张三锡曰金镜录载三十六舌辩伤寒之深浅吉凶可称详备然细讨究不过阴阳表里寒热虚实
而已陶节庵曰伤寒邪在表则舌无胎热邪在表则胎渐生自白而黄黄而黑甚则黑裂矣黑胎多凶若
根黑或中黑或尖黑皆属里热全黑则热极而难治常见外感挟内伤宿食重而结于心下者五六日舌
渐黄或中干而边润名中焙舌此则里热尚浅若全干无论黄黑皆属里证分轻重下之若曾经下或屡
下不减乃宿滞结于中宫也诊其脉之虚实及中气何如实者润而下之虚人神气不足当生津固中气
有用生津散对解毒汤而愈者有用附子理中汤冷服而愈者一则阴极似阳一则阳极似阴不可不辨
白胎属寒外证烦躁欲坐卧于泥水中乃阴寒逼其无根失守之火而然脉大不鼓当从阴证治若
不大躁呕吐者从食阴治之
白胎燥 虚而微热或不得汗或胃中少有饮而不行宜温解
白滑胎 虚寒胃寒阳气不振宜温
白胎起芒刺 津液不足胃中有物宜运动
黄胎 微热热渐入里或燥渴之象宜清解
灰色胎 胃中有物中气虚热渴而不能消饮者宜温解
黑色胎 热入里实燥浓者宜下滑润者水困火宜温虽黑而润所谓水极似火也不燥为异
凡伤寒辩舌者以舌属心而主火寒为水也水寒凌火舌受其困产后辨舌者以心主血也经云少
阴气绝则血不流故舌紫黑者为血先死
凡见黑舌要问曾食酸甜咸物否能染成黑色凡视舌色虽有成见亦必细审兼证及脉之虚实不
尔恐有毫厘千里之谬
张三锡说：《金镜录》记载了三十六种舌象，用以辨析伤寒病的深浅及吉凶预后，可以说非常详尽完备。然而仔细推敲探究，不过归结为阴、阳、表、里、寒、热、虚、实这八纲而已。
陶节庵说：伤寒邪气在表时，舌头上没有苔；若热邪在表（注：此处原文逻辑似有笔误，通常指邪入里或化热），舌苔逐渐生成，由白变黄，由黄变黑，甚至出现黑裂。黑苔多主凶险。如果根部发黑，或者中部发黑，或者尖端发黑，都属于里热证。全黑则说明热极，难以治疗。常见外感病夹杂内伤宿食，病情严重且结聚在心下部位，经过五六天后，舌头逐渐变黄，或者中间干燥而边缘湿润，称为“中焙舌”。这种情况里热尚浅。如果舌苔全干，无论黄色还是黑色，都属于里证，需根据轻重程度使用攻下法。如果曾经用过下法，或者多次使用下法后舌苔不减，那是宿食停滞结聚在中焦脾胃。诊察其脉象的虚实以及中气的强弱，实证且润泽的可攻下；虚人神气不足者，应当生津液、固护中气。有用生津散配合解毒汤治愈的，有用附子理中汤冷服治愈的。前者是阴极似阳，后者是阳极似阴，不可不加以辨别。
白苔属于寒证。如果外证表现为烦躁，想坐在泥水中，这是阴寒逼迫无根失守之火所致。脉象大但不鼓指，应当从阴证治疗。如果不特别躁动且有呕吐症状的，应从食积阴证治疗。
白苔干燥：因虚而有微热，或者无汗，或者胃中有少量水饮停滞不行，宜用温解法。
白滑苔：因虚寒、胃寒、阳气不振，宜用温法。
黄苔：微热，热邪渐入里，或者有燥渴之象，宜用清解法。
灰苔：胃中有积滞物，中气虚，有热渴但不能消化饮水，宜用温解法。
黑苔：热入里，实证、燥结浓重者，宜用下滑润法；若舌面湿润，是水湿困阻火气，宜用温法。虽然苔黑但湿润，所谓“水极似火”，与燥黑不同。
凡是伤寒辨舌，是因为舌属心，心主火，寒属水。水寒凌犯心火，舌头受其困扰。产后辨舌，是因为心主血。经云：少阴气绝则血液不流。所以舌色紫黑的，是血液先败死的征象。
凡是见到黑舌，要询问是否吃过酸、甜、咸的食物，能否染成黑色。凡是观察舌色，即使有成见，也必须仔细审查兼证以及脉象的虚实，否则恐怕会有毫厘之差导致千里之谬。
Zhang Sanxi stated: The *Jin Jing Lu* (Golden Mirror Record) documents thirty-six tongue presentations for differentiating the depth and prognosis of Shanghan (Cold Damage), which can be considered detailed and comprehensive. However, upon careful investigation, these ultimately reduce to the Eight Principles (Ba Gang): Yin, Yang, Exterior, Interior, Cold, Heat, Deficiency, and Excess.
Tao Jie'an stated: When pathogenic factors of Shanghan are in the Exterior, there is no coating on the tongue. If heat pathogens are present [note: text implies progression], the coating gradually forms, changing from white to yellow, then to black, and even cracking with a black appearance. Black coatings often indicate a poor prognosis. If the root, center, or tip of the tongue is black, it belongs to Interior Heat syndromes. A completely black tongue indicates extreme heat and is difficult to treat. It is commonly seen that external contraction complicated by internal injury and retained food stagnation, severe and knotted below the heart, results in the tongue gradually turning yellow after five or six days, or becoming dry in the center while moist at the edges; this is called "Zhong Bei Tongue" (Middle Roasted Tongue). In such cases, the Interior Heat is still shallow. If the coating is completely dry, regardless of whether it is yellow or black, it belongs to an Interior syndrome, and purgative methods should be used according to severity. If purgatives have been used previously or repeatedly without reducing the coating, it indicates that old stagnation is knotted in the Middle Jiao (Spleen and Stomach). One must diagnose the deficiency or excess of the pulse and the strength of the Middle Qi. For excess patterns with a moist surface, purgatives may be used; for deficient individuals with insufficient Shen Qi (Spirit Vitality), one should generate fluids and consolidate the Middle Qi. Some have been cured using Sheng Jin San (Fluid-Generating Powder) combined with Jie Du Tang (Detoxifying Decoction); others have been cured using Fuzi Lizhong Tang (Aconite Regulate the Middle Decoction) taken cold. The former represents Extreme Yin resembling Yang, and the latter represents Extreme Yang resembling Yin; these must not fail to be distinguished.
White coating indicates Cold. If external symptoms include irritability and a desire to sit in mud or water, this is due to Yin-Cold forcing the rootless, unanchored Fire outward. If the pulse is large but does not drum against the fingers, it should be treated as a Yin syndrome. If there is no extreme restlessness but vomiting occurs, it should be treated as a Food-Stagnation Yin syndrome.
Dry White Coating: Due to deficiency with slight heat, or inability to sweat, or slight retention of fluids in the Stomach not moving, warm resolution is appropriate.
Slippery White Coating: Due to deficiency-cold, Stomach cold, and failure of Yang Qi to flourish, warming is appropriate.
White Coating with Prickles: Due to insufficiency of body fluids and presence of material in the Stomach, movement (digestion/promotion) is appropriate.
Yellow Coating: Slight heat, heat gradually entering the Interior, or signs of dryness and thirst, clear resolution is appropriate.
Gray Coating: Presence of material in the Stomach, deficiency of Middle Qi, heat and thirst but inability to digest drinks, warm resolution is appropriate.
Black Coating: Heat entering the Interior, excess and dryness with thick accumulation, sliding down with lubrication is appropriate; if moist, it is water trapping fire, warming is appropriate. Although black and moist, this is described as "Extreme Water resembling Fire," differing from dryness.
In general, for Shanghan, tongue diagnosis is used because the tongue belongs to the Heart, which governs Fire, while Cold belongs to Water. Water-Cold overwhelms Heart-Fire, causing the tongue to suffer. For postpartum conditions, tongue diagnosis is used because the Heart governs Blood. The Classics state: "When Shaoyin Qi is exhausted, blood does not flow." Therefore, a purple-black tongue indicates that the blood has perished first.
Whenever a black tongue is seen, one must ask if the patient has consumed sour, sweet, or salty substances that could stain the tongue black. Whenever observing tongue color, even if one has preconceived notions, one must carefully examine accompanying symptoms and the deficiency/excess of the pulse; otherwise, a discrepancy of a hair's breadth may lead to an error of a thousand miles.