VARYING NEED OF SLEEP. 279 the muscles of voluntary motion become unable to continue the uninterrupted exercise of their functions; the limbs become relaxed, the spine becomes bent, and the head falls forward; and the mind meanwhile ceases from its labours, the faculties of judgment and memory are gradually suspended, and, finally, imagination, the last to quit and the first to return to its post, leaves it; and the external senses, first sight, then taste, then smell, then hearing, then touch, severally, and one by one, cease their exercise; and-this is sleep. "The shades descend, and midnight o'er the world ARMSTRONG. The necessity that exists for the temporary repose of such of the vital forces as are more or less under the control of the will, and liable to be unequally exercised, supplies a sufficient rationale of the uses of sleep. It illustrates the circumstance, that the young, in whom such vital forces are necessarily feeble, and in whom there is, moreover, a constant derivation and expenditure of such forces required for the completion of the growth, and for the development of the tissues, require more sleep than adults. It explains the fact, that, as old age advances, the expenditure of the vital forces becoming less and less, and the equilibrium of such forces being less disturbed, a smaller and smaller amount of sleep is needful to meet the requirements of the system. It exemplifies, and is in its turn illustrated by, the very different requirements of different individuals, in regard to the length of time needed for sleep; this being dependent on the degree to which the vital forces are made use of during the hours of wakefulness, on the degree to which these forces are made use of unequally, on the original strength and power of the tissues by which these forces are manifested, and on their condition as to power at different times. Thus, the man whose mind is occupied exhaustingly in the duties of his profession, will require more sleep in proportion to the amount of such expenditure; and the labourer, after his day of toil, will require more sleep in proportion to the severity of his exertions. Thus, the man who uses equally both the vital forces connected with his intellectual manifestations, and those concerned in the movements of his limbs, will require less sleep, than the man who exercises either of these varieties of vital force duly or unduly, while the equable expenditure of the vital forces in other ways is not secured. Again, those individuals in whom the vital tissues have been originally strong, can support a larger expenditure of vital forces without the need of sleep, than those whose tissues are of feebler organisation; and in such persons, the equilibrium and waste of the vital forces are more quickly restored; and the sleep may be VARYING NEED OF SLEEP. 281 taken without discomfort at longer intervals, and less sleep is found to be necessary. And again, according to the existing condition of the system as to strength or debility, is less or more sleep found to be necessary. Those who have become enfeebled, by the effects of disease or otherwise, require more sleep than is needful to them at other times. This opinion is not interfered with by the circumstance, that in existing morbid conditions, of febrile, inflammatory, or irritative character, the invalid often passes night after night, during days or even weeks, with little or no sleep. On the contrary, in these conditions, the vital forces are all in a state of unquestionable excitement, and so far in a state to undergo much and long-continued exertions; morbid although such state is in its character, and exhausting as must be the consequence of such exertions; often, beyond a doubt, exhausting to a degree inconsistent with the restoration of health, or even with the continuance of life. The effects of such morbid stimulus on the vital forces, and on their temporary capability of endurance and exertion, are evidenced in other ways, than in the time during which these forces can continue to act, without the repose or the equipoising effect of sleep. In cases of continued fever, many days, and in one case, that fell under my own observation, no less than three weeks,-have elapsed, during which the patients have literally been unable to swallow the smallest quantity of nutriment; and yet not only has life continued, but all the wearing and exhausting influence of disease has had to be contended with by the vital forces. In the case referred to, a perfect coma, from which the patient could not be aroused, while it precluded the possibility of mistake as to the fact of the entire abstinence from nutriment, at the same time determined that there should be as small an expenditure of tissue, as could consist with the continuance of life; and not only did the patient recover his consciousness, but he was eventually restored to health. The stimulus offered by diseased action to the vital forces is not, then, solely observable as to its effect of enabling the system to continue without sleep for considerable periods of time. As to this particular, however, the same thing is often observable, to a considerable degree, in cases of lunacy, and other morbid conditions affecting the sensorium. In an inferior degree, the same thing is noticed in cases of high mental excitement, whether from joy or grief, or from anxiety of mind; in which cases the great solace of sleep is often vainly sought for, night after night; and the system is supported by the mental irritant, under such deprivation of its wonted means of restoration and equipoise, until the powers succumb to the eventual exhaustion of the vital forces; or until the irritating influence becomes transferred to some one of the great organs, by the establishment of disease therein; or until, relief being afforded to the mind itself, the tension becomes relieved, and although left much exhausted, the system, by time and rest, gradually regains its tone and equilibrium. Such is sleep, and such are its uses. Perfect sleep PERFECT AND IMPERFECT SLEEP. 283 involves entire loss of consciousness, entire repose of the sensorium, entire rest of the mental faculties ; circulation, respiration, nutrition, and secretion alone involving movement and waste; the several other functions of the nervous system being in absolute repose, regaining their equilibrium, and recovering their intensity of power. But there are various degrees of less perfect sleep, in which one or more of the external senses may still be the means of producing impressions on the sensorium; in which the command over the muscles of voluntary motion may not be wholly suspended; in which even memory and imagination, uncontrolled by the judgment, and imperfectly tested by sensation or by the senses, may career wildly over the past, or create a present or a future out of its disarranged and diversified materials, overleap the possibilities of time and space, recall the dead to the stage of its creatings, cause years gone by to run their round again, filling and embellishing its unreal creations with a jumblement of the probable, the unlikely, and the impossible, and peopling them with whatever memory can recall, or fancy can create. Such are dreams,-the shades and phases, different gradations, of imperfect consciousness,-degrees of imperfect sleep. Their most curious feature is the degree to which, untrammelled by sensation, and unfettered by the judgment, the action of the mind, and especially as regards its imaginative powers, becomes vigorous and untiring. The rapid changes and quick succession of ideas, that may occur |