Physical exercise should never be too violent or too prolonged. Severe
physical labor, and athletic sports, if indulged in to an extreme
degree, produce undue excitability of the heart, and sometimes cause it
to become enlarged. There is a form of heart disease induced by undue
exertion which may be called a wearing out or wasting away of that
organ. It is common in those persons whose occupations expose them to
excessive physical labor for too many hours together. This feebleness of
heart is felt but little by vigorous persons under forty years of age,
but in those who have passed this age it becomes manifest. However, when
any person so affected is attacked by any acute disease, the heart is
more liable to fail, and thus cause a fatal termination.

Aneurism of the aorta or the large arteries branching off from it, which
is a dilatation of the walls of these vessels, caused by the rupture of
one or two of their coats, is generally induced by excessive physical
strain, such as lifting heavy weights, or carrying weights up long
flights of stairs, violent horseback exercise, or hurrying to catch a
train or street car.

[Illustration: Fig. 104.]

AN ERECT CARRIAGE is not only essential to health, but adds grace and
beauty to every movement. Although man was made to stand erect, thus
indicating his superiority over all other animals, yet custom has done
much to curve that magnificent central column, upon the summit of which
rests the "grand dome of thought." Many young persons unconsciously
acquire the habit of throwing the shoulders forward. The spinal column
is weakened by this unnatural posture, its vertebræ become so sensitive
and distorted that they cannot easily support the weight of the body or