A Lecture on the Preservation of Health | Page 6

the method which nature has provided to repair the exhausted constitution, and restore the vital energy; without its refreshing aid, our worn-out habits would scarcely be able to drag on a few days, or at most a few weeks, before the vital spring was quite run down; how properly therefore has the great poet of nature called sleep the chief nourisher in life's feast.--
'Sleep, that knits up the ravell'd sleeve of care, 'the death of each day's life, sore labour's bath, 'balm of hurt minds, great Nature's second course, 'chief nourisher in life's feast.'
From the internal sensations often excited, it is natural to conclude that the nerves of sense are not torpid during sleep; but that they are only precluded from the perception of external objects, by the external organs being rendered unfit to transmit to them the impulses of bodies, during the suspension of the power of volition; thus, the eye-lids are closed in sleep, to prevent the impulse of the light from acting on the optic nerve; and it is very probable that the drum of the ear is not stretched; it is likewise probable that something similar happens to the external apparatus of all our organs of sense, which may make them unfit for their office of perception during sleep.
The more violently the exciting powers have acted, the sooner is sleep brought on; because 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 considerable time, the excitability is exhausted, or becomes less fit to receive their actions. There are therefore three states in which living bodies exist.--
First, a state of accumulated excitability.
Second, a state of exhausted excitability.
Third, when it is in such a state as to produce the strongest and most healthy actions, when acted upon by the external powers.
From what I have said, it must appear, that life is a forced state, depending on the action of external powers upon the excitability; and that, by their continued action, if they are properly regulated, the excitability will be gradually and insensibly exhausted; and life will be resigned into the hands of him who gave it, without a struggle, and without a groan.
We see then, that nature operates in supporting the living part of the creation, by laws as simple and beautiful as those by which the inanimate world is governed. In the latter we see the order and harmony which is observed by the planets, and their