From the opinion which was long entertained, that mercury, in every form, was a substance highly poisonous, it is not surprising, that, upon its first introduction into medicine, it should have been used externally only. In this way it seems also to have been first employed in the venereal disease. But, from the tendency which mercury has to enter the system, when used in any form, it is not surprising that its effects, as exciting salivation, should soon have appeared from its use externally. To a salivation thus excited, it was but natural to attribute the cure. Hence, from its external employment on its first introduction, there are few clear instances of its efficacy as acting immediately upon the venereal virus. It is not, however, improbable, that, even in these early periods, some part of the influence which mercury had in the cure of _lues venerea_ was to be ascribed to an immediate action on the venereal matter. In this way the good effects, in many cases, reaped from fomentations of cinnabar, one of the modes of applying mercury first put in practice, were certainly, in some measure, to be accounted for. It may, then, be affirmed, that the use of mercury, so as to act immediately upon the affected part, is a mode of applying it as early as its first introduction in the venereal disease. And, from examining the history of this distemper, as well as the various means which have, at different times, been employed in the cure, it will appear, that the immediate action of mercury on parts affected by _lues venerea_, particularly in places most easily reached, such, for example, as chancres, has always been a common intention in practice. But enough has perhaps been said concerning the history of the immediate application of mercury. The present inquiry is with regard to the preparations now employed in this way, and the comparative advantage of each. Among the first, and perhaps the most common forms in which mercury has been, and still is applied, with a view of acting immediately upon the affected part, are the mercurial ointments, cerates, and plasters. In this, as will appear from the table which has been given, the mercury is rendered active by division. Little difference can arise from the substance with which the mercury is combined during the triture. All these preparations, therefore, may, with propriety, be considered together. To this head may be referred, the blue ointments, mercurial cerate, and common plaster with mercury, of the London College; and the mercurial ointment, and plaster, of the Edinburgh.