NITRATE OF SILVER^

429

When nitrate of silver is applied to an ulcer it produces a white film(owing to its union with the albumen, and perhaps also with the chloride,of the secretion.) This film in a few hours assumes a dark colour, andultimately forms a black eschar. This hardens, and in few days becomescorrugated, separates at the edges, and at length peels off altogether, leav-ing the surface of the sore beneath in a healed state (Higginbottom, op.cit. p. 10.) The intensity of the pain varies much in different cases; butit is, on the whole, very much less than might be imagined by those whohave not tried this remedy.

When applied to mucous membranes, a similar white compound of thenitrate with the animal matter of the secreted mucus is formed, and thisdefends the living tissue from the action of the caustic, so that the effectsare not so violent as might be expected. Thus the solid nitrate may beapplied to the mucous siuface of the vagina, anti even to the os uteri, incases ofleucorrhoea and gonorrhoea, oftentimes without exciting any painor inflammation : in some instances, however, it produces smarting pain,which lasts for several hours, but no serious effects have resulted from itsuse, even when, by accident, two drachms of nitrate have been left todissolve in the vagina. (Dr. Hannay, Land. Med . Gaz. xx. 185 ; also Mr.Bell, ibid. 473 ; and Dr. Jewel, Prat. Observ. on Leucorrhwa.)

Its chemical effects on the other mucous membranes are analogous tothose just mentioned ; but the pain which it produces varies with dif-ferent membranes, and in the same membrane under different states. Itsapplication to the conjunctiva is attended with acute pain, (especiallywhen inflammation is going on) though in general it soon subsides. Onall these surfaces it acts as an astringent.

The safety with which, in most cases, large doses of the nitrate arcadministered internally, must depend on the presence of the mucuswhich lines the internal coat of the stomach ; the animal matter of whichcombining with the nitrate prevents its action on the living tissue. It isdeserving of especial notice that larger doses may be exhibited withoutinconveniencing the stomach, in the form of pill, than in that of solution.Dr. Powell {Med . Trans, of the College of Phys. iv. 85) in some caseswas enabled to give 15 grains at a dose in the form of pills, while herarely found stomachs that could bear more than five grains in solution.Fouquier {Diet. Mat. Med . i. 403) has also remarked the greater activityof the solution. If cautiously exhibited, beginning with small doses andgradually increasing them, it may be exhibited for a considerable periodwithout producing any obvious changes in the corporeal functions, thoughit may be exercising a beneficial influence over the constitution, evincedby its amelioration of certain diseases, as epilepsy. In some cases it hascaused an eruption (Sementini, Quart. Journ. of Science, xii. 189; Copland,Diet. Pract. Med . i. 68.) If the dose be too large it causes gastrodynia,sometimes nausea and vomiting, and occasionally purging. Taken in anexcessive dose it acts as a corrosive poison; but cases of this kind arevery rarely met with. Boerhaave mentions an instance in which itcaused excruciating pain, gangrene, and sphacelus of the first passage.

All the above-mentioned symptoms are referrible to its local action,and from them we have no evidence of its absorption, or of the nature ofits influence over the general system. But the discoloration of the skin,presently to be noticed, fully proves that absorption does take place whenthe medicine is exhibited in small but long-continued doses. It exer-