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We are proceeding to a subject of much difficulty in theory, though of the greatest familiarity in fact; and I freely confess to you, that although I have endeavoured to investigate almost every opinion that has been offered upon it, from the time of Aristotle to our own day, I have never met with any thing in the least degree satisfactory, or capable of unravelling the perplexitles in which it lies entangled.

What can possibly be more opposite to each other than the two states of wakefulness and sleep!--the senses in full vigour and activity, alive to every pursuit, and braced up to every exertion,-and a suspension of all sense whatever, a looseness and inertness of the voluntary powers, so nearly akin to death, that nothing but a daily experience of the fact itself could justily us in expecting that we could ever recover from it.

And yet, while such is the lifelessness without, the mind, now destitute of the control of the will, is often overwhelmed with a chaos of ideas, rushing upon each other with so much rapidity, that the transactions of ages are crowded into moments, and so confused and disjointed, that the wildest and most incongruous fancies flit before us, and every thing that is possible becomes united with every thing that is impossible.

Such, however, are the ordinary means devised by Infinite Wisdom to revivify the animal frame when exhausted by the labours of the day; to recruit it for new exertions, and enable it to fill up the measure of its existence.

The order I shall take leave to pursue in discussing this abstruse subject will consist, first, in a brief examination of the more prominent hypotheses on sleep and dreaming that have been offered to us by ancient and modern schools: secondly, in a minute analysis of the feelings and phenomena by which these operations are characterized, agreeably to the series in which they occur: thirdly, in submitting the outline of a new theory to explain the entire process: and, lastly, in an application of such theory to a variety of other subjects of a similar and equally extraordinary nature.

Sleep inay be either natural or morbid. The former is usually produced by whatever exhausts the principle of life; as great muscular excitement, violent pain, vehement use of the external senses; or great mental excitement, as intense thought or severe distress. Morbid sleep is commonly occasioned by compression or commotion of the brain, and is hence often the result of congestion, plethora, or local injury to the skull.

Compression and commotion, though less frequent, are more direct and obvious causes: and hence the greater number of physiologists believe compression to take place, also, though in a slight degree, in every case of natural sleep; and in reality to constitute the immediate, while sensorial exhaus. tion only constitutes the remote, cause of this phenomenon. They appeal to the lethargic effect of a full stomach in infants, and of drunkenness in adulls, which they refer to congestion in the brain, in consequence of a greater influx of blood into this organ: and hence they reason that a similar sort of pressure is produced by some means or other in every case of sleep.

But what are the means of pressure thus referred to! And here a consideratile dificulty is felt by every school of physiologists: and two distinct schemes are devised to get rid of it. By the one we are directed to the arteral system, which, we are told, becomes peculiarly excited and overcharged in the organ of the brain during wakefulness, from the activity of the internal senses. By the other we are directed to the absorbent system, which from

• This esplanatinn to party, though not chiefly, adopted by the author of the elaborate article on seep. Reta's Cyclopedia, and the ince been fully embraced by Mr. Carmichael, in his learned Essay on the same activity is said to become worn out and rendered torpid in the same organ; and, hence, to be incapable of carrying off the fine fluid which is erpetually exhaling from the secernent vessels into the ventricles of the rain. Nothing, however, can be more unfounded than both these conjectures, and it is difficult to determine which of the two is the most so. But we are in no want of either of them, for we are in no want of the pressure which they are invented to account for. The principle of exhaustion alone will, I trust, be found sufficient to answer every purpose as a general cause of natural sleep; and, were it possible for us to add that of local pressure, the sleep would no longer be natural, but morbid. Before we proceed farther, however, I will just hint that Dr. Cullen supposes the nervous fluid or power to be disposed by nature to an alternating state of torpor and mobility.” He does not admit that it is ever exhausted and restored as a secretion;t and hence in sleep it is only suspended: and in consequence of this suspension the exercise of sense and volition is suspended, also.{ Narcotics do not, therefore, in his view, exhaust, but only suspend the nervous power or fluid, and thus induce sleep, which consists in such suspension. The apparently stimulant power of narcotics he derives from the vigilant exertion of the vis medicatrix naturae, the instinctive effort of nature to guard against such suspension of vital power as essentially mischievous, and, when carried to an extreme, fatal : and hence, narcotics are with him directly sedative, but only indirectly stimulant. He supposes both sleep and waking to take place upon each other merely by a law of alternation: an explanation that will satisfy few. But the chief attention of physiologists, both ancient and modern, has been directed to the subject of dreaming, which has usually but erroneously been regarded as a distinct process from that of sleeping. Let us next, therefore, as briefly as may be, and before we enter into a direct analysis of the phenomena that successively arise, take a glance at a few of the conjectures by which dreaming has hitherto been accounted for. Among the Greek philosophers we meet with two explanations that are worthy of notice; that of Epicurus, because of its ingenuity, and that of Aristotle, because it has descended to the present times. According to the Epicurean hypothesis of sensation, all the organs of external sense are stimulated to their appropriate functions, by the friction of an effluvium or emanation thrown off from the body perceived. This doctrine, which still holds good, and is uniformly employed in modern times to explain the senses of taste and smell, was equally extended by Epicurus to those of o and hearing: the former being supposed to depend upon an effluvium of exquisitely fine films, images, or species, as they were technically called, o issuing in every direction from every existing substance, somewhat in the manner in j snakes and grasshoppers cast off their skins annually, but almost infinitely finer, and altogether invisible. And as these rush against the eye, they were conceived to convey to it a perfect image of the object from which they are ejected. While sound was supposed to be excited in like manner by particles of a peculiar kind thrown off from the sonorous body, and rousing the ears by their appropriate stimulus. These effluvia of every kind were conceived to be so exquisitely attenuate that they can pass, as light, heat, or electricity does, through a variety of solid bodies, without being destroyed in their passage. The effluvia or pellicles of vision were supposed not unfrequently to arise from the very bodies of those that have been long buried; and to be capable not only of transpiercing the soil in which they are inhumed, and of stimulating the organs of external sight, but of winding through the substance of the flesh, and of stimulating the soul itself in the interior of the animal frame, especially when

Dreaming. LSce Transactions of the Association of Fellows and Licentiates of the King's and Queen's College of Physicians in Ireland, vol. ii. p. 48, 8vo. 1819, Dubl. His explanation of dreauling is that of Gall and Spurzheim, which the reader will find adverted to subsequently.

* Materia Medica, ii. 226. t lb. p. 223. # Ib. p. 226.

in a state of sleep, in which the external sense is closed, or of deep abstraction, in which it is inattentive; and thus of presenting to the soul in its naked state, as it may be called, pictures of objects no longer in existence. And hence these philosophers, with great ingenuity, though, as it now appears, with great incorrectness, undertook to solve many of the most difficult problems in nature; accounted for the casual appearance of spectres in the gloom of solitude and retirement, and directly unfolded to the world the “stuff that dreams are made of.”

It is needless to point out the errors of this system, for it has long sunk into disuse, never to rise again. And I shall therefore proceed to the rival hypothesis of Aristotle, which, though equally unfounded in fact, has been fortunate enough to descend to modern times, and to have met with very powerful advocates in M. Wolff" and M. Formey. It was the doctrine of Aristotle, that external sensations not only produce by their stimulus a variety of INTELLectual ForMs or images in the sensory, somewhat similar to the ideas of Plato, and for all practical purposes not very dissimilar to what is meant by ideas in the present day, but that these forms or ideas are themselves capable of producing another set of forms or ideas, though of a more airy and visionary kind:

As every shadow has itself a shade.

And to this secondary set, these slighter and more attenuate pictures of things, he gave the name of Phant Assis. In the opinion of this philosopher, dreams consist alone of these phantasms, or mere creatures of the imagination, first excited by some previous motion or sensation in the brain, and afterward continued in a more or less perfect series, according to the power of the imagination itself. The only difference I am able to trace between this theory, as started by Aristotle, and as restarted by Wolff, is in the greater regularity that the latter assigns to the phenomena of dreaming, than the former does: M. Wolff believing them to be, in their commencement, excited by a sensation, and in their succession and series of representations to be as much controlled by a peculiar system of laws, as the motions of the heavenly bodies. Formey appears to carry this point a little farther: his language is, if the dream be natural, it must necessarily originate agreeably to the law of sensation, and be continued by the law of imagination; and hence he concludes those dreams to be supernatural, which either do not begin by sensa tion or are not continued by the law of imagination. It may be sufficient to remark upon this theory, first that the phantasms of Aristotle have as little claim to entity as the species of Epicurus; next, that the assumption of a code of laws, or rather of two distinct codes of laws, to regulate the fleeting train of our ideas in dreaming, is in itself altogether visionary and gratuitous; and that if the term chance or fortuitousness, a very useful term and full of meaning in all languages, can with propriety be applied to anything, there is no subject to which it can be better applied than to that of dreaming; in which the will, the only legislator and controller of our ideas, has withdrawn its authority, and left the brain to a temporary lawlessness and misrule; and, lastly, that the distinction which is thus attempted to be drawn between natural and supernatural dreams is not only altogether fanciful, but could never be of any possible avail, even if well founded; for, in order to distinguish between the two, it would be necessary to be intimately acquainted with those laws of sensation and imagination which are here stated to regulate our natural dreams, and the suspension of which produce dreams of a superior character. We are touching upon a delicate, and, perhaps, a dangerous inquiry; but as it has been boldly handled in modern times, and made the foundation of a more daring speculation upon the subject, it must not be flinched from in our present discussion. That total absence of all natural law, which M. Formey supposes occasionally to take place in the act of dreaming, and to distinguish the supernatural from the natural vision, Mr. Andrew Baxter," and, since his time, Bishop Newton, conceive to take place in every instance of dreaming; and hence, that dreaming is at all times, and on all occasions, a supernatural operation. These excellent men divide dreams into two kinds, good and evil; and conceive two kinds of agents, good and evil spirits, employed in their production; and, consequently, account for the one or the other sort of dreams, in proportion as the one or other kind of agents obtains a predominancy. Now it must be obvious that this conjecture is just as destitute of all tangible basis as either of the preceding; that it can make no appeal to facts submitted to the senses. But, beyond this, its very foundation-stone consists of a principle that no man can readily grant who maturely weighs its full import; namely, that dreaming is altogether an unnatural operation; that nearly onehalf of our lives is spent in a direct intercourse with invisible beings; and that during this moiety of his existence man is no longer a free agent; his whole train of thoughts and ideas being not loose and dismantled, but run away with by foreign compulsion, and the work of a demoniacal possession. The difficulties into which such an explanation throws its adherents are incalculable. Let us confine ourselves to one more example. There can be no doubt that other animals have their dreams as well as man, and that they have them as vigorous and as lively. Every one has beheld his favourite dog, while asleep by the fireside in the winter season, violently stretching out his limbs, howling aloud, and at times starting abruptly, beneath the train of images of which his dream is composed. In what manner will such philosophers account for these various phenomena? Is dreaming a natural operation ? or are good and evil spirits the natural attendants upon dogs and cats, as well as upon mankind? The one or the other of these conclusions must follow ; and there can be no difficulty in determining which of them will possess the general suffrage. That dreams, like every other occurrence in nature, may occasionally become the medium of some providential suggestion, or supernatural communication, I am by no means disposed to deny. That they have been so employed in former times is unquestionable ; and that they have been so employed occasionally among all nations in former times is highly probable; and the peculiar liveliness with which the trains of our dreaming ideas are usually excited, and from a cause which I shall presently endeavour to explain, seems to point out such a mode of communication as peculiarly eligible. But I am at present attending to the natural phenomena alone, and can by no means enter into a consideration of such foreign interference, which, as it certainly has been, may still therefore be, for all we can prove to the contrary, occasionally introduced into them. In what may be called our own times, there are many valuable writers who have turned their attention to this curious subject, and who concur in the two following important positions: first, that the faculty, or at least the action, of the will is suspended during the influence of sleep: and, secondly, that in consequence of this suspension or discontinuance, the trains of ideas which persevere in rushing over the mind, are produced and catenated by that general habit of association which catenates them while we are awake. The power of the will, it is contended, is not necessary to the existence of ideas, which, therefore, may continue while such power is in a state of abeyance; but which, if they continue at all, must take the general order and succession imprinted upon them by the law of association, excepting in cases in which such law is broken in upon a variety of incidental circumstances, as uneasiness arising from a surcharged stomach, or other bodily sensations. Such are the two fundamental principles upon which the theories of Hartay, Darwin, and Dugald Stewart, are respectively built; and which, in various ways, and with almost equal ingenuity, they seem very satisfactorily to

* Psychol Emper see lon * Mem de l'Arad. de Berlin, ti

*An Inquiry into the Nature of the IIuman Soul, wherein the Immortality of the Soul is evinced from the Principles of Reason and Philosophy, 4to 1730

have established. But there is still a very important question, and which. indeed, constitutes the chief difficulty of the subject, and that which none of them have attempted to answer, or, at least, have satisfied themselves upon, while making such attempt. I mean, whence comes it to pass that ideas can at all exist in the brain during sleep, or that all the internal senses are not as much locked up as the external senses, and the faculty of the will?

In the course of the present lecture it will be my endeavour to account for this must curious phenomenon. But we must first follow up, in the series in which they appear to arise, the train of circumstances which accompany sleep and dreaming. The entire study is highly interesting, but requires close attention, in order to its being fully comprehended. And when we have advanced thus far, we shall obtain a clew, if I mistake not, to those equal'y abstruse and intimately connected subjects, sleep-walking, revery, and winter sleep; as well as to various other obscurities that ramily from the same source.

The fibres distributed over the moving organs of animals, I have already had occasion to observe, in a preceding lecture,* are of two sorts : those of the nerves, which are called sensitive fibres, and those more properly belonging to the muscles, which are called irritative fibres; which last, however, are always accompanied by a greater or less number of the former; by which, indeed, they becoine endowed with the sense of touch, as well as are rendered capable of contnbuting to the other external senses, and of maintaining a communication with the brain, from which the sensitive fibres issue, or in which they terminate.

Both these kinds of fibres become fatigued, exhausted, and torpid, in proportion to the length and violence of their exertion, and recover their power alone by rest. The weariness and flaccidity of the muscles of the arms or legs after extreme exercise, or exercise to which they have not been accustomned, may be adduced as a sufficient proof of the truth of this position.t In like manner, we neither hear, nor see, nor taste, nor seel, with the same accuracy, after any or all the organs of these various functions have been long upon the full stretch of action, with which we do on their first exertion in the morning. Increase or prolong this action, and their power will be still farther obtunded, till at length, like an over-wearied limb, they become perfectly inert and insensible, and give no account of whatever is passing around us; and it is this general torpitude or inaction of all the external senses, which we call SLEEP. By the exercise of the will, or by any other strong stimulus, this sleep or sensorial torpitude may be postponed; and, vice versa, by the consent of the will, it may be accelerated.

This, however, is sleep in its first or simplest shape alone: it is that which I shall take leave to call SLUMBER, and 6 the mere sleep, or torpitude of the organs of external sense; the will being drowsy, indeed, but still continuing in some degree awake: whence the sleeper, if he lie or sit in any uneasy position, exercises his muscles, which are still under the control of the will, and the position is changed. The other internal senses also, as those of memory, imagination, and consciousness, are in like manner, in a greater or Jess degree, awake; whence the mind is yet filled with ideas, that crowd upon one another with about an equal degree of regularity and consusion: and, if

• Pere! Lecture x p. 107

• The principles of the theory here advanced were first given to the world, hy the author, as far back as 1% 3, ia the extent subjowed to his translation of Lucretius, where the JMXI is treating of the cause and

THE of sleep, and may be found in vol. ii. p. 137-141 of that work. Several of the doctrines these laid down have been since advanced in various forns by different writers, though in some cases, very r ably. Without their having trused his explanation. Thus the immediate cause of sleep, advanced in te arot passage, is that chiesty rested upon by the author of the article on sleep in Dr. Rees's Cyclojuris, thought toe as adients to an occasional increased action in the vesses of the brain as a concurrent C. Anul the much of the c anation which will here be found to follow, respects the nature and

nena of dreaming have si! more lately been offered to the world by Dr Spurzhein, and adopted Irunn am by Mr. Carnhai of Du kan, with the tirption that they have in rovell Nucli.Ws with their

R de trine of a plurality of oryans in the brain, which, for reasons that will be given in a suhse 43 lecture (serirsin. Loxture 1 ), the precnt author cannot admiti and does not conceive is by any mancat necessary on the present occasion. Such coincidences of oprimion, however, ardicially tey stwold to sedental, and not scrived from his comment 0 Lucretius, are a considerable degree of curfirmaring to the general basis on which the theory rosts. The lecture, as now publisticd, was deliverod in the spring of isil

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