Thus, the students of the science of hypnotism are, and since the days of Mesmer have been, hopelessly divided into schools which wage war upon each other's theories, and dispute the correctness of each other's observations of facts. Mesmer's theory of fluidic emanations, which he termed "animal magnetism," seemed to account for the facts which he observed, and is still held to be substantially true by many votaries of this science. John Bovee Dods' electrical theory--positive lungs and negative blood--was sufficiently plausible in its day to attract many followers, as it afforded a satisfactory explanation of many phenomena which came under his observation. Braid's physiological explanation of certain classes of the phenomena afforded, in his time, much comfort to those who believe that there is nothing in man which cannot be weighed in a balance or carved with a scalpel. In our own day we find the school of the Salpêtrière, which holds that hypnotism is a disease of the nervous system, that its phenomena are explicable on physiological principles, that the suggestions of the operator play but a secondary _rôle_ in their production, and that they can be produced, or successfully studied, only in diseased persons. On the other hand, the Nancy school of hypnotists holds that the science can be studied with profit only in perfectly healthy persons, and from a purely psychological standpoint, and that suggestion is the all-potent factor in the production of all hypnotic phenomena. All three of the last-mentioned schools agree in ignoring the possibility of producing the higher phenomena of hypnotism, known as clairvoyance and thought-transference, or mind-reading; whilst the earlier hypnotists demonstrated both beyond the possibility of a reasonable doubt. Indeed, a committee of the ablest scientists of the Royal Academy of Medicine of France, after an investigation extending over a period of six years, reported that it had demonstrated the existence of such powers in the human mind.