The explanation of these phenomena consists in a recognition of the fact that certain persons are gifted with nervous organs which are sensitive and responsive to nervous impulses and muscular movements that are too delicate for recognition by the percipient apparatus of ordinary mankind. The more complicated forms of artificial somnambulism result from the complication and exaggeration of the results of this inordinate sensitiveness through the agency of artificial sleep. As in natural somnambulism, so in the hypnotic state, certain organs become totally anæsthetic, while the sensibility of others is wonderfully exalted. Cutaneous sensation may be completely abolished, and the patient may become utterly insensible to every painful impression. The reflex functions may be either suppressed or exaggerated, and the special senses of sight and hearing may be exalted to the highest degree. While in this condition the hyperæsthetic condition of the brain renders the subject peculiarly susceptible to impressions from the will of another, so that all his actions are obedient to the guiding influence of the person under whose control he has passed. According to Charcot,[93] three principal types of artificial somnambulism may be remarked among the hysterical subjects upon whom he experimented: (1) the _cataleptic_, (2) the _lethargic_, and (3) the _somnambulic_. Of these the first may be developed primarily by any abrupt and powerful impression upon a sensory organ. Gazing upon a brilliant light, fixing the eyes upon a piece of polished metal, or upon the shining eyes of a second person, the sudden clangor of a Chinese gong, may suffice to induce the cataleptic state. Dumontpallier[94] reports the case of a young woman who accidentally hypnotized herself by gazing into the mirror before which she was dressing her hair. This cataleptic state may also be secondarily induced by merely opening the eyes of a patient in whom a condition of hypnotic lethargy has been previously developed. If only one eye be thus opened, the corresponding side of the body alone becomes cataleptic. Closing the eyes causes the disappearance of this symptom, with complete restoration of the purely lethargic state. During the cataleptic condition the several tendinous reflexes disappear, neuro-muscular hyper-excitability ceases, the skin becomes insensible, but the special senses, particularly those of sight and hearing, maintain a partial activity. In this half-awakened state the senses may become avenues of suggestion from without for the production of movements; but, if left to themselves, the limbs remain motionless.