_Treatment._—The most appropriate treatment consists in the instant administration of any diluent, then of frequent doses of the chloride of soda, and lastly the antiphlogistic mode of subduing inflammation. The chloride of soda or lime decomposes sulphuretted hydrogen, the disengagement of which is the probable cause of death in the quickly fatal cases.[486] CHAPTER XIII. OF POISONING WITH ARSENIC. The third order of the irritant class of poisons includes the compounds of the metals. These are of great importance to the medical jurist. They are frequently used for criminal purposes; they give rise to the greatest variety of symptoms; and the medical evidence on trials respecting them, while much skill is required on the part of the witness to collect it, is also the most conclusive. It must not be inferred from their being arranged in the class of irritants that their action is merely local. In fact this is the case with a very few of them only, which produce chemical corrosion. The greater number likewise act indirectly on organs at a distance from the part to which they are applied. Nevertheless the most prominent symptoms generally produced by them are those of violent local irritation; so that they may be justly considered in the place which has been assigned them. The poisons included in this order are the oxides and salts of arsenic, mercury, copper, antimony, tin, silver, gold, bismuth, iron, chrome, zinc, barium, lead. Many other metals also form poisonous compounds with various acids and other bodies; but these are so rare as to be merely objects of physiological curiosity. Of all the varieties of death by poison, none is so important to the medical jurist as poisoning with arsenic. On account of the shameful facility with which it may be procured in this country, even by the lowest of the vulgar, and the ease with which it may be secretly administered, it is the poison most frequently chosen for the purpose of committing both suicide and murder. In 1837 and 1838 no fewer than 186 cases of fatal poisoning with arsenic were known to have occurred in England alone (see p. 90). Of 221 cases of murder by poison in France during ten years subsequent to 1829, in which the poison given was ascertained, there were 149 where the substance administered was arsenic.[487] It is fortunate, therefore, that there are few substances in nature, and perhaps hardly any other poison, whose presence can be detected in such minute quantities and with so great certainty. SECTION I.—_Of the Chemical Tests for the Compounds of Arsenic._