He separates somnambulism into three periods. The word here is used for this whole class of subjects as Richet himself uses it, viz., _torpeur_, _excitation_, and _stupeur_. In the first, which is produced by the so-called magnetic passes and the fixing of the eyes, silence and languor come over the subject. The second period, usually produced by constant repetition of the experiment, is characterized chiefly by sensibility to hallucination and suggestion. The third period has as its principal characteristics supersensibility of the muscles and lack of sensation. Yet let it be noticed that these divisions were not expressed in their present clearness until 1880; while in the years between 1872 and 1880, from an entirely different quarter, a similar hypothesis was made out for hypnotic phenomena. Jean Martin Charcot, the renowned neurologist of the Parisian Salpetriere, without exactly desiring it, was led into the study of artificial somnambulism by his careful experiments in reference to hysteria, and especially by the question of _metallotherapie_, and in the year 1879 had prepared suitable demonstrations, which were given in public lectures at the Salpetriere. In the following years he devoted himself to closer investigation of this subject, and was happily and skillfully assisted by Dr. Paul Richer, with whom were associated many other physicians, such as Bourneville, Regnard, Fere, and Binet. The investigations of these men present the peculiarity that they observe hypnotism from its clinical and nosographical side, which side had until now been entirely neglected, and that they observe patients of the strongest hysterical temperaments. "If we can reasonably assert that the hypnotic phenomena which depend upon the disturbance of a regular function of the organism demand for their development a peculiar temperament, then we shall find the most marked phenomena when we turn to an hysterical person." The inferences of the Parisian school up to this time are somewhat the following, but their results, belonging almost entirely to the medical side of the question, can have no place in this discussion. They divide the phenomena of hystero-hypnotism, which they also call _grande hysterie_, into three plainly separable classes, which Charcot designates catalepsy, lethargy, and somnambulism. Catalepsy is produced by a sudden sharp noise, or by the sight of a brightly gleaming object. It also produces itself in a person who is in a state of lethargy, and whose eyes are opened. The most striking characteristic of the cataleptic condition is immobility. The subject retains every position in which he is placed, even if it is an unnatural one, and is only aroused by the action of suggestion from the rigor of a statue to the half life of an automaton. The face is expressionless and the eyes wide open. If they are closed, the patient falls into a lethargy.