The first point to be noted is its intimate relations with suggestion. When hypnotism was first studied the general tendency, as is usual in such cases, was to regard it as a manifestation of some new force, and in accordance with the prevalent conceptions of the day, a force of a physical kind allied to those which were already known. Moreover, one of the most important features of the hypnotic state is the greatly enhanced suggestibility of the hypnotised person. It is one of the characteristic features of hypnotism that the receptivity of a hypnotised person towards suggestion is greatly increased, and there is reason to believe that this increase is especially great in relation to suggestions given by the hypnotiser unwittingly.
A second feature of the hypnotic state, which is closely linked with the heightened suggestibility, is a great increase in sensitiveness to sensory stimuli, or at least to certain kinds of sensory stimulus. A hypnotised person may become aware of and utilise indications given by organs of sense which produce no effect whatever upon his consciousness in the normal state.
A third feature of hypnotism is that it affords a characteristic example of suppression. When a person is hypnotised it is possible to blot out from his memory experience which in the normal state is directly accessible to consciousness, while, as already mentioned on more than one occasion, other experience which is normally inaccessible to consciousness may by means of hypnotism be brought to the surface. Moreover, any experience gained during the hypnotic state may become inaccessible to memory when the hypnotic state comes to an end, and seems to do so spontaneously unless special suggestions are given that it shall be remembered. A striking feature of this aspect of the hypnotic state is the ease with which it is possible to produce suppression of sensibility. Any sensory surface may be rendered wholly insensitive to stimuli to which it ordinarily responds. It is especially striking that this anæsthesia may occur in conjunction with the heightened sensibility which I have already mentioned. A hypnotised person may be wholly insensitive to certain kinds of sensory stimulus and show a vastly exaggerated receptiveness to others.
In the fourth place hypnotism affords a characteristic example of dissociation. During the hypnotic state in response to suggestion a person performs acts, it may be of a highly complex kind of which he is completely unconscious when the hypnotic state is over. The hypnotic state only differs from a characteristic attack of dissociation or a fugue in having been produced by the suggestion of another person.