would be the result, if the experiment were greatly protracted. Apoplexy, which consists of a turgid state of the cerebral vessels, produces perhaps the most complete sleep that is known, in so far that, while it continues, it is utterly impossible to waken the individual: no stimulus, however powerful, has any influence in arousing his dormant faculties. When the circulating mass in the brain is diminished beyond a certain extent, it has the same effect on the opposite state; whence excessive loss of blood excites sleep.

Opium, hyoscyamus, aconite, belladonna, and the whole tribe of narcotics, induce sleep, partly by a specific power which they exert on the nerves of the stomach, and partly by inducing an apoplectic state of the brain. The former effect is occasioned by a moderate-the latter by an over dose.

A heavy meal, especially if the stomach is at the same time weak, is apt to induce sleep. In ordinary circumstances, the nervous energy or sensorial power of this viscus is sufficient to carry on its functions, but when an excess of food is thrown upon it, it is then unable to furnish, from its own resources, the powers requisite for digestion. In

such a case it draws upon the whole body-upon the chest, the limbs, &c., from whence it is supplied with the sensorial power of which it is deficient; and is thus enabled to perform that which by its own unassisted means it never could have accomplished. But mark the consequences of such accommodation! Those parts, by communicating vigour to the stomach, become themselves debilitated in a corresponding ratio, and get into a state analogous to that from which they had extricated this viscus. The extremities become cold, the respiration heavy and stertorous, and the brain torpid. In consequence of the torpor of the brain, sleep ensues. It had parted with that portion of sensorial energy which kept it awake, and by supplying another organ is itself thrown into the state of sleep. It is a curious fact, that the feeling of sleep is most strong while the food remains on the stomach, shortly after the accession of the digestive process, and before that operation which converts the nourishment into chyle has taken place.

When, therefore, the sensorial power is sufficiently exhausted, we naturally fall asleep. As this exhaustion, however, is a gradual process, so is that of slumber. Previous to its accession, a feeling of universal lassitude prevails, and exhibits itself in

*

yawning, peevishness, heaviness, and weakness of the eyes; indifference to surrounding objects, and all the characteristics of fatigue. If the person be seated, his head nods and droops: the muscles become relaxed; and, when circumstances admit of it, the limbs are thrown into the recumbent position, or that most favourable for complete inaction. The senses then become unconscious of impressions, and, one after the other, part with sensation; the sight first, then taste, smell, hearing, and touch, all in regular order. The brain does not all at once glide into repose: its different organs being successively thrown into this state; one dropping asleep, then another, then a third, till the whole are locked up in the fetters of slumber. This gradual process of intellectual obliteration is a sort of confused

* We yawn before falling asleep and when we wake; yawning, therefore, precedes and follows sleep. It seems an effort of nature to restore the just equilibrium between the flexor and extensor muscles. The former have a natural predominancy in the system; and on their being fatigued, we, by an effort of the will, or rather by a species of instinct, put the latter into action for the purpose of redressing the balance, and poising the respective muscular powers. We do the same thing on awaking, or even on getting up from a recumbent posture-the flexors in such circumstances having prevailed over the extensors, which were in a great measure inert.

dream-a mild delirium which always precedes sleep. The ideas have no resting-place, but float about in the confused tabernacle of the mind, giving rise to images of the most perplexing description. In this state they continue for some time, until, as sleep becomes more profound, the brain is left to thorough repose, and they disappear altogether.

Sleep produces other important changes in the system. The rapidity of the circulation is diminished, and, as a natural consequence, that of respiration: the force of neither function, however, is impaired; but, on the contrary, rather increased. Vascular action is diminished in the brain and organs of volition, while digestion and absorption all proceed with increased energy. The truth of most of these propositions it is not difficult to establish.

The diminished quickness of the circulation is shown in the pulse, which is slower and fuller than in the waking state; that of respiration in the more deliberate breathing which accompanies sleep. Diminished action of the brain is evident from the abolition of its functions, as well as direct evidence. A case is related by Blumenbach, of a person who had been trepanned, and whose brain was observed to sink when he was asleep, and swell out when he was awake. As for the lessened vascular action in the

voluntary powers, this is rendered obvious by the lower temperature on the surface which takes place during the slumbering state. Moreover, in low typhus, cynanche maligna, and other affections attended with a putrid diathesis, the petechia usually appear during sleep when the general circulation is least vigorous, while the paroxysms of reaction or delirium take place, for the most part, in the morning when it is in greater strength and activity.

In some individuals the stronger and more laborious respiration of sleep is made manifest by that stertorous sound commonly denominated snoring. Stout apoplectic people—those who snuff much or sleep with their mouths open, are most given to this habit. It seems to arise principally from the force with which the air is drawn into the lungs in sleep. The respiratory muscles being less easily excited during this state do not act so readily, and the air is consequently admitted into the chest with some degree of effort. This, combined with the relaxed state of the fauces, gives rise to the stertorous noise. Snuffing, by obstructing the nasal passages and thus rendering breathing more difficult, has the same effect; consequently snuffers are very often great snorers. The less rapidly the blood is pro