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 of arsenic. Another remedy of the same nature is charcoal powder, which was proposed in 1813 with much confidence by M. Bertrand. That it has some efficacy when swallowed along with the poison seems to admit of no doubt; for the proposer of it himself swallowed five grains of arsenic in one dose along with charcoal in a state of emulsion, and sustained little inconvenience of any kind. In all probability it acts merely by enveloping the particles of arsenic. But it may possibly be also of service, if recently exposed to heat, by the superficial attraction it exerts over substances in solution; through means of which property it will remove many soluble substances from a fluid, and render them insoluble. Charcoal, however, has been proved to be destitute of all efficacy when not administered till after the arsenic is swallowed. The one must be given along with the other, otherwise it is useless.

For some time past the formation of an insoluble arsenite has been aimed at by most experimentalists who have endeavoured to discover an antidote for arsenic. But in general the arsenites, though very insoluble in water, are sufficiently so in weak acids or in organic fluids, so that they are soluble enough in the juices of the stomach to enter the blood in such quantity as to prove fatal. The only exception now admitted to exist is the arsenite produced when a solution of oxide of arsenic is brought in contact with the hydrated sesquioxide of iron. The compound thus formed is held to be insoluble in the secretions of the stomach; and consequently the hydrated sesquioxide of iron is usually regarded as a true antidote.

The substance, the Ferrugo of the Edinburgh Pharmacopœia,—a compound which differs little from the older preparation, the rust of iron, when not deprived of its combined water,—was announced in 1834 by Drs. Bunsen and Berthold as an effectual remedy even when given some time after the arsenic is swallowed. Their experiments were repeated with variable success. Similar results were obtained by MM. Soubeiran and Miquel, as well as MM. Orfila and Lesueur, in some experiments on dogs, and by M. Boullay on the horse. The last experimentalist found that the effects of a dose adequate ta occasion death are almost entirely prevented in the horse by giving the oxide of iron either immediately after the poison, or within four hours. Results of the same nature were obtained in this country by Mr. Donald Mackenzie. Others, however, such as Mr. Brett and Mr. Orton, have failed to observe any antidotal virtues, and even deny that the sesquioxide of iron can remove oxide of arsenic from a state of solution. But in 1840 the causes of these discrepant statements were explained by Dr. Douglas Maclagan, who found,