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ELEMENTS OF MATERIA MEDICA.

solution from which the silver lias been thrown clown by hydrochloricacid should be unchanged by the addition of hydrosulphuric acid, shew-ing the absence of lead and copper; and be completely volatilized byheat: if any saline residuum be obtained, the nitrate was adulterated.The white precipitate produced with either hydrochloric acid or chlo-ride of sodium should be readily dissolved by caustic ammonia : if chlo-ride of lead be present the effect will be otherwise.

Physiological Effects, (a.) On animals. — Orfila ( Toxicol. Gen.)found that it acted on animals as a powerfully corrosive poison. Whendogs were made to swallow it, gastro-enteritis was induced. No symp-toms indicating its absorption were observed. Dissolved in water, andthrown into the jugular vein, it produced difficult respiration, convulsivemovements, and speedy death.

( b.) On man. —The local action of nitrate of silver is that of a causticor corrosive. This might be expected, from observing its action on albu-men and fibrin—substances which form the principal part of the animaltextures. If a solution of nitrate of silver be added to an albuminousliquid, a white curdy precipitate is formed, composed of nitrate of silverand albumen, insoluble in caustic ammonia; and after some timebecoming coloured and ultimately blackish, from the partial or com-plete reduction of the silver : a soluble compound of albumen and nitrateof silver is formed simultaneously with the insoluble one. The actionof nitrate of silver on fibrin is analogous to that on albumen: that is,a white compound of nitrate of silver and fibrin is at first formed, butgradually the metal is reduced. These facts assist us in comprehendingthe nature of the changes produced by the application of nitrate of silverto the different tissues.

Applied to the skin it produces first a white mark (owing to its unionwith the coagulated albumen of the cuticle): gradually this becomesbluish grey, purple, and ultimately black, owing to the partial reductionof the silver, if the integument be moistened, and the nitrate appliedthree or four times, it causes at the end of some hours vesication, whichis attended with less pain than that produced by cantharides. In somecases it excites acute pain. In one instance in which I applied it freelyto the scalp for a cutaneous affection, fever with delirium was produced,which endangered the life of the patient (a girl of six years.) This isdeserving of notice, because in Mr. Iligginbottom’s work (Essay on theUse of the Nitrate of Silver , 2d ed. p. 198) we are told that nitrate ofsilver applied as a vesicant “ causes scarcely any constitutional irrita-tion, even in children.” In a few days the black and destroyed cuticlecracks and falls off, without any destruction of the subjacent cutis vera.

Applied to the hair or nails the nitrate stains them black, as in thecase of the cuticle; and, in consequence, it is one of the substances em-ployed as a hair-dye. When recently applied, the black tint of the hair,and even of the cuticle, may be removed by washing with a solution ofchloride of sodium, and then with ammonia-water, to dissolve the chlorideof silver which is produced (Journ. de Chim. Med . vii. 542.) To detectsilver in stained hair, the latter is to be treated with chlorine, by whichchloride of silver is produced, which is soluble in ammonia, and precipi-table from its solution by nitric acid (Devergie, Med . Leg. ii. 933.) Partof the black colour of the hair stained by the nitrate probably depends onthe formation of sulphurct of silver.