Last modified on January 5th, 2019


Homeopathic remedy Acidum Hydrocyanicum from A Manual of Homeopathic Therapeutics by Edwin A. Neatby, comprising the characteristic symptoms of homeopathic remedies from clinical indications, published in 1927.

      Prussic Acid. (HCN). The acidum hydrocyanicum dilutum of the British Pharmacopoeia is a 2 per cent. solution of the pure acid, and equal parts of it and rectified spirit make the 1c or 2x dilution of the British Homoeopathic Pharmacopoeia. Subsequent dilutions are made with rectified spirit. In nature prussic acid is found in the bitter almond and in the kernels of a number of fruits, notably the apple, cherry, plum and apricot, and in smaller quantities in the bark and leaves of these trees and also in those of the laurel (Prunus laurocerasus). It does not exist in the free state in the kernels and leaves, but in combination as a glucoside named amygdalin, of which it is a decomposition product, the amygdalin giving off prussic acid under the influence of water and a ferment, emulsin, which is present in the plant.


      PRUSSIC ACID is a general protoplasmic poison, and has an extremely rapid action. It first stimulates, and then paralyses the central nervous system. In very large doses it acts so rapidly that there is no time for symptoms to be developed- death is almost instantaneous, the animal experimented on falls to the ground with a slight convulsion or a scream, and death ensues in a few seconds from cessation of the circulation and respiration. In doses not so immediately fatal, prussic acid causes, first, salivation with burning and bitter taste followed by numbness in the mouth and throat. There are: confusion in the head, difficulty in breathing, and protruding eyes, with widely dilated and immobile pupils. A sensation of warmth is felt in the stomach accompanied with nausea, and vomiting takes place. The patient becomes unconscious and violent convulsions supervene that are primarily tetanic, there are trismus and opisthotonos, and the convulsions are associated with paralysis and involuntary evacuations from the bladder and bowels. Respiration becomes slow and gasping till it ceases, while the heart continues to beat fro some time after. An ordinary fatal dose is from 1 to 1 1/2 gr. of the pure acid.

It will be gathered from the above symptoms of poisoning that the stress of the poison falls on the medulla oblongata and lower parts of the brain. The inhibitory vasomotor centre is at first stimulated, and through the vagus causes a slow pulse; at the same time the blood-pressure rises from stimulation of the vasoconstrictor centres. Later, when stimulation gives place to paralysis of these centre, the blood-pressure falls, but, as by then the heart muscle has become affected and weakened, the pulse does not quicken but remains slow.

Prussic acid seems to have a specific action on the stomach and to lessen its movements.

The oxygen absorbed by the tissues is diminished by prussic acid, and there is lessened production of carbonic acid; on this account the oxyhaemoglobin of the blood is not reduced in the capillaries, so that the blood in the veins has the same bright colour as in the arteries. Post mortem the venous system is found distended with blood, while the arteries are empty, the vessels of the brain and cord are full of blood, the lungs tinged with it, and the mucous membrane of the stomach reddened.

Prussic acid is changed to sulpho-cyanides in the tissues, and as such is partly excreted in the urine.

Applied in solution to the skin, it produces numbness and partial loss of sensation, but these phenomena are purely local, as they do not occur from its internal administration. The action of prussic acid on the system is ver evanescent, and if the patient recovers from the poison he rapidly gets well.

The symptoms elicited from the provers of dilute prussic acid and of oil of bitter almonds and cherry-laurel water (laurocerasus) do not add many to those obtained from poisonous doses.

Mental.-Further symptoms from these sources are the mental, in which the prover shows himself ill-humoured, irritable morose and disinclined for work.

Head.-There is an intoxicated feeling in the head, confusion, giddiness, buzzing in the ears, and pressure, hardly amounting to pain, which shifts from one part of the head to another but is felt most in the forehead over the eyes, the parietal region and the occiput. There may be a shooting or boring pain in the orbits. A sensation of coldness in the forehead and vertex, as of a cold wind blowing over the part, is felt.

Eyes.-A mist comes before the eyes with dimness of vision, and the eyes are staring and wide open and the pupils dilated and immobile.

The face is red and appears as if swollen, and twitchings of the facial muscles and perhaps trismus occur.

Respiration.-In the larynx a scraping feeling is invariably produced, with hoarseness, increased secretion of mucus, and a constricted sensation in the throat and chest, accompanied by prickling in the bronchi which causes a hacking cough. There are sharp prickings, worse at night, or stabs in various parts of the chest, especially below the left nipple.

Circulation.-The pulse is in most cases slowed by about ten beats, but in a few cases is quickened.

Digestion.-The saliva is increased and there may be either nausea and a sensation of a lump in the stomach, followed by vomiting or, more usually, a sensation of emptiness at the epigastrium, with increase of appetite. Deglutition is spasmodic and an audible gurgling in the oesophagus and bowels has been noticed.

Urine is increased and watery.

Sleep.-In all the provers, as the effects were passing off, great sleepiness came on with sometimes irresistible yawning, and also general weakness and great weariness in the legs.

Chills and Heat.-Chills alternating with heat occurred, but the general tendency was to heat and perspiration.


      The medicinal use of prussic acid closely follows its pathogenesis and is confined to affections of the nervous, respiratory and circulatory systems and of the stomach.

Nervous.-The similarity of its convulsions to those of epilepsy has led in many cases to its successful employment in that disease when not due to an organic lesion. It should be given frequently and continuously. The tetanic nature of the convulsions of prussic acid renders it a remedy for tetanus (nux vom.) and it has also proved of service in chorea.

Respiratory.-Its action on the respiratory system suggests its employment in spasmodic respiratory disorders such as laryngismus stridulus, whooping-cough and recent spasmodic asthma, and for the dry, tearing cough, worse at night, that occurs in consumptives; in all these complaints it has proved its value.

Circulatory.-It is useful for functional cardiac complaints, such as palpitation and irregularity of the heart beats.

Digestive.-In gastric affections it has found a place amongst the remedies for dyspepsia, for neuralgic pains in the stomach and abdomen, for sinking at the epigastrium, especially at the climacteric, and for the vomiting of pregnancy. In these affections the symptoms are worse when the stomach is empty and better after food.

Skin.-Purple colour of the skin and mucous membranes is a distinguishing feature of prussic acid.. It has been used in cyanosis neonatorum. It has been applied externally to allay itching by its power to cause anaesthesia of the skin. Care must be taken that the surface is unbroken lest poisoning result.

It will be observed that none of the above diseases for which prussic acid is valuable are of a chronic nature nor depending on organic changes in the tissues; it has never been proved to effect permanent structural changes, its action though violent is transitory and its therapeutic sphere is the violent, transitory phases of illness. For the permanent, underlying causes other remedies must be sought for.


      1) Violent, transitory, spasmodic or convulsive affections.

2) Convulsive attacks of mainly tetanic character; tetanus, epilepsy (palliative).

3) Constriction in the throat, larynx and chest.

4) Spasmodic respiratory diseases; laryngismus, asthma, whooping- cough.

5) Gastric affections where there is a sensation of sinking at the epigastrium, which is relieved by taking food.

6) Purplish colour of the skin and mucous membranes,

7) Sleepiness, weariness of the limbs.


      From warmth of the room, night (cough).


      From open air and from food (gastralgia).

About the author

Edwin Awdas Neatby

Edwin Awdas Neatby 1858 – 1933 MD was an orthodox physician who converted to homeopathy to become a physician at the London Homeopathic Hospital, Consulting Physician at the Buchanan Homeopathic Hospital St. Leonard’s on Sea, Consulting Surgeon at the Leaf Hospital Eastbourne, President of the British Homeopathic Society.

Edwin Awdas Neatby founded the Missionary School of Homeopathy and the London Homeopathic Hospital in 1903, and run by the British Homeopathic Association. He died in East Grinstead, Sussex, on the 1st December 1933. Edwin Awdas Neatby wrote The place of operation in the treatment of uterine fibroids, Modern developments in medicine, Pleural effusions in children, Manual of Homoeo Therapeutics,

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