The old mesmerists (du Potet, Lafontaine) describe as a rare occurrence in hypnotic experiments a state of lethargy in which artificial awakening was impossible. After some time there was a spontaneous awakening, and no evil consequences were to be observed. Guermonprez described lately how a person had remained three days in hypnosis, nobody being able to wake him. These incidents have only been observed among hysterical subjects. Again, many of these cases have nothing whatever to do with hypnosis - are more probably instances of a state of lethargy. One thing is certain: there can be no question of hypnosis when rapport of any kind and all possibility of suggestion are wanting. Even a lethargic state occurring in a person being hypnotized must be held as something quite distinct from hypnosis. If we wish to make a rational comparison between two conditions we must consider the similarity of the symptoms they present, not the nature of the cause which has produced them.

Who is hypnotizable ? In order to settle this question without hypnotic experiments, Ochorowicz has invented a special instrument - the hypnoscope; it is an iron magnet in the form of a ring, which the person to be tested puts on his finger. Hypnotizable persons are supposed to experience certain sensations in the skin or twitchings of the muscles, while with the insusceptible nothing of the kind takes place. The researches of other investigators have not confirmed this (Ober-steiner, Gessmann, Grasset, Bottey). Other signs which are supposed to indicate susceptibility to hypnotism I consider untrustworthy.

Neither neurasthenia nor pallor, neither hysteria nor general feebleness of health, produce a disposition to hypnosis. Our ordinary hysteria, with its variable characteristics of headache and the feeling of a lump in the throat (globus), combined with the general hysterical desire to be interesting and to exaggerate the sufferings endured, produces, according to my experience and that of others, no special disposition to hypnosis. Certainly Charcot held that hysteria predisposed a sufferer from that malady to hypnotic influence, and some more recent investigators (Hirschlaff, Gumpertz) have expressed a similar opinion with respect to the deeper hypnotic state. I consider such opinions erroneous. The mistaken notion that hysterical or nervous patients are particularly susceptible to hypnotism results from the fact that most physicians have experimented with them only; besides which it is very easy to discover in all persons something which may be explained as a hysterical symptom if we only try to do so. This reminds one of the hereditary taint which we so easily detect in nearly every one. If, however, we consider every one who submits himself to a hypnotic experiment to be "nervous" (Morand), then, naturally, only nervous persons can be put into the hypnotic state.

In reality, as Sperling has rightly pointed out, if we are to take a pathological condition of the organism as a necessary condition for hypnosis, we shall be obliged to conclude that everybody has a mental twist - is not quite right in the head. For the rest, the old mesmerists (Brandis, Lichtenstadt, Wirth, and others) maintained that a healthy individual could not be mesmerized. In opposition to the assumption that general weakness is a predisposing factor, I may mention that Hansen always preferred muscular persons for his experiments, and I have myself hypnotized many muscular individuals, in some instances men of athletic build.

With regard to mental aptitudes, Forel believes that every mentally healthy human being is hypnotizable. In Liebeault's opinion heredity plays a great part in the disposition to hypnosis. It is universally agreed that the mentally unsound, especially idiots, even if not wholly insusceptible, are still very much more difficult to hypnotize than the healthy. However, A. Voisin succeeded in hypnotizing ten per cent. of the mentally unsound, by exercising the necessary patience. But apart from this I do not believe that intelligence plays any important part. Of course we are justified in assuming that the dull and stupid are not easily influenced, just as there are others who let their imagination come into play on the slightest provocation. On the other hand, I think that susceptibility to hypnotic influence should not be considered a gauge of the patient's intelligence. Mental excitement frequently prevents hypnosis. Inhibition is also often brought about by the subject's urgent desire to be hypnotized.

Emotional influences may also account for the fact that persons who are occasionally refractory, at other times readily submit to hypnotism.

It is altogether a mistake to consider the disposition to hypnosis a sign of weakness of will. Without doubt the ability to maintain a passive state has a predisposing effect This is why soldiers are in general easy to hypnotize. The ability to direct one's thoughts in a particular direction is also very favourable. This ability to give the thoughts a certain prescribed direction is partly natural capacity, partly a matter of habit, and often an affair of will Those, on the contrary, who can by no possibility fix their attention, who suffer from continual absence of mind, can hardly be hypnotized at all. It is specially among the nervous that many of this class are to be found - persons in whom a perpetual wandering of the mind predominates. The disposition to hypnosis is also not particularly common among those persons who are otherwise very impressible. There are plenty of people who believe all that they are told, yet they often offer a lively resistance when an effort is made to hypnotize them.

Hilger has attempted to ascertain the bearing of distinct mental factors on the general susceptibility of the individual to hypnotic influence. He hopes by these means to determine the possibility, or otherwise, of hypnotizing any particular person. Among the many factors incidental to the induction of hypnosis which Hilger has examined, the amount of confidence displayed by a patient in his doctor, and the treatment pursued, may be mentioned. Hilger examined 295 cases in this respect, and found that an increase in confidence was invariably accompanied by a rise in the percentage of those persons susceptible to hypnotism, especially where deep and rapid hypnosis could be attained. Moreover, he did not neglect the question of habitual or temporary docility on the part of his patients. The percentage of those hypnotizable, or susceptible of deep hypnosis, appears to have increased in 283 cases examined by him. Hilger puts his somnambulists into three catagories, in the lowest of which we get 10.64 per cent., in the second 34.07 per cent., and in the third 50.49 per cent.