I have further pointed out that what we really bring about under such conditions is a dissociation of consciousness. In the normal waking state the dissociation is transient, fleeting, disappearing at the very moment of its appearance, while in abnormal suggestibility the states are more or less permanent. In other words, the waking state tends to disappear under the conditions mentioned above. Now to induce sleep the first requirement is the displacement of the waking state. It is evident that the conditions that favor the suppression of the waking state would also favor sleep-states. As a matter of fact I have often observed in my patients and subjects that the conditions by which I intended to bring about a subconscious state in general and a hypnotic state in particular have often resulted in ordinary sleep. I have found quite frequently that the close observation of the conditions of monotony, limitation of the voluntary movements, limitation of the field of consciousness and of inhibition, brought about not a hypnotic state, but ordinary sleep. I began to experiment on myself and found that I could put myself almost at any time into a state of deep sleep by closing my eyes and keeping perfectly still, dismissing all ideas from my mind—closing shop, so to say. I was able to put myself into a quiet, prolonged and often very refreshing sleep. I have further succeeded in the treatment of many cases of insomnia, by following the same lines in bringing about good therapeutic results.

            After many years of experimentation and observation I have come to the conclusion that this could not possibly be an accidental matter, but that there must be some close interrelation between sleep-states and the conditions of normal and abnormal suggestibility. In other words, the conviction was almost forced on my mind by the facts that the conditions I found requisite for the induction of dissociated states and for normal and abnormal suggestibility in general play also an important role in the induction of sleep.

            There is one fact that is specially worth while noticing in the process of falling asleep, and that is, the circumstance that we do not tumble into it in spite of ourselves, that we go about it in a deliberate, may be cold-blooded fashion. We have to make up our minds and decide whether or no we want to go to sleep, or whether it is best for us to be asleep; and when we decide in the affirmative, we undress and go to sleep. The whole affair is not the after-effect of some narcotic, toxic, autotoxic bodies, nor the result of some involuntary automatic mechanism,—it is a voluntary act,—the result of decision. In this respect sleep is very similar to the abnormal state of suggestibility in which subjects can be artificially put. The state of abnormal suggestibility, the hypnotic state, is not induced by accumulation of toxic products in the system. The state can be brought about at will under the conditions described above. It is a purely voluntary affair, requiring the cooperation of the subject’s and the experimenter's attention, active and steady. In fact, subjects whose attention is poor,—imbeciles, idiots, insane persons or persons whose attention is constantly wandering and fluctuating, are extremely difficult to hypnotize.

            These significant facts so often overlooked by writers on the subject, force on one the conclusion that the psychic factor is of the utmost importance in the formation of sleep-states.

            If we now scrutinize the conditions under which drowsiness and sleep occur, we find that they differ in some very important points from those requisite in the induction of hypnotic states. In the bringing about of hypnosis the most favorable condition is the fixation of the attention on some object, perceptual or ideational. So much is this condition of fixation of importance that some writers describe the nature of the subconscious by this one condition of the attention, and characterize the hypnotic state, not without some show of plausibility, as a cramp of the attention. Such a sweeping statement is not entirely true to fact, but it is true that fixation of the attention, steady and persistent, without flinching, constitutes a very important factor in the induction of the hypnotic state. In sleep, however, we observe that the condition is somewhat modified,—it is not fixation of the attention that is conducive to sleep; in fact, fixation of the attention is more favorable to insomnia or to the prolongation of the waking state. What is requisite is a relaxation of the attention. If fixation of the attention is present at all, it is only present in so far as it is requisite to have the attention relaxed, which under some conditions requires either an effort of the will or the presence of specially favorable circumstances. It is the will to give up all active relations, sensory and motor, with the external environment. In hypnosis there is present at first a strained state of attention; in the induction of sleep the strain is practically reduced to its minimum. In the formation of sleep-states all active desire must cease. That is why people with intense, active desires and emotions find it so difficult to fall asleep. On the other hand such intense desires and strong emotional states may, if taken advantage of at a favorable moment, become the best condition for bringing about states of suggestibility, hypnosis and all forms of dissociation. In fact, in this respect we may say that the sleep-states differ fundamentally from hypnotic states. Suggestibility, which is the characteristic trait of subconscious states and of hypnotic states in particular, is absent in sleep-states. While hypnosis and allied states are characterized by a greater facility of reactions to external stimulations, the sleep-states on the contrary are characterized by an almost complete suppression of the more complex reactions associated with mental processes. In other words, in hypnosis and allied states there is a suppression or inhibition of the inhibitions present in waking life; in sleep, on the contrary, the inhibitions are intensified. If put in terms of the threshold theory advanced in my work, “Multiple Personality,” we may say that in hypnosis and allied states the thresholds are lowered, while in sleep states the thresholds are raised.

            If we turn once more to the conditions of sleep, we find that limitation of the field of consciousness and limitation of voluntary movements play a very important role in the bringing about of sleep-states. In this respect Huebel’s shrewd observation is correct,—the cutting off of all external stimulations tends to bring about a languid condition akin to sleep. Prisoners in solitary confinement, unless they find a source of mental activity by getting some external stimulations to awaken their mental life, have a tendency to sleepiness. Where attention is relaxed, or the interest in external impressions is gone, there drowsiness supervenes. In the limitation of voluntary movements a mass of muscular sensations as well as kinaesthetic sensations is kept from pouring into consciousness, the result is a lowering of mental activity, a rise of thresholds characteristic of sleep. The cutting off of external impressions is also of importance in hypnosis, as when the subject is asked to keep very quiet and make his mind a “blank.” Where there is a predisposition to states of dissociation the result of l imitation is not sleep but hypnosis, with a fall of thresholds.

            The most important and possibly fundamental condition common to sleep and subconscious states is that of monotony. In order to fall asleep we must dismiss all our interests, all our thoughts. Similarly, to induce hypnosis we tell the subject to try not to think of anything. We impoverish, we make monotonous, his mental life by making him think of “nothing in particular.”

            The fact that people may fall asleep even under intense stimulations is often adduced as a strong objection to the view that diminution of sensory stimulations is conducive to sleep. Thus Richet refers to the fact of “falling asleep at the opera, in spite of the light and the noise.” This objection is valid only if we leave out of account the importance of the factor of monotony. It is not so much the diminution of the intensity of stimulations which is of importance in the production of sleep, as the total mass of impressions. In fact, it is not so much the total volume as the progressive, ceaseless variability of the incoming impressions that counts in the keeping up of the restless activity of consciousness in its adjustment to the external conditions of the environment. Given a prolonged stimulation or a series of stimulations of the same intensity, consciousness becomes dulled and sleep ensues. In fact, the more intense the monotonous stimulations are, the deeper is the state of sleep.

            It is interesting to note that under such conditions the intensity of the series of monotonous stimulations tends to keep up the sleep-state. With the cessation of the monotonous stimulations the sleep-state tends to disappear. The miller falls asleep under the continuous uniform noise of his mill, and wakes with the cessation of the noise. In listening to lecturers in a medical school I found how easily the monotonous, uninteresting delivery put me into a drowsy state, and how I came back to myself with a start when the lecturer stopped. Inquiring among the students, I found that their experiences were quite similar to my own; they were kept in a semi-drowsy state by the long-drawn-out sentences, and kept awake by the lecturer’s resting-places. Many people who are used to the long, continuous hum of a large city such as New York, for instance, find it difficult to fall asleep in a quiet place.