In the venereal disease, different parts of the body are ulcerated, and kept in that state, from the activity of the venereal poison. When, therefore, these ulcers come to be healed, the natural conclusion is, that the activity of the virus, which occasioned and supported the ulceration, is destroyed. But if mercury applied to venereal ulcers does cure them, when that cure cannot be ascribed to any action of mercury, either upon the system in general as an evacuant, or upon the part particularly affected, as a stimulant, may we not, with justice, say, that it possesses a power of destroying the activity of this virus? in other words, that mercury is an antidote to the venereal poison? From this, then, it follows, that the action of mercury as an antidote, is not merely a thing possible, and analogous to what happens in other cases of nature; but that the real existence of such a power is incontestably proved. To this argument, it may indeed occur as an objection, that mercury does not in every case, from topical application, produce a cure of venereal ulcers. This, it might be imagined, should happen, did it operate in the manner here alledged. But it is to be remembered, that the venereal virus may often be so situated, while it produces an external sore, as to be totally out of the reach of any application made to the surface of that sore. And, even in cases where the seat of the virus is superficial, the mercury may be applied in such a form as will not readily admit of a conjunction with the virus. Those cases, therefore, in which mercury has failed of producing a cure, can never afford any sufficient reason for setting aside this argument. But, on the other hand, any one well vouched instance, in which mercury, by being topically applied, has produced a cure in the manner here alledged, is a sufficient foundation, for every thing which has been advanced from this fact, to prove the supposition of its being an antidote to the venereal poison. From what has been said, it appears, that mercury is an antidote to the venereal virus; and that, whether it be introduced into the circulating system, or used externally only, it comes in contact with the venereal virus in those parts in which it is lodged, previous to its producing a cure. It may, then, be reasonably concluded, that the theory formerly suggested is well founded; and that mercury cures _lues venerea_ from its power as an antidote, in consequence of its being actually applied to the venereal matter. In favour of this hypothesis, it may farther be urged, that it is confirmed by a proper attention to many phænomena attending the cure of _lues venerea_ by mercury; while at the same time it is not equally liable to objection, as the other theories which have been mentioned.