- Pindar.

400. The preceding chapters have carried us two steps upon our way. In Chapter II (Disintegrations Of Personality). we gained some insight into the structure of human personality by analysing some of the accidents to which it is subject; - the insistent ideas, the hysterical instabilities, the splits and alternations which seem to destroy that inward unity to the sense of which we instinctively cling. In the third chapter we viewed this personality in its normal waking state, and considered how that norm should be defined, and in what manner certain fortunate persons had extended the grasp of that inward concentration, and had integrated the personality still further by utilising uprushes of subliminal faculty to supplement or to crystallise the products of supraliminal thought.

The review of these two chapters indicates clearly enough what my next step must be. It is obvious that in my review of phases or alternations of personality I have left out of sight the most constant, the most important alternation of all. I have thus far said nothing of sleep. Yet that change of personality, at least, has been borne in on every one's notice; - not, certainly, as a morbid curiosity, but as an essential part of life.

Sleep must assuredly now be studied, and from two points of view.

Regarding sleep as an alternating phase of personality, we must consider what are its special characteristics and faculties. Regarding it as an integral factor in our earthly existence, and on an equal footing with the waking state, we must consider how the faculties of sleep, as of waking, can be improved and concentrated in the course of the physical and psychical evolution of man. Such improvement or concentration, however, presupposes a comprehension of the true nature of sleep which we are by no means entitled to take for granted.

401. First, then, let us consider the specific characteristics of sleep.

The definition of sleep is an acknowledged crux in physiology. And I would point out that the increased experience of hypnotic sleep which recent years have afforded has made this difficulty even more striking than before. A physiological explanation must needs assume that some special bodily condition, - such, for instance, as the clogging of the brain by waste-products, - is at least the usual antecedent of sound sleep. But it is certain, on the other hand, that with a large percentage of persons profound and prolonged sleep can be induced, in any bodily condition, by simple suggestion. Hypnosis, indeed (as Wetterstrand and others have shown) may be prolonged, with actual benefit to the sleeper, far beyond the point which the spontaneous sleep of a healthy subject ever reaches. A good subject can be awakened and thrown into hypnosis again almost at pleasure, and independently of any state either of nutrition or of fatigue. Such sleep belongs to those phenomena which we may call nervous if we will, but which we can observe or influence from the psychological side alone.

402. We can hardly hope, from the ordinary data, to arrive at a definition of sleep more satisfactory than others have reached. We must defer that attempt until we have collected something more than the ordinary evidence as to what occurs or does not occur during the abeyance of waking life. One point, however, is plain at once. We cannot treat sleep, - as it has generally been treated, - in its purely negative aspect. We cannot be content merely to dwell, with the common text-books, on the mere absence of waking faculties; - on the diminution of external perception, the absence of controlling intelligence. We must treat sleep positively, so far as we can, as a definite phase of our personality, co-ordinate with the waking phase. Each phase, as I believe, has been differentiated alike from a primitive indifference; - from a condition of lowly organisms which merited the name neither of sleep nor of waking. Nay, if there were to be a contest as to which state should be deemed primary and which secondary, sleep might put forward its claim to be regarded as the more primitive phase.

It is sleep rather than vigilance which prenatal and infantile life suggest; and even for us adults, however much we may associate ourselves in thought with the waking state alone, that state has at least thus much of secondary and adventitious that it is maintained for short periods only, which we cannot artificially lengthen, being plainly unable to sustain itself without frequent recourse to that fuller influx of vitality which slumber brings.

Out of slumber proceeds each fresh arousal and initiation of waking activities. What other activities may in slumber be aroused and initiated the evidence to be set forth in this chapter should help us to say. To some extent at least the abeyance of the supraliminal life must be the liberation of the subliminal. To some extent the obscuration of the noonday glare of man's waking consciousness must reveal the far-reaching faint corona of his unsuspected and impalpable powers.

403. Entering, then, upon a review of sleeping faculty, thus inevitably imperfect, we may best begin from the red end of our spectrum of consciousness; - the red end, which represents the deepest power which waking effort can exert upon our physical organism.

Our survey of the efficacy of sleep, indeed, must make its beginning beyond that limit. For assuredly in sleep some agency is at work which far surpasses waking efficacy in this respect. It is a fully admitted, although an absolutely unexplained fact, that the regenerative quality of healthy sleep is something sui generis, which no completeness of waking quiescence can rival or approach. A few moments of sleep - a mere blur across the field of consciousness - will sometimes bring a renovation which hours of lying down in darkness and silence would not yield. A mere bowing of the head on the breast, if consciousness ceases for a second or two, may change a man's outlook on the world. At such moments, - and many persons, like myself, can fully vouch for their reality, - one feels that what has occurred in one's organism, - alteration of blood-pressure, or whatever it be, - has been in some sense discontinuous; that there has been a break in the inward régime, amounting to much more than a mere brief ignoring of stimuli from without. The break of consciousness is associated in some way with a potent physiological change.

That is to say, even in the case of a moment of ordinary sleep we already note the appearance of that special recuperative energy which is familiar in longer periods of sleep, and which, as we shall presently see, reaches a still higher level in hypnotic trance.