_Symptoms._--These present many strange anomalies. In a large dose--an ounce or more--oxalic acid acts as a corrosive; in a smaller, as an irritant; and in a still smaller dose, as a cardiac sedative. Death has been known to occur so rapidly as to prevent any attempt at treatment. When the dose is large, an acid taste is experienced during swallowing, followed by burning pain in the throat and stomach. Vomiting then sets in, and in most cases continues till death, which may, however, occur when this symptom has existed from the first. The vomited matters may be simply mucus, mucus and blood, or dark coffee-grounds-looking matter. Unless the case is protracted, the bowels are rarely much affected, though purging and tenesmus have been noticed. Occult blood may be present in the fæces. Collapse now sets in; the pulse becomes feeble and scarcely perceptible, the skin cold and clammy, showing the action of the poison on the heart probably through the central nervous, as well as through the intra-cardiac ganglia. Should the treatment adopted prove successful, and life be prolonged, the patient complains of tenderness of the mouth, soreness of the throat, and painful deglutition. Pressure over the abdomen causes pain. Vomiting and purging are also frequently present; and if recovery takes place, convalescence is generally very gradual. The urine may contain a large quantity of albumen, casts are numerous, and oxalates in crystal form are present. [Illustration: Fig. 28.--Photo-micrograph of crystals of oxalic acid, × 50. (R. J. M. Buchanan.)] Oxalic acid acts as a poison when applied to a wound in any part of the body; and although this substance undoubtedly acts on the brain through the medium of the blood, it is a remarkable fact that _it cannot be detected in that fluid_, even when injected into the femoral vein of an animal which died in thirty seconds (Christison). Leeches, it is recorded, have been poisoned by the blood drawn by them from persons suffering from oxalic acid poisoning. The blood does not appear to undergo any physical change. Unlike the mineral acids, oxalic acid is still poisonous even when its corrosive and irritant properties have been destroyed by dilution. _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.