Acidum Hydrocyanicum. H,Cy. Prussic Acid. Is chiefly obtained by decomposing some of the compounds of Cyanogen, but is found also in the distilled water and oil of the Bitter Almond, and the Cherry Laurel. It is likewise produced when Amygda-line (a principle contained in Bitter Almonds, and the kernels of Peaches, Plums, and other fruits) is acted on by Emulsine. (See Amygdala.)

Dilute Hydrocyanic Acid. Acidum Hydrocyanicum Dilutum (Br. Ph.). Hydrocyanic Acid dissolved in Water, and constituting 2 per cent. of the solution. Sp. Gr. 0.997. Prepared by distilling Sulphuric Acid with Ferrocyanide of Potassium and Water.

Med. Prop. and Action. The pure acid is so powerful a sedative poison, that small animals made to breathe air saturated with its vapour died at periods varying from one to ten seconds. A single drop placed on the tongue of a rabbit killed it in eighty-three seconds; and three drops applied to the eye of a cat, caused death in twenty seconds (Christison). So powerful a poison is evidently entirely unsuited for ordinary medicinal purposes. The Dilute Acid is a powerful and direct sedative in doses of gutt ij. - iv. - vj., but the smaller dose should be always given at the commencement. Its action is principally directed on the brain and spinal cord. Dr. Lonsdale,* from a large number of well-conducted experiments, concludes that the immediate effects of the strong acid are exerted upon the brain and spinal cord; and that it also indirectly enfeebles, to a greater or less extent, the contractility of the heart. Dr. Meyer and others, however, consider that it may prove fatal independently of the brain and nerves; and that its fatal effect is owing to a paralysis of the heart, induced by the topical action of the blood, mixed with the acid, on that organ. In small medicinal doses, it acts as a direct sedative, reducing the force and frequency of the heart and arterial system, allaying vascular excitement and irritability, relieving spasm, and inducing a general sensation of tranquillity in the system. Its sedative action in irritable states of the stomach is well known. Externally applied (fl. drm. j. - fl. drs. ij. of the Dilute Acid in fl. oz. x. of Water) it is sedative and anodyne. Care should be taken not to apply it to an ulcerated or denuded surface, as it becomes, when thus applied, absorbed into the system, and may produce serious and even fatal effects. "Scheele's Acid" is about twice as strong as that of the Pharmacopoeia, containing 4 per cent. of the Anhydrous Acid; but different specimens of Scheele's Acid are found to vary in strength. For this reason, it should not be prescribed.

Dose of Acid. Hydrocyanicum Dil., eij. - evj. Of Scheele's Acid, half that quantity.

Incompatibles. The Mineral Acids; the Salts of Iron; Nitrate of Silver.

1532. Therapeutic Uses

Diseases of the Chest. In Spasmodic Asthma, we have a large mass of evidence in favour of Hydrocyanic Acid. Granville recommends it in what he calls Catar-rhous Suffocations; and, according to Thompson, the acid acts directly in this disease by relieving the oppressed state of the pulmonary circulation. Magendie, Elliotson, and others, speak highly of the advantage derived from it in these cases. When it arises in connection with disease of the heart, the relief can be only temporary. (Lonsdale.)

1533. In Angina Pectoris, it has been successfully employed by Brugnatelli, Granville, and others. Dr. Schlessier§; relates a very severe case which, after resisting all other remedies, yielded immediately to Prussic Acid.

1534. In Phthisis, Prussic Acid was recommended and employed by Brugnatelli, in 1807; by Brera, in 1809; by Magendie, in 1815; by Heincken, in 1821; by Granville, in 1820; and by other writers, both English and continental. It was chiefly employed by the above authorities in incipient Phthisis; but Prof. Fantonetti, || in 1839, advised it in the advanced stages, and relates three cases in which there existed large excavations, cured during its administration. Subsequent experience has shown that its value has been very much overrated. " Its action," observes Dr. Cowan,* "is undoubtedly sedative; and it may be prescribed with advantage for the cough, particularly in the early stages, when the system is irritable, and any spasmodic symptoms are present." It often tends, likewise, to allay sickness, and the epigastric pain. In Phthisis Trachealis, Dr. Thompson regards it as almost a specific; and in Hectic Fever, Dr. Granville employed it with great advantage.

* Edin. Med. Surg. Joum., No. lxi. p. 39. - A valuable memoir, from which much of this article is compiled.

Lancet, June 13,1846.

Treatise on the Internal Use of Hydrocyanic Acid, Lond. 1819. § Med. Zeitung, No. xv. 1841. || Gaz. des Hopitaux, Feb. 19,1839.

1535. In Bronchitis, Pneumonia, and Pleurisy, the use of Prussic Acid is strongly advocated by Dr. Granville; but, as vensesection was employed in all the cases adduced by him, it is difficult to say how far the acid assisted in effecting the cure. "There are cases of acute inflammation of the chest," observes Dr. Lonsdale, "in which, after profuse bleeding and evacuants have failed in arresting the disease, when the patient has become excessively weak and restless from want of sleep, and when depletion cannot be carried further with safety, that something of a soothing nature is required. Under these circumstances, Prussic Acid may be attended with considerable advantages; and it probably possesses a superiority over strictly narcotic medicines."