The most important remedial uses of arsenic are those connected with its antiperiodic power, and its alterative influence in chronic skin diseases, chronic rheumatism, and certain nervous affections.

1. Uses of Arsenic as an Antiperiodic. Next to Peruvian bark and its derivatives, arsenic is, I believe, generally admitted to be the most efficacious remedy in regularly periodical or intermittent diseases.

In intermittent fever, it has been much used, and with great success. As well from my own trials with it in the earlier period of my professional life, before quinia had come into use, as from the testimony of others, I believe that arsenic is adequate to the cure of intermittent fever in a very great majority of cases, and, indeed, that few will resist it if judiciously employed. it is not, however, so prompt in its effects as sulphate of quinia, at least in the doses in which it is quite prudent to employ it, and does ordinarily fail in a certain number of cases. These considerations have led to its general abandonment as the primary remedy in the disease; though it is still occasionally resorted to, when, from any cause, the preparations of Peruvian bark cannot be given, or fail of the desired effect. in some instances of old intermittents, in which quinia has been given often and largely, the system seems at length to lose in great measure its susceptibility to the influence of that medicine, which can, therefore, be no longer advantageously used, until a temporary abstinence shall permit a return of the susceptibility. Quinia is also believed, by the advocates of arsenic, to leave a greater tendency to relapse behind it. Under these two conditions, then, arsenic becomes a most valuable remedy in intermittents; to wit, when the susceptibility of the system to quinia has been much impaired, and when frequent and annoying relapses occur, which it has been found powerless to prevent. in young children, moreover, it has the advantage of being tasteless, or nearly so, in the form usually employed. One reason of the want of success, which some have complained of, is probably the use of insufficient doses. To interrupt the disease, it is necessary to make a strong impression, whatever may be the medicine used, whether quinia, opium, or arsenic. Before the proper management of quinia was well understood, failures with it were very common, in consequence of the small-ness of the doses. As much of the arsenic should be given at first as the system will tolerate; and the dose may be diminished as soon as signs of its operation are obtained, care being taken that it should not be permitted to irritate the stomach. it was upon this plan that our countryman, Dr. Thomas Mitchell, late Professor of Materia Medica in the Jefferson Medical College of Philadelphia, met with extraordinary success in the use of the remedy, so long since as the year 1820; and that, more recently, M. Boudin, of France, has obtained such astonishing results. in the hospitals of Marseilles, Versailles, and Paris, M. Boudin treated nearly 4000 cases of intermittent fever with arsenic; and he declared that, not once from the close of the year 1843 up to 1851, when the statement was made, had there been occasion to have recourse to sulphate of quinia. (Trousseau and Pidoux, Trait, de Thérap., 4e ed., i. 261.) in the treatment by arsenic, the stomach, if loaded, should be evacuated with ipecacuanha, and the bowels should be opened. M. Boudin has found that many patients bear three-quarters of a grain of arsenious acid, equivalent to ninety minims of Fowler's solution, daily for two or three days, but cease to tolerate this quantity afterwards, when the fever is interrupted. But his customary plan is to give from 1/140 to 1/70 of a grain of arsenious acid (one or two drops of Fowler's solution) every fifteen minutes, until he finds diminution of appetite, nausea, or headache produced, when he lessens the dose, or administers the medicine by the rectum. He has found that patients will bear a grain of the acid by the rectum, when the stomach has ceased to tolerate one-fifth or one-tenth of the quantity. He gives it as well in the days of the fever as in the intervening days; and, after having broken the succession of the paroxysms, he continues with the medicine, in such doses as the patient can well bear, for a longer or shorter period, according to the previous obstinacy of the disease; in the first attacks, about a week, and in old cases for a month or two. During the treatment he directs a good diet of animal food, the use of sound wines, if the patient is feeble, and abstinence from much watery drink. The division of the dose he insists on as an important measure. Out of 311 cases treated at Versailles in a period of 32 months, M. Boudin had but 10 relapses. (ibid., 262 and 263.) Dr. Mitchell gave fifteen or twenty drops of Fowler's solution, instead of the eight or ten drops ordinarily directed.

Intermittent neuralgia has also been effectually treated by arsenic. Periodical headache, which is in general purely neuralgic, is one of the affections in which it has been found most useful. I have succeeded with it after all other measures had failed. As in intermittent fever, its use has been generally superseded by sulphate of quinia; but there are cases in which the excitant influence of the latter medicine on the sensorium is contraindicated; and in these, arsenic may be resorted to with reasonable hope of success.

In all other regularly intermittent or periodical diseases arsenic probably possesses the same efficiency, and may be resorted to in the absence or inadmissibility of quinia, with reasonable hope of benefit. Such are intermittent coughs, diarrhoeas, and eruptions, especially urticaria.

In remittent diseases, of a regular paroxysmal or periodical character, much may be hoped for from the remedy. Remittent fever will sometimes yield to it; and, after the establishment of a regular remission in the affection, when sulphate of quinia from any cause cannot be given, and the stomach is not irritated or inflamed, the physician would be justified in having recourse to arsenic. The same may be said of remittent neuralgia; that is, a form of the disease in which a violent paroxysm of pain recurs at a certain time every day or every other day, with a moderated degree of pain in the interval.