张三锡曰∶金镜录载三十六舌，辨伤寒之深浅吉凶，可称详备。然细讨究，不
过阴阳、表里、寒热、虚实而已。陶节 曰∶伤寒邪在表，则舌无苔。热邪在表，
则苔渐生。自白而黄，黄而黑甚则黑裂矣。黑苔多凶。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。询其脉之虚实，及中气
何如。实者润而下之。虚人神气不足，当生津固中气。有用生脉散，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。
白苔属寒。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。
白苔燥 虚而微热，或不得汗，或胃中少有饮而不行，宜温解。
白滑苔 虚寒胃寒，阳气不振，宜温。
白苔起芒刺 津液不足，胃中有物，宜运动。
黄苔 微热，热渐入里，或燥渴之象。宜清解。
灰色苔 胃中有物，中气虚热，渴而不能消饮者，宜温解。
黑色苔 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。
凡伤寒辨舌者，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，用于辨别伤寒病的深浅及吉凶预后，可以说非常详尽完备。然而仔细推敲研究，（这些舌象的变化）不过是阴阳、表里、寒热、虚实这八纲辨证罢了。陶节庵说：伤寒邪气在表时，舌面上没有苔；如果是热邪在表，舌苔就会逐渐生成。舌苔由白色转为黄色，由黄色转为黑色，严重时甚至会出现黑裂。黑苔大多预后不良。如果舌根发黑，或舌中发黑，或舌尖发黑，都属于里热证。如果全舌皆黑，则是热极之证，难以治疗。临床上常见外感病兼夹内伤，因宿食积滞严重而结聚在心下部位的情况。经过五六天，舌苔逐渐变黄，或者中间干燥而边缘湿润，这种舌象称为“中焙舌”。这种情况说明里热尚浅。如果舌面完全干燥，无论苔色是黄还是黑，都属于里实证，应根据病情轻重使用泻下法治疗。如果已经使用过泻下法，或者多次泻下后症状不减，这是宿食停滞结聚在中焦脾胃所致。此时需要询问患者脉象的虚实情况，以及中气（脾胃之气）的状态。脉象实者，舌面润泽，可用泻下法治疗。对于正气虚弱、神气不足的人，应当生津液并固护中气。有用生脉散配合对解毒汤而治愈的案例。也有用附子理中汤冷服而治愈的案例。前者属于阴极似阳（真寒假热），后者属于阳极似阴（真热假寒），不可不加以辨别。
白苔属于寒证。如果伴有外在的烦躁症状，患者想要坐在泥水中，这是因为阴寒之邪逼迫无根失守的虚火浮越所致。此时脉象虽然大但按之无力（不鼓指），应当从阴证进行治疗。如果患者并不极度烦躁，而是出现呕吐症状，则应按食积阴证治疗。
白苔干燥且舌体虚软伴轻微发热，或者无汗，或者胃中有少量水饮停聚而不运行，适宜用温散解表的方法治疗。
白苔起芒刺：提示津液不足，胃中有实邪阻滞，适宜用消导运动的方法治疗。
黄苔：提示微热，热邪逐渐入里，或者是燥渴的表现。适宜用清热解里的方法治疗。
灰色苔：提示胃中有积滞，中气虚弱且有虚热，口渴但不能饮水（或饮水不解渴），适宜用温散解表的方法治疗。
黑色苔：提示热邪入里成实。舌苔干燥浓厚者，适宜用泻下法；舌苔滑润者，是水湿困阻火气，适宜用温法。虽然舌苔黑但湿润，这就是所谓的“水极似火”（真寒假热）。只要不干燥，就是异常情况。
大凡通过辨舌来诊断伤寒的，是因为舌属心，心主火。寒属水，水寒凌犯心火，导致舌头受到困扰。
产后通过辨舌来诊断的，是因为心主血。经书说：少阴肾气绝，则血液不流动。所以舌色紫黑的，是血液先已败死的征象。
凡是见到黑舌，一定要询问是否吃过酸、甜、咸的食物？因为这些食物可能会将舌染成黑色。凡是观察舌色，即使心中已有定见，也必须仔细审查兼有的症状，以及脉象的虚实。如果不这样做，恐怕会有毫厘之差导致千里之谬的错误。
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.