r intervals of rest, the vascular
excitement of the brain has not time to subside. A restless
irritability of temper and disposition comes on, attended with
sleeplessness and anxiety, for which no external cause can be
assigned. The symptoms gradually become aggravated, the digestive
functions give way, nutrition is impaired, and a sense of wretchedness
is constantly present, which often leads to attempts at suicide."

_Observations._ 1st. Moderation in mental exertion is more necessary
in old age than in early or mature years. In youth and manhood, the
exhaustion of the brain from over-excitement may be repaired, but no
such result follows over-exertion in the decline of life. "What is
lost then, is lost forever." At that period, the brain becomes
excited, and is soon exhausted when forced to protracted and vigorous
thought. Sir Walter Scott and President Harrison afford sad examples
of premature death from overtasked brains at an advanced period of
their lives.

2d. If the mind is incessantly engaged in the contemplation of the
same object, there is danger from over-exertion of the brain at any
period of life, but more particularly in old age. The more limited the
sphere of mental action, the greater the danger of the brain being
over-exercised. Hence the frequency of nervous diseases in poets,
mathematicians, and musicians.

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820. What often manifests itself from the want of proper intervals of
rest? Why is moderation in mental action necessary in old age? What is
the effect if the mind is incessantly engaged in the contemplation of
the same object?

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CHAPTER XL.

HYGIENE OF THE NERVOUS SYSTEM, CONTINUED.

821. Having pointed out the evils arising both from inadequate and
from excessive mental exertion, it remains to direct the attention to
some of the rules which should guide us in the exercise of the brain.

822. _We should not enter upon continued mental exertion, or arouse
deep feeling, immediately before or after a full meal._ Such is the
connection between the mind and body, that even in a perfectly healthy
person, unwelcome news, sudden anxiety, or mental excitement,
occurring soon after eating, will impede digestion, and cause the
stomach to loathe the masticated food.

823. The worst forms of indigestion and nervous depression are those
which arise from excessive mental application, or depressed feeling,
conjoined with unrestrained i