1Ibid., Dec., 1911-Jan., 1012. Richard Q. Badger, publisher.

We can see, therefore, that the sleep producing mechanism is still a mooted question. It is very probable that when we attempt to explain the mystery by ascribing a particular cause we are apt to err. Sleep appears to be produced by a number of factors acting more or less in unison, most of which are requisite but which vary with the individual. Moderate mental and physical fatigue, a comfortable posture and surroundings, and disinterest seem to be the main requirements. If any of these were to be singled out disinterest would probably be emphasized. That even this is a variable factor can be shown by the experiences of such men as Napoleon and Wellington who, we are told, could easily go to sleep though excited and engaged in heavy mental work. Personal experience teaches most of us, however, that the mind must be tranquil before Morpheus will visit us. Disinterest promotes sleep because it lures fantasy, and between the latter and sleep there is no great barrier. One who studies the various aspects of night-dreams and day-dreams will find that both have many common features. If a person is moderately fatigued, has a sense of well being and comfort, and allows his thoughts to flow pleasurably and as they will, fantasy assumes control, and soon sleep is upon him. Medicated pillows, warm baths, eating before retiring, and other methods often successfully used by insomniacs to promote sleep are useful because they produce comfort, hence fantasy. Granting that such is true, it, too, fails to reveal just what mechanisms are involved in the transition from wakefulness to sleep.

Be these points as they may, we know that sleep is a necessary state; in the words of Schopenhauer, "Sleep is to a man what winding up is to a clock. We know, also, that under suitable conditions it steals over us. We do not go to sleep immediately, however; we must first pass through an unnoticed stage of half-waking, half-sleeping termed the hypnagogic state, so-called from the Greek sleep, and leading - leading to sleep. We must pass through a similar stage before we awake. Usually the hypnagogic state lasts but a few seconds but it may be prolonged for as much as fifteen minutes. It is apt to be longer in passing from the sleeping to the waking state than the reverse. In the old and in insomniacs it is often unduly prolonged, so much so at times that these persons believe that they do not sleep at all. This belief is, of course, a self-deception, for even the most confirmed insomniac manages to sleep a few hours out of each twenty-four.

The hypnagogic state is interesting for many reasons. While in it one may note, on the curtains of the eyelids, various figures or scenes which are often the sources or instigators of dreams. In most adults, these hypnagogic images, popularly known as " faces in the dark," are unnoticed or excite no particular interest. When one is fatigued, has eyestrain, or is of a nervous temperament the images may stand out conspicuously. In children they are quite prominent. By paying attention to the eyelids on going to sleep it is sometimes possible to catch fleeting glimpses of these figures, which seem to be constantly changing; as a rule, when the attention becomes focused on them they quickly disappear.

The visions are due to many causes. Impressions from the eyes, though closed, due to circulatory or other changes in the eye ground, may, when transmitted to the brain, form or instigate various memory pictures; sensations from the muscles, viscera, and other parts of the body may act in like manner; further, ideas arising more or less independently of, and uninfluenced by, external or somatic stimuli may call forth, by association, visual-memory pictures which may be projected to the curtains of the eyelids.

The hypnagogic state is very much open to suggestion. Slight sounds may be magnified, so much so that the individual awakens startled. Hallucinations of being touched lightly, or being gripped in a vise may be experienced. One may also seem to hear voices. These hallucinations may be present in normal persons, though more prone to occur in nervous subjects. Sometimes the hypnagogic imagery is so vivid as to cause much fright, and the individual may believe that the characters seen are actually present in the room. Frederick Greenwood has given some good descriptions of hypnagogic imagery.1

As sleep is coming on the sensation of falling may be experienced. This is occasioned by the general relaxa-tion of the muscular system which occurs at this time. Should a person be much disturbed while in the hypnagogic state, the normal transition from waking to sleep or the reverse may be markedly disordered. Consciousness may fully awaken but the motor centres may awaken more slowly; this causes a temporary paralysis of the limbs, speech, and consequently an inability to move or talk. This form of paralysis, called nocturnal paralysis by some writers, may occur after a natural awaking. As a rule, the paralysis lasts but a short time; should it be prolonged it excites much mental disquiet. Fatigue, nervousness, general ill health may provoke it. On the other hand, disturbances during the hypnagogic state may cause an awakening of the motor centres but not of the sensory centres, or consciousness. Thus, the individual may walk, talk, carry out various complicated movements, but the mental images of a dream character remain, so that he acts like one living in a dream. As a rule, the motor and sensory centres awake at the same time, so that when one is able to move consciousness has been completely restored.

1 Imagination in Dreams, 1894, pp. 16-18, John Lane Co.

Once sleep has actually begun certain changes take place in the physical structures. The heart and respiratory rates become slower, less forcible; there is a fall in blood pressure; a warmth of the skin; an increased production of sweat. The stomach, intestines, kidneys, liver and other organs are active though at a lessened pace. Since the amount of work required of the physical structures is much less than when awake, these parts are enabled to rest. Since repair exceeds waste, the various structures are sufficiently recuperated after a due amount of sleep. We should note, however, that practically all the organs are in a state of activity, the only difference being a decrease in the amount of work.