Natural Analogies of Hypnosis. - Relation of Hypnosis to Sleep and other Conditions. - -Theory of Hypnosis. - Leucomaines and Animal Alkaloids. - Hughlings Jackson's Three Planes of the Central Nervous System. - Cortical Inhibition. - Morselli's Mental States and Centrifugal Equivalents. - Cortical Control. - Function stimulated by Hypnotism. - Foundations of Consciousness. - Chloroform and Hypnotic Anaesthesia contrasted. - McDougall's Views. - Individuality dependent on Continuity of Memory. - Pathological and Hypnotic Lethargy. - Alcohol and Hypnosis. - Researches of Tamburini and other Italian Scientists on Excretions during Hypnosis. - Hypnotism and Hibernation.

In the foregoing pages I have endeavoured to show that the hypnotic state has many analogies in ordinary life, and that it is not so much the creation of a new condition as the exaggeration of normal or partially normal ones. It is the intentional production of a physical state, similar to many which occur spontaneously in all persons under certain circumstances.

The phenomena of hypnotism have points in common with those of natural sleep, reverie, mental concentration, intense nervous excitement, religious ecstasy, post-epileptic states, as well as with the effects produced by alcohol and various drugs. There is also a close resemblance between some forms of hypnosis and hysteria, and the affinity between spontaneous and induced catalepsy and somnambulism is obvious. The distinguishing and characteristic feature of the hypnotic state is increase in the ideo-motor, ideo-sensory and reflex excitability of the brain, shown by increased readiness to receive, and increased ability to act upon suggestion.

To elucidate more clearly the rationale of hypnotism, I propose in the following pages to consider briefly the physiology of conditions resembling it, and the main points of difference between them.

I cannot but think that Bernheim has somewhat exaggerated the closeness of the analogy between hypnotic and natural sleep. To outward appearances the resemblance is certainly complete: hypnosis may pass into natural sleep; and sleep may partake of the characteristics of hypnosis in the same way that sleep may merge into coma, or may pass into an epileptic condition; but there are clear lines of demarcation between all these states, and the sleep of everyday life is distinct from its hypnotic counterfeit.

A short review of the etiology of natural sleep will render it more easy to understand the physiology of hypnotism. Sleep seems to depend upon several causes, and to be the resultant of their joint action. Some of these are of external and others of internal origin. First, there is exhaustion of potential energy in the brain cells, resulting from their functional activity; secondly, there is a condition of cerebral anaemia; and thirdly, there is an accumulation in the tissues, and especially in the brain centres, of waste products. To these we must add the factor of periodicity - that ebb and flow of organic life which has so potent an influence in all vital phenomena. To ensure sleep it is necessary that these agencies should be assisted by other conditions, and the most important of these are, the absence of exciting sensory stimuli, a comfortable posture, and a state of mental tranquillity and repose. Sleep is banished if there is cerebral congestion, if the mind is in a state of turmoil or excitement, or if stimulating and vivid sensory impressions are constantly arriving at the highest centres.

Muscular repose is also, as a rule, a necessary preliminary to sleep, though there are many instances in which soldiers and others under circumstances of exceptional fatigue have not been prevented from sleeping in the most strained and uncomfortable positions, any more than they have been kept awake by the continuous roar of battle or the blustering of the gale.

The chemical theory that sleep results from the accumulation of waste products (leucomaines) in the organs is now very generally held. Preyer supposes that kreatine and lactic acid are formed during the periods of mental activity, that they accumulate in the brain centres, and from their affinity for oxygen rob the cells of this element, upon an abundant supply of which their molecular activity depends. A sleeper from this point of view may therefore be considered as narcotized by the waste products of his own tissues. This theory also explains the periodicity of sleep, for these products are being constantly formed from tissue change during wakefulness, and as their quantity increases, they cause proportionate and progressive drowsiness, and finally sleep. During sleep or inactivity of the cerebral centres no formation of these products takes place, and the accumulation is gradually worked off and eliminated; a supply of oxygen again becomes available, and molecular energy is restored. When recuperation is complete, waking ensues, and the same process is again repeated.

It has, moreover, been found that the vital alkaloids formed during sleep have a convulsive and stimulating action on the nerve centres, whereas those which are formed during the day have a sedative and narcotic effect. The oxygen, which is so essential to the functioning of the highest centres, is partly derived from the blood, so that the cerebral respiration is a term in use; and is partly contained in a loosely combined state in the nervous tissue, in the same way as the oxygen required for the explosion of gunpowder is contained in the nitre of its composition (Lauder Brunton). The amount of oxygen, therefore, contained in the nerve tissue regulates the activity of the nerve cells, and when the German physiologist said that there was no thought without phosphorus, he might have added, nor without oxygen. Nerve energy is liberated by the explosive combination of the carbonaceous elements in the nerve tissue with oxygen; and if the supply of oxygen is adequate the explosive movements which initiate nervous impulses are vigorous and their psychical concomitants are correspondingly vivid. The necessity for oxygen in brain processes is shown by the benumbing and soporific effect of working in a crowded, ill-ventilated room.

The cerebral respiration is affected long before that through the lungs.