This section is from the book "Materia Medica And Therapeutics Inorganic Substances", by Charles D. F. Phillips. Also available from Amazon: Materia medica and therapeutics.
The earliest and most marked evidence of the constitutional action of iodine, whether taken by the mouth or injected hypodermically, is furnished by irritation and catarrh of the mucous membranes. If iodine itself be used, as in the form of tincture, there is more liability to local irritation of the mouth and stomach than with the alkaline iodides, but the distal mucous irritation is the same with all forms of the drug. It is shown mostly in the throat and bronchi, the nose and eyes - parts that are all exposed to contact with carbonic acid gas, which it is supposed decomposes the iodide salt as it is eliminated, so that free iodine exerts its local irritant effect (Rabuteau). Others trace a similar decomposition to contact with ozone in the blood or in the air (Buchheim and Kammerer: Virchow's Archiv). The irritation shows itself by pain and sense of pressure over the frontal sinuses, oedema, prickling, and heat about the nose and eyes, with sense of stuffiness and serous discharge like that of ordinary coryza. The dose that will produce these symptoms varies much with different persons, some being acutely affected by 1 or 2 gr., others not by 10 or even 20 gr. continued daily for a long time.
We have already noted characteristic arsenical effects upon the membrane of the mouth and intestinal canal. The lips, the nose, especially at its orifice, the anus, and the vulva often become similarly irritated and inflamed, and urethritis has been traced to medicinal doses of arsenic (Medical Record, 1878). On the mucous membrane of the eye the effect of the drug is often very early seen, so that it becomes a useful index of the degree of physiological action. Itching about the lids is first complained of, and a rough sensation as of dust in the eye; the conjunctiva is seen to be congested, and purulent secretion may be formed. Conjunctivitis is a frequent symptom in arsenical poisoning, and Dr. Taylor describes "tumid, everted lids and painful vision" in patients affected by arsenical papers, etc. (Ophthalmic Hospital Report, 1859, and British Medical Journal, ii., 1871).