Acidum Hydrocyanicum Dilutum.
Dose.—One to ten drops of the medicinal acid, in almond or arabic emulsion, or simple water: very cautiously increase the dose until its effects are apparent. The acid procured at different places, and in different parcels, is found to be very variable in its strength, and therefore requires the utmost precaution in its administration.
Therapeutic Action.—Prussic acid is sedative, anodyne, narcotic; it is an energetic poison. Its effects on all classes of animals are loss of sensation and voluntary motion, with convulsive movements. A single drop of the pure acid, applied to the throat or eye of a vigorous dog destroys it in a few seconds.
In small doses on man it produces an increased flow of saliva, irritation in the throat, bitter taste, nausea, quick and sometimes slow respiration, vertigo, pain in the head, drowsiness, and sometimes an increase, and at others a reduction, in the frequency of the pulse—salivation and ulceration of the mouth have occurred from its use.
In poisonous doses it causes faintness, vertigo, tetanic convulsions, insensibility, dilated pupils, small pulse, and difficult and spasmodic respiration. These symptoms continue but for a short time.
In very large doses death succeeds so speedily, that the foregoing symptoms are not manifested—the pulsations cease; two or three deep inspirations may occur, and finally a state of insensibility and death follows.
Post-mortem appearances generally present a glaring, or peculiar staring expression of the eyes and countenanoe, the peculiar odor of the acid is observed, and venous engorgement, while the arteries are empty; the blood is fluid and dark, or bluish, and the mucous membrane of the stomach injected.
The vapor of the acid produces numbness of the part to which it is applied from its action on the nerves. It acts as an irritant on the mouth and nose; causes salivation, vomiting and purging. It is supposed to be absorbed, and thus act on the brain and nervous system, but its effects are so rapidly manifested that many suppose it acts directly upon the nerves of the part to which it is applied, and its further action is extended to the sensorium-commune with the rapidity of electricity.
When prussic acid causes death, it may arise from an arrest of respiration, or from a stoppage of the heart's action. In some instances death occurs so suddenly that it can not be attributed to obstructed respiration; while in others the heart still pulsates, as has been observed by experimenting upon dogs and rabbits.
It appears to act as a direct sedative to the nerves, whether used externally or internally, and thereby suspends innervation, and hence its sedative action upon the vascular system, and its capacity to lessen pain and spasmodic action when present.
Hydrocyanic acid was at one time in high repute in pulmonary diseases, such as phthisis, asthma, pertussis, dyspnoea, spasmodic cough, chronic catarrh, etc., to allay nervous irritability and reduce vascular excitement. In incipient phthisis it is said to arrest the disease in some cases, while in the confirmed stages it acts as a palliative by lessening the cough, night-sweats and hectic symptoms.
Its exhibition in various neuropathic affections, as chorea, hysteria, epilepsy, tetanus, etc., has, it is asserted, been attended with manifest advantage. In imperfect digestion attended with pain in the stomach, it has been associated with tonics and found beneficial. It has been employed, with equivocal advantage, as an anodyne in cancer, tic doloureux, rheumatism, etc. Breva extolled it as an anthelmintic, but Elliotson has employed it without the least advantage for this purpose.
Antidotes.—The antidotes to this acid and those substances which contain it (as the cherry laurel, bitter almonds and its essential oil, etc.), or the agents found most effectual in the treatment of its effects, are chlorine, ammonia, cold affusions, and artificial respiration. Owing to the rapidly fatal character of the poison, physicians are but seldom called in season to treat its effects.