PUBLIC HEALTH LIBRARY CHAPTERS MENTAL PHYSIOLOGY. LOVDOK : rXIMTBD BT BPOTT18WOODB AKB CO. VBW-8TBBBT S(tUABB. CHAPTERS OK MENTAL PHYSIOLOGY. BY SIU HENRY HOLLAND, Bart. M.D. F.E.S. D.C.L. OXON. ETC. ETC. FELLOW OF THE ROYAL COLLEQB OF PHYSICIANS PHYSICIAN IN ORDINARY TO THE QUEEN PHYSICIAN IN ORDINARY TO H.R.H. THE PRINCE CONSORT. FOUNDED CHIBFLY OK CHAPTERS CONTAINED IN "MEDICAL NOTES AND REFLECTIONS' BY THE SAME AUTHOR. "0^ fBESIT SBCOND EDITION riSED AlfD BNLA.BaBB. LONDON LONGMAN, BROWN, GREEN, LONGMANS, & ROBERTS. 1858 4^ssy6 h5? .»R*f^ — . PUBUC HEALTH LlBRAR'f PREFACE TO THE SECOND EDITION. Another edition of this volume being required, - I have availed myself of the opportunity of making various additions and alterations, derived in part from further thought on these subjects ; in part from the progress of physical knowledge during the intervening time. I may mention, how- ever, that I have found no cause to alter any of the general views propounded in these papers. Nor have I thought it right, by any fresh hypothesis, or more ambiguous language, to seek exemption from the charge of having stated difficulties, without resolving them. These difficulties do actually exist ; and it is better for the interests of truth and science that they should neither be disguised nor qualified. In the case of those A3 VI PREFACE TO THE SECOND EDITION. which are not in their nature insuperable, I have everywhere endeavoured, as far as lay in my power, to suggest the direction and method of pursuit best fitted for overcoming them. Though these chapters are far from being offered as a complete treatise on Mental Physio- logy, yet I am willing to believe that the par- ticular topics they embrace, as well as the method of treating them, with constant reference to that law of continuity which pervades every part of creation, may serve to elucidate many points not coming directly under review. In further reference to this object, and for the better connexion of the whole, I have made a slight change in the order of the chapters ; placing first in the volume those which relate to the phenomena of Sleep, Dreaming, &c. It is the place fitly appropriate to a function which occupies nearly a third part of human existence ; and which, considered under the view I have especially sought to enforce, illustrates more variously and strikingly than any other, every part of Mental Physiology. London : May, 1858. PREFACE THE FIKST EDITION. Some explanation is necessary of the title and plan of this volume, that the reader may rightly apprehend not only the objects proposed, but also the method adopted to fulfil them. The title will be understood as expressing that particular part of Human Physiology which comprises the reciprocal actions and relations of mental and bodily phenomena, as they make up the totality of life. I need not dwell on the great interest of this subject. It is attested, as every part of this volume will show, not solely by the natural and healthy conditions of exist- ence, but even more remarkably by those of dis- order and disease. Scarcely can we name a morbid affection of body in which some feeling A 4 Vlll PREFACE TO or function of mind is not concurrently engaged — directly or indirectly — as cause or as effect. No physician can rightly fulfil his duties without an adequate knowledge of, and constant regard to, these important relations. I have adopted the title of Chapters on Phy- siology ; partly to avoid the profession of a com- plete treatise, which this is not; — partly to indicate that most of these topics, and even their titles, are taken from another work, the first edition of which was published thirteen years ago. Those who may have read my "Medical Notes and Reflections," will perhaps recollect such Chapters, as occurring in different parts of a volume chiefly devoted to subjects more strictly medical in character. Thus inter- posed, however, among the latter, they were deficient in the sequence and connexion natu- rally belonging to the topics they treat of; and which may be considered almost indispensable to a thorough understanding of the subject. This deficiency I have sought to supply in the present volume by bringing these several Chap- ters into one series ; and by adding others which have appeared necessary to the completion of THE FIRST EDITION. IX the plan proposed.* While preserving the titles of those derived from my former work, and fol- * These new chapters were originally intended for a second volume of my former work ; but I have thought it better to place them here, as well from their close connexion with the other sub- jects treated of, as also from a doubt I entertain as to the publica- tion of a second volume in the same form as the first. Though happily there are many reasons justifying the hope that this work has been useful to the profession, yet I am led to consider it as a fault in the original plan, that the subjects are too numerous, and too little connected in series, for that ready reference, which it is important both for the author and his readers to obtain. A few words more I may be permitted to add regarding this former work. In selecting the subjects for it, I chose those espe- cially which, as involving general relations, not perhaps sufficiently regarded, seemed best adapted to suggest new views as to the causes, character, and treatment of disease. In the discussion of the subjects so chosen, the plan of the volume limited me to certain general principles and outlines of inquiry. But I still entertain the hope that some of these topics may be more fully examined by other writers ; and under this view I venture to suggest a few of the Chapters, which seem especially to admit of such larger discussion. I would name the following : " On Here- ditary Diseases ; " " On Morbid Actions of Intermittent Kind ; " "On the Connexion of certain Diseases;" "On Diseases com- monly occurring but once in Life;" "On the Influence of Wea- ther in relation to Disease ;" " On disturbed Balance of Circula- tion and Metastasis of Disease." And to these I would willingly add (though I have myself applied the hypothesis only to the Indian Cholera) the general question regarding the Influence of Organic Matter in the atmosphere as a cause of disease — a subject which I feel assured will hereafter gain greatly in importance, and illustrate many points in pathology, hitherto unexplained or obscure. X PREFACE TO lowing the same general train of reasoning to the same conclusions in each, I must mention that they have been almost wholly rewritten, and very materially enlarged ; such alterations and additions being made necessary, partly for the connexion of the subjects thus brought into closer association ; principally from the recent accessions of knowledge on numerous points having express relation to them. Even since the last edition of my " Medical Notes," the rapid progress of Physiology — ever blending it- self more closely with the general laws and in- ductions of physical science — has converted into certainty many things which could then be offered only as surmises, unsupported by any direct proof. Much of course will be found in this volume which is familiar to those who have studied the subject, especially of late years. But, if I do not deceive myself, there are still certain facts not heretofore duly recognised or defined, and certain relations of phenomena requiring fuller illustra- tion than they have yet received. These I have sought to embody in the ensuing Chapters, in the order which seems best calculated to give THE FIRST EDITION. XI connexion and unity to the whole. To arrange under new combinations what is already known to uSj is often in itself a source of fresh knowledge, or a valuable means of correcting previous error. Various instances to this effect will, I trust, occur to the reader in his progress through the volume. I may add, that in the discussion of the subjects, though obliged to adopt certain divisions for the sake of clearness, I have kept in constant view that great law of continuity, which equally governs all mental and material phenomena. No conclusions are more secure, or more profitable, than those drawn from a careful notice of con- tinuous relations ; and of those gradations of change, which bring extreme cases within com- mon laws, and reconcile anomalies with facts familiar to experience. To this I would advert, as a principle I have largely applied in every part of the volume. The topics treated of are such in their nature as perpetually to bring us to the very confines of metaphysical speculation. Except in the case of one great question, which could not be put aside, I have carefully avoided passing over this boun- dary. Convinced of the general truth of the Xll PREFACE TO maxim, that " it is safer and easier to proceed from ignorance to knowledge than from error," I have endeavoured throughout to separate what is known from that which is unknown — what is capable of being reached by the human under- standing from that which is presumably unattain- able by it. The close adherence to this principle will probably expose me to the charge of having surrounded the subject with unresolved doubts and difficulties. But I think it far better to incur this imputation, than to assume a knowledge not yet possessed, or to cover the deficiencies of reason by any mere artifices of language. In different parts of this volume I have had occasion to advert to those Mesmeric phenomena and doctrines, and the topics collateral to them, which have draAvn so largely upon public atten- tion of late years. Having the interests of truth solely in view, it has seemed to me that such reference might most legitimately, as well as most usefully, be made, through the relation of the phenomena in question to those other parts of physiology, which I believe to explain their real nature, and the conditions on which they THE FIRST EDITION. Xlll chiefly depend. To this principle I have adhered in every part of the discussion. I prefaced my former work by a Chapter on the principles of Medical Evidence. I have re- tained this, with certain additions made to it, in the present volume ; since, though not directly associated with the subjects now treated of, the principles it suggests are of equal importance here, and cannot safely be neglected in any part of the discussion. CONTENTS. CHAPTER I. Page On Sleep --------l CHAP. ir. On the Relations of Dreaming, Insanitt, etc. - - 39 CHAP. III. Effects of Mental Attention on Bodilt Organs - - 79 CHAP. IV. On Mental Consciousness, in its Relation to Timb and Succession - - - - - - -115 CHAP. V. On Time, in further Relation to MENT^kx. Functions - 140 CHAP. VI. On the Memory, as affected by Age and Disease - - 150 XVI CONTENTS. CHAP. Vll. Page On the Brain as a Double Organ - - - - 179 CHAP. VIII. On Phrenology ------- 203 CHAP. IX. On Instincts and Habits - - - - - - 212 CHAP. X. On the Present State of Inquiry into the Nervous System 255 CHAP. XL On Medical Evidence ------ 329 MENTAL PHYSIOLOGY. CHAPTER I. ON SLEEP. I HAVE briefly stated, in the Preface, the reasons which now lead me to place this Chapter on Sleep at the beginning of my volume. No phenomenon of human existence illustrates so largely every part of Mental Physiology ; — nor does any one illustrate it with closer application to the practical uses of man. It concerns equally, indeed, both the physician and the metaphysical inquirer, to learn all the conditions of this wonderful function of life, and the causes by which they are affected and modified. Wonderful it may well be called ; for what more strange to our conception than that nearly a third part of our total existence should be passed in a state thus far detached from the external world! — a state in which personal consciousness and sense of identity are scarcely maintained ; in w^hich memory and reason are equally disturbed ; and yet, notwithstanding, one in which the fancy works variously B 2 ON SLEEP. and boldly, creating images and impressions that are frequently carried forwards into waking life, and blend themselves deeply and strongly with every part of our mental existence.* It is the familiarity with this great function of our nature which prevents our feeling how vast is the mystery it involves ; how closely interpreting all the phenomena of mental derangement, whencesoever produced; and, yet further, how singularly shadowing forth to our conception the greater and more lasting changes the mind may undergo without loss of its individuality. The subject, indeed, is far from having yet received all the notice it deserves, either from the physiologist or the physician. Various knowledge, it is true, has been gained of late, by closer inquiry into the physical con- nexions of sleep with other actions of the body ; and especially with those functions of the nervous system to which it is most intimately allied. But there is still ample scope for research ; having reference partly to the physiology of sleep, and its relations to these particular functions — partly to its connexion with the various forms and treatment of disease. And since, for the success of an inquiry of this nature, much depends on the method pursued, it will be an especial object of this chapter to indicate that manner of looking into the phenomena of sleep, which I consider best to illustrate * " Half our days we pass in the shadow of the earth, and the brother of death extracteth a third part of our lives," says Sir Thomas Browne ; a writer whose genius and eloquence give him a high place in English literature, as well as in that of the profession to which he belonged. ON SLEEP. a their nature, and the many seeming anomalies they bring before us. It is singular that in a state thus familiar, and filling so large a portion of the term of life, it should yet be difficult to distinguish that which is its most perfect condition — the condition furthest removed from the waking state. No certain proof of this can be liad either from our own recollections, or from the feelings on awakening. That which is often felt and described as heavy sleep, is generally, we have cause to presume, the least perfect form of it ; the very consciousness of such state, as well as the term unrefreshing usually applied to it, giving proof that it is not one of natural and complete repose. The recollections of sleep seem, indeed, in great part to depend on the dream or other condition immediately antecedent to awakening ; or even on the manner, abrupt or otherwise, in which waking takes place. But the whole phraseology, as well as feeling, connected with this part of life, has so much of poetic vagueness about it, that we cannot adopt with assurance any conclusion drawn from language only. The best proofs as to the point in question — though still, in many respects, ambiguous — are those derived from the observation of others. That may be presumed generally the soundest sleep in which there is seen by those around to be most complete tranquillity of the bodily organs commonly dependent on the will. Sen- sation or perception, the other great function of the brain involved in this state, furnishes evidence to the same point in the varying effect of stimuli applied to the senses when thus closed. And this test might B 2 4 ON SLEEP. perhaps be the most certain, were it not that we have cause to believe the different senses to be often unequally closed, even at the same moment of time ; with a further source of ambiguity arising from the occasional passage of sleep into coma, more or less complete, through gra- dations which cannot be defined by any limits we are able to draw.* Evidence by ready tests as to the soundness of sleep is of material value in practice; both in reference to the important point last mentioned, and because the physician is very liable to be misled by the error of the patient himself on this subject. The best proof which the latter can offer is probably the absence of con sciousness or recollection of having dreamed. For, whatever interpretation we may give to this most mysterious phenomenon of life, it seems certain that the state of consciousness or recollected dreaming is that which comes into closest connexion with our waking existence. It forms a passage or gradation from one state to the other; — an obscure and broken link, it may be, yet belonging to that chain which gives succession and continuity to all the phenomena of our being. This assumption, however, that the soundest sleep is to be interpreted by the absence of any recollected dreams, must not be taken in proof that no dreams have in such cases existed. The observation of those around on the acts of a sleeping man, including even speech * Aristotle, towards the end of his Book, TItpi 'EvvyrviutVy has some curious remarks on the subject, well illustrated by examples. All his writings on this, and other collateral topics, deserve much more intimate perusal than is given to them at the present time. ON SLEEP. 5 among them; and the recollections often occurring to himself afterwards of dreams of which there has been no memory at the moment of waking, — show that no such inference can rightly be drawn. The question as to this point, indeed, is one that has been much debated, and an absolute proof is hardly perhaps -within our reach. But the more probable opinion I think to be, that no moment of sleep is without some condition of dreaming ; — that is, that images are always present to the individual consciousness, and trains of thought founded thereon ; however vague and unreal in them- selves, and however slight, if any, the recollections they carry on to our waking existence. To believe otherwise is to suppose two different states of sleep, more remote from each other than we can well conceive any two conditions of the same living being; — one, in which sensations, thoughts, and emotions are present in activity and un- ceasing change; — another, in which there is the absence or nullity of every function of mind; annihilation, in fact, for the time, of all that is not merely organic life. Though we cannot disprove the latter view — and must admit the difficulty of explaining the sleep of an infant in any other sense — yet is it on the whole more rea- sonable to suppose that no state or moment of sleep is utterly without dreaming; the actual diversity of condition being testified chiefly, though very im- perfectly, by the varying recollection of what has passed through the mind during this periodical sepa- ration from the world without.* * This curious question is noticed explicitly by Aristotle, £iia Tiva aiTiav Ka£evdovTeCj ore jiev oveipuiTTOvaiv^ oTt ii ov' ^ (n'ftiaivti B 3 6 ON SLEEP. Without dwelling further on a question thus difficult of solution, we may better advert to a point of greater certainty, and of consummate importance in all our rea- sonings, practical and theoretical, upon sleep, viz., that it is not a unity of state with which we are dealing under this name, but a series of fluctuating conditions, of which no two successive moments are perhaps strictly alike. It may even be affirmed, with assurance, that these variations extend from complete wakefulness to the most perfect sleep of which we have cognisance either from outward or inward signs ; and that there is no- where any breach, or even sudden change, in that con- tinuity of actions which maj'^ be said to form the identity of our being. This is the view to which I have already alluded. In the symptoms, as well as treatment, of disease, a due regard to this fact is often of very mate- rial consequence. While, looking to the subject physio- logically, it is absolutely essential to the truth of our conclusions ; and will assist us, beyond any other mode of research, in explaining all the seeming anomalies of this great function of life. Attaching such importance to this view, and seeing Hiv 6.H Ka9(vSov(Tiv IvvTrviaZuVj aW oh fivijixovevovm. TIipi "Yirvov. Lord Brougham, in his Discourse on Natural Theology, holds an opinion the reverse of that stated above ; and vindicates, with his wonted power of argument, the belief that we dream only during the time of transition into and out of sleep, when the two states are graduating into each other. Descartes has tersely expressed an opinion bearing upon this question. " II me seroit bien plus aise de croire que I'&me ces- seroit d'etre, quand on dit qu'elle cesse de penser, que de concevoir qu'elle soit sans pensee." ON SLEEP. 7 the familiarity of the phenomena on which it is founded, we may well feel surprise that it should be so little re- garded in all common reasoning on the subject. We speak, indeed, of light sleep, or heavy sleep, or broken sleep ; but these and other vague phrases (often, as we have seen, erroneously applied) give little idea of that gradation of states which connects the waking and sleeping life of man — the extreme and opposite limits of his worldly being. Long and familiar habit can alone explain this indifference. In infancy, wonder, as an intellectual agent (and it has not inaptly been called " the mother of knowledge " *), is yet undeveloped. As life advances, the phenomena have become so habitual, that we satisfy ourselves with the vague phrase of natural ; and look carelessly on the wonderful aspects of sleep, as we usually see it in the healthy state ; or even when passing into the comatose condition of dis- ease. A child may be rocked or sung into a slumber of hours. A man may be speedily thrown into sleep by a certain posture of head, by a full stomach, by a dull or difficult book, by a monotonous sound, by repetition of numbers or forms of words, by over exercise and fatigue of the senses. Dreams come on, changing at every mo- ment ; various movements of the voluntary organs ; often articulate speech ; — yet all these things pass un- heeded before us from their familiarity. But let it hap- pen that similar conditions are produced by mesmeric * A fact well expressed long before by Aristotle, Aid yap to Sravfjidi^eiv o'l dvOpioTroi^ Ka\ vvv Kai to 7rp(0T0V ijpKavTO (piXotrocptiv. Metaphys. i. 12. B 4 8 ON SLEEP. passes or other similar means — thus placing the as- pects and acts of sleep in strong detached light — and the phenomena are looked upon with astonishment and awe. The deep interest which rightly belongs to sleep in its most ordinary state, is excited for the first time by the unwonted manner in which it is brought on ; and a great function of our nature, ever open to rational inquiry, is thus mystified and obscured to our reason by the manipulations of art. Kecurring now to this view of sleep, as a succession of ever-varying states, common experience will be found to furnish us with endless illustrations. Look, for ex- ample, to the passage from waking to sleeping, and see with what rapidity and facility these states often alter- nate with each other. It is in the act of transition that we may best authenticate our knowledge of these phenomena ; and the most ordinary incidents are full of instruction, if the mind be duly directed to observe them. Take the instance of a person seduced into slumber by an easy chair and warm room, aided perchance by a recent meal. He will feel himself (especially if there be talking around, or other causes impressing the senses) long lingering, as it were, on the very verge of sleep ; — at one moment conscious of what is going on about him; — then passing into confusion of thought ; — next losing for an instant all consciousness of things without; — and as suddenly, from the slightest cause of excitement, resuming it again. The rapid succession and variety of these changes show how multiform, yet ever continuous, are the states of the sensorium which ON SLEEP. 9 they thus interpret to us. Another familiar instance is that of being on horseback when much wearied from want of rest. Here, at every moment, the mind lapses into a dozing state, from which the loss of the balance of the body as frequently and suddenly arouses it. In this case, and in all of like kind, neither the sleep nor the waking consciousness is perfect ; but the mind is kept close to an intermediate line, to each side of which it alternately passes. No such line, however, really exists ; and it is merely a rapid shifting to and fro of conditions of imperfect sleep and imperfect waking, giving curious proof of the manner in which these states graduate into one another.* Or take another common case of a person seeking rest on an uneasy bed, or under the influence of pain or disordered digestion. Obviously even to himself, and still more to those around him, there is incessant alteration of the state of sleep; testified by various bodily movements, by partial consciousness to external objects, by dreams broken and renewed — a strange in- terlacing of the two conditions, which thus divide our existence. Watch again the loss of voluntary power in a person sinking quietly into sleep; — how gradual it is — how exact a measure of the state coming on. An object is grasped by the hand while yet awake — it is seen to be * Exact estimate of time is obviously difficult here : but I have frequently, when in a carriage, obtained proof that this alternation of the loss and recovery of waking consciousness must have oc- curred at least three times within a minute, by knowing the dis- tance crone over while the observation was made. to ON SLEEP. held less and less firmly, till at last all power is gone, and it falls away. The head of a person in a sitting posture gradually loses the support of the muscles which sustain it upright : it droops by degrees, and in the end falls upon the chest. Here, again, we have proof of the rapidity with which the loss and recovery of voluntary power may alternate on the confines of sleep. The head falls by withdrawal of power from particular muscles. The slight shock thence ensuing partially awakens and restores this power, which again raises the head. It is well known how often this may be repeated within a short space of time, each such motion implying a definite change in the voluntary power. The gradual changes which occur in the perceptions from the senses, while sleep is coming on, afford the same curious notices of the condition of the mind in its relations to the world without. The sight, the hearing, the touch, all show the progressive lessening of sensi- bility through every stage of change, with the same fluctuations which attend those of the voluntary power ; and giving similar proof that the state of sleep is ever varying in degree as respects these several functions. We find, for example, one condition of sleep so light, that a question asked restores consciousness enough for momentary understanding and reply ; and it is an old trick to bring sleepers into this state, by putting the hand into cold water, or producing some other sensation; not so active as to awaken, but sufficient to draw the mind from a more profound to a lighter slumber. This may be often repeated, sleep still going on ; but make the sound louder and more sudden, and complete ON SLEEP. 11 waking at once ensues. The same with other sensa- tions. Let the sleeper be gently touched, and he shows sensibility, if at all, by some slight muscular movement. A ruder touch excites more disturbance and motion, and probably changes the current of dreaming : yet sleep will go on ; and it often requires a rough shaking, particularly in young persons, before full wakefulness can be obtained. I have seen children pinched or pricked sharply with a pin, without other effect than that of making the slumber restless for a time. These various cases, which depend severally on the intensity of sleep, and on the kind and degree of the exciting causes without, will be found to explain many of those mesmeric appearances which are offered to us under a widely different interpretation. It is certain that the faculties of sensibility and volition are often unequally awakened from sleep. The case may be stated, familiar to many, of a person sleeping in upright posture, with the head falling over the breast; in whom sensibility is suddenly aroused by some external impression, but who is unable, for a certain time, to raise his head, though the sensation produced by this delay of voluntary action is often singularly distressing. The actions of chloroform, and other anaesthetic agents, curiously illustrate the same interesting fact; and merit even more attention than they have yet received, in reference to these and other phenomena.* * I have notes of several cases of disease, singularly illustrating this disjunction of sensibility and volition. In one remarkable case of a young lady, in whom, for many weeks together, a state of 12 ON SLEEP. The same mode of observation may be followed as to the higher mental faculties, to which these functions severally minister. The state of unconscious reverie (as distinguished from that voluntary abstraction which a man may exercise for the most exalted purposes) is one of the first conditions which intervene in the progress we are describing. The mind kept for some time, as often happens, in a state intermediate between sleep and waking, is capable of recognising those rapid and repeated changes by which it shifts to each side of the imaginary line ; and the moments of waking con- sciousness afford distinct and curious notice of the slumbering moments which have intervened — of those strange aberrations of thought (" the mimicry of reason," as Dryden well calls them), in which volition is dormant, and memory awake only to furnish incongruous images to the dream.* The self-analysis we can employ in trance lasting some hours came on at a certain time each day, the gradation of change was strikingly marked. The voluntary power in moving, speaking, &c., was wholly suspended, while the per- ception by the senses still remained. These next disappeared, and the trance became complete ; ending, after a time, in severe tetanic spasms, sometimes reaching the state of opisthotonos. The exact uniformity in the series of these morbid changes formed a striking circumstance in the case. The first step towards amendment was by irregularity in their occurrence. * Though poetry is not often admissible in discussions of this nature, I cannot forbear referring to some lines of Dante, which admirably express the transition we are describing : — " E tanto d' uno in altro vaneggiai, Che gli occhi per vaghezza ricopersi, E pensamenti in sogno trasniutai." ON SLEEP. 13 this case better shows than any reasoning how com- pletely these states graduate into each other, and to what extent the acts of the wakeful mind interpret those of the most perfect sleep. But the topic of dreaming, to which we here approach, is too large and curious to be submitted to this cursory survey; and, though hardly separable from any discussion of the nature and conditions of sleep, I must reserve to the next Chapter the observations I have to make on this subject. The facts belonging to Somnambulism afford the most remarkable illustration of the phenomena we have been recording. Though their rarer occurrence gives them the semblance of exceptional instances, they depend on similar causes, and express equally the rela- tions by which different states of sleep graduate into one another, and into the functions of the waking state. The fact, that we can often succeed, by the excitement of external impressions, in altering the acts of the som- nambulist without awakening him, is a striking proof of the various degrees in which the senses may be merged in the condition of sleep. Bichat, whose observations on the subject have all his wonted originality of thought and language, more distinctly propounds this view of the great function of which we are treating. The phrase, "Le sommeil general est I'ensemble des sommeils particuliers," ex- presses his view of the nature and complexity of this state, as one in which each separate sense and mental faculty may be at the same moment in very different conditions; even so far, that some may be deemed U ON SLEEP. awake, while others are wholly wrapt in sleep.* With slight qualification, particularly as to the latter point, this opinion must be admitted as best accordant with facts, and necessary indeed to the right explanation of the phenomena. It comes nearest to what may be termed a just theory of sleep; and any seeming deviation from simplicity in its first aspect is more than compensated by the facility it is found to give to all reasoning on the subject. The proofs are numerous, through instances of the kind already stated; and in ail such examples, the simpler and more limited the circumstances, the clearer is the evidence they set before us. Other facts still require tx) be noticed in illustration of these views. Though admitting sleep to come on by a series of gradations from the waking state, the con- sequence by no means follows that all these gradations must be gone through in the passage from one stage of sleep to another. The time occupied in transition is doubtless very different in different cases; and in many instances, particularly in certain nervous dis- orders, it would seem that the changes or alternations between two states remote from each other may take place with extreme abruptness; either in effect of external impressions, or from the sudden and inexplicable aberrations of dreams. It is highly probable, indeed, that the manner in which sleep is induced in each case, does much to determine its particular conditions at the * In conformity with this view, Bichat says of dreams, " lis lie sont autre chose qu'une portion de la vie animale echappee de I'engourdissement o^ Tautre portion est plong6e." ON SLEEP. 18 moment, in the first stage of slumber ; and possibly even its further course and duration. It may be brought on more or less suddenly ; and more or less completely, as respects the degree in which the senses are closed, and the mental functions altered or absorbed; and these diver- sities, equally observable in the passage again to the waking state, depend greatly in both cases on the circumstances under which the change of state begins. The causes which disturb or suspend sleep are as various as those which bring it on ; and are not less illustrative of the manner in which the change occurs. These results indeed might have been in part inferred from the views already propounded ; but they are confirmed to us by various evidence of facts ; and are obviously very important in the explanation of appearances which have recently perplexed the minds of many candid ob- servers.* Sleep, then, in the most general and correct sense of the term, must be regarded not as one single state, but a succession of states in constant variation : — this varia- tion consisting, not only in the dififerent degrees in which the same sense or faculty is submitted to it ; but also in the different proportions in which these several powers are under its influence at the same time. We thus associate together under a common principle all the phenomena, however remote and anomalous they may seem; — from the bodily acts of the somnambulist; * The observations of Mr. Braid, more especially, have done much to establish this fact of the altered character of sleep in effect of the manner in which it is brought on ; and this may be regarded as a very valuable part of his researches. 16 ON SLEEP. the vivid, but inconsequent, trains of thought excited by external impressions ; the occasional acute exercise of the intellect ; and the energy of emotion — to that profound sleep, in which no impressions are received by the senses ; no volition is exercised ; and no conscious- ness or memory is left, on waking, of the thoughts or feelings which have existed in the mind. Instead of regarding many of these facts as exceptions and ano- malies, it is sounder in reason to adopt such definitions of sleep as may practically include them all. And this, which can be done in perfect accordance with just physiological views, has been the course and tendency of modern inquiry on the subject. The principle is one, not merely sound and sufficient in theory, but beneficial in many points of practice, by solving difficulties which often occur in the aspect of symptoms and treatment of disease. In thus, too, following the various states and acts of sleeping through their relation to those of waking ex- istence, and tracing the gradations from one into the other, we obtain results of the same precise and prac- tical kind as those derived from pursuing the natural and healthy functions of mind into the different forms of insanity and mental disorder. Each part of these topics, so considered, illustrates every other ; furnishing suggestions which could not equally be derived from any other source. In this manner, again, of viewing sleep — not as one, but a series of complex and ever-varying states — we find the best explanation of those singular conditions of trance, mesmeric sleep, catalepsy, &c., which have served ON SLEEP. 17 at all times to perplex the world by the strange breach they seem to make between the bodily and mental functions ; by their unexpectedness in some cases ; and by the peculiar agency producing them in others. The latter circumstance is that especially which serves to disguise from us their real relation to other and more familiar affections of the nervous system. As respects magnetic sleep or trance, in particular, whatever its form or degree, there is no authenticated fact making it needful to believe that any influence is received from without ; beyond those impressions on the senses and imagination, which are capable in certain persons and temperaments of exciting unwonted or disordered actions throughout every part of the nervous system, and especially in the sensorial functions. There is no proof, such as science absolutely requires, of any mate- rial or spiritual emanations from one person producing these phenomena in another ; — the essential point in the whole question, as we shall have occasion to show when recurring to the subject in another chapter. We should not be justified in denying that mesmeric sleep may differ greatly in intensity, or other conditions, from sleep of ordinary kind. The views already stated as to the nature and infinite variety of this great func- tion make full allowance for such diversity ; depending partly on the manner in which the state is induced, partly on the peculiar habit of the persons thus acted upon. Further it is to be remarked, that this diversity is scarcely greater than we find among the natural con- ditions of sleep ; and that the mesmeric sleep is itself exceedingly various in kind and degree ; — from the vague c 18 ON SLEEP. state of reverie or half-trance, in which impressions are still received from the senses, and excite wandering actions of mind — to that deeper trance, in which, as in coma and other anaesthetic states, even violent stimuli applied to the body fail to awaken or produce any obvi- ous effect. This is a condition evidently remote from common sleep ; yet differing, as far as we can see, only in degree. The intermediate gradations express that general law of continuity which pervades and explains all these phenomena.* We must not quit this topic without noticing the striking results of what has been termed Hypnotism — the sleep or trance produced, not by mesmeric means, but by the act of the individual himself, made to con- centrate his vision fixedly for a certain time upon some one object. It apparently facilitates the effect if this object be of small dimensions ; and Mr. Braid's interesting experiments would seem to show, what may well be understood, that the posture of the head further favours the results. The simple fact, that the various physical character of the object gazed upon does in no way alter the effect, will readily be admitted as sufficient proof that the trance induced arises from causes within, and not from influences without, the body of the person thus affected. * Though the difference is presumably one of degree only, it leads to some curious inquiries regarding sensation, from the seeming fact that the sense of touch is that especially affected in these cases ; and that such experiments succeed chiefly in habits where this sense readily acquires a morbid sensitiveness; as in females where the hysteric temperament is strongly marked. ON SLEEP. 19 The evidence, indeed, furnished by these experiments in relation to mesmeric sleep, is simple and convincing as a negative to the main assumption, that this state is brought on by the influence of one human body on another. The effects are less in degree, inasmuch as the means employed less powerfully excite the imagina- tion. But they are expressly the same in kind ; and justify the conclusion, that all these states depend on affections of the nervous system, in persons of a certain temperament, and under certain modes of excitement.* All that relates to dreaming is of course subordinate to the general idea we have taken of the nature of sleep. I have already explained why, in this chapter, I refrain from entering into any details on this curious topic, so perplexing to the reason, so exciting to the imagination. There are but one or two points to which I mil here allude, from their connection with the inquiry into the physical conditions of sleep. The first is involved in the question why some dreams are well remembered, others not at all, or very imperfectly ? Two causes, at least, may be conjectured in explanation. One is, that in the former instance the sleep is really less complete in kind ; — that peculiar condition of brain less marked, upon which the imperfection of memory, if not also the exclusion of sensations, appears to depend. Another is, that the images and thoughts forming some dreams are * These researches of Mr. Baird on Hypnotism well deserve careful examination ; as do also his valuable experiments connected with Electro-Biology ; each inquiry illustrating the other by ana- logous facts and inferences. c 2 20 ON SLEEP. actually stronger and deeper in their impression than those of others ; — an expression too vague for use, were it not that we are obliged equally to apply it to that more common diversity of waking states, upon which the memory so much depends for all that regard its promptitude and completeness. The combination of these circumstances, with others perhaps less obvious, affords as much explanation as we can attain without more complete knowledge of the proximate causes of sleep. To the first probably we may look for interpre- tation of the old notion of the " sovmia vera " of ap- proaching day. The physical state of sleep is then less perfect ; — trains of thought suggested follow more nearly the course of waking associations ; — and the memory retains them, while earlier and more confused dreams are wholly lost to the mind. The latter, however, though lost at the moment, leave traces which, like the memory of waking acts, are capa- ble of being restored at a more remote time by new associations. This is a fact of great psychological interest. There are few who have not occasionally felt certain vague and fleeting impressions of a past state of mind, of which the recollection cannot by any effort take a firm hold, or attach it to any distinct points of time or place ; — something which does not link itself to any one part of life, yet is felt to belong to the identity of the being. These are not improbably the shades of former dreams ; the consciousness, from some casual association, wandering back into that strange world of thoughts and feelings in which it has existed during some antecedent time of sleep, without memory of it ON SLEEP. 21 at the moment, or in the interval between. A fervid fancy might seek a still higher source for this pheno- menon, and poetry adopt such ; but the explanation is probably that just given.* Another point requiring notice here respects those alleged mental actions during sleep, which, if truly related, might be called intellectual exercises rather than dreams ; — poetry composed and remembered ; — ques- tions of difficult argument discussed and solved, &c. Much allowance must be made in these instances for that exaggeration which love of the marvellous is so apt to engender. But still there remains enough of reality to require explanation, and this may be given in perfect accordance with the views we have sought to inculcate. The intellect works more vividly and clearly in such dreams, because the sleep at the time is less profound. The external senses may be still closed, yet the mind in some near approach to the activity of the waking state. If this cannot be wholly proved, we have at least much reason to presume it. The power often attained of waking at a fixed hour depends obviously on that law of habit which governs so largely the course of all our functions, and particularly those of animal life. The time in these cases cannot be altered without creating by especial means a new habit. When on any particular occasion the need of waking early produces the effect desired, it is merely because the sleep * The " "Ovap U Aiof IffTi " is an expression of ancient belief, not limited to poetry alone. Bayle, speaking on this subject, says, " Des tels faits, dont I'univers est tout plein, embarrassent plus les esprits forts, qu'ils ne le temoignent." c 3 22 ON SLEEP. itself is disturbed by the dominant idea of this necessity ; and is broken at repeated intervals, without any exact relation to the time required. The question as to the physical causes of sleep, remote and proximate, has been so much discussed, that I advert to it only for the purpose of simplifying what we know on the subject. The great object in view is manifestly the reparation of exhausted power. This need extends, in the most general sense, to life in ever}^ form ; but applies peculiarly to animal life, and bears some proportion here to the higher organisation and faculties of the species.* The law of intermittence, more distinct as we thus rise in the scale of functions, depends upon, and provides for, this necessity ; show- ing itself most expressly in that periodical repose to the two great functions of sensibility and volition which we name sleep; and which, so established, links itself closely with every other part of our mental and corpo- real existence. It may be that the varying conditions of this state, upon which I have so fully dwelt, have some relation to the exhaustion of one sense or faculty more than another ; but the evidence on this point is too obscure to justify any certain conclusions. Considering the proximate cause under this general law, it seems certain that it is to be found in some par- ticular change of condition of the nervous substance, having close relation to the functions in question ; — a '^ The hybernation of some animals appears as an exception to the principle ; this state, though recurring periodically, yet ob- viously depending on other causes than the mere need of rest. ON SLEEP. 23 state different from that of waking life, yet graduating into it on every side ; — incapable, perhaps, of being ever ascertained by observation, yet not the less real as a change on this account. We have proof, partly in the nature of the functions affected, which depend im- mediately on this portion of our organisation ; partly in the nature of the causes tending to produce sleep. These are all such as have influence, more or less directly, on the nervous system ; — fatigue of body or mind — exhaustion by pain or other strong impressions previously sustained — the absence of strong impressions on any of the senses — the action of various narcotics — particular conditions of the blood, and of circulation through the brain — certain stages of digestion— and, finally, certain impressions from mthout, acting more directly on the sensorium itself. The latter involve, as we have seen, some of the most curious conditions of the animal economy ; such as have at all times tended to perplex the understanding, and beget endless varieties of superstitious belief. In looking to these various causes which act on the sensorium to the production of sleep, we find again the advantage gained by viewing this state as one of un- ceasing change; not only in general intensity, but further, and more remarkably, in the degree in which different functions and faculties are involved in it. This is especially true as respects the influence of the circula- tion ; the most important of these causes, and that with which we have greatest practical concern, from our power of modifying its action. Knowing what we do of its frequent and rapid changes in the waking state, it is c 4 24 ON SLEEP. easy to understand how similar inequalities may so act on the brain and nervous system as to produce every degree of sleep, and constant variation in the particular functions submitted to it. Whether quality of blood, or the mechanical effects of quantity, or rate of movement, be most concerned (and there is reason from observation to admit all), equally will any such inequalities tend to produce the effects in question. And here, too, we must seek explanation of many of the irregularities of dreaming. It is certain that these greatly depend (probably much more than the varia- tions of the waking state) on the fluctuating circulation through the brain. We have many curious proofs how slight a difference of pressure, partial or general, on this organ, is capable of producing the most singular effects on its functions ; and disturbing not only the percep- tions of the senses, but all the higher operations of mind. Dreams are the most striking evidence and in- terpreters of this fact. Where they have been singularly vivid and consecutive through the night, I believe it will generally be found that there is some concomitant heaviness or oppression of head, indicating congestion or other disturbance of the vascular system there. And that this operates mainly as cause (though perhaps itself reciprocally acted upon) may be inferred from the previous conditions likely to disturb the circulation; and also from the frequent repetition of the same vivid- ness of dreams, with intervals of waking between. It must be admitted, however, that the order of occurrences is not wholly known to us here. The actions and reactions between the nervous system and ox SLEEP. 25 that of the circulation, are so numerous and compli- cated, that it is impossible to decipher them in detail ; or even, in many cases, to indicate which is cause and which effect. This, indeed, forms one great difficulty in our investigation of the physical causes of sleep. There is no reason to suppose it insuperable ; though a more absolute limit lies beyond, common to all re- searches of this nature, and stopping every further pro- gress in this direction. In investigating the nature of sleep, we must advert to the causes which prevent, as well as those which favour or produce it. These of course are chiefly the converse of the latter : but some of them deserve notice from the further illustrations they afford. The peculiar influence of certain substances, even of common articles of diet, as coffee and green tea, may be mentioned among them.* Though varying in different individuals, and often blended with other effects, yet is it distinct enough to furnish the same inferences as those we derive from opium in its action as a soporific. In both cases we have to presume a positive change of state, though doubtless of different kind for each, throughout certain parts of the nervous system. Any influence these agents can produce on the circulation, is wholly * The similarity of effects, and even of the peculiar sensations from coffee and tea, adverted to in my Medical Notes in evidence of some common principle, has since been illustrated by the re- searches of Liebig and Pfaff, proving the existence of an organic base (theine or cafeine) common to both ; and singularly related to those other organic bases, morphine, quinine, strychnia, &c., which are medicinal or poisonous according to their manner of use. 26 ON SLEEP. inadequate to explain the results. We know that opium, and other narcotic substances, have effects, locally applied, on nervous sensibility and the action of the muscular fibre ; — and there can be little doubt that when they produce sleep, it is the same singular influence, extended more widely over this part of the organisation ; and reaching, through the cerebral part of it, the higher faculties of our being. The length of time during which maniacs, in restless or violent activity, occasionally continue without sleep, is among the facts which seem to baffle all speculation. If venturing any hypothesis on the subject, it would be, that in some kinds of mania there is an actual excess in the production of that nervous power, by the exhaustion of which under ordinary circumstances sleep is pro- duced. That such excess of production in certain cases is a physiological fact, I shall seek to show in another chapter of this volume. Were this view as to its in- fluence on sleep, for which there are plausible reasons, capable of being proved, it would explain why the inter- vention of such state (designed to give time for repara- tion) should be so little needed in these cases. And, even without explanation of this curious anomaly, we may receive the fact as illustrating by analogy various minor cases, where we observe diminution of sleep for considerable periods, without any proportionate waste of power. There are seemingly differences in the capacity of the sensorium at different times for the performance of its functions ; similar action being attended with greater and more speedy exhaustion at one time than another. This is a fact familiar to the consciousness of ON SLEEP 27 every one; and which must be referred to physical variations (appreciable only by their effects) in the state of the nervous power ministering to these actions. It is a point worthy of note, though familiar, that whereas moderate mental occupation and excitement tend to produce sleep, excess in degree or duration of this state has the effect of preventing it. And this is true, whatever be the physical cause, not only as to strong emotions of mind, the influence of which is at times painfully proved to every one ; but even as to simple intellectual exertion, where the efforts are exces- sive, and too long protracted. Many remarkable in- stances have occurred to me in practice of habitual loss of sleep from this cause. Such effect is never to be neglected, as it is a token of what may become danger in various ways. The practical admonitions of the phy- sician are as necessary here, as in the treatment of fever or inflammatory disease; — the brain invariably suffering in the end, and in degree at all times, from exertions which produce this result. The slighter inroads of the habit can only be detected by the patient himself; but it is our duty to lead him to a right estimation of their consequences. The influence of the previous state of mind in pro- curing or preventing sleep is curious in every way. Minute observation here offers many seeming incon- gruities, which cannot be explained without knowing better than we do its physical causes, and their relation to the sensorial functions. What seems most needful for attaining it is the disengagement of the mind from any strong emotion, or urgent train of thought, such as 28 ON SLEEP. are often found in the night to press upon it with a sort of malignant power, repelling every etfort to shake them off. Grreat anxiety to bring on sleep implies in itself an emotion of mind, and is therefore more or less preven- tive of it. The various artifices of thought and memory used for the purpose often fail from this cause. When they succeed, it depends either on the exhaustion be- coming more complete, or on the mind being rapidly carried from one object to another; — a desultory state of this kind, without emotion, being apparently the con- dition most favourable to the effect desired. A great source of inequality and disturbance in sleep is doubtless to be found in the state of the viscera ; and especially of those by which digestion is performed. This process, going on during sleep, carries the ingesta through successive stages of change, and through different parts of the alimentary canal ; every such change, even under the healthiest action, altering in some way the state of the body, and the impression upon the sen- sorium ; — indirectly, through the circulation ; — or directly, by excitement to different parts of the nervous system; — or mechanically, by hindrance to the flow of blood in the great vessels, from pressure upon them in the epigastrium. Out of this general view many particular questions arise. Such are those which regard the cause of the sleepiness directly following a full or ill-digested meal ; or of the disturbance to sound sleep which often occurs in the middle of the night, six or seven hours after dinner, and is obviously connected with some part of the process of digestion. The first eflfect depends probably ON SLEEP. ^ on the loaded stomach itself ; and is testified by that laborious and imrefreshing sleep familiar to most per- sons at one period or other. The latter effect may depend on the colon becoming loaded about this time with what is received from the small intestines ; per- forming its functions with difficulty ; and from the recumbent posture creating disturbance by pressure on the great vessels and other surrounding parts. All such effects of digestion upon sleep are strikingly attested by its influence on dreaming ; and they are of course greatly varied in kind, and augmented in degree, from any actual disease of the organs concerned. Kestless nights form one in the long catalogue of distresses of the dys- peptic patient, and aggravate greatly the evils out of which they arise. Medicine in its dietetic part may do much here ; nor is the physician to disregard any means as trifling which can minister to so great a good. Whatever of wholesome change in diet may have been made in this country of late years, there is cause to think that we deal injuriously with the night by bring- ing the time of dinner so closely upon it. The.interval of four or five hours between the heaviest meal of the day, and the time of going to bed, is by no means that most favourable to sound rest. The early stage of digestion is passed over, during which there is natural tendency to repose ; and we seek it at a time when the system, as respects the influence of food, is taking up again a more active state ; and when exercise, rather than the recumbent posture, is expedient in forwarding healthily the latter stages of this process. The old method of supper at bed-time, in sequel to dinner in 80 ON SLEEP. the middle of the day, was probably better in regard to the completeness of rest at night ; and the habit of good sleep may often be retrieved by adopting a plan of this kind, when every anodyne has failed of effect. With all the facility the human body has of adapting itself to change of circumstances, there are cases where this can never wholly be done. And the connexion of digestion with sleep is so important and unceasing, that we have every cause to infer some relation as to time between the two functions, better fitted than any other to fulfil healthily the purposes of both. This it is the business of the physician to ascertain ; and though he cannot change the course of worldly habit in these matters, the knowledge so gained may at least become an important aid in the treatment of disease. The close dependence of sleep on the state of the alimentary canal makes it probable that evil is often incurred by giving purgatives habitually at bedtime. The custom is a common one ; and not least so in dys- peptic cases. Yet here especially every thing ought to be avoided which by irritation can disturb the sound- ness of rest; — a consequence often inevitable of the action on the membranes which most aperient medicines produce. Benefit may frequently be gained in such cases by changing the time of using these remedies ; or substituting others, where they cannot be dispensed with altogether. The relation of sleep to perspiration is a point of importance in the animal economy. It seems certain that this secretion or transudation, however it be termed, is augmented in a certain degree by sleep, in- ON SLEEP. il dependently of the influence of external causes.* The fact is connected with and illustrates certain of the phenomena of fever ; and is capable in various ways of practical application. There is reason to believe that this is the true cause of perspiration in very many cases, where medicines given to procure it receive credit for the effect. The influence of different diseases upon sleep, as well as the reciprocal effects of disturbance in this function, form a curious subject of inquiry; but so extensive and complex, that it can scarcely be pursued on any general principle. An important topic here is the relation of sleep to disorders of the brain; with some of which it has close kindred both in the functions affected, and in the apparent manner in which this takes place. There are many instances in which it would be difficult to recognise any other distinction than that of duration; though, from the difference of cause which this presumes, we may infer that other variations really exist. It is certain that the states of sleep and coma frequently graduate into each other, * The multiplied observations of Sanctorius and Keill on this subject are confirmed by the more recent inquiries of Dr. Ed- wards. The labours of Sanctorius in these parts of physiology are scarcely enough regarded at the present time. Two or three par- ticular results are quoted and requoted from him, without due notice of the vast mass of observations he collected, with singular diligence and fidelity, and often by very curious and instructive means of research. The modern method (for such it may be termed) of applying averages to results of this kind, is indispens- able, where the conditions are so numerous and so complicated with each other. S2 ON SLEEP. in such way as to show that the proximate physical conditions are nearly the same in both. Either name may be given to the state produced by moderate pressure on the brain, when a portion of the cranium is removed. In a remarkable example of this kind, which I saw in one of the English military hospitals at Santarem, when travelling in Portugal in 1812, there was cause from observation to infer, that the patient went through every grade between these conditions, in proportion to the degree of pressure applied. And instances are probably common to the same effect, though always liable to some doubt in their interpretation.* The judgment of the physician is often embarrassed in these cases; and practical injury may be the con- sequence of error. It is an observation of Dr. Wilson Philip, that no sleep is healthy but that from which we are easily aroused. And though the remark requires to be qualified by the consideration that sleep may be too light in kind to fulfil its purposes in the animal economy, it justly points out the opposite excess, and a state too closely verging on the conditions of brain which en- danger apoplexy. Changes of circulation in the head, however produced, are doubtless concerned in all these variations. The aid often obtained in bringing on sleep by placing the head low, and the difficulty of sleeping in an upright posture, are familiar proofs how much the state of the brain in sleep is determined by the * The experiments of Flourens, who produced a state resem- bling sleep by removing portions of the cerebrum, must be ad- mitted under the same suspicion which attaches to almost all ob- servations thus made. ON SLEEP. 33 general manner of circulation through it, independently of all partial inequalities. One degree of pressure seems essential to perfect and uniform sleep ; while a greater degree, without other alteration of state, assumes more or less the character of disease. The best inferences, in relation to practice, are generally to be derived from other concurrent symptoms; particularly from the degree of sensibility present, from the state of res- piration, and from the manner of action of the heart. I have already alluded to the probable effect of the quality, as well as quantity and distribution, of the blood upon the various states of sleep ; and may notice it again as one of the modes in which this natural function is affected by the presence and fluctuations of disease. There is reason to suppose that such effects chiefly depend on the proportion of venous blood present in the cerebral circulation, either from con- gestion in the great veins, or from imperfect arterial- isation in the lungs. But there are other changes less easily recognised than these — depending on the casual presence of foreign matters in the blood, or more fre- quently on the imperfect separation of those ingredients which it is the business of the excreting organs to remove — the existence of which diffuses disorder throughout the system; affecting the sleep frequently in such way as to give it the characters of a morbid state, sometimes verging on dangerous disease. Through this latter view more especially we are enabled to interpret the remarkable relation between the functions of the kidneys and the state of sleep ; a D £4 ON SLEEP. subject not until lately sufficiently regarded by pby- sicians, though attested by constant and familiar expe- rience, and illustrated by those more serious cases, where renal disease produces disorders of the brain ; of which disorders sleep, heavier and more prolonged than it ought to be, is the first stage and degree. The coma speedily ensuing upon entire suspension of urine, is a more striking example in point. With this topic too are further connected the effects of wine and other fer- mented liquors upon the brain, as regards both intoxi- cation and sleep ; these effects being manifestly related in some degree to the action of the kidneys, and vary- ing according to their state in different individuals and under different circumstances.* Connected closely with the preceding topics is the important practical question as to the proportion of sleep best fitted for health, and more especially for the well-being of the sensorial powers. It is obvious that this can be answered explicitly only for individual cases. One temperament undoubtedly requires more than another; nor can the sufficiency of the function be measured merely by number of hours, vaiying as it does in all that may be termed its intensity and com- pleteness. One person may, by profound sleep, gain more of repose and restoration in four hours, than another, imperfectly sleeping, does in twice the time. The remarks, already made, clearly point out these • In Dr. Christison's work on Granular Degeneration of the Kidneys, there are many important remarks on the connexion of these organs with the diseases of the brain. ON SLEEP. 35 distinctions, to which the mind and body have equal and similar relation. The results of deficiency of sleep are more familiar to us than those which belong to its habitual excess. Yet this excess, as a habit, may unquestionably exist. The brain may be kept too long, at each successive period of sleep, in a state which, though strictly speaking as natural as waking, is equally liable to be unduly extended; and which, as we have seen, may pass into disease by gradations scarcely to be defined. The ex- pressions of Aretseus, "TTrvoy iroWos 7ra)(yTr)9f apylrj, 6iJLi')(Xr] Trj9 alaOrjaLor and again, "Tirvos ttoXvs vapKo, ray a\