‘BUT I pray you let none of your people stir me. I have an exposition of sleep come upon me,’— says Bottom in the play.
What is this ‘exposition of sleep’? A commonplace natural phenomenon which we accept as we do air and water,— a bafflingly mysterious condition in which we are compelled to pass a full third of our earthly life,— yet sleep, strangely enough, has been little studied or written about in all our compendiums of learning. In the thirty thousand pages of the encyclopædia, which may be looked upon as in a sense a microcosm, an epitome of all the accumulated knowledge of the world, there are but two pages devoted to sleep. This measures the general interest of humanity in the subject. One would think that psychologists would find a special field in this eclipse of the mind for eight hours every day, yet those huge tomes of Baldwin — the dictionary of psychology —devote half a page to sleep. The practical interest of medical men is in the disorders of sleep, but they treat of it in their medical books almost wholly from the standpoint of therapeutics, seldom or never from that of etiology. The chief literature of sleep seems to be found among the poets, religious devotees and mystics. I shall not quote Shakespeare, but only say that his innumerable references to sleep and dreams and the disorders of sleep prove him to have been an extraordinary observer. An incomparable clinician was spoiled in him when he became a poet. But I shall quote some sentences from the writings of Iamblichus, the mystic, because they do present a theory of sleep that is never mentioned in the works of medical practitioners or physiologists, though believed in by multitudes at the present time.
‘The soul has a two-fold life, a lower and a higher. In sleep the soul is freed from the constraint of the body and enters, as one emancipated, on its divine life of intelligence.’
‘The nobler part of the soul is thus united by abstraction to higher natures, and becomes a participant in the wisdom and foreknowledge of the gods.’
‘Numbers of sick, by sleeping in the temple of Æsculapius, have had their cure revealed to them in dreams vouchsafed by the god.’
‘The night-time of the body is the day-time of the soul.’
The argument is that since we have no knowledge of anything in existence but matter and spirit (force), and since neither of these rests or has need of rest, the only logical explanation of sleep is that it affords an opportunity for the re-creation of the soul by union during the unconscious period with the great reservoir of spirit outside of ourselves in the universe about us.
We must turn to the physiologists for records of the accumulated data on sleep. In these newest books on physiology we find what scientists have to offer at the present time in relation to the subject. The main object of this essay is to present their assumptions and facts with some critical comments.
Since most living things exhibit periods of rest alternating with activity, it is assumed that this is a law of living matter. But is it a true law? Matter itself is apparently never at rest, from the points of force which compose atoms, to the whirling planets and suns; and living matter is made up of the physical atoms that never rest. It is doubtless the phenomenon of sleep that has led the physiologists to the dictum that all living matter must rest.
Since in sleep so many of the most active functions keep on practically unchanged, such as the circulation, respiration, secretion, and digestion, the preformed hypothesis had to be supported by such statements as that the heart gets its rest between the beats. The physiologist says it is a mistake to suppose that the heart needs no rest; that it does need it and obtains it in the pause after the second beat; that while the sleep of the heart is frequent - ly broken, the heart actually does rest in point of time half of its life, whereas the brain rests only one third of its life, despite its longer periods of sleep! Thus the original hypothesis is even more than satisfied.
‘The most important fact of sleep is the partial or complete loss of consciousness, and this phenomenon may be referred directly to a lessened metabolic activity in the brain tissue, presumably in the cortex cerebri.’1
There are two pure assumptions in this paragraph: first, that consciousness is probably a function of the cortex of the brain; and second, that the phenomenon of sleep depends upon lessened metabolic activity in the brain cortex. I will not go over all the arguments against the first assumption, but merely point out that consciousness is certainly not present in all parts of the cortex at any one time; otherwise all of our memories stored up through the five senses represented in diverse parts of the brain would be in the stream of consciousness simultaneously. In individuals who have lost large portions of the cortex through accident or disease, even to the extent of a hemisphere, consciousness may be unimpaired. The arguments against the second assumption, that sleep depends upon lessened metabolic, activity in the brain cortex, are also partly valid against the first assumption. Several experimenters have carefully extirpated the cerebral hemispheres of birds and other animals. Schrader’s studies are the best with which I am acquainted. Decerebrated pigeons, after the first shock of the operation, wander about the room untiringly the greater part of the day, perfectly coördinated in flying or walking, with good space-perception, seeing, avoiding obstacles, awake all day and sleeping at night. Goltz’s dogs without cerebral hemispheres presented the same phenomena of waking and sleeping, very restless when awake, and curling up like normal dogs when asleep.
In two cases of children observed by the writer, where little was left in either of cortex or brain, owing to disease, waking and sleeping conditions were noted. The child without cerebrum described recently by Edinger and Fischer2 lived to be nearly four years old and lay ‘motionless in sleep unless awakened.’
Apparently, then, neither cortex nor cerebrum is essential to sleep.
It is clear that we must restrict our definitions here. We cannot look upon the states of being awake or being conscious and of being asleep or being unconscious as equivalent or synonymous.
Consciousness now is regarded as related only to memory-associations which function in the cerebrum.
Thus, a creature may be awake but not conscious, as in decerebrated animals. On the other hand it may be asleep yet conscious (or, if you prefer, sub-conscious), as in dreams and somnambulism. For that matter one might quote James, who says that the quarrel between Descartes and Locke as to whether the mind ever sleeps or not is still unsettled.
Granted that consciousness and being awake are different states, the underlying anatomical and physiological conditions should be different. That summation of activities which we call being awake, evidently not cerebral, but determined by function in the basal ganglia and nerves, may by irradiation into the cerebral hemispheres arouse consciousness also. At any rate we must hereafter distinguish between the concept of sleep and the concept of unconsciousness.
Another dictum of the physiologists, emphasized in their latest works, relates to the dangers of sleeplessness. ‘Sleep is more important to life than nutrition, and insomnia kills sooner than starvation,’ — to quote the exact words of one. This has been a kind of tradition in medicine, and is reiterated again and again in these books, without any real evidence, so far as I know, to support it. Taught to every medical man of older generations and to every medical fledgling of to-day, it finds its way to general public acceptance, begetting in the lay mind terrors of insanity and death which haunt every unfortunate victim of insomnia. The fear of not sleeping is one of the commonest causes of insomnia. Yet I do not know of any medical evidence anywhere of disastrous results from insomnia, and have myself never seen any harm arise from sleeplessness, apart from the harm done by the fears and worries associated with the condition.
So far as I can discover, the only basis for the assumption that sleeplessness is more dangerous to life than starvation, is the experiments made over twenty years ago by Marie de Manasseïne on ten young puppies that died after four or five days of provoked insomnia. I do not know what means she used to keep the puppies awake, or how far the methods employed were in themselves injurious, nor do I know of any repetitions of the experiments by others. But I should think that experiments on young puppies that tend to sleep a great deal more than grown dogs after their months of antenatal sleep, would be unsatisfactory criteria for conditions in adult human beings. Not only does our experience with patients with insomnia contradict these deductions, but we all know of longlived normal human beings whose hours of sleep are far below the average eight hours. Humboldt with his three hours a day, Edison with four, and John Hunter with three to four hours, are oft-quoted examples. Patrick and Gilbert kept three healthy young men awake for ninety hours, — nearly four days, — and at the end of this time a small extra amount of sleep beyond the normal caused complete restoration.
There seems to be such a thing as intensive sleeping, just as we have intensive gardening and farming. It has been shown experimentally that repose is deepest during the first hour or two, and that sleep becomes more shallow, more superficial, thereafter; and it is conceivable that by sleeping intensively for two or three hours we might secure as much actual rest as we now obtain by dissipating it over seven or eight hours. It would be interesting to know more than we do about comparative sleep in the various animals. The authorities state that birds, despite their enormous activities and more intense metabolism, sleep very little. The dog, which appears to sleep so much, is said to be the most wakable of animals. Man is regarded as the soundest sleeper and the least wakable among all creatures. It has been suggested that this sleep-relation between dog and man, companions from preglacial ages, which has been so conducive to their mutual preservation, is another example of that duplex kind of life that we call symbiosis.
Now to a consideration of the theories of sleep. The mystic theory of Iamblichus has already been referred to. Then there is the theory of the psychologist Claparède, that sleep is a phenomenon of nature in the shape of a reaction of defense against fatigue. The theories described in the physiologies will, however, interest us most.
One is that the accumulation of acid waste-products in the blood, especially from muscle-activity in the shape of sarcolactic acid, brings on a gradually increasing loss of irritability in the brain-cells, finally resulting in unconsciousness. Lactic acid or lactate of soda injected into the blood brings on fatigue and finally unconsciousness. This theory assumes an action like that of a narcotic. One would think that one fact of normal sleep would invalidate the theory. That is that a sleeper can be instantly awakened and made as alert as at any hour of the day, in a few seconds of time and at any period of his sleep, which should hardly be the case if his blood is so charged with acid waste-products as to produce unconsciousness.
Another explanation is that the intra-molecular oxygen of the brain-cells is used up more rapidly in the waking state than the blood can supply it, and during sleep the store of oxygen is replenished.
The retraction theory had more vogue a few years ago than it has now. It was thought that the dendritic processes of the brain-cells, by retracting, broke connections so that the cells could be no longer stimulated. This mechanical theory assumes, like the theories just mentioned, that the braincells are the scat of consciousness, and that, connections being broken, they cannot be stimulated. But at least the cells of all the senses in sleep are not beyond the reach of stimulation, as the sleeper can at any time be awakened by their stimulation. The sleepwalker sees, hears, feels, walks, thinks, and is yet asleep.
The anæmia theory is pretty well founded. By observation of the brains of sleeping animals and of man also, through openings in the skull made by design or accident, and by the use of the plethysmograph, an actual diminution of blood in the brain and an increase in the extremities has been noted during sleep by many observers. Anæmia may be considered as a concomitant of normal sleep, but whether as cause or effect no one has yet determined.
This fact leads to the differentiation of another form of sleep from the familiar normal form. This is hypnotic sleep, in which the face is red, the retina hyperæmic, the arms diminished in volume in the plethysmograph, — conditions opposite to those of normal sleep. A curious condition too in hypnotic sleep is that none of the experiences during the unconscious period are remembered on waking. Many observers have noted increased frequency of respiration and heart-action and dilated pupils in hypnotism, as well as active knee jerks, all of which symptoms are in contrast with those of normal sleep.
I will digress a little further here, simply to refer to another variety or other varieties of sleep, namely, those due to anæsthetics and drugs. While some of the milder drugs induce an artificial sleep that simulates closely natural sleep, there are differences in certain effects of narcotics when we bear in mind the main features of normal sleep, which are, in brief, moderate slowing up of the general physiological functions such as circulation, respiration, digestion, and secretion, anæmia of the brain, contraction of the pupils, rolling up of the eyeballs, and, what is not mentioned in the books though certainly a usual feature of normal sleep, a certain easy wakability. It is much more difficult to awaken a person from these artificial sleeps. Henbane sleep has its special features of hallucinations, dilated pupils, and rapid pulse; haschish sleep its mildly manic exaltation and rapid flow of dream-consciousness; alcohol, ether, chloroform, opium, and so forth, each some distinctive quality in the sleep induced by them. These drugs and anæsthetics are supposed to act chemically upon the ganglion cells by some sort of loose evanescent combination with the lipoids or fatty substances of the cells.
After this digression let us return to the question of the cause of sleep. The authorities seem to seek in vain some explanation of its periodicity. It has never seemed to me that sufficient attention has been given to physical causes outside of the organism, — for instance to the planetary rhythm of day and night, which ordinarily coincides with the periods of activity and inactivity, waking and sleeping. The biologists have been busy a long time with the tropisms which influence all forms of life, and among these heliotropism is probably of the greatest importance. Loeb, in his Dynamics of Living Matter, says that ‘heliotropism plays a wide rôle in determining the behavior of animals, and there are animals whose life becomes, at certain periods of their existence at least, a function of light.’ This is undoubtedly true of plants as well. The turning of plants toward the light is heliotropism.
When lower forms of animal life are experimented with in the laboratory, the tendency is to diminished activity or complete rest (sleep) in the dark and to increased activity in the light. This chemical effect upon protoplasm in general becomes rhythmic with the alternating day and night, and in the hundred million years that led to the evolution of man, the original terrestrial protoplasmic rhythm became an established function of animal life. With the development of a nervous system this regular periodicity of action and inaction was doubtless taken over to a considerable extent by the neurons, as has occurred with other functions of protoplasm. If this be so, may we not look upon sleep, which robs us of twenty-three years of activity in our short lives of three score and ten, as a bad habit, as an incident or rather accident of our existence on this particular planet? One wonders for instance as to the relations of sleep and activity on a planet like Jupiter, with a ten-hour day (five hours of light and five hours of night), with six years of polar day and six years of polar night, and seasons each three years long. What about sleep on Saturn, with its luminous rings and eight moons, and also five hours of day and five hours of night? How about sleep on planets lit by duplex or triplex suns, or in the solar system of Theta Orionis with seven suns?
That the theory presented cannot be far wrong is borne out by the facts in another type of sleep which I have not yet mentioned, but which is conceded to be due to a terrestrial rhythm, namely the winter sleep and summer sleep of certain animals, — hibernation and æstivation. This seasonal rhythm of inactivity which is exhibited by many different species of animals, such as bats, hedgehogs, dormice, marmots, reptiles and batrachians, brown and grizzly bears, and so on, is physiologically only an exaggeration of normal diurnal sleep. All the functions are slowed down. Respiration, alimentation, and excretion are actually suspended in complete hibernation; circulation continues, but with enormous retardation, and temperature adjustment where such exists at all is in abeyance. The seasonal sleep of plants need only be mentioned as clearly a seasonal or terrestrial rhythm. If physical conditions of the planet determine the function of sleep, then we ought to find in Arctic experience some corroboration of the assumption. The natives of the Arctic regions spend most of the Arctic night in sleep. Nansen, in his Farthest North, tells of his companion and himself sleeping twenty hours out of the twenty-four. They woke up simply for food and to make notes and registrations. Greely says he allowed his officers and men to sleep only fourteen to sixteen hours daily, keeping them employed the rest of the time. It is the oncoming dark, sweeping around the world with each diurnal revolution, that lays all creatures low, like the wind across a field of wheat.
The work of man is a function of light, and since the days of the cavedwellers, all men have turned in to sleep when the light was gone and there was no stimulus to the senses to overcome the terrestrial rhythm. It is a rhythm that seems to be easily broken and not as important to life as nutrition, for instance. So that, when the need arises, man or animal may reverse the rhythm, work at night and sleep by day, to satisfy hunger or ambition.
Will it always be necessary to sleep the twenty-three years of our short span? With the ferment of mind now going on all over the civilized world, with increasing mental and spiritual work to do, with the introduction of newer and better methods of artificial illumination, will not the tendency be for the hours of sleep to grow shorter and shorter, and the time for the use of the mind longer? Does not the growing tendency to insomnia point to a transition period from the old-time periods of mental torpor to the time when man shall be able to use his cerebral engine every hour of his brief life? Need we worry about insomnia? Perhaps in time, by practice of ascetic economy in sleeping and eating, every one will be able to unlock those stores of reserve power described by James in his Energies of Men.