The readiest and best way of obtaining the beneficial effects of Iodine is by the use of Iodide of Potassium. This is a very soluble salt. The peculiar virtues of Iodine are not impaired, but rather improved, by its chemical combination with the alkali. And when we administer the Iodine itself, as in the tincture, there is no doubt that after entry into the blood it combines with some alkaline base. If the use of Iodine be continued for some time it has the effect of impoverishing the blood. It sometimes produces a vesicular eruption on the skin, and causes a considerable degree of irritation of the mucous membrane of the nose and eyes. The preparations of Iodine exert in the blood some special actions of a Catalytic kind, by virtue of which they are enabled to counteract the morbid actions of secondary Syphilis and of Scrofula. Iodine is not, like Mercury, a general Antiphlogistic; but it is a stimulator of the function of absorption, as are all the medicines that tend to impoverish the blood. This action in causing absorption can be no explanation of the blood-operations for which it is employed; for these are peculiar to it alone, whereas the other property is shared by other remedies. (p. 192.) Iodine is an Antisyphilitic. But this term is not applicable to it in exactly the same sense as to Mercury. Its use is confined to the later symptoms,--to Periostitis, and the late eruptions, as Rupia. Sometimes it even fails in these. This is generally when the primary disorder has not been met by Mercury. Some preparation of Mercury should then be administered for awhile; and the Iodide of Potassium may be given afterwards. Thus the disorder which is controlled by the latter medicine is so modified as to be something quite distinct from the primary Syphilis. The same medicine is an Antiscrofulic. It is applicable in all the forms of Scrofula, and in Goitre. Possibly it acts differently in such cases; but it is certain that there is often, in cases of confirmed Syphilis, a cachexy similar to that produced by Scrofula. In either disorder, when this cachexy is confirmed, Mercury is most objectionable. On the contrary, in primary Syphilis, and even in incipient Scrofula, Mercury may be used.