rious species of them we observe great differences in regard to the necessity of sleep. In like manner there are various kinds of clocks, some of which require winding up every twelve hours, others every week, others again every month, and others at still longer intervals. Thus the swallows, on the approach of winter, retire to caverns and morasses, where they sleep for five months together, till the return of warm weather. Such, too, is the case with the frogs; and serpents also have been found in winter in subterraneous holes. The tortoise, during that season, burrows the deeper into the sand, the colder it is; and lives in this torpid state, excluded from the air, till called forth by the warmth of spring. Even the fishes, in severe frost, bury themselves in the mud, and there pass their state of torpidity. The bear, the badger, and the marmot, lie the whole winter in holes, and it is related of the last, that it will not wake even when wounded with knives. This animal repairs, at the beginning of winter, to a hole which is the hereditary abode of a whole family of marmots from generation to generation. It first collects a quantity of hay, with which each individual of the family prepares a bed for itself. When they are all assembled, they close up the entrance to their retreat, lay themselves down, and sleep so profoundly that, as we are assured, they may be taken up and carried away without waking. It is said that, for a fortnight previously to its long sleep, this animal eats nothing, but drinks only, in order to cleanse the stomach, otherwise the food, by remaining in it so long, might become putrid; and it lies with its snout close to its belly, lest by respiration it should lose too much moisture. Thus each animal has its peculiar wants; and to such as would scarcely be able to find subsistence in winter, Nature has given bodies that require a sixmonths sleep, during which they need neither food nor drink. The bears have the precaution to gorge themselves against winter to such a degree, as if they meant to eat enough to last them all their lives. They go into winter-quarters with their hides distended by a load of superfluous fat; and waste away during the period of their sleep in such a manner that in spring they come forth again mere skeletons.

It is a fortunate circumstance for those persons who love to improve their minds and are fond of useful employment, that we are not subject to such protracted sleep, but can make shift with a few hours repose. I have heard, indeed, of the Seven Sleepers, and of Epimenides the Cretan, who, when a boy, went into a cave, where he fell asleep, and is said not to have awoke for forty-seven or fifty-seven years: a story which the apostle Paul perhaps had in his view, when he called the Cretans "liars," and some other hard names. My readers need not be informed what credit is due to these tales. At the same time we are not authorised to consider them as absolutely impossible; since many able men who have maturely weighed the matter, do not think it in itself totally unreasonable. Boerhaave admits that he discredits the story of the Seven Sleepers; but he adds, "I nevertheless believe that people may live a long time without meat or drink for, when they are once completely subdued by sleep, the pores close, and they may then live a long while before they are awakened by the slow and gradual waste to which they are subject. Haller remarks, that the Turks have a similar fable concerning giants who have slept for a great length of time, and praises an idea of Reaumur's concerning this suspension of

food and life. This great naturalist has demonstrated that the eggs of animals and insects, as well as the nymphs of caterpillars, may be kept merely by means of cold and the absence of exciting causes for years together before they are developed, and that the vital principle is nevertheless not extinguished, since the animals produced by the application of warmth from these eggs and nymphs are as brisk, and live as long as they would have done without this delay. On this foundation the great Maupertuis constructed a system for prolonging human life; and who knows but the plan may be some time or other carried into execution? I have no doubt of it for my part, if we can depend on the accuracy of the observation communicated by M. Bouguer, concerning a species of serpent in Peru, which, after being suspended to the branch of a tree or in a chimney, till quite dry, may be revived ten or twelve years afterwards, if left for some days in muddy water exposed to the sun's rays. We are so little enlightened in respect to such matters, that it may be deemed nearly as bold to laugh at this story as to give it implicit belief.

Be this, however, as it will, so much is certain, that we ordinary folks, who are neither Seven Sleepers nor Cretans, have no occasion to imitate the marmots, but that a sleep of a few hours is sufficient to recruit our lost strength, and to fit us for a new life of sixteen or eighteen hours. Corporeal fatigue, mental exertion, profound meditation, nay time itself, weaken our animal powers, and consume the vital spirits which are indispensably necessary for all occupations both of body and mind. I could relate to my readers how these effects are accounted for in the medical schools; but when I consider that after I had done, they would be just as wise as at first, I will spare them the explanation, and give in its stead a few useful rules how to turn sleep to the benefit of their health. So much they know, that we cannot live without sleep; that we sleep because we are weary; that we possess new strength when we wake, and hence it is to be inferred that the object of sleep consists merely in the recruiting of our strength. Well, we physicians also know just so much, and no more: for all that we conjecture beyond this is of no farther use than to relieve us from the disgrace of acknowledging our ignorance.

It is not a matter of indifference to health where we sleep. In many houses the bed-rooms are those which are found unfit for any other purposes. The poor frequently sleep in holes, where they have not so much room and air as a dog that is chained in his kennel. Many people in good circumstances have bed-chambers which are so small, dark, and dirty, that they would be ashamed to show them. This is an important error in the conduct of life. As we commonly spend a third part of the twenty-four hours in our bed-rooms, it behoves us to take all possible care that we may enjoy pure air for so long an interval, especially as we cannot well renew it in the night-time. To this end we ought never to sleep in the apartments in which we live during the day, but choose for a bed-chamber a spacious room exposed to the sun, that can be opened in the day for the admission of pure air and the dispersion of the vapours collected in the night. The beds should often be shaken up, and these as well as the bed-clothes exposed in the day to the sun and air. It is necessary to observe these rules if we would secure ourselves from the effects of vitiated atmosphere

Night is the best time for sleep. It is more quiet than the day; and it is then better for us to be in bed than up, because the warmth of the bed protects us from the cold and damps of night. It is also advisable to retire to rest before midnight. It is proverbially said, and with truth, that the soundest and most wholesome sleep is that which we obtain before twelve o'clock. If we remain up too long, we waste too much of our strength; hence result certain movements in the blood, which are a kind of consuming fever. The least degree of fever in the blood is well known to occasion restless sleep; and therefore it is never advisable to defer it till after midnight. It should farther be observed, that the occupations which we follow late at night are seldom conducive to health. We sit down either to read or write, and for so unhealthy a posture as sitting, the day is quite long enough, without our devoting to it part of the night also; or to study, and thus waste still more the animal powers which sleep ought to recruit and renew; or to feasting, by which we pamper a part at the expense of the whole, forgetting that sleep is the best feast of the animal nature. For the same reason I cannot approve of dancing at night, though it has this advantage over other nocturnal amusements, that it keeps up the transpiration which the cold of night is otherwise liable to check. As we ought daily to comply with the instinct which impels us to eat and drink for our nourishment, so we ought also to feed and to refresh the animal nature with sleep, and not suffer it to fast beyond the proper time.

Great heat, severe exertion either of body or mind, and hearty meals, sometimes dispose us to sleep in the day. It has been a subject of frequent discussion, whether sleep after dinner be wholesome or not. There can be no doubt that it is, when we feel heavy and disposed to sleep. Boerhaave was once of opinion that sleep after dinner is pernicious, and that the school of Salerno was in the right to proscribe it, and on the contrary to recommend bodily exercise after meals; but when he considered that all the animals, after appeasing the cravings of appetite, give themselves up to repose, and that the due digestion of food requires not only a large proportion of vital spirits, but also the easy and unrestrained movement of the abdomen, to neither of which bodily exercise conduces; he changed his opinion, and with Hippocrates, Galen, and other eminent physicians, recommended bodily exercise before dinner, and a nap after it with Felix Plater. The latter celebrated physician once attended a meeting of his colleagues, at which this question was debated. Every one condemned the practice, when Plater rose: "I am now seventy years of age," said he; "I have always taken my nap after dinner, and have never been ill in my life." Who could advance any thing against such an argument?

It is an important question, how long a person ought to sleep. Too long sleep overloads, too short stints the animal nature. The best sleep should continue no longer than till we are satiated with it. This satiety depends on a hundred different circumstances. A lively disposition does not require so much sleep as a phlegmatic temperament. We often hear people complain that they cannot sleep at night, who nevertheless are hearty and lively during the day, and who merely err in going to bed too early and lying too long. They retire to rest,

perhaps, at ten o'clock, and awake at three or four. Conceiving that to sleep well they ought to sleep the whole night through, they call that restlessness which is but the effect of vivacity. They do not require Jonger sleep. Their force is recruited in a few hours; after which they ought to rise, anticipate the sun, and pursue their occupations. The same is the case with the indolent, whose head and hands are alike unemployed. For them it were better that the day were twice as long, or that they made no difference between day and night. They should only lie down when they are sleepy, and rise as soon as they awake, and fall to some kind of work or other. I know a person who has by this method relieved himself from sleepless nights. He rose as soon as he awoke, be the hour what it would; employed himself for an hour, or till he grew sleepy, then lay down again and slept till morning. In a short time he could sleep the whole night through, especially after taking bodily exercise in the day. Sanctorious observed, that a person who sleeps from eight to ten hours transpires but little in the first five. In the three following the transpiration increases, and he becomes lighter in weight as well as in feeling. In a longer continuance of sleep the transpiration again diminishes. The blood gradually circulates more slowly. He feels chilly, and the limbs become heavy. Instead of acquiring new strength, he is oppressed with a lassitude which makes him more and more sleepy, and against which Sanctorious recommends bodily exercise and strong excitement of the passions. Unless recourse be had to these aids, such a person is in danger of the fate which befel a doctor of physic, of whom Boerhaave makes mention. Having conceived a notion that it was conducive to health to sleep a great deal, he went to bed in a dark and quiet place, and slept several days. When he was awakened, he was much more ignorant than he had been before. He again resigned himself to sleep; and on again awaking, he was a perfect idiot. Hence it is necessary to beware of sleeping too long. Nature herself in general prevents us from falling into the contrary extreme. These impulses must not be obstinately resisted, or we incur the risk of insanity. In this manner the fowler stupifies the falcon that he is about to train. He prevents it from sleeping for a certain time, and this breaks the spirit of the bird to such a degree, that its instructor can make it do whatever he pleases. The position of the body in sleep is likewise a point of some consequence. The head ought not to be too low, and there should be nothing to obstruct the free movement of the chest and abdomen. For this reason all night clothes ought to be loose. The body ought to be equally covered, and none of the limbs should be in such a posture as to keep the muscles in action. If you fall asleep with your hands clasped, you find on awaking that your fingers are dead and have no feeling. If you lie with crossed legs, they either contract that sensation which is called being asleep, or you get the cramp in them. It is hurtful to sleep much sitting on a chair; for if the legs hang down they are apt to be swollen in the morning, and if they are laid upon another chair, this position compresses the abdomen. Some maintain that it is best to lie on the right side, that the heart may move with greater freedom. The most rational course in this particular is for each individual to be guided by his own feelings, and to change his posture accordingly. Neither the light of day, nor even moonlight,

should be permitted to fall upon the eyes during sleep; otherwise they are liable to a dry burning heat in the day-time, and frequently to inflammation.

Every one would be glad to know by what means sleep may be promoted; for nothing is more unpleasant than to be weary and yet have to wait for sleep. The best method is fatigue, either by bodily or mental labour, and this is not the lot of the great, but of the humble and the slave. Who but recollects the soliloquy to this effect, which Shakspeare has put into the lips of Henry IV.? That of his valiant successor, though less poetical perhaps, for which reason it has not been so often quoted, is equally to the point:

"I know 'tis not the sceptre and the ball,
The sword, the mace, the crown imperial,
The intertissued robe of gold and pearl,
The farsed title running 'fore the king,
The throne he sits on, nor the tide of pomp
That beats upon the high shore of the world;
No, not all these, thrice-gorgeous ceremony,
Not all these, laid in bed majestical,

Can sleep so soundly as the wretched slave,
Who with a body fill'd and vacant mind

Gets him to rest, cramm'd with distressful bread,
who, from the rise to set,

Sweats in the eye of Phoebus, and all night
Sleeps in Elysium.

HENRY V. act iv. scene 1.

There are other means of promoting sleep, most of which, however, ought only to be known in order to be avoided. Corpulent persons are, almost without exception, disposed to profound sleep, which may more justly be regarded as the forerunner of apoplexy than the invigorator of animal life. Dionysius, the corpulent tyrant of Heraclea, slept so soundly, that to awake him it was necessary to thrust pins through the fat into his flesh. Apoplexy at length carries off such drowsy persons, and as their sleep was an image of death, so death in them exactly resembles sleep. Too long watching also tends to promote an unnatural drowsiness. Soldiers, after passing several nights without sleep during sieges, have been known to be so overpowered as to fall asleep on the batteries amid the thunder of bombs and cannon. Persons who have been cruelly prevented from sleeping for several weeks, have, after the seventh week, become so insensible, as not to be roused from their stupor when beaten ever so severely. The wellknown soporific medicines, it is true, occasion sleep; but it is so restless and unnatural, that it ought rather to be termed a disease than wholesome rest. This effect is produced not only by opium and preparations from it, but by various plants; for instance, the different species of henbane, nightshade, &c., the use of which should of course be avoided. In Italy there is a kind of lettuce, which, if eaten, occasions a mortal sleep. In India there is an herb, called there dutroa, but in the Maldive Islands moetol, bearing a round green-spotted pod, full of small seeds. Wild sage, herminum, makes people drowsy who remain long on a spot where it grows in abundance; and it is well known that a stupor seizes those who sleep where beans are in blossom, or in a room where lilies are placed. Upon the whole, it is pernicious