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.
It is calculated that one half of a child’s life is passed in sleep, and one quarter to one sixth of the adult existence; but for old age there is no essential period or limit. Old Parr slept almost constantly about the close of his life; while Dr. Gooch records the case of one whose period of sleep was only one quarter of an hour in the twenty-four. It is well to inure an infant to a _gradual_ diminution of its time of sleep, so that at ten years old its period should be about eight hours.