The phenomena of sleep, as observed by a bystander, are, for the most part, these. The features are relaxed, and give little or no expression, unless of bodily pain or distress, or of the sentiments of a dream, or of some long predominant passion, which has been so often denoted by certain muscles of the face, that these have acquired a fixed unnatural development from their constant exercise, and thus, even at a time of repose, they produce the semblance of emotions which may be really at rest. Ordinarily, however, the features exhibit no other aspect than that of passiveness. The eyelids are closed more or less completely; but in states of great debility, and especially in children, the closure is imperfect. The eyeballs are rolled upwards, so that the pupils, even in the semi-closure, are not fully exposed to the light; they may, however, be quite open to light, and sleep, nevertheless, occur, though such instances are extremely rare. The ears are not defended from causes of hearing in any other manner than by a relaxation of the muscle which keeps the drum of the ear on the stretch, and which is probably used only in the nicer discriminations of sound. Odorous particles reach the nerve of smell, but are not carried into it with that impetus which enables them to be more strongly perceived, and which requires a voluntary effort. Taste is not excited, partly because no substance is presented, and partly because the tongue is not pressed against the palate. The general sensibility of the body is not aroused, for the contact of clothes and the pressure of the chair or couch occasion impressions too slight and too habitual to be noticed. The sense of touch has no stimulus applied to it, for this involves muscular exertion, as in the application of the tips of the fingers.

In one way or other, then, the sleeper is withdrawn in some degree from the agents which affect the senses; but all these conditions may be absent, and yet sleep no less occur, for the only thing essential to this state is torpor of the nerves, or of the nervous centres with which they are connected.

We are generally made aware that a person sleeps by his insensibility to sounds, for the shutting of the eyes is obviously equivocal. If the slumber be light, the slightest touch may awaken him, an impression far slighter than that made by any part of his dress, or by the pressure of his body. This is owing to the novelty of the impression, a quality which always increases its effect; and I may remark, incidentally, that the mere cessation of an impression that was present at the time of falling asleep, may cause the sleeper to awake; thus, a person who sleeps while another is reading often starts when the reader pauses; and this removal of an impression is tantamount to a new impression, since the nerve is put into a condition different from what had existed for some time. The finger may have been so accustomed to the pressure of a ring that its pressure is unheeded, but let it be taken away, and the wearer is immediately reminded of its absence by the new feeling in the part.

As the slumber becomes more profound, the eye, the ear, and the skin become less impressible; strong light may stream through the semi-pellucid eyelids, loud noises may reverberate, and the individual may be touched, nay, moved, and yet he may not awake.

Not only, as we have seen, are the muscles of the face relaxed, but also those of the trunk and limbs. The muscles which are necessary for respiration continue to act, but their action is independent of the will, though occasionally assisted by it. The relaxation is generally gradual. If the sleeper is in the sitting posture, the grasp of the hand on the book, or any other object, gives way, the body inclines forward, or sideways, or backwards, according to the direction towards which gravitation directs it; the head falls towards the breast, because it is so articulated to the spine that its heavier portion is anterior to the centre of motion. The shock given by this descent of the head often rouses the sleeper sufficiently to make him bring it back to a position more accordant with his rank in the scale of animals; and then the will again slumbers, and the head is again degraded.

On examining the limbs, we notice that they are gently bent.* There are two sets of muscles which move the limbs; one set which bend the joints, the other which straighten them; they are technically called flexors and extensors, and they antagonise each other. In sleep the flexors are said to have the predominance; not, however, that this statement is quite correct, for neither set are positively in action. The limbs are found in a semi-flexed position, not because of a continued action of the flexor muscles, but because having been instinctively placed in that position, they remain in it when the muscles are reposing. They are instinctively so placed, in order that the body may rest more easily, because on a more extensive base, when the limbs are slightly bent. Anyone will find, when lying down on the side, and trying to rest with the limbs extended, that the points of support for the body are much fewer, and therefore that the pressure on the parts which are undermost is greater than if the limbs are moderately bent.†

These remarks on the sleeper all have reference to what I described to you as the Life of Relations, but we cannot close this first superficial study of his condition without noticing the respiration. It is slower than in the waking state, and it is more audible. The latter character depends on the air being drawn through the nostrils only, and with more force, because the inspirations are deeper. Sometimes, as in very profound sleep, the breathing is absolutely laborious ; the cause of which is either that the torpor natural to one part of the nervous system is extended to another which is very near it, and from which the nerves which animate the muscles of respiration derive their energy, or that the state of sleep, combined with the position, has caused such a fulness of the vessels about this part as to oppress its function. In coma, or morbid sleep, this phenomenon is very common. The circulation is also slower, that is, the beatings of the heart are less frequent; one reason for which is the suspended muscular action in the limbs, for no cause has a greater influence in quickening the circulation than muscular action; and the mode in which it operates is by compressing the veins, and so hastening the flow of blood through them towards the heart. Also there is, cceteris paribus, a direct proportion between the rate of circulation and the respiratory movements. Another fact worthy of notice, as to the organic life in sleep, is that the body is more easily affected by cold. Now, the body resists the action of outward cold, or, in stricter language, is enabled to part with a large portion of heat to the air and other surrounding objects by virtue of its own faculty of manufacturing heat. The animal caloric is formed in greater quantity, in proportion as the respiration and the circulation are more active; therefore it is not wonderful that during sleep cold should have a greater effect upon the body than during our waking moments. It is probable, also, that there is a direct relation through the nervous force, which seems to be intimately connected with the production of heat. Digestion and the assimilative function are, probably, more active during sleep; so also is the function of perspiration; but I must not dwell upon these points, as we have much before us.