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As stated in the *Huangdi Neijing* (Yellow Emperor's Inner Canon): The Heart opens into the tongue. The tongue is the mechanism of voice production. It also states: The meridian of the Foot-Taiyin Spleen connects with the Stomach, ascends to flank the pharynx, connects with the root of the tongue, and scatters beneath the tongue. The meridian of the Foot-Shaoyin Kidney follows the throat and flanks the root of the tongue. From this, we can deduce that the tongue serves as an external indicator of the Heart, Kidney, Spleen, and Stomach. The Heart governs Blood; therefore, the natural color of the tongue is red. Cheng Wuji stated that "the tongue is the sprout of the Heart," naturally red and lustrous. In the third or fourth day of a Shanghan (Cold Damage) disease, a membrane appears on the tongue, white and slippery like moss. In severe cases, it may be dry and rough, yellow, or black. These variations reflect the depth of heat pathogenic factors. The Spleen governs Dampness, while the Stomach governs Dryness; the Kidney governs the Five Fluids. The formation of coating on the tongue results from Stomach Heat steaming Spleen Dampness, causing them to knot together. Thus, the coating is white and slippery, or grey-slippery, or black-slippery, all indicating the upward flooding of Spleen Dampness. If a yellow coating forms, it indicates that heat has entered the Stomach. Subsequently, it may become scorched black, develop prickles, or become coarse, rough, dry, or shriveled, even curling short. This occurs because Stomach Heat has reached its extreme, with Dryness burning upwards, and Kidney Yin being exhausted downwards, unable to transport fluids via the Lianquan and Yuying acupoints to moisten the root of the tongue. Therefore, the root of the tongue primarily reflects the condition of the Heart and Kidney; the membrane reflects the control of the Sanjiao (Triple Burner) interior membranes; and the coating reflects the steaming of Qi by the Spleen and Stomach. The Heart belongs to the Upper Jiao, so the tip of the tongue reflects the Upper Jiao; the Kidney belongs to the Lower Jiao, so the root of the tongue reflects the Lower Jiao; the Spleen and Stomach belong to the Middle Jiao, so the center of the tongue reflects the Middle Jiao. The exterior-interior, cold-heat, Qi-blood, and deficiency-excess conditions of all Zang-Fu organs are fully manifested on the tongue. This is because the Jing-Qi (Meridian Qi) of the Zang-Fu organs is transmitted through the membranes and collaterals of the Sanjiao to distribute to the root of the tongue. Consequently, when there is a coating on the tongue, one must distinguish its color; when there is no coating, one must distinguish the natural color and texture of the tongue body. This constitutes the third major principle in diagnostic methods. The specific diagnostic methods have been detailed in the preceding sections on Six Meridians tongue coatings and the subsequent Summary of Tongue Diagnosis, so they will not be repeated here.

[Comment by Xiu]: Du Qingbi's *Shejing* (Mirror of the Tongue) from the Yuan Dynasty is still considered too brief; Zhang Danxian's *Shejian* (Mirror of the Tongue) from the early Qing Dynasty seems too verbose. The one that strikes the right balance between brevity and detail is likely Yu's *Bieshe* (Differentiation of the Tongue).

[Comment by Lian]: Mr. Liang Te Yan from Maoming said: The tongue is located above the lungs, and its couli (pores/skin texture) connects with the intestines and stomach. Pathogenic factors in the abdomen steam and ferment, revealing themselves clearly. Whether illness exists is obvious and reliable. Combined with inspection, listening/smelling, inquiry, and palpation, one can judge the truth or falsity of exterior-interior, cold-heat, and deficiency-excess. Although not always perfectly accurate, it is rarely far off. Zhou Xue Qiao, a fellow scholar from Shanghai, said: The tongue membrane is connected to various organs of the digestive tract, thus reflecting diseases of the gastrointestinal tract. It also has a close relationship with the circulatory and respiratory systems. The method of examining coatings takes moisture and dryness as the two main outlines. When blood heat is excessive, the color is red; when blood cold is present and blood volume is low, the color is pale (similar to changes in gums and lips). If there is dry stool in the Stomach and bile has nothing to do, it flows backward upward, turning the color yellow. The reason for black color indicates toxicity in the blood. Since the tongue is related to the Heart, Lungs, Liver, Stomach, Large Intestine, and Small Intestine, the coating color is a key basis for treatment. Western doctor Ke Weiliang said: On the surface of the tongue, there are papillae containing neural-like structures responsible for taste. There is also coating used to observe disease, which is most beneficial. Observing these together, tongue differentiation is the most important aspect of diagnosis, consistent between Chinese and Western medicine, and truly evidence-based. Zhang Danxian's *Shejian* lists diagrams and prescriptions but is verbose and lacks essential points. Only Ye Tianshi's (Mr. Xiangyan) *Wenre Lun* (Treatise on Warm Diseases) stands out uniquely in differentiating tongue colors, truly a miraculous and untransmitted method. Therefore, I appended his theories from Shi Feinan's revised edition to express my admiration.

(1) At the onset, if the tongue coating is white and lacks fluids, it indicates dryness-heat damaging Lung fluids. Light and clear heat-clearing herbs should be used, following the principle of treating upper disorders by dispersing upwards. Examples include Apricot Seed (Xingren), Platycodon Root (Jiegeng), and Butterfly Pea Flower (Niubang). Acrid and moistening herbs resolve binding constraints; Mulberry Leaf (Sangye) and Melon Rind (Loupi) clear dryness lightly. Accompany with Gardenia Bark (Shanzhipi) and Forsythia Fruit (Lianqiao) for their slight bitterness and dryness, as dryness corresponds to Metal, and slight bitterness overcomes Metal. If the tongue coating is white with a crimson base, it indicates Dampness suppressing Heat. One must guard against it becoming dry. Use acrid, bland, light, and clear methods to drain Dampness and vent Heat, ensuring Dampness does not suppress Heat. For example, use Sanren Tang (Three Seeds Decoction), substitining Cardamom Seed (Kouren) for Cardamom Peel, with slight addition of Reed Rhizome (Lugen) to clear and transform. If the initial tongue coating is white, dry, and thin, it indicates deficiency of Stomach and Kidney Yin. If consciousness is not clouded, use Little Rehmannia Root (Xiao Shengdi), Scrophularia Root (Yuanshen), and Ophiopogon Tuber (Maidong) to save Yin; Honeysuckle Flower (Yinjinhua), Anemarrhena Rhizome (Zhimu), Reed Rhizome (Lugen), and Bamboo Leaf (Zhuye) to vent pathogens. Especially add acrid-moistening herbs to vent pathogens. If consciousness is immediately clouded, add opening-closing agents like Puji Dan or Ningshang Wan. Delay leads to internal closure and external collapse, which is untreatable. If the tongue coating is white, dry, and thick, purge with Tiaowei Chengqi Tang, accompanied by clearing, moistening, and nourishing Yin herbs like Fresh Rehmannia Root (Xian Shengdi), Scrophularia Root (Yuanshen), Pear Juice, and Reed Rhizome (Lugen). If the tongue coating is white, greasy, and not dry, with extreme subjective chest oppression, it belongs to heavy Spleen Dampness. Use Jiaganzhengqi San or Sanren Tang, removing Apricot Seed, Reed Rhizome, and Talcum, adding Acorus Rhizome (Shengtoucao) and Medicated Leaven (Shenqu) for acrid-bland opening transformation and aromatic elimination of turbidity. If the tongue swells and cannot retract into the mouth, it belongs to extreme stagnation of Spleen Dampness and Stomach Heat, with toxin spreading to the mouth. Add Raw Rhubarb Juice (Sheng Dahuang Zhi) to the previous method to promote urination/bowel movement, and the swelling will subside. If the tongue coating is white, thick, sticky, and greasy, with a sweet taste and expulsion of turbid saliva, it is Pi Dan (Spleen Pheromona), caused by accumulation of Spleen-Stomach Damp-Heat Qi fighting with grain Qi, overflowing upwards when full. Also use Jiaganzhengqi San with Acorus Rhizome and Medicated Leaven. If the tongue coating resembles alkali color, or white coating interspersed with one or two yellow stripes, it indicates retained food stagnation mixed with turbid pathogens. Add herbs to promote middle-jiao circulation and eliminate stagnation to the previous method; otherwise, fear knotting and inability to vent from the Membrane Source. If the white coating is thick like accumulated powder, and the tongue flesh on the four sides is purple-crimson, it is Wen Xie (Warm Pathogen) from damp-earth郁蒸 (stagnant steaming), manifesting as Wen Yi (Plague-Warmth). Follow Da Yuan Yin and Sanren Tang, modifying to vent pathogens and prevent transmission. If the coating is white and not dry, or yellow-white mixed, or grey-white without thirst, absolutely do not administer bitter-draining or purgative-clearing methods. This indicates Dampness stagnation not yet reached, or chronic Phlegm-Fluid retention. Even with epigastric distension and pain, do not attack. Use opening-draining methods like Apricot Seed, Cardamom, Tangerine Peel, and Platycodon Root, slightly bitter and slightly acrid to ventilate Qi stagnation.

(2) If the tongue coating is yellow and turbid, with tenderness upon pressing the chest and diaphragm, or spontaneous pain, or distension, this is mixed Damp-Heat. Use bitter-descending and acrid-unblocking methods, such as Trichosanthes Fruit (Gualou), Fritillaria Bulb (Beimu), Wendan Tang, Xiaoxianxiong Tang, Banxia Xiexin Tang, and Huangqin Husshi Tang. However, yellow coating must have a "geological" quality (thick and rooted) to use bitter-acrid heavy agents. If the yellow coating is smooth and unrooted, it indicates formless Damp-Heat with signs of deficiency. Use Gualou, Beimu, Gardenia (Zhizi), and Forsythia (Lianqiao), slightly acrid and slightly bitter, lightly clearing and transforming. Absolutely avoid bitter-acrid heavy agents. If the tongue coating is old yellow or grey-yellow like agarwood color, with geological quality, not slippery but rough, or with cracks in the center, or thick in the center, the pathogen has transmitted inward and knotted with retained food. The epigastrium and abdomen must be full and painful; purging is necessary. If such a tongue coating is not seen, fear Dampness gathering in Taiyin causing fullness, Cold-Heat-Damp complexity causing pain, or Damp blocking Qi mechanism causing distension. Still follow acrid-bland-warm methods to open and transform. If the coating is yellow, thin, and dry, treat it similarly to the previously mentioned white, thin, and dry cases.

(3) When Heat pathogen transmits to the Ying (Nutrient) level, the tongue color must be crimson without coating. If the tongue is crimson but has yellow-white coating in the center, or looks like coating but isn't, this is Heat stifling and constraining in the Qi level burning fluids, not involving the Blood level. Use the previous acrid-moistening pathogen-venting and light-clearing heat methods. Absolutely avoid bitter-cold ice-freezing and yin-nourishing greasiness, which would cause Qi-level pathogens to be suppressed and sink inward, resulting in pure crimson without coating. Some cases, not due to ice-freezing, show pure bright crimson tongue with clouded consciousness, indicating pathogen transmitting to the Pericardium Luo. Use Water Buffalo Horn (Shuixiujiao), Fresh Rehmannia Root (Xian Dihuang), Honeysuckle (Yin), Forsythia (Qiao), Curcuma Tuber (Yujin), Fresh Acorus Rhizome (Xian Shichangpu), Bamboo Sap (Zhuli), and Ginger Juice (Jiangzhi). In clearing and transforming, assist with acrid-moistening opening-closing. If the person usually has much Phlegm, once external heat sinks, the interior collaterals close immediately. Must simultaneously use Ningshang Wan or Puji Dan/Wan. Delay risks extreme closure and fainting. If the tongue is crimson looking dry but feels moist to touch, this indicates chronic fluid deficiency, with Damp-Heat steaming turbid Phlegm clouding the Pericardium. Lightly drain Heat, assist with Ningshang Wan to open. If the tongue color is purple-dark and feels moist, this indicates pre-existing Blood stasis in the chest-diaphragm fighting with Heat. Use Fresh Rehmannia, Water Buffalo Horn, Moutan Cortex (Danpi), Salvia Root (Danshen), Red Peony Root (Chishao), Curcuma (Yujin), Trichosanthes Root (Huafen), Peach Kernel (Taoren), and Lotus Rhizome Juice (Ou Zhi) to cool Blood and resolve stasis. Otherwise, stasis and Heat combine, blocking orifices, leading to mania-like symptoms. If the tongue is purple and swollen, it is Wine Toxin rushing to the Heart. Add Raw Rhubarb Juice to the previous method. If the tongue is crimson, wants to extend but cannot exit the mouth, and resists teeth when trying to extend, this is Phlegm blocking the tongue root with internal stirring of Liver Wind. Add Bamboo Sap, Ginger Juice, Arisaema Cum Bile (Danningxing), and Fritillaria (Chuanbei) to clearing-transforming formulas to resolve Phlegm-Heat. Do not use greasy/nourishing herbs that suppress Fire. Crimson tongue with dryness indicates Evil Fire injuring Ying. Use Xijiao Shengdihuang Tang. Some cases, due to suppression by cold-cool and yin-nourishing herbs, often become drier with more clearing and drier with more nourishing. Use sweet-ping and sweet-run herbs, assisting with acrid-moistening to vent pathogens, so fluids return. If there are fragmented yellow-white spots on the tongue, Gan Sores (mouth ulcers) are about to appear. White film like mold or ulcerated spots covering the tongue and mouth is called Kou Mi (Oral Candidiasis/Mucositis), due to Stomach-Kidney Yin deficiency, lack of central support, and Damp-Heat steaming mixed. Symptoms are difficult to treat;酌情 use Daochi San combined with Xijiao Dihuang Tang. Large red dots on the tongue indicate Heat-Toxin attacking the Heart. Use Daochi and Xijiao Dihuang, adding Coptis Rhizome (Huanglian) and Gold Juice (Jinzhi). Or add slight Raw Rhubarb Juice. Crimson and dry center of tongue indicates Stomach Heat burning up to Heart Ying. Clear Heart and Stomach. Crimson and dry tip indicates Heart Fire flaming upward. Use Daochi to drain the Fu organ. Crimson and bright/shiny tongue, or crimson but not fresh, even dry-dull-withered, or pale/colorless like a pig kidney, indicates extreme exhaustion of Stomach-Kidney-Liver Yin and loss of Shen spirit in the tongue. Urgently use Jiagazhonggan Tang, adding Glehnia Root (Shashen), Polygonatum Stem (Yuzhu), Chicken Egg Yolk (Jizihuang), and Tortoise Plastron (Sheng Guiban), sweet-ping and moistening to save.

(4) Black is the color of the Kidney. Thick, dry, black coating indicates Gastrointestinal pathogen knotting injuring Kidney Yin. Urgently use Dachengqi Tang with salty-bitter purgation. Thin, dry, black coating: use Tiaowei Chengqi Tang to mildly harmonize, or Zengye Chengqi Tang to moisten and purge. If the tongue is pale-black with insufficient fluids, this is Rootless Fire floating up due to Kidney Deficiency. Urgently use Fumai Tang, Shengmai San, or Liuwei Dihuang Wan to save. Grey-black, cyan-dark, slippery, and moist coating, or tongue without coating but not dry, with smoke-like shadows appearing, no heat sensation, no thirst, or cold limbs, indicates Deficient-Cold syndrome, the image of Water overcoming Fire. Urgently use Liyin Jian to warm. If the tongue is short and retracted, it indicates exhaustion of Liver-Kidney Qi, difficult to treat.