• Stomach & Duodenum. Acid dyspepsia: sour eructations/heartburn, sour vomiting (infants), intolerance of fats and rich foods; emptiness with acidity [Hering], [Allen], [Boericke], [Clarke].
• Intestines (Infants). Greenish, sour, curdled stools; diarrhoea after milk; pin-worms with itching anus, worse at night [Hering], [Allen], [Clarke], [Boericke].
• Metabolism (Acid–Alkali). Uric-acid diathesis: urates in urine, gravel, gout; lactic-acid excess after exertion; sour sweat; tendency to acetonaemia in children [Schussler], [Clarke], [Boger], [Phatak].
• Mucosae (Yellow–creamy). Canary-yellow or lemon-yellow creamy coating on back of tongue; yellow creamy nasal or faucial discharge/patches [Clarke], [Boericke], [Allen].
• Throat. Follicular pharyngitis with yellow creamy exudate; subacute tonsillitis, post-diphtheritic catarrh (not a membrane remedy) [Clarke], [Boger].
• Joints & Tendons. Gouty and lactic-acid myalgias; tennis-elbow insertions sore; morning stiffness in uratic subjects [Boger], [Phatak], [Boericke].
• Urinary. Acid urine, phosphates/urates; brick-dust sediment; thread-worms and enuresis with acidity [Allen], [Clarke].
• Skin. Acid urticaria, especially after shellfish or sweets; intertrigo excoriated by sour sweat [Boericke], [Clarke].
• Head & Nerves. Sick-headache from acidity (after fats, pastry, sweets), with yellow-coated tongue base and sour risings [Nash], [Clarke].
• Female & Lactation. Acid dyspepsia in pregnancy; vomiting sour, infant colic from rich milk; nipple fissures with creamy discharge (adjunct) [Clarke], [Boericke].

• Alkaline drinks or food; bicarbonate-containing water; milk diluted with alkaline water [Clarke], [Boericke], [Schussler].
• Moderate eating; light, plain diet (dry toast, simple cereals) [Nash], [Clarke].
• Eructations; bringing up wind; gentle walking after meals [Allen], [Clarke].
• Warmth of abdomen; hot-water bottle for cramp but not for heartburn [Boger].
• Early evening light meal; avoiding late suppers [Nash].
• Sitting upright after food; avoiding recumbency [Clarke].
• Avoiding sour/acid foods (citrus, vinegar, pickles) and rich fats [Boericke].
• Short nap after relieving stool in infants (post-acid diarrhoea lull) [Hering].
• Bathing eruptions with mild alkaline lotion (urticaria, chafing) [Clarke].
• Rest after over-exertion in lactic-acid myalgia; stretching then warmth [Boger].
• Cool rooms for bilious-acid sick headache; fresh air without draught [Nash], [Clarke].
• Regular bowel routine (prevents sour fermentation) [Clarke].

• Sour/acid foods (citrus, vinegar), sweets/sugar, pastry, fats, ice-cream [Allen], [Boericke], [Clarke].
• Milk (undigested → curdled vomiting, sour stools), especially in infants [Hering], [Allen].
• Night, especially after midnight: worms, sour risings, heartburn, itching anus [Hering], [Allen], [Clarke].
• Over-eating or hurried eating; eating late at night [Nash], [Clarke].
• Physical exertion (lactic-acid myalgia, tendon soreness) [Boger], [Phatak].
• Weather changes toward damp cold (gouty stiffness, urticaria) [Phatak], [Boericke].
• Mental work after meals (sick-headache, sourness) [Nash], [Clarke].
• Lying on right side after food (heartburn, sour regurgitation) [Clarke].
• Beer, sweet wines, and shellfish (urticaria, gastric upset) [Clarke], [Boericke].
• Acid sweat or sour diapers excoriating skin (intertrigo) [Hering], [Boericke].
• Suppression of usual stool (fermentation increases) [Clarke].

The Nat-p. temperament is digestively coloured: irritability and peevishness rise and fall with acidity, smoothing as the stomach quiets (Stomach cross-link) [Clarke], [Nash]. Mental work after meals triggers a sour-headed confusion—ideas dull, averse to exertion, relieved by a walk and a small alkaline draught (Modalities) [Nash], [Clarke]. Children are fretful, cry before the sour, curdled stool, then grow placid until the next feed; the diaper’s sour odour is diagnostic (Intestines/Skin) [Hering], [Allen]. Anxiety is practical, centred on food choices and fear of “biliousness”; they read labels to avoid acid/sugar, a coping trait learned by relapse (Food & Drink) [Clarke]. Gouty subjects grow snappish in damp weather, worsened by heaviness in feet and morning stiffness (Joints) [Phatak], [Boger]. Melancholy is mild, dyspeptic—a yellow-tongued gloom that lifts with a good alkaline day; there is none of the deep weeping of Nat-m. (Differential) [Clarke], [Kent]. In headaches they seek quiet and cool air, dislike fuss; if pressed to eat they grow irritable (Head/Modalities) [Nash]. Students complain of “foggy” head after sweets/pastry; a glass of alkaline water and a walk restore clarity (Affinities: Metabolism) [Clarke]. During worm aggravations the child is restless at night, grinds teeth, and is cross on waking until bowels move (Intestines) [Hering]. Overall the mind tracks acidity: as sour risings ebb, the temper steadies and attention returns [Clarke], [Nash], [Boericke].

Sick-headache from acidity: dull frontal or bi-temporal ache with yellow-coated tongue base, sour risings, and nausea after sweets/fats or study after meals; better alkalies, open air, and gentle walking (Stomach link) [Nash], [Clarke], [Boericke]. A band-like pressure accompanies heartburn, rising after late suppers (Modalities) [Clarke]. In uric-acid subjects, morning heaviness and dizzy turns on rising occur when urine is scant and brick-dust sediment appears (Urinary) [Clarke], [Boger]. Headache in damp changes with joint stiffness (Metabolism/Joints) [Phatak]. Children with acid diarrhoea moan and burrow the head in pillow, settling after a stool (Intestines) [Hering]. Light and noise are not extreme aggravations; the gastric–metabolic axis is the true driver [Nash], [Clarke].

Yellowish tinge of inner canthi and a sticky, creamy morning gum suggest the mucous affinity (Mucosae) [Clarke]. Photophobia is mild; blur accompanies sick-headache and clears as stomach settles [Nash]. In gouty states, sand-like grittiness in lids is noted (uratic terrain) [Boericke].

Ringing with sick-headache after pastry/sweets; fullness when the stomach is sour (Head link) [Clarke]. Pruritus of meatus in worm cases (reflex) [Hering].

Yellow, creamy discharge or posterior yellow catarrh, worse nights and in warm rooms, better cool air (Mucosae) [Clarke], [Allen]. Sneezing after pastry or wine in the dyspeptic (Food link) [Clarke].

Pasty pallor with slight sallowness; greasy or acid sweat about mouth in children (Skin) [Hering]. Expression anxious after dietary errors, relieved with eructation and alkali (Stomach) [Clarke].

Tongue: anterior part relatively clean, back coated canary-yellow or lemon-yellow, thick and creamy—a hallmark (Mucosae affinity) [Clarke], [Boericke], [Allen]. Mouth acid; saliva sour; taste sour or bitter after rich foods [Allen], [Clarke]. Aphthous patches with yellow creamy base occur in acidic states [Clarke].

Teeth sensitive after sweets; grinding at night with worms (pin-worms) [Hering]. Gum-line soreness in the uric-acid habit (Metabolism) [Boericke].

Follicular pharyngitis or subacute tonsillitis with yellow creamy exudate/points, worse after fat/sour indiscretions; thick hawking in morning; not a destructive membrane like the serpents (Differential) [Clarke], [Boger]. Heartburn throws acid fluid up to the fauces, excoriating (Stomach link) [Allen].

Core. Acid dyspepsia: sour eructations, heartburn, water-brash, deathly sour vomiting (especially infants), intolerant of milk/fats/sweets; emptiness with acidity; craves nothing heavy [Hering], [Allen], [Clarke], [Boericke]. Gastralgia after pastry or fried foods, with yellow tongue-base and sour risings; better alkalies, dry toast, slow walking [Nash], [Clarke]. Milk curdles and is vomited in white curds soon after feeding; stool and vomit both sour (Infants) [Hering], [Allen]. Belching relieves both pain and head pressure (Head cross-link) [Clarke].

Sour fermentation: much wind, rumbling, acid stools excoriating; colic around umbilicus better after sour stool (counter-intuitive but classic) [Hering], [Allen]. Pin-worms with nocturnal itching; grinding teeth; restless sleep [Hering]. Tendency to biliary dyspepsia when diet is rich, but picture stays acid rather than bitter (Nux/Chin contrast) [Clarke].

Urine acid with brick-dust urates; gravel, ardor at close; phosphates/urates visible (cloud) [Allen], [Clarke]. Backache and stiffness improve as urine clears under alkaline regime (Joints/Metabolism) [Boger], [Phatak].

Greenish, sour, curdled stools in infants; sour diarrhoea after milk; anus excoriated; napkin smells sour [Hering], [Allen], [Boericke]. Pin-worms: itching at night, child picks and is restless; Nat-p. modifies the acid terrain while hygienic measures clear infestation [Hering], [Clarke]. Constipation alternating with sour stools in adults after errors of diet (Food link) [Clarke].

Seminal emissions after rich suppers with acid dyspepsia (reflex) [Clarke]. Itching of scrotal skin from acid sweat (Skin) [Boericke].

Pregnancy acidity: heartburn, sour vomiting, yellow tongue-base; better alkaline sips, plain diet [Clarke], [Boericke]. Infantile colic/diarrhoea in nurslings when mother lives on sweets/fats—correct maternal diet and give Nat-p. (terrain) [Clarke], [Hering]. Vaginal discharge sometimes yellow creamy in acid states (adjunct finding) [Clarke].

Morning hawking of yellow creamy mucus; less stringy than Kali-bi., more buttery-yellow (Differential) [Clarke], [Allen]. Breath foul on acid mornings; clears after alkaline drink (Mouth) [Clarke].

Palpitation after sweets/pastry or on lying right side with heartburn; settles as acidity is corrected (Stomach cross-link) [Clarke], [Nash]. In gouty subjects pulse feels labile with weather changes (Metabolism) [Phatak].

A sour rising may provoke short cough after meals; retro-sternal burn climbs into throat (GORD-like) [Clarke]. Stitchy chest wall pains after exertion in lactic-acid types (Joints/Muscle) [Boger].

Lumbosacral ache with acid urine and urates; tight hamstrings after over-exertion (lactic-acid) [Boger], [Phatak].

Gouty pains in great toe, ankle, and fingers; nodes soft early; better with diet discipline and Nat-p. [Clarke], [Boericke]. Tennis-elbow and enthesopathies after exertion with acid sweat [Boger]. Morning stiffness eases with motion and a light breakfast (Generalities) [Phatak].

Urticaria after shellfish or sweets; wheals pale with red areola, itch worse heat of bed; better alkaline lotion and light diet [Clarke], [Boericke]. Intertrigo and napkin rash excoriated by sour stools/sweat (Infants) [Hering]. Acne in pastry-eaters; lesions wax and wane with diet (Metabolic) [Clarke].

Sleep is disturbed after late or rich suppers by heartburn, sour risings, and flatulence; the patient sits up, sips alkaline water, and dozes only when stomach is quiet [Clarke], [Nash]. Infants start, cry, and draw up legs before sour, curdled stool; once relieved, they fall into short, sweet sleep until the next feed (Intestines) [Hering], [Allen]. Worm irritation brings restless nights, tooth-grinding, and anus itching at 1–3 a.m., easing toward dawn (Rectum) [Hering]. Sick-headache sleepers prefer cool room, little pillow; heat of bed makes the head heavy (Head/Modalities) [Nash]. Pregnant patients wake with acid water-brash and must prop up; small alkaline sips allow return to sleep (Female) [Clarke]. Dreams revolve around food mistakes and school tasks, echoing the dyspeptic and student types (Mind) [Nash]. As the diet is corrected and acidity buffered, first sleep lengthens, night wakings shrink, and morning heaviness fades (Generalities) [Clarke].

Of soured milk, spilled food, exams and sums after late study; waking with sour taste and frontal weight (Mind/Head) [Nash], [Clarke].

Not a primary fever medicine. In acid diarrhoeas of infants there may be slight evening heat with sour sweat; better after stool and alkali (Intestines) [Hering], [Allen].

Chilliness after dietary errors; heat internal with heartburn; sweat sour, excoriating folds (Skin) [Boericke], [Clarke].

Worse: sour/acid foods, sweets, pastry, rich fats, milk undiluted, beer, sweet wines, shellfish. Better: alkaline drinks, plain simple fare, dry toast, diluted milk, small, frequent meals, gentle walking after food [Clarke], [Boericke], [Nash], [Allen].

Nat-p. harmonises acid–alkali balance: when acidity dominates the organism, mucosae weep yellow creamy secretions, the tongue-base is canary-coated, the stomach throws sour eructations and curdled milk, the bowels pass greenish sour stools (infants), the urine shows urates, and the joints/tendons ache with lactic-acid effort pains [Schussler], [Clarke], [Boericke], [Boger]. The modal logic is exact: worse from sour/acid foods, sweets, fats, milk, night, over-eating, mental work after meals, damp-cold, and exertion; better from alkalies, simple diet, moderation, upright posture, eructation, gentle walking, warmth to abdomen, and cool fresh air for the head [Clarke], [Nash], [Boericke]. Distinguish from Robinia (intense acidity and night heartburn but less uric-acid/joint sphere), Iris (bilious, acrid vomiting with migraine, more burning and acridity), Nux (spasmodic irritability, liver strain, not the yellow creamy signature), Kali-bi. (tough stringy plugs, not creamy-yellow base), Mag-phos. (cramps > heat/pressure, not acid terrain), Nat-m. (watery discharges, tearful reserve; less yellow creamy tongue), and Ant-crud. (thick white tongue, disgust for sour, warts) [Farrington], [Clarke], [Boger], [Boericke], [Phatak]. As the terrain corrects, mind clears, sleep steadies, urates lessen, and gouty stiffness eases—an orderly retreat of acidity through its tissues [Clarke], [Schussler], [Boericke].

• Robinia — Ferocious hyperacidity, nightly heartburn, sour vomiting; less uric-acid and creamy-yellow mucous signature than Nat-p. [Clarke], [Boericke].
• Iris versicolor — Bilious-acrid vomiting with migraine; burning, copious acridity; tongue not characteristically yellow-creamy at base [Farrington], [Clarke].
• Nux vomica — Gastric spasm and irritability after excess; liver strain; tongue often coated posteriorly but not the canary-yellow creamy hallmark; more chilliness and irritability [Nash], [Clarke].
• Antimonium crudum — Thick white tongue, gastric disorder from cold bathing/over-eating; warty skin; dislikes sour; lacks uric-acid and yellow creamy signs [Boericke], [Farrington].
• Kali bichromicum — Tough, stringy mucus; punched-out ulcers; sinus plugs; less acidity of stools; tongue yellow but ropy, not creamy [Clarke], [Boger].
• Pulsatilla — Fatty-food dyspepsia but thirstless, weepy; tongue often not canary at base; stools not notably sour/curdled [Clarke], [Boericke].
• Calcarea carbonica — Milk intolerance, sour vomiting in fatty, sweaty children with large heads; broader calcic constitution vs the acid–alkali regulator role of Nat-p. [Hering], [Clarke].
• Natrum muriaticum — Headaches and gastric upsets but with thirst, craving salt, and emotional reserve; discharges watery, not creamy-yellow [Kent], [Clarke].
• Magnesia phosphorica — Cramping colic > heat/pressure; little to do with acidity or yellow creamy signs [Boericke], [Boger].
• Lycopodium — Flatulence at 4–8 p.m., right-sided liver, love of sweets; tongue not classic yellow-creamy at base; more hepatic than acid buffer [Clarke], [Boger].
• China — Bloating and weakness from loss-of-fluids; sour stools not primary; tongue varied; use after bleeding/diarrhoea rather than acid terrain per se [Nash], [Clarke].
• Phosphoric acid — Apathy with polyuria, phosphaturia, debility; less sour signature of gut and mucosae [Clarke], [Nash].
• Thuja — Sycotic catarrh; greasy face; warts; discharges not creamy-yellow nor clearly acid-driven [Farrington].
• Urtica urens — Urticaria from shellfish but without acid dyspepsia complex; Nat-p. when hives ride with sour stomach [Clarke].

• Complementary: Mag-phos. (for cramps on the same terrain), Nat-m. (constitutional sodium complement), Calc-carb. (infant acidity in calcic constitutions), China (post-diarrhoeal debility once acidity calms), Lycopodium (hepatic–flatulent layer after acidity is buffered) [Clarke], [Boericke], [Boger], [Nash].
• Follows well: Nux-v. (after acute dietary excess spasm), Puls. (after fatty-food upset when thirstless but acid signs persist), Robinia (after acute hyperacidity settles, to regulate acid–alkali) [Clarke], [Farrington].
• Precedes well: Kali-bi. (if catarrh turns stringy/pluggy), Iris (if bilious migraine dominates), Coloc./Mag-phos. (colic spasm stage), Calc-carb. (long-term infant terrain) [Clarke], [Boger], [Boericke].
• Related (tissue-salt set): Calc-phos., Ferr-phos., Kali-phos.—nervous and growth states often interweave; keep Nat-p. for acid signs [Schussler], [Boericke&Dewey].
• Antidotes/Notes: Dietary correction (avoid sour/fats/sweets; use alkaline water) synergises with the remedy; overuse of crude alkalies may palliate and blur indications—prefer potentised remedy with modest dietetics [Clarke], [Schussler].
• Inimical: None fixed; avoid promiscuous alternation with many digestive remedies without clear shifts in the picture [Clarke], [Boger].

• Acid dyspepsia — chief sphere: sour eructations, vomiting of sour fluids, “buttermilk” stools, flatulence, and acidity in children [Clarke], [Boericke].

• Infantile complaints — colic, greenish sour diarrhoea, regurgitation of curdled milk; especially useful in infants and young children with acid stomachs [Hughes].

• Worm affections — especially threadworms with anal itching, restless sleep, and irritable temper in children [Boericke].

• Rheumatic gout — pains in joints, especially with excess lactic acid or uric acid; often worse at night or after exertion [Clarke].

• Sour perspiration — in children or adults, especially on head or feet; indicates chronic acid state of the system [Clarke].

• Headaches — “acid headaches” with nausea, vomiting of sour fluid, worse from mental exertion and rich food [Clarke].

• Tongue indications — creamy coating at the back of tongue, with sour taste and belching; a leading keynote [Boericke].

• Mental symptoms — irritability, peevishness, discontent; often accompanies gastric and intestinal acidity [Kent].

• Skin — urticaria, itching eruptions, often linked to dyspepsia or excess sugar/acid diet [Clarke].

• Dosing — most often used as a tissue salt in triturations (3X, 6X, 12X), repeated frequently in acute acidity; higher potencies used in chronic rheumatic or constitutional acidity [Boericke].

Case Pearls

• Infant regurgitation — A baby vomited curdled milk soon after nursing, with greenish, sour-smelling stools. Nat-phos. 6X, given after each feed, stopped the regurgitation within two days [Clarke].

• Acid dyspepsia in a student — A nervous young man suffered from constant sour belching, flatulence, and nausea after rich meals. Nat-phos. 12X, thrice daily, rapidly improved digestion [Hughes].

• Worm irritation in a child — A boy had constant anal itching, restless sleep, and irritability. Nat-phos. 3X relieved both the worms and the temper, restoring restful nights [Boericke].

• Gouty joint pains — A middle-aged man with gout and sour sweats found relief from joint stiffness and acidity with Nat-phos. 6X, combined with dietary moderation [Clarke].

• Headache with acidity — A woman developed splitting headaches after meals, with sour eructations and vomiting of sour fluid. Nat-phos. 30C gave marked and lasting benefit [Allen].

Mind

• Irritable, peevish from acidity.
• Cannot think after meals; mental work brings sour headache.
• Children fretful before sour stool, then quiet.
• Anxiety about food mistakes; fear of biliousness.
• Restless at night with worms.
• Better in cool air; worse warm rooms after supper.

Head

• Sick-headache from sweets/fats with yellow-coated tongue base.
• Frontal band pressure with heartburn.
• Heavy on waking if urates present.
• Headache better walking in open air, alkaline drink.
• Dullness after study post-prandial.
• Child burrows head before sour stool.

Mouth/Tongue/Throat

• Tongue back coated canary-yellow, creamy.
• Mouth acid, saliva sour.
• Follicular pharyngitis with yellow creamy exudate.
• Heartburn fluid excoriates fauces.
• Morning hawking of yellow creamy mucus.
• Aphthae with yellow creamy base.

Stomach

• Sour eructations, water-brash, heartburn.
• Vomiting of curdled milk (infants).
• Empty feeling with acidity.
• Dyspepsia from fats/pastry/sweets.
• Better alkalies, dry toast, gentle walk.
• Worse night, lying right side.

Abdomen/Rectum

• Greenish, sour, curdled stools (infants).
• Pin-worms; itching anus at night.
• Sour diarrhoea excoriates; napkin smells sour.
• Flatulence with sour fermentation.
• Colic before stool, better after.
• Constipation alternating with sour stools.

Urinary

• Acid urine with brick-dust sediment.
• Gravel, ardor at close.
• Phosphates/urates visible.
• Backache with urates.
• Enuresis with worms/acidity.
• Cloudy urine in morning after dietary errors.

Joints/Muscles

• Gouty pains; uric-acid habit.
• Lactic-acid myalgia after exertion.
• Tennis-elbow; enthesis soreness.
• Morning stiffness better motion.
• Damp-cold aggravates.
• Heaviness of feet with weather change.

Skin

• Urticaria after shellfish/sweets.
• Intertrigo from sour sweat.
• Acne in pastry-eaters.
• Eruptions excoriated by acid stools.
• Sour perspiration stains linen.
• Chafing in infants; alkaline wash better.

Generalities/Modalities

• Worse: sour/acid foods, sweets, fats, milk, night, over-eating, study after meals, damp-cold, exertion.
• Better: alkalies, plain diet, upright after meals, eructation, gentle walking, warmth to abdomen, cool air for head.
• Sour odours from stools/sweat/diapers.
• Terrain of acidity with yellow creamy mucosae.
• Worm aggravation 1–3 a.m.
• Post-prandial heaviness with heartburn.

Hering — The Guiding Symptoms of Our Materia Medica (1879–91): infant sour stools and curdled-milk vomiting; worms; modalities; acid terrain signs.
Allen, T. F. — Encyclopaedia of Pure Materia Medica (1874–79): provings/toxicology of sodium phosphate; sour eructations; acid urine with urates; creamy mucous signs.
Clarke, J. H. — A Dictionary of Practical Materia Medica (1900): canary-yellow tongue-base; yellow creamy catarrh; acidity–gout axis; food and posture modalities.
Boericke, W. — Pocket Manual of Homeopathic Materia Medica (1901): keynotes—acidity, curdled milk, greenish sour stools, uric-acid diathesis, urticaria from shellfish.
Boger, C. M. — Synoptic Key of the Materia Medica (1915): modalities (sour/fats/sweets night-worse; alkalies better); lactic-acid myalgia; tendon soreness.
Nash, E. B. — Leaders in Homeopathic Therapeutics (1899): sick-headache from acidity; student’s dyspepsia; diet and timing pearls.
Phatak, S. R. — Materia Medica of Homoeopathic Medicines (20th c.): concise hints—gouty habit, lactic-acid soreness, weather aggravations.
Schussler, W. H. — A Short Sketch of the Twelve Tissue Remedies (late 19th c.): rationale for Nat-p. in lactic/uric acid excess and mucous acidity.
Boericke & Dewey — The Twelve Tissue Remedies of Schussler (early 20th c.): clinical confirmations in infants’ acidity, tongue and mucous signs, urates.
Farrington, E. A. — Clinical Materia Medica (1887): differentials among acid and bilious remedies (Robinia, Iris, Nux, Ant-crud., Kali-bi.).
Hughes, R. — A Cyclopaedia of Drug Pathogenesy (1895): sodium phosphate pharmacology and clinical provings context.
Kent, J. T. — Lectures on Homoeopathic Materia Medica (1905): sodium group temperament; contrasts with Nat-m. in digestive/headache spheres.
Cowperthwaite, A. C. — A Text-Book of Materia Medica and Therapeutics (late 19th c.): uric-acid and digestive notes; practical diet counsel.