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The tongue is the orifice of the Heart (Xin). The Heart belongs to Fire. A red tongue color is the normal hue of Fire; a slight coating on the upper part indicates the accumulation of Fire: this is the tongue color of a healthy person. If one falls ill, the Ministerial Fire (Jun Huo, referring to Heart Fire) becomes deficient internally, and the Stomach lacks the nourishment of grain qi, causing the tongue color to change and a coating to form. People nowadays mistakenly claim that food stagnation in the chest leads to a tongue coating, which is illogical. If coatings were generated by food, why do healthy people who eat several times a day have no coatings? If it is argued that healthy people digest food immediately while sick people retain it leading to coatings, why is there no coating on the first or second days of illness, but a coating appears on the third or fourth days when food intake has ceased? Thus, the theory that "food presence causes coatings" can be known as erroneous. Medical texts distinguishing thirty-six types of tongues exaggerate and complicate matters without any empirical verification. Physicians of the world, unaware that these are false statements, rely on them rigidly when treating diseases; this does not save patients but rather harms them.

The tongues of healthy people naturally have no coating; if slightly present, it is merely faint, appearing between pale white and pale yellow! Only when the heat-fire qi of the Sanjiao (Triple Burner) is invaded by cold will a white, slippery coating appear on the tongue, accompanied by fever and loss of appetite. When deficiency-heat in the Middle and Upper Jiao steams each other, a sticky and dirty coating forms. A pale yellow or slightly yellow coating indicates Spleen/Stomach (Middle Earth) deficiency; a gray-brown or sauce-board colored coating indicates Middle Earth cold. A purple tongue indicates deficiency-cold; a deep purple tongue indicates severe deficiency-cold. A bright purple tongue indicates long-standing disease with fire decline and the Earth (Spleen) losing its source of generation; a pale white and bright tongue indicates long-standing Yin deficiency with internal depletion of Ying Blood. A black coating indicates the decline of Jun Fire, allowing the Water color (Kidney Water) to ascend. It must be understood that the tongue belongs to Fire; when Fire displays its true color, it is the tongue of a healthy person. In a healthy person, the five fires shine brightly, like the sun illuminating the sky, eliminating shadows; how could there be a coating? Only in severe Shanghan (Cold Damage) diseases, when Jun Fire is dim, does the Sanjiao Xiang Fire (Ministerial Fire) invade the position of Jun Fire, causing abnormal tongue colors.

The invasion of Jun Fire by Xiang Fire is not due to an excess of Xiang Fire, but a deficiency of Jun Fire. Physicians, failing to understand the need to support the dim Jun Fire, instead suppress the ascending Xiang Fire with cooling medicines. This further depletes Jun Fire, exhausts Xiang Fire, scatters the spirit and consciousness, inevitably leading to death. In healthy people, Stomach Qi is abundant, the Sanjiao is harmonious, and Jun Fire shines brightly. Whatever flavors enter the mouth—sour, salty, sweet, or bitter—they pass through without leaving a coating. When ill, Stomach Qi is empty, the Sanjiao fails in its duties, and Jun Fire declines. If flavors enter the mouth, encountering sour, salty, sweet, or bitter elements, they stagnate on the tongue and generate a coating. People do not believe this; they only observe that after children take medicine, the medicinal color condenses on the tongue and does not fade, or when adults eat sour food, the tongue coating turns black. These are the signs. Black is the color of Water. In Shanghan, a black coating is often explained by the theory of "extreme heat resembling water," yet prescriptions still advocate cooling. The phrase "extreme heat resembles water" refers to the principle that things reverse when they reach an extreme. Having reversed, treatment should follow the nature of the disease (Cong Zhi), not oppose it (Dui Zhi). Opposing treatment suits cooling, but following treatment suits warming. Alas, in identifying tongues, deficiency is mistaken for excess, and cold for heat; failing to trace the root and clarify the source, errors are passed down as truths. Although abnormal tongue colors can also indicate excess-heat syndromes, only one or two out of ten cases are excess-heat, corresponding to Yangming/ShaoYang/Taiyang diseases; seven or eight out of ten are deficiency-cold, corresponding to Taiyin/Yangming/Jueyin diseases.

If an abnormal tongue has red spots as large as mustard seeds, it is a deficiency-heat tongue. If the tongue color is normal but has red spots as large as mustard seeds, it is an excess-heat tongue. If the tongue has a black coating due to extreme heat, the coating floats high on the surface without damaging the tongue body itself, appearing black or gray; this is the indication for Rhinoceros Horn (Xi Jiao), Scutellaria (Huang Qin), Coptis (Huang Lian), and Gypsum (Shi Gao). This occurs in only one out of a hundred cases! Regarding indications for Da Cheng Qi Tang (Major Order the Qi Decoction) and Xiao Cheng Qi Tang (Minor Order the Qi Decoction), the tongue may also be dry and black, but the patient must speak forcefully; although the spirit seems confused, the original spirit remains condensed within. Treatment with Cheng Qi Decoctions leads to recovery, also occurring in only one out of a hundred cases! If the blackness is scattered and moist, with gray-purple edges, it is a deficiency-cold tongue. If the blackness is condensed and withered, resembling scales on top, it is a severe deficiency-cold tongue; both are suitable for Ginseng (Ren Shen), Atractylodes (Bai Zhu), Cinnamon Twig (Gui Zhi), and Prepared Aconite Root (Fu Zi), and strictly prohibit cooling medicines. If Stomach Qi is exhausted, the entire tongue resembles a cocoon, hard and yellow, or hard and black; such a tongue has less than one chance in a hundred of survival. My method of tongue diagnosis differs from medical texts, and readers may not believe it. However, if you do not discard my words, the number of deaths caused by misdiagnosis will be reduced.