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as those of disease or excessive grief, the vital or involuntary organs themselves are fatigued and exhausted; and when the exhaustion is complete, they also, like the organs of external sense, sleep or become torpid: in other words, Death ensues, the living principle ceases, and the spirit separates from the body. The resemblance, therefore, between Death and Sleep is not less correct upon the principles of physiology, than it is beautiful among the images of poetry. Sleep is the Death or torpitude of the voluntary organs, while the involuntary continue their accustomed actions. Death is the Sleep or torpitude of the whole. Every organ of the animal frame recovers from its fatigue or torpor by rest, provided the principle of life continues. Hence the organs of external sense, in a definite period of time, and a period generally proportioned to the degree of their exhaustion, reacquire their accustomed vigour, are alive to the influence of their appropriate stimuli; and the smallest excitement applied to any one of them throws the whole once more into action, in consequence of their habit of acting associately and by common consent. In other words, the man awakes from Sleep; he rouses himself from the temporary Death of the organs of external sense. Were it possible for the principle of life to continue during a total rest or torpitude of the vital or involuntary organs, as it does during that of the voluntary, there can be no doubt that these also would, in time, recover from their exhaustion; and that the man would, in like manner, awake from the total torpitude, the sleep or death of the entire frame; but this in man, excepting under very particular circumstances, and circumstances I shall advert to presently, is impossible. The rule of nature is, that as soon as the vital or involuntary functions are discontinued, the principle of life ceases; the soul deserts the body; the laws of chemistry, hitherto held in subjection by a superior control, assert their authority; and the whole visible system falls a prey to corruption and ruin. When the organs of external sense have recruited themselves by repose, I have already observed that the stimulus that rouses the one rouses at the same time the rest, from a habit of association. From the same habit, the torpitude produced by exhaustion in any single organ is propagated through every other, and the sleep becomes common to the whole: although it is also unquestionable that the whole are fatigued, or partially exhausted, in consequence of the general stock of sensorial power having been borrowed, in a considerable degree, from the rest, and expended at a single outlet. The sensitive fibres of the organs of external sense are equally affected, and of course become equally exhausted, whether a stimulus be applied at the one end or at the other, the end terminating externally or that connected with the brain: and hence, internal excitements, as those of severe study, intense grief, undue eating or drinking, or febrile diseases, produce the same effect as causes operating from without. In either case, the sleep or torpitude produced is sound or healthy under a certain degree of exhaustion alone: hence, mankind sleep most refreshingly after a moderate or accustomed fatigue, moderate or accustomed study, moderate or accustomed meals. If the stimulus be a little increased beyond this medium, an undue and morbid proportion of sensorial power is secreted, which postpones, indeed, the torpitude or sleep for the present, but at the expense of the general strength of the system, and an expense to which the vital organs themselves contribute something: whence a far deeper and heavier sleep or torpitude ensues than would have ensued with a less proportion of fatigue. If such torpitude take place before the vital organs are totally exhausted, it is confined to the organs of sense alone, which hereby progressively recover their accustomed activity and vigour. But if the vital organs be also exhausted before the torpitude ensues, it will be propagated to themselves, the living principle will cease, and the sleep will be the sleep of death. Violent and continued pain or labour, as external stimuli, violent and continued fevers, violent and continued grief, a very inordinate debauch, as internal stimuli, are all liable to produce these effects; and the one or the other will take place in oroportion to their excess and extremity. 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 whh 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 Drecise 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 Revert? 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 laws of chemical affinity, which it evinces in every ordinary case of the death or

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