It is probable that iodine acts in this disease, much as it does in metallic poisoning, by assisting the elimination of a morbid material. It has been maintained, indeed, by Dr. Basham and others, that its influence is best seen in cases which have been previously treated by mercury; and Dr. Budd and Dr. Garrod have given instances in which mercurial influence was dormant until excited by the administration of iodides, when profuse salivation occurred, and recovery ensued. But there can now be no question that the drug has curative powers of its own, independent of mercurial action; they are evidenced especially in the later, or tertiary stages of constitutional syphilis, when either the mucous membranes are affected, as in deep ulceration of the fauces, or the bones are attacked with periostitis or nodes, or the skin suffers with rupial or lupoid eruption, or the brain-membranes are thickened, or gummatous deposits are formed in any of the viscera. In such conditions it usually acts far better than mercury, although this latter drug is more advisable in some eye-inflammations, such as iritis; and again, in a certain proportion of undefined syphilitic cases, an iodide of mercury will give better results than either medicine alone.

By causing the absorption of deposits and thickenings in various parts of the body, iodides cure, at the same time, many secondary and dependent symptoms, such as nocturnal pains, neuralgia, paralysis, dulness of sense or intellect, and convulsive paroxysms. The dose of iodide of potash is a matter of much importance, and need be limited only by the susceptibility or idiosyncrasy of the patient, and the progress of the disease; it may vary from 1 or 2 gr. up to 60 gr., two or three times daily, and the best results have sometimes been obtained from heroic doses, when ordinary ones have failed.

Elliotson gave 30 to 60 gr., or more, for a dose (Lancet, i., 1832), and Ricord commonly prescribed the same amount. Sir A. Cooper, Drys-dale, Pollock, and others, have given instances of the value of such quantities (British Medical Journal and Lancet 1867-68); and more recently Dr. Buzzard has pointed out the importance of large doses, especially in syphilitic affections of the nervous system (Lancet, i., 1873).

In hereditary syphilis I prefer mercurial treatment, though infants generally bear iodides well.

Mr. Berkeley Hill has stated that the iodide of ammonium or of sodium will sometimes cure when the potassium salt has failed, and this fact should be remembered in practice (British Medical Journal, ii., 1871).