Science from an Easy Chair

by Sir E. Ray Lankester

It is curious how incomplete at present is the physiologist’s knowledge of both the actual condition of the brain in sleep and of the immediate causes which produce that condition. It is probably true (though it is disputed) that the brain becomes pale during sleep, owing to a contraction of the blood vessels, and that the inactivity of the brain arises from this condition. But it is not obvious what determines the contraction of these vessels at the definitely recurring period of sleep. It is probable that the nervous tissue of the brain is, as are the muscles of the body, poisoned or choked (as it were) by the chemical products of the day’s activity, and so readily cease to be active until the injurious products have had time to be carried away by the blood stream. Muscular substance undoubtedly is affected in this way, and that great muscle the heart, though never resting for a lengthened period, rests after each pulse or contraction, and recovers itself in the brief interval.

It is also probable that the exhaustion by the day’s activity of the oxygen stored up in the various tissues of the body produces a condition of quiescence whilst the store is replenished. Stimulation of the nerves through the sense-organs of sight, hearing, and touch will prevent or retard this natural quiescence, and the cessation of that stimulation is favoured first of all by the darkness of night and by the closing of the eyelid, as well as by the removal of clothes which more or less irritate the skin; also by the would-be sleeper taking up a position of perfect rest, and by the exercise of his will, withdrawing his brain as much as possible from all external influences. The would-be sleeper also controls, when possible, that internal stimulation of the brain which we call attention. It is the failure (owing to unhealthy conditions) to control the latter which leads to the most serious kind of sleeplessness, when the brain gets for hours out of restraint and works incessantly like an independent existence. The disturbance of the nervous system set up by irritation of the digestive organs, whether accompanied by pain or not, is an independent cause of sleeplessness which often co-operates with the first, and is (through the mechanism of the nerves) often set going (though it may arise independently) by an unhealthy excess in the excitement of the brain’s activity. There is no panacea for sleeplessness; the only thing to do is to consult a first-rate physician, and strictly follow his advice.

There are many irregularities and abnormal manifestations of sleep. There is the sleep which is induced by drugs such as opium, chloral, and alcohol, and that induced by chloroform, ether, and nitric gas. There is the heavy sleep accompanied by stertorous breathing, and there is the unconscious condition called “coma.” Then there is the prolonged sleeping called “trance,” of which that of the Sleeping Beauty, only to be broken by a kiss, is an example. It is not possible, in the present state of knowledge, to give an adequate account and explanation of the condition of the brain in these different forms of sleep, nor of the causes which induce that condition. One of the most interesting forms of sleep is the condition called “somnambulism,” or sleep-walking, in which part only of the brain is asleep, and other parts connected with various degrees of mental activity are in waking order. Sleep-walking is a condition which occurs spontaneously. On the other hand, “hypnotism” is the name for a peculiar kind of sleep produced intentionally by an operator on a patient by certain treatment and direction. In one of the stages of artificially induced hypnotic or “mesmeric” sleep—called the somnambulic stage—only so much of the brain is asleep as is concerned with conscious memory. The brain receives stimulation through the sense-organs, and the patient has the eyes open and appears to be awake. In this state he is peculiarly open to suggestion by words, which can be made to set up the most extraordinary illusions and consequent behaviour. On “waking” the patient has no memory of what has occurred, though a suggestion received in the somnambulic stage may persist in the unconscious memory, and cause conduct on the part of the patient (many hours after the brief hypnotic sleep has passed) which is entirely inexplicable by the patient himself or by those who are not aware of the fact that he had received a “suggestion” or “direction” when in the hypnotised state. The senses of smell, hearing, and touch are often abnormally acute in a hypnotised patient, but there is no evidence to show that the brain of such a person can be influenced or “communicated with” excepting through the ordinary channels of the sense-organs. “Day-dreaming” and “reverie” are conditions resembling the hypnotic sleep. The brain of each of us is constantly doing much of its work in a state of partial hypnotism, and the term “unconscious cerebration” has been used to describe it. A most interesting and difficult chapter of the study of mental disease belongs here.

The prolonged sleep of some animals in the winter, called “hibernation,” seems to be closely similar to ordinary sleep, but is set up by the depressing action of continuous cold instead of by the daily recurring quiescence of night and by the exhaustion due to the day’s activity. Many animals—such as the marmot and dormouse, the frog and the snail—exhibit this winter sleep. It has been found by experiment that even in midsummer the dormouse can be made to “hibernate,” by exposing it artificially to a low temperature, and hibernating animals can be roused from their long sleep by bringing them into warmth. During the winter sleep hibernating animals take no food, the pulse is slowed down, and the body temperature falls. The scattered fat of the body, and fatty matter and other material stored in special structures called “hibernating glands,” are oxidised and slowly consumed during this period, which may last for three or even four months. The animal on waking is often in a very emaciated condition.

It is undoubtedly the case that the human natives of high latitudes (such as the Norwegians), where there is no night in full summer, and where there is prolonged darkness in winter, have acquired the habit of keeping awake for many days in succession in summer, whilst making up for the loss of sleep by excessive indulgence in it during the winter. It is by no means clear how far man is capable of resisting the demand for recurrent daily sleep without injury to health. Undoubtedly many men are compelled by their avocations to sleep by day and wake by night. The length and duration of “spells of sleep” and the power to sleep little or not at all at one season, and almost uninterruptedly at another, without injury to health, are matters of habit, occupation, and circumstance. We have no ground for saying that every man “ought” to sleep eight hours or more per diem, or, on the contrary, for insisting that he should only sleep five or less. All depends on what he is doing when he is awake, and what other people are doing (so as to disturb him) when he is asleep; and we do not even know whether ten or twelve hours’ sleep would injure a man, were he able to take it, nor can we suggest how it would injure him supposing it did not interfere with his feeding and exercise.

As to quantities of sleep, there is the curious fact that the amount habitually taken in the civilised communities of this part of the world differs at different ages. Babies sleep a good part of the twenty-four hours, and probably schoolboys and schoolgirls (under our present conditions of life and work) ought to be given ten hours or more. Whilst adult men sleep from six to eight or nine hours, it is a curious fact that old people—not very old people, but those of sixty-five or thereabouts—often find themselves unable to sleep more than four hours at night, and take an hour or two in the daytime to make up for the deficiency. I remember hearing Mr. Darwin state this as to himself to his physician, Sir Andrew Clarke, who said it was very usual at his age, and difficult to explain, since at a greater age, when a man is called “very old,” a more or less continuous somnolent condition sets in. The father of a great judicial dignitary of these days, himself a barrister in large practice, when he was sixty years old would snatch fifteen or twenty minutes’ sleep at any and every opportunity throughout the day, even at the midday meal sometimes, so as altogether to disconcert those who were with him, and he told me that he never slept more than four hours at night, but got up and commenced work at four in the morning. The cessation in early old age of the desire for more than half the amount of sleep taken by younger men suggests that the regulating cause of the number of hours which are needed for sleep may be simply and directly the actual amount of work done by body and mind. This imperceptibly becomes less as men grow older, and so less recuperative sleep is necessary, though what work they do may be more effective and better adjusted to its purpose when they have arrived at the condition which is called “old age.”

We have seen that sleep in its widest sense comprises the simple condition of quiescence brought about in even the minutest living things by the recurring night, as well as the strangely elaborated varieties of cessation of activity in the whole or parts of the brain of man and of his body. Some of these cessations of activity naturally and spontaneously occur in unsophisticated mankind, when darkness falls on the earth at each succeeding evening. And it is hardly possible to doubt that a tendency to periodic sleep has become fixed in the substance of living things by the alternation of night and day—as well as in some cases by the change of the seasons.

I must conclude these notes about sleep by relating a very curious case of sleep, resembling the winter-sleep of higher animals, on the part of a snail. This was the case of a desert snail from Egypt, which was withdrawn into its shell, the mouth of the shell being closed with a glistening film secreted by the snail, as is usual with snails in this country in winter when they sleep. The desert snail in question was affixed to a tablet of wood in a glass case in the natural history department of the British Museum on March 25, 1846. On March 7, 1850, that is four years afterwards, it was noticed by a visitor looking at the case that the snail had emerged from his shell and discoloured the paper around, but had again retired. So the officials unlocked the case and removed the snail from the tablet and placed him in tepid water. He rapidly and completely recovered, crawled about as a wide-awake snail should, and sat for his portrait. This may be regarded as an instance of unusually long sleep, natural to this species of snail, and related probably to the frequently prolonged dryness of the snail’s surroundings.

We are led by such a case as this on to what are called examples of “suspended animation.” Wheel-animalcules, and some other minute creatures which are found living in tiny pools of water, on the bark of trees, and in the hollows of leaves, naturally dry up when the water evaporates. You may dry them yourself in a watchglass; they appear as nothing more than shapeless dust particles mixed with the dried mud of a drop of dirty water. They may be kept in this state for months—even years. I do not know that any limit has been ascertained. But when you add pure rain-water to the dust in the watchglass, it softens, and in less than an hour the little wheel-animalcules have softened too, and expanded into life, swimming about whilst the delicate spikes on their “wheels” vibrate regularly as though they had never ceased to do so, and as though the animalcules had not for years been dried-up little mummies.