Hydrocyanicum acidum

Hydrocyanic acid is the aqueous solution of hydrogen cyanide (HCN), a volatile, highly toxic compound historically obtained from Prussian blue and bitter almond kernels. Toxicology demonstrates rapid inhibition of cellular respiration leading to sudden loss of consciousness, convulsions, respiratory arrest, and cardiac collapse—central medullary failure with intense vagal phenomena—features that strongly shape the homœopathic picture of spasms, apnoea, and instantaneous prostration [Hughes], [Hering], [Allen]. The mother tincture is prepared from a measured dilute solution of HCN in water (careful standardisation is required), from which triturations and centesimals are made according to pharmacopeial rules [Allen], [Clarke]. In crude medicine small drops of dilute prussic acid were once used as antitussive and gastric sedative; overdosage rapidly proves fatal, a fact mirrored in the remedy’s collapse and suffocation states [Hughes], [Clarke]. [Toxicology]

The pathogenesis arises chiefly from toxicologic observations, small provings, and abundant clinical confirmations in spasmodic respiratory affections (whooping-cough with cyanosis, laryngismus stridulus), epileptiform seizures, anginal collapse, choleraic prostration, and sudden syncope with gasping [Allen], [Hering], [Clarke]. Hahnemann and his contemporaries recorded effects and dosing cautions; later compilers (Allen, Hering) integrated poisonings and clinical experience into the remedy picture [Hahnemann], [Allen], [Hering], [Clarke]. [Proving] [Toxicology] [Clinical]

Hydrocyanic acid epitomises the medicine of the last breath: the organism halts without warning—breath, heart, consciousness—then seizes a single gasp and fights back to a flicker of life. The themes are abruptness, silence, and reflex excitability. Abruptness: attacks begin and end in an instant, with no prodrome beyond a tremor, a hush, or a child’s fixed stare. Silence: in whooping-cough and laryngismus there is a long, awful pause before any sound; in syncope there is no struggle, only a slack fall or stiffening arc; in angina there is constriction without a cry. Reflex excitability: the slightest noise, touch, or attempt to swallow may throw the medullary switch again, re-arresting breath or launching a convulsion [Hering], [Clarke], [Allen]. Kingdom-wise (inorganic acid), the action is direct, chemical, and central; miasmatically syphilitic, it wreaks arrest and dissolution where other remedies inflame. The modalities frame the essence: worse warm, close rooms; worse least motion, noise, touch; worse swallowing and after eating; better cold air, fanning, head low, quiet, and, paradoxically, gentle warmth to chest/epigastrium as a subjective comfort. These recur in Mind (terror of suffocation), Head (blackness on rising), Throat (glottic and œsophageal spasm), Heart (instant power-failure), Respiration (apnœa → gasp → a few breaths), and Skin (blue, cold, clammy).

Differentially, Hydrocyanic acid must be separated from Carbo-veg. (collapse wants air with gaseous distension and a somewhat steadier rhythm; Carbo-veg. is the chronic asphyxiant, Hydrocy. ac. the explosive one), Laurocerasus (similar cyanosis and need for air but slower, less convulsive, more pulmonary), Camphor (icy, but heat is intolerable and spasm is less), Opium (deep, noisy coma without the prolonged silent pause), and Cuprum (convulsions with more clonic violence and less medullary arrest). In pertussis, Corallium rubrum delivers a torrent of coughs; Hydrocyanic acid delivers a long, terrible pause before a feeble gasp. In angina, Glonoinum throbs and bursts; Hydrocyanic acid grips and stops. The clinical art is to recognise the choreography: the hush, the blue, the gasp, the cold sweat—then to place the patient at a window, cool the room, quiet the surroundings, and give the remedy while supporting with measures that match its modalities [Clarke], [Boericke], [Boger].

In practice, Hydrocyanic acid is invaluable when the respiratory centre forgets its work in paroxysms—infantile laryngismus, asphyxia neonatorum, whooping-cough with long apnœic pauses, epileptiform fits with cyanosis, anginoid collapses, and choleraic sinkings with hiccough—especially in nervous, excitable subjects and in the aged exhausted by chronic catarrh. It is not a fever remedy; it is the medicine of the medulla. Improvement is read not in warmth or appetite first, but in lengthening of intervals, shortening of the silent pause, lessened startle-provoked spasm, and a steadier, quieter breath at night.

• Medulla oblongata and respiratory centre—apnoea, Cheyne–Stokes-like gasping, sudden suspension of breathing; spasm of glottis; laryngismus (see Respiration, Throat). [Hughes], [Hering], [Clarke].
• Vagus and heart—instantaneous cardiac weakness, irregularity, syncope, anginoid constriction “as if grasped,” precordial anxiety with cold sweat (see Heart, Chest). [Clarke], [Boericke].
• Cerebro-spinal axis—epileptiform convulsions, opisthotonos, trismus; sudden loss of consciousness (see Mind, Extremities, Back). [Allen], [Hering].
• Larynx and bronchi—whooping-cough with cyanosis, long silent apnœic pauses, then explosive cough; scanty expectoration (see Chest/Respiration). [Clarke], [Boger].
• Stomach and cardia—violent cardialgia, spasm of œsophagus, incessant hiccough, collapse after gastric pain (see Stomach, Throat). [Allen], [Clarke].
• Peripheral circulation—cyanosis, marble coldness, cold clammy sweat; asphyxia neonatorum (see Skin, Generalities). [Hering], [Boericke].
• Infant and senile states—infantile laryngismus, asphyxia at birth; senile syncope with gasping (see Respiration, Generalities). [Clarke], [Boericke].

The mental picture is dominated by suddenness. There is instant loss of consciousness with pallor or lividity, eyes fixed, jaw clenched, and a profound, deathly silence broken only by gasps—then brief revival and anxiety about the heart and breath, a “fear of the next stop” (Mind ↔ Heart/Respiration) [Hering], [Clarke]. When consciousness persists, the patient is terrified, grasps at the throat or chest, and begs for air, a panic strictly secondary to suffocation (Better fanning; Worse warm room) [Clarke], [Boericke]. Irritability and hyper-excitability show as startle from the least noise or touch, which may precipitate a convulsion or laryngospasm (Worse noise/touch) [Hering], [Allen]. Between paroxysms there is dullness, prostration, and a dread of movement, knowing a faint may recur on rising (Worse motion; Better rest) [Clarke]. Memory and sustained thought fail in the exhausted convalescent; any mental effort seems to draw breath away to the head, and the patient sinks back with sighing (Generalities). Melancholy may follow frequent asphyxial attacks, coloured by a sense of imminent death in the night; yet when breathing steadies in cool air the mind clears (Better cool air) [Clarke]. In children there is sudden silence before a cry, then a long gasp and whoop; fear is seen in the eyes more than heard in words (Respiration). The mental portrait, therefore, is not a temperament but a reflex echo of vital arrest: terror of suffocation, instantaneous blankness, and extreme sensitivity to external stimuli [Hering], [Clarke].

Sleep is broken by silent apnœic pauses—the bed-partner hears nothing and then a great gasp; the patient wakes in terror, cold and sweating (Worse night; Better open air) [Clarke]. Drowsiness in the day alternates with sudden starts and jerks; on dropping off a spasm seems to catch the breath (Mind/Extremities). Dreams of suffocating rooms and of falling into water occur, but sleep is too light for elaborate narratives. Only when the window is open and the room cool will the patient sleep in runs; any stuffiness renews the cycle.

Dreams, when remembered, are of choking, being buried alive, or struggling in a crowd for air; they are abruptly cut by waking gasps [Clinical], [Clarke]. With improvement they lessen; there are no peculiar erotic or sanguinary dreams particular to this remedy.

The Hydrocyanic acid centre is the instant arrest of life-processes: breath stops, heart forgets, consciousness flickers; then, with air and quiet, function returns briefly—only to threaten stoppage again. The keynotes are suddenness, silence, cyanosis, gasping, convulsion, and collapse. Modalities are constant: worse least motion, warm close rooms, noise, touch, swallowing; better cool air, fanning, quiet, pressure/warmth to chest and epigastrium (the latter as a subjective comfort), and head low at rest [Clarke], [Boericke], [Allen], [Hering]. Affinities thread medulla and vagus (Respiration/Heart), larynx (glottic spasm), stomach cardia (cardialgia, hiccough), and the convulsive axis (Extremities/Back). Compare Carbo-veg. (collapse wants air but with flatulence and desire to be fanned constantly), Laurocerasus (cyanosis with cough and heart weakness, less convulsive), Camph. (icy collapse unable to bear heat), Opium (apoplectic coma with stertor; less spasm), Cupr. (blue, spasmodic whooping-cough with violent clonic spasms). Choose Hydrocyanic acid when the silence before the gasp, the instantaneous loss of power, and the reflex excitability to small stimuli dominate the case [Clarke], [Boger], [Boericke].

Fever is not characteristic; chill and collapse predominate. In pertussis or bronchitis, slight evening heat may precede the suffocative cycle, but temperature is usually sub-normal during attacks [Clarke]. If high fever appears, choose another remedy for the fever and retain Hydrocyanic acid for the apnœa if the keynote persists.

Chill with deadly pallor; heat is scant and transient; sweat cold and clammy, especially forehead and chest during paroxysm [Clarke], [Boericke]. The alternation pallor→blue→sweat is typical. The patient craves air and coolness, though the skin itself is cold (paradox of asphyxia) (Modalities).

Vertigo occurs on sitting up or turning the head, with blackness before the eyes and a sense of “going off”; returning to the pillow restores some steadiness (Worse motion; Better rest/head low) [Clarke], [Allen]. Headache is pressing and band-like after a suffocative spell; the scalp is cold and damp. Face and head alternate pallor and lividity; the temporal arteries seem to stand still during apnœic pauses, then throb on recovery (Generalities/Heart) [Clarke]. The pupils dilate widely; the gaze fixes or rolls upward in convulsions (Eyes). The slightest sound may cause a shock through the head with a threatening of spasm (Worse noise) [Hering]. There is often post-paroxysmal heaviness, as if the head were full of lead; sleep restores only if breathing remains steady. The cranial picture continuously mirrors the respiratory and cardiac status: arrest → pallor/blue → heaviness, then transient relief by air and quiet [Clarke], [Boericke].

Pupils dilated, glassy; lids half open; stare fixed during apnœa; conjunctivæ pale or slightly livid [Hering], [Allen]. Vision darkens suddenly on rising; black spots precede a faint (Head linkage). On revival the eyes wander and then focus with effort; any bright light or abrupt movement re-excites the tendency to spasm (Worse light/noise) [Hering]. Lachrymation is slight; there is no inflammatory eye picture; the ocular signs are neurological and circulatory. Twitching of lids may usher a fit; after it, the eyes remain heavy and the patient avoids exertion (Generalities).

Roaring or rushing in the ears precedes syncope; hearing seems distant as if the room were receding [Clarke]. Sudden noises precipitate spasm—slamming doors, a shout, even a spoon on a table (Worse noise) [Hering]. No primary otitis; the ear signs are vascular and reflexive, fading when the respiration is steadied by cool air (Modalities).

Nostrils flare during gasps; alæ nasi quiver; the tip is cold and blue (Skin). Odours may disgust or nauseate the patient; tobacco odour aggravates faintness [Clarke], [Hughes]. Sneezing is absent; the nasal sphere speaks in colour (livid) and movement (flaring) rather than discharge.

Face sudden pallor, then lividity; lips and eyelids blue in apnœa; expression anxious or blank [Hering], [Clarke]. Jaw clenched (trismus), froth at lips in violent seizures; after spasm the face is deathly and bathed in cold sweat (Chill/Heat/Sweat) [Allen]. Warm rooms colour the cheeks briefly, then suffocation returns; open air restores a little pink, confirming Better air (Respiration). The facial picture is wonderfully decisive in whooping-cough paroxysms: silence, then drawn face, blue lips, long gasp, weak cough, and collapse (compare Cupr., Cor-r.) [Clarke], [Boger].

Tongue cold, pale; saliva frothy; speech fails suddenly during attacks; voice thin and whispering after (Throat/Respiration) [Hering], [Clarke]. Teeth clench in spasm; grinding may occur. Taste is indifferent; nausea follows gastric spasm. The mouth becomes dry in warm rooms and humidified by cold air, paralleling breath-ease (Modalities).

Trismus during convulsions; jaws set; biting the spoon (convulsive pattern) [Allen], [Hering]. Dental pain is not a feature; the dental note is mechanical: jaw clamps shut in spasm, then relaxes with the first good gasp.

Constriction of throat “as if grasped,” swallowing difficult or impossible; liquids threaten to suffocate as they are seized by spasm of œsophagus and glottis [Clarke], [Allen]. Laryngismus stridulus in children: sudden arrest, fixed stare, no sound, long pause, then crowing inspiration and collapse (Worse at night, Better air) [Clarke], [Boericke]. The fauces look pale; there is no hot sore throat; this is nervous spasm of the gate of breath. Talking aggravates; the patient whispers a word or two and gestures for air (Respiration).

Constriction across the sternum “as if a weight lay” with intense anxiety; patient grasps the chest, demands air, is cold, blue, and limp—an anginoid picture of functional arrest (Heart linkage) [Clarke], [Boericke]. Chest feels empty and powerless after paroxysm; voice husky or extinguished. Pressure and gentle warmth to the chest may comfort between spells (Better pressure/warmth). Stitching pains are not central; the suffering is suffocative rather than inflammatory.

Pulse quick, small, irregular—or suddenly fails; cold sweat and precordial fear accompany every pause [Clarke], [Boericke]. Angina pectoris with faintness and gasps suggests Hydrocyanic acid when spasm and arrest feel central; Glon., Cact. and Spig. stand near; choose by the instantaneous collapse and respiratory arrest (Differentials) [Clarke], [Boger]. Palpitations are less the issue than sheer power-failure: the heart seems to forget to beat, then hurries in a flutter upon revival. Pressure, warmth, and fresh air sustain the patient until the interval lengthens.

Genius-loci: sudden arrest of breathing; long silent interval; then a deep, laboured gasp, followed by a few quick breaths and perhaps a feeble cough; colour swings from pallor to blue and back—this cycle repeats with terrifying brevity [Hering], [Clarke]. Laryngismus stridulus in infants, whooping-cough with prolonged apnœic pause, cyanosed face, and cold sweat, then scant cough—Hydrocyanic acid has often cut the paroxysms by shortening the silent interval and relieving the glottic spasm (Better cold air, fanning) [Clarke], [Boger]. Respiration is shallow between attacks; the chest scarcely moves; sighing attempts interrupt the stillness. Warm, close rooms invariably aggravate; open windows and night air are gratefully taken (Modalities) [Clarke], [Boericke].

Cardialgia is violent, gripping like a mailed hand at the pit of the stomach, extending to the chest with sudden prostration and cold sweat; the attack may end with a faint or gasp (Heart/Stomach cross-reference) [Allen], [Clarke]. Nausea and vomiting may accompany, but the hallmark is collapse rather than irritative diarrhœa. Hiccough violent, incessant in some cases, exhausting the patient; each shock threatens to arrest breath (Worse motion, Worse after eating) [Allen], [Clarke]. The epigastrium is sensitive to pressure during attacks, yet steady warmth may soothe (Better warm application). Breadth of appetite varies; often there is disgust for food after an attack. Rich or hot foods in close rooms precipitate sinking and gasping (Modalities).

Abdomen cold to the patient’s feeling; colic is not striking unless part of a general spasm; walls may tremble during fits [Hering]. Flatulence rises with eructations that sometimes break an impending faint (Better eructation) [Allen]. Stools are not the centre of the case, but sudden choleraic collapse with bluish skin and hiccough falls within Hydrocyanic acid’s sphere (compare Verat., Camph.) [Clarke], [Boericke].

Diarrhœa, when present, is watery with sudden prostration, icy extremities, and thready pulse; anus contracts spasmodically during paroxysms [Clarke]. Constipation is not characteristic. Incontinence may accompany a convulsion; sphincters relax in the final gasp (Generalities).

Suppressed urine during collapse, then a flood as circulation returns; involuntary urination may occur in convulsions [Hering], [Allen]. Burning or tenesmus are not prominent. Albuminuria is not a keynote; the renal sphere reflects the circulatory troughs and peaks.

Aversion to food; slightest meal may bring sinking at epigastrium and hiccough (Stomach) [Allen]. Desire for cold water in sips during laryngeal spasm; large draughts provoke choking (Throat). Alcohol and tobacco aggravate suffocation; stimulants after collapse are poorly borne (Generalities) [Hughes], [Clarke].

Sexual sphere not primary. Sudden syncope during coitus has been noted in sensitive, anginoid patients (Heart linkage) [Clarke]. No urethral catarrh image. The male picture is cardiopulmonary rather than genito-urinary.

Syncope and laryngeal spasm in pregnancy or labour (rare) have been recorded; fainting with cold sweat and gasps (obstetric caution) [Hering]. No characteristic uterine bleeding or menstrual signature; selection rests on the respiratory-cardiac triad in the gravid or parturient patient.

Neck stiff; opisthotonos in severe fits; spinal muscles contract in shocks that lift the trunk (convulsive arcs) [Hering], [Allen]. After paroxysms, dorsal aching and weakness persist; any jar recalls the tendency to spasm (Worse jar). The back shares the general convulsive and collapsed tone, settling as respiration steadies.

Twitchings begin in fingers and toes, mount to hands and feet, then to forearms and legs; clonic jerks pass into tonic spasm with thumbs adducted, toes flexed (convulsive sequence) [Hering], [Allen]. Hands cold, bluish; nails livid; sweat clammy; in severe attacks the limbs lie flaccid like dead weights between shocks (Skin/Chill cross-link). On recovery they tingle as circulation resumes. Least touch or noise renews movements (Worse touch/noise).

Icy coldness with clammy sweat, bluish pallor; cyanosis of lips and nails in every paroxysm [Clarke], [Hering]. Eruptions are not part of the remedy; colour, moisture, and temperature decide. In choleraic states the skin is marbled; in whooping-cough it is first white, then blue, then slowly pink on relief. The surface tells the tale of air—shut it off and the patient is blue; give it and life returns.

Asphyxia / Collapse

• Carbo vegetabilis: collapse with desire for air and fanning; more gastric flatulence and lack of reaction; Hydrocy. ac. is more explosive, with silent arrest and convulsion. [Nash], [Clarke].
• Laurocerasus: cyanosis, coldness, dyspnœa; cough with little expectoration; less convulsive than Hydrocy.; both crave air; Lauro. is slower, more pulmonary. [Clarke], [Boericke].
• Camphora: icy collapse, great coldness; cannot bear external heat; less gasping cycles and less laryngeal spasm than Hydrocy. ac. [Boericke], [Kent].
• Opium: apoplectic coma with stertorous breathing and insensibility; Hydrocy. ac. has silent apnœa, sudden gasps, reflex-provoked spasms. [Hering], [Clarke].

Spasm / Convulsions

• Cuprum metallicum: violent clonic spasms, blue face, thumbs clenched; spasms start in fingers; cough ends in spasm; Hydrocy. ac. more medullary arrest with silent apnœa. [Boger], [Clarke].
• Cicuta virosa: tetanic, opisthotonic convulsions with frightful distortion; less respiratory arrest-gasp cycle than Hydrocy. ac. [Hering], [Farrington].
• Nux vomica: convulsions with extreme spinal irritability and conscious struggle; Hydrocy. ac. shows sudden blankness and cardiac-respiratory standstill. [Kent], [Clarke].

Whooping-cough / Laryngeal spasm

• Corallium rubrum: rapid successive coughs until breath fails; face purple; sound is shrill; Hydrocy. ac. shows longer silent pause and more collapse. [Boger], [Clarke].
• Ipecacuanha: suffocative cough with much nausea and vomiting; Ipec. lacks the long apnœic silence and the convulsive arrest of Hydrocy. ac. [Farrington], [Clarke].
• Antimonium tartaricum: rattling with inability to raise; drowsy and cyanosed; Hydrocy. ac. less rattling, more sudden stop-and-gasp. [Boger], [Boericke].

Angina / Cardialgia

• Glonoinum: bursting head, throbbing carotids, heat; Hydrocy. ac. shows cold sweat, instant collapse, and gasping rather than throbbing congestion. [Clarke], [Kent].
• Cactus grandiflorus: iron-band constriction and cardiac spasm; less apnœic silence; Hydrocy. ac. more medullary arrest with gasp cycles. [Clarke], [Boericke].

Choleraic collapse

• Veratrum album: profuse vomiting and diarrhœa with icy collapse; Hydrocy. ac. has less GI storm and more hiccough/apnœa; both icy and prostrate. [Nash], [Clarke].
• Tabacum: deadly nausea, cold sweat, relief from cool air; Hydrocy. ac. more silent apnœa and convulsive element. [Clarke].

• Complementary: Laurocerasus—shared cyanosis and air-craving; Lauro. for slower pulmonary-cardiac failure, Hydrocy. ac. for abrupt arrest with convulsion. [Clarke], [Boericke].
• Complementary: Carbo vegetabilis—after reviving reaction in deep collapse with air-desire, Hydrocy. ac. cuts the apnœic-convulsive paroxysms. [Nash], [Clarke].
• Complementary: Cuprum metallicum—whooping-cough with spasm; Hydrocy. ac. when apnœic silence predominates, Cupr. when clonic spasm dominates. [Boger], [Clarke].
• Follows well: Aconitum—after stormy onset, if fear subsides but arrest-gasp cycles persist. [Kent].
• Follows well: Antimonium tart.—when rattling stage has lessened, yet long silent pauses remain. [Boger].
• Precedes well: Phosphorus—if later haemorrhagic lung weakness remains after apnœa abates. [Farrington].
• Related (angina): Glonoinum, Cactus—distinguish by collapse and gasp vs throbbing/constrictive patterns. [Clarke].
• Antidotes (toxicologic): Ammonia, chlorine, oxygen, and iron salts chemically; in practice, fresh air and artificial respiration are immediate measures (medical emergency). [Hughes], [Clarke].
• Inimicals not specified; avoid routinism; individualise on the arrest-gasp signature. [Clarke], [Boericke].

Indications: Laryngismus stridulus (infants); asphyxia neonatorum (supportive); whooping-cough with prolonged apnœic pauses, cyanosis, cold sweat; epileptiform or tetanic convulsions triggered by noise/touch; angina pectoris with instantaneous collapse and gasps; violent hiccough with suffocative tendency; choleraic or gastro-cardial collapse with cardialgia and cold sweat [Clarke], [Hering], [Allen], [Boericke], [Boger]. Posology: For violent paroxysms many authors used low to medium potencies (3X–6X–12C) repeated at short intervals during the crisis, then extended; in high-strung nervous persons and in pertussis, 30C–200C may be effective when the arrest-gasp signature is clear—reduce as the silent pause shortens [Clarke], [Dewey], [Kent]. Repetition: During acute attacks dose more frequently, then taper as intervals lengthen; in infants, give sparingly and monitor respiration closely (medical co-management). Adjuncts: immediate cool, moving air; head low; absolute quiet; avoid jarring; gentle chest-pressure/hand warmth for subjective comfort; in suspected poisoning or profound collapse, urgent medical measures (oxygen/airway) are paramount while the remedy may be given as an adjunct [Hughes], [Clarke].
Case pearls:
• “Whooping-cough with long silent apnœa, blue face, cold sweat—Hydrocy. ac. 30C shortened the pause; child slept with open window thereafter.” [Clinical], [Clarke], [Boger].
• “Laryngismus in a restless infant—startles from the least sound; Hydrocy. ac. 6X with strict quiet and fresh air cut paroxysms.” [Hering], [Boericke].
• “Anginoid arrest at night; wakes gasping, pulse gone, forehead cold—Hydrocy. ac. 200C removed the nightly ‘stop and gasp’.” [Clinical], [Clarke].
• “Hiccough with suffocation after gastric spasm; Hydrocy. ac. 6X calmed shocks and steadied breath.” [Allen], [Clarke].

Mind

• Mind—Fear—of suffocation—during attacks; begs for air. Decisive in arrest–gasp states. [Clarke].
• Mind—Unconsciousness—sudden—apoplexy-like. Instantaneous blankness hallmark. [Hering], [Allen].
• Mind—Startled—noise from—convulsions, laryngismus agg. Reflex excitability pointer. [Hering].
• Mind—Anxiety—precordial—with cold sweat. Ties heart and breath. [Clarke], [Boericke].
• Mind—Irritability—after attacks—exhaustion with dread of movement. Post-paroxysmal tone. [Clarke].
• Mind—Desire—air—must be fanned/open window. Air-craving confirmation. [Clarke], [Boericke].

Head

• Head—Vertigo—on rising—blackness before eyes—faints. Motion-agg. syncope. [Clarke], [Allen].
• Head—Heaviness—after suffocative paroxysm. Residual medullary fatigue. [Clarke].
• Eyes—Pupils—dilated—convulsions/ syncope with. Neurologic sign. [Hering].
• Face—Pallor—then cyanosis—apnœa during. Colour swing hallmark. [Clarke].
• Head—Noise—agg.—threat of spasm. Reflex rubric. [Hering].
• Head—Sweat—cold—forehead—attacks during. Collapse marker. [Boericke].

Throat & Larynx

• Throat—Constriction—choking—swallowing agg. Core œsophago-glottic spasm. [Clarke], [Allen].
• Larynx—Spasm—laryngismus stridulus—children. Capital indication. [Boericke], [Clarke].
• Voice—Lost—after suffocative paroxysm. Exhausted register. [Clarke].
• Swallowing—Liquids—suffocate—agg. Pathognomonic spasm. [Clarke].
• Cough—Whooping—long apnœa before whoop—cyanosis. Hydrocy. signature. [Boger], [Clarke].
• Respiration—Wants windows open—fanning amel. Air modality. [Boericke], [Clarke].

Stomach

• Stomach—Pain—cardialgia—collapse with—cold sweat. Gastro-cardiac nexus. [Allen], [Clarke].
• Hiccough—violent—threatens suffocation. Shock-to-apnœa rubric. [Allen].
• Nausea—after eating—sinking at epigastrium—faintness. Post-prandial collapse. [Clarke].
• Eructations—ameliorate—impending faint. Small rescue sign. [Allen].
• Stomach—Spasm—warmth/pressure amel. Palliative pointer. [Clarke].
• Appetite—aversion—after attacks. Exhaustion rubric. [Clarke].

Chest & Respiration

• Respiration—Arrest—sudden—followed by gasps. Core pathognomonic rubric. [Hering], [Clarke].
• Respiration—Apnœa—long silent pause—pertussis. Selection clincher. [Boger].
• Chest—Constriction—across sternum—anxiety with. Anginoid sign. [Clarke].
• Respiration—Cold air—amel.—warm room—agg. Master modality. [Clarke], [Boericke].
• Cough—Paroxysmal—cyanosis—collapse. Severe pertussis rubric. [Clarke].
• Respiration—Cheyne-Stokes-like—periodic gasps. Medullary pattern. [Hughes], [Clarke].

Heart

• Heart—Syncope—sudden—cold sweat. Cardio-vagal collapse. [Clarke], [Boericke].
• Pulse—Irregular—intermittent—weak—attacks during. Rhythm arrest. [Clarke].
• Angina pectoris—apnœa—collapse—air-craving. Differentiates from throbbing angina. [Clarke], [Boger].
• Palpitation—faintness with—motion agg. Motion-triggered failure. [Allen], [Clarke].
• Precordium—Anxiety—grasping sensation. Subjective hallmark. [Clarke].
• Heart—Warmth/pressure—amel.—subjective only. Palliative note. [Clinical], [Clarke].

Extremities / Nervous

• Convulsions—epileptiform—noise/touch agg. Reflex convulsive rubric. [Hering].
• Opisthotonos—attacks with. Severe spasm sign. [Allen].
• Trismus—jaws clenched—froth at mouth. Tetaniform aspect. [Hering].
• Hands—Blue—cold—sweaty—attacks during. Peripheral cyanosis. [Clarke].
• Weakness—sudden—collapse—least motion. Global prostration sign. [Clarke].
• Trembling—post-paroxysmal—exhaustion. Recovery rubric. [Clarke].

Generalities

• Generalities—Asphyxia—tendency to—paroxysmal. Central essence. [Clarke], [Hering].
• Generalities—Collapse—sudden—cold sweat. Crisis marker. [Boericke].
• Generalities—Air—craves—fanning amel. Master modality. [Clarke].
• Generalities—Motion—least—agg.—syncope. Bedside caution. [Allen].
• Generalities—Noise/touch—agg.—spasm. Reflex excitability. [Hering].
• Generalities—Warm room—agg.—open air—amel. Environmental key. [Clarke].

Hahnemann, S. — Materia Medica Pura / Chronic Diseases (1821–1834): early notes on Acidum hydrocyanicum effects and cautions; proving fragments (spasm/collapse).
Hering, C. — The Guiding Symptoms of Our Materia Medica (1879–1891): toxicology and clinical confirmations—apnœa, convulsions, laryngismus, cyanosis.
Allen, T. F. — Encyclopædia of Pure Materia Medica (1874–1879): collated provings/poisonings; gastric spasm, hiccough, syncope, whooping-cough data.
Hughes, R. — A Manual of Pharmacodynamics (late 19th c.): physiological action (medullary and cardiac depression); toxicologic sequence; therapeutic deductions.
Clarke, J. H. — A Dictionary of Practical Materia Medica (1900): clinical picture—laryngismus, pertussis with long apnœa, anginal collapse; modalities; relationships.
Boericke, W. — Pocket Manual of Homœopathic Materia Medica (1901): keynotes—spasms, asphyxia, whooping-cough, collapse, cold sweat; modalities.
Boger, C. M. — Synoptic Key of the Materia Medica (1915): repertorial pointers—long apnœa before whoop, reflex excitability, collapse differentials.
Kent, J. T. — Lectures on Homœopathic Materia Medica (1905): comparative insights—Camph., Carbo-veg., Laurocerasus, Glon., Cupr.—miasmatic framing.
Nash, E. B. — Leaders in Homœopathic Therapeutics (1899): collapse/spasm comparisons (Carbo-veg., Verat., Camph.) applied to Hydrocyanic acid states.
Dewey, W. A. — Practical Homœopathic Therapeutics (early 20th c.): pertussis, laryngismus, hiccough, angina groupings; posology hints.
Farrington, E. A. — Clinical Materia Medica (1890): organ-affinity method; nervous–respiratory axis; differentials in spasmodic diseases.
Tyler, M. L. — Homœopathic Drug Pictures (20th c.): vivid clinical notes on arrest-gasp cycles and bedside management (air, quiet) with Hydrocyanic acid.