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Zhang Sanxi stated: The *Jin Jing Lu* (Golden Mirror Record) documents thirty-six tongue presentations, used to distinguish the depth and prognosis of Shanghan (Cold Damage diseases), which can be considered quite detailed and comprehensive. However, upon careful investigation, these variations essentially boil down to Yin-Yang, Exterior-Interior, Cold-Heat, and Deficiency-Excess [Bian Zheng Ba Gang]. Tao Jianyuan stated: When Shanghan pathogens are at the Exterior, there is no coating on the tongue. If heat pathogens are at the Exterior, the coating gradually appears. The coating changes from white to yellow, from yellow to black, and in severe cases, it becomes black and cracked. Black coatings often indicate a poor prognosis. If the root, center, or tip of the tongue is black, all belong to Interior Heat syndromes. If the entire tongue is black, it indicates extreme heat and is difficult to treat. Clinically, one often encounters external contraction complicated by internal injury, where retained food stagnates severely and knots below the heart. After five or six days, the tongue coating gradually turns yellow, or the center becomes dry while the edges remain moist; this presentation is named "Zhong Bei She" (Middle-Baked Tongue). This indicates that the Interior heat is still shallow. If the entire surface is dry, regardless of whether the coating is yellow or black, it belongs to an Interior Excess syndrome, and purgatives should be administered according to the severity. If purgatives have already been used, or if symptoms persist despite repeated purgation, this indicates that retained stagnation is knotted in the Middle Jiao. One must inquire about the deficiency or excess of the pulse, and the state of the Middle Qi (Spleen-Stomach Qi). In cases of excess with a moist tongue, purgation is appropriate. For patients with deficient constitution and insufficient Shen Qi (Spirit Qi), generating fluids and consolidating Middle Qi is required. There are cases cured using Sheng Mai San (Generate the Pulse Powder) combined with Dui Jie Du Tang (Antidote Decoction), and cases cured using Fuzi Lizhong Tang (Aconite Regulate the Middle Decoction) taken cold. The former represents Extreme Yin resembling Yang (True Cold False Heat), while the latter represents Extreme Yang resembling Yin (True Heat False Cold); these must not fail to be distinguished.

White coatings belong to Cold syndromes. If accompanied by exterior restlessness, where the patient desires to sit in mud or water, this is caused by Yin-Cold forcing the rootless, unanchored fire to float outward. Although the pulse may appear large, it lacks force upon pressure (does not drum against the fingers); treatment should follow the Yin syndrome protocol. If the patient is not extremely restless but suffers from vomiting, it should be treated as a Food Stagnation Yin syndrome.

Dry white coating with deficiency and slight heat, or inability to sweat, or slight retention of fluids in the stomach that fails to circulate, warrants warm resolution.

White and slippery coating: Indicates deficiency-cold or stomach-cold, with failure of Yang Qi to invigorate; warming methods are appropriate.

White coating with prickles: Indicates insufficiency of body fluids and presence of pathogenic matter in the stomach; methods to promote movement and digestion are appropriate.

Yellow coating: Indicates slight heat, heat gradually entering the Interior, or signs of dryness and thirst. Clearing and resolving methods are appropriate.

Gray coating: Indicates pathogenic matter in the stomach, deficiency of Middle Qi with empty heat, thirst without ability to consume drinks; warm resolution is appropriate.

Black coating: Indicates heat entering the Interior and becoming Excess. If dry and thick, purgation is appropriate. If slippery and moist, it indicates water trapping fire; warming methods are appropriate. Even if black but moist, this is referred to as "Extreme Water resembling Fire" (True Cold False Heat). The lack of dryness is the distinguishing feature.

In general, for diagnosing Shanghan via tongue inspection, the tongue is associated with the Heart, which governs Fire. Cold is associated with Water; when Water-Cold overwhelms Heart-Fire, the tongue suffers its constraint.

For postpartum diagnosis via tongue inspection, it is because the Heart governs Blood. The Classics state: When Shaoyin Qi perishes, blood flow ceases. Therefore, a purple-black tongue indicates that the blood has first perished.

Whenever a black tongue is seen, one must ask if the patient has consumed sour, sweet, or salty foods, as these can stain the tongue black. When inspecting tongue color, even if one holds a preconceived notion, one must carefully examine accompanying symptoms and the deficiency or excess of the pulse. Otherwise, there is fear of errors arising from a slight deviation leading to a great mistake.