(3) In subacute and chronic inflammations of various kinds, such as exudations or effusions in connection with the joints and serous cavities, and some forms of pulmonary consolidation, iodide of potassium may promote absorption by stimulating the local nutrition. The local application of iodine "paint" is combined in such cases.

(4) Scrofula is benefited by iodine, especially when it affects the lymphatic glands, enlargements of which are treated by the liniment, by the ointments of the iodides of lead or cadmium, or by interstitial injections (rarely); internally by iodide of iron, or iodine mineral waters, such as the water of Woodhall. On the contrary, phthisis is rarely benefited by iodides, unless there be a syphilitic taint present.

(5) In chronic rheumatism, when debility is not a prominent symptom, in gonorrhceal rheumatism, and in the arthritis of syphilis, the iodide may be beneficial. In chronic arthritic gout it is probably useless, or even prejudicial.

The nervous system, respiratory centre, heart and vessels, and the body temperature are all unaffected by iodine; and the depressing effect on these of large doses of iodide of potassium is believed to be caused by the potassium. The remarkably useful effect of potassium in relieving or curing aneurism is due to the reduction of the blood pressure by the alkali, the coagulating effect of iodine on the blood, and the specific effect of iodine on the chronic inflammatory changes (often syphilitic) in the wall of the artery which have led to the dilatation.

4. Remote Local Action And Uses

Iodine is rapidly excreted, appearing in the urine, the mucous secretions generally, and specially in those of the air-passages, the perspiration, saliva, bile, and milk. Part of the sodium salt which reaches the excreting organs is thrown out unchanged, part is decomposed, and iodine is again set free to exert its local action remotely.

The diuretic effect of iodide of potassium is not marked unless large doses be given, and probably depends upon the alkali, not on the iodine. The latter may, however, have an alterative action upon the kidney, and the iodide may therefore be used in some forms of chronic Bright's disease, combined with other remedies.

The excretion of iodine by the mucous membrane of the respiratory tract is of most interest to the therapeutist. In certain subjects and probably when iodide of potassium contains free iodine as an impurity, its exhibition produces a series of distressing symptoms known as "iodism," consisting of coryza, the watery discharge from the nose being sometimes profuse; sneezing; intense pain of a bursting character over the frontal sinuses, commonly called "headache; " swelling and redness of the gams, hard and soft palate and fauces, foulness of the tongue, and increase of the mucus of the mouth; cough and frothy expectoration, and a sense of heat and rawness in the trachea and chest. The phenomena of irritation of the respiratory mucosa by the out-going iodine are therefore identical with those produced by the immediate action of iodine by inhalation, but in a minor degree. When the secretion is deficient, the mucous membrane of the bronchi swollen and dry, and cough useless and painful, iodide of potassium is thus a valuable expectorant, quickly inducing a flow of thin mucus, by establishing secretion, or by liquefying tenacious mucus which may be plugging or irritating the bronchi. It is, further, an indirect antispasmodic, given with great benefit in asthma and emphysema. The iodide of ethyl (non-officinal) inhaled as vapour may rapidly relieve the spasm of asthma. Iodide of potassium is sometimes given in other respiratory diseases, e.g. in pneumonia, if the consolidation threaten to persist.

In escaping by the skin the liberated iodine produces in certain individuals peculiar eruptions, generally papular or slightly vesicular, rarely purpuric. The value of the drug in tertiary syphilitic diseases of the skin no doubt depends partly on this influence.

6. Action And Uses Of The Several Preparations Containing Iodine

1. Cadmii Iodidum: Unguentum Cadmii Iodidi. - The ointment only is employed, and combines the stimulant effects of the two elements. It is rubbed into the skin over enlarged glands, stiff joints, etc. See Cadmium.

2. Ferri Iodidum: Pilula Ferri Iodidi and Syrupus Ferri Iodidi combine the action of the two important elements, and are especially indicated and extensively employed when iodine has to be administered for a length of time to anaemic subjects. This is the form in which iodine is usually given in scrofula, the syrup being a favourite remedy for strumous children.

3. Hydrargyri Iodidum Rubrum possesses chiefly the action of the per-salts of mercury, and is used accordingly. See Hydrargyrum.

4. Hydrargyri Iodidum Viride is also a mercurial rather than an iodide in its action, and is employed in syphilis much like calomel.

5. Sulphur is Iodidum is now used externally only, and is believed to produce the combined effects of the two alteratives.