SLEEP

(Germ, schlaf.) That state of the body in which the functions of sensation and volition are suspended, while the vital functions retain their usual activity: the operations of the mind, if not at perfect rest, are disconnected with external objects. Healthy or natural sleep usually comes on with a peculiar sense of muscular la itude, gaping, and desire of repose; the eyelids fall, and there is general muscular relaxation. The sense of hearing is that which is longest retained; and we generally hear what is going on about us, and even feel inclined to take occasional part in conversation, long after the eyes are closed. The quantity of sleep required by different individuals is various, from six to nine hours being the average proportion. Indolent listle persons, and especially those who indulge in the luxuries of the table, and a|re in good health, will often slumber away from eight to ten hours daily; while others of active dispositions, and who live abstemiously, will be satisfied with four or five hours of sleep: and such persons are generally more disturlied by dreams than the former. Very young children sleep away much of their time, and so also do many old persons. Sleep is often prevented by intense thought, by anxiety, and other mental affections; and also by hunger, and by the application of cold to a jjart of the body. When a person has been over-fatigued by bodily exertion, sleep is also often courted in vain; and there are many stimuli by which its acce ion at the usual times is prevented or retarded, such as strong tea,coffe^, small doses of opium, and several other articles of medicine and diet. Bodily exercise and mental tranquillity, a full meal, the absence of light, noise, and other disturbing causes, are circumstances generally favourable to sleep; but in all these respects various habits often greatly interfere, and persons accustomed to very active lives when suddenly deprived of their usual occupations often sleep worse than before, indolence becoming an apparent stimulant. A ■ distended stomach keeps some individuals awake; and others cannot sleep in a dark room, or in the quiet of the country, who have been used to a night lamp, and to the rumbling of carriages over a London pavement. The proximate cause of sleep has been discu ed by several eminent physiologists, but without any very satisfactory results: it is, in fact, as entirely beyond our grasp, as are the other functions of the nervous system. See Dreams. [s. 1136]