Post-mortem Appearances.—The mucous membrane of the mouth, tongue, and throat is corrugated, white, and softened. The tongue is sometimes of a brownish colour, and sordes appear on the teeth. The stomach is in some cases pale, soft, and very brittle, and contains a dark, grumous, acid liquid; at other times it presents several semi-gelatinous spots, looking as if they had been boiled. Enlarged blood-vessels filled with dark-coloured blood are also seen ramifying over the internal surface of the organ. Perforation is of rare occurrence. The intestines generally escape with some slight inflammatory redness, unless the case is unusually prolonged. In some cases the stomach is quite healthy, no morbid appearance being found in any portion of the alimentary canal.
Fig. 29.—Photo-micrograph of crystals of oxalic acid, × 50.
(R. J. M. Buchanan.)
Chemical Analysis.—From organic mixtures the acid may be separated by dialysis, and the tests applied, or it may be obtained in crystals by precipitating it from the boiled and filtered organic mixture with acetate of lead. The precipitate washed is then decomposed by sulphuretted hydrogen and filtered, the filtrate concentrated to drive off excess of sulphuretted hydrogen, and then set aside to crystallise, which, if the acid be present, it does in slender prisms. From the contents of the stomach the acid may be separated by partial drying over a water bath, extraction with hot alcohol acidulated with a little hydrochloric acid, filtering the alcoholic solution, evaporating to dryness, and dissolving the residue in water. Should, owing to the treatment adopted, oxalate of lime in white chalky masses be found in the stomach, these should be washed and then boiled with pure carbonate of potash. A partial decomposition takes place, insoluble carbonate of lime and soluble oxalate of potash are present in the liquid, which, when filtered and neutralised with nitric acid, may be tested with the following reagents:
1. Nitrate of silver gives a white precipitate, soluble in cold nitric acid; the precipitate dried and heated on platinum foil is dissipated in a white vapour with slight detonation.
2. Calcium chloride or sulphate produces a white precipitate with oxalic acid; the test is more delicate if the acid be first neutralised with ammonia. The precipitate is immediately dissolved by hydrochloric or nitric acid, but not dissolved by oxalic, tartaric, acetic, or other vegetable acid. Lime-water should not be used as a test, as it gives precipitates with other acids; the sulphate largely diluted is not open to this objection.
3. Lead acetate gives a white precipitate soluble in nitric acid. On clothes, parchment, &c., the spot or spots must be well boiled, and the above tests applied to the solution. The stains may vary from a brownish-red to orange-red colour.
Fatal Dose.—Three drachms have caused death in one hour; sixty grains caused the death of a boy sixteen years of age, but recoveries have been known to take place after an ounce and an ounce and a half had been swallowed.
Fatal Period.—Death has resulted in ten minutes from a dose of one ounce. The shortest period has been three minutes. The time varies with individuals, even when the same quantity is taken. In the case of two girls who each swallowed an ounce of oxalic acid, one died in ten minutes, and the other in thirty minutes. Death usually takes place within from half an hour to an hour, although it has been delayed for five days.
Treatment.—Water should not be given, as it increases the solubility of the acid, and thus assists in the more extensive absorption and diffusion of the poison. The carbonates of potash and soda should be avoided, as the oxalates of these alkalies are themselves poisonous. The stomach tube should not be used. Lime is the best antidote, as the oxalate of lime is insoluble, and may be given in the form of common whiting; a pint of saccharated lime water may be given. Vomiting should be promoted. In the stage of collapse the case must be treated on general principles.