notic condition may be induced in susceptible persons by a feeble, continued, and regular stimulation of the nerves of touch, sight, or hearing; and may be terminated by a strong or sudden change in the stimulation of these same nerves.
The physiological explanation of the hypnotic state which Heidenhain ventures to suggest is, that a stimulus of the kind just mentioned has the effect of inhibiting the functions of the cerebral hemispheres, in a manner analogous to that which is known to occur in several other cases which he quotes of ganglionic action being inhibited by certain kinds of stimuli operating upon their sensory nerves.
In a more recent paper, embodying the results of a further investigation in which he was joined by P. Grutzner, Heidenhain gives us the following supplementary information:
The muscles which are earliest affected are those of the eyelids; the patient is unable to open his closed eyes by any effort of his will. Next, the affection extends in a similar manner to the muscles of the jaw, then to the arms, trunk, and legs. But even when so many of the muscles of the body have passed beyond the control of the will, consciousness may remain intact. In other cases, however, the hypnotic sleep comes on earlier.
Imitative movements become more and more certain the more they are practiced, so that at last they may be invariable and wonderfully precise, extending to the least striking or conspicuous of the changes of attitude and general movements of the operator. Professor Berger observed that, when pressure is exerted with the hand at the nape of the neck upon the spinous process of the seventh cervical vertebra, the patient will begin to imitate spoken words. It is immaterial whether or not the words make sense, or whether they belong to a known or to an unknown language. The tone in which the imitation is made varies greatly in different individuals, but for the same individual is always constant. In one case it was a hollow tone, "like a voice from the grave"; in another almost a whisper, and so on. In all cases, however, the tone is continued in one kind, i. e., it is monotonous. Further experiments showed that pressure on the nape of the neck was not the only means whereby imitative speaking could be induced, but that the latter would follow with equal certainty and precision if the experimenter spoke against the nape of the neck—especially if he directed his words upon it by means of a sound-funnel. A similar result followed if the words were directed against the pit of the stomach. It followed with less certainty when the words were directed against the larynx or into the open mouth, and the patient remained quite dumb when the words were directed into his ear, or upon any other part of his head. If a tuning-fork were substituted for the voice, the note of the fork would be imitated by the patient when the end of the fork was placed on any of the situations just mentioned as sensitive. By exploring the pit of the stomach with a tuning-fork, the sensitive area