The iodides are among the most diffusible substances. They have a bitter, saline, and very disagreeable taste. In a few minutes after being swallowed, the taste of iodide of potassium returns in the mouth, and, during a course of this salt, the saliva is constantly charged with it. In the stomach, in considerable doses, they produce first a cooling sensation, followed by warmth, and even burning. They pass into the blood with great rapidity. It is said that the base is changed in the blood, and the iodides of ammonium and potassium become iodide of sodium. In the blood they probably undergo no further changes, and do not, so far as is known, modify the composition of that fluid. At the points of elimination from the free mucous surfaces (nasal, faucial, and bronchial mucous membrane), the chemical changes which ensue set free ozone, and the irritation there experienced is probably in part due to the iodine, separated from its combinations by the action of that agent (Buchheim). Elimination doubtless takes place by the broncho-pulmonary, faucial, and salivary glands, but chiefly by the kidneys. The diffusion of the iodides into and out of the blood takes place with such rapidity that in fifteen minutes they may be detected in the saliva and in the urine.

Diverse opinions have been expressed in regard to the influence of the iodides over the assimilative functions. By the syphilographers it is held that the iodides promote constructive metamorphosis, and that a gain in body-weight is a result of their use. This opinion is developed in this way: The subjects of syphilis in its constitutional form emaciate, and their forces are depressed; but, when the iodides are given them, the virus is eliminated, and the organism at once reacts. In the physiological state the iodides increase waste and the elimination of the products of waste, and emaciation with a general depression of the vital functions ensues, when they are administered for lengthened periods.

The proof of the statements just made has been afforded us by the researches of Duchesne, who has ascertained that a decided increase in the amount of urea excreted results from the action of the iodides, especially of the iodide of potassium, and this enhanced metabolism of the nitrogenous elements persists for several days after their administration has ceased. Bouchard, so long ago as 1872, had ascertained the same fact. The other iodides—of ammonium, sodium, and calcium— act in a similar manner during the time of their administration, but their subsequent effects are far feebler and shorter in duration.

The tincture of iodine acts in a manner similar to iodide of potassium, but it has a more powerful effect in increasing nitrogenous waste, as represented in the excretion of urea. An important observation has been made by Duchesne as to the influence of iodine in the condition of interstitial nephritis with albuminuria. He notes that when increasing doses of the tincture are given, the quantity of albumen lessens and finally disappears entirely. As the actions of iodine and of its combinations are really so different in character as well as in power, it becomes important to ascertain which may be the better fitted for particular service. Laségue had, long ago, empirically ascertained that tincture of iodine should be preferred to iodide of potassium, whenever it is necessary to stimulate the retrograde metamorphosis—to increase oxidation, or to enact the part of "alterative."