IODINE is obtained from kelp (the ash of marine plants) and is a bluish black scaly substance. It strikes an intense blue color with starch, and when heated gives off an irritating purple vapor. It likewise imparts a yellowish-brown stain to the skin (which may be removed by liquor potassæ) and mucous membranes, and slowly corrodes these tissues. Iodine is an active poison, although its effects are variable. Some constitutions are violently affected by two or three grains, whereas others are uninjured by ten or twenty. Iodine is commonly employed in medicine in combination with potassium (iodide of potassium). Of this substance very large doses may be given (thirty grains or more, three times a day) in tertiary syphilis, with none but good effect. The _symptoms_ of poisoning by iodine consist of an acrid taste, tightness about the throat, epigastric pain, vomiting, and purging, especially if much has been taken. In a case which came under observation, a man took an ounce of the compound tincture of iodine, in mistake for a purgative draught. He was immediately seized with an intense burning pain in the throat and epigastrium, and vomiting, followed by great thirst, headache, and syncope. The vomiting was encouraged, large quantities of arrowroot given, starch enemata administered, and in twelve hours all the symptoms had disappeared, leaving him in a state of exhaustion, from which he recovered in a few days. In chronic poisoning (iodism) there are signs of irritation of the alimentary canal, often a measly eruption, ptyalism, running from the nose and eyes, mental and bodily depression, and loss of flesh. Nothing leads to the belief that it causes absorption of the testicles or mammæ, as is often asserted. The _post-mortem appearances_ would be those due to an irritant poison, namely, inflammation and softening of the stomach; the mucous membrane being detached in different parts, and stained of a yellow color. The _treatment_ should consist in the encouragement of vomiting, and the free administration of amylaceous fluids, as gruel, arrowroot, boiled starch, &c. This should be continued until the matters vomited are of their natural color; for as long as any iodine remains they will be rendered blue, iodide of starch being formed. The crystals _of iodide of potassium_ are white cubes, very soluble in water, and permanent in the air; though when impure they have a yellowish tinge, and are deliquescent. In a few instances this valuable medicine appears to have given rise to troublesome symptoms, even when administered in small doses. Mr. Erichsen has reported a remarkable case, in which five grains produced coryza, conjunctivitis, difficulty of breathing, and other serious effects, promptly ceasing with the discontinuance of the medicine. The _treatment_ must consist in emptying the stomach by emetics or the stomach-pump, and administering starchy diluents.