If a stimulus affecting the organs of sense, at which end soever applied, be intolerably pungent or forcible, the sensorial power will be exhausted immediately, and the organ directly affected will become instantly torpid. Hence sounds, intolerably loud, make us deaf; excessive light blinds us; acrimonious smells or savours render us incapable of smelling or tasting. And hence an abrupt shock of joy or grief, a sudden and intense paroxysm of fever, large quantities of wine or spirits, as internal causes, produce morbid lethargy, palsy, apoplexy, which are only so many modifications of the sleep or torpitude of the sensitive and irritative fibres. If the same abrupt and violent cause be sufficient to act upon the vital organs, as well as upon those of external sensation, the torpor becomes universal, and the sleep is once more the sleep of death. It is in this manner that death is produced by a stroke of lightning.

As violent stimuli produce sudden and occasionally irrecoverable torpitude, either general or local, stimuli less violent induce a tendency to the same effect. Hence the nostrils of persons not accustomed to snuff are more forcibly agitated by its application, than those that have been in the use of it: the eyes of persons accustomed to sleep in the glare of the sun, find no inconvenience from exposure to the light of the morning; while those who usually sleep in total darkness are awoke by its stimulus. And so of the rest. On this account a very small portion of light, of sound, or of exercise, are sufficient sources of exhaustion to those who are not in the habit of using great external or internal activity. Hence savages and quadrupeds, who use but very little internal activity, and no more external activity than is necessary to gratify their passions and satisfy their hunger, become torpid upon very slight excitements. Hence infants become exhausted upon still slighter excitements; as the exercise of being carried, the mere breath of the air, or the digestion of milk alone in the stomach; either of which, but especially the whole collectively, is sufficient to make them sleep soundly:-so soundly, indeed, that no common stimulus is able for a long time to rouse them from their torpor. In other words, it requires a period of many hours for the external organs to recover from their exhaustion. The smallest undulatory motion in the uterus, perhaps, or the very action of the vital organs themselves, may be sufficient to wear out, from time to time, the sensorial power of the fetus on its first formation: and hence the fetus sleeps, with few intermissions, through the whole period of parturition.

For the same reason, persons in advanced age are far less impressed by common stimuli than in any former part of their lives; from a long series of exposure to their influence, the organs of sense are become more torpid, and hence they require less sleep, and at the same time less food. The vital organs partake of the same disposition, and they are in consequence less liable to violent or inflammatory disorders. But the general torpitude increasing, the heart is stimulated with greater difficulty; a smaller portion of sensorial fluid is secreted by the brain; a smaller portion of nutriment is thrown into the circulation from the digestive organs; the pulse and every other power gradually declines, till at length, if ever man were to die of old age alone, he would die from a total torpor or paralysis of the heart. But debilitated as every organ is become long before such a period can arrive, the general frame is incapable of resisting the smallest of the more trivial shocks, whether external or internal, to which man is daily exposed: in other words, there is no reservoir of sensorial power to supply the local or temporary demand; and the man dies, even at last, from sudden exhaustion, rather than from progressive paralysis.

Sleep, then, is a natural torpitude or inertness, induced upon the organs of the body and the faculties of the mind, by fatigue and exhaustion; and in a physiological survey, consists of the three stages of slumber, dreaming, and lethargy. In slumber, the exhaustion is slight, and is almost confined to the organs of external sense, the will only inclining to their inertness: in dreaming, the exhaustion is usually more considerable, the will altogether associating in their inertness: in lethargy, the exhaustion extends to and

embraces the mental faculties. When the system is under the influence of disease, the usual course of the phenomena of sleep and dreaming is often disturbed and interrupted; and when the torpitude extends to the vital organs, the effect produced is death.

But the chief difficulty in the subject of dreaming remains still to be accounted for. How is it possible for thoughts or ideas to exist in the brain, and be continued, while the will, which usually regulates them, and the external senses which give birth to them, have their continuity of action broken in upon? I shall endeavour to explain this difficulty in language as familiar as I can employ.

A certain, but a very small, degree of stimulus applied to any of the cerebral fibres of the human body, whether sensitive or irritative, instead of sensibly exhausting them, seems rather to afford them pleasure; at least the fibres are able to endure it without becoming torpid, or, which is the same thing, requiring sleep or rest.

Hence every gentle sight, and every gentle sound, or any other gentle object in nature, to what sense soever it be directed; the still twilight of a summer evening; the mild lustre of the moon, interwoven with the foliage of forest scenery; the reposing verdure of a spreading lawn; soft playful breezes; the modest fragrance of roses and violets; the light murmurs of a rippling stream; the tinkling of a neighbouring sheepfold, and the sound of village bells at a distance, are all stimuli that produce no sensible exhaustion; and, on this very account, form some of the most agreeable images in nature. In like manner, the orbicular motion of the lips in a sucking infant is a source of so much comfort, and attended with so little exhaustion, that whether sleeping or waking, it will generally be found mimicking the action of sucking, when at a distance from its nurse; and, perhaps, not thinking of such action itself. A person who, from habit, has acquired a particular motion of any one of his limbs, a twirl of the fingers, or a swinging of one leg over the other, perseveres in such motion from habit alone, and feels no torpitude or exhaustion in the fibres that are excited, although it might be intolerably fatiguing to another who has never acquired the same custom.

It is probable, then, that thought, and the action of the vital organs, are of this precise character. We are totally ignorant, indeed, of the mysterious mode by which either the one or the other was produced at first; but we see enough to convince us that the stimulus is, in both cases, equally pleasing and gentle. And hence both actions continue without exhausting us, except when unduly roused; and form a habit too pertinacious to be broken through by any ordinary opposition.

Thought, then, is to the sensory that which the motions I have just spoken of are to the muscles which are the subjects of them. Both continue alike, whether we be reflecting upon the habit or not: but the habit of thinking is so much older, and consequently so much deeper-rooted, than that of any kind of muscular motion, except the muscular motion of the vital organs, that it is impossible for us to subdue it by the utmost efforts of the will: whence, like the action of the vital organs, it accompanies us, not only at all times when awake, but in all ordinary cases during sleep, and is the immediate and necessary cause of our dreaming.

Thought can only be exercised upon perceptions introduced into the sensory by the organs of external sense; and hence the chief bent of our thoughts must be derived, whether sleeping or waking, from the objects or perceptions that most deeply impress us. The train of thoughts, then, that recurs from habit alone, as in sleep or total retirement from the world, must generally be of this description: in the former case, however, by no means correctly or perfectly; because there are others also which have a tendency to recur, and neither the will nor the senses are in action to regulate or repress them. Whence, as I have already observed, proceeds a combination of thoughts or ideas, sometimes only in a small degree incongruous, and at other times most wild and heterogeneous; occasionally, indeed, so fearful and extravagant as to stimulate the senses themselves into a sudden renewal

of their functions, and consequently, to break off abruptly the sleep into which they were thrown.

Let us pursue this train of reasoning, and it will lead us to account, if I mistake not, for some of the most extraordinary facts that are connected with the recondite subject of sleep and dreaming.

I have just observed that the stimulus of our ideas in dreaming is often sufficient to rouse the external senses generally, and to awake us all of a sudden. But this stimulus may also be of such a kind, and just such a strength, as to excite into their accustomed action the muscles of those organs or members only which are more immediately connected with the train of our dreams, or incoherent thoughts, while every other organ still remains torpid. And hence, the muscles chiefly excited being those of speech, some persons talk; and others, the muscles chiefly excited being those of locomotion, walk in their sleep, without being conscious on their waking of any such occurrence.

Whatever be the set of fibres that have chiefly become exhausted from the labour or stimulus of the day, the rest, as I have already noticed, partake of the torpitude from a habit of association; exhausted in some degree, also, themselves, by the share of sensorial power which, as from a common stock, they have contributed towards the support of the debilitated organ. But it sometimes happens, either from disease or peculiarity of constitution, that all the organs of external sense do not associate in such action, or yield alike to the general torpor of the frame: and that the auditory, the optical, or some other sense continues awake or in vigour while all the other senses are become inert; as it does also that such particular sense, like the muscles of particular members, as observed just above, is awoke or restimulated into action in the midst of the soundest sleep, by the peculiar force and bent of the dream, while all the rest continue torpid.

If the organ of external sense thus affected with wakefulness be that of hearing, a phenomenon may occur which has often been noticed as far back, indeed, as the times of the Greek and Roman poets, but which has never hitherto, I believe, been satisfactorily explained; the dreamer may in this case hear a by-stander who speaks to him; and if, from a cause above specified, he should also have happened to talk in his sleep, so as to give the bystander some clew into the train of thoughts of which his dream is composed, a conversation may be maintained, and the by-stander, by dexterous management, and the assumption of a character which he finds introduced into the dream, may be able to draw from the dreamer the profoundest secrets of his bosom; the other senses of the dreamer, instead of hereby rousing to detect the imposition, being plunged into a still deeper torpitude, from the demand of an increased quantity of sensorial power to support the exhaustion which the wakeful or active organ is, in consequence, sustaining. This, however, is a case of rare occurrence, though it seems to have occurred occasionally. If the wakeful organ be that of sight, and the dreamer, from a cause just adverted to, be accustomed to walk instead of to talk in his sleep, he will be able to make his way towards any place to which the course of his dream may direct him, with perfect ease, and without the smallest degree of danger. He will see more or less distinctly, in proportion as the organ of sight is more or less awake; yet from the increased exhaustion, and of course increased torpor of the other organs, in consequence of an increased demand of sensorial power from the common stock to support the action of the sense and muscles immediately engaged, every other sense must necessarily be thrown into a deeper sleep, or torpor, than on any other occasion. Hence the ears will not be roused even by a sound that might otherwise awake him; he will be insensible, not only to a simple touch, but to a severe shaking of his limbs; and may even cough violently without being recalled from his dream. Having accomplished the object of his pursuit, he may safely return, even over the most dangerous precipices, for he sees them distinctly, to his bed; and the organ of sight, being now quite exhausted, or there being no longer any occasion for its use, may once more associate in the general torpor, and the dream take a new turn and consist of a new combination of images.

The view we have thus taken of sleep and dreaming will explain a variety of other curious phenomena in natural philosophy, which have usually been supposed of very difficult elucidation.

What is REVERY? It is the dream of a man while awake. He is so intently bent upon a particular train of thought, that he is torpid to every thing else: he sees nothing, he hears nothing, he feels nothing; and the only difference between the two is, that in common dreaming, the sensitive and irritative power of the external senses is exhausted progressively and generally, while the will partakes of the exhaustion; and that in revery the whole is directed to a single outlet, the will, instead of being exhausted, being riveted upon this one point alone; and the external senses being alone rendered torpid from the drain that is thus made upon them to support the superabundant flow of sensitive and irritative power expended upon the prevailing ecstasy.

It was my intention to have cited a few singular instances of this wonderful aberrancy of the mind; and to have followed them up with a momentary glance at those interesting subjects so closely connected with it, nightmare, delirium, madness, idiotism; but the time will by no means allow me, and I hasten to close with a few observations upon winter-sleep and the revivification of certain animals after their appearing to be dead.

Upon a general survey of the preceding observations, it should follow that every part of the animal system may safely sleep or become torpid except the vital organs, or those that act independently of the will; and that the moment these participate in the torpor the principle of life ceases, and the spirit separates from the body. Why the principle of life should even then cease we know not, for we know not what produced its union at first. There are various circumstances, however, which prove that this, though a general rule, is not a rule without its exceptions. We have all heard and read of such extraordinary occurrences as trances, or apparent absences of the soul from the body: we have heard and read of persons who, after having been apparently dead for many days, and on the point of being buried, have returned to a full possession of life and health; and although most of these histories are wrapped up in so much mystery and superstition, as to be altogether unworthy of notice, there are many too cautiously drawn up and authenticated to be dismissed in so cursory a manner. But let us proceed to a few facts of a similar, yet of a more extraordinary kind, and which are or may be within the personal knowledge of every one.

In cases of suspended animation by hanging, drowning, or catalepsy, the vital principle continues attached to the body after all the vital functions cease to act, often for half an hour, and sometimes for hours. In the year 1769, Mr. John Hunter, being then forty-one years of age, of a sound constitution, and subject to no disease except a casual fit of the gout, was suddenly attacked with a pain in the stomach, which was shortly succeeded by a total suspension of the action of the heart and of the lungs. By the power of the will, or rather by violent striving, he occasionally inflated the lungs, but over the heart he had no control whatever: nor, though he was attended by four of the chief physicians in London from the first, could the action of either be restored by medicine. In about three-quarters of an hour, however, the vital actions began to return of their own accord, and in two hours he was perfectly recovered. "In this attack," observes Mr. (now Sir Everard) Home, who has given an interesting memoir of his life, "there was a suspension of the most material involuntary actions: even involuntary breathing was stopped: while sensation, with its consequences, as thinking and acting, with the will, were perfect, and all the voluntary actions were as strong as before."

In the whole history of man I do not know of a more extraordinary case. The functions of the soul were perfect, while the most important functions of the body, those upon which the life depends absolutely, in all ordinary cases, were dead for nearly an hour. Why did not the soul separate from the body? and why did not the body itself commence that change, that subjection to the aws of chemical affinity, which it evinces in every ordinary case of the death or

inaction of the vital organs? Because in the present instance, as in every instance of suspended animation from hanging or drowning, the vital principle, whatever it consist in, had not ceased, or deserted the corporeal frame. It continued visible in its effect, though invisible in its essence and mode of operation.

Let us apply this remark to the subject_immediately before us: it will serve as a ready clew to its intricacies. In many animals, then, and in most vegetables, the living principle often continues in the same manner to reside in and to actuate the organic frame; while the vital functions, as they are called, and, in conjunction with these, all the other functions of the system, remain inactive, not for an hour only, but for months and sometimes for years. It does so in the seeds of plants and the eggs of animals, so long as they are capable of germinating or pullulating. It does so in most animals, and perhaps in all vegetables, that sleep or become torpid during the winter-season; for though in a few hibernating animals, as the hedgehog and Alpine marmot, we trace a small degree of corporeal action from their appearing thinner on returning to activity in the spring, the greater number, like dormice and squirrels, exhibit no diminution whatever. It does so, in a more extraordinary manner, in the ears of blighted corn; which, though incapable of filling and fattening, and seemingly lifeless and effete, still contain a seed that may be rendered productive of a sound and healthy increase. It does so in various species of the moss; in various species of the snail, in one or two of the snake, in the wheel-polype, sloth, and tile-eel, and a variety of other animals and animalcules, that, like many of the preceding, have been kept apparently dead and in the form of dried preparations, totally destitute of irritability, altogether withered, and in substance as hard as a board for months and years,-in some instances as long as twenty years, and have afterward been restored to life and activity upon the application of warmth, moisture, or some other appropriate stimulus.*

These are extraordinary facts, and may be difficult to be comprehended: but they are facts, nevertheless, and may be proved at any time and by any person. But there is a fact still more extraordinary, and of infinitely higher moment; and one in which we are all infinitely more interested-a fact to which these remarks naturally lead, and which they may serve in some degree to illustrate; it is the termination of the sleep of death, the resurrection of the body from the grave.

LECTURE VIII.

ON VOICE AND LANGUAGE; VOCAL IMITATION, AND VENTRILOQUISM. LANGUAGE, in the fullest scope of the term, is of two kinds; natural and articulate or artificial. The first belongs to most animals; the last is peculiar to man it is his great and exclusive prerogative. This also is of two divisions; oral or vocal, which constitutes speech; and literal or legible, which constitutes writing. The first of these divisions shall form our subject for the present study; the second we will examine in a subsequent lecture. At the root of the tongue lies a minute semi-lunar shaped bone, which, from its resemblance to the Greek letter v, or upsilon, is called the hyoid or u-like bone; and immediately from this bone arises a long cartilaginous tube, which extends to the lungs, and conveys the air backward and forward in the process of respiration. This tube is denominated the trachea or windpipe; and

* Snails revived after being dried fifteen years and more.-Phil. Trans. 1774, p. 432.

See also Mr. Bauer's Croonian Lecture "On the Suspension of the Muscular Powers of the Vibrio Tri tici.-Phil. Trans. 1823, Art. i. He has revived this curious worm after perfect torpitude and apparent death for five years and eight months, merely by soaking it in water.

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† Study of Medicine, vol i p. 457, edit. 1.