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The tongue appears cyan, or cyan-purple and cold with a slippery coating, indicating a Cold syndrome. If the tongue is cyan-purple with a scorched and dry surface, or swollen and enlarged, or curled and shortened, it indicates a Heat syndrome.
Extreme Cold can also cause the tongue to curl and shorten because sinews and vessels contract when exposed to Cold; however, the surface will certainly not be scorched and dry.
If the tongue is stiff, short, and shortened, accompanied by mental confusion and unclear speech, the prognosis is fatal. (Note: There are cases of Phlegm syndromes where the root of the tongue is stiff and shortened, which are excluded from this discussion.) In Heat diseases, if the tongue body ulcerates and the heat does not subside, the prognosis is fatal. In Yin-Yang Exchange disease (a relapse after recovery from Shanghan due to sexual activity), if the tongue protrudes several inches, the prognosis is fatal. In Shanghan, if the heat is confined to the exterior, there is no coating on the tongue. When pathogenic Heat transmits inward, the coating gradually forms, changing from white to yellow to black, from moist to dry, then cracking, becoming rough instead of slippery, and developing prickles. These changes represent levels corresponding to the depth and severity of the Heat. (The coating arises because internal Heat causes the Spleen Qi to become obstructed and stagnant; dietary fluids and Jingye accumulate internally, manifesting as a coating externally. If Spleen Qi is not stagnant, digestion proceeds normally, and Jingye circulates freely; even with severe Heat, a coating may not form. This principle should be understood.) The details are as follows:

Pure White Tongue: In Shanghan, a tongue with a white and slippery coating indicates that Heat has just entered the interior but still retains exterior symptoms; cooling herbs should be added to exterior-releasing formulas. Another cause is deficiency-cold in the Stomach, where cold-fluid retention accumulates above the diaphragm, forming a white slippery coating. Severe closure of the Spleen can result in a coating white as accumulated snow. In Zang-Jie syndrome (detailed in *Shanghan Lun Jin Yan*), a white slippery coating requires careful differentiation. In Warm-Heat diseases, if high fever and thirst appear immediately upon onset, with a red tongue body and white coating, even if slippery, Baihu Tang (White Tiger Decoction) should be used to clear internal Heat, resolving the exterior spontaneously; exterior-releasing drugs must absolutely not be used. At the initial stage of seasonal epidemics, the coating may be white like piled powder.

White Mixed-Color Tongue: In Shanghan, when Heat enters the Stomach, the white coating turns yellow. If white predominates over yellow and the coating is slippery, exterior symptoms persist, and exterior-releasing formulas with cooling herbs are appropriate. If yellow predominates over white, and the coating is dry and rough without exterior symptoms, either clearing or purging methods may be used. (If there is retained food, phlegm, or blood stasis causing a slippery coating requiring purging, refer to the "Yellow Mixed-Color Tongue" section below.) If the coating is dry, cracked, and develops prickles, purging is undoubtedly required. In Warm-Heat diseases and epidemics, even if the coating is slippery, formulas such as Liangge San (Cool the Diaphragm Powder), Baihu Tang, or Chengqi Tangs should be used to clear Heat and purge the interior; releasing the exterior is strictly contraindicated.

Pure Yellow Tongue: A slippery coating requires careful examination. If Heat has not yet consolidated, purging should not be performed immediately. However, in summer, purging is appropriate without waiting for the coating to become dry.

Yellow Mixed-Color Tongue: If the root is yellow and hard, the tip is white, the center is neither very dry nor slippery, the tongue is short and cannot extend, and the patient exhibits delirium and restlessness, this indicates concurrent Phlegm and Food Retention; Da Chengqi Tang (Major Order the Qi Decoction) with Shengjiang (Fresh Ginger) and Banxia (Pinellia Rhizome) should be used. If the tongue color is cyan-purple but the coating is thick and yellow, with cracks, and the patient feels dry mouth but the tongue surface is not dry, this is a Yin syndrome with Food Retention. The pulse may be deep, fine, and hidden, or deficient, large, and rough. If pressing the epigastrium or around the umbilicus reveals hardness and pain, accompanied by frequent passage of gas, Da Chengqi Tang should be used urgently, with Sheng Fuzi (Raw Aconite Root) decocted separately to assist Dahuang (Rhubarb Root and Rhizome) in purging. If the pulse is deficient and large, Huanglong Tang (Yellow Dragon Decoction) should be used. For extreme Heat with restlessness, add Shengdi (Rehmannia Root) and Maidong (Ophiopogon Tuber), especially suitable in summer. If the coating is yellow but not dry, in winter, Fuzi Lizhong Tang (Aconite Regulate the Middle Decoction) combined with Xiao Chengqi Tang (Minor Order the Qi Decoction) should be used for purging. Generally, an accumulated coating, even if Yin signs are present, indicates deficiency with excess; urgent purging is required, though the method differs from standard practice. Furthermore, if there is Phlegm-fluid, water, or blood stasis in the Middle Jiao, the coating is often not dry; one must not delay treatment due to the lack of dryness. (In Summerheat syndrome with blood stasis, the center of the tongue is often black and moist; do not mistake this for a Yin syndrome.)

Pure Black Tongue: A whole tongue covered with black coating might be salvageable in summer, as intense heat causes pathogenic Fire to scorch internally and externally, facilitating black coating formation, allowing for purgative treatment. In winter, this sign indicates certain death.

Black Mixed-Color Tongue: If the center is black and the edges yellow, use Chengqi Tang for purging. If the edges are white, use Da Chaihu Tang (Major Bupleurum Decoction) for purging. If prickles and fissures develop, regardless of edge color, if the base of the fissures is red and vibrant, urgent purging is required. If the entire tongue is black, it is untreatable. If the tongue is ulcerated and curled, it is also untreatable. If worm-like projections appear, although caused by Dampness, it indicates Liver injury and is a critical condition. Generally, blackness at the tip is mild, while blackness at the root is severe. In summer, Summerheat often presents with black tongues; if the edges are red and the center is black and dry, Baihu Tang is indicated. All the above describe Excess Heat, but Deficient Heat also exists. If the tongue center is black or gray-black without an accumulated coating, the tongue shape is withered and thin, and not very red, accompanied by irritability, thirst, deafness, persistent fever, constipation for five to ten days, non-distended abdomen without tenderness on palpation, unconfused spirit, insomnia, muttering when sleeping slightly, smiling, or sighing, this is Deficient Heat due to exhaustion of Jingye and drying of Blood. Large doses of Liuwei Wan (Six-Ingredient Pill with Rehmannia) combined with Shengmai San (Generate the Pulse Powder) and Zhigancao Tang (Honey-Fried Licorice Decoction) are appropriate. Misuse of Chengqi Tang will lead to death. If Cold strikes directly, without initial fever, the tongue center becomes black (not changing from yellow), and although black, it is slippery and the tongue is small and thin; urgent warming is required.

Red Tongue: In Warm-Heat diseases and epidemics, with intense internal Heat toxicity, a slippery coating means purging is not yet appropriate; Huanglian Jiedu Tang (Coptis Decoction to Relieve Toxicity) or Baihu Tang may be used. If dry with yellow, white, or black coatings, along with prickles, cracks, pits, ulcers, or raised spots, these are indications for purging. Another type appears tender like new tissue, seemingly moist but actually severely dried out, caused by improper sweating or purging leading to fluid exhaustion; this is mostly untreatable, and Shengmai San is recommended. Red Wei Tongues (tongues that are flaccid and immobile) and red, thin, withered, and elongated tongues are also difficult to treat.

Purple Tongue: Caused by concurrent alcohol toxicity, the color is deep purple and red, and dry. If pale purple with cyan slipperiness, it indicates direct invasion by Cold; careful differentiation is needed.

Gray (can be Cold or Heat), Jiang-color/Jam-color (scorched yellow, indicating Heat with Food Retention), Blue (color of Wood overcoming Earth and failure), and various tongues during pregnancy (red face with cyan tongue indicates fetal death with maternal survival; cyan in both indicates death for both; moisture is favorable, witheredness is unfavorable) all require detailed examination.
In summary, regardless of the coating color, dryness always indicates Heat; only slipperiness requires careful scrutiny.