The attitude of the medical profession toward mental influence in the treatment of disease is neither friendly nor hostile. It simply regards it as it would any other remedial agency, a given drug, for instance, a bath, or a form of electricity or light. It is opposed to it, if at all, only in so far as it has tested it and found it inferior to other remedies. Its distrust of it, so far as this exists, is simply the feeling that it has toward half a hundred ancient drugs and remedial agencies which it has dropped from its list of working remedies as obsolete, many of which still survive in household and folk medicine. My purpose is neither to champion it nor to discredit it, and least of all to antagonize or throw doubt upon any of the systems of philosophy or of religion with which it has been frequently associated, but merely to attempt to present a brief outline of its advantages, its character, and its limitations, exactly as one might of, say, calomel, quinine, or belladonna. As in the study of a drug, the chief points to be considered are: What are its actual powers? What effects can be produced with it, both in health and sickness? What are the diseases in which such effects may be useful, and how frequent are they? In what way does it produce its effects, directly or indirectly? The first and most striking claim that is made for mental influence in disease is based upon the allegation that it has the power of producing disease and even death; the presumption, of course, being that, if able to produce these conditions, it would certainly have some influence in removing or preventing them. Upon this point the average man is surprisingly positive and confident in his convictions. Popular literature and legend are full of historic instances where individuals have not merely been made seriously ill but have even been killed by powerful impressions upon their imaginations. Most men are ready to relate to you instances that have been directly reported to them of persons who were literally frightened to death. But the moment that we come to investigate these widely quoted and universally accepted instances, we find ourselves in a curious position. On the one hand, merely a series of vague tales and stories, without date, locality, name, or any earmark by which they can be identified or tested. On the other, a collection of rare and extraordinary instances of sudden death which have happened to be preceded by a powerful mental impression, many of which bear clearly upon their face the imprint of death by rupture of a blood-vessel, heart failure, or paralysis, in the course of some well-marked and clearly defined chronic disease, like valvular heart-mischief, diabetes, or Bright's disease.