In the lighter grades of hypnosis there are psychical accompaniments, and the patient knows the limb is being moved, but is unable to prevent it, or can only do so by making great efforts. In the more advanced stages he loses all, or nearly all, sensation in the limb when it is moved by the operator, so that he often says that it ' seems to no longer belong to him' (hypotaxis).

The analgesia of profound hypnosis is easily explained. It is sometimes more apparent than real, and then resembles that of incomplete narcosis. The subject suffers at the time, but on awaking has forgotten the circumstance. If hypnotized again and questioned, he will say that he felt the pain, but not sufficiently to cause him to shake off the lethargy which oppressed him. But in many cases there is absolute anaesthesia, and the patient is completely ignorant of what is being done to him. We know that anaesthesia may be produced in three ways - by acting on the arrangements of the highest centres, so as to cause cessation of their functions; by acting on the peripheral endings of nerves, and destroying their irritability; and by destruction or inhibition of the tract conveying sensation from the periphery to the brain. Chloroform acts in the first manner by setting up chemical changes in the brain cells, and hypnotism influences the same nervous arrangements by dynamic inhibition of the molecular activity of the cells. Cocain is an anaesthetic of the second class; and in poisoning by curara, and in the cutaneous anaesthesia of locomotor ataxy, we see the third cause at work.

The anaesthesia produced by suggestion alone, as in the cases referred to on pp. 81, 217, can be explained by supposing that the centres of tactile sensation - which Ferrier localizes in the hippocampal region and the neighbouring temporo-sphenoidal convolutions, where also probably painful sensations are received (Lauder Brunton) - are put out of action by some inhibitory action akin to that which obtains in the local anaesthesia so common in hysteria; and which probably proceeds from some irritation of distal origin, acting as an inhibitory influence. The sensation of pain is due to some condition of the cerebrum itself, and is caused by the arrival at the highest centres of intense afferent currents from the seat of injury. Liebeault supposes that in perfect health there is an equilibrium in the distribution of nervous force, which is upset in disease. Disease is accompanied by either excess or deficiency of nerve energy in the centres innervating the affected organs, and hypnotism enables us to check and correct this disarrangement. This theory is not without support, for we frequently see excessive and irregular action in one organ, associated with deficient action in others in the same subject.

Centres are constantly discharging their energy through the most traversed channels, and nerve energy is being sent to the organs which have already absorbed most of it - e.g., an uncontrolled and excessive nerve influence is constantly being sent along the nerve tract concerned with the movement of a limb in hysterical contraction. Hypnotism may be supposed to act in such a case by enabling us, through suggestion, to divert or transform the nerve energy which is thus being misdirected. Professor William McDougall, of Oxford, the eminent psychologist, is doing much original research in the field of hypnotism, and he gives this theory the latest scientific expression thus: ' By withdrawing the nervous current from a much overworked or unduly irritable nervous centre or bodily organ, and by isolating it through induction of a relative dissociation of the centre, rest may be secured and a bad habit of over-action may be suspended, as, e.g., in neuralgia; while by repeatedly directing a powerful stream of innervation through some other channel a too sluggish organ - e.g., the bowel in constipation - may be brought back to action and healthy functioning.' *

Dr. McDougall supposes that the nervous system consists of a series of arcs arranged in dispositions or systems associated according to heredity and habit. The cortical centres are being continually gently stimulated by the arrival from the sensory nerves of freed nervous energy or neurokyme (Oscar Vogt). In health and under normal conditions, there is an equable and moderate dissipation of this neurokyme through all the organs and tissues making our coenthesis or systemic consciousness, and constituting that state of perfect health which is characterized by a sense of general well-being without undue consciousness of any one organ. This state of equilibrium explains the state of some happy individuals who say they don't know what it is to be ill, and of other unhappy ones who never appreciate good health until they lose it.

* Address delivered to the Psycho-Medical Society, and published in Brain, 1908.

Whatever theory we may adopt as to the ultimate causation of the hypnotic state - and theories are almost as numerous as writers on the subject - we at least know that its phenomena are of subjective origin, and that they depend upon the inhibition and dynamogenesis of some centres, and the disconnection of others which ordinarily act in association.

How this dissociation is effected is of course a point of immense interest, and is, in fact, the crux of the whole matter. Its rationale must remain a matter of theory, as it depends on changes of the most subtle nature. But we know at least as much about the action of hypnotism as we do about that of many drugs which we use every day. It probably depends upon intracellular changes in the arrangements of molecules, whereby the discharge of nerve energy is prevented. The clogging of these molecules, and their consequent failure to respond to stimuli, through the ingestion of chloroform and other drugs, their excessive stimulation by coffee or small quantities of alcohol or opium, and their abnormal stimulation by belladonna or Indian hemp, belong to a different order of events. Natural sleep remains the closest analogue to hypnosis; but in sleep the inhibition extends to all the centres and their functions, and cannot be in part overcome by verbal suggestion; this is the important point of difference between the two states. Moreover, as we have seen, not only can the inhibitory influence be exerted in any direction we wish by verbal suggestion, but its correlative condition, dynamogenesis, can be treated in the same way.

The rapid and even instantaneous induction of hypnosis in 'good subjects' can be explained by the setting up of a nerve habit, so that on the exhibition of the accustomed stimulus the molecules fall at once into their former combinations. I have already said that for this reason we should be careful to make the exciting cause a combination of circumstances which would not be likely to occur spontaneously. The tendency of the sequence of events to repeat themselves on the application of the accustomed stimulus is often seen in hypnosis. If on the occasion of the first hypnotization the patient's arm has been fixed in a certain attitude at the moment the process was completed, it is very probable that the arm will spontaneously assume the same attitude at each subsequent sitting. In fact, the position will become an integral part of the process, unless the impression is removed by suggestion.