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The original formula of Baihu Tang (White Tiger Decoction). Add Renshen (Ginseng Radix et Rhizoma) 3 liang. Decoct and take as previously directed.

Baihu (White Tiger) refers to the Metal Spirit of the West. Its primary action is on the Lung, not exclusively targeting the Yangming channel. The addition of Renshen here indicates treatment focusing on the Stomach of Yangming. According to the classic text regarding Baihu Tang syndrome, there is no mention of thirst. However, in formulas containing Renshen, symptoms described include dry mouth with thirst, severe restlessness with thirst, or a desire to drink several sheng of water. These conditions mostly arise after sweating, vomiting, or purging, where internal heat remains unremoved and stomach fluids are nearly exhausted. Thus, adding Renshen to Baihu Tang transforms its function from clearing metal and washing away heat to benefiting the stomach and moistening dryness. This achieves the dual benefit of draining the "son" (Earth/Stomach) to supplement the "mother" (Metal/Lung), reaping advantages for both.

Furthermore, the Baihu Tang syndrome primarily aims to disperse pathogens and wash away heat; therefore, it is unsuitable to add Renshen, which might retain the pathogen. Here, Renshen is added to rescue the failing stomach qi. Hence, using Renshen to benefit the stomach allows Baihu Tang to synergistically achieve its effects of clearing heat and relieving thirst.

How could the ancient sages lightly add any herb when establishing formulas?

Chaihu (Bupleuri Radix) 8 liang, Huangqin (Scutellariae Radix) 3 liang, Renshen (Ginseng Radix et Rhizoma) 3 liang, Gancao (Glycyrrhizae Radix et Rhizoma) 3 liang, Banxia (Pinelliae Rhizoma Praeparatum) 8 liang (washed), Shengjiang (Zingiberis Rhizoma Recens) 3 liang (sliced), Dazao (Jujubae Fructus) 13 pieces (torn open).

Take these seven ingredients, add 12 sheng of water, decoct to obtain 6 sheng, remove the dregs, and decoct again to obtain 3 sheng. Take 1 sheng warm, three times daily.

This is the principal formula for Shaoyang disease. According to Zhang Zhongjing, bitter taste in the mouth, dry throat, and vertigo are attributed to Shaoyang disease. The pathogens of Shaoyang mostly transmit from Taiyang. At this stage, situated at the boundary between half-exterior and half-interior, righteous qi and pathogens contend, resulting in alternating chills and fever, fullness and discomfort in the chest and hypochondrium, silence with lack of appetite, irritability, and a tendency to vomit. These are mandatory symptoms of Shaoyang disease. Since the pathogen is not in the exterior, sweating and emesis are inappropriate; since it is not in the interior, reckless purgation is inappropriate. Only Xiaochaihu Tang serves as a harmonizing agent. However, transmitted pathogens are often elusive. Symptoms may include: vexation in the chest without vomiting, thirst, abdominal pain, hardness and fullness under the ribs, palpitations in the epigastrium with difficult urination, absence of thirst with slight body heat, or coughing. These are not mandatory symptoms of Shaoyang disease, but when seen in Shaoyang illness, specific modifications apply, though the general principles remain centered on Xiaochaihu Tang.

Note: Chaihu grows by absorbing the Qi of one Yang. Shaoyang pathogens cannot be resolved without it. Combined with Gancao to harmonize exterior and interior, these are indispensable herbs in Xiaochaihu Tang. Shengjiang disperses Taiyang cold externally, allowing half-exterior pathogens to be released outward. Huangqin clears Yangming heat internally, allowing half-interior pathogens to penetrate inward. Banxia has the ability to eliminate fluid retention, used here to descend rebellious qi and stop vomiting. Dazao excels in harmonizing the middle, used to calm the Spleen (Earth) and subdue the Liver (Wood). Renshen is used not primarily to tonify righteousness, but because the pathogen is at the half-exterior/half-interior boundary; it pre-emptively supports the interior qi to prevent the pathogen from entering inward. This serves as the specific main formula for alternating chills and fever, chest/hypochondriac fullness, silence with anorexia, irritability, and vomiting. The modification methods are detailed below based on this formula.

Renshen is used in this formula because of the contention between pathogen and righteous qi, thus aiding righteousness. Banxia is used because of vomiting and fullness, thus stopping vomiting. If there is only vexation without vomiting, there is no fluid retention; why use Banxia to eliminate fluids? Vexation without vomiting differs from the "vexation with vomiting" of the main syndrome; it represents heat pathogens clustering and about to enter the interior. Using Renshen here would not restore righteousness but rather solidify the pathogen, causing significant harm. Therefore, remove Renshen and add Gualou Shi (Trichosanthis Fructus). Gualou Shi descends hot phlegm and opens chest bi-obstruction.

Banxia is acrid, warm, and drying, suitable for cold-damp phlegm but not hot phlegm. If thirsty, fluids are exhausted, leaving no phlegm to attack. Although this formula contains Huangqin, Gancao, and Dazao to nourish righteousness and dispel heat, stomach fluids require Renshen to stimulate their generation. Thus, adding Renshen awakens stomach qi, and combined with Gualou Gen (Trichosanthis Radix) to generate fluids and moisten dryness, Renshen poses no risk of supporting the pathogen.

Huangqin is bitter and cold, used here to clear half-interior heat. If abdominal pain occurs, yang pathogens have sunk into Taiyin; how can they tolerate the bitter cold of Huangqin? Why use Shaoyao (Paeoniae Radix Alba) instead? Although the syndrome belongs to Taiyin, the cause is yang pathogens sinking in. Thus, Shaoyao is used to constrain Spleen yin. When Taiyang disease transfers to Taiyin, Shaoyao is added to Guizhi Tang, e.g., Guizhi Jia Shaoyao Tang. When Shaoyang disease involves Taiyin, Shaoyao is added to Chaihu Tang, i.e., this formula's modification. Later practitioners rigidly associate drugs with diseases, claiming Shaoyao stops abdominal pain. Consider: is Shaoyao suitable for Taiyin cold-damp syndromes? For heat-induced severe pain? Unknowingly, when yang pathogens sink inward, Chaihu, Renshen, Shengjiang, and Banxia in this formula are sufficient to raise yang qi and resolve spleen/stomach distress. Adding Shaoyao to constrain yin returns pathogens to yang and calms yin; pain ceases without direct analgesia, adhering still to harmonization.

Dazao is used in this formula to fear Wood (Liver) overacting on Earth (Spleen), thereby calming the middle. If hardness/fullness exists under the ribs, pathogens stagnate in the middle jiao, making Dazao's stabilizing nature inappropriate. The hypochondrium belongs to Shaoyang; hardness/fullness indicates qi and blood knotting. Thus, Muli (Ostreae Concha) assists Chaihu: one to dissipate qi-level knots, the other to soften blood-level hardness.

Shaoyang belongs to Wood. Wood overacting on Earth means Earth cannot control Water, leading to palpitations and difficult urination. Using Huangqin would aid water pathogens to form malaria. For difficult urination, diuresis is indicated. This formula already uses Renshen, Gancao, Shengjiang, and Dazao to support Earth; adding Fuling (Poria) for its bland leaching property guides water out.

Thirst is a sign of pathogens intending to enter the interior. Absence of thirst indicates no interior syndrome. External slight heat indicates Taiyang exterior syndrome persists. With exterior pathogens unresolved, Renshen risks solidifying pathogens and should be removed. Adding Guizhi (Cinnamomi Ramulus) changes the table-interior harmonizing structure to focus on the exterior.

Cough belongs to water pathogens attacking the Lung. Renshen and Dazao are unsuitable for cough. Shengjiang is sufficient for exterior dispersion but insufficient for warming the interior; thus, Ganjiang (Zingiberis Rhizoma) replaces Shengjiang to disperse cold and eliminate water. Wuweizi (Schisandrae Fructus) is used because the Lung is not primarily diseased, but cough results from water pathogens rising from below. Wuweizi and Ganjiang are used together: one to disperse water pathogens, the other to astringe lung rebellion. This differs from wind-fire invading the Lung, where Wuweizi is contraindicated. Huangqin is retained to control ministerial fire and preserve lung yin.

Note: Xiaochaihu Tang governing Shaoyang is a critical juncture in Shanghan. Exiting leads to Yang, entering leads to Yin. All yang pathogens entering yin rely on Shaoyang guarding the gates to prevent rapid entry into yin. Must treatment not be cautious? Any syndrome from other meridians can accompany Shaoyang disease. Its modification methods are precise and logical. Readers of Zhang Zhongjing's works must study this section carefully.

In Shanghan or Zhongfeng, if Chaihu patterns exist, observing one symptom suffices; all need not be present. This does not teach lax differentiation. Disease entering Shaoyang stands at the intersection of yin and yang. It either exits to yang or enters yin. Upon seeing one Shaoyang symptom, use Chaihu to lead pathogens out from Shaoyang, preventing inward entry. Note that broad differentiation criteria correspond to critical treatment points. Transmitted Shaoyang pathogens often present with variable or absent symptoms; how can every symptom be observed?

Regarding thirst: differences exist in progression. In Shanghan after 4-5 days, with body heat, aversion to wind, stiff neck, fullness under ribs, warm hands/feet, and thirst, this is Shaoyang combining with Taiyang. Treatment follows Shaoyang, not Taiyang. If thirst develops after taking Chaihu Tang, it belongs to Yangming. Treatment then follows Yangming, not Shaoyang. Thirst syndromes require careful examination.

Shaoyang pulse is wiry. If Taiyang disease unresolved transfers to Shaoyang without vomiting/purging, presenting with deep-tight pulse, hardness/fullness under ribs, dry retching, inability to eat, and alternating chills/fever, the deep-tight pulse indicates pathogens preparing to enter from Shaoyang. Urgently use Xiaochaihu Tang to lead pathogens out from Shaoyang, resolving Taiyang pathogens naturally.

Yangming disease with hardness/fullness under ribs, constipation, vomiting, and white tongue coating indicates pathogens have not congealed in Yangming. Use Xiaochaihu Tang to unblock the upper jiao, allowing fluids to descend, harmonizing the Stomach and resolving Yangming pathogens.

In women with heat entering the blood chamber, heat pathogens have sunk into the yin levels due to deficiency. Why use Xiaochaihu Tang, a Shaoyang formula? Among the Three Yin and Three Yang, Shaoyang is the pivot from yang to yin. Yang heat pathogens crossing Shaoyang into yin must urgently be led out from yin via Shaoyang.