Is described as a different form of natural sleep, and all the causes which bring on fatigue are capable of bringing on hypnotism in suitable subjects. Two of the leading hypnotic states are lethargy and catalepsy, the former being analogous to deep sleep, and the latter to a light slumber. In lethargy the respiratory movements are slow and deep; in catalepsy slight, shallow, very slow, and separated by a long interval. In lethargy the application of a magnet over the region of the stomach causes profound modifications in the breathing and circulation, while there is no such effect in catalepsy. This shows the connection of hypnotism with magnetism, and various other experiments with magnets have produced some remarkable results. Here it may be added that Dr. Gessmann, a Vienna scientist who has made a specialty of hypnotic studies, has invented and successfully applied an instrument called a hypnoscope, consisting of an arrangement of magnets for the purpose of ascertaining whether any person is a good hypnotic subject. The experiments demonstrate that sensation in the hypnotic states varies between the two opposite poles of hyperaesthesia and anaeesthesia; in other words, the senses may be extraordinarily exalted, as in somnambulism, or, as in lethargy, they may be extinct, except sometimes hearing. In somnambulism the field of vision and acuteness of sight are about doubled, hearing is made very acute, and smell is so intensely developed that a subject can find by scent the fragment of a card, previously given him to feel, and then torn up and hidden. The memory in somnambulism is similarly exalted. When awakened the subject does not, as a rule, remember anything that occurred while he was entranced, but, when again hypnotized, his memory includes all the facts of his sleep, his life when awake and his former sleeps. Richet attests how somnambules recall with a luxury of detail scenes in which they have taken part and places they have visited long ago. M----, one of his somnambules, sings the air of the second act of the opera "L'Africaine" when she is asleep, but can not remember a note of it when awake. There is a theory that no experience whatever of any person is lost to the memory; it is only the power to recall it that is defective. The authors of this work say that, while the exaltation of the memory during somnambulism does not give absolute proof to the theory that nothing is lost, it proves at any rate that the memory of preservation is much greater than is generally imagined, in comparison with the memory of reproduction, or recollection. "It is evident," they say, "that in a great number of cases, where we believe the memory is completely blotted out, it is nothing of the kind. The trace is always there, but what is lacking is the power to evoke it; and it is highly probable that if we were subjected to hypnotism, or the action of suitable excitants, memories to all appearance dead might be revived."