of six, seven, or eight o'clock in the morning, at the different seasons of the year, is what is evidently, in this country, the most conducive to health.

I may conclude this chapter by mentioning more particularly, some of the more important causes of sleep and of wakefulness.

A moderate and adequate exercise of the faculties of the mind, not only renders sleep more necessary, but puts the system into that state in which sleep is most likely to occur, and to be tranquil and refreshing in its character. An immoderate use of the mental faculties excites the nervous system in an undue degree, superinduces irritability, and either altogether prevents sleep, or renders it uneasy, partial, dreamy, and rather exhausting than cordial in its effects. If the mind be not only exercised unduly, but the depressing passions of grief or anxiety be likewise at work, the effect is largely added to.

"Sleep, gentle Sleep,

Nature's soft nurse, how have I frighted thee,
That thou no more wilt weigh my eye-lids down,

And steep my senses in forgetfulness?

Why, rather, Sleep, liest thou in smoky cribs,

Upon uneasy pallets stretching thee,

And hush'd with buzzing night-flies to thy slumber;

Than in the perfum'd chambers of the great,

Under the canopies of costly state,

And lull'd with sounds of sweetest melody?

O thou dull god, why liest thou with the vile,

In loathsome beds; and leav'st the kingly couch,
A watch-case, or a common 'larum bell?

Wilt thou upon the high and giddy mast

Seal up the ship-boy's eyes, and rock his brains
In cradle of the rude imperious surge;

And in the visitation of the winds,

EXCITING CAUSES OF SLEEP.

Who take the ruffian billows by the top,
Curling their monstrous heads, and hanging them
With deaf'ning clamours in the slippery clouds,
That, with the hurly, death itself awakes?
Can'st thou, O partial Sleep! give thy repose

To the wet sea-boy in an hour so rude;
And, in the calmest and most stillest night,
With all appliances and means to boot,
Deny it to a king?"

295

SHAKSPEARE.-Henry IV., Part 2, Act 3, Sc. 1.

Tranquillity of mind is one of the best of sleeping draughts, the surest and most effectual plea that can be offered in the court of Somnus; whereas sleep is driven away by a memory over-busy in recalling the past, especially if the picture be of dark and sombre character, or by a busy imagination, delineating a gloomy future.

Darkness favours sleep, and light is unfavourable to it. Those sounds which are loud, discordant, and irregular, are usually great preventives of sleep ; while the sounds that are low, musical, and regular, almost always assist it. It is well known, that the hum of bees, the murmur of running waters, the swelling and falling tones of music, and even the unvarying tones of a drawling speaker or reader, induce sleep; and the sleeper is often found to awaken when such sounds are discontinued. An ancient remedy suggested for sleeplessness, was to let water fall from some little height, drop by drop, into a metal pan, the regular and monotonous tones of which might induce sleep. Provided that the sounds be at regular intervals, whether they be near or distant, loud or low, musical or harsh, seems, after

some little usage, to have little effect of interfering with the sleep. The loud and dissonant but measured clanking of the heavy hammers of large forges worked by steam power, are not found to interfere with the sleep of those accustomed to such neighbourhood. The uninterrupted sleep of those who occupy the houses in the great thoroughfares of busy and populous cities, illustrates the same fact; as does the sleep of the seaman in the storm-tossed ship, notwithstanding the violent rocking of the vessel and the creaking of the cordage. Certain odours, as that of freshly gathered flowers,-particularly such as have a faint fragrance, rather than a powerful smell,-have often been observed to induce sleep. The praises that have been so often lavished on the sleep-inviting merits of a bed of heather, may perhaps be referred to this head. The odours of the violet and the mignonette appear to be of this kind. The narcotic virtue ascribed to a pillow filled with the petals of the poppy flower, is probably due to their faint odour, rather than to the infinitesimal doses of morphia, which they may be supposed to exhale along with their fragrance. Some people appear to be remarkably affected in this way by certain odours. The sense of touch-the last of the external senses that is found to yield to sleep, and the first to shake off its trammels,-influences sleep in an important degree. Contact with hard, or rough, or cold substances, has sometimes the effect of inducing sleep, but more commonly either renders the sleep imperfect, or chases it away.

As it is in the organic functions alone that signs

EXCITING CAUSES OF SLEEP.

297

of life are left, when perfect sleep has locked up all the other functions of the nervous system, so the principal preventives of sleep are derived from their derangements. Digestion in its different stages, the circulation of the blood, the respiration, the secreting and excreting organs and tissues, if defectively carried on, may modify or prevent sleep.

In the earlier stages of digestion, owing to the larger quantity of blood that is then directed to the stomach, and the larger amount of nervous power that has then to be supplied to that viscus, the powers of the mind become in a greater or less degree more sluggish, and the will to exert either mind or body is more or less diminished. The degree to which this obtains varies much, according to the quantity and the kind of food that has been taken, and according to the tone and healthiness of the stomach and the general system. In the later stages of digestion, on the contrary, some degree of buoyancy, and an aptitude for any or every kind of work, intellectual or bodily, usually comes on; and this is followed by some degree of languor or restlessness, and this by an appetite for another meal. It might be supposed from these premises, that it would be well to sleep immediately after the meals, and so interfere as little as might be with the determination of the vital forces to the chymification of the food. Experience shows that such a proceeding would be wrong under ordinary circumstances. It is admitted, that sleeping during the first stage of digestion accelerates and facilitates the digestive process; and the digestive

powers may be so weak, that, without such aid, the stomach may not be able to digest even the lightest, and simplest, and smallest quantity of food. Under such circumstances, or in minor degrees of such conditions, the indulgence of sleep after the meals may be most justifiably prescribed; but unless in some such states of system, the practice is found to hurry forward unduly the first stages of digestion, to cause the food to pass from the stomach into the bowels prematurely and crudely, and to produce some degree of excitement and feverishness of the system when the person awakes, and to involve a risk of eventual irritation and derangement of the bowels. In general, even in dyspeptic cases, and in feeble conditions of the system, when not of very severe or extreme character, simply sitting still for a longer or shorter time after the meals, fulfils every needful intention, without risking eventual derangement of the intestinal functions. It may be added, that the common practice among the studious, of devoting those moments of buoyancy and vigour which commonly follow the completion of the first stage of digestion to any sedentary occupation, is anything but advisable for the dyspeptic. Those are emphatically the golden moments which should be devoted by dyspeptics to exercise of the body; promoting, as muscular exercise is admitted to do, the action of the liver, the elimination of the chyle and its conveyance to the current of the circulation, and the propulsion of the egesta through the bowels. In the larger number of those who lead sedentary lives, but who may not