Cognate in some of its essential characteristics to the phenomenon of obsession is that of _dual personality_; and although it has nothing to do with the question of spiritism, it may as well be noted here as elsewhere. By this term is not meant the duality of mental organization which pertains to every human being, but it refers to a specific phenomenon which has received that name from recent scientific observers. It is characterized by a complete loss of knowledge of personal identity. The patient assumes a new name, a new personality, and a new character, the last being often in marked contrast to the normal one in every essential particular. The old personality is sometimes completely forgotten, and sometimes it is remembered only as a person whom the patient has once known. In some instances the two personalities alternate at somewhat irregular intervals. In others, the phenomenon occurs only once in a lifetime. In others, several different personalities will be assumed at different times. In all these cases certain characteristics constantly reappear, the most notable appearing in the fact that the new personality is always consistent with itself; that is, it is always the same, whenever it reappears. Its moral characteristics are sometimes in marked contrast to the lifelong character developed in the normal state, but it never varies from one time to another. If a dozen different personalities should be assumed at different times, each would always be consistent with itself. The incidents occurring during the continuance of one interval of the abnormal personality will always be remembered whenever the same personality reappears, so that the existence of the new personality, when it reappears with frequency, is practically continuous; that is, the intervals of normal consciousness do not seem to be remembered. The normal personality, however, never remembers aught of what occurred during the abnormal interval. As before remarked, the abnormal personality sometimes remembers the existence of the normal one, but always as that of a third person, upon whom it often looks, and of whom it sometimes speaks, with pitying contempt. It generally happens, in case two or more abnormal personalities are assumed, that each remembers all the other abnormal characters, but regards them as third persons having no connection whatever with itself.