辨质者。辨明其舌之木质也。其质虽满舌属胃。而内含经络甚多。与心脾肝肾实互
相关系。凡病之虚实。症之吉凶。多于此中诊断之。故辨质较观形察色。尤为扼要。
凡舌质坚敛而兼苍老。不论苔色白黄灰黑。病多属实。舌质浮胖而兼娇嫩。不拘苔
色灰黑黄白。病多属虚。此辨舌质老嫩。断病虚实之要诀。
凡舌质柔软。伸缩自由者。气液自滋。舌质强硬。伸缩为难者。脉络失养。但舌强
与舌短不同。舌短者舌系收紧。舌强者舌质坚硬。此辨舌质软硬。察液润燥之要诀。
凡看舌质。先辨干滑燥润。干者津乏。扪之而涩。滑者津足。扪之而湿。燥者液涸
。扪之而糙。润者液充。扪之而滑。如病初起而舌即干者。津竭可知。病久而舌尚润者
。液存可识。望之若干。扪之却滑者。若湿热蒸浊。其色黄亮。若瘀血内蓄。其色紫黯。
望之若润。扪之却燥者。若气浊痰凝。其苔白浓。若气虚伤津。其苔白薄。他如阴虚阳
盛者。其舌必干。阳虚阴盛者。其舌必滑。阴虚阳盛而火旺者。其舌必干而燥。阳虚阴
盛而火衰者。其舌必滑而润。此辨舌质干滑燥润。断病津液充乏。阴阳盛衰之要诀。
凡舌质有光有体。不论白黄灰黑。刮之而里面红润。神气荣华者。凡病多吉。舌质
无光无体。不拘有苔无苔。视之
而里面枯晦。神气全无者。凡病皆凶。此辨舌质荣枯。断病吉凶之要诀。
凡舌圆大碎嫩。其质红润者。皆属心经虚热。病尚可治。舌枯小卷短。其质焦紫者
。皆属肝肾阴涸。病多速死。此辨舌质圆嫩枯短。断病虚热阴涸之要诀。
凡舌色如朱柿。光如镜面或如去膜猪腰子。或敛束如荔枝壳。或干枯红长。而有直
纹透舌尖者。病皆不治。尚属显而易见之舌质已枯。更有生气虽绝。而舌质上面。反罩
一层苔色。洁白似雪花片。呆曰如豆腐渣。或如嚼碎饭子。 白兼青。枯白而起糜点。
视其舌边舌底。必皆干晦枯痿。一无神气。乃舌质已坏。脏气皆绝也。病皆速死。此辨舌
质无神无气。断病必死之要诀。
辨别舌质，就是辨明舌头的本质结构。虽然整个舌体归属于胃，但内部包含众多经络，与心、脾、肝、肾等脏腑有着密切的相互关联。凡是疾病的虚实性质、症状的吉凶预后，大多可以通过观察舌质来诊断。因此，辨别舌质比观察舌苔形状和颜色更为关键。
凡是舌质坚硬收敛且显得苍老粗糙的，无论舌苔是白色、黄色、灰色还是黑色，病情多属实证；凡是舌质浮胖娇嫩柔软的，无论舌苔是灰色、黑色、黄色还是白色，病情多属虚证。这是通过辨别舌质的“老”与“嫩”，来判断疾病虚实的关键要点。
凡是舌质柔软，伸缩自如的，说明体内气液充足滋润；凡是舌质僵硬强硬，伸缩困难的，说明脉络失于滋养。但是，“舌强”（舌头僵硬）与“舌短”（舌头短缩）是不同的概念。舌短是因为舌系带收紧，舌强则是舌体本身质地坚硬。这是通过辨别舌质的软硬，来考察津液润燥情况的关键要点。
凡是观察舌质，首先要辨别其干燥、滑利、燥裂或润泽的状态。干燥者，津液匮乏，触摸时感觉涩滞；滑利者，津液充足，触摸时感觉湿润；燥裂者，津液枯竭，触摸时感觉粗糙；润泽者，津液充盈，触摸时感觉光滑。如果疾病初起而舌面即干燥，可知津液已竭；病程长久而舌面依然润泽，可知津液尚存。看起来干燥，触摸却滑利的，若是湿热蒸腾浊气所致，舌色黄亮；若是瘀血内停蓄积，舌色紫暗。看起来润泽，触摸却干燥的，若是气浊痰凝所致，舌苔白厚；若是气虚损伤津液所致，舌苔白薄。其他如阴虚阳盛者，舌必干燥；阳虚阴盛者，舌必滑利。阴虚阳盛且火旺者，舌必干燥且燥裂；阳虚阴盛且火衰者，舌必滑利且润泽。这是通过辨别舌质的干、滑、燥、润，来判断疾病中津液的充乏以及阴阳盛衰情况的关键要点。
凡是舌质有光泽且有形体，无论舌苔是白、黄、灰、黑何色，刮去舌苔后里面红润，神气荣华的，凡病多吉兆；凡是舌质无光泽且无形体，无论有无舌苔，看里面枯槁晦暗，毫无神气的，凡病皆凶兆。这是通过辨别舌质的荣润与枯败，来判断疾病吉凶预后的关键要点。
凡是舌形圆大、破碎娇嫩，舌质红润的，都属于心经虚热，病情尚可治疗；凡是舌形枯瘦、小卷短缩，舌质焦紫的，都属于肝肾阴液枯竭，病情多迅速致死。这是通过辨别舌质的圆嫩、枯短，来判断疾病属于虚热还是阴液枯竭的关键要点。
凡是舌色像朱砂柿子一样红，光亮如镜面，或者像剥了膜的猪腰子，或者紧缩束拢像荔枝壳，或者干枯红长并有直纹透至舌尖的，这些病都难以治愈，这已经是显而易见的舌质枯败之象。更有甚者，虽然生机已绝，但舌面上反而覆盖一层舌苔，洁白如雪花片，呆板如同豆腐渣，或者像嚼碎的饭粒，白色中兼带青色，干枯发白并出现糜烂斑点。查看其舌边和舌底，必定都是干燥晦暗、枯萎痿软，毫无神气，这是舌质已经败坏，脏腑之气全部断绝的表现，病情都会迅速致死。这是通过辨别舌质是否无神无气，来判断疾病必死结局的关键要点。
Differentiating the tongue body involves identifying its fundamental structure. Although the entire tongue is associated with the Stomach, it contains numerous meridians and is closely interconnected with the Heart, Spleen, Liver, and Kidney. The deficiency or excess nature of diseases, as well as the auspicious or ominous prognosis of symptoms, can mostly be diagnosed through the examination of the tongue body. Therefore, differentiating the tongue body is more crucial than observing the tongue coating's shape and color.
When the tongue body is firm, tight, and appears aged or coarse, regardless of whether the coating is white, yellow, gray, or black, the condition is mostly Excess (Shi). When the tongue body is swollen, puffy, delicate, and tender, regardless of whether the coating is gray, black, yellow, or white, the condition is mostly Deficiency (Xu). This is the key to determining the deficiency or excess of a disease by distinguishing between an "aged" (lao) and "tender" (nen) tongue body.
When the tongue body is soft and moves freely, it indicates that Qi and fluids are nourishing. When the tongue body is stiff and difficult to move, it indicates that the collaterals are lacking nourishment. However, "stiff tongue" (She Qiang) differs from "short tongue" (She Duan). A short tongue results from the tightening of the lingual frenulum, whereas a stiff tongue refers to the hardness of the tongue body itself. This is the key to examining the moisture or dryness of fluids by distinguishing between soft and hard tongue bodies.
When observing the tongue body, one must first distinguish between dry, slippery, rough, and moist states. Dryness indicates a lack of fluids, feeling rough to the touch. Slipperiness indicates sufficient fluids, feeling wet to the touch. Roughness indicates depleted fluids, feeling coarse to the touch. Moisture indicates abundant fluids, feeling smooth to the touch. If the tongue is dry at the onset of illness, it indicates exhaustion of fluids; if the tongue remains moist after a long duration of illness, it indicates the presence of fluids. If the tongue appears dry but feels slippery to the touch, it may be due to damp-heat steaming turbid pathogens, presenting with a bright yellow color; or due to internal accumulation of blood stasis, presenting with a purple-dark color. If the tongue appears moist but feels dry to the touch, it may be due to turbid Qi and congealed phlegm, presenting with a thick white coating; or due to Qi deficiency damaging fluids, presenting with a thin white coating. Furthermore, in cases of Yin deficiency with Yang hyperactivity, the tongue will be dry; in cases of Yang deficiency with Yin hyperabundance, the tongue will be slippery. In cases of Yin deficiency with Yang hyperactivity accompanied by blazing fire, the tongue will be dry and rough; in cases of Yang deficiency with Yin hyperabundance accompanied by declining fire, the tongue will be slippery and moist. This is the key to determining the sufficiency or insufficiency of fluids and the balance or imbalance of Yin and Yang by distinguishing between dry, slippery, rough, and moist tongue bodies.
If the tongue body has luster and form, regardless of whether the coating is white, yellow, gray, or black, and upon scraping, the interior is red and rosy with a flourishing spirit, the prognosis for most diseases is auspicious. If the tongue body lacks luster and form, regardless of the presence or absence of coating, and the interior appears withered and dull without any spirit, the prognosis for all diseases is ominous. This is the key to determining the auspicious or ominous prognosis of a disease by distinguishing between a vibrant/flourishing (rong) and withered/dull (ku) tongue body.
If the tongue is round, large, fragmented, and tender with a red and rosy body, it belongs to Deficient Heat in the Heart Meridian, and the disease is treatable. If the tongue is withered, small, curled, and short with a scorched purple body, it belongs to Exhaustion of Yin in the Liver and Kidney, and the disease often leads to rapid death. This is the key to distinguishing between Deficient Heat and Yin exhaustion by observing the round/tender versus withered/short characteristics of the tongue body.
If the tongue color is like a persimmon, shiny as a mirror, or like a pig kidney without membrane, or tightly gathered like a lychee shell, or dry, red, elongated with straight lines extending to the tip, these conditions are incurable. These are obvious signs of a withered tongue body. Even worse, although vital energy is exhausted, a layer of coating may appear on the tongue surface, white like snowflakes, stiff like tofu dregs, or like chewed rice grains, white mixed with green, dry and white with eroded spots. Examining the sides and underside of the tongue reveals they are dry, dull, withered, and flaccid, devoid of spirit. This indicates that the tongue body is ruined and the Qi of the Zang organs is completely exhausted, leading to rapid death. This is the key to determining a fatal prognosis by identifying a tongue body devoid of spirit and Qi.