As this is a form in which a quantity of very active mercury may suddenly be introduced into the body, it may be supposed well adapted for producing some alleviation in urgent symptoms. From the tendency it has to act upon the surface of the body, it may be presumed to be a preparation of great utility against cutaneous affections from a venereal cause. If recourse is had to the examination of facts, it will be found, that the conclusion, which would here be drawn from reasoning, is confirmed by experience; and that, in reality, the solution of corrosive sublimate may be employed with peculiar advantage in both these cases. Thus much with regard to calomel and corrosive sublimate. Many other preparations, of an intermediate degree of acrimony between these, such, for example, as the _mercurius calcinatus_, are likewise in common use. But the cases to which we would be inclined to suppose these best adapted, may easily be learned from what has been said of the two extremes. ------------------------------------------------------------------------ CHAP. VII. _Of the Cautions to be observed in the Employment of Mercury in Lues Venerea._ FEW medicines, from which any considerable advantages can be obtained in the cure of diseases, are of such a nature that they can, in every circumstance, be exhibited without any inconveniency. On the contrary, the greater activity any medicine possesses, the more reason there is to apprehend disagreeable accidents from its being improperly used. When active medicines, therefore, are employed, it becomes, in every case, an object of particular attention, while we endeavour to obtain all the good effects which may be derived from them, to avoid those bad consequences which they are most apt to induce. These ends are to be obtained only by careful attention to many circumstances. Of the accidents most to be guarded against, not a few are, in a great measure, the natural consequence of the medicine itself. Although, in some constitutions, and with particular treatment, they will arise more readily than in others; yet they may happen in any constitution, and with any treatment. As occurring, therefore, most generally, they deservedly claim to be first considered. It has already been observed, that every medicine, in proportion to its activity, is more apt to be followed by consequences not always to be wished for. It may therefore be laid down as a general rule, that active medicines should be employed only in cases where they are absolutely requisite. If this rule is proper with regard to any medicine, it must be so of mercury.