The mind, then, as it is manifested to us (for deeply important is it that we confound not the perfect and pure, because unembodied essence of the soul, with its combined existence in the brain—that union from which a thought is born), the mind cannot exert itself beyond a certain period without a sensation of fatigue in the brain, as palpable as the exhaustion from excessive muscular exertion. And this depends on a natural law, that organs after acting a certain given period, flag and lose their energy. Thus the first harbinger of sleep is the closing of the lids from languor, and relaxation of the muscles. Muscular fibre will, however, regain its expenditure by simple rest, requiring a certain period for this re-accumulation, like the charging of an electrical jar. Sleep, however, is not always a sequence of exhausted irritability of muscle; we may be too tired to sleep; and thought and memory also will keep the mind awake, and prevent nervous energy from renewing corporeal vigour.
The excitement of thought beyond certain limits is both painful and destructive, evincing its effects by various grades of mental disorder, from simple headache to confirmed mania. Our first ray of hope, in fever, is often the coming on of a quiet sleep, and in the sad cases of delirium tremens we must either sleep or die; the effort of philosophical determination to overcome the depression only adding to its intensity, as in the case of a person worn out by labour, in attempting to labour on. This conflict cannot be more pertinently exemplified than by some passages in the life of Collins, by one who knew him well:—
“He languished some years under that depression of mind which unchains the faculties without destroying them, and leaves reason the knowledge of right without the power of pursuing it. These clouds which he perceived gathering on his intellects, he endeavoured to disperse by travel, and passed into France; but found himself constrained to yield to his malady, and returned. His disorder was no alienation of mind, but general laxity and feebleness, a deficiency rather of his vital than intellectual powers. What he spoke wanted neither judgment nor spirit, but a few minutes exhausted him, so that he was forced to rest upon the couch, till a short cessation restored his powers, and he was again able to talk with his former vigour.”
I believe that sensibility and fatigue of mind, by inducing sleeplessness, may often be the source even of mania.
The sleep of animals is usually light, especially that of birds, and they are easily startled when at roost. The cackling of the geese on their awaking, you know, saved the Roman capitol. Yet sleep is altogether very nearly balanced with waking. Some animals sleep often, like the cats, but they are long awake, and prowling in the night. The python and the boa are also long awake, and then sleep for many days during the process of digestion. Indeed, all the feræ fall into sound sleep after feeding; while the ruminants scarcely sleep at all; nor do they crouch like the feræ, with the head between the legs: but then their whole life is one scene of quiet; rumination is a mindless reverie. The West Indian slaves and the Hottentots, or woolly bipeds, resemble the brute animal in this, that they fall asleep as soon as their labour is concluded.
That activity of mind in excess may induce even mania, I may offer two impressive, although negative, proofs, from the records of Dr. Rush.—“In despotic countries, and where the public passions are torpid, and where life and property are secured only by the extinction of domestic affections, madness is a rare disease. Dr. Scott informed me that he heard of but one single instance of madness in China.”
“After much inquiry, I have not been able to find a single instance of fatuity among the Indians, and but few instances of melancholy and madness.”
I may add, that Baron Humboldt assures us of this immunity among the wild Indians of South America.
Ida. And may not this melancholy effect be averted by caution and rule? We have a saying in Herefordshire, that “Six hours are enough for a man, seven for a woman, and eight for a fool.”
Ev. There cannot be a fixed rule on that point, except the prevailing law of nature,—the feeling of necessity; but this may often lead astray.