In many matters that come under the notice of medical experts there is room for honest differences of opinion. Of such nature are questions of sanity and insanity. It must be remembered that these are, after all, _relative_ terms. Reason leaves its seat by almost imperceptible steps. Who can determine with exactness the line that separates eccentricity from madness--responsibility from irresponsibility? Moreover, the phenomena upon which opinion is based are, in such cases, so hidden, so complex, so obscure, that in the half-lights of a few short interviews they will often be seen differently by different observers. In scarcely any of its parts does toxicology belong to this class of subjects--certainly not at all in so far as it deals with mineral poisons. To a great extent it is a fixed science--a science whose boundaries may be widened, whose processes may be rendered more delicate, but whose principles are in great measure settled for ever. Not in the imperfections of the science, but in the habits of the American medical profession and in the methods of our criminal procedures, lies the origin of the evils complained of. Some of the causes of the present difficulties are readily to be seen. One is the common ignorance of legal or forensic medicine among the members of the profession. In none of our medical colleges is legal medicine taught as a part of the regular course or as an essential branch of study. Consequently, when the student graduates he has only heard a few passing allusions to the subject from professors of other branches. Unfortunately, this is more or less true of many other medical subjects of importance: helped out, however, by his mother wit, and impelled by necessity, the imperfectly-educated graduate after a time becomes very generally a skillful practitioner. During the period of growth his daily needs govern the direction of his studies, which are therefore more or less exclusively confined to the so-called practical branches. Forensic medicine is not one of these, poison cases are comparatively rare, and to be called upon to give a definite opinion upon such matters before a legal tribunal happens not once in the lifetime of most medical men. Consequently, to a great part of the American medical profession legal medicine is a veritable _terra incognita_.