Why Do We Sleep Early Theories

Information on the early theories to describe why we sleep. Early Thoughts and Sleeping Theories.

Why Do We Sleep?

Sleep has long been regarded as one of the most baffling of the many knotty problems that science has been called upon to solve.  The scientist, of course, in common with the layman, has always recognized and appre ciated its essentially beneficent character, so happily expressed in the words of the immortal Sancho Panza, "Blessings on him who invented sleep !  The mantle that covers all human thoughts ; the food that appeases hunger; the drink that quenches thirst ; the fire that warms ; the cold that moderates heat; and, lastly, the general coin that purchases all things; the balance and weight that make the shepherd equal to the king and the simple to the wise."  But, while recognizing the kindly and restorative role played by sleep in the scheme of animate existence, the scientist almost as much as the layman, until lately at all events, has been in the dark with respect to its nature and mechan ism.  Even the conditions that determine its production have been but vaguely and partially understood, with the result, as every doctor knows, that sleeplessness still constitutes a great stumbling-block in medical practice.

Early Thoughts and Sleeping Theories

Science, in fact, has quite generally been content with describing the phenomena of sleep, as one may readily ascertain by examining the now voluminous literature on the subject.  Even when explanations have been attempted, they have usually resolved themselves into descriptions of states that accompany sleep rather than demonstrations of the factors that cause it.  Thus, the investigations carried on by Durham, Hammond, Howell, Mosso, in the early 1990s and others, alleged to prove that cerebral anaemia, or deficiency of blood in the brain, was the great cause of sleep, really proved nothing more than that certain circulatory changes may take place during sleep. 

Or if the theories advanced are truly explanatory as is the case with the chemical and pathological theories which attribute sleep to a poisoning of the system by toxic substances that accumulate in the blood they suffer from the serious objection that sleep often occurs under conditions in which the factors stressed cannot reason ably be assumed to have a part.  Small wonder, therefore, that many writers have ventured on nothing more than an elaboration of the obvious, like Marie de Mana cei'ne, the Russian authority, whose the ory of sleep is summed up in the distinctly non-explanatory phrase: "Sleep is the resting-time of consciousness."


Recently, however, a decided advance has unquestionably been made in our understanding of this fundamental fact in the life both of man and of the lower animals.  It is an advance due in part to the progress of biological and physiological research, but even more due to the extraordinary development of that youngest of the sciences, psychology, which in the past few decades has made so many important contributions to the fund of human knowledge.  Not a few of these, it is worth noting, have wholly or partly originated from the increased atten tion that the modern psychologist has paid to the realm of sleep.

Our present appreciation of the marvelous extent to which one's intellect, one's character, and even one's health are affected by "subconscious" emotions and memories ; our appreciation of the formative influence of the most trivial details in one's environment, and of the possibility of adjusting the environment in such a way as to make unfailingly for physical, mental, and moral upbuilding; our fuller comprehension of the principles that underlie and give valid ity to scientific "psychotherapy," or heal ing by suggestion, of which the medical fraternity is beginning to make systematic and effective use all this has been largely due to recent psychological study of the phenomena that occur either in ordinary, "natural" sleep, or in those allied sleeping states induced by drugs or hypnotic procedures. 

Naturally enough, from studying the phenomena of sleep, the investigators have been led to study sleep itself, with results which, if they do not altogether dispel its mystery, have at least afforded clearer insight than ever before into its nature, significance, and causal conditions matters of considerable practical as well as theoretical importance, particularly in this age of stress and strain with its imperative demand for the most efficient utilization of human resources, and its
equally inexorable tax on the human organism.

The great difficulty has always been to formulate an explanatory hypothesis which excluding the various types of pseudo sleep that manifestly result from abnormal conditions would adequately account for the many strange anomalies presented by sleep.  Any hypothesis to be satisfactory has to explain, for example, why sleep pre dominates over waking life in the case of the very young, why it has a smaller share in middle life, and why it tends in old age to become dominant once more, or, with no ill effects, to be even less in evidence than in the years of greatest virility.  Any sound theory has to explain the seeming paradox between the periodical onset of sleep after exertion and its frequent with drawal when the exertion has been at all excessive.  It has also to explain the well established fact that the amount of sleep required is by no means proportionate to the amount of intellectual or muscular effort previously expended, so that we often find men of intense mental or physical activity for instance, Napoleon, Frederick the Great, Schiller, Humboldt, Mirabeau, the English surgeon John Hun ter, and our own Thomas A. Edison getting along very well with four or five hours' sleep a night, as compared with the eight or nine hours of less energetic individuals. 

Then, too, there is the familiar and most embarrassing occurrence of sleep in public places the church, the theater, the opera-house on the part of persons suffering neither from fatigue nor from any interruption to their regular night's rest; and, opposed to this, the chronic wakefulness of the insomniac in the dark and quiet of his home, utterly worn out yet unable to sleep.

These are only a few of the puzzling phases that have to be accounted for, and that have combined to baffle until now all
efforts at a consistent and comprehensive explanation of sleep.  But with the development of modern psychology, and, above all, with the increased appreciation it has enforced of the preponderating in fluence of the psychical factor in all aspects of human existence, real progress towards such an explanation has, as was said, been made.  It is now known that sleep, contrary to the belief formerly so widely entertained, is no mere passive, negative state, the product of toxic or other harmful elements, but is an active, positive function, a protective instinct of gradual evolution and dependent for its operation partly on the will and partly on the environment.  It is the result of a certain reaction between the central nervous system and the stimuli impinging on it, its object being not so much the recuperation of the organism from the effects of the activities of the in tervening period of waking life, as to save the organism from the destructive consequences of uninterrupted activity.  Or as one investigator, Doctor Boris Sidis, the well-known American medical psycholo gist, affirms :

"Sleep is not a disease, not a pathological process due to the accumulation of toxic products in the brain or in the system gener ally.  Sleep is not an abnormal condition; it is a normal state.  Like the waking states, sleep states are part and parcel of the life-existence of the individual.  Wak ing and sleeping are intimately related they are two different manifestations of one and the same life-process one is as nor mal and healthy as the other.  One cannot help agreeing with Claperede's biological view that sleep is a positive function of the organism, that sleep belongs to the funda mental instincts.  As Claperede forcibly puts it:

"' Sleep is a protective function, an in stinct having for end, in striking the animal with inertia, to prevent it from arriving at
a condition of exhaustion.  We sleep, not because we are poisoned or exhausted, but so that we shall be neither poisoned nor exhausted.'"

In order for sleep to function, however, sundry requirements must be complied with, and it is not the least important outcome of the recent researches that, by the two fold method of experiment and observation, they have pretty definitely established just what these requirements are.  Especially noteworthy in this connection is the experi mental work carried on by Doctor Sidis, and leading him to the conclusion just quoted.

His study of sleep was a direct out growth of his labors in medical psychology, since it had as its starting-point the dis covery that an ingenious technique he had devised for putting nervous patients into a "dissociated" state as a preliminary to psychotherapeutic treatment, had the further effect, when prolonged, of causing them to fall asleep.  This technique, which he calls hypnoidization, and which is some thing quite distinct from hypnotism, may best be described in his own words :

"The patient is asked to close his eyes and keep as quiet as possible, without, how ever, making any special effort to put him self in such a state.  He is then asked to attend to some stimulus, such as reading or singing, or to the monotonous beats of a metronome.  Or he may be asked to fixate his attention on some object, while at the same time listening to the beats of the metronome.  His eyes are then closed, he is to keep very quiet, while the metro nome or some other monotonous stimulus is continued.  After some time, when his respiration and pulse are found somewhat lowered, he is asked to concentrate his attention on a subject closely relating to the symptoms of his malady.  In other words, the patient is in a hypnoidal state, favorable to the emergence of subconscious memories." 

Now, observing that the state thus in duced was not only exceedingly unstable and transitory, but tended to result in a more or less profound sleep, Doctor Sidis conjectured that it might be identical with the "borderland" state through which it has long been known that people always pass when falling asleep.  If this were the case, it could logically be inferred that the conditions essential to the causation of the hypnoidal state as outlined in the pas sage just quoted that is to say, fixation followed by relaxation of the attention, limitation of voluntary movement, limita tion of consciousness, and monotonous stimulation were precisely the conditions operant in the production of sleep.  His scientific curiosity and interest aroused, Doctor Sidis now began, in his own laboratory and in the laboratory of the Harvard Medical School, a long series of experiments on different animals frogs, guineapigs, cats, and dogs and on children of a few days to several years old, applying to each as far as was possible the conditions he had found favorable for the bringing about of the hypnoidal state in adult men and women.

In every case he discovered that when he limited the sensory impressions by closing the eyes, inhibiting voluntary movements, and applying a monotonous stimulus such as a gentle stroking of the subject's body there resulted a state closely an alogous to the hypnoidal condition, and followed by a state of sleep.  A quotation from Doctor Sidis's detailed account of his experiments with some puppies will give an idea of the methods employed by him and the results obtained in the case of animals :

"Two puppies of about two months old ; very lively, excitable, and barking violently.  After some struggle each one was wrapped in a cloth so that even the fore paws did not protude.  At first they were greatly excited by the proceeding, and pro claimed their indignation by loud yelping.  I took my turn with each one separately.  The puppy was held down firmly and given no chance to move its body or to struggle with its paws.  I also closed the puppy's eyes with my fingers.  The puppy struggled and wriggled under my hand, but I held on tightly.

"Gradually the puppy ceased its struggles and became very quiet.  Respiration became slow and regular.  I gradually released my grip on the dog, when I found that its eyes were firmly closed.  The puppy was fast asleep.

"The same performance was carried out in the case of the other puppy.  .  After five minutes, during which time I held the dog tightly and kept all the extremities in close grip, the puppy passed into a quiet state and fell asleep as the first one did.  Respiration was slow and uniform.  Both puppies slept peacefully.  There was no response to external stimuli.  Limbs were in a state of relaxation.  In spite of the noise in the neighboring room the puppies kept on sleeping.  After twenty minutes one of the puppies woke up, made some show of struggle, but the eyes remained shut and he fell asleep again.  I tried to loosen the cloth in which the puppies lay enwrapped.  My manipulations did not disturb their sleep.  .  .  .

Three new puppies were very tractable.  They fell asleep with the greatest ease imaginable.  The puppies were about two and a half weeks old, were quite gentle and showed almost no resistance.  The same phenomena were present as in the other dogs; they went to sleep under the same conditions, their paws for a brief period of a few seconds were extended and slightly resistive.  Limbs retained the position given to them.  The eyelids were firmly shut and there was resistance to attempts to force them open.  When forced open the eyeballs were rolled up, and the eyelids closed as soon as they were let go.  The puppies seemed to possess the power of sleeping indefinitely.  Now and then suck ing and snapping movements were observed.  They slept for more than an hour, and would have gone on sleeping had they not been rudely shaken out of their peaceful repose.  "The experiments were repeated with the same results.  As the puppies got older the manifestations of the transient, inter mediate state became more pronounced catalepsy was more evident on falling asleep.  The same held true in the case of waking up.  There was a slight stiffness and catalepsy of the paws for a brief period when the puppy emerged from sleep.  On falling asleep the puppies did not tumble at once into that state, they opened and shut their eyes, when my fingers were released from pressing their eyelids.  They kept on blinking the eyes.  The lids came nearer together and finally closed.  The same process of blinking was observed on waking; they seemed to wake and fall asleep again, thus being really in the intermediary, hypnoidal state, hovering be tween waking state and sleep, both on going to and coming out of sleep.  .  .  .

"I may add that I also carried out similar experiments on a dog of six months old.  As the dog was used to me I had no difficulty in inducing sleep.  I made him keep quiet and then closed his eyes firmly.  He went to sleep.  When I tried to open his eyes they resisted.  When I opened them I found the eyeballs rolled up, nictitating membrane over part of sclera, and pupils were contracted.  There were present the same manifestations of hyp noidal states, the slight catalepsy on falling asleep and a similar, though somewhat slighter, catalepsy on awaking.  There was little difficulty in putting the dog to sleep.  With the repetition of the experiments it was easier to put him into hypnoidal states and sleep under the conditions of monotony, limitation of voluntary move ments, and inhibition.  The dog was very lively otherwise, but when put under the conditions of monotony and limitation of voluntary activity, he sank into a passive state and then into a state of sleep." 

In the case of the children with whom Doctor Sidis experimented, he discovered that, as compared with adults, they reacted far more readily to his methods for bringing on sleep, and this he saw reason to attrib ute to the inferiority of their mental de velopment.

"This ease of induction of sleep," is the way he explains it, "is furthered by the comparatively small amount of variability of conscious activity present in the child the variability of mental content being an important factor in keeping up the fresh ness, continuity, and qualitative intensity of consciousness.  Now, as the child de pends entirely for the variability of its consciousness on muscular activity and external impressions, we can well realize that when those sources become limited and monotonous the child falls under the influence of all the important conditions requisite for the induction of sleep.  The child, in short, has no inner wealth of men tal life to fall upon ; it has little if any inner resources ; that is why it falls an easy prey to sleep when the external resources lose their variability, become uniform and monotonous."  1

The longer he experimented, the stronger became Doctor Sidis's conviction that in monotony we have the central fact in the causation of sleep.  When we sleep, we do so because our consciousness is no longer stimulated by a sufficient variety of sensations to keep us in a waking state.  The variety, for that matter, may actually be present.  But sensation-strain has fatigued our attention ; for us, variety itself has temporarily become monotonous, and we fall asleep.  Or if, when our customary sleeping-time arrives, we nevertheless find ourselves in an alert state, but feel that we ought to go to sleep, we proceed to put ourselves to sleep by a process that instinc tively duplicates the conditions of exper imental hypnoidization.  That is, we undress and recline in bed, thereby markedly limiting our voluntary movements ; we ex tinguish the light and close our eyes, limiting the sensorial field and producing the monot onous stimulation of darkness ; we relax our attention, and presently we fall asleep.

Much the same view, which obviously makes sleep chiefly dependent on the character of the stimuli received by the consciousness, is maintained by other re cent experimental students of the subject, especially the European scientists Verworn and Huebel.  On the other hand, it has been sharply criticised by at least one investigator, another medical psychologist, Doctor I. H. Coriat, whose own experi ments 1 have led him to the conclusion that the main factor in the induction of sleep is the influence, not of monotonous stimuli, but of muscular relaxation.  "When we relax, the motor phenomena become less ened, and this tends to produce drowsiness and finally sleep, due to a diminution of peripheral stimuli from the muscles to the brain, produced by the act of muscular relaxation."  Doctor Coriat admits, how ever, that the muscular relaxation itself may result from a relaxation of the atten tion, and thus he still leaves the way open for the application of the monotony theory as explanatory of the sleeping state.  (Reported by Doctor Coriat in The Journal of Abnormal Psychology, vol.  VI, pp.  329-367.)

Moreover, it is possible to cite many instances of sleep occurring under conditions of muscular tension, as in the case of travelers falling asleep on horseback, and soldiers on the march, without any diminu tion of their ability to ride and walk, carry their rifles in the proper position, keep in step, etc. W. A. Hammond, one of the earlier scientific investigators of sleep, testi fies that he himself often slept on horseback, and specifically calls attention to the phenom enon of sleeping pedestrianism as ex hibited by Galen and the Abbe Richard, the latter of whom "states that once when coming from the country, alone and on foot, sleep overtook him when he was more than half a league from town.  He con tinued to walk, however, though soundly asleep, over an uneven and crooked road."  Galen similarly walked more than two hundred yards while in a deep sleep, and "would probably have gone further but for the fact of his striking his foot against a stone and thus awaking."


Occurrences like these would be impossible if muscular relaxation really were funda mental to sleep.  But they are quite com patible with the monotony theory, which indeed has the merit of offering a more complete and convincing explanation for the various anomalies of sleep than does any other theory.  It finds also striking corroboration in facts of every-day obser vation, as well as in occasional happenings of an extraordinary character, which both reinforce it and are themselves difficult of explanation without resort to it.

Take, for example, the application of the theory to explain the somnolence of infancy by stressing the feebleness of in tellectual development in the very young child and the consequent lack of diversity of its interests.  The explanation hitherto usually advanced for this is that children sleep more than adults because they need more sleep as compensation for the strain of the growth process.  If this were so it would follow that with the attainment of organic growth there would always be an appreciable diminution of the sleeping time.  But the fact actually is that certain types of adults and these invariably persons of inferior intellectual develop ment tend, like children, to spend much of their lives in sleep.

Such is the case with idiots and imbeciles, and it is also the case with savages, who, as was long ago pointed out by Dugald Stew art, have a habit of falling asleep when their minds are unoccupied.  So, too, that shrewd philosopher-statesman, Jefferson, re corded in his "Notes on Virginia," "The existence of the Negro slaves in America appears to participate more of sensation than reflection.  To this must be ascribed their disposition to sleep when abstracted from their diversions and unemployed in their labor."  In this connection should be cited also the experience of the unfor tunate youth, Caspar Hauser, whose career has deservedly and for more than one reason been often made the subject of scientific discussion.

Caspar Hauser, to recall the facts as briefly as possible, was an unhappy German lad, kept prisoner in a dungeon from early childhood, in absolute solitude, and without so much as a glimpse of men, animals, the sky, the sun, the moon, the stars, or any other object in the external w r orld.  In 1828, at the age of seventeen or eighteen, he was taken from his place of confinement and turned adrift in the streets of Nurem berg.  The charitable persons who took charge of him soon discovered that his mental state was little more advanced than that of a few-months-old baby, and that, like a baby, he easily and frequently fell asleep.  It seemed impossible for him to remain awake after sunset, and in the daytime to take him outdoors was enough to plunge him into a deep sleep, even in a roughly jolting vehicle.  Says one of his teachers, writing some months after his mysterious appearance in Nuremberg :

"Caspar sinks, even yet, whenever he rides in a carriage or a wagon, into a kind of death sleep, from which he does not easily awake, whether the vehicle stops or rolls on ; and in this state, how roughly soever it may be done, he may be lifted up or laid down and packed or unpacked wllli out his having the least perception of it.  When sleep has once laid hold of him, no noise, no sound, no report, no thunder, is loud enough to wake him."  1

Here, clearly, is the case of a youth long past the age of infancy, and experiencing not at all the need of sleep as an aid to bodily growth, yet sleeping as an infant sleeps.  Only by assuming that both in his case and in that of the ordinary babe the determining factor is at bottom the paucity of the mental life, quickly rendering all stimuli monotonous by reason of in
ability to differentiate and be intelligently interested in them, is it possible, it seems to me, to arrive at a satisfactory explan ation.

In like manner the monotony theory en ables us as nothing else does to under stand the enormous variations in the time taken for sleep by adults of approximately similar physical constitutions.  It surely is no mere coincidence that, as common observation shows, the men and women who habitually, and without untoward conse quences, take a shorter night's rest than the majority of their fellows, are men and women of unusual intellectual keenness and a wide range of interests.  Such people are seldom "bored"; they find food for thought and entertainment in everything; they are alive in every way.  Typical in this connection is the case of Rudolf Virchow, as narrated by Doctor James J. Walsh, who undoubtedly gives it the correct explanation :


"For more than a year I lived close to the great German pathologist Virchow, and found that his varied interests were probably the secret of his power to devote himself to work for many hours a day, take only a small amount of sleep, and yet live healthily and happily for over eighty years.  Frequently he did not leave the Prussian Legislature until 1 A.M., or even later, and yet he seldom failed to be at his laboratory before 7 : 30 o'clock in the morning, though it was several miles from his home and took over half an hour to get there.  Besides pathology he was deeply interested in anthropology and in most of the biological sciences, and his favorite hobby was the practical care of the health of the city of Berlin.  From the time that Berlin, just after the Franco-Prussian War, began to grow out of the half-million provincial town that it was into the great world capital that it became, Virchow had charge of the health of the men engaged on the sewer farms of the city.  .  .  .  His visits to the farms, his planning for the prevention of the spread of disease, his deep interest in the reports and the constant improvement of conditions, instead of hampering his other intellectual activity by wasting brain force, probably proved restful by diverting the blood stream away to the cells that occupied themselves with this other and very different problem, and so proved a benefit, not an evil."  1

And, as Virchow's case further suggests, unless disease w r eakens their elasticity of mind, persons of keen and varied interests usually retain even in extreme old age, the ability to do with less sleep than other people.  Whereas it is equally a common place of observation that persons of in ferior intellectual activity or of a compara tively limited mental outlook, persons whose lives are cast in a dull routine, are as a rule inclined to indulge in exceptionally long periods of sleep, like the proverbial farmer who "goes to bed with the hens."  That they do so, it may safely be affirmed, is because the stimuli of their environment more readily become tedious and monoto nous to them, and they sleep as a defense reaction against ennui.

All of which would suggest, of course, that most of us sleep longer than is really necessary.  Personally I have no doubt that this is the case.  It has been exper imentally shown that, even following pro tracted vigils, a surprisingly small amount of sleep is needed to effect complete re cuperation.  In one particularly interesting set of experiments, made some years ago by Professor Patrick and Doctor Gilbert in the psychological laboratory of the University of Iowa, three members of the teaching staff were kept continuously awake for about ninety hours.  Being then allowed to go to bed, they found it necessary to make up only from sixteen to thirty-five per cent, of the time lost from sleep.  Students of sleep are agreed, in fact, that it is the quality of sleep that counts rather than the amount, and that certain dangers, physical and mental, attend the develop ment of an undue "sleep habit."  To quote Marie de Manace'ine, who has given special attention to this aspect of the sleep problem : "If a man sleeps longer than the repose of consciousness and the repair of the tissues require, there will, in the first place, be an enfeeblement of consciousness from lack of exercise ; and, in the second place, an adaptation of the vessels to an abnormal state of the nutritive circulation, to the detriment of the functional circulation.  Consequently we may have ground to apprehend trouble in the respiratory ex change and an over-production of carbonic acid not a matter of indifference to the organism, which may sooner or later be injured thereby." 

For these reasons Madame de Manaceme strongly, and justly, deprecates the practice indulged in by too many nurses, and even mothers, of artificially prolonging the sleep of their children out of a selfish desire to have more time to themselves ; and she approvingly recites the German saying, "He has been rocked into stupidity," as epigrammatically expressive of something more than a mere witticism.  Nevertheless, if at every age of life it is important to guard against any tendency to excessive sleep, and if there is reason to believe that the majority of people sleep more than is actually necessary, it would be highly imprudent to ad vise any arbitrary shortening of the hours of sleep.

This can safely be achieved only through the gradual process of consciously or un consciously habituating the mind to act more vigorously and expansively a pro cess which seems to have the dual effect of prolonging the waking period and at
the same time of prolonging it without injury to the organism.  No doubt this is partly due to an improvement in the quality of the sleep taken, but it must also be due in part to a positive strengthening of the constitution by an increased exercise of the mental powers, a view borne out by the interesting circumstance that the great thinkers of the world the Spencers, Glad stones, and Franklins have generally been long-lived, notwithstanding that in many cases they were of frail physique in youth.

But to develop a shorter sleep habit with out basing it on an increase in mental devel opment can only have disastrous effects, for the reason that an excessive strain will necessarily be imposed on a brain accus tomed to function actively only so many hours each day.  That is why, however true it may be to say that four or five hours' sleep should be enough for any man, most men at present require a much longer sleeping-time, and will continue to require it until, with the progress of educational reforms, a maximal brain development shall happily become the rule, not the exception.  Even then there must go apace with increase in mental activity an in creased power of moral control a power which will enable men to think hard but calmly, to meet the vicissitudes of life with fortitude, to withstand all incentives to impatience, anxiety, worry.  Otherwise the greater activity of their minds will inevitably become a source of positive danger, by rendering them easy victims to that cerebral over-stimulation which leads not to too much sleep but to too little.

What, then, under present conditions, should be the sleeping-period for the average person?  To this question, reply might well be made in the words of Madame de Manaceme :

"During the first four or six weeks of Jife Upere ought to be two waking hours during the day, and as the baby grows the duration of this period should gradually increase.  Between the ages of one and two years, children need eighteen to sixteen hours of sleep out of the twenty-four ; be tween two and three years, seventeen to fifteen hours ; between three and four years, sixteen to fourteen hours ; between four and six years, fifteen to thirteen hours ; between six and nine years, twelve to ten hours ; between nine and thirteen years, from ten to eight hours.

"At the critical age of puberty, during the transition from childhood to adoles cence, the duration of sleep should be some what augmented.  At the end of this period it may be reduced to from seven to nine hours; and only after the completion of growth, at the age of nineteen or twenty, can it be safely brought as low as six to eight hours a day.  Those who have reached middle age, the age at which con sciousness and the other psychic faculties have attained the zenith of their develop ment, may content themselves with even less, but only so long as they are in perfect health.  On the whole, it may be said that eight hours is, on the average, the amount which adults may most wisely devote to sleep. 

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