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ONSIDERING the length of time that so-called "animal magnetism," "mesmerism," or "electro-biology," has been before the world, it is a matter of surprise that so inviting a field of physiological inquiry should have been so long allowed to lie fallow. A few scientific men in France and Germany have indeed, from time to time, made a few observations on what Preyer has called the "Kataplectic state" as artificially induced in human beings and sundry species of animals; but anything resembling a systematic investigation of the remarkable facts of mesmerism has not hitherto been attempted by any physiologist in our generation. The scientific world will therefore give a more than usually hearty welcome to a treatise which has just been published upon the subject by a man so eminent as Heidenhain. The research of which this treatise is the outcome is in every way worthy of its distinguished author; for it serves not only to present a considerable and systematic body of carefully observed facts, but also to lead the way for an indefinite amount of further inquiry along the lines that it has opened up.

Heidenhain conducted his investigations on medical men and students as his subjects, one of them being his brother. He found that, in the first or least profound stage of hypnotism, the patient, on being awakened, can remember all that happened during the state of mesmeric sleep; on awakening from the second or more profound stage, the patient can only partially recollect what has happened; while in the third, or most profound stage, all power of subsequent recollection is lost. But, during even the most profound stage, the power of sensory perception remains. The condition of the patient is then the same, so far as the reception of sensory impressions is concerned, as that of a man whose attention is absorbed or distracted; he sees sights, hears sounds, etc., without knowing that he sees or hears them, and he can not afterward recollect the impressions that were made. But the less profound stages of hypnotism are paralleled by those less profound conditions of reverie in which a passing sight or sound, although not noticed at the time, may be subsequently recalled by an effort of the will. Further on in his treatise Heidenhain tells us that, even when all memory of what has passed during the hypnotic state is absent on awakening, it may be aroused by giving the patient a clew, just as in the case of a forgotten dream. This clew may consist only