External

They have none. They do not irritate, and they are absorbed by the unbroken skin in very small quantities.

Internal

There is much uncertainty about the action of iodides, which is not surprising when we remember the powerful chemical affinities of iodine. Binz teaches that they are decomposed in the body by small quantities of nascent oxygen (set free by living protoplasm) acting upon an iodide which is in an acidulated solution, the acid being provided by carbon dioxide. Thus KI+H2O+Co2=Khco3+HI, and then 4HI+O2=2H2O + 2I2. We have just shown that iodine acts as an absorbent and that it leads to leucocytosis; and that iodides act by virtue of the iodine set free from them in the body is supported by the fact that the older physicians produced the same therapeutic effects by giving iodine internally as we procure with iodides, and that iodine taken internally will produce symptoms of iodism. Potassium iodide replaced iodine in therapeutics because it does not cause the same gastro-intestinal irritation. The beneficial effects of iodides are so very marked in syphilis that in this disease they must have some specific action in addition to their general power as absorbents. They also have a specific effect on the mammary gland, for they lessen the secretion of milk. In long-continued large doses they cause atrophy of the testicles and breasts. Some believe that they aid in the elimination of lead, and this may be due to the fact that lead albuminate is soluble in solutions of potassium iodide. Occasionally considerable general depression is produced by large doses of potassium iodide; but this is probably due to the potassium, and not to the iodine, and in this case the syrup of hydriodic acid can be substituted. The iodides are rapidly eliminated by the urine, saliva, sweat and mucous membranes. When taken in excess they produce a number of symptoms known as Iodism.

Iodism

This occurs in three forms. (1) The symptoms are those of gastric irritation only. (2) The patient complains of heavy pain over the frontal sinus, running at the nose, sore throat, increased secretion of saliva, and an eruption on the skin, consisting of patches of erythema. In rare cases there is albuminuria. The inflammation about the fauces may spread to the gums or down the trachea, setting up laryngitis, tracheitis, and bronchitis. These symptoms have been ascribed to an excessive formation of free iodine produced as mentioned above - and this is supported by the fact that they can be checked by large doses of sodium bicarbonate, which keep the fluids of the body alkaline, and thus prevent the formation of free iodine - and also to the decomposition of iodides by nitrites, for minute traces of these are believed to exist in saliva, nasal and bronchial mucus, and sweat, and they will liberate free iodine from potassium iodide. It is stated in support of this view that sul-phanilic acid (dose, 60 to 90 gr. 4. to 6. gm.), which forms a very stable compound with nitrous acid, will prevent iodism.

Nervous troubles, neuralgia, singing in the ears, convulsive movements, disturbed intellection and rarely atrophy of mammae and testicles may be noticed. (3) Iodic cachexia, which is characterized by rapid emaciation; severe cardiac palpitation and ravenous appetite, are also prominent symptoms. The susceptibility of people to poisoning by iodides varies very much. Treatment. - The chewing of pellitory will hasten the elimination of iodine in the chronic forms.

Therapeutics of the Iodides

The most important use of iodides is for syphilis; their value for the primary and secondary stages is comparatively slight, but they are invaluable for the tertiary stage, as they often cause the rapid absorption of nodes, gummata and other syphilitic deposits. The pharmacopoeial dose may often be exceeded: patients sometimes take two, three, or even four drachms 8. to 16. gm. a day. Large doses are especially used in syphilis of the nervous system. Daily doses of an ounce, 30. gm., are not infrequently necessary in these cases. No symptoms of iodism are likely to appear until the disease subsides. Potassium iodide is often prescribed with corrosive mercuric chloride; red mercuric iodide is formed and dissolved in the excess of potassium iodide.

Chronic rheumatoid arthritis is often treated, and sometimes with benefit, by small doses of potassium iodide continued for a long while, but probably ferrous iodide is more useful. So-called gonorrhoeal rheumatism is often treated with potassium iodide but the syrup of hydriodic acid is preferable. It frequently aids the absorption of chronic inflammatory products, even when they are not syphilitic. Therefore certain forms of joint disease, of pleurisy and of pulmonic consolidation sometimes yield to treatment by this drug. The attempt has been made to cure aneurisms which are inaccessible to surgery by giving potassium iodide for long periods, for it is thought that it aids the coagulation of blood in them; but as at the same time the patient is always kept in bed, it is difficult to say how much of any improvement that may happen to take place is due to the iodide. Occasionally it relieves the pain of aneurism or of angina pectoris. It is a valuable expectorant, particularly the ammonium salt, and sometimes cures cases of bronchitis when other remedies have failed. Lately, chronic Bright's disease has been largely treated with the drug. Lardaceous disease of the kidneys and other organs is benefited by it. The potassium salt is recommended for the symptom asthma, and in some cases does much good. It is occasionally given to decrease the secretion of milk. Potassium iodide perhaps causes an increased excretion of both lead and mercury if they exist in the body, and is therefore occasionally given in chronic poisoning by these metals. Sodium iodide is not so much used; it probably produces the same effects as the potassium salt, but does not occasion so much depression. Ammonium iodide may be given if the potassium salt causes depression, and it is said that rubidium iodide not official (dose, 5 to 20 gr. .30 to 1.20 gm.) is sometimes better tolerated than the potassium salt.

Strontium iodide has been recently introduced, and is used for the same purposes as the other iodides. It is believed that it is less likely to disturb the stomach, cause acne, and depress the heart than the remaining iodides. In many instances the syrup of hydriodic acid can be substituted with advantage for the iodides. It is not so likely to produce iodism, nor does it so readily give rise to the "iodide punishment." Its pleasant taste is grateful to most patients; it should, however, be administered, well diluted, one-half hour before meals, or at least upon an empty stomach. Some of the commercial preparations are likely to decompose readily, especially when made from tartaric acid and potassium iodide, and are objectionable from the amount of syrup which is administered when large doses are employed.