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Water has the nature of flowing downward, and fire has the nature of flaming upward; this is the natural principle. The Sanjiao (Triple Burner) is the pathway for water and grain, while Jinye (Body Fluids) are the refined transformation of Qi. They circulate through the Sanjiao to restrain Fire. Currently, dry mouth with thirst indicates Qi deficiency, where excessive Fire leads to the depletion of Body Fluids. The *Classic* states: Liver Heat causes sour taste in the mouth; Heart Heat causes bitter taste; Spleen Heat causes sweet taste; Lung Heat causes pungent taste; Kidney Heat causes salty taste; or a bland taste indicates Stomach Heat. If there is thirst, it results from Heat in the Five Zang Organs, driven by Fire. However, Fire does not flare up unless there is Deficiency; if it flares up and is not resolved, Body Fluids cannot ascend to restrain Fire. Since Fire flames upward, it scorches the Heart and Spleen, causing Body Fluids to sink and the "Huachi" (oral cavity/saliva pool) to dry up, thereby causing thirst. Thirst signifies the dryness and withering of the essence of the Zang-Fu organs. Treatment should appropriately clear Heat and moisten Dryness; once Qi transformation is restored, Body Fluids will generate naturally, and once Heat is removed, irritability and thirst will cease.

If thirst occurs before the eruption of smallpox (or measles/rash), it is appropriate to use methods that disperse and resolve, clearing heat and transforming dampness; after the rash erupts, internal Heat will naturally subside, or one may use Ziling Tang (Purple Talc Decoction) added with Gegen (Kudzu Root) and Jingjie (Schizonepeta). If thirst occurs after the eruption, one should tonify Qi and Blood, using Baoyuan Tang (Preserve the Origin Decoction) added with Maidong (Ophiopogon) and Wuweizi (Schisandra). If diarrhea is present, Shenyin Baizhu San (Ginseng and Atractylodes Macrocephala Powder) should be used as the main formula. If thirst is caused by Yin Deficiency with Hyperactive Fire, it is most difficult to treat.所谓 Yin Deficiency refers to Blood Deficiency. Blood Deficiency cannot be rapidly supplemented because Blood and Qi are vastly different: Qi is formless, whereas Blood is formed. Formless things possess Shen (Spirit/Divine function) and can flourish momentarily; formed things lack Shen and require nourishment over time. Therefore, treatment should employ Dihuang Wan (Rehmannia Pill), added with Rougui (Cinnamon Bark) and Wuweizi, which both tonifies Kidney Yin and ensures there is fire under the pot (Mingmen Fire), so that the lid naturally does not dry out; this is indeed the sacred medicine for treating Deficiency-type thirst.

In cases where smallpox induces thirst, drinking water is contraindicated; otherwise, the movement of Body Fluids will be obstructed, making dryness and thirst worse. Furthermore, after the scabs form, they may fall off late or abscesses may develop. This is because the Spleen and Stomach belong to Earth, dislike Dampness, prefer Moisture but hate Cold, and govern the muscles externally. Drinking cold water causes internal weakness of the Spleen and Stomach and external stagnation of the muscles, freezing the Body Fluids and preventing Ying and Wei Qi from circulating fully, thus leading to delayed scab shedding or abscess formation.

Drinking water also has Yin and Yang distinctions: Those with Excess Yang and Deficient Yin do not feel cold even when consuming ice snow; those with Excess Yin and Deficient Yang do not feel hot even when consuming boiling water. Thus, fever with thirst, cold limbs, spontaneous diarrhea, and preference for hot drinks indicate Excess Yin and Deficient Yang, treated by tonifying Yang. Fever with thirst, constipation, hot hands and feet, and preference for cold drinks indicate Excess Yang and Deficient Yin, treated by nourishing Yin. Irritability with heat, red face, and white eyes indicate Empty Heat in the Kidney Meridian, treated by nourishing the Kidney. During the peak of the rash, if sudden failure to crust occurs, with warmth in the head and cold in the feet, abdominal distension, diarrhea, shortness of breath, and irritability/thirst, this indicates severe Deficiency-Cold; urgently administer Ren Shen (Ginseng), Bai Zhu (Atractylodes), Rou Gui (Cinnamon Bark), and Fu Zi (Aconite). Strictly avoid cold-natured medicines, honey water, and fruits; otherwise, Body Fluids will constrict, turning into intense thirst, with Cold Qi attacking internally forcing Yang upward, worsening abdominal distension, wheezing, thirst, and diarrhea, leading to death.

Generally, thirst belongs to Heat, but it always stems from the dryness and withering of Zang-Fu Body Fluids, and is truly not an Excess condition. Regarding abdominal distension with thirst, diarrhea with thirst, cold toes with thirst, palpitations with fright with thirst, warm body with thirst, hot body with pale face and thirst, chills with unceasing thirst, urgent breathing with teeth grinding and thirst, and increased thirst after drinking water—these nine symptoms are especially not Excess Heat. One should urgently warm the interior and rescue collapse, nourishing Body Fluids to prevent death from itching/collapse, wheezing, and thirst. If treated as a Heat syndrome, danger and death will appear immediately.

Thirst at the onset of the disease often has corresponding patterns, but one must distinguish between responding (normal) and non-responding (abnormal) signs. In the first two to three days, fever and thirst indicate toxin accumulation in the interior and Heat pathogen scorching; treatment should avoid premature pushing-out of toxins. After the fourth day, fever and thirst indicate Body Fluids leaking outward to transform into pus; treatment should use Ren Shen (Ginseng); these are all responding signs. Only after crusting, when pathogens are fully transformed and no residual evil remains in the interior, if extreme thirst suddenly appears, it indicates gradual consumption of True Qi and rising Fire-Toxin; this is a non-responding sign. Urgently provide detoxification, nourishing Yin, generating fluids, and benefiting the throat. If thirst gradually decreases, it is auspicious; if it turns to increased thirst, it will inevitably change into wheezing and distension, becoming critical.

Those who can eat but have thirst have Lung Heat. The *Classic* says: Heart transfers Heat to the Lung, transmitting as Ge Xiao (Diaphragmatic Consumption). This is due to Heart Fire flaming upward, assaulting Lung Metal, steaming the diaphragm, and consuming Body Fluids. The pathology is in the Upper Jiao, treated with Renshen Baihu Tang (Ginseng White Tiger Decoction) added with Huanglian (Coptis). Those who cannot eat but have thirst have Spleen Deficiency. Because the Spleen's Yuan Qi is weak, it cannot transport Body Fluids for the Stomach. The pathology is in the Middle Jiao, and one must guard against diarrhea; thus, Shenyin Baizhu San (Ginseng and Atractylodes Macrocephala Powder) is appropriate. Spontaneous diarrhea with thirst indicates the pathogen has transmitted to the Kidney. Spontaneous diarrhea with thirst belongs to Foot Shaoyin (Kidney) Deficiency, hence the desire for water to self-rescue. The Kidney governs the five fluids, its meridians connect to the Lung, and it ties to the root of the tongue. If the pathogen transmits to the Kidney, opening and closing functions fail, causing spontaneous diarrhea; diarrhea causes Body Fluids to flow downward, drying up Kidney Water, which cannot moisten the tongue upward, causing extreme thirst. The pathology is in the Lower Jiao, treated with Yigong San (Extraordinary Merit Powder) to warm.