should be purified, needs the requisite amount of pure blood to give
them vigor and health. When the blood is not of this character, the
lungs themselves lose their tone, and, even if permitted to expand
freely, have not power fully to change the impure quality of this
circulating fluid.

458. The health and beauty of the skin require that the blood should
be well purified; but, if the arteries of the skin receive vitiated
blood, pimples and blotches appear, and the individual suffers from
"humors." Drinks, made of various kinds of herbs, as well as pills
and powders, are taken for this affection. These will never have the
desired effect, while the causes of impure blood exist.

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455-462. _Give the hygiene of nutrition._ 455. What is the effect of
impure blood upon the bones? On the muscles? 456. On the digestive
organs? 457. On the lungs? 458. What is the effect if the vessels of
the skin are supplied with vitiated blood?

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459. If the nutrient arteries convey impure material to the brain, the
nervous and bilious headache, confusion of ideas, loss of memory,
impaired intellect, dimness of vision, and dulness of hearing, will be
experienced; and in process of time, the brain becomes disorganized,
and the brittle thread of life is broken.

_Observations._ 1st. An exertion of any organ beyond its powers,
induces weakness that will disturb the nutrition of the part that is
called into action; and it recovers its energy more slowly in
proportion to the excess of the exertion. The function of the organ
may be totally and permanently destroyed, if the exertion is extremely
violent. We sometimes see palsy produced in a muscle simply by the
effort to raise too great a weight. The sight is impaired, and total
blindness may be produced, by exposure to light too strong or too
constant. The mind may be deranged, or idiocy may follow the excess of
study or the over-tasking of the brain.

2d. When the function of an organ is permanently impaired or destroyed
by over-exertion, the nutrition of the part is rendered insufficient,
or is entirely arrested; and then the absorbents remove it wholly or
partially, as they do every thing that is no longer useful. Thus, in
palsied patients, a few years after the attack, we often find scarce
any trace of the palsied muscles remaining; they are reduced almost to
simple cellular tissue. The condition of the calf of the leg, in a
person