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(These situations are largely consistent with the differentiation principles of Shanghan [Cold Damage] and Wenbing [Warm Diseases].)

The presence of coating on the tongue is like moss growing on the ground. Ground moss arises from moisture rising upward; tongue coating is generated by the fluids of the Spleen and Stomach ascending to the surface. Therefore, in a healthy person, there is often a layer of floating white coating or a layer of floating yellow coating on the center of the tongue. In summer, when damp-earth Qi prevails, the coating tends to be thicker and slightly yellow, but it does not cover the entire tongue nor become rigid and stagnant. Those with a constitutional excess of damp-heat in the Spleen and Stomach often have thick white coating throughout the year, or grayish-yellow coating in the center of the tongue. When illness occurs, the fluids of the Spleen and Stomach may be constrained by pathogenic factors, or due to diarrhea and dysentery causing Spleen Qi to sink, the tongue may appear without coating, or thinner than usual. (I once treated a case where cold-dampness was mistakenly treated with cooling agents, resulting in persistent hiccups, jaundice-like yellowing of the body, yet the tongue was clean without coating. The pulse at the right Guan position was exclusively deep, fine, and weak, indicating Sinking of Spleen Qi. Whenever Water-Qi assaults the Heart and Stomach Yang sinks, the tongue often suddenly becomes devoid of coating; if prolonged, it turns dark or purple.) In cases of insufficient fluids in the Stomach and Kidney, the tongue is often red without coating, or has a red line in the center, or many red spots on the tip and edges. This describes the general appearance of a normal tongue's coating. (I have seen healthy individuals with a coin-sized, smooth, pale purple area in the center of the tongue who only suffered from nocturnal emissions, with no other illnesses.)

If illness is present, the tongue will certainly show coating. Pathogens hide inside, while the coating manifests outside; this is reliable and accurate, leaving no room for error. Physicians rely primarily on this to grasp the condition, so it must not be neglected.

Fenghan [Wind-Cold] belongs to cold-dry pathogens, while Fengwen [Wind-Warmth] belongs to warm-dry pathogens. Fenghan initially affects the exterior, whereas Fengwen first injures the Qi level of the Lung Meridian. Thus, the tongue often lacks coating; even if there is a thin white or yellow coating, it is slippery. As the pathogen gradually transmits inward, it binds with fecal matter in the Stomach and Intestines, causing the coating to thicken, turn from white to yellow, then to black and dry. Its appearance is rigid and stagnant. Only after purgation does the coating begin to decompose ("rot"). "Rot" refers to a loose, non-rigid state. As the rot recedes, a new layer of thin, floating coating grows, indicating the complete resolution of the pathogen.

Some cases present with white coating from the onset that is dry like white sand, named "Sha Tai" [Sand Coating]. This indicates excessive warm-dry pathogen, requiring rapid purgation assisted by sweet-cool fluids-nourishing herbs. There are also cases where the coating turns black but remains moist, or where one or two white strips appear within yellow-black coating, or where the front of the tongue is dry but the root has thick white coating; these are due to concurrent dampness or phlegm-fluid retention. Conversely, if the coating is yellow or black but washes off thinly without a base ("ge di"), it indicates Yin deficiency of the Stomach. The presence or absence of a base in the coating is a major distinction between deficiency and excess patterns. (I once observed a patient with a thick, rigid white coating at the tongue root resembling water-soaked material, with two red flesh spots appearing on both sides, indicating accumulation of cold-water in the Lower Jiao and failure of True Yang to circulate.)

Dampness is a turbid pathogen with numerous complicated presentations. Wind-damp attacking the exterior typically presents with slippery, white, non-thick coating; cold-damp attacking the interior typically presents with greasy, white, thick coating.

Shuwen [Summerheat-Warmth], Shiwenn [Damp-Warmth], Wenyi [Plague-Warmth], and Wenre [Warm-Thermal] diseases all stem from the stagnation and steaming of damp-earth Qi. Dongwen [Winter-Warmth] arises because Yang fails to store itself properly, representing residual damp-earth steaming Qi. These pathogens enter through the mouth and nose into the Membrane Source (Lung/Stomach), manifesting from the interior outward. Chunwen [Spring-Warmth] results from winter cold injury, where cold stagnates and transforms into heat over time. Cold-dry Qi can bind fluids and water-retention, hiding in the Membrane Source, mixing with heat, and manifesting from the interior. Shushi wanfa [Late-onset Summerheat-Dampness], known as Fushu [Hidden Summerheat], occurs when summer heat-damp hides in the Membrane Source, and autumn cool-dry Qi from the exterior suppresses the internal summerheat-damp, triggering an outbreak via exterior pathogens moving interior pathogens. Shushi maji [Summerheat-Damp Malaria] also often arises this way. Since hidden pathogens and seasonal pathogens emerge from the interior, they often involve dampness. Thus, from the onset, the tongue shows white coating that is thick, not thin; greasy, not slippery; rough like accumulated powder; or mixed with pale yellow. When transmitting to the Stomach and transforming into fire, binding with fecal matter, it changes from white to yellow, black, and dry. However, Shuwen and Shiwenn pathogens often present as mixed yellow-white, appearing yellow or white, either yellow-greasy or gray-yellow, but never dry. Even if there are signs suitable for purgation, such as constipation or difficult defecation, one should use prepared Rhizoma Pinelliae (Xia Baihuang) gently to purge, because a non-dry coating suggests no dry feces in the intestines; stool resembles spoiled sauce, so aggressive purgation is contraindicated. This summarizes the tongue coatings of dry pathogen, damp pathogen, and mixed dry-damp pathogens. (From Shi Feinan's *Yi Yuan*.)

The tongue is the orifice of the Heart; all diseases manifest on the tongue. By distinguishing its color, the syndrome becomes clear. The tip governs the Heart, the center governs the Spleen and Stomach, the sides govern the Liver and Gallbladder, and the root governs the Kidney. If fluids are normal and there is no dry thirst, fever still indicates an exterior syndrome. If the coating is coarse and white, becoming thick and greasy, it indicates cold pathogen entering the Stomach, combining with turbid fluid retention and transforming into fire. At this stage, taste perception is lost; use Rhizoma Pinelliae (Banxia) and Herba Agastaches (Huoxiang). When the thick greasy coating turns yellow, the pathogen has transformed into fire; use Rhizoma Pinelliae (Banxia) and Radix Scutellariae (Huangqin). If severe heat is untreated, it turns black, indicating extreme Stomach fire; use Gypsum Fibrosum (Shigao) and Rhizoma Pinelliae (Banxia). If black and dry/cracked, remove Rhizoma Pinelliae (Banxia) and use solely Gypsum Fibrosum (Shigao), Radix Anemarrhenae (Zhimu), Ophiopogonis Radix (Maidong), and Radix Trichosanthis (Huafen) to moisten. As thick coating recedes and the tongue body turns red, it indicates fire burning and water deficiency; use Rehmanniae Radix (Shengdi), Adenophorae Radix (Shashen), Ophiopogonis Radix (Maidong), and Dendrobii Caulis (Shihu) to nourish. This represents exterior pathogen transmitting inward. In cases of Spleen-Stomach deficiency-cold, the tongue is white, devoid of coating, and moist; severely, lips, mouth, and complexion appear sallow and pale, possibly due to diarrhea or dampness, lacking Spleen fire. Quickly use Codonopsis Radix (Dangshen), Fried Atractylodis Macrocephalae Rhizoma (Jiaozhuzhu), Aucklandiae Radix (Muxiang), Poria (Fuling), Glycyrrhizae Radix et Rhizoma Praeparata (Zhigancao), Zingiberis Rhizoma (Ganjiang), and Jujubae Fructus (Dazao) to boost Yang. For severe deficiency threatening collapse, add Aconiti Lateralis Radix Praeparata (Fuzi) and Cinnamomi Cortex (Rougui). For Spleen heat, the center coating is thin yellow; use Radix Scutellariae (Huangqin). For Heart heat, the tip is red, possibly with prickles; use Radix Et Rhizoma Rhei (Huanglian), Ophiopogonis Radix (Maidong), and Core Carapis (Zhujuanxin). For Liver heat, the sides are red or prickle; use Bupleuri Radix (Chaihu) and Gardeniae Fructus (Heishanzhi). Thick yellow coating in the center indicates mild Stomach heat; use Dendrobii Caulis (Shihu), Radix Anemarrhenae (Zhimu), Radix Trichosanthis (Huafen), and Ophiopogonis Radix (Maidong). Thick black-dry coating in the center indicates severe Stomach heat; Gypsum Fibrosum (Shigao) and Radix Anemarrhenae (Zhimu) are essential. If gums, lips, and mouth turn black, the Stomach is about to rot; rescue requires large doses of Gypsum Fibrosum (3-4 liang), Raw Radix Et Rhizoma Rhei (1 liang), plus Fen Jin Zhi (Faecal Golden Juice), Ren Zhong Huang (Human Middle Yellow), fresh Rehmanniae Radix juice, Asparagus Cochinchinensis Radix juice, Ophiopogonis Radix juice, and Lonicerae Flos Dew. This is common in epidemic macules and Shanghan syndromes. I once treated an only son, using over 14 jin of Gypsum Fibrosum before macules erupted and disease subsided; this relied entirely on diagnostic insight. Black coating that is moist indicates Kidney deficiency; use Liuwei Dihuang Wan (Six-Ingredient Pill with Rehmannia). Full-tongue red-purple without coating is called Jiang She [Crimson Tongue], also indicating Kidney deficiency; use Shengdi, Shudi, Tiandong, Maidong. After illness, a crimson tongue shiny like a mirror, or dry throat without desire for cold drinks, indicates extreme Kidney Water deficiency; use large doses of Liuwei Dihuang Wan to save fluids, otherwise desiccation ensues. (From Jiang Bihua's *Yi Jing*.)

Tongue coating arises from internal heat causing Spleen Qi stagnation, leading to accumulation of food fluids internally, thus manifesting externally. If Spleen Qi is not stagnant, digestion proceeds, fluids circulate, and even with high heat, coating may not form. (In my practice, patients with internal cold-damp often lack coating until warming-dispersing formulas are administered, after which white coating appears, turns yellow, and the disease resolves.) Cyan tongue, or cyan-purple and cold/slippy, indicates cold syndrome. Cyan-purple, dry/scorched, swollen, or contracted tongue indicates heat syndrome. Extreme cold also causes contraction due to cold contracting sinews, but it will not be dry/scorched. Tongue stiffness, shortening, coma, and confused speech indicate untreatable conditions. Phlegm disorders can cause tongue hardness/contraction and coma/speechlessness; differentiate by physical signs, color, and pulse. In heat diseases, tongue ulceration with unrelenting heat is fatal. In Shanghan, Yin-Yang Yi disease with tongue protruding several inches is fatal. (Note: This is actually relapse due to sexual exhaustion, not Yin-Yang Yi. From Guo Yuanfeng's *Mai Ru*.)