Origin. - Prepared by shaking a solution of silver nitrate with solution of potassa and washing the precipitate.

Description and Properties. - A heavy, dark, brownish-black powder, liable to reduction by exposure to light; odorless, with a metallic taste; very slightly soluble in water and insoluble in alcohol.

Dose. - 1/2-2 grains (0.03-0.12 Gm.) [1 grain (0.065 Gm.), U. S. P.].

Antagonists and Incompatibles. - The silver nitrate is incompatible with the alkalies and their carbonates, chlorides, hydrochloric and tannic acids, potassium iodide, solutions of arsenic, and many of the organic acids.

Silver oxide is rapidly oxidized, forming explosive compounds with chlorides and organic substances.

Synergists. - Preparations of copper, lead, and zinc aid the action of silver salts.

The silver nitrate and its preparations and the silver oxide are the only salts which possess any value as astringents or caustics.

The silver nitrate is the typical astringent salt, and its physiological action will be hereafter considered.

Physiological Action. - Metallic silver is practically of no use in medicine, though of great value in surgery, because of its inertness. Silver nitrate is the salt of silver chiefly employed.

Externally and Locally. - It is a powerful caustic, but does not wound very deeply, as it forms an eschar by coagulating the albumin of the tissue, thus protecting the underlying structures. The eschar is white, but on exposure to light very soon becomes black, owing to the fact that the silver is reduced to its metallic state. The albuminate is soluble in chloride.

Like lead salts, silver salts are hemostatic. They are severely irritant to mucous membranes when used in solution. Soluble silver salts are actively bactericidal.

Internally. - Digestive System. - Weak solutions are astringent to mucous membranes, first contracting then dilating the bloodvessels. Stronger solutions are caustic. Weak solutions cause increased secretion of intestinal glands and larger flow of bile. The nitrate is frequently precipitated as the insoluble chlorides in the stomach and is later absorbed as an albuminate.

Silver salts have little or no action on the general functions of the body.

Absorption and Elimination. - It is absorbed from the stomach and eliminated very slowly, chiefly by the feces, a small portion being excreted by the kidneys.

Untoward Action. - Long-continued use of silver nitrate produces discoloration of the skin (argyria), either general or more pronounced in particular spots, such as the face. Even when the skin is perfectly intact the application of nitrate of silver will discolor it, and 1/4 grain (.016 Gm.) has caused palpitation of the heart and irregular pulse. Silver accumulates in the tissues.

Poisoning. - A poisonous dose of silver nitrate produces a violent gastro-enteritis. The earliest symptom is an intense pain in the abdomen, followed by vomiting and purging. The abdominal muscles are hard and retracted, the face livid and covered with perspiration and wearing an anxious expression. The lips are blanched, gradually becoming black; the vomited matter is blackish and sometimes resembles milk-curds.

Epileptiform convulsions, delirium, and paralysis ensue, the latter symptom being of centric origin.

Death results from shock. A large amount of mucus is thrown into the bronchial tubes by the lining mucosa.

Treatment of Poisoning. - The chemical antidote is common salt. It is essential to protect the mucous membrane of the esophagus and stomach, and at the same time dilute the poison as much as possible, for which purposes large quantities of salt water and soap water or milk are valuable. Opium allays the pain and irritation.

Chronic poisoning, or argyria, results from prolonged medicinal use of silver nitrate or its employment as a hair-dye for any length of time. The drug is deposited in all parts of the body, being especially manifest in a slaty, permanent discoloration of the skin. The first symptoms are discoloration of the sclerotic conjunctivae and a dark line on the inner side of the lips. Ulcerative stomatitis may occur, or even gastric ulcer.

Treatment of Chronic Poisoning. - There is no known method of curing argyrosis when once developed. One hundred and fifty grains seem the limit. If more than this amount of the silver be given the discoloration is apt to occur. Considerable individual variation exists. Localized argyrosis has been known to occur after continued local applications of nitrate of silver to the larynx and pharynx.

Therapeutics. - Externally and Locally. - A very important use of silver nitrate is that of preventing ophthalmia neonatorum, a 2 per cent. solution being dropped into the eyes. For adults a 2 to 4 per cent. solution is used in various forms of conjunctivitis, the eyelids being painted with a camel's-hair brush, and the solution being washed off immediately to prevent discoloration. The nitrate-of-silver stick may also be used.

Felons, boils, and bedsores may sometimes be aborted by the use of a strong solution - 20 grains to 1 ounce - of silver nitrate.

An injection of 2-3 grains (.12-20 Gm.) to the pint is beneficial in subacute gonorrhea and leucorrhea. This may also be used as a wash in pruritis ani and vulvae, to relieve the itching. The stick may be applied to uterine ulcers.

As a caustic it is used in indolent ulcers and chancroids, stimulating them and producing a healthy granulating surface.

After a cold, when the throat feels raw and sore, an application of 10 grains (0.6 Gm.) to the ounce (30.0 Cc.) is very beneficial, and the same may be used in inflammations of the pharynx, fauces, and mouth. A spray of 10 grains (0.6 Gm.) to the ounce (30.0 Cc.) is very effective in laryngeal croup, tracheitis, chronic ulceration of the larynx, and whooping-cough. The caustic pencil is used in tonsillitis, sore nipples, mercurial sore mouth, and poisoned, lacerated, and punctured wounds. A solution of 1-2 grains (.06-. 12 Cc.) to the ounce (30.0 Cc.) is valuable in otorrhea, vesical catarrh, and balanitis.

Internally. - Dr. Pepper recommends this salt in intestinal ulcerations, given in keratin-coated pills. It is excellent for gastric ulcer, in which it may be combined with opium. Gastralgia and chronic gastritis, ulceration of the rectum, dysentery, and diarrhea of typhoid have been remarkably benefited by its use. For stomach affections 1/6-1/4 grain (.01-016 Gm.) is given, and for intestinal an enema of 3-10 grains (.20-.64 Gm.) to the ounce (30.0 Cc).

It has been used in congested conditions of the cord, locomotor ataxia, epilepsy, and chorea. It is of no permanent value in any of these conditions.

Argentic oxide is not so active as the nitrate. It has been employed for checking sweats, and, owing to its less caustic action, it may be preferable to the nitrate in gastric ulcer and gastralgia.

Administration. - The dose of silver nitrate is 1/6-1/4 grain (.01-.016 Gm.), and for a constitutional effect should always be given in pill form during the process of digestion.

The keratin-coated pill is to be administered for intestinal disorders, and when a local action on the alimentnry canal is desired an ordinary pill should be given one to two hours before meals.

It is well to discontinue the drug for a short time after three or four weeks treatment, the salt being so slowly eliminated that its prolonged use is very apt to result in argyria.