hemselves, must either become inactive and weak,
or work upon themselves and become diseased.

But let the situation of such persons be changed; bring them, for
instance, from the listlessness of retirement to the business and bustle
of a city; give them a variety of imperative employments, and place them
in society so as to supply to their cerebral organs that extent of
exercise which gives health and vivacity of action, and in a few months
the change produced will be surprising. Health, animation, and acuteness
will take the place of former insipidity and dullness. In such
instances, it would be absurd to suppose that it is the _mind itself_
which becomes heavy and feeble, and again revives into energy by these
changes in external circumstances. The effects arise entirely from
changes in the state of the _brain_, and the mental manifestations and
the bodily health have been improved solely by the improvement of its
condition.

The evils arising from excessive or ill-timed exercise of the brain, or
any of its parts, are numerous, and equally in accordance with the
ordinary laws of physiology. When we use the eye too long or in too
bright a light, it becomes bloodshot, and the increased action of its
vessels and nerves gives rise to a sensation of fatigue and pain
requiring us to desist. If we turn away and relieve the eye, the
irritation gradually subsides, and the healthy state returns; but if we
continue to look intently, or resume our employment before the eye has
regained its natural state by repose, the irritation at last becomes
permanent, and disease, followed by weakness of sight, or even
blindness, may ensue, as often happens to glass-blowers, smiths, and
others who are obliged to work in an intense light.

Precisely analogous phenomena occur when, from intense mental
excitement, the brain is kept long in a state of excessive activity. The
only difference is, that we can always see what happens in the eye, but
rarely what takes place in the brain. Occasionally, however, cases of
fracture of the skull occur, in which, part of the bone being removed,
we _can see_ the quickened circulation in the vessels of the brain as
easily as in those of the eye. Sir Astley Cooper had a young gentleman
brought to him who had lost a portion of his skull just above the
eyebrow. "On examining the head," says Sir Astley, "I distinctly saw
that the pulsation of the brain was regular and slow; but at this time
he was agitated by