The relationship of hypnosis to normal sleep is unmistakable, and I agree with Licbeault when he says that the former is only distinguishable in its essence from the latter by the fact of the connection between the sleeper and the hypnotist. But one must not confuse the term "sleep" with the term "exhaustion." Besides, two different ideas are unfortunately mixed up unclearly in the term "tiring" : the subjective feeling of the tiring and the objective exhaustion. Both these do not by any means always fall together. Sleepiness and the subjective feeling of tiring are also by no means identical, although they are often associated. I may perhaps be permitted to state some important facts here.

Physiology is wont to say that sleep is produced by tiring, but this is incorrect. Even if true exhaustion of the brain usually calls forth a subjective feeling of tiring, and the latter is usually associated with sleepiness for its own sake, we must maintain in opposition to this: (1) that extreme exhaustion often creates sleeplessness; (2) that one often becomes more sleepy from sleeping; (3) that feelings of tiring, sleepiness, and real exhaustion often appear entirely independent from one another; and (4) that sleepiness usually appears at definite, habitual (autosuggested) hours, and disappears in spite of increasing exhaustion, when one has overcome it.

The facts are quite unexplainable by the very unsatisfactory chemical theories of the physiologists (the lactic acid theory of Preyer, etc.). For my part, I have never been able to determine the soporific action of lactic acid, and regard the alleged confirmation of this action as. suggestive. I have achieved incomparably better results with spring water, together with suitable suggestion.

The physiologists (Kohlschuetter) have attempted to measure the intensity of the sleep by the measure of the sound required to awaken. How little one proves by this is shown by the fact that an accustomed noise soon fails to awaken, even if it is very loud- - e.g., an alarm - while soft unaccustomed noises awaken at once. Many an anxious mother is awakened by the faintest noise on the part of her child, while she is not disturbed by the snoring of her husband or by some such accustomed noise.

Silent processes, as well as tedious, monotonous processes, which do not require a change of conceptions, make us sleepy; and comfortable positions of the body and darkness do the same. Associated phenomena, such as yawning, nodding, stretching the limbs, which increase the subjective feeling of sleepiness, and which, as is well known, are very infectious, also play a part.

I stated that the habit of going to sleep at a particular time calls forth a powerful sleepiness daily at that time; but certain places, the voice of a certain person, lying back in an easy-chair in which one is accustomed to go to sleep, listening to a sermon, lying in a certain position, a horse-hair mattress for one person and a feather bed for another, etc., and, above all, the closing of the eyelids, are all very common sleep-bringing means. Why is this? One has hitherto called it habit, "associated accustoming"; but we must recognize that these facts are absolutely analogous to an unconceived autosuggestion. My small two-year-old son has accustomed himself to go to sleep with a handkerchief in his right hand held up to his face. He could not sleep for a long time when we took it away from him. Some people can only sleep after certain things have taken place (after reading, winding up a watch, etc).

But the most powerful of all these associations is the closing reflex of the orbicularis. For this reason this is the best suggestion for sleep. 1

1 Von Schrenck- Notzing - "The Significance of Narcotic Drugs in Hypnotism" (Schriften der Gesellschaft for psychologische Forschunq, Leipzig: Abel, 1891) - considers that one should accept that our natural sleep and hyponotic sleep are different, because the oxidation products (tiring products!) are accumulated. Ho given as a proof for this, among others, the impossibility of resisting sleep after great exertion. But we do not deny the influence of the oxidation products, which are produced by a prolonged waking activity of the brain, and we, too, emphasize that the dissociated or relative condition of rest of the brain in sleep is suitably fitted for the production of the necessary chemical syntheses- - i.e., for the reintegration of the brain. We realize that exhaustion of the brain normally can form the strongest associative cause of the suggestion of sleep, and when this has reached a considerable pitch can act irresistibly. When we say that the suggestive actions are produced by conceptions, we are perfectly aware that the conceptions in their turn are always dependent on the physical and chemico-physiological (and also pathological) conditions of the brain elements. The form of the brain changes in the melancholic calls forth, for example, by the means of association, his ideas of self-accusation. The facts mentioned above prove very clearly that normal sleep usually takes place rapidly and as a result of suggestion. One is therefore compelled not to identify it with suggestion, although one recognises the adaptation of sleep to exhaustion of the brain and the usual association of sleep with the same. The suggestve action is therefore just as physical as are the changes in the brain produced by the products of exhaustion, and one must not deny that the latter furthers the mechanism of sleep as a rule. That normal sleep without the hypnotist and without exhaustion can set in in precisely the same way as it does in hypnosis is certain, and proves that this condition of activity of the brain is a thing in itself, and that exhaustion is quite another thing. There is no doubt that the accumulation of carbonic acid in the blood produces more extensive respiration, and that in consequence we cannot hold the breath for any length of time. But this does not prove that the respiratory movements are alone dependent on the carbonic acid in the blood, and still less that the accumulation of the carbonic acid in the blood and respiratory movements are identical processes. We know that the latter are produced by muscles and motor nerve centers, and that even our will (our brain) can accelerate and stop them. The acceleration of the respiratory movements from accumulation of carbonic acid in the blood is a much more direct, more powerful, and more intimate association than the production of sleep by exhaustion of the brain. But, nevertheless, it would never occur to us to regard the voluntarily produced (unnecessary) movements of respiration as belonging to a species different from that of those movements which are produced in asphyxia. The suggested sleep (hypnosis) and the natural sleep are not more essentially different from one another. The brain mechanism of both is the same, even if it can be set into action in different ways. (See also Sec. 10.)