Of Poisoning with Silver.
Of the preparations of silver, the only one which requires notice is the nitrate or lunar caustic.
It exists in two forms,—crystallized in broad, transparent, colourless tables,—and fused into cylindrical, crystalline, grayish pencils. Both forms are essentially the same in chemical nature.—The most convenient tests are, 1, Hydrochloric acid, or any hydrochlorate, which even in a state of extreme dilution causes with it a dense white precipitate, passing, under exposure to light, into dark brown; and 2, Ammonia, followed by the solution of oxide of arsenic; if the nitrate of silver is not too much diluted it gives a dark brown precipitate with ammonia, soluble, however, in an excess of that alkali; and when the solution has thus been restored, arsenic throws down a lively yellow precipitate, passing rapidly to brown, if left exposed to the light.
Most organic substances, but in particular all animal fluids, with the exception of gelatin, decompose nitrate of silver.
It appears from the experiments of Orfila, that, like the chlorides of tin, the nitrate of silver is a deadly poison when introduced into the veins; but that, by reason of its facility of decomposition, it cannot enter the blood through ordinary channels in a quantity sufficient to develope any remote action. When two grains in solution were injected into the jugular vein of a dog it died in six minutes, difficult respiration being the chief symptom; the third part of a grain caused death in four hours and a half, violent tetanus having preceded death; and in both animals the blood in the heart was found very black and the lungs gorged, or vivid red. According to Mr. Blake, the salts of silver when directly introduced into the blood, do not act on the heart, but operate by causing obstruction of the capillary system. If they are injected into the aorta, the systemic capillaries are obstructed, the nervous system is consequently oppressed, respiration is arrested through the medium of this nervous oppression, and death takes place by asphyxia, the heart continuing to beat vigorously. If again they are injected into a great vein, immediate obstruction of the pulmonary capillaries takes place, so that the blood ceases to be transmitted to the left side of the heart.[[1174]]
To the violent action exerted by nitrate of silver when directly admitted into the blood, its effects through the medium of the stomach bear no proportion or resemblance. Thus, when twelve grains of the salt were introduced into the stomach in the solid state, its effects were so slight as not to be distinguishable from those of the ligature on the gullet practised to prevent its discharge by vomiting. When introduced in a state of solution, however, and in a larger dose, in the dose of 36 grains, for example, it is more energetic. Death ensued in thirty-six hours, but without any particular symptoms; and in the dead body the villous coat of the stomach was found generally softened, and corroded near the pylorus by little grayish eschars like those formed by this poison on the skin.[[1175]]
Hence it appears that nitrate of silver does not act remotely, but simply as a local irritant and corrosive. The corrosion it produces is incompatible with its absorption in large quantity. This inference is confirmed by the experiments of Schloepfer, on its effects when introduced into the trachea. He found that it caused inflammation of the windpipe, and pneumonia passing on to hepatization of the lungs, but no symptom referrible to a remote action.[[1176]] Its pure corrosive properties have long pointed it out to the surgeon as the most convenient of all escharotics.
Nitrate of silver is absorbed, however, in the course of its action. It would seem to be absorbed when it is taken medicinally in frequent small doses. It is not easy to account otherwise for the singular blueness of the skin, sometimes observed after the protracted use of lunar caustic as a remedy for epilepsy and other diseases.[[1177]] The effects of the poison on the constitution in such cases are not very well known. It appears, however, that considerable doses may be taken for a great length of time without injury, and that the first and only unpleasant effects produced by its too free administration are such as indicate simply an injury of the stomach. The only exception to this general statement I have met with is a case by Wedemeyer, where, after the remedy had been taken for six months on account of epilepsy, that disease disappeared, and dropsy, with diseased liver at the same time commenced, and soon proved fatal. It is probable, however, that the nitrate of silver had no share in the ultimate event. In this instance the whole internal organs were more or less blue; and metallic silver, it is said, was found in the pancreas, and in the choroid plexus of the brain.[[1178]] Silver has been found in the urine of persons who were taking it medicinally. A young man who had used the nitrate for some time observed that his urine became muddy soon after being passed, and that the sediment became black if exposed to the light; and when the sediment was digested in ammonia, chloride of silver was detached by neutralizing the ammoniacal liquor.[[1179]]
But it also appears that some nitrate of silver is absorbed when it is given in a single large dose. For in animals poisoned with it Orfila found that silver may be detected in the liver and spleen by charring these organs with nitric acid as in the instance of poisoning with copper, and then treating the residue with boiling diluted nitric acid, and adding hydrochloric acid to the solution. He also found silver in the urine by charring the extract with heat, acting on the charcoal with ammonia, and saturating the filtered ammoniacal solution,—chloride of silver being then detached.[[1180]] These results have been confirmed by the experiments of Drs. Panizza and Kramer of Milan,[[1181]] who found silver in the blood after the administration both of the nitrate and chloride.
Boerhaave has noticed a case of poisoning with this substance, but in very brief terms. He says it caused gangrene. Schloepfer in his thesis notices a case by Dr. Albers of Bremen in which croup was brought on by a bit of lunar caustic dropping into the windpipe. M. Poumarede has related an instance of poisoning with an ounce of nitrate of silver in solution. A few hours afterwards the individual was found insensible, with the eyes turned up, the pupils dilated, the jaws locked, and the arms and face agitated with convulsions. A solution of common salt was immediately given as an antidote. In two hours there was some return of consciousness, and abatement of the convulsions, but still complete insensibility of the limbs, with redness of the features, and pain in the stomach. In eleven hours he could articulate. For thirty-six hours he continued subject to fits of protracted coma; but he eventually recovered. Sixteen hours after taking the poison he vomited a large quantity of chloride of silver.[[1182]]