盖闻道原于天。而具于心。心者生之本。形之君。至虚至灵。具众理而应万事者也。其窍开于舌。其经通于
舌。舌者心之外候也。是以望舌。而可测其脏腑经络寒热虚实也。约而言之。大纲有五。一曰形容。二曰气
色。三曰苔垢。四曰津液。五曰部位。五者分论。则其体明。五者合观。则其用达矣。由是察其形容。舌常有刺
也。无刺者。气衰也。刺大刺多者。邪气实。刺微刺少者。正气虚。舌常无纹也。有纹者。血衰也。纹少纹浅者。衰
之微。纹多纹深者。衰之甚。舌肿者。病在血。舌痿者。病在肉。舌偏斜者。病在经。舌缺陷者。病在脏。舌战动者。
病在脾。舌纵舌缩者。病在心。舌裂舌烂者。病在脉。舌卷舌短者。心肝之证候。舌强舌硬者。心脾之病形。弄
舌者。太阴之形症。啮舌者。少阴之气逆。诸太过者病在外。诸不及者病在内。此皆形容之目也。由是观其
气色。舌赤者。心之正色也。深赤者为太过。淡红者为不及。深而紫者。血分热。淡而白者。气分寒。深青者。瘀
血疼痛。淡黑者。气血虚寒。深赤而黑者。热极。淡白而青者。寒深。诸色浅者正虚。诸色深者邪实。明润而有
血色者生。枯暗而无血色者死。此皆气色之目也。由是视其苔垢。舌常有苔也。无苔者虚也。苔垢薄者。形
气不足。苔垢浓者。病气有余。白苔者病在表。黄苔者病在里。灰黑苔者。病在少阴。苔色由白而黄。由黄而
黑者。病日进。苔色由黑而黄。由黄而白者。病日退。此皆苔垢之目也。由是审其津液。滋润者其常。滑涩者
其变。滑为寒。寒有上下内外之辨。涩为热。热有表里虚实之分。此皆津液之目也。由是分其部位。手少阴
通舌本。足少阴挟舌本。足厥阴络舌本。足太阴连舌本。散舌下。舌本在下。舌尖在上。舌中为内。舌边为外。
左病者应在左。右病者应在右。而凡形容之变。气色之殊。与夫苔垢之分。津液之辨。皆可以是推之。此部
位之目也。夫然后举夫五者之大纲。以参究五者之细目以合观。化而裁之。推而行之。其理无穷。其用不
尽矣。虽然五者之用。固在通变。而五者之变。又在求神。神也者。灵动精爽。红活鲜明。得之则生。失之则死。
变化不可离。斯须不可去者也。是又五法之本也。他如诸书之条目。选录于后篇。学人合五法而察之。参
四诊而治之。庶乎其不悖矣。
听说“道”源于天，而体现于心。心是生命的根本，形体的主宰，极其虚空且灵动，具备各种道理并能应对万事万物。心的窍穴开于舌，其经脉连通于舌，所以舌是心的外在征象。因此，通过观察舌象，就可以推测脏腑经络的寒热虚实情况。概括来说，主要有五个大纲：一是舌的形状与神态（形容），二是舌的气色，三是舌苔的厚薄污垢，四是津液的润燥，五是舌的部位。这五项分别论述，就能明确舌体的本质；综合观察，就能通达其应用。
由此观察舌的形状与神态：舌面上常有芒刺。没有芒刺的，是正气衰弱；芒刺粗大且多的，是邪气实盛；芒刺细微且少的，是正气虚弱。舌面通常没有裂纹。有裂纹的，是血液衰少；裂纹少且浅的，是衰少轻微；裂纹多且深的，是衰少严重。舌体肿胀的，病在血分；舌体痿软无力的，病在肌肉；舌体偏斜的，病在经络；舌体有缺损的，病在脏；舌体颤动的，病在脾；舌体纵伸或短缩的，病在心；舌体开裂或溃烂的，病在脉；舌体卷曲或短小的，是心和肝的证候；舌体强硬或坚硬的，是心和脾的病形；弄舌（舌头伸出舔唇）的，是太阴病的形态症状；咬舌的，是少阴经气逆乱。凡是表现过于亢盛的，病在外；凡是表现不足的，病在内。这些都是关于舌形状与神态的观察要点。
由此观察舌的气色：舌色红润，是心的正常颜色。深红色属于太过，淡红色属于不及。深紫色，是血分有热；淡白色，是气分有寒。深青色，是瘀血疼痛；淡黑色，是气血虚寒。深赤色兼黑，是热极；淡白色兼青色，是寒深。所有颜色浅淡的，是正气虚弱；所有颜色深沉的，是邪气实盛。色泽明润且有血色的是生证，枯暗无血色的是死证。这些都是关于舌气色的观察要点。
由此观察舌苔污垢：舌面上通常有苔。没有苔的，是虚证。苔垢薄的，是形体和正气不足；苔垢厚的，是病气有余。白苔，病在表；黄苔，病在里；灰黑苔，病在少阴。苔色由白变黄，由黄变黑的，说明病情日益加重；苔色由黑变黄，由黄变白的，说明病情日益减轻。这些都是关于舌苔污垢的观察要点。
由此审视津液：滋润是正常的，滑利或涩滞是变化。滑利主寒，寒证有上、下、内、外的区别；涩滞主热，热证有表、里、虚、实的区分。这些都是关于津液的观察要点。
由此分辨部位：手少阴心经通连舌根，足少阴肾经夹持舌根，足厥阴肝经络系舌根，足太阴脾经连接舌根并散布于舌下。舌根在下，舌尖在上。舌中部对应体内，舌边缘对应体表。左侧有病，应在左侧反映；右侧有病，应在右侧反映。而凡舌形状神态的变化、气色的差异、苔垢的区别、津液的辨别，都可以据此进行推断。这就是关于部位的观察要点。
这样之后，举起这五方面的总纲，来参究这五方面的细目，综合观察，融会贯通，推演施行，其中的道理无穷无尽，应用也不尽相同。虽然这五方面的应用在于通晓变化，但这五方面的变化又在于探求“神”。所谓“神”，是指灵动精爽、红活鲜明，得到它则生，失去它则死，这种生机不可分离，片刻也不能缺失。这又是五种诊法的基础。其他如各类书籍中的条目，将选录在后篇。学习者若能结合这五种方法去观察，参合望闻问切四诊去治疗，大概就不会违背医理了。
It is heard that the Dao (the Way) originates from Heaven and is embodied in the Heart. The Heart is the root of life and the ruler of the form; it is extremely empty and spiritual, possessing all principles and responding to all matters. Its orifice opens at the tongue, and its meridians connect to the tongue; thus, the tongue is the external manifestation of the Heart. Therefore, by observing the tongue, one can infer the cold, heat, deficiency, and excess conditions of the Zang-Fu organs and meridians. In summary, there are five main categories: first, the shape and spirit (Xingrong); second, the color and luster (Qise); third, the coating and turbidity (Taiwu); fourth, the body fluids (Jinye); and fifth, the location (Buwai). When discussed separately, these five clarify the substance; when observed together, they reveal their application.
From this, observe the shape and spirit: The tongue surface often has prickles (Manci). The absence of prickles indicates Qi deficiency; large and numerous prickles indicate Excess pathogenic factors; minute and few prickles indicate Deficiency of healthy Qi. The tongue surface usually lacks cracks. The presence of cracks indicates Blood deficiency; few and shallow cracks indicate slight deficiency; many and deep cracks indicate severe deficiency. Tongue swelling indicates pathology in the Blood level; tongue flaccidity indicates pathology in the muscles; tongue deviation indicates pathology in the meridians; tongue defects indicate pathology in the Zang organs; tongue tremors indicate pathology in the Spleen; tongue protrusion or retraction indicates pathology in the Heart; tongue fissures or ulcers indicate pathology in the vessels; tongue curling or shortening are syndromes of the Heart and Liver; tongue stiffness or hardness are pathological forms of the Heart and Spleen; tongue fidgeting (licking lips) is a morphological symptom of Taiyin disease; tongue biting indicates rebellion of Shaoyin Qi. Manifestations that are excessive indicate pathology in the exterior; manifestations that are insufficient indicate pathology in the interior. These are the items concerning the observation of shape and spirit.
From this, observe the color and luster: A reddish tongue is the normal color of the Heart. Deep red indicates excess; pale red indicates insufficiency. Deep purple indicates Heat in the Blood level; pale white indicates Cold in the Qi level. Deep cyan indicates blood stasis and pain; pale black indicates Qi and Blood deficiency with Cold. Deep crimson mixed with black indicates extreme Heat; pale white mixed with cyan indicates deep Cold. All light colors indicate Healthy Qi deficiency; all dark colors indicate Pathogenic Excess. Bright, moist, and blood-colored tongues indicate survival; dry, dull, and bloodless tongues indicate death. These are the items concerning the observation of color and luster.
From this, inspect the coating and turbidity: The tongue usually has a coating. The absence of coating indicates Deficiency. Thin coating indicates insufficiency of form and Qi; thick coating indicates surplus of pathogenic Qi. White coating indicates pathology in the Exterior; yellow coating indicates pathology in the Interior; gray-black coating indicates pathology in Shaoyin. If the coating color changes from white to yellow, and from yellow to black, the disease progresses daily; if it changes from black to yellow, and from yellow to white, the disease recedes daily. These are the items concerning the observation of coating and turbidity.
From this, examine the body fluids: Moisture is normal; slipperiness or roughness are variations. Slipperiness indicates Cold, which must be differentiated into upper/lower and interior/exterior; roughness indicates Heat, which must be differentiated into exterior/interior and deficiency/excess. These are the items concerning the observation of body fluids.
From this, distinguish the locations: The Hand-Shaoyin meridian connects to the tongue root; the Foot-Shaoyin meridian flanks the tongue root; the Foot-Jueyin meridian links to the tongue root; the Foot-Taiyin meridian connects to the tongue root and scatters under the tongue. The tongue root is inferior, and the tongue tip is superior. The center of the tongue corresponds to the interior, and the edges correspond to the exterior. Pathology on the left should manifest on the left; pathology on the right should manifest on the right. Thus, any variations in shape/spirit, differences in color/luster, distinctions in coating/turbidity, and analyses of body fluids can be inferred thereby. This constitutes the items concerning location.
Thereafter, taking the general outline of these five aspects to investigate their specific details, and observing them comprehensively, integrating and adapting them, and pushing them into practice, the principles are infinite and applications inexhaustible. Although the utility of these five lies in understanding change, the change within these five lies in seeking "Shen" (Spirit/Vitality). Shen refers to being agile, crisp, vibrant, and bright; possessing it leads to life, losing it leads to death. This vitality cannot be separated from change and cannot be absent for even a moment. This is the foundation of the five methods. Other entries from various books will be selected and recorded in subsequent chapters. Students who combine these five methods for observation and integrate them with the Four Diagnostic Methods for treatment will likely not deviate from the correct principles.