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Whenever observing the tongue color and distinguishing the coating, there are only three colors: white, yellow, and black. These are the presenting colors of the coated tongue. When observing the tongue body color and distinguishing the tongue substance, there are also three colors: crimson (Jiang), purple, and green/blue (Qing). These represent changes in the tongue substance itself.

A thin white coating indicates cold pathogen at the exterior; it is appropriate to use releasing-the-exterior methods. Alternatively, it may indicate stagnant Qi failing to flow smoothly; using methods to promote Qi circulation is appropriate. A thick white coating suggests inherent cold in the Zhongwan (epigastrium); warming the middle is appropriate. Alternatively, it may indicate unresolved damp-phlegm; resolving phlegm is appropriate. If accompanied by cracks covering the surface, it mostly indicates cold-dampness; warming and transforming is appropriate. If the coating appears greasy like alkali, it mostly indicates turbid heat; clearing and transforming is appropriate. If the white coating is thick with prickly, scorched cracks on top, feeling rough or coarse when touched, it mostly indicates extreme heat manifesting as a lower-jiao excess syndrome; urgent use of cold purgatives is required. Only if the coating is pale white and almost absent does it indicate deficiency-cold; warming and tonifying is appropriate. There are also cases belonging to heat; treatment should be guided by pulse and symptoms. A white coating resembling cooked rice is called "white coating," commonly known as "dull white coating"; such conditions are mostly incurable.

Regarding yellow coatings, although the pathogenic heat has gradually deepened, distinctions exist between those with residual white and those without, as well as between those with substance and those without. A yellow coating with white, thin and lacking substance, indicates that the exterior pathogen has not yet resolved and heat has not yet damaged body fluids; promoting Qi circulation and venting the exterior remains appropriate. A yellow coating that is turbid, lacks white, and has substance indicates that the pathogen has bound in the interior. The more severe the yellow turbidity, the deeper the pathogen has entered the interior, and the more intense the heat binding. If caused by damp-heat with much phlegm, pungent and bland herbs for clearing and transforming are appropriate. If caused by damp-heat combined with food stagnation, bitter and pungent herbs for unblocking and descending are appropriate. However, if the coating is yellow and rough, yellow and dry, or severely yellow with gray/black tints, yellow with dry sand-like points, or yellow with central fissures, all belong to interior heat-excess syndromes; rapid purgation is necessary to preserve body fluids.

As for black coatings, variations include those with green/blue or purple tints, scorched and dry, or moist. A green-black coating with a slippery tongue body indicates water overcoming fire, mostly representing spleen-kidney yin-cold syndromes; urgently breaking yin and restoring yang is required. A purple-black coating with a scorched and dry tongue body indicates extreme fire resembling water, mostly representing exhaustion of stomach-kidney yin fluids; urgently clearing fire and saving yin is required. Other types include gray color (i.e., light black): gray-white and slippery indicates cold-damp damaging spleen Yang; warming the spleen and transforming dampness is appropriate. Gray-black and dry indicates damp-fire damaging spleen Yin; moistening the spleen and saving yin is appropriate. Mustard-sauce color (i.e., yellow mixed with black) mostly results from cold damage complicated by food stagnation, with turbid rot rising upward; urgent clearing and purging is required. Light color indicates survival; dark color indicates death. Survival follows if purgation leads to bowel movement; death follows if it does not. This is the key to distinguishing coating colors. Details regarding the six meridians' tongue coatings have been discussed elsewhere and will not be repeated here.

Regarding tongue body colors changing from red to crimson to purple, these present color without coating. One type arises from blazing Heart channel heat robbing collateral blood; nourishing blood and clearing the nutritive level is appropriate, while nourishing yin and restoring the pulse is used for severe deficiency. Another type arises from flourishing Liver channel fire robbing collateral blood; cooling blood and unblocking collaterals is appropriate, while clearing fire and extinguishing wind is used for excess pathogens. Only a green/blue tongue reveals the true color of the Liver, indicating that the vital Qi of the stomach is extremely depleted. Despite differences between green-black cold transformation and green-purple heat transformation, efforts to save the patient often fail. This is also recorded in the section on six meridians' tongue coatings for scholars to reference. This constitutes the key distinction between coating color and tongue body color.

[Commentary by Xiu]: Zhang Danxian, basing his work on Shen Douyuan's tongue diagnosis, made slight modifications and compiled *She Jian* (Mirror of Tongues), containing one volume and 120 tongue diagrams. Borrowing each color, he generated dozens of diagrams per color; his language was often forced and obscure, potentially confusing readers. Yu's few words already captured the essence.

[Annotation by Lian]: Liu Jiren from Dongjiang authored *Cha She Bian Zheng Xin Fa* (New Methods for Observing Tongues and Distinguishing Syndromes). His eight methods for examining the tongue are: 1. Observe tongue color; 2. Observe tongue substance (substance also has color, size, and thermal characteristics; swelling filling the mouth with teeth marks indicates blood heat; base color differs between purple and red); 3. Observe the tip (white coating covering the tongue with red prickles at the tip contraindicates warm-drying herbs); 4. Observe the center (coating on sides but none in center, or vertical/horizontal fissures); 5. Observe the root (presence of continuous coating behind the root, presence of large fleshy tumors); 6. Observe the edges (whether coating aligns with edges); 7. Observe dryness/moisture (two major guidelines: touching reveals slipperiness or dry prickliness; some appear moist but feel dry, others appear dry but feel moist); 8. Observe old/tender (coarse/aged indicates excess; plump/tender indicates deficiency). In Chapter One, discussing the principle of tongue coating, he states: The tongue is the external manifestation of the Stomach, facilitating food transport into the esophagus and stomach. The tongue tissue is innervated by the fifth cranial nerve pair, its function relying entirely on this nerve's movement. Two purple-blue veins under the tongue are the Lesser Yin Kidney meridian ascending, named Jinjin and Yuye acupoints, generating saliva to moisten the tongue substance and mix with food. TCM uses coating for syndrome differentiation because it accumulates on the surface and is easy to identify, yet fails to understand why coating forms, leading to significant diagnostic errors. Thus, principles must be studied. The tongue surface consists of numerous tiny papillae. When invisible, microscopes are needed; when visible, they resemble thorns, feeling prickly, varying in visibility, size, smoothness, or elevation, changing constantly with symptoms. Coating is turbid qi from food putrefaction in the stomach accumulating on papillae. [Lian notes: Although coating rises from stomach turbidity, its origin lies in the gastrointestinal mucosa layer by layer, as the tongue membrane directly connects to the GI tract.] With three meals daily, the coating changes thrice, called "living coating," indicating no disease. Changes occur because food digestion causes turbidity to descend (coating recedes), then putrefaction causes turbidity to rise (coating reforms). Without turbidity, coating is thin/few; with turbidity, it is thick/abundant. This is normal. Slightly yellow is the correct color. White represents Lung color; if Stomach Yang is suppressed by diet, dampness accumulation, or sticky saliva, the correct color cannot reach the surface, causing temporary whiteness. Green/blue is an absolute sign of danger; its appearance portends critical condition. Other intermediate colors are detailed later for study. His views are clear and serve as a goal for observation.

Coating color relates most closely to excess and deficiency. Yellow-turbid coating indicates excess; bitter-pungent descending methods apply. Yellow-white mixed with faint gray indicates deficiency; light-clear Qi-transforming methods apply (e.g., Apricot Seed, Cardamom, Tangerine Peel, Kankudzu Root). Thick-yellow with rough prickles indicates excess; purgation applies. Thin-yellow and smooth indicates deficiency; purgation is strictly contraindicated. Black with prickles indicates excess (dry feces in intestines confirmed); purgation is urgent. Black like smoldering coal, hidden and smooth indicates deficiency; cold/heat deficiency requires referencing pulse/symptoms. White like salt or powder indicates excess; bitter-pungent opening/descending methods apply. Dry powdery coating indicates intense excess heat; bitter-cold direct descending is urgent. Thin-light white and tender-smooth white indicate deficiency; Qi/Yang deficiency requires careful pulse/symptom analysis. This is the key to distinguishing excess/deficiency in coating observation.

[Commentary by Xiu]: Zhang Jingyue stated that diagnosing Cold Damage via coating color to distinguish exterior/interior and cold/heat is reliable. However, using tongue color to distinguish excess/deficiency is error-prone. For example, black coating can be excess due to fire scorching, or deficiency due to water depletion. Yin-deficiency Cold Damage may mimic Yang patterns with charcoal-black, prickle-filled, cracked tongues; sweet-warm water-nourishing herbs reduce symptoms but leave the black tongue unchanged. Days later, a black crust peels off revealing fresh flesh, indicating skin/collateral scorching with revival. Thus, black prickles do not always mean excess; tongue substance age/tenderness and pulse/symptom excess/deficiency must be carefully analyzed.

[Annotation by Lian]: Yang Qiancun's method states: Coatings turning from white to yellow, yellow to scorched, or dry-black-cracked, especially with plump edges and slippery bases (or dry/tender bases without fluid, sandpaper-like texture, or lychee-shell contraction), often result from labor injuring Spleen/Lung, causing Qi-deficiency fever. Misdiagnosing as Cold Damage and using dispersants worsens deficiency/heat. Misdiagnosing as excess heat and using cold herbs traps Yin, causing deficient fire to flare. Hence white-to-yellow-to-scotched-to-black progression. Regardless of pulse/symptoms, large doses of Ginseng and Aconite Nourishing Harmony Decoction administered frequently often save lives. However, the tongue substance is invariably plump and tender. Coating dryness/moisture is secondary. If coating turns black due to excess fire, the shape is firm/constricted, color aged/coarse, and substance never plump/tender. Observers must know this. Disease excess/deficiency verified by coating determines syndrome nature, not constitutional nature.

Tongues with substance, firm/constricted/aged, regardless of coating color (white/yellow/gray/black), extending from center to edge, resistant to wiping/scraping, with rough/sticky/greasy base lacking fresh redness, are rooted true coatings, indicating internal stagnation. Tongues without substance, floating/plump/tender, regardless of coating color, covering center but not edges, easily removed by wiping/scraping, with pale-red/moist base lacking dirtiness, are unrooted false coatings, indicating severe interior deficiency. Even if coating covers fully, disappearing after eating with a round/plump/tender substance, it is also false/living coating. Eating loquat stains coating yellow; eating olive stains it green-black; these are dyed false colors. Thus, substance vs. no substance, extension to edges vs. center-only, distinguishes excess/deficiency. This is the key to distinguishing true/false coatings.

[Annotation by Lian]: Lu's *Lenglu Yihua* states: Tongue examination is reliable but not absolute. Justice says: If black tongue is found, ask about consuming sour/salty foods which dye it black, not disease-related. Dyed black is moist, not dry, and scrapes off. Only moist deficiency-cold tongues can be dyed; dry excess-heat tongues cannot. To observe coating dryness/moisture, forbid drinking water before examination. *Chongqing Tang Suibi* states: Pale tongue/white coating can indicate heat; thick-yellow-full coating can indicate cold; crimson tongue/no fluid can indicate phlegm; pulse/symptoms/urination/stool must be cross-referenced. Yellow coating looks white under lamplight. Thus, tongue signs are helpful but not infallible; careful scrutiny prevents misdiagnosis. Yu's statement that tongue diagnosis requires flexible application reflects profound experience.

Thin coating indicates initial exterior pathogen; thick coating indicates deep interior stagnation. However, thin/loose/non-substantial coatings that wipe off indicate sufficient Zheng Qi transforming pathogen. Even thin/greasy coatings indicate shallow pathogen entry; promoting Qi to vent pathogen is appropriate. Thick/greasy/substantial coatings that resist wiping indicate turbid stagnation. Thick/loose coatings indicate resolved interior stagnation; light-clear harmonizing is appropriate. This is the key to distinguishing thickness/looseness/greasiness.

Consistent coating color (white/yellow/gray/black) with variations in thickness/smoothness/dryness/moisture/lightness/darkness belongs to constant coatings; treat based on pulse/symptoms. Tongues changing multiple times daily (white-to-yellow, yellow-to-black, appearing/disappearing, red/black alternating) are variable coatings, indicating ominous prognosis. This is the key to distinguishing constant/variable coatings.

Coatings transforming from greasy to loose, thick to thin, indicate decreasing interior stagnation, termed true recession. Continued growth of thin-white new coating indicates recovering Stomach Qi and advancing grain Qi, a auspicious sign. Sudden disappearance of full-thick coating leaving dirty/greasy/rough base with red points or hair-like lines is false recession; thick coating returns within 1-2 days. Full-thick coating with central patch loss, fissures, or depressions showing red/dry base warns of fluid exhaustion/middle collapse; medication must be cautious. Sudden disappearance of thick coating leaving smooth/dry tongue indicates impending Stomach Qi extinction, mostly ominous. This is the key to distinguishing true/false recession and patch-loss/exhaustion.

Rough coatings indicate turbidity; sticky coatings indicate phlegm-saliva. Distinction between thick-greasy and thick-putrid is crucial. Thick-greasy usually indicates food stagnation or damp-stagnation; scraping yields mixed results. Slight thickness resisting scraping, even with fire-transformation drying, retains a layer of sticky saliva on the tongue body, constituting common thick-greasy coating. Thick-putrid usually results from Stomach fluid corruption, differing into pus-putrid and mold-putrid. Pus-putrid coating is white-with-faint-red, sticky/thick like wound pus, common in internal abscesses: Lung/Intestine abscesses show white-putrid coating; Stomach abscess shows yellow-putrid; Liver/Waist abscesses show purple-black-putrid; Chancre/toxic nodes show white-putrid. Mold-putrid coating features white film like mold or millet-grain-like erosions spreading from throat via esophagus to entire tongue/mouth/lips/teeth, seen in Damp-Warmth, Warm-Toxin, Hidden Summerheat, Dysentery, Syphilis, and Malnutrition syndromes. This results from Stomach body corruption, where fluids transform into turbid-heat, lacking a stabilizing force, steaming upward. Regardless of white/yellow putridity, prognosis is mostly poor, constituting thick-putrid mold coating. This is the key to distinguishing rough/sticky and thick-greasy/thick-putrid.

Regarding tongue body color: Red is normal. Paler than red indicates Blood deficiency. Pale-red without coating, slightly yellowish-white, indicates Qi failing to transform fluids. Very pale-red with green tint indicates Blood-level deficiency-cold, seen in uterine cold, dead-coating-in-abdomen, or chronic dysentery with extreme deficiency. Darker than red is crimson, indicating Blood heat. Crimson tip indicates Heart fire flaming upward. Crimson root indicates internal dryness from Blood heat. Uniform crimson without coating, or seemingly coated with stickiness, indicates Blood heat complicated by turbidity. Deep crimson turning purple, purple moist/dark indicates Stomach stagnation with blood stasis. Purple dry/dull indicates Liver-Kidney Qi exhaustion. Crimson-to-purple-to-black indicates collateral stasis transforming into toxin, blood exhaustion, incurable. Tongue body without coating, faintly covered with black sheen, indicates inherent Stomach dryness, common in smokers. This is the key to distinguishing pale/dark tongue colors.

[Annotation by Lian]: Tongue coating is like moss on ground; ground moss grows from rising damp; tongue coating grows from Stomach steaming Spleen damp rising. Normal people often have a layer of floating-white or floating-yellow coating. In summer, damp-earth dominance makes coating thicker and slightly yellow, but not full/stiff. Those with inherent Spleen-Stomach damp-heat often have thick-white coating year-round or gray-yellow center. During illness, Stomach-Spleen fluids oppressed by pathogen, or sinking Qi from diarrhea/dysentery, may result in no coating or thinner-than-normal coating. Kidney-Stomach fluid insufficiency leads to red tongue without coating, or red points on tip/edges. A red line in the center, called "chicken-heart coating," indicates severe Blood deficiency. This summarizes normal tongue coatings. Always ask patients about their habitual coating before clinical observation for accuracy.

[Commentary by Rongzhai]: All coating colors have treatments; only tongue substance changes are difficult to treat. However, even if substance changes, observe life/death of color: Living means underlying redness is still visible, indicating Qi/Blood stagnation, not organ failure. Dead means underlying area is completely dry/dull/withered, lacking vitality, indicating organ Qi cessation, i.e., True Organ Color. Among tongue colors, black is hardest to differentiate, but "finding ease within difficulty" exists: Black-dry-scrolled-hard/swollen/curled/prickly indicates excess-heat; pulse surging-rapid-deep-solid, symptoms high-fever/manic, treat with Baihu or Chengqi formulas. Black-white/gray/purple-moist-soft indicates deficiency-cold; pulse weak, symptoms aversion-to-cold, treat with Sini category. Such records exist in ancient/modern literature; this example illustrates the method.