There is a wide circle of diseases, in which mercury has been proved by abundant experience to be useful, and in which its beneficial effects cannot be referred entirely to any of the obvious therapeutic modes of action hitherto noticed, or to any combination of them. A partial explanation has been sought in the rather vague dogma, that the metal exercises a revolutionizing influence; substituting a morbid state of its own creation for that previously existing, and, having thus subverted the disease against which it may have been directed, spontaneously retiring after a time, and yielding the system, in a sound state, to the government of its own legitimate vital forces. It will be readily perceived that this explanation consists of little more than words, and absolutely explains nothing. We may advance a step further in the solution of the problem. It has been already stated, more than once, that mercury has the property of promoting the disintegration of the tissues; in other words, of stimulating that part of the process of nutrition which consists in the removal of the old structure, without in a corresponding degree promoting that other part of it, the business of which is to replace the loss. It may be supposed to produce this effect by causing, through its presence in the blood, a more rapid oxidation of the ultimate constituents of the tissues. But, whatever may be the mode of operation, the effect may be conceived to be, a removal of the old structure in which the previously existing disease was seated, and a substitution of new structure, stamped with its own readily effaceable characters. The morbid processes which mercury has thus shown itself capable of subverting are, among others, inflammation, syphilis, and perhaps fever.

a. Antiphlogistic Action. - After blood-letting, there is probably no remedy more powerfully antiphlogistic than mercury. it is not upon any theoretical grounds that this opinion, so generally received among medical men, was formed, or is maintained. it rests solely upon observation. Mercury is administered; and, as soon as the sore-mouth, indicating its effects on the system, is perceived, an amendment of the disease often begins to take place; and there is a regular advance towards health, under the continued influence of the remedy. This has been so often seen, and so often continues to be seen, in the daily experience of practitioners, that nothing but a strong prepossession can resist the weight of evidence, in proof of the extraordinary antiphlogistic powers of the medicine. There are some, however, who, admitting its powers, are deterred from using it by their fears. it cannot be denied that mercury is capable of doing much harm if abused; but of what powerful medicine cannot this be said? We are indebted for much of the odium which rests upon it, in the popular mind, and of which empirics are ever ready to take an unprincipled advantage, to the reckless abuse of it in the hands of careless and ignorant practitioners, and to a want of caution in its use, of which even the most enlightened among our predecessors were not altogether guiltless. Now that the properties of the medicine are better understood, it is wholly unnecessary to incur the risk of those evils which were formerly but too frequent; at least, the cases are extremely few, in which, if judiciously used, it will inflict any serious or lasting injury. I was in the habit of prescribing mercury for more than forty years, and must have administered it during that period, in public and private practice, to some thousands of persons; yet I can conscientiously state that I have not seen a single case, in my own practice, in which I was satisfied that the remedy left any permanent ill effect behind it, unless perhaps a more rapid decay of the teeth in a few instances; and I have never witnessed an instance of fatal result. I am fully convinced that it may be used as safely as any other very efficient remedy; and even more safely than many which might be mentioned, and which are given habitually by persons who profess an abhorrence for mercurials.* in cases, however, of typhoid inflammation, or others of an asthenic character, in which depletion by the lancet may be forbidden, I commence, immediately after purgation, with the use of mercurials, with the view to salivation, combining with them whatever other medicines circumstances may seem to require. But, in such cases, a smaller amount of the medicine is required daily; and the blue mass may in general be usefully substituted for the calomel, as milder and less apt to disturb the bowels.

As to the method in which mercury acts as an antiphlogistic, something may possibly be ascribed to the increase of the secretions; but this is much too slight to be the chief cause of its favourable effects, which probably depend mainly on the change in the tissues above referred to, and its influence on the blood. Some attribute the effects chiefly, if not exclusively, to the latter cause; the blood being, as they suppose, rendered less capable of supplying matter of exudation to the inflammatory process, and peculiarly indisposed to the formation of false membrane. it is to cases of pseudomembranous inflammation, that they conceive it peculiarly applicable, in consequence of its remarkable anti-plastic property. But I entertain strong doubts upon this point. The blood during ptyalism is apt to exhibit the buffy coat; and every one has seen, as a consequence of severe mercurial stomatitis, abundant exudation of matter, bearing at least a close resemblance to false membrane. Besides, in the treatment of serous inflammation, as of the pleura, pericardium, and peritoneum, though the disease may be subdued, we discover no tendency to a disturbance of the process by which the exuded fibrin undergoes organization, as union between the opposing surfaces is effected. Nor is the efficiency of the medicine, according to my experience, best displayed in cases of plastic inflammation. I am quite sure that bronchitis and mucous enteritis yield to it with as great facility as pleurisy or peritonitis. if its antiplastic property were its chief recommendation, we should find it rather injurious than beneficial in the inflammation of typhoid diseases; while, in my experience, it is in these affections that it displays its best antiphlogistic powers. I believe that these powers depend less on its influence upon the blood, than on the change it produces in the solids; in other words, upon a revolutionizing or substituting property, which unseats existing diseased action, probably by disintegrating the tissue in which it is seated, and establishes its own, by replacing the removed structure with a new one from the mercurialized blood. That it produces inflammation in the mouth, is no proof that it cannot cure ordinary inflammation. The stomatitis of mercury is peculiar, and I have no doubt that a pre-existing obstinate inflammation of the ordinary kind, occupying the same parts, would be found, upon the subsidence of the mercurial, to have been displaced by it. The great advantage of the mercury is, that the specific disordered state which supersedes the disordered state pre-existing, whether it amount to inflammation, as in the mouth, or to a mere gentle excitement of the function, as in most of the organs, quickly subsides upon the removal of the cause, and leaves a normal, though possibly a somewhat debilitated condition behind it.