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The tongue presents with a white periphery and a black center. If the pulse is deep and faint, the condition is difficult to treat. If the pulse is floating and slippery, diaphoresis (sweating method) may be employed. If the pulse is deep and excess, purgation may be employed. If this tongue manifestation appears at the onset of the disease, it indicates an extremely critical and dangerous state. It should be treated with Tiaowei Chengqi Tang (Stomach-Harmonizing Purging Decoction).

[Commentary by Jie] This tongue manifestation should be interpreted in four distinct scenarios. First, when the tongue periphery is white and the center is black, accompanied by a deep and faint pulse. If this tongue appears immediately upon the onset of illness, without prior transformation from white or yellow coating, nor due to tongue shrinkage, it signifies cold pathogen directly attacking the Zang organs, causing Cold-Water to overwhelm the Heart, with Kidney color manifesting externally. Urgent treatment with warming agents is required; any delay will lead to failure. Hence, it is said to be "difficult to treat." This corresponds to Zhang Xugu's statement: "Regarding black coating, there are significant differences between deficiency/excess and cold/heat. If the coating is moist rather than dry, or if there is no coating resembling soot, it precisely indicates Kidney Water overacting on Heart Fire, representing extreme Yang deficiency." Second, when the pulse is floating and slippery, diaphoresis may be employed. This aligns with Zhang Zhongjing's *Shanghan Lun* (Treatise on Cold Damage), which states: "Heat on the exterior and Cold on the interior, Baihu Tang (White Tiger Decoction) is indicated." Third, when the pulse is deep and excess, purgation may be employed. The tongue appears black in the center without coating, and the tongue base is dry with visible fine cracks, indicating Excess-Heat in the Stomach meridian. Treatment is suitable with Sanhuang Baihu Tang (Three-Yellow White Tiger Decoction: Coptidis Rhizoma, Scutellariae Radix, Gardeniae Fructus, Gypsum Fibrosum, Anemarrhenae Rhizoma, Glycyrrhizae Radix et Rhizoma, Oryzae Fructus). In cases where pathogenic heat transmits inward causing the tongue to turn black due to heat accumulation, dryness, and excess, with fluids scorched and parched, urgent purgation is needed to remove heat stagnation and preserve fluids. Thus, Tiaowei Chengqi Tang is used. This resembles Wang Mengying's view: "If the tongue center has no black coating but the root has a dry black coating, purgation is appropriate." Fourth, if this tongue appears at the very onset of the disease, it represents Cold Pathogen directly invading the Three Yin meridians. The tongue must be moist, and the condition is perilous and acute, leaving little time for rescue. Hence, it is described as "extremely critical."

When the tip has white coating covering two parts and the root has black coating covering one part, body pain and aversion to cold are invariably present. If thirst is not severe and fluid intake is low, Wuling San (Five-Ingredient Powder with Poria) is indicated. If spontaneous sweating and thirst occur, Baihu Tang (White Tiger Decoction) is indicated. If diarrhea occurs, Jiedu Tang (Detoxification Decoction) may be used. This too is a critical condition.

[Commentary by Jie] White coating with black spots, or black streaks that are sticky, belongs to Dampness syndrome of the Taiyin Qi level. Therefore, symptoms include body pain, aversion to cold, and thirst with desire for minimal drinking. Treatment should focus on promoting dampness resolution and harmonizing the Spleen, hence Wuling San is the primary formula. If the blackness spreads from the root to the tip, becoming unscrapable and unable to be moistened, the pathogen has transformed into Heat, which is drying and consuming Stomach fluids. Consequently, symptoms of spontaneous sweating and thirst appear, and Baihu Tang (White Tiger Decoction) is used to clear Stomach Heat. If Heat pathogen shifts from the Yangming to the Taiyin, the deeper the heat, the heavier the toxicity. At this stage, the coating turns purely black without prickles. Because the Heat-Toxin has nowhere to vent, it rushes to the Large Intestine causing sudden profuse diarrhea, resembling dysentery. Rapid use of Jiedu Tang (Detoxification Decoction) to resolve intestinal Heat-Toxin is paramount. However, once the condition reaches this stage, it is extremely critical.

[Baihu Tang Analysis] In Zhang Zhongjing's *Shanghan Lun*, Baihu Tang uses Jingmi (Coix Seed/Rice Grain - specifically Oryza sativa var. japonica, often translated as Rice Grain or Glutinous Rice depending on context, here distinguished from Nuomi) rather than Nuomi (Glutinous Rice). This is likely because Nuomi is sweet and warm, capable of arresting sweating, whereas Jingmi is sweet and neutral, enters the Lung, clears irritability and heat, and stops thirst. Ke Yunbo stated: Yangming pathogens transform via Heat; thus, there is aversion to heat rather than cold. Heat steams outward, causing spontaneous hot sweat. Heat scorching the Stomach causes thirst and desire for water. Pathogen is abundant and excess, resulting in a slippery pulse. Yet, since it remains in the channels, the pulse also floats. Yangming belongs to the Stomach, governing muscles. Although there is great Heat, it has not formed solid excrement, so bitter-cold herbs alone cannot treat it. Shigao (Gypsum Fibrosum) is acrid and cold; acridity resolves muscular heat, coldness subdues Stomach fire. Cold nature sinks, acridity moves outward, mastering both interior and exterior functions, thus serving as the Sovereign herb. Zhimu (Anemarrhenae Rhizoma) is bitter and moistening; bitterness drains fire, moisture nourishes dryness, thus serving as the Minister herb. Gancao (Glycyrrhizae Radix et Rhizoma) and Jingmi harmonize in the Middle Jiao, draining fire from Earth, embodying the sweet nature of agriculture. Cold agents become milder with them; bitter drugs become less harsh with them, allowing their sinking properties to linger in the flavor. With these two as Assistant/Advisor herbs, the great cold nature does not damage the Spleen and Stomach. When decocted and entering the Stomach, it distributes to the Spleen and returns to the Lungs, spreading fluid essence, resolving great irritability and thirst. Baihu (White Tiger) is the Metal Spirit of the West; naming the decoction after it implies that when Autumn Metal rules, summer heat naturally resolves. Adding Renshen (Ginseng Radix) supplements Middle Qi and generates fluids, coordinating with Gancao and Jingmi to counteract the cold of Shigao and Zhimu, draining fire without injuring Earth, ensuring absolute safety.

[Jiedu Tang Analysis] Wang Ang stated: Extreme cold is called Yin Toxin; extreme heat is called Yang Toxin. This formula is named Huanglian Jiedu Tang (Coptis Detoxification Decoction). Huanglian (Coptidis Rhizoma) acts as the Sovereign to directly resolve Heart Meridian Fire-Toxin; Huangqin (Scutellariae Radix) drains Lung Meridian Fire-Toxin; Huangbai (Phellodendri Cortex) drains Kidney Meridian Fire-Toxin; Zhizi (Gardeniae Fructus) unblocked-drains Sanjiao Fire-Toxin, allowing all Fire-Toxins to exit via the Bladder.