Vaso-Motor System

The vaso-motor centre in the medulla is first briefly stimulated, but soon profoundly paralyzed; blood-pressure therefore falls very low.


The respiratory centre is paralyzed even more readily than the cardiac or vaso-motor centres, consequently the respirations quickly diminish both in force and frequency. Unless the heart has been instantaneously stopped by a large dose, asphyxia is the cause of death, and the heart goes on beating after the respirations have stopped. Occasionally, if the dose be small, all three centres may be at first very transitorily stimulated, so that for a few seconds the pulse and respiration may be increased in frequency, and blood-pressure may rise.

Nervous System

Cerebrum. - Medicinal doses of hydrocyanic acid have no effect on the cerebrum. Toxic doses cause deep insensibility and coma. In man convulsions are rarely seen; in animals they are common. It is probable that the coma and convulsions are due to the direct effect on the brain, but they may in part be due to the altered circulation through it, or the asphyxia.

Peripheral Nerves And Muscles

In animals dead of hydrocyanic acid poisoning these are unexcitable. This paralyzing effect is due to direct action on the nerves and muscles themselves, for it does not occur in the peripheral part of a limb if it is connected with the rest of the body only by its nerve. In this case, as no blood is circulating through the distal part of the limb, no hydrocyanic acid reaches it; but if the acid be applied locally to the severed limb, the nerve and muscles are paralyzed. This explains the local anaesthetic effect of hydrocyanic acid.

Shortly before death the spinal cord is paralyzed. The pupil is dilated. We do not know of any effect of hydrocyanic acid on the kidneys, nor how it is excreted. It slightly reduces the temperature.

Therapeutics of Potassium Cyanide and Diluted Hydrocyanic Acid


Lotions of a strength of about 1 to 48 of the diluted acid in water are valuable for allaying itching due to any cause. If the skin is abraded they must not be used.


Hydrocyanic acid may be administered as the official diluted acid, oil of bitter almond (3 to 14 per cent. of acid), bitter almond water, cherry laurel water (B. P.), the fluid extract, infusion and syrup of wild cherry, and as potassium cyanide. Reference should be made to each of these. Small doses, 2 to 3 minims . 12 to .20 c.c of the diluted acid, are used for their sedative effect on the nerves of the stomach, to allay vomiting, and to relieve gastric pain, whatever be their cause, and often with good effect. A useful way of giving it is in an effervescent draught. Since the effect of the remedy is transient, it should be given at frequent intervals. It is a common ingredient of cough mixtures, for by its depressing effect on the central nervous system it diminishes reflex excitability, and is consequently most serviceable for a dry, hacking cough by means of which nothing is expectorated. The uses of potassium cyanide are similar to those of hydrocyanic acid.



With a large dose of hydrocyanic acid the symptoms usually begin in a few seconds; it is rare for them to be delayed more than two minutes. The patient is perfectly insensible; the eyes are fixed and glistening, the pupils dilated, the limbs flaccid, the skin cold and clammy. The respiration is slow, deep and convulsive; the pulse almost imperceptible. Hydrocyanic acid kills by respiratory failure, Post-mortem. - There may be an odor of hydrocyanic acid about the body, which is very livid. The fingers are clenched, the jaws firmly closed and there is froth at the mouth; the eyes are fixed and glistening and the pupils dilated. The stomach may be a little reddened; the blood is very dark.


Wash out the stomach immediately; the physician almost never has the opportunity. If emetics are available, large doses must be given promptly, for every moment is important. Vomiting may be induced by inserting the finger into the throat. Give ether or brandy and 1/50 gr. .0013 gm. of atropine subcutaneously. Use inhalations of Ammonia and artificial respiration. Cold affusions, or alternately hot and cold, may be available. Antal, from an experience of forty instances of poisoning, believes that Cobalt nitrate is the best chemical antagonist. A thirty per cent. solution of hydrogen dioxide may be employed to wash out the stomach. Intravenous injections of sodium hyposulphite (producing theoretically the relatively harmless sulphocyanide) enable animals to survive an otherwise lethal dose.

18. Potassii Bichromas, see Chromium.

19. Potassii Hypophosphis, see Phosphorus.