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The external manifestation of the center of the tongue (She Xin) should originally be moist and red. If the redness deepens to crimson, it indicates mild heat; if the exterior is red and the interior is purplish, it indicates severe heat; a slippery white coating with a deep, slow, fine, and tight pulse suggests internal cold due to organ deficiency and knotting; a dry and thin coating indicates emptiness of both Qi and fluids; a yellow or black coating that is moist indicates shallow interior heat; a scorched, dry coating with prickles and cracks clearly indicates profound heat; if a slippery black coating appears alongside Shaoyin disease patterns, it signifies Water overcoming Fire, a condition with no hope of survival.

[Note] The tongue is the external indicator of the Heart. A color that is red and lustrous indicates health. If upon initial contraction of pathogenic factors, both the interior and exterior are deeply red, it indicates the presence of heat. If the exterior is red and the interior is purple, it indicates extreme heat. A slippery white coating indicates exterior cold. As the coating gradually becomes thicker and denser, it indicates transmission to the Shaoyang channel. For heat syndromes, acrid-cool diaphoresis is appropriate; for cold syndromes, acrid-warm diaphoresis is appropriate. Involvement of the Shaoyang channel manifests as cold in the chest and heat in the Dantian, which can be harmonized by Xiao Chai Hu Tang (Minor Bupleurum Decoction). Here, "chest" refers to the exterior and superficial aspect; "Dantian" refers to the interior and deep aspect. This does not refer directly to the anatomical chest or Dantian, but rather implies that half-interior heat has not yet fully formed, while half-exterior cold remains. Therefore, a white tongue coating can indicate either cold or heat. If a slippery, thick coating appears simultaneously with Yin-pattern pulses, it indicates organ deficiency and cold knotting, treated with Li Zhong Tang (Regulate the Middle Decoction) plus Zhi Shi (Immature Bitter Orange) to warm and resolve the knot. If a dry, thin coating appears simultaneously with Yang-pattern signs, it indicates Qi deficiency and fluid exhaustion, treated with Bai Hu Jia Ren Shen Tang (White Tiger Plus Ginseng Decoction) to clear heat and tonify. If a white coating gradually turns yellow, this indicates the pathogen moving from the exterior to the interior, with heat still shallow; if exterior symptoms persist, San Huang Shi Gao Tang (Three Yellows and Gypsum Decoction) is indicated; if the pathogen has entered the interior, Liang Ge San (Cooling Diaphragm Powder) is indicated. If the coating is scorched, dry, black, with prickles and cracks, it indicates profound interior heat, treated with Zhi Zi Jin Hua Tang (Gardenia Golden Flower Decoction). If accompanied by abdominal fullness and pain, Da Cheng Qi Tang (Major Order the Qi Decoction) is indicated. Red is the color of Fire; Black is the color of Water. If black coating appears with Yangming/Shaoyang/Yangming patterns, it represents extreme heat mimicking its counteracting element (Water); clearing heat and purging may still be curative. If black coating appears with Three Yin patterns, it signifies Water overcoming Fire, a fatal prognosis. Physicians may wipe the tongue with fresh Ginger; if the black color fades slightly, urgent rescue with Fu Zi Li Zhong Tang (Aconite Regulate the Middle Decoction) or Si Ni Tang (Frigid Extremities Decoction) may save the patient.

Pathogenic factors transmitting to the interior must first pass through the chest, then spread to the hypochondrium, involving the Shaoyang channel. Taiyang disease presents with a floating pulse and only chest fullness; if unrelieved after passing through stages, it may involve the Yangming channel. Dry retching, tidal fever, and chest-hypochondriac fullness require Da Chai Hu Tang (Major Bupleurum Decoction) plus Mang Xiao (Mirabilite) for dual harmonization. If the heart and abdomen radiate to the hypochondrium with hard, full, painful distension, accompanied by dry retching and urinary retention, Shi Zao Tang (Ten Jujube Decoction) is used to attack the retained fluid.

[Note] Pathogenic factors transmitting to the interior necessarily start from the chest. If the pulse is floating and only chest fullness is present without extending to the hypochondrium, it still belongs to the Taiyang exterior, treated with Ma Huang Tang (Ephedra Decoction). If both the chest and hypochondrium are full, it belongs to the Shaoyang channel, treated with Xiao Chai Hu Tang (Minor Bupleurum Decoction). If unresolved after ten-plus days, with chest-hypochondriac fullness, dry retching, and tidal fever, this is Shaoyyang syndrome combined with Yangming syndrome, treated with Da Chai Hu Tang (Major Bupleurum Decoction) plus Mang Xiao (Mirabilite) for dual harmonization. If the exterior syndrome has resolved, and there is hardness, fullness, and pain in the epigastrium and abdomen radiating to the hypochondrium, accompanied by dry retching and dysuria, this is retained fluid with interior excess, treated with Shi Zao Tang (Ten Jujube Decoction) to purge.