_Post-mortem Appearances._—The mucous membrane of the fauces, œsophagus, and stomach is generally white and brittle, but often colored with the brown mucous matter discharged. The stomach often contains a black fluid, like coffee-grounds, consisting principally of altered blood; and its sub-mucous coats are vascular and dark colored. The stomach though seldom perforated, may yet be so softened as to be with difficulty removed entire, and sometimes this is not possible. This softening may be due to the post-mortem action of the poison; but its effects during life in softening and bleaching the mucous membrane are sufficiently marked. Occasionally the stomach is black and gangrenous looking. If death has occurred quickly, the small intestines are seldom much affected; but where the symptoms have been protracted there are usually signs of congestion and inflammation. _Treatment._—Chalk, whiting, or magnesia, suspended in water, or in some demulcent fluid, must be administered immediately; and if necessary, vomiting should be excited by tickling the fauces, or administering emetics of sulphate of zinc and ipecacuan, followed by large quantities of emollient drinks. The antidote, to be effective, must be given as soon as possible, the plaster of the apartment, or any form of mortar being used in the absence of the remedies just mentioned. Alkalies (soda, potash, or their carbonates) are not only useless, but they form salts with oxalic acid, which are as injurious as the acid itself. When there are symptoms of collapse, stimulants are to be freely employed. From the tendency to softening, the stomach-pump should not be used. _Tests._—Crystals of oxalic acid are met with as four-sided prisms, colorless, without odor permanent in the air, and very acid; this last character distinguishing them from crystals of sulphate of magnesia and sulphate of zinc. The crystals, when heated, melt, and are dissipated without combustion, and leaving no residue. This character is important as a means of distinguishing oxalic acid from other similar crystals. They are soluble in from eight to twelve parts of cold water. This acid may be thus recognised in solution: 1. _Nitrate of silver_ throws down, with oxalic acid, an abundant white precipitate (oxalate of silver), which is soluble in nitric acid. The oxalate of silver, when dried and heated on platinum foil, detonates, and is dissipated in a white vapor. 2. _Sulphate of calcium_ causes a white precipitate with oxalic acid (oxalate of calcium) which is soluble in nitric or hydrochloric, but not in any vegetable acid. The solution containing the acid should be concentrated before testing, if it be not present in considerable quantity.