I have no wish to affirm that such phenomena must be due to an action of this kind, but to draw attention to the fact that we are ignorant of the power in which they originate, and that such being the case, it is quite possible that their most violent and terrible forms may be aroused by the influence of a power external to the mind itself. Equally ignorant are we of the causes of even their milder manifestations. Whatever may be the hopes which are entertained of the future triumphs of science, it is not too much to assert, that it has not yet reduced these abnormal conditions of the mind to any thing like a scientific law, and that it has not succeeded in tracing the phenomena to the exclusive operation of a force acting within the mind itself. In truth our mental science is ignorant of their causes: and for aught that it can affirm to the contrary, many of them may be due to causes human, superhuman, or a combination of the two. In cases where we are profoundly ignorant, dogmatical assertions should be carefully avoided. While such phenomena are incapable of explanation by the action of known mental forces, the students of mental science are not justified in affirming that possession contradicts its known truths. I fully admit, however, that there is a system of professed mental science, which, if its truth could be proved, would establish the fact that possession was impossible. I need hardly say that I allude to that which affirms that thought is the result of a function of the brain, and nothing else. According to the views of these philosophers, the brain secretes thought as a gland secretes its own peculiar secretion. Until this philosophy has succeeded in proving the truth of its first principles, it is useless to consider its bearing on this particular question.