Derivation.—Iodine exists in certain marine vegetables, particularly the fuci or common sea weeds, which have long been its most abundant natural source. Iodine is also found in the animal kingdom, as in the sponge, oysters, cod liver oil and eggs, and in the mineral kingdom, in sea water in small quantities, in certain salt springs. It is obtained commercially from one of these sources.

Properties.—Iodine is heavy, bluish-black color, dry and friable, rhombic plates, having a metallic luster, a distinctive odor, and a sharp and acrid taste. Iodine imparts a deep brown, evanescent stain to the skin, and slowly destroys vegetable colors. Soluble in about 5000 parts of water and in 10 parts of alcohol at 77° F., freely soluble in ether, chloroform or carbon disulphide; its solution in alcohol or in an aqueous solution of potassium iodide has a reddish color; its solution in chloroform or carbon disulphide has a violet color.

Actions.—Iodine internally is an antiseptic, alterative, resolvent and irritant. Full doses persisted will produce a state of debility and emaciation termed iodism. Externally it is applied as an antiseptic, disinfectant, parasiticide, deodorant, stimulant, desquamatic, absorbent and counter-irritant. Iodine is one of the best antiseptics for surgical purposes. The tincture iodine especially kills all disease producing bacteria in one minute, whereas it takes a one in one thousandth solution of bichloride of mercury more than half an hour to destroy the same micro-organisms. The tincture of iodine also possesses unusual penetrating power on the dry skin, finding its way into the hair follicles and cutaneous glands. Iodine must not be applied to the wetted skin because the wetting causes the skin cells to swell and thus prevent the iodine from penetrating into the sebaceous and sudoriparous glands, the very action upon which the special germicidal action depends.

Uses.—Iodine is of most value applied externally, or locally. In sterilizing the skin for an emergency operation the hair should be clipped and shaved dry and the tincture of iodine applied without washing the skin. For other operations the skin may be scrubbed with soap and shaved and dried before applying the tincture. The tincture should always dry on the skin before the operation is begun.

The method used in human surgery for sterilizing the skin, and recommended by leading surgeons, consists in first of cleansing the skin with gasoline to remove the grease and then applying the tincture of iodine in full or half strength.

Tincture of iodine applied is of some value in the treatment of periostitis with osseous deposits, as splints, bone-spavin, ringbone, sidebones, etc. It is used for enlargements of glands as goiter in dog.