'**> 
 
 * o 
 
 ° 'O .\v * 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 o > 
 
 ? ^ 
 
 
 r oK 
 
 ^^ .i 
 
 
 
 ^tt. ••• AT <?> 0> 
 
 W 
 
 >* 
 
 
 
 O^ *© . » * A 
 
 O. *o 
 
 6* *•*!.?• o. 
 
 
 V *r ^ V 
 
 jp-nK 
 
 v *r 
 
 & 
 
 
 ^°^ . 
 
 v s> 
 
 * 
 
 
 * «f <i. V 
 

 £~* 
 
 o V. 
 
 10 * -ftp ^, oWJf&W* AV ^ . 
 
 v »P-i 
 
 .• * ^ V 
 
 V^>° V"V V*^V v^ 
 
 
 V 
 
 "*<>* 
 .«««?* 
 
 
 *P^ V 
 
 
 
 •o. *♦.. 
 
 o_ . 
 
 ;./V ,«Ao*fc\. >*.!«:.* ^stf^V 
 
 
 £* ^\ 
 
 p*^l^.*< 
 
 O^ *•>•** A 
 
 
 <r ♦ 
 
 °o 
 
 .<* .' 
 
 o V 
 
 : r*++ V 
 
 
 
 
 
 .0 
 
 
 ^ < 
 
 o > 
 
 v '^r'- 
 
 
 \^ 
 
 <^ " ' «« 
 
AN EXPERIMENTAL^ 
 STUDY OF SLEEP 
 
 (From the Physiological Laboratory of the 
 Harvard Medical School and from Sidis' Laboratory) 
 
 
 
 {A 
 
 BY 
 
 BORIS SIDIS, M.A., Ph.D., M.D. 
 
 Author Of PSYCHOPATHOLOGICAL RESEARCHES //" 
 
 in Mental Dissociation 
 
 BOSTON: RICHARD G. BADGER 
 
 XTbe (Borbam press 
 
 1909 
 
 m v 
 
Copyright 1908 by Boris Sidis, M.D. 
 All Rights Reserved 
 
 ^ 
 
 t> 
 
 ,^> 
 
 "9 
 
 LIBfjARY Of CONGRESS 
 Two Copies Received 
 
 DEC 22 1808 
 
 _ Copyritfni tntry 
 CLASS CX XXt, No. 
 COPY \ . * U 
 
 Gbe $orbam press, JSoston, Ta. 5. B. 
 
TO 
 DR. MORTON PRINCE 
 
 in appreciation of his originality in Philosophy and 
 Psychology and of his staunch friendship towards 
 
 THE AUTHOR. 
 
CONTENTS 
 
 Part I — Experimental 
 
 Chapter 
 
 I. 
 
 Introductory Remarks . 
 
 I 
 
 Chapter 
 
 II. 
 
 Theories of Sleep 
 
 3 
 
 Chapter 
 
 III. 
 
 The Conditions of Sleep 
 
 9 
 
 Chapter 
 
 IV. 
 
 Intermediary States 
 
 14 
 
 Chapter 
 
 V. 
 
 The Induction of Sleep States 
 
 . 19 
 
 Chapter 
 
 VI. 
 
 Experiments on Frogs . 
 
 21 
 
 Chapter 
 
 VII. 
 
 Experiments on Guinea-Pigs 
 
 . 29 
 
 Chapter 
 
 VIII. 
 
 Experiments on Cats 
 
 • 33 
 
 Chapter 
 
 IX. 
 
 Experiments on Dogs . 
 
 • 39 
 
 Chapter 
 
 X. 
 
 Experiments on Children 
 
 • 54 
 
 Chapter 
 
 XI. 
 
 Motor Reactions of -Lnfants, Childrer 
 
 l and 
 
 Adults in Subwaking and Sleeping States 67 
 
 Part II — Theoretical 
 
 Chapter XII. 
 
 Chapter XIII. 
 Bibliography 
 
 Cell Energy, Threshold, " Stimulus-Exhaus- 
 tion " and Sleep ..... 
 
 Motor Consciousness and Sleep . 
 
 75 
 9i 
 99 
 
PART I 
 EXPERIMENTAL 
 
 Hypotheses non fingo" 
 
 — Newton. 
 
AN 
 
 EXPERIMENTAL 
 
 STUDY OF SLEEP 
 
 Chapter I 
 
 Introductory Remarks 
 
 WRITERS on sleep complain that little attention 
 has been paid to the subject, that it is sufficient 
 to open a text-book on physiology to be con- 
 vinced of the fact that the physiology of sleep 
 is almost entirely neglected, inasmuch as the school-physi- 
 ologist usually dismisses the subject with a few phrases, 
 often quite general and devoid of meaning. It is quite true 
 that while one cannot as a rule be satisfied with the imperfect 
 state of textbook-physiology which usually lingers in the hind 
 ranks of the battle-ground of science, still one cannot blame 
 the text-books for avoiding such a delicate subject, the 
 nature of which is so uncertain and so highly problematic. 
 In addition to the uncertainty of the subject of which 
 the more conservative of school-physiologists fight shy, there 
 seems to be an ill defined feeling which is not without some 
 good foundation, namely, that sleep is not entirely a physio- 
 logical subject, that sleep presents some very important 
 aspects that need be taken into consideration which the 
 
2 An Experimental Study of Sleep 
 
 physiologist is unable to deal with by his usual methods 
 and from his standpoint alone. 
 
 Moreover there may be another reason for the indif- 
 ference of school-physiology to a subject which is otherwise 
 of such a vital importance in the whole domain of animal 
 life. Man is more interested in active than in passive 
 states. It is therefore natural that the physiologist should 
 devote his attention more to waking life than to sleeping 
 states. Besides, physiology dealing essentially with activi- 
 ties and functions tends to ignore states which are usually 
 regarded as the very acme of inactivity. With the advance 
 however of biological, physiological and psychological 
 sciences even states of passivity can no longer be ignored, — 
 their conditions, causation and nature must be studied and 
 closely investigated, especially if those states are found 
 present throughout the ascending line of animal life. The 
 conditions for the study of sleep become all the more favor- 
 able as we reach man. We find that sleep-states in man's 
 life are no longer instable and taken by snatches, because the 
 watchfulness requisite in wild-life under the constant strain 
 of the struggle for existence no longer obtains. In man's 
 life sleep-states become more or less organized, systematized 
 and are no longer disturbed, — they alternate rhythmically 
 with waking states. More than one-third of man's life is 
 passed in sleep, — it seems that this fact alone should 
 indicate the importance of sleep-states in man's cycle of 
 biological and physiological processes and should arouse 
 the interest of the scientific investigator. As a matter of 
 fact some scientific thinkers have given the subject of sleep 
 a good deal of their attention. Although text-book physi- 
 ology passes over the subject with a few meaningless phrases, 
 the literature of sleep is really very extensive. It may be 
 well before we proceed with the exposition of our own 
 observations and experiments on sleep to give first a brief 
 review of the chief theories on sleep. 
 
Chapter II 
 
 Theories of Sleep 
 
 FROM the very earliest times man wondered about 
 sleep and attempted some explanation of it. It 
 was supposed that in sleep the soul wanders away 
 from the body and leaves it in a lifeless condition. 
 Many of the savage tribes are on that account afraid to 
 waken people lest the soul may be frightened away and not 
 return at all to the body. That is why even at present we 
 often hear the saying that sleep is the companion of death. 
 On the other hand death is often described as sleep. On 
 the same basis dreams were explained by the primitive 
 mind, — the soul in sleep leaves the body and wanders 
 away; on its wanderings the soul meets with all kinds of 
 adventures and it is such experience that gives rise to 
 dreams. In sleep the wandering soul, not encumbered by 
 the gross body, can visit great distances in a short time and 
 can even communicate with heavenly powers, — with angels 
 and gods. 
 
 The impassive soul reluctant flies, 
 Like a vain dream, to these infernal skies. 
 Modern spiritualists adopt this ancient belief in full or 
 express it as "the release of human personality from the 
 subliminal. " 
 
 The scientific theories of sleep are numerous, but they 
 can be reduced to a few main types. This reduction will 
 help the reader to become oriented in the vast literature that 
 has gathered about the subject. The theories of sleep may 
 be classified as follows: 
 
 theories, which may be sub- 
 
 I) 
 
 The Physiological 
 
 
 divided into: 
 
 
 a) Mechanical 
 
 
 and 
 
 
 b) Chemical 
 
 2) 
 
 Pathological 
 
 3) 
 
 Histological 
 
 4) Psychological 
 
 5) Biological 
 
4 An Experimental Study of Sleep 
 
 The mechanical theories are of the circulatory variety 
 and are usually much favored by physicians, — they attempt 
 to explain sleep by changes in the blood circulation of the 
 cerebrum. As far back as the eighteenth century the theory 
 of sleep greatly in vogue among the physiologists was — 
 congestion of the brain favored by the position of the head. 
 This view was entertained by Haller, J. Miiller, Hartley and 
 others. Cappie has somewhat enlarged on it, inasmuch 
 as he ascribes sleep to the venous congestion of the brain. 
 This congestion of blood was supposed to bring about pres- 
 sure on the brain with the result of depression of all the 
 cerebral functions. The great psychologist Hartley sum- 
 marises the physiological theories of his time thus: "It 
 appears then that during sleep the blood is accumulated in 
 the veins and particularly in the venal sinuses which surround 
 the brain and spinal marrow. . . . And it is agreeable 
 to this that in most dissections after lethargies, apoplexies, 
 etc., the venal sinuses of the brain and consequently those 
 of the spinal marrow which communicate freely with them 
 are particularly full. ... It follows therefore that the 
 brain and spinal marrow will be particularly compressed 
 during sleep, since the blood then takes up more space, is 
 particularly accumulated within the cavities of the skull 
 and vertebrae, and the hardness of these bones will not 
 suffer them to yield or make more room. ... In short 
 this compression will result in sleep." These generalizations 
 were favored by observations on the famous case of the 
 Parisian beggar whose injured skull gave the opportunity 
 to observe the rise and fall of the exposed cerebrum in the 
 waking or sleeping state. Recently Mosso claimed the 
 same causation of sleep and on similar observations. As 
 to the circulatory changes proper, two opposing views have 
 been taken. Some, such as Durham, CI. Bernard, Kussmaul 
 Howell, Lehman, de Fleury ascribe sleep to cerebral anemia. 
 Others again, such as Brown, Czerny, Broadman maintain 
 that sleep is due to cerebral hyperemia. Claperede in 
 reviewing the circulatory theories of sleep quotes Richet's 
 apt criticism: "Sleep and waking states bring about all 
 kinds of changes in cerebral circulation depending but little 
 on the position of the head. Birds whose hemispheres have 
 
An Experimental Study of Sleep 5 
 
 been removed still present the same changes of sleep and 
 waking. Biologically regarded, sleep is a far more general 
 phenomenon than that of the presence of a brain irrigated by 
 a blood circulation. Finally the activity of a tissue is not 
 entirely dependent on the amount of blood circulating in it." 
 There are however still more cogent objections to such 
 theories of sleep, objections which clearly show the incon- 
 gruence of the circulatory theories. We shall point them 
 out further in our present study. 
 
 We may turn now to the chemical theories which are 
 far more favored by the conservative physiologist, inasmuch 
 as they fall in with what the physiologist regards as more 
 scientific. With the experiments of Pettenkofer and Voit 
 on the respiratory quotient new life was injected into sleep 
 theories. Those two investigators have found the respiratory 
 quotient ^ is diminished during sleep. The tissues 
 absorb relatively more oxygen during the day than during 
 the night. This fact of the using up and impoverishment of 
 blood of intermolecular oxygen started new life in the theories 
 of sleep. Pfliiger, Sommer and others attempted to work 
 out a scientific theory of sleep based on research of the bio- 
 chemistry of the cell and the intermolecular activity of the 
 oxygen-molecule or atom. Pfliiger's authority lent vitality 
 to this view so that even Heubel whose theory of sleep is 
 really psychological in character tries to shelter it under 
 Pfliiger's physiological wings. 1 
 
 With the chemical theories we pass by degrees into the 
 pathological theories of sleep. Already in the early part of 
 the nineteenth century Marshall Hall proposed the view that 
 sleep was a kind of epilepsy. This view however met with 
 little favor, because of lack of facts to support it. With the 
 advance of chemistry and of its application to physiological 
 research, and especially with the rise of the modern views of 
 the role of autointoxication and toxins in diseases, the patho- 
 logical theories of sleep were resuscitated under the new 
 guise of autointoxication. Obersteiner and Preyer launched 
 the theory that sleep was arTautointoxication of the system 
 by toxic matters accumulating in the blood, due to the 
 
 1 We may possibly refer to Loeb's work on heliotropism and sleep of butterflies as 
 an example of a purely bio-chemical view of sleep. See Dec. Public Univ., Chicago, V. I. 
 
6 An Experimental Study of Sleep 
 
 activity of the various tissues. Lactic acid was supposed 
 to be the particular substance in question. Others such as 
 Dubois ascribed the same state to the accumulation of 
 carbonic acid. These were followed by a host of writers 
 such as Binz, Errero, Bouchard, Breisacker and others. 
 The toxic and autotoxic theories of sleep enjoy quite a wide 
 popularity, because they fall in with the scientific notions 
 of the age. Those theories would make of sleep a patho- 
 logical state, but the facts are against such a view. 
 
 By the middle of the nineteenth century, when physio- 
 logical experiments on nerve-conduction were at their 
 height, Purkinje proposed the theory that sleep might be 
 due to the Interruption of neural conductivity between the 
 cortical matter and the rest of the cerebrum. This view 
 was further developed by Mautner, Warlomont, Oppen- 
 heimer and others. As a further modification of the same 
 theory, but based on more fundamental physiological 
 processes may be mentioned Verworn's theory which refers 
 sleep and waking-states to processes of assimilation and 
 dissimilation going on in the organism. At the same time 
 with Verworn, Van Gieson and Sidis worked out their theory 
 of sleep, basing it on similar processes, namely on anabolism 
 and catabolism and developing the interrelation of waking 
 and sleeping states with the symptom complexes of nervous 
 and mental diseases. The theory of Van Gieson and Sidis 
 is based on the variability of different levels of neuron 
 energy. We may dismiss this latter theory in a few words 
 as we shall discuss it in our study. We can only say here 
 that the theory is essentially based on the concept of neuron- 
 energy. 
 
 This brings us close to the famous theories of retractility 
 of neuron-elements which have been of late utilized by many 
 writers for various purposes. The development of the 
 histology of the nervous system and especially of neuro- 
 pathology have brought new life to the solution of the prob- 
 lem of sleep. The biological investigations of the cell by 
 Kolliker, Remak, Nageli, Hoffmeister, Virchow, Max 
 Schultze, Hertwig, Fol, Van Beneden, Strassburger, Heiden- 
 hein, Boveri and many others opened up new horizons for 
 theories of cellular activities. Naturally the sleep theories 
 
An Experimental Study of Sleep 7 
 
 came in for their share. It was not however until the 
 researches of Golgi and Ramon Y Cajal had laid the 
 foundation for their famous doctrine of independence and 
 contiguity of neural elements that the theories of sleep could 
 seize on some tangible anatomical facts and work them for 
 their benefit. Ramon Y Cajal was the first to advance 
 the view that the~ neuroglia-cells by their expansions and 
 contractions bring about dissociations and associations of 
 the neural elements with the consequent loss or reappear- 
 ance of normal waking-states. A somewhat different, but 
 closely analogous theory was launched into the scientific 
 world by Mathias-Duval. Instead of the retractility of 
 neuroglia cells proposed by Cajal, Duval advanced the view 
 that the neurons and their protoplasmic processes are 
 endowed with contractility or retractility and that the func- 
 tioning and loss of functioning of neural elements are due 
 to contractions and expansions of the protoplasmic processes 
 of the neurons. Demoor, Pupin, Berger and others have 
 enlarged on this hypothesis. At first even Verworn accepted 
 this hypothesis, although he discountenanced it afterwards. 
 Sidis assumed provisionally the same hypothesis for abnor- 
 mal dissociative manifestations, but refused to accept it as 
 an explanation for the phenomena of sleep which do not 
 warrant the assumption of such hypothesis. 
 
 The psychological theories of sleep date from antiquity. 
 The popular explanation is very simple, — it is a description 
 of the phenomena, a description which the popular mind 
 often takes for an explanation of the phenomena in question. 
 Sleep is an abeyance of mental life, sleep is a rest of con- 
 sciousness. Modern physiologists and psychologists who 
 maintain the psychological theory of sleep have not much 
 improved on that statement. The only modern substitute is 
 that of inhibition. Brown-Sequard, Wundt^ Siemens, Forel, 
 Oscar Vogt, all in different scientific phraseology refer 
 sleep to inhibition of cerebral activity, especially of the 
 frontal lobes where mental activity is supposed to " reside," 
 according to some authors. Manaceine in her work on 
 sleep echoes this view and comes to the conclusion that 
 "sleep is the resting state of consciousness." Surely it is an 
 elaboration of the obvious, if one has to write a whole volume 
 
° An Experimental Study of Sleep 
 
 in order to arrive at such an important conclusion. The only 
 one who really made some advance in the psychological 
 theory of sleep was Heubel, Privatdocent at Kiev University, 
 Russia. I can say his is an excellent piece of work based on 
 a series of well performed experiments. Unfortunately, 
 when I started my experiments, I was not acquainted with 
 the work of that investigator. I have gone over in my 
 experimental research a good deal of the same work and may 
 say that Heubel's experiments have been fully confirmed by 
 me. Although Heubel's theory is incomplete, there is 
 a good deal of truth in it and his work well deserves the 
 attention of the student of sleep. His veiw may be briefly 
 
 summarized in the following statement: Mental activity 
 
 depends on the incoming peripheral, sensory stimulations; 
 where such peripheral sensory stimulations are absent, 
 mental activity is in abeyance and sleep results. In other 
 words, brain activity depends on sensory activity which in 
 its turn depends on peripheral stimulations. Psychologically 
 stated, consciousness is a function of sensations which in 
 their turn are a function of external stimuli or impressions. 
 In accordance with this view a series of experiments have 
 been carefully carried out by Huebel. As my own experi- 
 ments were carried out on somewhat similar lines I shall 
 refer again to Huebel's work, when I give an account of my 
 experiments, in order to test a somewhat similar theory 
 arrived at from totally different considerations, viewing the 
 subject of sleep not only from a physiological and psycho- 
 logical, but also from a biological standpoint. 
 
 An altogether different departure from the usual 
 theories of sleep was recently taken Jxy Claperede. He 
 points out that biologically regarded, sleep has its significance 
 not as a passive state, but as an active instinct, like all the 
 other instincts of animal life. To put it in his own words : 
 "Le sommeil n'est pas un etat purement negatif, passif, il 
 n'est pas la consequence d'un simple arret de fonctionne- 
 ment: il est un fonction positive, un acte de ordre reflexe, 
 un instinct, qui a pour but cet arret de fonctionnement; 
 ce n'est pas parce que nous sommes intoxiques, ou epuises, 
 que nous dormons, mais nous dormons pour ne pas l'etre." 
 This biological view of Claperede forms one of the most 
 
An Experimental Study of Sleep 
 
 9 
 
 valuable contributions to the theory of sleep. It throws 
 altogether new light on the subject of sleep, and many 
 obscure until now unexplained facts can be understood in the 
 new light of the biological standpoint taken by Claperede. 
 Claperede's physiological theory of inhibition is not as clear, 
 but with some modification I think it could well harmonize 
 with my views and my work on sleep. While accepting 
 the views of Claperede, my standpoint taken in this study is 
 based on investigations published in previous works of mine 
 mainly dealing with the subject of dissociative states in 
 general. 
 
 Chapter III 
 
 The Conditions of Sleep 
 
 TAKING the well-known dictum of Newton, " Hypoth- 
 eses non fingo," let us start with facts before we 
 attempt to form any idea as to the nature and 
 character of that apparently mysterious state known 
 as sleep. In order to understand a highly complicated 
 phenomenon it is well to study the circumstances under which 
 it occurs and investigate the conditions that favor the mani- 
 festation of the state. Now in studying the conditions of 
 normal and abnormal suggestibility, I pointed out in my 
 "Psychology of Suggestion" that the following conditions 
 are requisite to bring about those peculiar subconscious or 
 subwaking states which form the soil favorable for the 
 growth and development of implanted suggestions. 
 
 Conditions of 
 Normal Suggestibility Abnormal Suggestibility 
 
 i) Fixation of attention 
 
 2) Distraction of attention 
 
 3) Monotony 
 
 4) Limitation of voluntary 
 
 movements 
 
 5) Limitation of conscious- 
 
 ness 
 
 6) Inhibition 
 
 7) Immediate execution of 
 
 the suggestion 
 
 1) Fixation of attention 
 
 2) 
 
 3) Monotony 
 
 4) Limitation of voluntary 
 
 movements 
 
 5) Limitation of conscious- 
 
 ness 
 
 6) Inhibition 
 
 7) 
 
10 An Experimental Study of Sleep 
 
 I have further pointed out that what we really bring 
 about under such conditions is a dissociation of conscious- 
 ness. In the normal waking state the dissociation is tran- 
 sient, fleeting, disappearing at the very moment of its 
 appearance, while in abnormal suggestibility the states are 
 more or less permanent. In other words, the waking state 
 tends to disappear under the conditions mentioned above. 
 Now to induce sleep the first requirement is the displacement 
 of the waking state. It is evident that the conditions that 
 favor the suppression of the waking state would also favor 
 sleep-states. As a matter of fact I have often observed in my 
 patients and subjects that the conditions by which I intended 
 to bring about a subconscious state in general and a hypnotic 
 state in particular have often resulted in ordinary sleep. 
 I have found quite frequently that the close observation of the 
 conditions of monotony, limitation of the voluntary move- 
 ments, limitation of the field of consciousness and of in- 
 hibition, brought about not a hypnotic state, but ordinary 
 sleep. I began to experiment on myself and found that I 
 could put myself almost at any time into a state of deep 
 sleep by closing my eyes and keeping perfectly still, dismissing 
 all ideas from my mind — closing shop, so to say. I was 
 able to put myself into a quiet, prolonged and often very 
 refreshing sleep. I have further succeeded in the treatment 
 of many cases of insomnia, by following the same lines in 
 bringing about good therapeutic results. 
 
 After many years of experimentation and observation 
 I have come to the conclusion that this could not possibly 
 be an accidental matter, but that there must be some close 
 interrelation between sleep-states and the conditions of 
 normal and abnormal suggestibility. In other words, 
 the conviction was almost forced on my mind by the facts 
 that the conditions I found requisite for the induction of 
 dissociated states and for normal and abnormal suggestibility 
 in general play also an important role in the induction of 
 sleep. 
 
 There is one fact that is specially worth while noticing 
 in the process of falling asleep, and that is, the circumstance 
 that we do not tumble into it in spite of ourselves, that we 
 go about it in a deliberate, may be cold-blooded fashion. 
 
An Experimental Study of Sleep 
 
 II 
 
 We have to make up our minds and decide whether or no 
 we want to go to sleep, or whether it is best for us to be 
 asleep; and when we decide in the affirmative, we undress 
 and go to sleep. The whole affair is not the after-effect of 
 some narcotic, toxic, autotoxic bodies, nor the result of some 
 involuntary automatic mechanism, — it is a voluntary act, — 
 the result of decision. In this respect sleep is very similar 
 to the abnormal state of suggestibility in which subjects can 
 be artificially put. The state of abnormal suggestibility, 
 the hypnotic state, is not induced by accumulation of toxic 
 products in the system. The state can be brought about 
 at will under the conditions described above. It is a purely 
 voluntary affair, requiring the cooperation of the subject's 
 and the experimenter's attention, active and steady. In 
 fact, subjects whose attention is poor, — imbeciles, idiots, 
 insane persons or persons whose attention is constantly wan- 
 dering and fluctuating, are extremely difficult to hypnotize. 
 These significant facts so often overlooked by writers on the 
 subject, force on one the conclusion that the psychic factor 
 is of the utmost importance in the formation of sleep-states. 
 If we now scrutinize the conditions under which drowsi- 
 ness and sleep occur, we find that they differ in some very 
 important points from those requisite in the induction of 
 hypnotic states. In the bringing about of hypnosis the 
 most favorable condition is the fixation of the attention on 
 some object, perceptual or ideational. So much is this 
 condition of fixation of importance that some writers describe 
 the nature of the subconscious by this one condition of the 
 attention, and characterize the hypnotic state, not without 
 some show of plausibility, as a cramp of the attention. 
 Such a sweeping statement is not entirely true to fact, but 
 it is true that fixation of the attention, steady and persistent, 
 without flinching, constitutes a very important factor in the 
 induction of the hypnotic state. In sleep, however, we 
 observe that the condition is somewhat modified, — it is not 
 fixation of the attention that is conducive to sleep; in fact, 
 fixation of the attention is more favorable to insomnia or to 
 the prolongation of the waking state. What is requisite 
 is a relaxation of the attention. If fixation of the attention 
 is present at all, it is only present in so far as it is requisite 
 
12 An Experimental Study of Sleep 
 
 to have the attention relaxed, which under some conditions 
 requires either an effort of the will or the presence of 
 specially favorable circumstances. It is the will to give 
 up all active relations, sensory and motor, with the external 
 environment. In hypnosis there is present at first a strained 
 state of attention; in the induction of sleep the strain is 
 practically reduced to its minimum. In the formation of 
 sleep-states all active desire must cease. That is why 
 people with intense, active desires and emotions find it so 
 difficult to fall asleep. On the other hand such intense 
 desires and strong emotional states may, if taken advantage 
 of at a favorable moment, become the best condition for 
 bringing about states of suggestibility, hypnosis and all 
 forms of dissociation. In fact, in this respect we may say 
 that the sleep-states differ fundamentally from hypnotic 
 states. Suggestibility, which is the characteristic trait of 
 subconscious states and of hypnotic states in particular, is 
 absent in sleep-states. While hypnosis and allied states are 
 characterized by a greater facility of reactions to external 
 stimulations, the sleep-states on the contrary are characterized 
 by an almost complete suppression of the more complex 
 reactions associated with mental processes. In other words, 
 in hypnosis and allied states there is a suppression or inhibition 
 of the inhibitions present in waking life; in sleep, on the 
 contrary, the inhibitions are intensified. If put in terms of 
 the threshold theory advanced in my work, "Multiple 
 Personality," we may say that in hypnosis and allied states 
 the thresholds are lowered, while in sleep states the thresholds 
 are raised. 
 
 If we turn once more to the conditions of sleep, we find 
 that limitation of the field of consciousness and limitation 
 of voluntary movements play a very important role in the 
 bringing about of sleep-states. In this respect Huebel's 
 shrewd observation is correct, — the cutting off of all external 
 stimulations tends to bring about a languid condition akin 
 to sleep. Prisoners in solitary confinement, unless they 
 find a source of mental activity by getting some external 
 stimulations to awaken their mental life, have a tendency to 
 sleepiness. Where attention is relaxed, or the interest in 
 external impressions is gone, there drowsiness supervenes. 
 
An Experimental Study of Sleep 13 
 
 In the limitation of voluntary movements a mass of muscular 
 sensations as well as kinaesthetic sensations is kept from 
 pouring into consciousness, the result is a lowering of mental 
 activity, a rise of thresholds characteristic of sleep. The 
 cutting off of external impressions is also of importance in 
 hypnosis, as when the subject is asked to keep very quiet 
 and make his mind a "blank." Where there is a predis- 
 position to states of dissociation the result of limitation is 
 not sleep but hypnosis, with a fall of thresholds. 
 
 The most important and possibly fundamental con- 
 dition common to sleep and subconscious states is that of 
 monotony. In order to fall asleep we must dismiss all our 
 interests, all our thoughts. Similarly, to induce hypnosis 
 we tell the subject to try not to think of anything. We 
 impoverish, we make monotonous, his mental life by making 
 him think of "nothing in particular." 
 
 The fact that people may fall asleep even under intense 
 stimulations is often adduced as a strong objection to the 
 view that diminution of sensory stimulations is conducive 
 to sleep. Thus Richet refers to the fact of "falling asleep 
 at the opera, in spite of the light and the noise." This 
 objection is valid only if we leave out of account the im- 
 portance of the factor of monotony. It is not so much the 
 diminution of the intensity of stimulations which is of 
 importance in the production of sleep, as the total mass of 
 impressions. In fact, it is not so much the total volume as 
 the progressive, ceaseless variability of the incoming im- 
 pressions that counts in the keeping up of the restless activity 
 of consciousness in its adjustment to the external conditions 
 of the environment. Given a prolonged stimulation or 
 a series of stimulations of the same intensity, consciousness 
 becomes dulled and sleep ensues. In fact, the more intense 
 the monotonous stimulations are, the deeper is the state 
 of sleep. 
 
 It is interesting to note that under such conditions the 
 intensity of the series of monotonous stimulations tends to 
 keep up the sleep-state. With the cessation of the monoto- 
 nous stimulations the sleep-state tends to disappear. The 
 miller falls asleep under the continuous uniform noise of his 
 mill, and wakes with the cessation of the noise. In 
 
14 An Experimental Study of Sleep 
 
 listening to lecturers in a medical school I found how easily 
 the monotonous, uninteresting delivery put me into a drowsy 
 state, and how I came back to myself with a start when the 
 lecturer stopped. Inquiring among the students, I found 
 that their experiences were quite similar to my own; they 
 were kept in a semi-drowsy state by the long-drawn-out 
 sentences, and kept awake by the lecturer's resting-places. 
 Many people who are used {o the long, continuous hum of 
 a large city such as New York, for instance, find it difficult 
 to fall asleep in a quiet place. 
 
 Chapter IV 
 
 Intermediary States 
 
 IN many cases where it is requisite to find the causation 
 of the mental trouble, and hypnotization is not 
 possible, I have for many years employed a method 
 which has been giving excellent results, both theo- 
 retical and practical. By means of this method, which I 
 have termed hypnoidization, I have been able to induce 
 states closely allied to sleeping states on the one hand, and 
 to hypnosis on the other. This work may be regarded as 
 established, having since been confirmed by many other 
 investigators, as well as by my assistants and collaborators 
 in my laboratory. 
 
 Basing myself on the conditions which I have elsewhere 
 described for the induction of states of normal and abnormal 
 suggestibility, as well as for the bringing about of dissociated 
 states in general, I have applied the same or similar con- 
 ditions in cases where hypnosis was not possible. The 
 result was the induction of peculiar states which I termed 
 hypnoidal. The hyp/ioidal state is of an intermediary 
 character, intermediary between the waking state on the 
 one hand, sleep and hypnosis on the other. Here specially 
 lies our present interest in these peculiar states. The patient 
 or the subject while in this state hovers between hypnosis 
 and sleep. Now he may be in a condition which can only 
 be characterized as light hypnosis, and then again to one's 
 surprise the person is found to be in his normal waking 
 state. The state evidently is highly unstable. 
 
An Experimental Study of Sleep 1 5 
 
 The oscillations of the different states may be followed 
 by variations in respiration. Thus the respiration is some- 
 what unequal in the waking state, becomes quietened and 
 more uniform in hypnosis. When, again, in the hypnoidal 
 state the respiration is slow and with little or almost no 
 variations, it becomes disturbed when the patient passes into 
 waking state, and becomes uniform when he passes into 
 hvpnosis or sleep. 
 
 The method of hypnoidization shows clearly how the 
 conditions of normal and abnormal suggestibility are utilized 
 and modified in the induction of hypnoidal or intermediary 
 states. I say modified, because it is just on such slight 
 modifications and variations of the conditions mentioned 
 above that the whole matter of hypnoidal states hinges. 
 A quotation from a previous work of mine giving a short 
 description of the methods of hypnoidization and of the 
 character of the hypnoidal state will be opportune here. 
 " The patient is asked to close his eyes and keep as quiet as 
 possible, without however making any special effort to put 
 himself 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. When the reading is over, the pa- 
 tient with his eyes shut is asked to repeat it and tell what 
 comes into his mind during the reading, or during the repeti- 
 tion, or immediately after. This should be carried out in a 
 very quiet place, and the room, if possible, should be dark- 
 ened so as not to disturb the patient and thus bring him out of 
 the state in which he has been put. As modifications of the 
 same method, — the patient or subject is asked to fixate his 
 attention on some object, while at the same time listening 
 to the beats of a metronome; the patient's eyes are then 
 closed, he is to keep very quiet, while the metronome or 
 some other monotonous stimulus is continued. After some 
 time, when the patient's respirations and pulse are found 
 somewhat lowered, he is asked to concentrate his attention 
 on a subject closely relating to the symptoms of the malady 
 or to the submerged subconscious state. In other words, 
 the patient is in a hypnoidal state favorable for the emergence 
 of subconscious experiences. 
 
 " The patient again may be asked to be very quiet to 
 
1 6 An Experimental Study of Sleep 
 
 move, or change position as little as possible, and is required 
 to look steadily into a glass of water on a white background 
 with a light shining through the contents of the glass ; 
 a mechanism producing monotonous sounds is set going, 
 and after a time, when the patient is observed to have 
 become unusually quiet, he is asked to tell what he thinks 
 in regard to his symptoms. In other cases it is sufficient 
 to put the patient in a relaxed condition, have his eyes shut 
 and tell him to think hard of the particular dissociated states." 
 
 Now in working with the method of hypnoidization 
 I have often observed in using it that the patient at first tries 
 to concentrate his attention and seems to fall into slight 
 hypnosis, but pretty soon he is fully awake. In closely 
 watching this condition I found that at first the patient 
 attempted to fixate his attention, then lost control over it. 
 His attention being relaxed he fell into a sleep-state, out of 
 which he emerged again, owing to the partial presence of 
 the idea of the necessity of concentration of the attention, 
 as well as to the partial watchfulness present. It is this 
 alternate and incomplete relaxation and concentration of 
 the attention that keeps the patient on the borderland of 
 wakefulness, hypnosis and sleep. In some cases the 
 hypnoidal state passed into hypnosis. Thus in one of mv 
 cases, V. F., at first I obtained only hypnoidal states, but 
 after some time the hypnotic state gained ground and the 
 subject passed into typical hypnosis and finally into a som- 
 nambulistic state. In other cases I have observed that 
 preliminary to the passing into the hypnotic state proper 
 a short interval is present which may be regarded as a hyp- 
 noidal condition. In many other cases the patient is not in 
 the hypnotic condition, but still there are phenomena 
 present which remind one strongly of the hypnotic state. 
 
 The close relationship of the hypnoidal state and of 
 hypnosis is sometimes forcibly brought to the mind of the 
 experimenter. Some patients while in the hypnoidal state 
 are observed to become unusually quiet, less talkative, 
 relaxed and after a time distinctly cataleptic. The patient 
 has apparently passed into hypnosis. In most of the cases 
 the hypnosis is of very brief d uration. On the other hand, 
 in other cases the subject falls into a sleeping state without 
 
An Experimental Study of Sleep 17 
 
 as much as touching on hypnosis. The hypnoidal state is 
 on the borderland of waking, sleep and hypnosis. .Sub- 
 waking seems to be an appropriate descriptive term of the 
 hypnoidal state. Like sleep and hypnosis, the subwaking 
 hypnoidal state greatly varies as to depth and duration: 
 it may range from the full waking consciousness to deep 
 hypnosis. The same patient may at various times reach 
 different levels, so that not all the hypnoidal states are of 
 the same depth; and in that respect they are very much like 
 sleep and hypnosis, which really are not always of the same 
 depth. 1 
 
 What is specially characteristic of the hypnoidal states 
 is the difficulty of fixing them for any length of time, — they 
 dissolve into mist as soon as an attempt is made to seize 
 them, — they are extremely fleeting and evanescent. What 
 specially interests us is the close relationship of the hypnoidal 
 state with sleep-states. The hypnoidal state is the bridge 
 that connects the waking state not only with hypnosis, but 
 also with sleep. To enter sleep or hypnosis one has to pass 
 through the intermediate state, the hypnoidal state. 
 
 We may also add that this holds true not only in the 
 case of passing into any of the hypnotic or sleep-states, but 
 also in the case of passing out of them. A close observation 
 of cases will show that in awakening from hypnosis, as well as 
 from sleep, there is present a short period occupied by 
 a peculiar condition of consciousness, a condition which 
 is no other than the hypnoidal state. It is such states 
 between sleeping and waking, whether on the way to or 
 from sleep, that may be designated as subwaking, and are 
 akin to hypnoidal states. 
 
 The subwaking states are characterized by the trait of 
 suggestibility. Suggestions are fully possible in such con- 
 ditions. In fact, in all those cases where hypnosis is im- 
 possible or impracticable the hypnoidal states can be util- 
 ized for the same purpose. The subwaking or hypnoidal 
 states are utilized by me and by many other investigators in 
 a systematic and methodical way for the obtaining of sub- 
 merged subconscious experiences. This clearly shows that 
 the subwaking states, while being of the character of sleep- 
 states, are also in close touch with states of dissociation. 
 
8 
 
 An Experimental Study of Sleep 
 
 One important characteristic of all subwaking states is 
 the formation of hallucinations which indicate states of 
 dissociation under which alone hallucinations can take place. 
 On falling asleep hallucinations crowd consciousness, and on 
 awakening a crowd of phantastic percepts, often giving rise 
 to disconnected dreams, haunt "the halls of consciousness. " 
 We may possibly term the intermediary subwaking states 
 leading into sleep as hypnagogic states and the dream- 
 hallucinations formed hypnagogic hallucinations; the inter- 
 mediary subwaking states which arise on coming out of 
 sleep we may term hypnapagogic states (from vttvos, sleep; 
 and aTrayw, lead away); the dream hallucinations formed 
 may be termed hypnapagogic hallucinations. In passing 
 from waking states into sleep and again from sleep into 
 waking, we pass through those intermediary subwaking 
 states. We may graphically represent those intermediary, 
 transient, subwaking states as follows : 
 
 In other words, in going to sleep or rising out of it as 
 well as in entering into hypnosis and its allied states and 
 coming out of them the transitory, subwaking, hvpnoidal 
 states are passed through. The subwaking states may 
 therefore be regarded as truly intermediate. The subject 
 in passing through the subwaking hypnoidal states may 
 either fall asleep or pass into hypnosis. Facts thus clearly 
 indicate that sleep-states are closely interconnected with 
 
An Experimental Study of Sleep 19 
 
 intermediary subwaking states discovered in my investi- 
 gation of the subconscious. In the study of sleep then we 
 must devote our attention to the investigation of transitory 
 subwaking states which form the transition between waking 
 and sleeping. 
 
 Chapter V 
 
 The Induction of Sleep-States 
 
 OWING to the kindness of Dr. Walter B. Cannon, Pro- 
 fessor of Physiology at the Harvard Medical School, 
 I was given the opportunity and facilities to perform 
 some experiments at the Physiological Labora- 
 tory of that institution. I wish to thank Dr. Cannon for all 
 the kindness and consideration he has shown me in the 
 carrying out of the experiments on sleep at his laboratory. 1 
 
 Guided by the work, on account of which was given in 
 the previous chapters, I undertook a series of experiments on 
 the induction of sleep in different animals. I thought it 
 might be well, since sleep belonged to animals as well as to 
 man, to start my experiments on animal life, beginning with 
 lower animals and ending with man. My experiments were 
 carried out on frogs, guinea pigs, cats, dogs, infants and 
 adults. It occurred to me to use the same methods to bring 
 about sleep under the conditions of normal and abnormal 
 suggestibility in all those various representatives of the 
 ascending scale of animal life. I consequently tried to 
 induce sleep under the conditions favorable for the bringing 
 about of the intermediary, subwaking, hypnoidal states. 
 Now I pointed out above, that the transient character of the 
 subwaking hypnoidal states was due to the variability of the 
 conditions under which they were induced. Hence the fact 
 of oscillation or instability of such states, the subject now 
 plunging into hypnosis, now into sleep, and then again 
 emerging into the light of the waking state. Hence the 
 mixed manifestations observed in the subjects, when in the 
 hypnoidal state, now presenting the traits of hypnosis and 
 
 1 I take here the opportunity to acknowledge my obligations to Dr. Morton Prince 
 and to Dr. W. B. Cannon for the many helpful suggestions given to me in the revision 
 of the manuscript. 
 
20 An Experimental Study of Sleep 
 
 now of sleep. My point therefore was to induce sleep and 
 its allied states, subwaking and hypnoidal, keeping as closely 
 as possible to the conditions of normal and abnormal 
 suggestibility. 
 
 Now I found in my experiments on the induction of the 
 intermediary hypnoidal states in man that the conditions 
 of monotony, limitation of the voluntary movements, limi- 
 tation of the field of consciousness were of the utmost 
 consequence. In my present experiments on animals I 
 followed the same line of work and as far as possible repro- 
 duced the same conditions. I tried to limit the incoming 
 sensory impressions, to limit the voluntary movements and 
 thus produce a monotonous state by the continuous inhibition 
 of new and varied stimulations. After narrowing down the 
 animal's psychophysiological activity I invariably found that 
 when I succeeded in maintaining closely the same conditions 
 which had been found favorable in human subjects for the 
 induction of subwaking states, the animal uniformly fell 
 into a passive condition closely analogous to the subwaking 
 state and in many instances into a deep sleep. The condition 
 of the animal was often strikingly similar to the one observed 
 in the human subject. The respirations and pulse were 
 lowered, while mental activity in the higher animals, alert- 
 ness of sensory and motor reactions to external stimulations 
 in the lower animals became greatly reduced and even 
 completely suppressed. In the higher animals, such as dogs, 
 a transitory cataleptic state, a state in which the voluntary 
 muscles retained the position given to them, could be 
 observed accompanied by a disturbance of respiration and 
 heart beat. The slight disturbance then subsided and 
 calmness supervened. The calm lasted but for a brief 
 period of time and the disturbances reappeared. The 
 latter were once more succeeded by calm which ended by 
 full waking state or by a deep sleep. In other words, the 
 experiments, the details of which are adduced further on, 
 allow me to draw the conclusion that I had here the typical 
 manifestations observed under the same conditions in my 
 human subjects. \ found here the manifestations charac- 
 teristic of the intermediary hypnoidal states, the animal 
 now passing into waking and now falling into sleep. 
 
An Experimental Study of Sleep 21 
 
 Of course, in the case of the frogs the interpretation of 
 the manifestations is rather uncertain. Still even in the 
 frogs as the course of the experiments advanced the results 
 stood out more clear and distinct, especially when viewed 
 in the light of the experiments performed on the higher 
 animals. 
 
 Chapter VI 
 
 Experiments on Frogs 
 
 IT is probably best to begin with the facts and give 
 their interpretation afterwards. It seems advisable 
 to give the reader a clear and full account of my 
 work as a whole, to avoid being entangled in 
 a mesh of unnecessary details. While I experimented on 
 a great number of frogs I present here but a few typical 
 experiments. The reader will thus be in a far better 
 position to get a fair view of the work and be more enabled to 
 judge critically the conclusions drawn from the experiments. 
 When the frog is put on its back, its lower lid (its only 
 eyelid) is drawn up. If kept in the same position for a few 
 minutes, the frog ceases to struggle and becomes quiet. 
 The lower lid is kept shut, but when the lid is drawn down 
 the frog becomes lively. If the frog is put on its back and 
 stroked gently, the eyes close, the lower lid being pulled up. 
 The frog becomes very quiet, but soon becomes again lively. 
 The. frog was kept on its back for a few minutes; it was 
 held down and its voluntary movements were restricted; 
 it soon became cataleptic. There was a change in the 
 respiration as shown by pneumographic tracings. 
 
 A cloth was wrapped round the frog's head. The frog 
 remained very quiet apparently in a very deep "sleep." 
 The eyelids were found drawn up. The same experiments 
 were repeated on other frogs, small and large, and the same 
 results were obtained. 
 
 When a cloth is put on the eyes of the frog so as to 
 exclude all light, the frog sinks into a state of rest. It is 
 cataleptic and can then be put in any unnatural position; 
 it does not make any attempt to change its position. The 
 frog reacts but feebly to sensory stimuli; the eyelids are 
 found to be drawn up. 
 
22 An Experimental Study of Sleep 
 
 The experiments were then somewhat modified, — 
 the eyelids of the frog were held together with collodion 
 painted over them. At first the frog struggled and was very 
 restless, but soon it became very quiet, apparently sunk 
 into deep "sleep." 
 
 The more often the frog is put in that apparent "sleep" 
 or rest-state the easier it is afterwards to induce the same 
 condition. 
 
 A big lively frog was blinded. It was easily put in any 
 position, though it would not have retained such awkward 
 postures in its normal healthy state, before it was deprived 
 of sight. It may be well to add that the experiments were 
 performed after the frog recovered from the shock of the oper- 
 ation. The blinded frog could be manipulated far more 
 easily than any other specimen of its kind. It could be 
 placed in any awkward position and would remain so 
 indefinitely until disturbed. No frog with its eyesight 
 unimpaired would have remained for a moment in such 
 awkward uncomfortable positions. The frog, for instance, 
 was hung up by its front limbs on a board, it remained in 
 the same position until disturbed. The frog was put over 
 the edge of a jar where it hung with the front limbs, the 
 body and hind legs relaxed in the jar. It remained in this 
 uncomfortable position until disturbed. 
 
 The blinded frog was left in the jar for a few days and 
 then the same experiments were repeated with the same 
 results. The frog was turned on its back, it remained in 
 the same position, as if frozen and turned to stone. The 
 flame of a match was applied to him and he responded to 
 the pain stimuli very sluggishly, but did not turn over. 
 The respiratory and swallowing movements were reduced 
 from 60 to 48 per minute. If left undisturbed, he would 
 remain in the same position indefinitely. 
 
 The frog was put in a jar; he tried to jump out of it, — 
 body and forelimbs were outside the jar, but the hind legs 
 remained in the jar dangling. He remained in this position 
 without any change. It seemed as if he fell "asleep" and 
 "forgot" about the jumping out; it reminded one of the 
 story of the sleeping kingdom. 
 
 To control the experiments on the blinded frog I took 
 
An Experimental Study of Sleep 23 
 
 a healthy frog which was not operated and closed its eyes 
 firmly. It was put in a very awkward position. It remained 
 hanging over the board without any movement for a period 
 of 5 minutes. Respirations became very slow. In this 
 position I could carry it round the laboratory without 
 disturbing it in the least. After 5 minutes it opened its 
 eyes slowly and changed its position. 
 
 The blinded frog was put in an upward sitting posture. 
 Its back was supported by a board so that it should not 
 tumble over. In this attitude it remained without change 
 for a long time. 
 
 A healthy, not blinded frog, was then taken and after 
 having closed its eyes firmly with my fingers for a period 
 of a few minutes it was put in a sitting posture similar to 
 the one given to the blinded frog. The healthy frog re- 
 mained, as if stiffened in the same position. Respiration 
 fell to 48 per minute. During the whole period of the 
 experiment the respiration and heart beats were greatly 
 reduced. Response to sensory stimuli was very sluggish; 
 the limbs were in a state of relaxation. 
 
 After a few weeks the blind frog was still alive and 
 kicking. It kept very quiet and could easily be put into 
 a cataleptic state. 
 
 The blind frog remained in the same position, when 
 left to itself. It remained in any posture given to it. When 
 put over the edge of the jar, it remained in the same position 
 without changing a single muscle. During this time it 
 reacted very sluggishly to external stimulations. Respi- 
 ration and heart beats were very much retarded. 
 
 Similar experiments were carried out by me on a num- 
 ber of frogs with the same results. In some cases interesting 
 effects of inhibition could be observed. Thus in one of the 
 actively respiring frogs with pronounced swallowing move- 
 ments the latter ceased, when the muscles of the hind legs 
 were seized and sharply and violently pressed or pinched. 
 
 Frogs were placed on their backs and then a heavy 
 weight was put on them to hold them for a few minutes in 
 the same position. The frogs soon fell into a cataleptic 
 state and remained in that state even when the pressure 
 was removed. The lower eyelids were found drawn up, 
 
24 An Experimental Study of Sleep 
 
 the eyes were partly closed. Some of the frogs when 
 released from the pressure, relaxed their extremities and 
 remained in a quiet state. 
 
 Similar experiments I carried out on a number of frogs; 
 the results were of the same character. It is interesting to 
 observe that when the frogs open the eyes and turn to their 
 usual position they remain for some time very quiet. 
 
 There is one point to which I want to draw special 
 attention and that is the significant fact that when the frogs 
 are put in the cataleptic condition, and are from time to 
 time restrained from righting themselves to their normal 
 position, they finally fall into a very quiet state, — the limbs 
 are relaxed and remain in a relaxed condition, the respiration 
 and heart beat are greatly reduced and there is little response 
 to external stimulations to which, though of slight intensity, 
 they would have responded in their normal "waking" state 
 by jumping away. In this respect I can fully confirm 
 Huebel who pointed out this fact in his excellent work on 
 the frog. 
 
 When I carried out the above experiments on the frog, 
 I was unacquainted with Huebel's remarkable work. I 
 was glad on reading that observer's experiments to find that 
 the work done by me did not stand by itself, but that I had 
 struck a path which had been trodden by a previous explorer 
 having a similar goal in view. Now when I began my 
 experiments on frogs I hesitated to speak of "sleep" in frogs. 
 When however I continued my experiments, I could not help 
 coming to the conclusion that there are such states as sleep 
 in frogs and that those states can be induced under conditions 
 very similar to those we had found in human beings. Still I 
 greatly hesitated to term the states induced in frogs " sleep ;" 
 I termed them "rest-states." I had however a lurking 
 suspicion that they might really be of the nature of sleep- 
 states found in human subjects. I was therefore glad to 
 find that Huebel had fearlessly and unhesitatingly described 
 those rest-states by the term we describe similar states in 
 human beings, — namely, sleep. I then took courage and 
 walked with less hesitation and with more confidence on 
 a path that had been unfortunately left untrodden and 
 neglected by the foot of the scientific explorer. 
 
An Experimental Study of Sleep 25 
 
 I must, however, add that I am not quite so sure as 
 Huebel is that the "rest-states," induced in the frog and 
 described in my experiments, are sleep-states, but I do think 
 that they are closely analogous to what we regard as sleep- 
 states in the higher animals. 
 
 Without knowing of Huebers work I came pretty nearly 
 to the same results. I observed as Huebel had before me 
 that frogs after they had been put in the characteristic cata- 
 leptic condition described by investigators, such as Czermak, 
 Preyer, Danilewsky and others, that the frog passed into 
 a quiet state, the limbs, though keeping apparently the same 
 position, really not being any longer cataleptic, but rather 
 relaxed, that the respiration and heart beats were greatly 
 lowered and that if the frog could be left in this state without 
 any disturbance, it would remain in that quiet condition for 
 a very long time. 
 
 I did not observe as Huebel did that the frogs put in 
 such states remained in it for over five hours, but I did observe 
 that if the environment and external stimulations could be 
 kept quiet, the frogs would remain in their passive states 
 for a very long time. Unfortunately, the place where I 
 worked was rather noisy; in fact unusually so, for the success- 
 ful carrying out of such delicate experiments. I should not 
 wonder then that I could not fully get all the results that 
 Heubel got who was working under more favorable con- 
 ditions. I am not quite ready to claim that the passive 
 states in which the frogs fall are really sleep-states, a claim 
 defended very strongly by Heubel, but I do favor Heubel's 
 statement and think that the states of the frog, after the 
 cataleptic state has passed, is very much like what is usually 
 regarded in the higher animals as sleep. 
 
 Now if we scrutinize more closely the series of experi- 
 ments carried out on the frogs, we find present the conditions 
 of monotony and of limitation of voluntary movements as 
 well as of limitation of what may be regarded in the frog as 
 consciousness, or of the limitation of the activity of the 
 sensorium by cutting off the regularly incoming sensory 
 stimulations. As a result we find something analogous to 
 what we should have expected in the human subject under 
 like conditions, namely, the presence of peculiar passive 
 
26 An Experimental Study of Sleep 
 
 states, — that is all that we are thus far justified to say of 
 them, observed and described as they are by experimenters 
 who do not have the possibility of getting the subjective 
 experience of the animal under observation. 
 
 What we find in the state of the frog is a condition 
 somewhat analogous to what we have found in our experi- 
 ments in human subjects, namely the presence of intermediary 
 states of the subwaking or hypnoidal type. The symptoms 
 observed differ somewhat, but in general they may be regared 
 as alike. We find a passive state with cataleptic mani- 
 festations. The state varies from catalepsy to relaxation 
 or what may be regarded as lethargy, and again from 
 passivity to activity, from sluggish to very lively reactions 
 in response to external stimulations. We have therefore 
 here, manifestations which remind one of like manifestations 
 in the human subject, namely subwaking, hypnoidal states 
 which are on the borderland of waking, hypnosis and sleep. 
 Of course, we should not expect to find that frogs which 
 stand so low in the scale of vertebrates would manifest 
 phenomena of the same character as the higher vertebrates, 
 but we should expect that some similar phenomena, though 
 otherwise widely different, would be present. This is pre- 
 cisely what we find in the frog. We find the general 
 characteristics, though rather vague, of what is after- 
 wards fully developed in man as the subwaking, hypnoidal 
 state. 
 
 We must remember besides that the hypnoidal state 
 is very unstable and its manifestations, having the charac- 
 teristics of waking-state, sleep and hypnosis, greatly vary in 
 different individuals and at different times in the same 
 individual. We should therefore expect that the hypnoidal 
 state would show still more radical differences from the 
 typical in the various species of animals, especially in those 
 that stand so fa-r apart from each other as frog and man. 
 What is surprising to me is not the fact of the variation and 
 great difference of the hypnoidal state in the frog as con- 
 trasted with man, but that the difference is really not far 
 greater, considering the gap that exists between the two 
 organisms. In fact, the similarity is far more striking than 
 is the difference between the hypnoidal states of the two 
 
An Experimental Study of Sleep 27 
 
 contrasted organizations so widely apart in the scale of 
 evolution. 
 
 Mv view then is that the phenomena observed in the frog 
 are hypnoidal in character. The phenomena themselves 
 as well as the conditions under which they are induced 
 warrant my view of the hypnoidal nature of the states. 
 
 In this respect we can well understand the apparent 
 disagreement of the early observers on the subject. Czermak 
 and Danilewsky regard the phenomena as being of the 
 hypnotic order, Heubel regards them as being more of sleep- 
 states, while Preyer views them as being the results of fright 
 which give in the waking-state cataleptic manifestations 
 closely similar to those observed in hypnosis. Verworn 
 who regards the phenomena as "Lagecorrectionen" due 
 to central inhibitions really does not conflict with any of 
 the views. It is simply a general physiological hypothesis 
 which may be in accord with any view, a physiological 
 hypothesis which may or may not be true; it is a hypothesis 
 far removed from the special facts and should be tested on 
 its own merits. My point of view is not a matter of hypoth- 
 esis, but describes and explains the phenomena in terms of 
 states having similar manifestations and produced under 
 the same conditions, states which are more developed and 
 stand out more pronounced in higher animals. These 
 states possess many of the characteristics of the waking 
 state, sleep and hypnosis. Hence the reason why the early 
 observers regarded the phenomena as waking states, as 
 Preyer did; others regarded them as hypnosis, a view 
 maintained by Czermak, Heidenhein, Danilewsky; while 
 other investigators regarded the phenomena as sleep-states. 
 As a matter of fact the phenomena and the conditions under 
 which they are induced make the view highly probable that 
 the different investigators are not far away from the truth, 
 but not being acquainted with the peculiar hypnoidal states 
 described, they observed the phenomena in too one sided 
 terms, in terms of sleep, or hypnosis, or of waking-states. 
 In reality the phenomena and the conditions under which 
 they are induced point strongly to the fact that the states are 
 hypnoidal in character, states which partake at once of all 
 the three apparently contradictory manifestations, — waking, 
 
28 An Experimental Study of Sleep 
 
 sleep and hypnosis. Now the manifestations of the waking- 
 state, and now the symptoms of sleep, and now again of 
 hypnosis predominate. In short, the state induced in the 
 frog under the conditions of monotony, limitation and inhi- 
 bition is a variety of the subwaking, hypnoidal states. This 
 induced hypnoidal state being intermediary in character 
 may either partake of the catalepsy of hypnosis strongly 
 modified and manifesting itself differently in the frog than 
 in the human subject, or may again go over into the passive 
 state of "sleep" or some state analogous to it. 
 
 It is perhaps of importance ' to call attention to the 
 significant fact that the first stages induced in the frog are 
 rather of an unstable character, — the frog when put on its 
 back and kept down for but a short time falls into an appar- 
 ently cataleptic state of short duration. The animal soon 
 rights itself and is fully awake as before. This instability 
 is very characteristic. Now the hypnoidal states are just 
 characterized by this fundamental trait of instability. It is 
 only when the condition of monotony, limitations of 
 voluntary movements and inhibition are sufficiently pro- 
 longed that the catalepsy becomes more or less fixed for some 
 period of time, and when this passes off, and the conditions 
 under which the frog is kept are continued still further, it is 
 only then that the frog sinks into a passive state which may 
 last indefinitely, unless brought out of it by some strong 
 stimulation. It seems to me then, that if we take all this 
 into consideration, we cannot possibly describe the state in 
 which the frog is put in other terms than what we have on 
 other occasions discovered to be the intermediary, sub- 
 waking, hypnoidal state. 
 
Chapter VII 
 
 » 
 
 Experiments on Guinea-Pigs 
 
 WITHOUT going into physiological speculations 
 let us once more return to our facts. 
 In the pathological Institute of the New 
 York State hospitals, I had occasion to carry on 
 a few experiments on guinea-pigs. One of the guinea-pigs 
 was put into a cataleptic condition by gentle stroking, 
 while another was put into a similar state by simply seizing 
 him suddenly. The guinea-pigs lost the control of their 
 extremities and could not move even when stimulated by 
 strong electric currents. After a few minutes left in the 
 same position the guinea-pigs recovered the use of their 
 extremities. The holding down of the animal to one 
 position of the limbs, the gentle stroking, or the strong 
 emotion of fear favored the condition of monotony and 
 inhibition. In my present experiments I tried something 
 similar, namely, to put the guinea-pig under the same 
 conditions of experimentation under which I put the frogs 
 and my human subjects. 
 
 A guinea-pig was bound with straps and plaster strips 
 and was left in this condition over night. In the morning 
 he was found in the same place, — he could not free him- 
 self. He was very much weakened and paralyzed. He 
 did not struggle much and could easily be put into a passive 
 state. Unfortunately it was hard to say whether the passive 
 state was due to his weakness or to the conditions under 
 which he was artificially put. 
 
 Young guinea-pig, of a few days old; very lively. I 
 took him in my hands and kept him quietly and then put 
 a blind on his eyes as I did in the case of the frogs. At 
 first he struggled, then became very quiet. Respiration 
 fell from 120 to 90 per minute. He remained in the same 
 posture for about 35 minutes. He did not respond to 
 stimuli such as intense noises. After fifteen minutes 
 respiration was regular and fell to 60 per minute. The 
 guinea-pig looked like a ball of immovable matter, — the 
 
 29 
 
30 An Experimental Study of Sleep 
 
 only thing indicating life was the regularity of the respira- 
 tions. After a few minutes I found that he started at intense 
 stimuli, but still did not change posture. As he was near 
 the end of the board his foot slipped from relaxation of the 
 limbs, he changed posture, but remained immovable. 
 After half an hour he began to stir and move his head 
 slightly. 
 
 On closing the pig's eyes there was a difference in 
 respiration, — the respiration fell and became more uniform. 
 
 I tried now to modify somewhat the experiments. I 
 found that the pigs were extraordinarily lively animals and 
 struggled a good deal. Now in my experiments on human 
 beings where there was too much opposition to the induction 
 of subwaking states, I could reduce the opposition by the 
 use of hypnotics and anaesthetics. I tried similar experi- 
 ments on my frogs, but the results were not satisfactory. 
 The anaesthetized frogs either reacted very much like 
 normal animals, or when given a somewhat larger and more 
 effective dose soon died. I attempted to paint the skin of 
 the frog with collodion to exclude stimulations of the skin, 
 but the frogs died in convulsions. When I soaked their 
 skin in chloroform or ether I had the same results. Evidently 
 the skin of the frog absorbed the chloroform or ether and 
 produced undesirable poisonous effects. Since however I 
 did have success with my human subjects under similar 
 conditions, I thought I might have some favorable result 
 in the case of the guinea-pigs. 
 
 A guinea-pig was put under chloroform for a few 
 seconds. Respiration fell to 48 per minute. Reflex 
 movements were well preserved. Eyes were partly closed. 
 The guinea-pig started every time, but did not react to sound 
 or light-stimuli, and very sluggishly reacted to pain-stimuli. 
 He shivered and then closed his eyes. About 15 minutes 
 later he began to react to stimuli. The reactions conformed 
 to Pfliiger's law 1 .- Stimulations called forth reactions on the 
 same side. About half an hour later the pig began to feel 
 pain, cried on sharp pinching of the front paw. Respiration 
 was still greatly reduced. By closing his eyes and by 
 continuous gentle stroking of his back, it was easy to make 
 
 1 See p. 87, footnote. 
 
An Experimental Study of Sleep 31 
 
 him fall asleep. He rolled up in a ball and seemed to sleep 
 quite comfortably. 
 
 Guinea-pig under ether for about a minute. Respi- 
 ration and heart-beat greatly lowered. Muscles were 
 relaxed; eyes were half closed in sleep. Later on he awoke 
 and was fully alive to external stimulations, though not so 
 lively as usual. I put him in my hand, kept him very quiet 
 and closed his eyes. He evidently fell asleep as he did not 
 open his eyes when I removed my hand from them; on 
 the whole the pig kept unusually quiet without stirring 
 a muscle. 
 
 A guinea-pig was put under ether for 30 seconds. 
 Reflex of wiping with forepaws was present. Reactions 
 to stimuli were rather sluggish. After a few minutes the 
 pig awoke, but had a tendency to go to sleep again when I 
 put him in my hand, kept him very quiet and closed his 
 eyes. He fell into a quiet sleep, his muscles relaxed; 
 respiration and heart-beat were much lowered. When 
 disturbed, he became fully awake and began to eat, but went 
 immediately to sleep again, when put in my hand and kept 
 quiet. Now and then a passing state of resistance of limbs 
 was observed. The limbs once changed often retained 
 the posture given them. This state however was far from 
 being as marked as it was found in the case of the frog. 
 
 When light was excluded from one of the eyes of the 
 animal the other eye began to contract and close; the animal 
 became unusually quiet. Anything that excluded visual 
 sensory stimuli and brought about limitation of the voluntary 
 activity of the pig produced a state very much akin to sleep 
 with now and then a slight catalepsy quickly followed by 
 relaxation of the limbs. 
 
 A guinea-pig was fixed on a board, — he kicked violently. 
 Collodion was used to fasten his eyelids together and as 
 in the case of the frog, he became quiet and ceased to make 
 attempts at fighting. 
 
 A guinea-pig breathed chloroform for two seconds 
 only. It seemed to have affected the animal sufficiently 
 to make him quiet. He did not fight; lost a good deal of 
 his liveliness. I put my hand on him, restricting his move- 
 ments. He did not resist; I then closed his eyes; he remained 
 without stirring in the same posture. 
 
32 An Experimental Study of Sleep 
 
 When I closed one eye of the animal, the other closed 
 also and the animal seemed to have gone to sleep, the limbs 
 being in a relaxed condition. 
 
 After some time he opened his eyes again; chewing 
 movements were present; active, lively and restless, sniffing 
 about in all directions. I once more took him in my hand, 
 kept him very quietly, but firmly, — his activity subsided, he 
 ceased to struggle, eyes became contracted as well as pupils; 
 finally eyes closed very slowly. The animal sank into 
 a state of torpitude. Respiration and heart-beat fell. 
 
 Thus far we may say that the experiments on guinea- 
 pigs gave results somewhat similar to those of the frogs, 
 though the cataleptic states were not so pronounced, — in 
 fact they were very transient. Still the induction of sleep 
 was brought about under conditions of monotony, limitation 
 and inhibition. It was far more difficult to bring about rest 
 or passive states in guinea-pigs than in frogs, on account 
 of the great liveliness and ceaseless activity of the pigs. 
 It may be objected that the anaesthetics somewhat modified 
 the result, because it might be claimed that the sleep-states 
 induced were really due to the anaesthetics used. This 
 objection however can be easily obviated by the rejoinder 
 that the action of the anaesthetic was only to reduce the 
 extraordinary activity and restlessness of the animal and 
 thus make it easier to induce sleep. The sleep-states 
 themselves were really produced under the same conditions 
 as were the ones induced in frogs and in my subjects. In 
 fact even when the guinea-pigs were really lively and active 
 it was sufficient to subject them to the conditions described, 
 when they gradually fell into a state very much of the 
 character of hypnoidal states and sleep. The phenomena 
 though were not so well marked as in the frogs. 
 
Chapter VIII 
 
 Experiments on Cats 
 
 IN passing now to my experiments on higher animals 
 the results seem more striking and convincing. As 
 in the case of the frogs, I can only quote some of the 
 experiments performed, it would take up too much 
 space of the present paper to quote all of them. Besides 
 little will be gained by a literal transcription of my note- 
 book, since many of the experiments are simply repetitions of 
 one another. I shall bring as many facts before the reader 
 as will sufficiently introduce him to the work and make him 
 so familiar with the experiments performed that he may be 
 enabled to follow closely the various threads that go to form 
 the main strength of the present research. 
 
 A young kitten of about six weeks, very lively, runs about 
 playfully, wide awake. When put on its back, it struggled 
 violently. I then put the kitten in a cloth, kept it firmly so 
 as to limit all the struggles and voluntary movements. At 
 first it struggled and fought, but I restrained the kitten as 
 much as possible, and then I closed its eyes for about a 
 minute. The struggles ceased gradually and the kitten 
 passed into a passive state of sleep. When I relaxed my 
 grip on its body, it remained in the same position without 
 moving a limb. At first the respirations went up and also 
 the heart-beats. But as the kitten became more passive 
 and went into deep sleep, the respirations and heart-beat 
 fell. The kitten was deeply asleep, did not react to sound 
 stimuli or to light ; eyelids were firmly closed. At first a 
 slight resistance in the outstretched paws, strongly suggestive 
 of hypnotic catalepsy, was observed, soon the paws were 
 fully relaxed and easily changed to any position, but without 
 retention of impressed posture. The sleep lasted for more 
 than twenty minutes and would have lasted longer, had it 
 not been for the fact that I disturbed the kitten's repose to 
 continue my experimental work. 
 
 The same experiments were repeated again and again 
 under the same conditions of monotony, limitation of volun- 
 
 33 
 
34 An Experimental Study of Sleep 
 
 tary movements and inhibition. The results were uni- 
 formly the same. It may be well to call the reader's atten- 
 tion to the fact that holding the kitten down firmly, thus 
 limiting its voluntary activity, is really at the same time 
 conducive to greater monotony of peripheral sensations 
 coming from the action and movements of the muscles, 
 joints, synovial surfaces and so on; so that the factor of 
 limitation largely aids the condition of greater monotony. 
 Although the pressure exercised on the animal during re- 
 strictions may be intense, still, as we have pointed out, it is 
 not so much the intensity of the sensory mass which keeps 
 up the waking state, as the manifoldness and the volume 
 of sensations and reactions ceaselessly varying from moment 
 to moment as to quantity, quality and intensity. 
 
 The kitten was restricted in its movements; it was held 
 down for some time, but it did not go easily into a quiet 
 state. I found that the best arrangement was to enwrap 
 the extremities, the hind extremities at least, in a cloth. 
 This limited the voluntary movements effectually. It was 
 still easier, when all the extremities were enwrapped in a 
 cloth. When now I put my fingers over the kitten's eyes 
 and closed them, there was little resistance and in a few 
 seconds, not more than half a minute, the little thing was 
 extremely quiet and in a minute or so it was fast asleep. The 
 fingers were then removed, the kitten's eyes remained firmly 
 shut. In fact, the eyelids resisted all efforts to open them. 
 When forcibly opened, the eyeballs were found rolled up 
 and the pupils were contracted. The kitten would have 
 probably kept on sleeping for some time, if judged by what 
 had been observed in other kittens under similar conditions, 
 had it not been disturbed in order to have the experiments 
 repeated. 
 
 The kitten was snugly put away in a cloth, and all four 
 extremities were restricted from voluntary movements. At 
 first the kitten struggled a little, but was soon quieted. I then 
 shielded the kitten's eyes with my hands, while I held it firmly 
 for a few seconds only. The kitten's eyelids became half 
 closed and finally closed fully. When the extremities were 
 tested immediately, they were found resistive and slightly 
 cataleptic. Occasionally the resistance was quite marked. 
 
An Experimental Study of Sleep 35 
 
 The cataleptic state was rather transient. In some experi- 
 ments I even succeeded in raising the paws into uncomfort- 
 able postures where they remained without change for a brief 
 period of time. After a few seconds the catalepsy of the 
 extremities passed off and the limbs were in a state of re- 
 laxation. The kitten did not react to stimuli, such as sound, 
 light or smell; even slight pinching, change of the extremi- 
 ties, shifting of the posture of the body did not produce any 
 reaction. When aroused from sleep, the kitten yawned 
 and stretched its paws, looked sleepy and reacted sluggishly 
 to external stimulations. 
 
 Kitten struggled hard when put on its back. It was 
 enwrapped in cloth and still kept on its back, where it was 
 held firmly without being allowed to turn over or even to 
 move. I then closed the kitten's eyes. After a minute it 
 remained in the same position. The kitten was lying 
 quietly on its back, though the position was rather unusual 
 and the whole attitude was very uncomfortable. The paws 
 were raised in the air and at first there were manifestations 
 of resistivity about the joints, but soon the resistivitv passed 
 off and the limbs, though raised, were really soft and relaxed. 
 A little later the paws dropped slowly and remained in a 
 state of relaxation. The catalepsy was replaced by lethargy. 
 The kitten did not react to pressure or to tickling of the 
 paws. When sounds were produced close to its ear, the 
 ear moved, but otherwise, the posture of the kitten remained 
 unchanged. Tickling of nostrils made it move its head, but 
 the kitten remained in the same posture with eyes firmly shut. 
 
 The kitten was wrapped in its cloth as usual. At 
 first the kitten was greatly excited and squealed. It was 
 rather more difficult to make the kitten quiet than it was 
 in previous experiments. The excitement was antagonistic 
 to sleep. When finally quieted, which took some time, the 
 result was even more successful than on previous occasions. 
 The kitten was fast asleep. Before going into the sleep- 
 state the same phenomenon of transient catalepsy and re- 
 sistance was quite marked. The limbs then assumed a 
 relaxed condition. It slept so soundly that stimuli that 
 would have awakened the kitten on previous occasions did 
 not disturb it at all, but simply called forth reflex reactions. 
 
'36 An Experimental Study of Sleep 
 
 The kitten slept for more than half an hour. It was then 
 rudely awakened by me. The kitten was very sleepy and 
 soon closed its eyes and sank once more into a deep sleep. 
 
 Three kittens eight days old. Eyes were open. Their 
 movements were still incoordinate. They resisted, when 
 put upon their backs. The kittens were wrapped in a cloth 
 one by one. At first they struggled violently, but after- 
 wards they became quiet and fell into a deep sleep. The 
 limbs were in a state of relaxation. No manifestation of 
 rigidity or of catalepsy could be observed while passing into 
 or coming out of sleep. The induction of sleep took some 
 time, but a few repetitions made the onset of sleep easier. 
 
 The kittens were wrapped in a cloth and their move- 
 ments were restricted. After a little struggle and spitting 
 they went to sleep. This time no symptoms of catalepsy 
 could be observed. The kittens were probably too young 
 to manifest any of these phenomena, for later the phe- 
 nomena of catalepsy during the time of going into and coming 
 out of sleep were, relatively speaking, quite marked. Closing 
 the eyes did not play such an important role in young kittens 
 as did the condition of limitation of voluntary movements. 
 In this respect young kittens behave somewhat similar to 
 young infants. 
 
 Kitten, two and one half weeks old; very lively. It 
 struggled to get free. After three minutes the kitten was 
 put to sleep; it was wrapped in a cloth and slept peace- 
 fully. On my attempt to open its eyes there was a little 
 resistance, but not marked. On examination the eyeballs 
 were not found rolled up, but they looked staring and 
 sleepy, and the pupils were contracted. The kitten closed 
 its eyes immediately after and went to sleep again. There 
 was little or no response to external stimulations of sound. 
 In the next room much noise was made by a carpenter 
 hammering with all his force. This was not favorable to 
 sleep, but the kitten was deeply asleep and remained un- 
 disturbed. The kitten slept for fifteen minutes and was 
 awakened by me for further experimentation. 
 
 The cloth has proved itself an excellent factor in putting 
 the animals to sleep. This may be due to the fact that the 
 movements are well limited without much pressure; the 
 
An Experimental Study of Sleep 37 
 
 pressure present is more evenly distributed, hence, also 
 more monotonous, a circumstance which greatly helps in 
 bringing about sleep. The conditions must all cooperate 
 to bring about monotony. 
 
 An attempt was made to put a kitten to sleep without 
 the cloth. The animal was harder to handle, it took me 
 some ten minutes before the kitten was made quiet. It 
 fell asleep but for a brief period of time, possibly not more 
 than a minute. Then it opened its eyes. Now for that 
 short period the paws were found extended, somewhat re- 
 sistive to but retentive of impressed movements. The paws 
 trembled visibly. This tremor was due to the incoordina- 
 tion of the motor activity of the kitten. 
 
 I observed in my experiments on subjects and patients 
 that sudden fright might bring about subwaking states and 
 sometimes even hypnotic and somnambulistic states. Now 
 when tested on kittens similar results were obtained. When 
 the kitten happened to be specially refractory, it was fright- 
 ened by sudden strong stimulations or by suddenly turning 
 it around and around. To my great surprise I found that 
 the kitten's struggles subsided, — the respiration became 
 lowered and the kitten was asleep. As the experiments 
 gave like results the few described will be sufficient for our 
 purpose. 
 
 When one of the kittens was very excited and in a fight- 
 ing mood, I seized it suddenly, kept it down firmly, the animal 
 became very quiet, fell into a passive state and then was 
 fast asleep. 
 
 Of three young kittens I seized one after another quite 
 suddenly. The kittens became much excited. One after 
 another was put in a cloth, their limbs wrapped all round 
 and kept down quite firmly, so that they could not move. 
 There was but little opposition and still less fighting. By 
 way of intensifying the effect they were given a couple of 
 good shakings, the little ones became quiet, and fell into a 
 sound sleep. They did not react to sensory stimuli; their 
 paws were slightly resistive at first and then relaxed. Respi- 
 ration, from being labored and quick, became quiet, uniform, 
 easy and lowered. 
 
 These experiments were repeated by me over and over 
 
38 An Experimental Study of Sleep 
 
 again and with the same results, showing that the latter 
 were not a matter of accident. In fact I found that 
 when I wanted to put the little kittens to sleep speedily, 
 to frighten them by shaking was the surest way of putting 
 them into a more agreeable mood and thus send them off 
 without delay into a sound sleep. 
 
 In the experiments on the kittens we find the phenomena 
 of the subwaking states somewhat more developed than in 
 the guinea-pigs or in the frogs. The cataleptic phenomena 
 are not so pronounced as they are in the frog, but the mani- 
 festations of the subwaking states approach more closely 
 the manifestations observed by me in human subjects. 
 The state is more hypnoidal in character, there is present 
 the transient, scarcely perceptible catalepsy which appears 
 for but a moment, giving way immediately either to sleep 
 or to the waking state. Of course, we should not expect to 
 meet with a typical, fully developed suggestibility or som- 
 nambulistic state in guinea-pigs or in kittens, considering 
 the fact that even in man, the imbecile, the idiot and the 
 mentally obtuse hardly go into any such state. It requires a 
 mind of a highly organized constitution to get into a state 
 of abnormal suggestibility and of somnambulism with their 
 accompanying manifestations. What, however, we do find 
 is the characteristic instability of the manifestations of the 
 intermediary, subwaking, hypnoidal states, having some of 
 the most general somatic symptoms of hypnosis, such as 
 slight catalepsy, but leading into a passive condition on 
 the intensification of the state. The state in which the 
 animal is plunged under the condition of monotony and 
 limitation is hypnoidal leading toward sleep. 
 
Chapter IX 
 
 Experiments on Dogs 
 
 AS we come nearer to the higher animals we find it 
 easier to interpret the phenomena under observa- 
 tion and experimentation. The subwaking states 
 become more defined and sleep is fully recognized 
 at the first moment of its oncome. Thus in dogs we can 
 more easily interpret the different motor activities in relation 
 to their subjective correlatives and accompaniments. Man 
 can so closely put himself into the subjective mood of the 
 dog he knows that he can understand apparently the 
 slightest expression of the animal's wishes and emotions. 
 The artificial selection of the most intelligent and most de- 
 voted dogs as well as the constant companionship with the 
 human race could not but affect the canine races and bring 
 the most manifold expression of their emotions, wishes, and 
 desires within the scope of human interpretation. Dogs 
 have the mental touch of man and are described by the poet 
 as dreaming in their sleep : 
 
 "Consueta domi catulorum blanda propago 
 Degere, saepe levem ex oculis volucremque soporem 
 Discutere, et corpus de terra corripere instant, 
 Proinde quasi ignotas facies atque ora tuantur." 
 Lucretius describes vividly the active dreams of the 
 hound hunting in his sleep : 
 
 "Venatumque canis in molli saepe quiete 
 Jactant crura tamen sudito, vocesque repente 
 Mittunt, et crebras reducunt naribus auras, 
 Ut vestigia si teneant inventa ferarum: 
 Experge factique sequntur inania saepe 
 Cervorum simulacra, fugae quasi dedita cernant; 
 Donee discussis redeant erroribus ad se." 
 Dogs have some imagination, even if they are not poets, 
 and cannot retort man in kind. Dogs, standing higher in 
 the scale of development, lend themselves far better than the 
 rest of lower animals for the study of sleep. As adult dogs 
 are rather difficult to manage for sleep experiments, because 
 
 39 
 
40 An Experimental Study of Sleep 
 
 of the excitement in which they are thrown and because of 
 their resistance to being handled by men other than their 
 masters, I selected for my experiments young dogs, especially 
 puppies. I did the same thing in the case of cats for the 
 same reason, as grown-up cats are still more unmanageable 
 than dogs. It is true, as Huebel has pointed out, that if the 
 master of the dog should try his hand, he would no doubt 
 succeed in putting the dog to sleep. Puppies are very docile, 
 they get easily adapted to a new person, and do not mani- 
 fest the individual liking of their master and the abhorrence 
 of strangers as grown-up dogs do. I have no doubt that if 
 a grown-up dog should be put by his master under the con- 
 ditions of monotony, limitation and inhibition, the success 
 would almost be certain in each and every case. In fact, 
 I tried the experiment on an older dog of mine with great 
 success every time I put the dog under the requisite condi- 
 tions conducive to the oncome of subwaking states and sleep. 
 I shall give an account of these experiments in this research. 
 I find that dogs, like men, easily fall into subwaking states 
 and sleep. 
 
 There is also another reason why I chose puppies for 
 my experiments. Puppies, especially very young ones, 
 sleep a good deal and not having the nervous activity and 
 distractions of older dogs are more amenable to the condi- 
 tions of subwaking states and sleep. In carrying out experi- 
 mental work it is best to select the material and put it under 
 the most favorable conditions. 
 
 We may pass now to the experiments proper. I quote 
 from my notes those experiments which are typical of the 
 rest. 
 
 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 forepaws did 
 not protrude. At first they were greatly excited by the 
 proceeding and proclaimed their indignation by loud yelp- 
 ing. 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 
 
An Experimental Study of Sleep 41 
 
 its struggles and became very quiet. Respirations 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 The puppies 
 kept on sleeping the sleep of the just. After a sleep of 
 about an hour I had to disturb the repose of the little ones 
 and wake them up, as I had to leave the laboratory, other- 
 wise they might have slept much longer. 
 
 The cloth was now uniformly adopted by me in my 
 experiments for the control of the voluntary movements. 
 Unless the little ones were wrapped in the cloth there was 
 great difficulty to restrict their activity. The puppies fought 
 like furies. One of them was specially unmanageable. A 
 few shakings quieted him. The puppy was wrapped in 
 a cloth and after a few minutes went into a deep sleep. It 
 withdrew the paws on irritation or on pinching, but the eyes 
 remained firmly shut. Respiration and pulse were slow. 
 
 The puppies were put to sleep under the same condi- 
 tions. This time they could not sleep soundly, on account 
 of the continuous noise in the next room. They woke up 
 every time, but fell asleep again. They growled in their 
 sleep, evidently reacting to the external noises, but they did 
 not wake up. One of the puppies turned on one side, 
 apparently to make himself more comfortable and kept on 
 sleeping. They were, however, to-day more restless than 
 they were on former occasions. Maybe hunger gnawed 
 at their entrails, maybe it was the noise of the school that 
 the puppies could not stand. After about a quarter of an 
 
42 An Experimental Study of Sleep 
 
 hour they woke up and looked like two little surly pups. I 
 gathered them once more up into the folds of my cloth, and 
 gently, but firmly, forced them to sleep again. They went 
 to sleep much more easily with no fighting. When passing 
 into sleep, I tested the forepaws of each of the puppies. As 
 this time the forepaws were quite free, I could observe well 
 their position, change them, and manipulate them. At 
 first the limbs showed some resistance to change of retained 
 position impressed on them, a slight cataleptic state. Then 
 the limbs relaxed and remained in this condition till the 
 end of the experiment. This time the noise in the adjoin- 
 ing room ceased and the youngsters seemed no longer dis- 
 turbed. I let them sleep for about three quarters of an 
 hour, when I began to tickle them, pinch them slightly, and 
 change the position of the paws. They began to move 
 restlessly and gradually got out of sleep. The eyes opened 
 lazily, and they evidently felt ready to go to sleep again. 
 Before waking up fully there was a slight state of resistance 
 in their forepaws, catalepsy seemed to return again. This 
 slight catalepsy in regard to retained postures and to changes 
 of the position of the extremities lasted a few seconds and 
 disappeared. Thus in getting out of sleep the puppies passed 
 once more through some subwaking state with its accom- 
 panying catalepsy. 
 
 The puppies were put to sleep again. The conditions 
 of monotony and limitation were the same as before. Fore- 
 paws were free, protruding from the cloth. When the pup- 
 pies sank into sleep, the paws were slightly resistive. The 
 least disturbance brought the puppies out of the passive 
 state. Typical manifestations of subwaking, hypnoidal 
 state were present. Respiration gradually fell, the 
 passive state became intensified, and the puppies fell into 
 a sound sleep. The paws became fully relaxed. The eye- 
 lids were firmly shut and at first resisted pulling apart. 
 When the eyelids were separated, the eyeballs were found 
 rolled up; pupils were in state of contraction. When I let 
 go the eyelids, they closed again and remained firmly shut. 
 There was almost no response to external sensory stimula- 
 tions. The puppies slept half an hour, when I began to 
 waken them slowly, again before full waking a slight cata- 
 
An Experimental Study of Sleep 43 
 
 lepsy was observed in the limbs, the puppies passed through 
 the intermediary, hypnoidal state. They looked sleepy 
 when they opened their eyes and kept closing them. 
 They stretched their little paws as after a good sleep and 
 yawned. 
 
 One of the puppies was very irritable and surly; it 
 fought like a little fury. It squealed, barked and yelped. 
 After a little jostle in the cloth it fell asleep peacefully. 
 Again a slight catalepsy of the limbs was observed for a 
 brief period of a few seconds, then relaxation set in. The 
 puppy slept very soundly; it did not react to stimuli of 
 medium intensity. Reflexes of forepaws were present and 
 when the stimuli became summated the paws changed posi- 
 tion, the body then also tended to change its posture. The 
 eyelids were firmly closed; when opened by force, the eye- 
 balls were found rolled up and the pupils contracted. 
 
 The other little puppy was more amenable to treat- 
 ment, — it did not resist, but seemed to be resigned to its 
 fate. When wrapped in the cloth, it was very good natured. 
 When I put my fingers on its eyelids and had them firmly 
 shut, the puppy remained in the same position without 
 fighting. Respiration was quiet, uniform, lowered. As 
 the puppy sank into sleep the paws were found slightly 
 resistive to bending; they were extended, but soon became 
 relaxed and remained so throughout the sleep state. The 
 puppy slept quite peacefully. Reflexes of forepaws were 
 present. It did not react to slight stimulations, such as 
 tickling or pinching of the skin, or even to pricking of the 
 forepaws. It did not react by shifting the body or by wak- 
 ing up and opening the eyes, it only moved the forepaw that 
 had been stimulated. The eyelids were firmly shut and 
 resisted opening. When opened by force, the eyeballs were 
 found rolled up, so that the whites or the sclera could be 
 well seen partly covered by nictitating membrane. The 
 dog was awakened by summation of slight stimulations. 
 
 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 
 
44 An Experimental Study of Sleep 
 
 same conditions, their paws for a brief period of a few sec- 
 onds 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 sucking and snapping movements were observed. 
 They slept for more than an hour and would have gone on 
 sleeping had not they been rudely shaken out of their peace- 
 ful repose. 
 
 The experiments were repeated over again with the 
 same results. As the puppies got older the manifestations 
 of the transient, intermediate state became more pro- 
 nounced, — 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 between waking 
 state and sleep, both on going to and coming out of sleep. 
 With the repetition of the experiments the little fellows 
 earned to go to sleep with greater and greater ease, mani- 
 festing, as time went on, more and more clearly the charac- 
 teristic symptoms of subwaking and sleep states. After 
 a time there was no need to keep their eyelids closed with 
 my fingers; it was enough to shade their eyes with my hand 
 or with any opaque body and the eyes after a few seconds 
 began gradually to close. A slight tremor of the eyelids 
 was observed as they kept on opening and closing, somewhat 
 similar to what we find in the first stages of hypnosis. Only 
 here it was not really hypnosis, but the hypnoidal state, 
 partaking of hypnosis, waking state and sleep. The pup- 
 pies did not really go into any hypnosis, but into something 
 bordering closely on the hypnotic state. Instead of going 
 
n Experimental Study of Sleep 45 
 
 into the hypnotic state, however, as the fully developed 
 human subject would occasionally do, the puppies went 
 into sleep. 
 
 What interested me most in the puppies was the fact of 
 their habituation to the sleep-procedures. They seemed 
 to like the whole procedure and had no objection to my 
 manipulations, so that after a time I even ventured to put 
 them to sleep on the table without wrapping the cloth 
 round their limbs; the little fellows went to sleep as cheer- 
 fully and as soundly as before. They lost all fear and 
 lent themselves readily to the operations. It was thus 
 sufficient for me just to put them down on their sides, and 
 it did not matter on which (they would not sleep on their 
 backs), when the puppies, of their own account, almost, 
 went into their customary subwaking and sleep-states. 
 
 Those puppies were gone and another puppy, an un- 
 trained one of the same litter, had taken their place. This 
 little fellow was about a couple of months old and was 
 a hard nut to crack. He was sturdy, fat and refractory. I 
 had quite a tussle with him. It took me more than half 
 an hour to appease him. He became quiet for a few min- 
 utes and seemed to have gone off into a passive condition 
 closely bordering on sleep, but he was soon up and in arms 
 again. Maybe the loud knocking in the adjoining room 
 disturbed the experiments. 
 
 I wrapped him all round in the cloth and shutting his 
 eyes firmly with my fingers and holding him down tightly 
 with my hands, I finally succeeded in moderating his ardent 
 temper. The loud barking gradually subsided, and finally 
 degenerated into growling. This growling really added to 
 the monotony of the sensations. The growling then dimin- 
 ished and the little fellow began to breathe more quietly, 
 the heart-beat due to excitement subsided, and the puppy 
 fell asleep. He slept quietly for about ten minutes only 
 and woke up again. His eyes looked sleepy and he yawned 
 for some time. 
 
 An attempt was made to put him to sleep under the 
 same conditions of monotony and limitation, but it was 
 difficult to quiet him. He barked and struggled and re- 
 fused to let himself be controlled. It was decided to let 
 
46 An Experimental Study of Sleep 
 
 him go for that day. This condition kept on for several 
 days. The most that could be done with him was to wrap 
 him in the cloth, hold him firmly with the hands, and have 
 his mouth shut. 
 
 I confess that at first I almost despaired of ever break- 
 ing the youngster into the game. I kept at him, however, 
 and after a long series of trials the little fellow did not meet 
 me any longer with such feelings of opposition. Finally 
 one day after a hard tussle and a few severe shakings 
 I decided to leave him to himself. To my great surprise 
 the puppy became quiet, his eyes became perceptibly nar- 
 rower, and at last he fell asleep. The sleep was very sound. 
 He did not open his eyes when I changed the position of 
 his paws, nor did he even open his eyes when I tickled the 
 paws or pricked them. The only response to those stimu- 
 lations was the reflex movement of the paws, drawing them 
 away from the direction of the stimulus. The eyes were 
 firmly shut, and when I attempted to separate the eyelids, 
 the latter resisted quite perceptibly my efforts. When I 
 did open the eyelids, the eyeballs rolled up and the pupil 
 was contracted. The puppy slept for about half an hour. 
 I decided to awaken him and see what he would do and 
 also to observe the stages which he would pass in getting 
 out of the sleep-state. The cloth was unrolled. This 
 awakened him. He opened his eyelids, stretched his fore- 
 paws and was going to sleep again; the eyes closed. On 
 testing his forepaws, there was some resistance, though very 
 slight, but it could be noticed on attempting to bend the 
 paw at the joint. The eyes opened and closed; finally 
 they opened fully and the little fellow stretched out his 
 paws and yawned with a good relish as after a delightful 
 sleep. At last then my long efforts were crowned with 
 success. The puppy did fall asleep and in waking was 
 observed to pass through the characteristic stages of hypnoidal 
 states. 
 
 The advantageous moment was then seized to push 
 the matter for all it was worth, to again induce sleep under 
 the conditions of monotony and limitation now that the 
 puppy proved so obliging and went off into sleep on its own 
 account. The cloth was wrapped round the puppy's limbs 
 
An Experimental Study of Sleep 47 
 
 holding him down firmly. I closed his eyes with my 
 fingers; the puppy, having been just awakened from his 
 deep sleep, felt more gracious and did not kick much, opposed 
 but little and in a few minutes fell into a deep sleep. After 
 sleeping for about a quarter of an hour he was awakened. 
 On awakening for a brief period the presence of the inter- 
 mediary, subwaking, hypnoidal state was observed. I 
 immediately proceeded to put him to sleep again, giving 
 him no respite and plunging him rapidly in succession 
 from waking into sleep and then again from sleep into 
 waking states. This process was kept up a few times until 
 it was quite certain that the little fellow was under control. 
 The puppy got thus habituated to manipulations as well as 
 to the rapid transitions from waking to sleeping and back 
 again. Every time he was brought out of sleep the puppy 
 was very quiet and did not resist my efforts to put him to 
 sleep again. At first I did not dare to observe closely and 
 especially to experiment on the first stages of going into 
 sleep, lest I might disturb the puppy and thus break the 
 charm, as I was anxious that he should first of all be habitu- 
 ated to the process and to the sleep-states under the condi- 
 tions of monotony and limitation and should cease to show 
 resistance. After a number of experiments the puppy be- 
 came tractable and thenceforth the experiments could 
 be carried on without any further protests and rows on his 
 part. 
 
 From now on the experiments proceeded in peace. 
 When occasionally the little fellow became obstreperous, 
 a few shakings brought him to his senses. 
 
 After wrapping the puppy in the cloth, and holding 
 him firmly with both hands, I closed his eyes with my fin- 
 gers. After a few seconds the puppy fell asleep. The 
 eyelids were firmly closed. When an attempt was made 
 to open them, they resisted; when the eyelids were sepa- 
 rated forcibly, the eyeballs were found rolled up. There 
 was contraction of the pupils and when darkened with the 
 palm of my hand, the reaction was very sluggish. When 
 the conjunctiva was touched with my fingers, there was a 
 slight reaction of closing the eyelids and slight shifting of 
 head and body, but the puppy remained asleep. He slept 
 
48 An Experimental Study of Sleep 
 
 for about half an hour and was awakened for further experi- 
 mentation. On awakening, the puppy passed as usual 
 through the transient subwaking state characterized by 
 slight catalepsy of the extremities. 
 
 The puppy was put to sleep again with the cloth about 
 his extremities; the forepaws were more or less loosened 
 for observation and experimentation. The head was left 
 protruded out of the cloth so as to observe the changes. 
 This condition was always observed in my experiments on 
 sleep, only in some cases the head was kept a little covered 
 so as to keep out the light. In this case I had the head 
 fully uncovered. My fingers were kept on the puppy's 
 eyelids, but I removed them in a few seconds. The eye- 
 lids were found partly closed and I observed a peculiar 
 tremor of the eyelids similar to that found in human 
 subjects before falling into the hypnotic state. The eyes of 
 the puppy were shaded with the palm of the hand. Gradu- 
 ally the eyelids closed tremulously. It could be distinctly 
 seen how they opened partly, and then closed again. After 
 the eyelids became fully shut, a peculiar phenomenon 
 strikingly analogous to one manifested in hypnotic subjects, 
 was observed; the puppy seemed to try to open the eyes 
 but could not do it. He tried evidently quite hard to raise 
 the eyelids, but only succeeded in raising a part of the lids, 
 thus exposing a slit of the sclera; the eyeballs in this in- 
 effectual effort of the puppy to open its eyes were seen to 
 be rolled up. The eyelids closed again. The efforts on 
 the part of the puppy to open its eyes were repeated a few 
 times and each time the attempts were in vain. The eyelids 
 then closed and remained so. This is so striking and so 
 similar to what is observed in the hypnotic subjects that one 
 is almost tempted to describe this condition as hypnosis. At 
 any rate one is justified in saying that we observe here a 
 phenomenon which is strikingly analogous to the hypnoidal 
 state. In going, then, into the sleep-state the puppy passed 
 through a state which is evidently on the borderland of 
 sleep and what in the human subject is described as hyp- 
 noidal. This borderland state forming an intermediary state 
 between waking on the one hand, hypnosis or sleep on the 
 other, is just what characterizes the subwaking, hypnoidal 
 
An Experimental Study of Sleep 49 
 
 state. There seemed little doubt that in going into sleep 
 the puppy did pass through hypnoidal states. 
 
 Another fact that may be of interest in the sleep of 
 this puppy, as well as of the other puppies under observa- 
 tion, was the shivering in going to sleep. The extremities 
 trembled when raised and a transient state of resistance and 
 catalepsy was often observed. This catalepsy was specially 
 pronounced when the forepaw or any other of the extremi- 
 ties was extended and a little manipulated. It seems as 
 if we give here a suggestion to the puppy, as is the case with 
 the state of abnormal suggestibility in the human subject. 
 I may add that these manifestations of the hypnoidal state 
 were not so marked on awakening. 
 
 After control was gained over the puppy he could be 
 handled safely. It was thought it might be well for the 
 sake of the experiment to irritate the dog a little and see 
 what would be the result. He was forcibly pressed and 
 choked very slowly so as to avoid the sudden onset of ex- 
 citement. He yelped, but it seemed that the habit of going 
 to sleep was even stronger than the excitement. In spite 
 of all the irritation the puppy soon became quiet and when 
 his hind limbs were wrapped around, he soon was disposed 
 to fall asleep. With my fingers I just covered his eyelids, 
 but did not press on them. It was just the merest sugges- 
 tion of pressure on the eyes, but the little fellow went into 
 a sound sleep. Before falling asleep I observed the usual 
 blinking of the eyes, the opening and closing of the eyelids 
 and twitching of the orbicularis palpebrarum as well as 
 the rise and fall of the eyelids until the eye became com- 
 pletely closed. On attempting to open the eyelids there was 
 great difficulty in separating them. On examination the 
 eyeball was found to be rolled up, the pupil contracted 
 and not reacting to light. The conjunctiva was found 
 almost insensitive. The dog responded to stimulations by 
 reflexes of the forelimbs and on stronger stimulations by 
 movements also of the hind limbs, but he did not wake up. 
 At first the limbs were slightly resistive, especially when I 
 manipulated them, pressing and kneading the muscles of 
 the upper front leg. The cataleptic state of the extremi- 
 ties was, as usual, only transient and the limbs remained 
 
50 An Experimental Study of Sleep 
 
 during the whole state of sleep in a condition of relaxation. 
 The same state, though slighter, was as usually, also present 
 when the dog was aroused from his sleep by a summation 
 of stimuli. 
 
 The sleep-experiments were carried out on this formerly 
 refractory puppy with great ease. In fact, the facility with 
 which sleep was induced far exceeded the experiments 
 performed on any of the animals handled before. It could 
 only be compared to the ease with which a subject on 
 repetition of hypnotization goes into hypnosis. Still it is 
 not possible to regard the sleep of the puppy as hypnosis. 
 There is no suggestibility present, nor that characteristic 
 psychophysiological plasticity of associations and dissoci- 
 ations during or after hypnosis. The state in which the 
 puppy falls is nothing else than normal sleep. Only 
 in passing into that condition there are present manifesta- 
 tions which recall the hypnotic state. The reason is very 
 simple, the puppy is passing through a state which is inter- 
 mediary in character between waking state and sleep. 
 This intermediary state is hypnoidal in nature and has 
 some manifestations which are analogous to hypnosis in 
 the higher and more developed mental states of man. In 
 the dog we have the foreshadowing of what is afterwards 
 fully found in man alone.- The hypnoidal state precedes 
 and succeeds sleep. 
 
 As I continued my sleep-experiments on the puppy, 
 it became easier and easier to put the little one to sleep; 
 so much so that after a time I could put the puppy into 
 sleep, first passing through all the stages observed, though 
 the cloth, that magic for the induction of sleep, was no 
 longer used. I put the puppy on the table, just kept him 
 quiet by patting him a little, and pretty soon off the little 
 fellow went into the land of Nod. 
 
 The puppy was put on the table, then laid down on 
 his side — he did not resist, he kept as quiet as a little lamb. 
 His eyes were shaded with a screen and the little fellow 
 marched off into sleep. To produce sleep in the puppy 
 after a few weeks' training was just child's play. The con- 
 trast to his previous unmanageable condition was great 
 indeed. It was now possible with the greatest ease to have 
 
An Experimental Study of Sleep 51 
 
 him pass from sleep to waking and from waking to sleep. 
 The contrast here was also very surprising, the puppy 
 played, ran around, barked violently and in a few moments 
 he was fast asleep with limbs relaxed and immovable, with 
 eyes firmly closed, eyeballs rolled up, pupils contracted, 
 conjunctiva anaesthetic, and all the sense-organs dulled and 
 stupefied, as if by a hypnotic or anaesthetic. In a few 
 moments more the puppy was up again, gave a yawn or 
 two and was as restless and playful as ever. The transition 
 from one state into the other was so rapid that it was almost 
 marvellous. 
 
 The puppy was found very restless, barking and jump- 
 ing, but as soon as he was put on the table, his limbs were 
 kept quiet for a few moments, his eyes shaded; his eye- 
 lids began to blink and the muscles around the eyes to 
 twitch, and the fellow began to shiver, not from fear, as 
 the heart-beat was not accelerated, but slower, and the 
 respiration was tranquil and lowered. The shivering was 
 one of the phenomena observed in puppies, when on their 
 way into sleep. What was specially interesting in the series 
 of sleep-experiments was not only the significant fact that 
 the puppy under the conditions of monotony and limita- 
 tions was going off into sleep without resistance and delay, 
 but that before going to sleep, when the eyes were about 
 to begin to blink, and the eye-muscles to twitch, the little 
 fellow raised his eyes to me and looked at me and then, as 
 if satisfied that everything was all right, off he went into his 
 sleep contentedly. This state is often observed in the hyp- 
 notic subject. 
 
 It seemed to me worth while to test whether the per- 
 sonality of the experimenter had any influence. When 
 putting the puppy to sleep, I called Dr. Cannon to see it 
 to test the phenomena of the subwaking hypnoidal state. 
 To my great surprise I found that I could not succeed with 
 the puppy as well. There was some difficulty in putting 
 him to sleep, although there was not really active resistance. 
 It took me some time before I could put the puppy to 
 sleep and then test for the hypnoidal state and show it to 
 Dr. Cannon. There seems then to be a true personality- 
 element present in the experiments. 
 
52 An Experimental Study of Sleep 
 
 I then left the puppy for about a week. I wanted to 
 see whether it would make any difference in the ease of 
 putting him into the sleeping condition. After more than 
 a week, I found that he did not submit so cheerfully as 
 before. It took me fully ten minutes to put him in a state 
 of sleep. Finally he did go into a sleeping condition with 
 all the symptoms characteristic of the subwaking and sleep- 
 ing state. In about a quarter of an hour he woke up, but 
 soon fell asleep again and slept for another half hour, after 
 which he was awakened. He seemed sleepy and looked 
 ready to go to sleep again, which he really did after I had 
 kept his limbs and body quiet for a few seconds and the 
 eyes shaded. Thus the habit was quickly re-established. 
 
 To bring the personality-coefficient, so to say, more to 
 the foreground, I decided that the dog should be put to 
 sleep under the same conditions of monotony and limitation, 
 not by me, but by another person. I asked Mrs. S. to 
 lend me a hand in the present experiments and see what 
 she could do with the puppy in putting it to sleep. The 
 puppy was kept quiet on the table without being put into 
 the cloth as I had been lately conducting my experiments; 
 but the result was not successful. Mrs S. then resorted 
 to the old conditions, namely to the cloth. The puppy 
 went to sleep, but after some considerable trouble, though 
 I must say he did not show any fight as I should have 
 expected. It was then easy enough to put him to sleep 
 without any cloth, though Mrs. S. could not accomplish 
 it as easily as I could. There is then present a personality- 
 coefficient in putting the puppy to sleep, but the coefficient 
 is very slight in the puppy at least. The conditions of 
 hypnoidal states and sleep, namely monotony and limitation, 
 are the most important. For Mrs. S. could put the puppy 
 to sleep; it was only a matter of time. Monotony, limita- 
 tion and inhibition may thus be regarded as the condi- 
 tions under which we can induce in the dog sub-waking 
 hypnoidal states and 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 
 
An Experimental Study of Sleep 53 
 
 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 hypnoidal 
 states, the slight catalepsy on falling asleep and a similar, 
 though somewhat slighter catalepsy on awakening. 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, 
 limitations of voluntary movements and inhibition. The 
 dog was very lively otherwise, but when put under the con- 
 ditions of monotony and limitation of voluntary activity, 
 he sank into a passive state and then into a state of sleep. 
 
 We see, then, that dogs are subject to the same condi- 
 tion of sleep-states as is the case with the other animals 
 experimented upon. In fact the experiments on dogs bring 
 out the fact that the conditions requisite to induce hypnoidal 
 states in men also hold good in the case of dogs. The 
 hypnoidal states, both on falling into, as well as rising from 
 sleep, are far more pronounced in the dog than in the lower 
 animals experimented upon; the states themselves come 
 up far more closely to similar states observed in men under 
 the same conditions of monotony, limitations and inhibi- 
 tion than they do in lower animals, such as the frog, the 
 guinea-pig or the cat. 
 
 Phylogenetically regarded the hypnoidal is the primitive 
 "rest-state" out of which sleep and hypnosis have become 
 differentiated. The lower the animal the more insecure, 
 the more instable are its "rest-states," The animal must 
 be on the alert in its rest, and "sleep", if at all, with its eyes 
 open, so to say. It must be quick to wake and run from 
 danger or if it cannot get away, it must "freeze and feign 
 death"; in other words it must be able for the sake of pro- 
 tection to fall into a state of catalepsy. Hence the rest- 
 states must partake of waking, sleep and hypnosis, that 
 is, must be essentially hypnoidal in character. 
 
 The experiments on dogs are more instructive than the 
 ones carried out on the other animals, because they clearly 
 bring out the general principle of monotony and limitation 
 in the causation of sleep. Diminution in the variability of 
 the volume of sensory impressions brings about the state of 
 sleep. 
 
Chapter X 
 
 Experiments on Children 
 
 THE experiments on animals were followed by experi- 
 ments on children. The subjects were of different 
 ages ranging from infants a few days old, to child- 
 ren twelve and thirteen years of age. 
 It is well known that children usually fall asleep more 
 easily than adults; they sleep longer and also more soundly. 
 This is specially the case with young children and par- 
 ticularly with infants. We know that an infant passes 
 most of its time in sleep, when it does not eat. We should 
 expect therefore that the material would readily lend itself 
 to our present purpose of experimentation, — to the induction 
 of sleep-states. Now as a matter of fact, I find that in a 
 number of my cases dealing with children it is no difficult 
 task to put them to sleep, or to induce some form of sub- 
 waking state, hypnoidal or other closely allied to it. The 
 child easily falls into a subwaking hypnoidal state which 
 may either pass into hypnosis or into sleep. When trying 
 to put children to sleep I have often obtained a hypnotic 
 condition and on the other hand when attempting to put 
 my little patients into a hypnotic state I have only suc- 
 ceeded in putting them to sleep. Before going, however, 
 into either the hypnotic or sleep-state, I observed by close 
 examination the presence of the hypnoidal state induced 
 under the conditions of monotony and limitation of volun- 
 tary movements. 
 
 Since limitation of the voluntary activity, limitation of 
 the field of consciousness and inhibition all help to a greater 
 monotony, we may characterize the whole set of conditions 
 requisite for the induction of sleep as the conditions of 
 monotony. In children and especially in infants voluntary 
 activity and the field of consciousness are undeveloped and 
 limited, we should expect that the child would form a far 
 better soil than the adult for the induction of the interme- 
 diary sub-waking states and sleep. This is precisely what 
 we find to be the case. 
 
 54 
 
An Experimental Study of Sleep 55 
 
 Moreover, the mind of the child, and more particularly 
 of the infant, specially depends on muscular activity and 
 on the wealth of incoming sensory impressions. That is 
 why the child and the infant take such delight in motor 
 activity, — in tasting, testing, and handling things. If now 
 the motor activity is limited and the main source of sensory 
 impressions, such as sight, is restricted, and if the environ- 
 ment is kept in a state of monotony, such as darkness and 
 lack of auditory stimulations, or monotony is brought about 
 by a continuous noise and buzzing of some instruments 
 producing a uniform noise, the child, on account of the 
 poverty of its inner mental life, easily falls into a subwaking 
 hypnoidal state and then into sleep. 
 
 This ease of induction of sleep is furthered by the com- 
 paratively small amount of variability of conscious activity 
 present in the child — the variability of mental content being 
 an important factor in keeping up the freshness, continuity 
 and qualitative intensity of consciousness. Now as the 
 child depends entirely for the variability of its consciousness 
 on muscular activity and external impressions, we can well 
 realize that when those sources become limited and monot- 
 onous, 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 mental life to fall upon; it 
 has little, if any inner resources; that is why it falls an 
 easy prey to sleep and hypnosis, when the external resources 
 lose their variability, become uniform and monotonous. 
 
 It may be well, however, to point out the fact that the 
 conditions of sleep are somewhat different in the case of 
 infants of a few days or of but a few weeks old. Young 
 infants sleep most of the time. The waking periods are 
 brief and alternate with long periods of sleep. Really the 
 infant's state is one of sleep and he only wakes to eat. 
 We may characterize the infant's waking states as feeding 
 periods. The perceptual world may be regarded as practi- 
 cally non-existent for the infant — ego and non-ego are 
 absent. The external world is in a chaotic state with no 
 interests, even instinctive ones, as yet present. The sen- 
 sory organs are as yet undeveloped and the sensory elements 
 are all incoordinated and unrelated. Even the raw ma- 
 
56 An Experimental Study of Sleep 
 
 terial going to make up the future world of the individual 
 is still in an extremely imperfect state. In short, the 
 material presented by the undeveloped sense-organs is 
 chaotic, undifferentiated and is at its minimum. There 
 is really no external world for the infant and whatever sen- 
 sory impressions are present lack meaning and interest. 
 
 But if the sense-material coming from the sense-organs 
 which is to build up the infinite wealth of the external 
 world is still undeveloped and lacks all significance, it is 
 quite different with the sensations coming from the internal 
 organs, from the viscera. The visceral, organic sensations 
 stand out in the foreground of what may be regarded as 
 the infant's consciousness. Visceral, sensory material forms 
 the main substance of the infant's universe. Ccencesthesis 
 plays the predominant, if not the only role, in the life of the 
 newborn. We can fully realize the importance and signi- 
 ficance of ccenaesthetic sensations in the case of the infant, 
 because the processes of growth and nutritive functions 
 are all engrossing. The newborn is a vegetative being; 
 it is all belly, stomach; it is a little glutton, it has to grow 
 and that very rapidly; it lives for that purpose — it eats and 
 sleeps. The waking periods are sparse, short and far be- 
 tween, the infant wakes to eat, and when filled to the point 
 of regurgitation, it sleeps. 
 
 In this respect it may be well to observe the character- 
 istic motor reactions of the newborn; the sucking move- 
 ments are the only ones that are well coordinated, respond- 
 ing regularly to external impressions. Thus in my experi- 
 ments I have long ago described the interesting fact that 
 in his early life the newborn responds to external stimula- 
 tions with sucking movements. If the infant, for instance' 
 is put to the breast and has his fill and the sucking move- 
 ments stop, they will again be reinstated by any stimula- 
 tions of his sense-organs. Make noise close to the infant's 
 ears or throw some rays of light on his eyes, or tickle him, or 
 cause him pain, or tug at the nipple, and the infant responds 
 with sucking movements. In other words, all reactions 
 of the newborn are coordinated and essentially adapted 
 to nutritive purposes. Nutrition and its psychic correla- 
 tive, ccencesthesis, form the essence of the infant's early life. 
 
An Experimental Study of Sleep 57 
 
 It is therefore clear that the conditions of monotony of 
 external sensations and of limitations of voluntary activity, 
 an activity really absent, as well as limitation of the field 
 of consciousness, can hardly be of any import in the young 
 infant. The gnawing of hunger, intestinal discomfort and 
 pain play the only important role. In the early life of the 
 baby visceral activity and its concomitant ccenaesthesis 
 possess the greatest amount and intensity of qualitative 
 variability that keep up the limited consciousness of the 
 waking state. When the child is hungry, it is fidgety, cries 
 and is awake; when hunger is appeased, the waking state 
 lapses and the baby falls asleep. The waking state is a 
 brief passing phase in the feeding of the baby, a feeding 
 phase which begins and terminates in sleep. 
 
 If now we take all that into consideration, we should 
 not expect to meet with clearly defined subwaking states 
 and sleep under the conditions of monotony and limitation 
 in the case of the newborn as we find it to be the case in 
 the lower animals a couple of weeks old, or as we find it in 
 the fully developed man. The young of the lower animals 
 have a shorter training period and have a far larger amount 
 of ready made and easily developed instincts or psycho- 
 motor reactions than the baby. When the newborn is put 
 under the conditions of monotony and limitation of the 
 incoming external impressions and under restriction of vol- 
 untary activity which does not as yet exist in him, the results 
 are necesarily unsatisfactory. If the infant is full to the 
 point of regurgitation, it goes to sleep, and if it is hungry 
 the closing of the eyes and the attempts to hold it down by 
 force are often quite ineffectual. The baby keeps on cry- 
 ing to the great discomfiture of the experimenter. The 
 easiest and possibly the best way to bring about monotony 
 in the newborn is to soothe the youngster's bowels. It 
 again the young baby has indigestion, stomach-ache and 
 cramps, closure of the eyes and holding the little one quiet 
 without permitting him to kick will hardly do. In such 
 cases the best way is to bring about monotony and limita- 
 tion of ccencesthesis. Giving the baby to suckle may appease 
 temporarily the active peristalsis of the intestines and the 
 little fellow may pass into the land of Nod; or we may press 
 
58 An Experimental Study of Sleep 
 
 uniformly on the abdomen and keep on rocking the little 
 body at a uniform rate. By thus effecting a monotony and 
 limitation of the bowel-consciousness and intestinal activity 
 we can bring about a state of sleep. Still, even in the very 
 young infants I succeeded, when the little one happened to 
 be specially well disposed, in putting it to sleep by keeping 
 it very quiet and closing its eyes. In one case I succeeded 
 in putting to sleep a refractory infant under the usual con- 
 ditions of monotony and limitation by closure of eyes and 
 holding down the baby's extremities from being too active. 
 Usually, however, in very young babies I somewhat modi- 
 fied my proceedings of monotony and limitation by address- 
 ing myself to the baby's inner intestinal consciousness. In 
 older babies and young children of over a year, I did not 
 vary my usual proceedings in the induction of sleep under 
 the conditions of monotony, limitation of voluntary activity 
 and of the field of consciousness. 
 
 We may now pass to the experiments. I shall follow 
 here the same course as in my account of the experimental 
 work performed on the lower animals, I shall not burden 
 the reader with unnecessary details, but shall give a few 
 cases of experiments, typical of the rest. 
 
 Boy of twelve days; he was quiet; he looked into 
 empty space, seemed not to be specially hungry nor ill dis- 
 posed. I covered his eyes with my hand and restrained 
 the movements of his limbs. He wriggled a little under the 
 restraint, but soon became very quiet. When after a min- 
 ute's time I removed my hand from his eyes, the eyelids 
 remained shut. Breathing was quiet and uniform. I 
 tried to pull apart the eyelids and found them resistive. 
 When I forcibly separated his eyelids, I found the eyeballs 
 rolled up, pupils contracted. He slept this way for a few 
 minutes. When he awoke I made a second attempt to put 
 him to sleep, but this time with no success. The little 
 fellow wriggled and squirmed. The eyes rolled incoordi- 
 nately and looked vacantly into space. Closure of his eyes 
 was of no avail. I then modified the procedure, patted 
 his back, soothed his belly, and shut out the light from his 
 vacantly blinking eyes. Gradually the little man relaxed 
 his eyelids, began to work them and fell asleep. This 
 
An Experimental Study of Sleep 59 
 
 time he slept for about a quarter of an hour. I then awak- 
 ened him by summation of slight stimulations. During 
 the course of awakening, I observed a short state of resis- 
 tance in the extremities. He was again put to sleep in the 
 same way and when going into sleep the same state of re- 
 sistance and catalepsy of the extremities was observed. The 
 sleeping state was very deep, inasmuch as the little fellow 
 was not disturbed by any sensory stimulations and only a 
 good shaking brought him out of this deep state of sleep. 
 
 A girl of ten days; very quiet. I restrained her motor 
 exuberance and with the other hand I closed her eyes; she 
 at first resisted and cried, but after a couple of minutes 
 she fell asleep. Respiration, quiet and equable. Eyelids 
 resisted attempts to pull them apart. Eyeballs were found 
 rolled up; pupils were contracted. I made another attempt 
 and found it somewhat more difficult, but the child became 
 quiet, had eyes closed for a couple of minutes and opened 
 them again. The third time the success was even less 
 marked. I then once more resorted to my method of back 
 patting, bowel-soothing, by rubbing and patting the abdomen 
 and monotonous rocking movements. The little girl was evi- 
 dently pacified and went to sleep. When falling asleep, there 
 was a short stage of catalepsy, the raised hand remained for 
 a short period, a few seconds, in the position given to it, then 
 a state of relaxation set in. This relaxation of the limbs did 
 not persist during sleep, but now and then I could succeed 
 in giving a cataleptic attitude to the arm. Soon the arm 
 dropped and then again it was possible to put it into a cata- 
 leptic condition. The sleep was evidently not stable; the 
 little girl apparently kept on oscillating between sleep and 
 waking state. It seems to me, however, that it is more 
 probable that the sleep-state in young infants is not differ- 
 entiated as it is in the case of adults or of older children. 
 The phenomena of sleep also present some characteristics 
 of hypnosis and hypnoidal states, possibly, because the 
 states of hypnosis proper are as yet embryonic — hypnotic 
 or hypnoidal manifestations thus appearing in sleep. 
 
 Boy of ten days. I had great difficulty in putting 
 him to sleep by the ordinary methods of closure and re- 
 striction of muscular activity. I had to resort to my modi- 
 
60 An Experimental Study of Sleep 
 
 fied method — patting, tapping and rocking until he fell 
 asleep. In passing into sleep there was a slight state of 
 rigidity and catalepsy of the limbs which soon changed to 
 one of relaxation, but in the middle of sleep, when tested 
 again for catalepsy, he developed one but it passed off and 
 could not be again noticed until several minutes later I 
 tested during that interval; limbs were found to be in a state 
 of relaxation. 
 
 The interesting fact about the infant's sleep is that 
 once asleep the infant is not so easily roused. This fact 
 is sometimes very striking, especially, when the child has 
 had its fill, and still more, when it has had its bath. To 
 arouse the infant from its sleep is then pretty difficult and 
 I have worked hard over the baby before I could disturb 
 its peaceful repose. Some of the infants I have occasionally 
 found so deeply immersed in sleep that even shaking could 
 not arouse them. I had to give up all attempts to bring 
 them out of the state of Nirvana and had to wait for a more 
 favorable occasion. 
 
 Girl seven days old. Ordinary ways of putting to 
 sleep did not work here and I had to resort to the rocking, 
 patting and tapping before my efforts were crowned with 
 success. The girl fell asleep in a state of rigidity and cata- 
 lepsy soon replaced by relaxation. The eyeballs were rolled 
 up, but the child was restless. I put her again under the 
 same conditions of monotony and this time she slept more 
 peacefully — I had in fact, some difficulty in waking her. 
 The state of awakening was characterized by a greater resis- 
 tance of the limbs than the sleep-state. Still, even in her 
 sleep I could now and then discover a cataleptic state. The 
 sleep of the infant appears to have a mixed symptomatology 
 of sleep and hypnosis. The characteristic manifestations of 
 sleep, however, predominate. 
 
 Boy two weeks old. I left him in the same position, 
 but only shut his eyes forcibly with my fingers for not more 
 than twenty seconds. He opened the right eye after thirty 
 seconds, and the left eye remained closed for a minute 
 and a half. This incoordination is observed in young 
 infants. He did not fall asleep, however, before I tried 
 the monotonous rocking, the baby being placed with his 
 
An Experimental Study of Sleep 6 1 
 
 belly downwards resting on the palms of my hands thus 
 causing a uniform pressure. In sleep I observed a catalep- 
 tiform state. Hands remained in the attitude given to 
 them. This lasted for but a few seconds. 
 
 I can induce sleep in the boy by the following pro- 
 cedure which is really another modification of the conditions 
 of monotony and limitation of muscular activity. I either 
 rock him for a time, while sitting quietly in the chair or 
 take him in my hands and walk around with him, which 
 also induces monotonous rocking movements. During all 
 this time I sing to him some monotonous ditty. Sleep is 
 more rapid in its onset, when the belly is pressed with my 
 hands uniformly. The boy's eyes begin to close, first 
 becoming as if fixed, hazy and vacant. He closes the eye- 
 lids, opening and closing them alternately, the eye is fixed 
 in the same direction. The eyelids then close, then half 
 open. The slit of the eye becomes narrower and narrower 
 and finally the eyelids close and open no more; the little 
 fellow is sound asleep. If his position is left unchanged, 
 he remains asleep for a very long time. If, however, he 
 is put in the crib, he wakes in about five or ten minutes. 
 
 When the boy is six weeks old, I can induce in him 
 sleep, by simply closing his eyelids and singing to him some 
 monotonous ditty. When the boy is not tired and has had 
 a good sleep before, he falls into a peculiar state. He is 
 apparently not asleep and still he is unable to open his eyes 
 for a couple of minutes and even more. When he is fatigued, 
 he immediately goes into a deep sleep. 
 
 Boy three months old. Can easily be put to sleep by 
 monotonous stimulations usually of the character described. 
 When asleep, he is slightly cataleptic; the lethargic condi- 
 tion, however, predominates. The limbs remain for some 
 time in the position given to them, although the position 
 is a very uncomfortable one. When he rapidly falls into 
 deep sleep, he often retains the limbs, especially the arms 
 in the same position, however awkward, in which they were 
 put at the moment when he fell asleep. 
 
 In following the course of the child's sleep-states, I 
 find that between the sleeping and waking states there is 
 frequently, in fact there is almost always present, an inter- 
 
62 An Experimental Study of Sleep 
 
 mediary period of semi-waking, semi-sleeping state, or what 
 is found by me to be present in lower animals as well as in 
 man, when falling asleep, namely a subwaking, intermediary, 
 hypnoidal state. This state is of long duration, sometimes 
 lasting several minutes. It begins with the contraction of 
 the levator palpebrarum, with twitching and trembling of 
 the eyelids, the eyes gazing vacantly into space. The eye- 
 lids open and close unequally, the eyeballs begin to turn 
 up, the pupil is contracted. If in this state, he is addressed 
 in a caressing way with which he is familiar and which in 
 the full waking state he greets with a smile and a kick, he 
 now starts violently, the limbs going up, and he utters his 
 peculiar cry of great fright. Often, however, when he is 
 in this intermediary hypnoidal condition instead of passing 
 back to the waking state, he falls into a deep sleep. When 
 passing from this hypnoidal state into sleep, he is often 
 seen to smile and almost laugh, occasionally he makes 
 movements of mastication, sometimes gives a start and a 
 cry, and keeps on sleeping. It is a form of hypnagogic 
 or even dream-hallucinations. 
 
 As to the states which form the transition stages be- 
 tween sleep and full awakening or the intermediary states 
 in his getting out of sleep, I have often had the opportunity 
 to observe the following spontaneous manifestations. When 
 the soundly sleeping child is awakened by a noise, he throws 
 up his arms, as if in fright, half opens his eyes and falls 
 immediately asleep again. The fingers of the hands remain 
 open and extended, as if in a cataleptic state. When I try 
 to close them, I find them resisting and after a time they 
 close gradually. The rest of the body is in a state of 
 relaxation. I observed it accidentally as the result of an 
 unintended noise, but I since tried to reproduce some similar 
 sudden noises and obtained like results. 
 
 When the boy was three and a half months old, I put 
 him to sleep under the usual conditions of monotony and 
 limitations of muscular activity. He fell asleep, his right 
 hand and fingers remaining in cataleptic state, he kept them 
 in the same position when he went to sleep. The fingers 
 were outstretched and the arm raised. I tried to bend one 
 of the fingers, there was no resistance, but curiously enough 
 
An Experimental Study of Sleep 63 
 
 as we find it to be in hypnosis, the finger soon returned to 
 its former position. The arm remained in the raised posi- 
 tion for about three and a half minutes and then gradually 
 dropped. The child remained quiet in this position of 
 fully relaxed limbs for about four minutes then suddenly 
 gave a subdued cry of distress, probably due to some dream; 
 the arms went suddenly up, especially the left one which 
 remained in a raised position with fingers tightly closed. 
 This lasted for about two minutes and a half. I tried to 
 open one of the fingers, and met with no resistance. I kept 
 the finger in state of extension for about a minute: as soon 
 as I let the finger go, it returned to its original bent position. 
 I soon observed him roll his eyeballs under the still tightly 
 shut eyelids; then he opened his eyes, smiled at me and 
 fell asleep again. As he was falling asleep with eyelids 
 closed I could see the eyeballs roll, while the face retained 
 its smile for a couple of minutes longer, as if smiling in his 
 sleep at me. The state is evidently an almost fully devel- 
 oped subwaking, hypnoidal phase, bordering on waking, 
 hypnosis and sleep. In fact we observe here already the 
 suggestibility of hypnosis which is on the way to become 
 differentiated from sleep and hypnoidal state. 
 
 We may now give a rapid review of experiments carried 
 out on older children ranging from the age of four to the 
 age of fourteen. The hypnoidal states become more marked, 
 the hypnotic and even somnambulistic states come to the 
 foreground, and we find that when sleep is induced we often 
 get mixed manifestations of a subconscious order. Mixed, 
 however, and still ill-defined as they are, when compared 
 with the adult states, both the subconscious and sleep states 
 are induced under similar conditions of monotony and limi- 
 tation of voluntary movements. In trying to induce sleep 
 we may get a subconscious hypnotic state and on the other 
 hand in making an attempt to bring about a hypnotic state, 
 we may get a state of sleep. A good deal depends on the 
 fact whether or not we have eliminated the other conditions 
 requisite for hypnosis, but not for sleep. The indispensable 
 conditions, however, both for hypnosis and sleep are mo- 
 notony and limitation of voluntary activity. These condi- 
 tions are all the more indispensable as we have demonstrated 
 
64 An Experimental Study of Sleep 
 
 from our experiments that in order to reach either hypnosis 
 or sleep the intermediary, subwaking, hypnoidal state must 
 first be passed through. This intermediary state between 
 waking on the one hand and sleep and hypnosis on the other, 
 can only be induced under the conditions of monotony and 
 limitation of voluntary activity. 
 
 A boy of four was put in a dark room; the metronome 
 was set going, beating slow measure. The child was 
 told to lie down on a lounge, stretch out his hands and 
 legs and keep perfectly quiet. His eyes were then shut. 
 After a few minutes his respiration became lowered and 
 regular. He ceased to reply when talked to. At first 
 his arm showed some slight rigidity, but soon after, the 
 arm fell into a state of relaxation. He was not in a hyp- 
 notic state as he did not answer any questions and did not 
 take any suggestions. When after a quarter of an hour 
 he was awakened, he did not remember anything about 
 talking to him, nor could we obtain it of him by any methods 
 reaching the subconscious. He was really asleep and did 
 not perceive anything during that period. These experi- 
 ments were repeated a number of times with the same 
 results. I observed that unlike hypnosis which can be 
 induced in rapid succession, one state not differing very 
 much from the other, in this particular case as the induction 
 of the state was repeated, it was more difficult to bring it 
 about, the state became lighter and lighter and the child 
 was brought out of it by talking to him. 
 
 Boy of seven. I put him in a darkened room. My 
 electric battery was set going. I told him to keep quiet and 
 shut his eyes. After a few minutes he began to yawn, I 
 told him to stop. He stopped and I soon observed that his 
 little hand clutched mine convulsively, I tried the arm, 
 raised it; it remained in the same position. I then chal- 
 lenged him to open his eyes. He could not do it. I let 
 him alone in a very passive condition; respiration regular 
 and quiet. When after ten minutes I came to him again, 
 I called him by name; he did not answer. When I began 
 to talk to him, he woke up. During the ten minutes he 
 passed into sleep. This transition from hypnosis into sleep 
 was effected through the intermediacy of the hypnoidal 
 
An Experimental Study of Sleep 6^ 
 
 state which forms the borderland of the waking and sleeping 
 states. The general conditions of monotony and limitation 
 of voluntary activity that favor hypnosis also favor sleep. 
 
 Boy nine years of age. I put him into a chair, told 
 him to be quiet and then closed his eyes. He was passive, 
 answered my questions; could open his eyes when chal- 
 lenged. When, however, left alone with his eyes shut and 
 his limbs relaxed, he was found to be fast asleep. He did 
 not answer any questions, did not take any suggestions, 
 did not react to stimulations of medium intensity. When 
 spoken to sharply, he woke up. Both before and after the 
 sleep-state there was a short period when the passivity 
 was quite marked and some resistance as well as disposition 
 to leave the limb where it was placed, although he changed 
 the position of the limb when challenged. In passing then 
 into sleep as well as out of it he passed through the inter- 
 mediate hypnoidal state. 
 
 Girl of thirteen. When put under the conditions of 
 monotony and limitation of voluntary activity, she fell 
 from the transient hypnoidal state into hypnosis and thence 
 into deep somnambulism. After an hour, when left to the 
 monotonous state of her somnambulistic consciousness, she 
 passed into typical sleep, as she ceased to answer ques- 
 tions and woke up when the questions and suggestions were 
 given to her in the usual insistent way. From somnambu- 
 lism she passed into sleep. On other occasions, when closely 
 watched, it was observed that this transition was effected 
 through the intermediary hypnoidal state. The girl passed 
 from the waking state into hypnosis and somnambulism 
 and then again back into the hypnoidal state and then fell 
 into sleep. 
 
 Boy aged thirteen. I put him into a quiet state. Met- 
 ronome was beating slowly. Voluntary movements of the 
 boy were restricted. The boy was then told to close his 
 eyes. I put my fingers over them and kept them shut for 
 a few minutes. When I raised my hand, I found that his 
 eyes remained closed. His arm, when raised remained in 
 the same position. When his arm was bent, he could not 
 extend it, but when after a few minutes I began to talk to 
 him, he woke up. He was evidently in the hypnoidal state 
 
66 An Experimental Study of Sleep 
 
 on the way to hypnosis or to sleep. On another occasion 
 he actually fell into hypnosis not being able to move his 
 eyelids or his arms and even took various suggestions. After 
 a few minutes he ceased to be in communication with me 
 and when suggestions were given to him as they had been 
 given to him before, he did not take them, but woke up 
 when loudly spoken to. In other words he fell asleep, and 
 the loud voice disturbed his sleep. 
 
 Boy of fourteen; he had difficulty in going to sleep 
 under the conditions of monotony and limitation, but when 
 these conditions were long continued, he finally went into 
 the hypnoidal state. As I feared to disturb him by too 
 much questioning I left him without change to his monoton- 
 ous environment. After about a quarter of an hour he 
 was fast asleep, snoring in the chair. 
 
 Thus we find that in infants and children, as in the 
 lower animals, sleep, hypnosis, and hypnoidal states are 
 intimately related, sleep presenting complex manifestations 
 of subconscious states which become fully developed in the 
 adult. 
 
Chapter XI 
 
 Motor Reactions and the Nature of Sleep 
 
 BEFORE we conclude the account of the experi- 
 ments it may be of interest to make a brief state- 
 ment of a statistical inquiry in regard to our mode 
 of going to sleep. It is usually supposed that 
 the course and mode of our activities are due to voluntary 
 decisions, that they are irregular, changeable with mood 
 and caprice as our whimsical will is. We are free agents 
 and anything we decide to do we can do in any old way; 
 we do it just as we please and it does not matter to us what 
 the course and arrangement be, provided the will wills it 
 so. As a matter of fact we are far more creatures of habit 
 and instinct than of reason and will. This holds especially 
 true of our fundamental reactions, such as the induction of 
 sleep. If we ask the ordinary person on which side he goes 
 to sleep or on which side he falls asleep most comfortably, 
 the question puzzles him at first. At the first blush it seems 
 to him he can go to sleep on either side; it does not matter. 
 When the question is repeated to him and made clear and 
 he begins to think about it, he soon finds out that he has 
 a definite way of going to sleep. Should he try to go to 
 sleep in a somewhat different manner, he would find it very 
 difficult to fall asleep. We have definite ways of reactions 
 which are due either to habit or to the structural arrange- 
 ment and mode of function of our organism. 
 
 Manaceine in studying motor reactions in sleep has 
 found that right-handed people react in their sleep with 
 the left hand, while left-handed react with their right hand. 
 I have similarly experimented on human subjects and could 
 not confirm Manaceine's results. In my experiments on 
 infants I found that in early infancy the reactions in sleep 
 differ but little from that of waking state. The reactions 
 are undifferentiated, but I found that later on in the course 
 
 6 7 
 
68 An Experimental Study of Sleep 
 
 of the child's development, the motor reactions mostly con- 
 form to Pfluger's laws of reflex action. 1 To quote from my 
 notes : 
 
 Boy two weeks old; sound asleep. I tickled his left 
 nostril: bilateral reaction, both hands are thrown up at 
 once. When the tickling is more intense or more persistent 
 and prolonged, motor reactions in both legs are induced. 
 The same holds true in the case of the tickling of the right 
 nostril, the reactions are bilateral and become more diffused 
 bilaterally, if the stimulus is more prolonged or more intense. 
 
 The baby reacted in the same way in the waking state, 
 so that there was no difference in the reactions of the two 
 states. 
 
 When the baby is fast asleep, I tickle the right temple, 
 the response is a slight reaction with the left hand. This is 
 really accidental. On other similar occasions the reaction 
 is of the right hand and sometimes the reaction is of both 
 hands and also of both legs, according to the intensity or 
 to the cumulative effect of the stimulation. 
 
 I invariably found that a slight stimulation given the 
 first time produced a reaction, while a second and third 
 stimulation of the same intensity often produces no result. 
 
 (*) The following are Pfluger's laws of reflex action. 
 
 (I) Law of unilateral reflexes. 
 
 If peripheral stimulations cause contraction in only half of the 
 body, the contraction always occurs on the same side as the stimulus, 
 and in general those muscles contract whose nerves arise from that 
 segment of the cord, to which the irritated sensory nerve belongs. 
 
 (II) Law of reflex symmetry. 
 
 If the effects of stimulating a sensory nerve upon one side extend 
 to the other side, only such motor fibres are called into activity which 
 correspond with those which are already excited on the stimulated side. 
 
 (III) Law of unequal contraction on the two sides. 
 
 If the contraction is unequal on the two sides, the stronger reflex 
 is always on the side of stimulation. 
 
 (IV) Law of reflex irradiation. 
 
 (1) When stimulation of a cerebral nerve causes reflex contrac- 
 tion, the motor nerve concerned is invariably either in the same level 
 as the sensory nerve, or it is further downward toward the medulla 
 oblongata. (2) When stimulation of a spinal nerve causes reflex con- 
 traction beyond its own segment, irradiation always takes place toward 
 the medulla oblongata. 
 
 (V) The law of three locations of reflex contractions. 
 
 Upon stimulation of a sensory nerve, reflexes can occur in only 
 three parts of the body. These are: 
 
 (a) at the level of the stimulated nerve. 
 
 (b) in parts innervated from the medulla oblongata. 
 
 (c) in the whole body. 
 
An Experimental Study of Sleep 69 
 
 Boy six weeks old. Tickling of the left ear excites at 
 first movements in the head, in the trunk and then in both 
 hands; when the stimulation is continued, the whole body 
 becomes involved in the reaction, then the left hand is 
 raised. The same holds true in the case of the right ear, — 
 the movements are first in the head, then spread to the 
 trunk, then to the lower extremities, then only to the side 
 specially stimulated. In other words the reaction is at first 
 diffused and then only becomes more special, — the hand is 
 raised corresponding to the side stimulated. This mode 
 of reaction holds true both in waking and sleeping states. 
 
 Boy twelve weeks old. I observed an interesting phe- 
 nomenon which may be described as that of associated 
 movements. The infant has both hands in his mouth. 
 When one hand is taken away from the mouth the other 
 goes off simultaneously, as if an invisible power has pulled 
 it away at the same time. 
 
 Boy thirteen weeks old. When he was asleep, I tickled 
 his left temple, he reacted with the left hand. Tickled his 
 right temple, reacted with the left hand again. When the 
 stimulus became more intense and prolonged, he moved 
 his head, left hand and also the right hand. 
 
 I tickled the left foot when the boy was asleep, both 
 hands reacted, the left hand having the start; I tickled the 
 right foot, both hands reacted, the left hand having the start 
 again. 
 
 Tickled the left temple; moved right hand; tickled 
 right temple moved right hand again. The reaction is 
 indeterminate, — sometimes it is bilateral and sometimes 
 crossed. There actions do not conform to Pfliiger's laws. 
 On the whole bilateral reactions predominate. 
 
 When the child was asleep, I passed a pencil over the 
 whole length of the left side of his face, — he reacted with the 
 left hand first and then started with both. I passed the 
 pencil over the right side of the face, he threw up both hands, 
 the right having the lead. 
 
 Now and then one can begin to observe the manifesta- 
 tion of Pfliiger's laws. When the child was asleep, I tickled 
 his right foot; he drew away the foot. When the stimula- 
 lation is slight, the right foot alone reacted; when the 
 
JO An Experimental Study of Sleep 
 
 stimuli became summated he also reacted with the right hand. 
 The same holds true, when the left foot is tickled, — on slight 
 stimulations the left foot is drawn away; on continuous 
 stimulation the left hand also reacts. 
 
 Reactions of four months' old babies and older con- 
 formed more and more to Pfliiger's laws. 
 
 Experiments on older children give results of like 
 character. Boy of seven years; when asleep, I tickled the 
 right side of his face, the right hand reacted; I tickled the 
 left side of face, the left hand reacted. When stimulations 
 became summated or more intense the whole trunk reacted. 
 
 In experimenting on adults in the waking state the 
 results are somewhat uncertain. When touching with a 
 moistened object the right side of the face, for instance, and 
 telling the subject to wipe it immediately, sometimes the 
 right and sometimes the left hand reacts. One can often 
 observe that when the subject reacts to sudden irritations, 
 Pfliiger's laws hold good; and sometimes one can observe 
 reactions with the left hand alone, the right hand being used 
 for more differentiated movements. 
 
 Experiments on adults, when asleep, almost entirely 
 conform to Pfliiger's laws of reflex reaction, especially is 
 this the case, if the person has his hands free or sleeps on 
 his back. In cases of hypnoidal states and hypnosis, the 
 reactions are somewhat modified. If the subject happens 
 to react with one hand, he keeps on reacting with it. Thus 
 when the subject is touched with a wet or irritating object 
 and is told to react, if it be the right side, he reacts with 
 the right hand. If now the left side is similarly stimulated, 
 the right hand keeps on reacting crossing to the left side. 
 This takes place, even if there is a long series of stimula- 
 tions, — the subject reacts with the hand he first starts to 
 react with. This may be largely due to subconscious sug- 
 gestion. I observed similar reactions in very suggestible 
 subjects even in the waking state. 
 
 Manaceine's results are not confirmed by me, and still 
 there is some truth in Manaceine's statement. Now I 
 have suspected for some time that if the condition of limi- 
 tation of voluntary movements is one of the important 
 factors in the induction of sleep, we should expect that it 
 
An Experimental Study of Sleep Ji 
 
 would not be a matter of indifference on which side we rest. 
 We should expect that, if the right side is the more active, 
 that the limitation of the voluntary movements would be 
 more marked on that side. In carrying on my experiments 
 on children and adults when in their sleeping states, I had 
 occasion to observe that there was a definite course in the 
 motor reactions, in the process of falling asleep. There is 
 method in sleep. Some people go to sleep only on their back 
 and find it difficult to fall asleep otherwise, while others 
 who go to sleep on their side and who form the greater 
 majority always go to sleep on the same side; there are 
 very few who can fall asleep indifferently on either side. 
 Moreover, my observations have shown me that by far the 
 majority of right-handed people go to sleep on the right side, 
 while left-handed people go to sleep on their left side. I 
 further verified this interesting fact by statistical inquiry 
 among my patients as well as among Harvard students. 
 Some of the right-handed people who go to sleep on the 
 right side may after some time turn to their left to change 
 position, while others keep on sleeping on the same side 
 through the whole night. The majority change position, 
 the right-handed to the left and the left-handed to the right. 
 More than seventy-five per cent of right-handed people have 
 given records to the effect that they sleep on the right side 
 or rather fall asleep on that side. Of the left-handed per- 
 sons, I find only one out of ten who falls asleep on the right 
 side. One case is specially interesting to quote: "Up to 
 my seventh year I slept on my right side and I was right- 
 handed. At about the age of seven I met with an accident, 
 I was run over by a team and my right side was injured so 
 that I could not use the limbs of the right side. I used my 
 left hand only, I began to sleep on my left side. This I 
 did up to my fifteenth year. I then began to practice with 
 my right hand too and am now ambidextrous. I sleep 
 now on either side. I use both hands." 
 
 Some claim that the reason why they sleep on the right 
 side is because of the dreams produced by the pressure of 
 the heart when sleeping on the left; but it is interesting to 
 observe that others sleeping on their left write in their 
 accounts that they cannot sleep on their right side, because 
 
72 An Experimental Study of Sleep 
 
 of the bad dreams, restlessness and nightmares produced. 
 Some claim that it is simply a matter of habit, but the very 
 fact that habit should give such a large percentage of right- 
 handed, sleeping on the right side,and of left-handed, sleeping 
 on their left side, points to a fundamental condition of our 
 functioning activities and mode of rest. This condition 
 we have found in the variability of our consciousness, 
 by the ceaseless variations of the incoming sensory 
 impressions from sense organs, muscles, joints and various 
 other organic activities. The kinesthetic sensations coming 
 from the motor activities of our muscles and joints are very 
 important in this respect. To bring about a state of rest 
 and sleep, we must have the condition of monotony and 
 limitation of voluntary movements, hence we can well see 
 the reason why right-handed people whose right side is 
 more active limit that side, while left-handed people prefer 
 to limit the left side most active in them. We can also 
 partly account for Manaceine's results, namely that in 
 sleep, right-handed people react with their left hand which 
 remains free as they sleep on the right side, while left-handed 
 people react in sleep with their right hand, because they 
 sleep on their left side. Manaceian's explanation is 
 pointless in referring these reactions to the activities of the 
 right and left hemispheres. According to Manaceine the left 
 hemisphere of right-handed people is fatigued and hence in 
 sleep the right hemisphere and the left hand have the ascen- 
 dency. This explanation is fanciful and does not agree with 
 facts. For when the experiments are carried out rigorously, 
 the reactions are found to conform, with the exception of very 
 youn infants, to Pflugers laws. 
 
 Thus the experiments and observations made on lower 
 animals, infants, children and adults all point in one direc- 
 tion, they point to the fundamental conditions of sleep, to 
 monotony and limitation of voluntary movements. Taking 
 as my motto the dictum "hypotheses non fin go" I strictly 
 followed the logic of facts. Sleep is not so much due to 
 merely cutting off sensory impressions, be they intense or 
 faint, as to the monotony of sensory impressions which in 
 fact may even be intense and numerous. It is the invari- 
 ability of sensory impressions that reduces the organism 
 to the passive state which we experience as sleep. 
 
PART II 
 THEORETICAL 
 
Chapter XII 
 Cell-energy, Threshold, "Stimulus-exhaustion" and Sleep 
 
 WE may advance in a tentative way the following 
 theory which should be regarded as a pro- 
 visional hypothesis of the causation of sleep. 
 One of the main characteristics of living 
 protoplasm is its adaptability to the conditions of the ex- 
 ternal environment. External stimuli give rise to reactions 
 of adjustment on the part of living substance. This prop- 
 erty known in physiology as irritability is specially charac- 
 teristic of all living matter or of what Huxley so aptly de- 
 scribes as "the physical basis of life." Verworn defines 
 the irritability of living substance "as its capacity of reacting 
 to changes in its environment by changes in the equilib- 
 rium of its matter and its energy." In other words, living 
 tissue responds to external stimulations with some discharge 
 of energy. The form of the discharge depends on the 
 peculiar protoplasmic structure, according as it is muscle, 
 gland, nerve cell or but slightly differentiated protoplasm, 
 such as amoeba or bacterium. The character of the reac- 
 tion to stimuli depends on the state of organization of the 
 living tissue. 
 
 The delicacy of response of living matter to external 
 stimuli has its limit. Very weak stimulations do not call 
 forth any reaction. Living tissue can only be set into activ- 
 ity by stimuli of certain intensity. If the stimulus falls 
 below that intensity, the protoplasm does not react. This 
 holds true of all cells, from the simplest bacterium and infu- 
 sorium to the most highly differentiated muscle-cell or neu- 
 ron. The minimal intensity below which the stimulus 
 remains ineffective is regarded as the threshold of stim- 
 ulation. As Howell puts it: "A stimulus too weak 
 to give a response with a motor nerve is usually designated 
 in physiology as subliminal; a similar stimulus with sen- 
 sory nerves is frequently expressed by the equivalent term 
 of subliminal, that is below the threshold, so a stimulus 
 just strong enough to provoke a perceptible reaction is the 
 
 75 
 
76 An Experimental Study of Sleep 
 
 minimal stimulus for efferent nerves and the threshold 
 stimulus for sensory nerves." "Exceedingly feeble stimuli" 
 says Landois "are without effect. The degree of intensity 
 of stimulation that originates the first trace of sensation is 
 called the threshold of sensation or the threshold-value." 
 The same is more clearly put by Verworn: 
 
 "Let us imagine an organism or part of an organism, 
 e.g., a muscle, under conditions in which no stimulus affects 
 it, and let us bring to bear upon it a stimulus, e.g., the gal- 
 vanic current, which varies in intensity from zero upward 
 and can be graded easily and delicately. Then we should 
 expect the muscle to exhibit phenomena of stimulation, i.e., 
 to perform a contraction, as soon as the intensity is increased 
 above 0. But this does not happen. The intensity can 
 be increased considerably before the muscle performs even 
 the slightest twitch. Only when the intensity has reached 
 a certain degree does the muscle respond with a contrac- 
 tion; from here on the contraction is never wanting, and 
 up to a certain degree becomes more energetic the more 
 the intensity is increased. The stimulus, therefore, begins 
 to operate only at a certain intensity, and this point is termed 
 the threshold of stimulation. Below the threshold the stimu- 
 lus is ineffective; above it the effect increases with the 
 increasing intensity of stimulus. For the different forms 
 of living substance the value of the threshold is very differ- 
 ent. Thus, nerve-fibres are put into activity by extremely 
 feeble galvanic stimuli, while Amoeba demands very strong 
 currents. The same is true of all other varieties of stimuli 
 in relation to the various forms of living substance." 
 
 Psychologically we may agree with Stout that "the 
 point at which it (the stimulus) is just indistinguishable, — 
 so that the least increase would make it distinguishable is 
 called stimulus-threshold." | 
 
 Kiilpe's definition is short; "the just noticeable stimu- 
 lus is technically termed the stimulus-threshold (die Reiz- 
 schwelle)." 
 
 With the increase of stimulations the irritability of the 
 living substance diminishes, the threshold rises. The same 
 minimal stimulus will no longer bring about a reaction, the 
 stimulus must be increased in intensity before any effect 
 
An Experimental Study of Sleep 77 
 
 can take place. Perhaps the best account of it is given by 
 Verworn in his "General Physiology." 
 
 "If a living object be stimulated by long-continued, 
 oft-repeated, or very strong stimuli, after some time it passes 
 into the condition of fatigue. The general characteristic 
 of fatigue is a gradual decrease of the irritability of the 
 living substance. This is expressed especially in the fact 
 that with increasing fatigue, the intensity of the stimulus 
 remaining the same, the result of the stimulation becomes 
 constantly less. 
 
 "We have already become acquainted with some ex- 
 amples of this fact in considering galvanic stimulation. If 
 a constant current of average strength be passed through 
 an Actinosphcerium, at the moment of making, there begin 
 to appear at the anode marked phenomena of contraction. 
 The protoplasm of the pseudopodia flows centripetally 
 until the latter are drawn in. Then the walls of the vacu- 
 oles break; and a granular disintegration of the protoplasm 
 results, which proceeds constantly farther from the kathode 
 during the passage of the current. This disintegration, 
 beginning with great energy, becomes slower and less ex- 
 tensive the longer the current flows, and after some time 
 is at a complete standstill. This means that the living sub- 
 stance of the Actinosphcerium becomes fatigued in the 
 course of continual stimulation, and decreases in irritabil- 
 ity; hence the stimulus, which at first induced pronounced 
 phenomena of disintegration, later produces no reaction 
 at all. Pelomyxa is fatigued still more rapidly than Acti- 
 nosphcerium. Stimulation for a few seconds is sufficient 
 to make individuals of this genus wholly non-irritable to 
 currents of equal intensity; a much greater intensity is 
 then required to call out the same reaction/' 
 
 The principle of variability of stimulation is of great 
 importance in the reaction of nerve-tissue. When the stimu- 
 lus remains invariable, both in intensity and quality, no 
 reaction follows. This is clearly brought out in experi- 
 ments on nerve-tissue. "The electrical current" says 
 Landois,' "exerts its strongest irritant effects upon a nerve 
 at the time of its entrance into the nerve and at the time 
 
 1 Text-book of Physiology. 
 
78 An Experimental Study of Sleep 
 
 of its disappearance. In like manner any rapid increase 
 or decrease of the current passing through a nerve has a 
 strong irritant effect. If on the other hand, the current 
 be allowed to pass gradually into the nerve trunk or to dis- 
 appear, or the current passing through the nerve be gradu- 
 ally increased or diminished, the visible signs of nerve irri- 
 tation are much less marked. In general, the stimulation 
 is most pronounced the more rapid the current-variation 
 within the nerve, that is the more suddenly the strength of 
 the current passing through the nerve is increased or dimin- 
 ished." This holds true in the case of the nerve, in which 
 as Bowditch has shown there is little or no fatigue; where 
 fatigue is present the principle of variability becomes a 
 factor of the utmost consequence. The principle of vari- 
 ability of stimulation plays a very important role in cells 
 in general, and in nerve-cells in particular where fatigue 
 easily sets in and the threshold is raised with the continu- 
 ation of stimulation and with the successive discharges of 
 cell energy. Variability of stimulation and fatigue influence 
 the fluctuations of thresholds. 
 
 It may be well to bring here the recent work of Sher- 
 rington in regard to the relation of neuron threshold and 
 the discharge of neuron energy. Sherrington points out 
 that among the characteristic differences between conduc- 
 tion in nerve-trunks and in reflex arcs (where nerve-cells 
 are interpolated), we find in the latter "Irreversibility of 
 direction instead of reversibility as in nerve-trunks, fatiga- 
 bility in contrast with the comparative unfatigability of 
 nerve-trunks," and "much greater variability of the thresh- 
 old of stimulus than in nerve-trunks." Sherrington points 
 out that "in certain cases, especially in Invertebrata, obser- 
 vation (Apathy, Bethe, etc.), indicates that many nerve 
 cells are actually continuous one with another. It is note- 
 worthy that in several of these cases the irreversibility of 
 direction of conduction which is characteristic of spinal 
 reflex arcs is not demonstrable; thus the nerve net in some 
 cases e.g. Medusa, exhibits reversible conduction (Romanes, 
 Nagel, Bethe and others). But in the neuron-chains of 
 the gray centred system of vertebrates histology on the 
 whole furnishes evidence that a surface of separation does 
 
An Experimental Study of Sleep 79 
 
 exist between neuron and neuron. And the evidence of 
 Wallerian secondary degeneration is clear in showing that 
 that process observes strictly a boundary between neuron 
 and neuron and does not transgress it. It seems therefore 
 likely that the nexus between neuron and neuron in the 
 reflex arc, at least in the spinal arc of the vertebrae involves 
 a surface of separation between neuron and neuron " "In 
 view therefore of the probable importance physiologically 
 of this mode of nexus between neuron and neuron it is con- 
 venient to have a term for it. The term introduced has 
 been synapse." "At each synapse there is a neuron thresh- 
 old. At each synapse a small quantity of energy, freed in 
 transmission, acts as a releasing force to a fresh store of 
 energy not along a homogeneous train of conducting material 
 as in a nerve-fibre pure and simple, but across a barrier 
 which whether lower or higher is always to some extent 
 a barrier." 1 
 
 Assuming then the principle of variability of stimula- 
 tion of neuron energy and neuron threshold in regard to the 
 liberation of neuron energy, principles advanced in my 
 previous works, we can return to our subject under dis- 
 cussion, namely sleep. We may regard sleep as a reaction 
 of protoplasm and as such we may express it in terms of 
 neuron threshold and neuron energy liberation. 
 
 If a series of stimulations are kept up without variation, 
 the sensory threshold gradually rises and finally the stimuli 
 fall out of consciousness, they fail to awaken the psycho- 
 physiological systems which have responded to the same 
 stimulations before, because of the rise of the thresholds. 
 This psycho-physiological law, characteristic of all tissues 
 and psycho-neural systems, underlies the phenomena of 
 sleep. As the cell or the neuron keeps on reacting to 
 stimulations the disposable physiological energy becomes 
 lowered and there is greater economy in the liberation of 
 cellular or of neuron-energy. The cell or neuron does not 
 respond to the same intensity of stimulus with the same 
 amount of energy. In other words, the threshold rises. 
 Should the stimulation keep on acting without variation, 
 both as to quantity and quality, the threshold rises so high 
 that the stimulus can no longer step over the threshold and 
 
 1 Sherrington, "The Integrative Action of the Nervous System." 
 
80 An Experimental Study of Sleep 
 
 can no longer call forth any reaction in the cell. We say 
 that the cell or the neuron is fatigued or exhausted. Really 
 this is not so much due to the exhaustion of the cell as to the 
 exhaustion of the stimulus, — it is the stimulus that has 
 exhausted itself. Vary the stimulus in quantity or in qual- 
 ity and the cell or neuron reacts once more. 1 We may 
 possibly best describe this general physiological fact of 
 cellular reaction by the term of " stimulus-exhaustion." 
 By repetition the stimulus exhausts itself and can no longer 
 call forth a reaction in the cell, although the cell may other- 
 wise possess a large amount of disposable energy. 2 
 
 As far as the particular stimulus is concerned the cell may 
 be regarded as asleep. The stimuli are withdrawn. Put- 
 ting the same general law in different terms we may say 
 that sleep is produced by monotony. 
 
 The cell or the neuron may be regarded as a reservoir 
 of energy. With the great biologist, Strassburger, we 
 may describe the cell as " energid." Conceived in terms 
 of energy the cell possesses various levels of energy. The 
 
 1 This may be related to the interesting experiments referred to by 
 Sherrington: 
 
 "When the scratch-reflex elicited from a spot of skin is fatigued, the 
 fatigue holds for that spot, but does not for the reflex as obtained from 
 the surrounding skin. The reflex is then tired out to stimuli at that spot 
 easily obtainable by stimulation two or more centimetres (half an inch) 
 away. This is seen with either mechanical or electrical stimuli." 
 
 {The Integrative Action of the Nervous System, Sherrington) 
 
 2 "The singleness of action from moment to moment thus assured 
 is a keystone in the construction of the individual whose unity it is the 
 specific office of the nervous system to perfect. Releasing forces acting 
 on the brain from moment to moment shut out from activity whole 
 regions of the nervous system, as they conversely call vast other regions 
 into play." 
 
 "An arc under long continuous stimulation of its receptor tends 
 even when it holds the common path, to retain its hold less well. Other 
 arcs can then more readily dispossess it. A stimulus to a fresh arc has, 
 in virtue of its mere freshness, a better chance of capturing the common 
 path." 
 
 "This waning of a reflex under long-maintained excitation is one of 
 the many phenomena that pass in physiology under the name 'fatigue.' 
 Its place of incidence lies at the synapse. It seems a process elaborated 
 and preserved in the selective evolution of the neural machinery. It 
 prevents long continuous possession of a common path by any one reflex 
 of considerable intensity. It favours the receptors taking turn about. 
 It helps to ensure serial variety of reaction. The organism, to be suc- 
 cessful in a million-sided environment, must in its reactions be many- 
 sided." 
 
 (Sherrington, Address British Association for the Advancement of 
 Science, 1904). 
 
An Experimental Study of Sleep 8 1 
 
 main levels of cellular energy have been described by me 
 in former works as dynamic, static and organic. 
 
 By dynamic energy is meant that portion of energy 
 which the cell can dispose of in its relations and reactions 
 to the stimuli of the external environment. 
 
 By static energy is designated that portion of energy 
 which is used only for the life maintenance of the cell, both 
 in relation to other cells and to its own molecular consti- 
 tution. It is the energy requisite to keep up its morpho- 
 logical organization and internal physiological functions. 
 
 By organic energy is meant the energy contained in the 
 tissues of the dead cell not as yet decomposed into its inor- 
 ganic constituents. 
 
 The levels of cellular energy are not different in kind. 
 They merely represent progressive phases or stages of the 
 same process of cellular activity. 
 
 In its relations with the external environment, the cell 
 does not utilize the whole of its dynamic energy. A large 
 amount of it lies fallow, so to say, and remains inaccessible 
 to the ordinary stimulations of the external environment. 
 This amount of unused energy may be termed stored, reserve 
 energy. 1 For the cell stores up energy as it stores food, in 
 order to be able to meet the various emergencies that may 
 arise in the course of its relations with the external world. 
 In respect to storing up energy the law of stimulus- 
 exhaustion may be regarded as a safeguard to the cell. The 
 same qualitative stimulus cannot draw more than its allotted 
 portion of energy. If the stimulation continues and attempts 
 to draw more than its share the door, so to say, closes and 
 the stimulus knocks in vain against a locked door. The 
 threshold rises with each successive stimulation. When the 
 maximum amount is drawn, there is no longer response to 
 that particular stimulus, or rather to say, to that particular 
 qualitative stimulation of a definite intensity. In regard to 
 it the cell no longer reacts, — it is asleep. In order to 
 respond again to the particular stimulus of a certain intens- 
 ity and quality, the cell must recuperate its special form of 
 energy. When this recuperation is effected, the cell is 
 once more ready to react to the given stimulus. 
 
 1 See my Studies in Psychopathology, Boston Medical and Surgical 
 Journal, 1907. 
 
82 An Experimental Study of Sleep 
 
 The liberation of cellular energy in response to external 
 stimuli may be regarded as the active waking states, while 
 the restitution or passive rest-states of the cell, during which 
 the threshold is raised and cellular recuperation takes place, 
 may be regarded as sleeping states. 
 
 From the standpoint of cell metabolism, waking states 
 are correlative with katabolic changes, while sleeping states 
 are correlative with anabolic conditions. When the cell is 
 active and awake, it liberates energy; when it sleeps, it 
 stores energy. This process of storing up energy is going 
 on all the time to some extent. If a stimulus of a certain 
 intensity and quality keeps on liberating energy, it may 
 arrive after some time at the maximum, when the threshold 
 rises so high that the cell no longer reacts. 1 In respect to 
 that stimulus the katabolic, active, waking state ceases and 
 is replaced by the anabolic, sleeping states. The cell may 
 thus be awake to all other stimulations, but in regard to 
 the special stimulus it is asleep. We may say that the cell 
 is asleep partially. When the liberation of energy has 
 reached the maximum point, and the thresholds are raised 
 
 1 "Whenever by a stimulus applied to an irritable substance, the 
 potential energy there stored up is liberated the following phenomena 
 may be observed: (1) A so-called latent period of variable duration 
 during which no effects of stimulation are manifest; (2) A very brief 
 period during which the effect of stimulation reaches a maximum; (3) A 
 period of continued stimulation during which the effect diminishes in 
 consequence of the using up of the substance containing the potential 
 energy — i.e., a period of fatigue; (4) A period after the stimulation has 
 ceased in which the effect slowly passes away. 
 
 The curve dra-wn by a muscle in tetanic contraction, as shown iu 
 the diagram, illustrates this phenomenon. Thus, if AD represents the 
 duration of the stimulation, AB indicates the latent period, BC the period 
 of contraction, CD the period of fatigue under stimulation, and DE the 
 after-effect of stimulation showing itself as a slow relaxation. When 
 light falls upon the retina corresponding phenomena are to be observed." 
 
 An American Text-Book of Phvsiologv, William H. Howell, Vol. 
 II, p. 343. 
 
An Experimental Study of Sleep 83 
 
 in regard to most or to all the ordinary stimuli of the external 
 environment, the cell may be said to be fully asleep. 
 
 Should however, the liberation of energy by various 
 stimuli keep on and begin to liberate the reserve energy 
 levels and then pass over into the levels of static energy, the 
 cell falls into a pathological waking state. 
 
 We may represent the relation of the different levels 
 and their correlative states by the following diagram. 
 
 What is true of the cell holds also good of systems of 
 cells and neurons constituting a multicellular organism. 
 The condition of monotony and the law of stimulus-exhaus- 
 tion play a very important role in the various changes and 
 adaptations of life-activity. Stimuli which have exhausted 
 themselves by their monotony drop out and are replaced by 
 new ones until the whole round of stimuli is gone through 
 and the organism ceases to respond to its external environ- 
 ment, — falls asleep. 
 
 The rise of threshold after stimulation holds true in 
 the whole domain of biological activities. If the gastroc- 
 nemius muscle of the frog, for instance, is stimulated, say 
 by an electric current, the muscle with successive stimula- 
 tions responds less readily with contraction and this becomes 
 more evident with the onset of fatigue. Pffefer in a series 
 of extremely interesting experiments has shown that sper- 
 matozoids of ferns are attracted by malic acid, the pro- 
 gressive response of the attraction of the cell requiring 
 a constant increase of the degree of the concentration of 
 the acid, the increment of stimulations bearing within cer- 
 tain limits a constant ratio to the total stimulus. The 
 threshold rises with each successive stimulation. 
 
 In the sphere of sensation we find the same rise of 
 threshold. We are all acquainted with the fact that an 
 additional candle or lamp, for instance, in well lighted 
 room does not produce the same sensory effect as when 
 brought into a more or less dark room. An electric light 
 in the sun is scarcely perceptible. An additional ounce 
 to a lifted pound does not feel as heavy as when raised by 
 itself. A sound added to another sound or to a noise sounds 
 less loud than when appearing isolated or when the same 
 sound is breaking upon silence. The same relation holds 
 true in the case of other senses. 
 
8 4 
 
 
 » 
 
 An Experimental Study of Sleep 
 
 Cktfnic $kl<c /(bcA^e. <*(mtotc 
 
 
 flee. 
 Mb 
 
 
 &Jl 7 L 
 
 2 
 
 y- 
 
 %oJL 
 
 
An Experimental Study of Sleep 85 
 
 This same truth is still more clearly brought out in the 
 fact that if we take a certain stimulus as a unit giving rise 
 to a definite sensation, then as we progressively ascend 
 and add more and more, units of the same stimulus, the 
 qualitative intensity of the sensation is far from rising pro- 
 portionately. If we take for instance, the weight of an 
 ounce as our unit of stimulation, then the successive moments 
 of unit-stimulations, that is of ounces, will not give rise 
 to as distinct and similar sensations as did the initial stimu- 
 lation. The second ounce will give a sensation fainter 
 than the first one and the third fainter than the second 
 and so on until a point is reached, when the sensation of 
 an additional ounce will not at all be appreciated, will 
 dwindle away and almost reach the zero-point. In the 
 same way, if the pressure of a gramme is excited in the 
 hand, successive increments of grammes will not in equal 
 degree increase the sensory effect. The additional incre- 
 ments of grammes, though they are equal units of stimula- 
 tion, give rise to fainter and fainter sensations, until finally 
 all sensory appreciation of the added unit fades away and 
 disappears. If the hand is immersed in water say at the 
 freezing point, an addition of ten degrees will be perceptibly 
 appreciated, while successive increments of ten degrees 
 each will be felt less and less and finally will not be noticed 
 and will become difficult to detect. In short, the threshold 
 rises with each successive stimulation. 
 
 To bring about a sensory response of an already stimu- 
 lated sense-organ the intensity of the stimulus must be 
 relatively increased. This is what constitutes Weber's 
 law. The continuous progressive sensory response of a 
 sense-organ requires a constant increase of stimulation 
 which within certain limits, bears a constant ratio to the 
 total stimulus. 1 This law is sometimes summed up by 
 
 1 By noting for each strength of stimulus the addition required to 
 evoke a just perceptible alteration of sensation, a series of quantities is 
 obtained expressing the law according to which sensation alters when 
 stimulation is increased. This expression is the so-called "law" of Weber. 
 It says that a given stimulus is perceived less when added to a large than 
 to a small one, or that an addition to a large stimulus is perceived less 
 than an addition to a small one, unless it, relatively to the stimulus, is 
 as great. The "law" may be phrased variously in physiological theory. 
 It may be interpreted as not physiological at all, but psychological. The 
 
86 An Experimental Study of Sleep 
 
 physiologists and psychologists in the statement that the 
 stimulus rises in a geometrical and corresponding sensa- 
 tion in an arithmetical progression, or as Fechner expresses 
 it, " the sensation varies as the logarithm of the stimulus. " 
 We are probably nearer the truth, if we limit ourselves to 
 the statement that " the increase of the stimulus necessary 
 to produce a just perceptible difference in the sensation 
 bears a constant ratio to the total stimulus." In short, 
 activity raises the threshold. The phenomena fall under the 
 law of stimulus-exhaustion. Each reaction to an external 
 stimulus raises the threshold of that stimulus and with its 
 repetition becomes finally excluded, temporarily, at least, 
 from the cycle of living stimuli, that is, such as are capable 
 of bringing about reactions and adjustments to the external 
 environment. The excluded stimulus is ignored, becomes 
 non-existent for the organism. The organism is asleep for 
 that stimulus. 
 
 In the course of the daily activity of the individual the 
 thresholds of sensitivity and of sensori-motor reactions in 
 response to the stimuli of ordinary life rise gradually, the 
 stimuli fall below the threshold of living reactions. The 
 mass of stimuli of the external world constituting the exter- 
 nal environment of the individual drops out of the life-cycle 
 of the individual and for the time being ceases to exist for 
 him. The individual is asleep, asleep for that environ- 
 ment. In other words the stimuli of the external world 
 by their continuous action have become monotonous, have 
 raised the thresholds and have become excluded from the 
 life existence of the individual who is now deeply asleep for 
 that given environment. 
 
 disproportion between increment of stimulus and increment of sensation 
 may take place in purely psychological events and processes. Wundt 
 is of that opinion. He points to the wide occurrence of such a ratio in 
 all psychical activity as outcome of the relativity inherent in every con- 
 scious process. Waller finds the response in a nerve trunk directly 
 stimulated, as judged by action current, increase much more nearly 
 directly as the increase of external stimulus than does the response from 
 muscle when nerve is stimulated, or from nerve when retina is adequately 
 stimulated. Waller's evidence seems to point to the law being in part 
 a function of the nerve-cell endings; probably, therefore, applicable to 
 synapses as to motor plates. Delbceuf considers the law an expression 
 of ever-increasing proportion of loss of effect in the central nervous 
 system, due to "fatigue." (Sherrington in Schafer's Text-Booh of Physi- 
 ology, Vol. II, p. 981.) 
 
An Experimental Study of Sleep 87 
 
 Should an appreciable variation occur in the environment 
 at about the time when the organism is ready to fall asleep 
 the external world becomes again a living reality. The 
 individual becomes alive and wide awake to what is going 
 on around him. If an appreciable change in the total mass 
 or in some stimuli constituting the environment takes place, 
 the individual may be awakened out of his sleep. Should 
 the variation occur in some of the stimuli, their thresholds 
 become lowered and the individual, though asleep in regard 
 to all else, is awake in regard to them. This partial wak- 
 ing state is the soil in which dreams develop most luxuri- 
 antly. We do not dream, when we are asleep, we dream, 
 when we are awake. 1 
 
 The individual may be asleep to all else and still be 
 awake to special stimuli whose thresholds are very low. 
 The mother watching over her babe, the nurse, the physi- 
 cian attending their patients may be sound asleep to loud 
 noises, but are alive and wide awake to the slightest changes 
 in their charges. They have lost touch with the whole 
 external world, but the ones cared for still have a firm hold 
 on them. High as our bridges are raised for the whole 
 world, they are low for the ones we care for. 
 
 Let an appreciable change occur in the stimuli to which 
 we are awake, an amount of energy immediately is drawn 
 from the reserve store, the thresholds barring the entrance 
 to the host of intruders are lowered and we are once more 
 in communication with the external world, — our sleep is 
 gone and we are wide awake. We can thus be wide awake 
 in the very depth of our sleep. The possibility of shaking 
 off the grip of sleep under appropriate circumstances and 
 especially the highly significant fact of wakefulness in the 
 very depths of sleep form insuperable difficulties for all 
 those plausible, apparently scientific theories of sleep, 
 theories based on circulation, engorgement, anemia or hyper- 
 emia, narcosis and autointoxication. We can watch in 
 our sleep, count the flow of time and awake at the right 
 moment. The fact that we can sleep and still watch and 
 keep awake in regard to special objects and particular 
 persons shows that sleep is not a matter of blood circulation 
 
 1 My work on dreams will be published in a separate essay. 
 
88 An Experimental Study of Sleep 
 
 or of intoxication by accumulation of waste products in the 
 system. Sleep is not a disease, not a pathological process 
 due to the accumulation of toxic products in the brain or 
 in the system generally. Sleep is not of those fatal uncon- 
 trollable onsets characteristic of the morbid processes, such 
 as epilepsy, sunstroke, or apoplexy, nor is sleep a sort of 
 narcolepsy. Sleep is not a disease, it is not, as the chemical 
 speculators would have it, a kind of narcosis of the system 
 by the poisons of fatigue products. Sleep is not patho- 
 logical, it is essentially physiological in character. We do 
 not go to sleep, because we are poisoned and wake up when 
 the poisons are eliminated. We go to sleep at our own 
 sweet will and can wake at pleasure. We can wake at any 
 moment and can even be awake in the very depths of our 
 sleep. 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. Waking and 
 sleeping are intimately related, — they are two different 
 manifestations of one and the same life-process, — one is 
 as normal 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 fundamental instincts. As Claperede forcibly puts it: 
 "Le sommeil est une fonction de defense, un instinct qui 
 a pour but, en frappant 1'animal d'inertie, de l'e npecher 
 de parvenir au stade d'epuisement: ce n'est pas parce que 
 nous sommes intoxiques, ou epuises, que nous dormons, 
 mais nous dormons pour ne pas l'etre." 
 
 If we look at the matter from a psychological stand- 
 point, we may say that sleep is a rise of the thresholds of 
 mental aggregates or of moments consciousness. I have 
 pointed out in a former work 1 of mine that to minimize the 
 expenditure of neuron energy and reach the minimum of 
 consciousness constitutes the tendency of psvchomotor life. 
 We can fully realize the importance of this tendency, if we 
 regard it from a teleological point of view. In the struggle 
 for existence or in the economical system of competition of 
 modern life the saving of unnecessary expenditure, where 
 only possible, is of the highest consequence. Organisms 
 
 1 Multiple personality. 
 
An Experimental Study of Sleep 89 
 
 that can best effect such an economy of energy will be best 
 fitted to survive. Those organisms that are enabled to 
 reduce to its minimum the friction and loss of neuron energy 
 have the advantage of possessing at their disposal a greater 
 amount of energy to cope with new circumstances, with 
 novel conditions, and react better and in a more favorable 
 way when confronted with changes in their environment. 
 This economizing becomes absolutely indispensable in the 
 life-existence of higher organisms, the environment of which 
 is highly complex. The reduction of psychomotor activity 
 to the least amount of psychophysiological expenditure, in 
 other words, to the minimum of consciousness is the law of 
 psychomotor life in general and of the highest representatives 
 of that life in particular. 
 
 I have further pointed out in the same work that this 
 economizing is by no means an endless process, there is a 
 certain minimum of consciousness beyond which psychic 
 states cannot pass. This minimum of consciousness once 
 reached, must remain stationary, for a fall below it is the 
 arrest of the activity of the mental aggregate. In other 
 words, there is a certain minimum below which conscious- 
 ness cannot be reduced with impunity. Reduce the con- 
 sciousness of the total psychic aggregate by lowering the 
 sensibility of its constituents and the whole mental system 
 will cease to function. Now under the conditions of mono- 
 tony and limitation of psychomotor activity the moment- 
 threshold rises until the psychic minimum vanishes and the 
 organism is asleep. 
 
 Putting the matter again in teleological terms we may 
 say that we go to sleep when we relinquish our hold on the 
 relations of our external environment. We fall asleep 
 when our consciousness is fagged, when we wish no longer 
 to enter into communication with the external world, when 
 we lose interest in our surroundings. When our interest 
 in external existence fags and fades away, we go to sleep. 
 When Our interests in the external world cease, we draw up 
 the bridges, so to say, interrupt all external communication, 
 as far as it is possible, and become isolated in our own for- 
 tress and repair to our own world of organic activity and 
 inner dream life. We fall asleep when the vital interests 
 
90 An Experimental Study of Sleep 
 
 in external being have fallen into the background of con- 
 sciousness; we awake when those interests are aroused. 
 When the struggle for existence ceases we repair to our 
 castle and battlements. Sleep is the interruption of our 
 intercourse with the external world ; — it is the laying down 
 of our arms for a respite in the struggle of life. Sleep is 
 a truce with the world. When all psychomotor reactions 
 to the stimuli of the external environment cease, we sleep. 
 We sleep, because we are no longer interested to take an 
 active part in the battle of life. From a teleological stand- 
 point we may say that sleep is a dismissal of the external 
 world with all its vicissitudes, troubles and pains. We 
 cease to desire, we cease to react, and we sleep and dream 
 in peace. 
 
 And when evening descended from heaven above, . 
 And the earth was all rest, and the air was all love, 
 And delight, tho' less bright, was far more deep 
 And the day's veil fell from the world of sleep, 
 
 And the beasts, and the birds, and the insects were drowned 
 In an ocean of dreams without a sound; 
 Whose waves never mark, tho' they ever impress 
 The light sand which paves it, consciousness. 
 
 — Shelter 
 
Chapter XIII 
 
 Motor Consciousness and Sleep 
 
 THE condition of limitation of voluntary movements 
 plays an important role in the induction of sleep 
 states. This is due to the fact that motor con- 
 sciousness not only forms the main body of our 
 mental activity, but also that ideo-motor life is more sub- 
 ject to changes from slight stimulations than is our purely 
 sensory life. Motor elements are highly plastic and modi- 
 fiable; they enter readily into ever new combinations. 
 From a biological standpoint one can realize the impor- 
 tance of the great modifiability displayed by sensori-motor 
 and ideo-motor elements, since in the adaptation of the 
 organism to its environment it is these elements that are 
 mainly employed in reaction to stimuli of the external 
 world. From the standpoint of adaptation a slight differ- 
 ence of sensory experience may give a widely different and 
 highly complex motor reaction. 
 
 Psychomotor processes form the most important and 
 largest portion of mental life. With the exception of man, 
 all the representatives of the animal kingdom, from the 
 lowest to the highest forms, represent but different stages 
 in the evolution of sensori-motor life. The great majority 
 of mankind still leads a life closely allied to animal sensori- 
 motor states. Instance the delight of children in their 
 plays, and the all absorbing interest of college students in 
 their baseball and football games. Even in the highest and 
 most developed forms of mental activity motor ideas and 
 representations are by far the most predominant. With- 
 out motor elements ideational life is arrested. It is these 
 sensori-motor and ideo-motor elements that constitute the 
 " stream, the flow, the current " of our mental life. Motor 
 elements enter freely and easily into combinations with all 
 other elements of mental life. 
 
 This ease and high plasticity of ideo-motor elements is 
 specially well brought out in hypnosis. Sensori-motor and 
 ideo-motor suggestions are taken before purely sensory 
 suggestions; paralysis, catalepsy, contracture, all kinds of 
 
 9i 
 
92 An Experimental Study of Sleep 
 
 motor and kinesthetic illusions and hallucinations are 
 easily induced even in the very light stages, while it is only 
 in the deeper stages that changes of ideo-sensory elements 
 can be brought about. The induction of purely ideo-sen- 
 sory illusions, hallucinations or delusions, positive and 
 negative, can only be effected in the very deep stages of 
 hypnosis. The freedom in forming new combinations and 
 associations makes the suggestion of motor ideas and repre- 
 sentations highly effective. 
 
 Throughout the scale of animal life, from the lowest to 
 the highest forms, intelligence is intimately related to the 
 degree of development of the muscular system and to the 
 delicacy of motor adjustments. Among the lower forms 
 of life the Cephalopods are well equipped with powerful 
 muscular arms capable of executing a great variety of vigor- 
 ous movements. Now the Cephalopods also possess a more 
 highly developed nervous system with a higher grade of 
 mental functions than the rest of the Mollusca. The 
 great activity of ants and bees is notorious and their instinc- 
 tive psychic life is the richest among the Arthropoda. Note 
 the great variety of motor adjustments of the beaver and 
 also of the intelligence that goes along with it. Birds 
 possessed of a high degree of activity and motor adapta- 
 bility are also the most intelligent of their kind, such for 
 instance as the different species of talking birds. Notice 
 the activity and great agility of the fox and also the unusual 
 cunning for which the animal is so celebrated in song and 
 fable. The suppleness of the dog, his quick reactions to 
 stimulations, the resources of his motor adjustments and 
 the great extent of his modifiability under changing con- 
 ditions are all well known and along with them goes a high 
 degree of mental activity. Of all the Mammals the Ouad- 
 rumana are the most active, the most imitative, and with the 
 exception of man, they are also the most intelligent. When 
 we come to man we cannot help admiring the high com- 
 plexity and extreme delicacy of his motor adjustments. 
 Most marvellous however is the human hand, that divine 
 organ which gives shape and form to works of art, to all 
 outward visible manifestations of civilization. The great 
 artists and thinkers of antiquity held the human hand in 
 
An Experimental Study of Sleep 93 
 
 great veneration. One of the great Greek philosophers 
 did not even hesitate to declare that man's superiority over 
 the brute was due to his hand. Finally in the wonderfully 
 delicate motor adjustments of speech we find clearly illus- 
 trated the intimate relation between motor and psychic 
 activities. 
 
 Experiments prove the same truth of the importance 
 of motor elements in our mental life. If a series of syl- 
 lables or numbers is given to memorize, after one reading, 
 five out of ten can be remembered, though with some diffi- 
 culty; but if the syllables or numbers are written down at 
 the same time, though not looked at during the writing, a 
 far greater percentage such as six or seven syllables can be 
 remembered. If the motor elements in a train of ideas are 
 suppressed, the order of the series becomes confused and 
 even totally destroyed, showing that the motor ideas are 
 important links in trains of association of ideas. Motor 
 elements form the nucleus of consciousness. 
 
 Biologically regarded, voluntary activity, will, is the 
 power of the organism to adjust itself to the conditions of 
 the external environment. In its last psychological analy- 
 sis voluntary activity, will, consists of ideo-motor elements, 
 of various modes of adaptations. Will, consisting of kin- 
 aesthetic elements, constitutes the active subject of per- 
 sonality and individuality. If this be realized, then the 
 vital importance of motor consciousness cannot be too highly 
 overrated. Motor consciousness is at the very heart of per- 
 sonality. We are what we can accomplish. Extreme vari- 
 ability and adaptability of reactions to environment are 
 the main characteristic traits of intelligence, will, person- 
 ality. 
 
 The readiness of psycho-motor elements and groups to 
 enter into ever new combinations gives rise to the forma- 
 tion of a great wealth of associations which help to make 
 the labile psycho-motor groups and systems easy of recall. 
 In fact it may be said that the ease of recall is proportionate 
 to the mass of associated kinesthetic elements. The great 
 modifiability and variability of systems of motor elements 
 requisite in the adaptation of the organism to the varying 
 conditions of life, to its environment, make the ever greater 
 
94 An Experimental Study of Sleep 
 
 instability of motor elements an imperative necessity in the 
 struggle for existence. 
 
 Forming the predominant elements, both as to inten- 
 sity and mass, of the most complex, relatively stable, though 
 ceaselessly shifting groups and systems, constituting the 
 highly developed organization of mental life, the motor 
 elements, presentative and representative, are also the first 
 to become involved in the process of dissociation. In the 
 various forms of nervous and mental diseases, under differ- 
 ent conditions of intoxication and auto-intoxication, in the 
 traumas caused by shock, physical and psychic, the deli- 
 cate movements of adjustment are the first to become affected ; 
 dissociations of systems of motor elements are first to occur. 
 
 The instability of psycho- motor elements maybe brought 
 in relation with the fact of the early affection of muscular 
 and kinesthetic sensitivity and with the predominance of 
 sensori-motor over purely sensory symptoms, so frequently 
 occurring in the course of nervous diseases. With this 
 may be correlated the significant fact referred to bv Mosso 
 that " all substances which slowly destroy the organism 
 must produce phenomena analogous to those of curari 
 since the motor nerves. . . . have less vitality than the 
 sensory." It may also be observed in passing that cellular 
 kinoplasm with the "kinocentrum," the centrosome and its 
 archoplasmic structures, possibly the most primitive organ- 
 oids of the cell, similarly manifest a high degree of vari- 
 ability and instability. 
 
 Motor elements mav be regarded as the labile consti- 
 tuents of consciousness; — they become easily and fre- 
 quently dissociated and dropped into the subconscious; but 
 for that very reason they are also very easily reproduced 
 or regenerated. In this respect motor elements follow the 
 general biological law of organic regeneration: Organs 
 that are easily and frequently lost in the struggle for exis- 
 tence are also easily regenerated, as for instance, the legs 
 and claws of Crustacea or the tentacles of the starfish and 
 the octopus. Dissociated systems of motor elements often 
 become regenerated and under pathological conditions, 
 when synthesis is impossible, they may recur with great 
 persistence giving rise to the most uncontrollable tvpes of 
 
An Experimental Study of Sleep 95 
 
 insistent ideas and impulses and to various forms of so- 
 called "psychic epilepsy/' especially of the motor type, 
 closely mimicking typical organic epilepsy. Such disso- 
 ciated, subconscious systems, like rudimentary, aborted 
 organs, the appendix, for instance, may often prove very 
 injurious to the organism. The recurrence of such sub- 
 conscious, submerged, dissociated systems has its parallel 
 in the biological phenomena of reversion or atavism. 
 
 The fact that psycho-motor elements enter easily into 
 combinations and form extensive associative systems, makes 
 them easy of recall and hence persistent in memory. From 
 an educational standpoint one realizes the importance of 
 this fact. Children learn things best not by abstract notions, 
 not by looking at objects and hearing of things, but by 
 acting out whatever is taught them. Motor consciousness is 
 more vital than sensory. In the training of the mentally 
 defective the best method followed is that of motor instruc- 
 tion, — to get at the meaning of things by means of action, 
 even if it be automatic at first. As a matter of fact even the 
 normal and well balanced mind gets at the meaning of things 
 by handling them, by having the attributes and qualities 
 of the objects and processes to be learned acted out. Acting 
 forms the greater part of man s life. 
 
 Forming as motor consciousness, does the very heart of 
 mental activity, we can well realize the paramount import- 
 ance of the condition of limitation of voluntary movements. 
 By limiting the motor activity of the organism we impover- 
 ish its mental processes and lower the heart-beat of mental 
 life. The active nucleus of psycho-motor reactions becomes 
 passive, the organism becomes disabled in its response to the 
 stimulations of the external environment, the thresholds rise 
 and the organism is no longer in relation with the external 
 world. When motor activity with its concomitant motor- 
 consciousness becomes lowered, restricted, and fades away, 
 the organism becomes necessarily passive and passes into 
 sleep. 
 
 Thus monotony and limitation of voluntary movements 
 work in one direction, — they tend to raise the thresholds 
 of psychomotor reactions, they cooperate in the induction 
 of sleep. These conditions are usually brought about natu- 
 
96 An Experimental Study of Sleep 
 
 rally in the course of the daily or nightly life activity of the 
 individual organism, or the conditions may be produced 
 artificially. In both cases the result is the same, — the 
 organism falls asleep. In the life of higher animals the 
 two cases may often combine. When the individual has 
 fagged out his life interests in his active relations with his 
 surroundings, when the stimuli have become monotonous 
 to him and his activity with its correlative motor conscious- 
 ness has become limited and lowered, he makes artificial 
 arrangements for the intensification of the conditions of 
 monotony and limitation of voluntary activity. He seeks 
 for a dark nook, closes his eyes to exclude as much as pos- 
 sible all extraneous disturbing stimulations and tries to lie 
 down quietly and comfortably, restricts his voluntary move- 
 ments, breaks his connection with the external world and 
 goes to sleep. The organism falls into sleep, when the 
 thresholds rise, wakes and rises when the thresholds fall. 
 
 Looked at from a purely physiological standpoint and ex- 
 pressed in terms of energy, of the "cell-energy," sleep maybe 
 regarded as the onset of fatigue, as the onset of exhaustion of 
 the levels of dynamic energy in response to external stimuli. 
 The law of stimulus-exhaustion comes here into plav as 
 we have indicated in our discussion of cell-energy. Each 
 particular stimulus has its maximum amount of energy 
 which can be drawn upon, under ordinary conditions of daily 
 life. As the special stimulus approaches its limit, it works 
 under greater and greater difficulties, draws less <md less 
 energy and finally ceases to awaken any response, — the 
 threshold is raised to its maximum and the organism, as far 
 as that special stimulus is concerned, is no longer awake, — 
 the organism is asleep. In the course of its daily activity the 
 same takes place in regard to most of the objects, to most 
 or to all of the stimuli that constitute the external world of 
 the organism. The stimuli of the external world have drawn 
 all that was permitted to them on their bank accounts, so 
 to say, and the account for the time being is closed. Noth- 
 ing more is permitted to go out. No stimulus of ordinary 
 life is permitted to draw over and above a certain amount. 
 There must always be ready capital for unusual situations, 
 for emergencies. When the stimuli have drawn their due 
 
An Experimental Study of Sleep 97 
 
 and the organism is left with its reserve energy, — libera- 
 tion of energy with its accompanying waking states ceases. 
 The organism is no longer awake to the stimuli and is 
 asleep. 
 
 As in the waking states the katabolic processes predom- 
 inate, so in sleep the reverse processes, the anabolic, take the 
 upper hand. The organism begins to recuperate its losses 
 and fills up the accounts drawn upon by the stimuli of the 
 external environment, when in active relation with them. 
 With the increase of the income of energy the raised thresh- 
 olds begin to fall until a point is reached when the stimuli 
 once more overstep the lowered thresholds and once more 
 gain access to the stores of life-energy, — the organism 
 awakes and enters into active relations with the external 
 environment. 
 
 Regarded then from various standpoints, sleep is a 
 rise of moments-thresholds under conditions of monotony 
 and limitation of voluntary movements. In this respect 
 sleep strongly contrasts with hypnosis. In hypnosis the 
 individual is specially accessible to any kind of sugges- 
 tions coming from the external world, the psycho-motor 
 reactions are greatly lightened and are released by the sug- 
 gestion or external stimulus with great facility, far greater 
 than in the waking state. This great facility is often 
 expressed by the statement that in hypnosis the inhibitions 
 are removed. What specially characterizes hypnosis is the 
 fact of fall of thresholds present in individuals, with a predis- 
 position to states of dissociation; in sleep, on the contrary 
 we have found from our study, the general characteristic 
 is the rise of psycho-motor thresholds. In passing from the 
 waking state into the subwaking hypnoidal state the indi- 
 vidual may either pass into hypnosis with its dissociated 
 states and lowered psycho-motor thresholds or may go into 
 sleep with raised psycho-motor thresholds. The process of 
 redistribution of thresholds takes place in the intermediary, 
 hypnoidal states. When the redistribution of thresholds in 
 the hypnoidal states brings about a fall of thresholds due 
 to predisposition to and further cultivation of dissociations, 
 the result is hypnosis; when the redistribution in the hyp- 
 noidal states brings about a rise of thresholds, the result is 
 sleep. 
 
98 An Experimental Study of Sleep 
 
 Biologically regarded, sleep is as much an instinct as 
 hunger or sex. 
 
 Phylogenetically and ontogenetically, the sleep-states 
 of higher animals are developed out of undifferentiated, 
 intermediary, subwaking, hypnoidal-like states found in the 
 resting states of the lower representatives of animal life. 
 The hypnoidal state is the primitive rest state out of which 
 sleep arises. Briefly put, the hypnoidal state is the germ 
 of sleep. 
 
 Physiologically and psychologically regarded, sleep is 
 an actively induced passive state in relation to the external 
 environment; the psycho-physiological systems have their 
 thresholds raised in relation to external stimulations; the 
 rise of threshold is induced by a mass of impressions pos- 
 sessing little or no variability, by limitation or by relative 
 withdrawal of stimulations, or what is the same, by monotony 
 of stimulations and by limitation of voluntary movements. 
 
BIBLIOGRAPHY 
 
 Abercrombie, Inquiries. 
 
 Achasheff, K Kasuistik Narkolepsii. Med. Sbornik, Warsaw. 
 
 1896. 
 Ackerrman, Versuch einer physischen Darstellung der Lebens- 
 
 krafte. 
 Baldwin, Senses and Intellect. 
 
 Ballet, Sommeil pathologique, Rev. de Med. 1882. 
 Barthez, Nouveaux Elements de la Science de THomme. 
 Bauchard, Lectures on Auto -intoxication in Disease. 
 Benjamin, Uber den Schlaf, Allg. Z.f. Psychiatrie, 1898. 
 Berger & Loewy, Etat des yeux pendant le sommeil, J. de 
 
 l'Anat. 1898. 
 Bergson, Le Reve, Bull. Inst. Psych, int. Mai. 1901. 
 Bernard, CI. La Science Experim. 1878. 
 Bigelow, Mystery of Sleep, Harper. 1897. 
 Binns, Anatomy of Sleep. 1843. 
 Binz, Ueber den Traum. 1878. 
 Blondet, Observation de sommeil lethargique. Gaz. hebd. 
 
 October, 1864. 
 Blodgett, A. N., A Case of Narcolepsy. Am. J. of Med. Sc. 
 
 August, 1906. 
 Boirac, La Veille continee dans le sommeil. 
 Borgherini, Schlafahnlicher Zustand bei Thieren, Neur. Centrb. 
 
 1891. 
 Bouchard, Lecons sur les auto-intoxications. 1887. 
 Breisacker, Zur Physiologie des Schlafes, Du Bois' Arch. 1891. 
 Breuer und Freud, Studien ueber Hysteric 
 Brodie, Benjamin, Psychological Inquiries. 
 Brodman, Plethysmographische Studien am Menschen, J.f.Ps. 
 
 & Neur. 1902. 
 Brown, Compound Fractures of Cranium, Am. J. Med. i860. 
 Brown Sequard, Lecons sur les nerfs vaso-moteurs. 1872. 
 
 Le sommeil, Arch, de Phys. 1889. 
 Brunelli, II letargo. Riv. ital di Sc. nat. 1903. 
 Burdach, Physiologie. 
 Camp, Carl D., Morbid Sleepiness, The J. of Abnormal Psych. 
 
 May, 1907. 
 
 99 
 
100 Bibliography 
 
 Camuset, Apropos de la narcolepsie, Gaz. de Hop. 1880. 
 Cappie, J., Causation of Sleep. 
 
 The Intracranial Circulation. 
 Carpenter, Physiology. 
 
 Charcot, M., Attaque du sommeil, Gaz. de Hop. 1888. 
 Chavigny, M., Narcolepsie, Soc. Med. de Hop. de Lyon. 1904. 
 Chesley, Does the Mind Ever Sleep ? 
 
 Claperede, Ed., Esquisse d'une theorie biologique du som- 
 meil. Archives de Psychologie, February, March, 
 
 1904. 
 Corning, Brain Rest. N. Y. 1885. 
 Cousins, Ward, A Case of Profound Sleep, Med. Times 
 
 April 18, 1863. 
 Cox, Sleep and Dream. 
 Czermak, J. N., Nachweis echter hypnotischer Erscheiriungen 
 
 bei Thieren. 
 Czerny, Z. Zur Kenntniss des phys. Schlafes, Jahrb. f. 
 
 Kindheilk. 1896. 
 Daddi, Sulle alterazioni degli el. d. sys. ner. nell insonnia ex- 
 
 perim. Riv. di Pat. ner. e ment. III. 
 Dana, On Morbid Drowsiness, The J. of Ner. Men. Dis. 1884. 
 Danilewsky, Ueber die Hemmungen, Pfliiger's Archiv Bd. 
 
 XXIV. 1881. 
 Recherches physiologique sur l'hypnotisme des ani- 
 
 maux. 
 Beobachtungen und Versuchen iiber hypnot. Zust. 
 
 bei Thieren, Pfliiger's Archiv. 1873. 
 De Beer, Der Schlaf der Fische, N. Wien. Tag. 1895. 
 DeBoeck & Verhoegen, Contr. a l'etude de la circ. cereb., 
 
 J. de Med. Bruxelles,. 1890. 
 Delboef, Le Sommeil et les reves. 
 
 Demoor, La plasticite des neurones et le mechanisme du som- 
 meil, Bull, de la Soc. d'Anthr. de Bruxelles, XV. 
 
 1896. 
 De Sanctis & Neyroz, Exp. Invest. Cone, the Depth of Sleep, 
 
 Psych Rev. 1902. 
 Die Traume. 
 Devaux, E , Theorie osmotique du sommeil, Arch Gen. de 
 
 Med. 1906. 
 Dickson, Essays on Sleep 
 
Bibliography ioi 
 
 Didrichson, V. K., K voprosu o nervnoi bessonnitsi. 
 Drsdow, V. J., Morbus hypnoticus, Arch. f. Psych, u. Ner- 
 
 venkrankheiten, Bd. 13. 
 Dubois, R., Etude sur le mechanisme de la thermogenese et du 
 sommeil Ann. de l'Univ. de Lyon XXV. 1896. 
 Le centre du sommeil, C. R. Soc. Biol. 1901. 
 Sommeil naturel par autonarcose carbonique, C. R. 
 S. Biol. 1901. 
 Dugas, Le Sommeil. 
 
 Durham, The Physiology of Sleep, Guy's Hosp. Rep. i860. 
 Duval, Theorie histologique du sommeil, Soc. de Biol. 1895. 
 Edwards, J. Report of a case of Somnolency, Lancet V. I. 
 
 1884. 
 Errera, Le mechanisme du sommeil, Bull. Soc. Anthr. Brux- 
 elles. 1895. 
 Pouquoi dormons nous? Rev. sc. July, 1887. 
 Theorie toxique du sommeil, Soc. de biol. 1891. 
 Ewen, A Case of Narcolepsy, Bost. Med. and Sur. J. June, 
 
 1893. 
 
 Fechner, Elemente der Psychophysik. 
 
 Fere, Ch., Le Sommeil paraxystique, Semaine Medicale. 1893. 
 
 Crises de courbature, Annales Med. Psych. 1888. 
 
 Note sur l'apathie epileptique, Rev. de Med. 1891. 
 
 Note sur la narcolepsie epileptique, Rev. de Med. 1898. 
 Fischer, F., Epileptoid Schlafzustande, Arch, f Psych. uNervkr. 
 
 Bd. 8. 
 Fleming, Note on the Induction of Sleep, Br. & For. Med. Rev. 
 De Fleury, Grands symptomes neurastheniques. 
 Flint, Text Book of Physiology. 
 
 Foot, A. W., Narcolepsy, Dublin J. of Med. Sc. V. 82. 
 Forel, Der Hypnotismus. 
 
 Observations sur le sommeil du loir, Rev. de l'Hyp. 
 1887. 
 Forneris, Du role de la glande thyroide, Gazette Sarda. 1858 
 Foster, A New Standpoint in Sleep Theories Am., J. of Psych. 
 
 12. 1900. 
 Franceschi, F., II sonno patalogico, Riv. di pat. ner. e mentale 
 
 v. 9 
 
 Franck, Recherches sur les mouvements du cerveau. J. de 
 Tanat. 1877 
 
102 Bibliography 
 
 Freud, Ueber den Traum. 
 
 Friedman, M. Ueber die nichtepiletischen Absencen, Deut 
 
 Arch. f. Nervenheilk. 1906. 
 Gairdner, British Med. Jour. Oct. 30, 1875. 
 Galton, Inquiries. 
 
 Gay, J., Sleeping Girls. Lancet. July 3, 1880. 
 Gelineau, De la narcolepsie, Gaz. de Hop. 1880. Las 
 Gilbert, J. A., Loss of Sleep, Am. Medicine, IX, 1902. 
 Gilles de la Tourette, Des attaques du sommeil hysterique. 
 Girondea, De la circulation cerebrale. 
 Haffner, Schlafen u. Traumen. 
 Hagen, Psychologie und Psychiatric 
 Hammond, On Sleep. 
 Hanseman, Unters, ueber d. Wintershlafsorgan, Engelm., Arch. 
 
 f. Phys. 1904. 
 Hartley, Observations on Man. 
 
 Hayman, Sleeping Girl of Turville. Lancet. June 12, 1880. 
 Heerwagen, Statistische Unters, ueber Traume und Schlaf. 
 Henke, Hypothese iiber den Schlaf, Z. F. R. Med. Bd. XIV 
 Hennings, J. Ch. Von den Traumen. 
 Heubel, Abhangigkeit des wachen Gehirnzustandes von aus- 
 
 seren Erregungen, Pfliiger's Arch. XIV. 1877. 
 Hildebrandt, Der Traum. 
 
 Hill, The Physiology and Pathology of Cerebral Circulation 
 HOLLAND, Henry, Chapters in Mental Physiology. 
 Horvath, Beitr. z. Lehre uber den Winterschlaf, Verh d. phs. 
 
 med. Ges. Wiirzburg. 1878. 
 Howell, A Contribution to the Theory of Sleep, J. of Exp. 
 
 Med. 1897. 
 Hughlings, Jackson, Med. Times and Gazette. Dec. 6, 1862. 
 Jacoby, Falling Asleep while at Work, N. Y. Med. Rec 1890. 
 James, Psychology, V. I. 
 
 Jamieson, Edinburgh Med. Jour. July, 1871. 
 Kircher, A., Ars magica. 
 Kirchoff, Psychiatric 
 Kohlschiitter, Mechanik des Schlafes, Z. f. rat. Med. 1869. 
 
 Messungen der Festigkeit des Schlafes. 1862. 
 Kulpe, Outlines of Psychology. 
 Lajoux, Decouverte de la cause du sommeil naturel. 
 
Bibliography 1 03 
 
 Lamacq, Quelques cas de narcolepsie, Rev. des Med. 1897. 
 
 Landois, Text Book of Physiology. 
 
 Langlet, Physiologie du sommeil. 
 
 Lasegue, L'appetit du sommeil, Gaz. de Hop. January, 1882. 
 
 Lauhsen, Schlaf & Schlaflosigkeit, Bed. kl. Woch. 1897. 
 
 Legrand, Un cas de narcolepsie, France Med. 1888. 
 
 Lehman, Die Korperlichen Aeusserungen Psychischer Zustande 
 
 Levi, Somnolence, Arch. Gen. de Med. 1896. 
 
 Lewes, Physiology of Common Life. 
 
 Liebault, Streifzuge in das Gebiet der passiven Zustande, des 
 
 Schlafes und der Traume Z. F. Hyp. 1893. 
 Lombard, Varieties of the Normal Knee Jerk, Am. J. of Ps 
 
 1887. 
 Loney, D. W., An Obscure Case, Med. Record. June, 1888 
 Lorand, Myxoedema & maladie du sommeil, Presse Medicale 
 
 1905. 
 Macario, Du sommeil. 
 
 MacCormack, A Case of Narcolepsy, Brain. 1889. 
 Macfarlane, Dreaming. 
 Mackowitz, V., Z. Kasuistik der Schlaftrunkenheit, Arch. f. 
 
 Krim. Anthropol. 1903. 
 Macnish, Philosophy of Sleep. 
 Madden, T. M., On Lethargy or Trance, Dublin J. of Med .Sc 
 
 1881. 
 Maillard, Etude sur le sommeil. 
 Makenzie, Circulation of the Blood during Sleep, J. of M. Sc 
 
 1891. 
 Manaceine, Son kak tret zhisni tsheloveka. 
 Manaceine, Le sommeil. 
 Marduel, Note sur un cas de maladie du sommeil, Lyon Med 
 
 1872. 
 Marshal Hall, Practical Observations and Suggestions in 
 
 Medicine. 
 Martin, L. de St., Influence du sommeil, C. R. Ac. des Sc. 
 
 1888. 
 Matas, Morbid Somnolence, New Orleans Med. and Surg. J 
 
 January, 1884. 
 Maury, Le sommeil. 
 Mauthner, Pathologie u. Physiologie des Schlafes., W. Med. 
 
 Woch. 1890. 
 
104 Bibliography 
 
 Mays, Ueber die Bewegungen des Menschl, Gehirns, Virchow's 
 
 Arch. Bd. 88. 
 Mendel, Ueber Anfalle von Einschlafen, Lyon Med. 1872. 
 Michelson, Unters. uber die Tiefe des Schlafes, Psych Arb. II. 
 
 1897. 
 Michelson, Die Tiefe des Schlafes. 
 Moll, Der Hypnotismus. 
 Monninghoff u. Piesbergen, Messungen ueber die Tiefe des 
 
 Schlafes, Z. f. Biologic 1883. 
 Moore, C. A., On Going to Sleep. 
 
 Morgan, Sir T. C, Sketches of the Philosophy of Life. 
 Mortimer, Granville, Sleep and Sleeplessness. 
 Mosso, Fear. 
 
 Sulla circulazione del sangue nel cervello. 1880. 
 Muller, J. Handbuch der Physiologic 
 Mumford, Waking, Sleeping and Dreaming. 
 Myers, Human Personality. 
 Nicard, Le sommeil normal. 
 
 Obersteiner, Zur Theorie des Schlafes, Z. f. Psychiatric 1872. 
 Oppenheim, Lehrbuch der Nervenkrankheiten. 
 Oppenheimer, Physiologie des Schlafes, Du Bois* Archiv. 1902. 
 Parish, E., Ueber die Trugwahrnehmung. 
 Parmentier, De la forme narcoleptique, Arch. Gen. de Med 
 
 1891. 
 Patrick and Gilbert, On the Effects of Loss of Sleep, Psych. 
 
 Rev. III. 
 Pettenkofer u Voit, Ueber die Kohlensauerausscheidung 
 
 und Sauerstoffaufnahme wahrend des Wachens und 
 
 Schlafens, Sitzb. d. Kngl. Ak. d. Wiss. zu Miinchen 
 
 1866-67. 
 Pfluger, Theorie des Schlafes, Arch. f. Phys. V. 10. 1875. 
 Pictet, A., Obs. sur le sommeil chez les insects, Arch, de Ps. 
 
 1904. 
 Pilcz, Ueber die psych. Erscheinungen des Schlafes, W. Med. 
 
 Woch. 1891. 
 Playfair, On Sleep, North. J. of Med. 1844. 
 Popov, M. N., K patologii Bessonitzi, Archiv. Psychiat 1897. 
 Porter, K. H., Narcolepsy. 
 
Bibliography 105 
 
 Preyer, Ueber eine Wirkung der Angst bei Thieren, C. f. Med. 
 
 Wiss. 1873. 
 Die Cataplexie und der thierische Hypnotismus. 
 Ueber die Ursache des Schlafes. 1877. 
 Prevost, Sur le sommeil. 
 
 Prince, Morton, The Dissociation of Personality. 
 Pupin, Le Neurone. 
 Purkinje, Wagner's Handworterbuch der Physiologic III. 
 
 1846. 
 Rachel, Tissue-Metamorphosis and Sleep, Med. Record. 1883. 
 Radestock, Schlaf und Traum. 
 Ray, Mental Hygiene. 
 Rayner, H., Sleep in Relation to Narcotics, J. M. Sc. July, 
 
 1902. 
 Regis, Mental Medicine. 
 Renaudin, Sur lTnfluence pathologique de lTnsomnie, Annals 
 
 Medico Psychologiques T. III. 
 Rich, B., Ueber den physiologischen und pathologischen Schlaf. 
 Richardson, The Phenomena of Sleep. 
 Robert, Der Traum. 
 
 Rosenbaum, Warum mussen wir schlafen ? 1892. 
 Rousseau, Observ. de narcolepsie, Encephale. 1881. 
 Rummo, E. Ferranini, La circulation du sang dans le cerveau 
 
 del homme pendant le sommeil. 
 Sahlmen, Ein fall von Schlafsucht, Berl. kli. Wochensch. 1881. 
 Sajo, Der Schlaf der Insekten, Prometheos VII. 1896. 
 Salmon, A. Sull origene del sono. 1905. 
 Schleich, Die Neuroglia u. ihre Beziehung z. Schlaf, Z. f. pad. 
 
 Ps. 1904. 
 Scholz, Sleep and Dream. 
 
 Sergueyeff, Physiologie de la veille et du sommeil. 
 Sidis, B., The Psychology of Suggestion. \ 
 
 Psychopathological Researches. 
 Multiple Personality. 
 Studies in Psychopathology, B. Med. and S. J. March, 
 
 1907. 
 Hallucinations, Psych. Review. 1904. 
 Sherrington, The Integrative Action of the Nervous System, 
 Simpson, The sleep of Molluscs, Pop. Sc. Monthl. I. 1894. 
 
106 Bibliography 
 
 Skerrit and Stewart, A Case of Potracted Sleep, Br. Med. J. 
 
 1898. 
 Soca, Sommeil, Nouv. Ic. de la Salp. 1900. 
 Sollier, Genese et Nature de l'Hysterie. 1897. 
 Sommer, Neue Theorie des Schlafes, Z. f. rat. Med. 1868. 
 Soukhanoff, S., A Case of Pathological Sleep, The J. of Men. 
 
 Pathology. October, 1902. 
 Spitta, Schlaf und Traumzustande. 
 Stefanowska, Examen du cerveau de souris endormis, J. de N. 
 
 1900. 
 Storring, G., Vorlesungen ueber Psychopathologie. 
 Stout, Manual of Psychology. 
 Strumpell, Beitrage z. Theorie des Schlafes. Pfliiger's Archiv. 
 
 XV. 
 Szczypiorsky, Plusieurs attaques de sommeil paradoxal. chez un 
 
 aliene, Annales Med. Psych. November, 1891. 
 Tarchanoff, Obs. sur le sommeil normal, Arch, ital de Biol. 
 
 1894. 
 TsCHlscH,Eksperim,iscledovanie vnimania vo vremia sna,Obosr. 
 
 Psych. 1896. 
 Tissie, Les Reves. Exp. sur Pattention pendant le sommeil, 
 
 Rev. de Ps. 1896. 
 Van Gieson and Sidis, Neuron Energy, Arch, of N. and 
 
 Psychop. 1898. 
 Vaschide et Pieron, Psychologie du reve. 1902. 
 
 devaluation du temps pendant le sommeil, Int. des 
 
 Biol. I. 
 Verworn, Beitrage z. phys. des Centralnervensystem. 1898. 
 
 General Physiology. 
 Vogt, Zur Kentniss des Wesens des Hypnotismus, Z. f. Hyp. 
 
 i8 95 . 
 
 Vulpian, Lecons sur Pappareil vaso-moteur. 
 
 Wernicke, Lehrbuch der Gehirnkrankheiten 
 
 Weygandt, Beitrage z. Psych, des Traumes, Phil. Stud. XX. 
 
 Beitr. z. Psych, des Schlafes. Ber. ueber d. I. Kon. 
 
 f. exp. Psych. Giessen. 1904. 
 Wundt, Hypnotismus und Suggestion. 
 Outlines of Psychology. 
 
 Grundiizge der phys. Psychologie. 
 Wurtz, The Chemistry of Sleep, Popular Sc. Mo. 1894. 
 Zbinden, La crainte de l'insomnie, Arch, de Psych. II. 
 
 t Ap '09 
 
An Experimental Study 
 
 of Sleep 
 
 BORIS SIDIS 
 

 
 
 «b^ ism*;* ^ 
 
 ^V V^\/ ^v^V v^v 
 
 
 
 V ^ 
 
 ,4°, 
 
 o V 
 
 .* *> 
 
 
 
 
 
 * ^ 
 
 ^ 
 
 *<?* 
 
 >* ♦ •VL'. 
 
 »"i»*" f° 
 
 
 
 4V ,£. 
 
 Sfcfe %/ &K* V><° f^hfe %/ .££' 
 
 
 . A <>* .ill*. *> V s .'•». %, 4<r ,^Lr, <> v 
 
 ^^ •' 
 
 ♦^ 
 
 
 
 v >*~v-.WV V-- 
 
 
 a si 
 
 A0 
 
 4q 
 
 
 

 
 <> 
 
 % 
 
 
 s? "Ob 
 
 .6* 
 
 
 7 *A* * 
 
 ^°x. 
 
 
 \/ 
 
 
 V* 3» v** #• %/ .'££&- <w 
 
 ®OOK"BfNDlNC « 
 
 M, DCK|T0WN. PA § 
 
 ^_Ou*(ih Bound 
 
 *\