ecause the excitability is sooner exhausted, and
therefore, sooner requires the means of renewing it; and on the
contrary, the more weakly the exciting powers have acted, the less
is a person inclined to sleep. Instances of the first are, excess of
exercise, strong liquors, or study, and of the latter, an under
proportion of these.

A person who has been daily accustomed to much exercise, whether
mental or corporeal, if he omit it, will find little or no
inclination to sleep; he may however be made to sleep by taking a
little diffusible stimulus; for instance, a little warm punch, or
opium: these act entirely by exhausting the excitability to that
degree which is compatible with sleep; and when their stimulant
effect is over, the person soon falls into that state.

But though the excitability may have been sufficiently exhausted,
and the action of the external powers considerably moderated, yet
there are some things within ourselves, which stimulate violently,
and prevent sleep; such as pain, thirst, and strong passions and
emotions of the mind. These all tend to drive away sleep, but it may
be induced, by withdrawing the mind from these impressions;
particularly from uneasy emotions, and employing it on something
which makes a less impression; sleep, in such cases, is frequently
brought on by listening to the humming of bees, [1] or the murmuring
of a rivulet; by employing the mind on subjects which do not require
much exertion, nor produce too much commotion; such as counting to a
thousand, or counting drops of water which fall slowly.

It sometimes happens, as has been well observed by Dr. Franklin,
that an uneasy heat of the skin, from a want of perspiration,
occasioned by the heat of the bed-cloaths, will prevent sleep; in
this case, he recommends a method, which I believe will often
succeed--namely, to get up and walk about the room till you are
considerably cooled; when you get into bed again, the heat of the
skin will be diminished, and perspiration become more free, and you
will probably sleep in a very few minutes. [2]

By induction we have discovered two of the principal laws by which
living bodies are governed; the first is, that when the ordinary
powers which support life have been suspended, or their action
lessened for a time, the excitability, or vital principle
accumulates, or becomes more fit to receive their actions; and
secondly, when these powers have been acted upon violently, or for a
consid