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[Formula of Xiao Chai Hu Tang]
Chai Hu (Bupleuri Radix) half a jin, Huang Qin (Scutellariae Radix) three liang, Ren Shen (Ginseng Radix) three liang, Ban Xia (Pinelliae Rhizoma) half sheng (washed), Gan Cao (Glycyrrhizae Radix et Rhizoma) three liang (roasted), Sheng Jiang (Zingiberis Rhizoma Recens) three liang (sliced), Da Zao (Jujubae Fructus) twelve pieces (torn open).
The above seven ingredients are decocted in one dou and two sheng of water, reduced to six sheng. The dregs are removed, and the liquid is further decocted until three sheng remain. Take one sheng warm, three times a day.

Modifications:
If there is irritability in the chest but no vomiting, remove Ban Xia and Ren Shen, and add one Gua Lou Shi (Trichosanthis Fructus). If there is thirst, remove Ban Xia, increase Ren Shen to four liang and a half, and add Gua Lou Gen (Trichosanthis Radix) four liang. If there is abdominal pain, remove Huang Qin and add Shao Yao (Paeoniae Radix Alba) three liang. If there is plenitude and hardness in the hypochondrium, remove Da Zao and add Mu Li (Ostrea Concha) four liang. If there is palpitation of the heart and difficult urination, remove Huang Qin and add Fu Ling (Poria) four liang. If there is no thirst but slight fever on the exterior, remove Ren Shen and add Gui Zhi (Cinnamomi Ramulus) three liang; take warm until slight sweating occurs, then it resolves. If there is cough, remove Ren Shen, Da Zao, and Sheng Jiang, add Wu Wei Zi (Schisandrae Fructus) half sheng, and Gan Jiang (Zingiberis Rhizoma) two liang.

[Explanation of the Formula]
When pathogenic factors transmit to the Taiyang and Yangming channels, methods such as sweating, emesis, and purgation may be used. When pathogenic factors transmit to the Shaoyang channel, only the harmonizing method is suitable; sweating, emesis, and purgation are all contraindicated. This is because the pathogen is located between the interior and exterior, entangled within the internal boundaries of the body. Those at the exterior level involve external pathogenic factors causing disease; those at the interior level involve the body's own qi being affected. The pathogen and healthy qi are stuck between these two levels, neither advancing nor retreating, thus establishing the harmonizing method. Chai Hu is used to resolve the cold in the exterior of the Shaoyang channel, and Huang Qin is used to clear the heat in the interior of the Shaoyang fu-organ. There is still concern that if the Zhengqi (healthy qi) of the Taiyin in the interior is deficient, the pathogen in the Shaoyang channel will take advantage. Therefore, Sheng Jiang, Da Zao, and Ren Shen are used to harmonize the middle jiao and strengthen the interior qi in advance, preventing the interior from being invaded by pathogens, thereby achieving harmony and resolving the exterior. Laypeople do not examine where the pathogen resides, whether it is truly between the interior and exterior, or whether harmonization is appropriate, nor do they distinguish between yin and yang similarities. They simply use Xiao Chai Hu Tang as a standard prescription. Physicians feel safe using it, and patients like its mild nature, unaware that this routine approach causes significant harm. Therefore, physicians must identify diseases early and plan accordingly.

[Collected Explanations]
Cheng Yingmao said: The formula is named Xiao Chai Hu Tang to correspond with the Shaoyang channel. The principle of the formula and its modifications fully embody the concept that "when the upper jiao is unobstructed, fluids descend, and stomach qi becomes harmonious." In the formula, Chai Hu soothes the liver wood, allowing pathogens at the semi-exterior to be dispersed outward; Huang Qin clears fire, allowing pathogens at the semi-interior to penetrate inward; Ban Xia resolves phlegm-fluids and directs rebellious qi downward; Ren Shen tonifies internal deficiency and assists the generating qi; Gan Cao assists Chai Hu and Huang Qin to harmonize the interior and exterior; Sheng Jiang and Da Zao assist Ren Shen and Ban Xia to circulate Ying and Wei qi. They support each other, preventing pathogens from moving inward and facilitating their resolution outward. Regarding modifications: Irritability without vomiting indicates dryness and excess of fire pressing on the chest, so Ren Shen and Ban Xia are removed, and Gua Lou Shi is added. Thirst indicates dryness has consumed fluids and pressed on the lungs, so Ban Xia is removed and Gua Lou Gen is added. Abdominal pain indicates wood qi scattering into earth, trapping stomach yang, so Huang Qin is removed to calm earth, and Shao Yao is added to restrain wood. Plenitude and hardness in the hypochondrium indicate that when pathogens linger, wood qi becomes excessive, so the sweet and緩 (relaxing) Da Zao is removed, and the salty and softening Mu Li is added. Palpitation and difficult urination indicate water pathogens invading the heart, so the bitter-cold Huang Qin is removed, and the bland-draining Fu Ling is added. No thirst but slight fever indicates cold at the semi-exterior lingering in the muscles, so Ren Shen is removed and Gui Zhi is added to resolve it. Cough indicates cold at the semi-exterior entering the lungs, so Ren Shen and Da Zao are removed, Wu Wei Zi is added, Sheng Jiang is replaced with Gan Jiang to warm, and although lung cold exists, Huang Qin is not reduced for fear that Gan Jiang might aid heat. In summary, pathogens in Shaoyang represent heat between the interior and exterior that is stagnant and failing to ascend, so Xiao Chai Hu Tang is used, following the principle of ascending, descending, floating, and sinking.

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In Shanghan (Cold Damage) or Zhongfeng (Wind Strike), if Chai Hu syndrome appears, seeing just one symptom is sufficient; it is not necessary for all symptoms to be present.

[Note]
This follows the previous text. Regardless of whether it is Shanghan or Zhongfeng, once pathogens transmit to Shaoyang and the disease is between the interior and exterior, if Chai Hu syndrome is present, seeing just one symptom allows for treatment with Xiao Chai Hu Tang modified according to symptoms, without waiting for all symptoms to manifest.

[Collected Notes]
Fang Youzhi said: This follows the previous article regarding the main principles of diagnosing Shaoyang channel diseases.
Zheng Zhongguang said: "Having Chai Hu syndrome, seeing just one symptom is sufficient" means that alternating chills and fever is a Chai Hu symptom. Additionally, if any one of the accompanying symptoms such as hypochondriac fullness, vexation, and frequent desire to vomit appears, it indicates a semi-exterior semi-interior condition. Thus, "vomiting with fever" is treated with Xiao Chai Hu Tang. Because Chai Hu is a pivot-regulating agent, it can be used when wind-cold is neither entirely in the exterior nor entirely in the interior. Therefore, symptoms need not all be present, and the formula has modifications. However, similar conditions requiring differentiation must be carefully examined. For example, hypochondriac fullness and pain, or thirst with vomiting upon drinking water, are not indications for Chai Hu Tang. Similarly, mere desire to vomit, chest pain, and loose stools are not Chai Hu syndrome; these require detailed differentiation.

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In Shanghan, if the Shaoyang pulse is small, the disease is about to resolve.

[Note]
Shanghan includes Zhongfeng. On the third day, pathogens enter Shaoyang. If the pulse is large, it indicates excess pathogens and potential transmission. If the pulse is small now, it indicates declining pathogens and impending self-resolution.

[Collected Notes]
Cheng Yingmao said: A small pulse indicates yang harmonizing with yin, meaning pathogens have retreated and healthy qi is recovering.
Zhang Xiju said: Three days is the period governed by Shaoyang; a small pulse indicates disease retreat.

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On the fourth or fifth day of Shanghan, if there is fever, slight aversion to wind, stiffness of the neck and nape, hypochondriac fullness, warm hands and feet, and thirst, Xiao Chai Hu Tang should be administered.

[Note]
On the fourth or fifth day of Shanghan, pathogens are in the three yang channels. Fever and aversion to wind are Taiyang symptoms; neck stiffness is a Taiyang-Yangming symptom; hypochondriac fullness, warm hands and feet, and thirst are Yangming-Shaoyang symptoms. This marks the beginning of a combined disease of the three yang channels. One must weigh the urgency of each to treat appropriately. However, hypochondriac fullness, warm hands and feet, and thirst reveal the tendency of pathogens to move from exterior to interior and converge in Shaoyang. Therefore, treatment focuses solely on Shaoyang. Xiao Chai Hu Tang is used to harmonize the interior and exterior. In this combined disease of the three yang channels, it is not necessary for all Chai Hu symptoms to be present; rather, the method of Chai Hu should be applied.

[Collected Notes]
Fang Youzhi said: Although symptoms of the three yang channels are present, treatment focuses on Shaoyang using Xiao Chai Hu Tang because the pathogens in Taiyang and Yangming are weak, while Shaoyang is closer to the interior and interior symptoms are manifest. Thus, focusing on Shaoyang harmonization achieves multiple benefits.
Yu Chang said: Normally, combined disease of the three yang channels would be treated with exterior-releasing methods. However, warm hands and feet plus thirst indicate external pathogens pressing toward Shaoyang, with a clear trend toward the interior. Using acrid-sweet dispersing methods would increase heat and consume fluids. Therefore, the harmonizing method of Xiao Chai Hu Tang is used to stop yang pathogens without injuring yin fluids, achieving two goals at once. According to modifications, if there is no vomiting but thirst, removing Ban Xia and adding Gua Lou Gen is correct.
Zhang Zhicong said: "Warm hands and feet" means the hands and feet are not cold. It is not the patient's subjective feeling of warmth, but what the physician feels upon palpation. Otherwise, how could one say "fever" and then "warm hands and feet"?
Wang Hu said: This case involves simultaneous disease of the three yang channels, with more emphasis on Shaoyang. By the fourth or fifth day of Taiyang Shanghan, saying "body heat" instead of "fever and aversion to wind" indicates Taiyang pathogens are fading. Mentioning "neck stiffness" instead of "dry nose and inability to sleep" indicates Yangming pathogens are also fading. Only hypochondriac fullness is specific to Shaoyang. Coupled with warm hands and feet and thirst, this indicates the trend of pathogens transmitting to the interior is evident.

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In Yangming disease, if there is tidal fever, loose stools, normal urination, and persistent hypochondriac fullness, administer Xiao Chai Hu Tang.

[Note]
Tidal fever in Yangming disease usually accompanies hard stools and frequent urination. Here, loose stools and normal urination indicate this is not the tidal fever of Yangming fu-organ involvement. Moreover, the persistent hypochondriac fullness indicates a Shaoyang syndrome. Therefore, treatment does not follow Yangming but targets Shaoyang with Xiao Chai Hu Tang.

[Collected Notes]
Wang Kentang said: Yangming disease refers to "stomach house excess." Calling it Yangming disease despite loose stools implies the presence of Yangming exterior signs: body heat, sweating, aversion to heat rather than cold.
Cheng Yingmao said: Tidal fever in Yangming disease seems like stomach excess. However, stomach excess requires hard stools and frequent urination. Loose stools and normal urination indicate heat not yet in the fu-organ. Combined with hypochondriac signs, Xiao Chai Hu Tang is undoubtedly indicated.

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In Yangming disease, if there is hypochondriac plenitude and hardness, constipation, vomiting, and a white coating on the tongue, Xiao Chai Hu Tang may be given. When the upper jiao becomes unobstructed, fluids descend, stomach qi harmonizes, and the body sweats profusely, resolving the disease.

[Note]
Constipation, hypochondriac plenitude and hardness, and vomiting in Yangming disease indicate transmission from Yangming to Shaoyang. If the tongue coating is yellow and rough, residual Yangming heat remains, and Da Chai Hu Tang should be used to resolve both. Here, a slippery white coating indicates transmission to Shaoyang, so Xiao Chai Hu Tang is used to harmonize. Unobstructing the upper jiao stops vomiting; descending fluids facilitates bowel movement; harmonizing stomach qi removes plenitude and hardness. Consequently, the body will sweat profusely and resolve.

[Collected Notes]
Cheng Zhi said: This states that Yangming combined with Shaoyang should use Xiao Chai Hu Tang. Not only do loose stools indicate stomach is not excess; even with constipation and vomiting, it indicates pathogens have not entered the interior. Plenitude is in the hypochondrium, not the abdomen; a white, non-yellow tongue coating indicates many Shaoyang signs. Thus, Xiao Chai Hu Tang should be used to differentiate yin and yang, leading to upper-lower harmony, profuse sweating, and withdrawal of exterior-interior pathogens.
Cheng Yingmao said: Hypochondriac plenitude and hardness, constipation, and vomiting are indications for Da Chai Hu Tang. Xiao Chai Hu Tang is used here because the white tongue coating still carries exterior cold. If the coating were rough rather than slippery, indicating dry tongue, vexation, and extreme thirst, it would mean interior heat has consumed fluids, and this formula would be contraindicated. Furthermore, "upper jiao unobstructed" refers to hypochondriac plenitude; "fluids descend" refers to tongue coating and vomiting; "stomach qi harmonizes" refers to constipation. The previous article identified Yangming disease via tidal fever; this one identifies it via constipation.

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If a patient with Chai Hu syndrome is mistakenly treated with purgation, and the Chai Hu syndrome persists, administering Chai Hu Tang again will cause shivering and shaking followed by fever and sweating, leading to resolution.

[Note]
For Chai Hu syndrome, if purgation is mistakenly used instead of Chai Hu Tang, and the syndrome remains unchanged, Chai Hu Tang can be administered again to resolve it. However, due to mistaken purgation, the condition is likely deficient. Thus, resolution involves shivering with heat and shaking with cold, representing the struggle between pathogen and healthy qi, followed by sweating and resolution.

[Collected Notes]
Fang Youzhi said: Shivering and shaking constitute "battle sweat." Resolution requires this because the interior is deficient after purgation.
Cheng Zhi said: Pathogens returning to the exterior cause shivering heat; post-purgation deficiency causes shaking movement.

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Six or seven days after contracting disease, if the pulse is slow, floating, and weak, with aversion to wind and cold, and warm hands and feet, and the physician has purged two or three times, resulting in inability to eat, hypochondriac fullness and pain, jaundice of the face and body, neck stiffness, and difficult urination: if Chai Hu Tang is given, heavy sensation in the rectum will follow. If originally thirsty but vomiting upon drinking water, Chai Hu Tang is contraindicated. Vomiting hiccups upon eating food.

[Commentary]
The phrase "vomiting hiccups upon eating food" is an interpolation. There are cases of vomiting upon eating, but never hiccups.

[Note]
Six or seven days after contracting disease is the time when Shaoyang transmits to Taiyin. A slow pulse is a Taiyin pulse; floating and weak is a Taiyang pulse; aversion to wind and cold is a Taiyang sign; warm hands and feet is a Taiyin sign. The physician failed to use Chai Hu Guizhi Tang to harmonize and instead purged two or three times, losing both exterior and interior. Now, inability to eat and hypochondriac fullness and pain seem like Shaoyang signs but are not truly Shaoyang. Jaundice indicates Taiyin signs are complete; neck stiffness indicates Yangming pathogens persist. Difficult urination indicates fluid loss from repeated purgation. These result from physician error, mixing interior and exterior, and combining yin and yang diseases. If one mistakenly gives Chai Hu Tang based on the rule that "one symptom is sufficient," specifically hypochondriac fullness and pain, rectal heaviness will follow, pushing pathogens deeper into Taiyin. Although there is thirst, it is due to fluid loss from purgation. Vomiting upon drinking is not the original Shaoyang vomiting but caused by error; thus, Chai Hu Tang is contraindicated.

[Collected Notes]
Cheng Zhi said: Previously, it was stated that seeing one Chai Hu symptom is sufficient. Here, it warns that hypochondriac fullness and pain may also be unsuitable for Chai Hu, serving as a caution.
Cheng Yingmao said: Differentiating by thirst: in the previous case, warm hands and feet with thirst indicated interior heat without repeated purgation, allowing natural fluid metabolism. Here, thirst with vomiting upon drinking indicates throat dryness and fluid depletion from repeated purgation and middle deficiency, unable to metabolize water, unrelated to stomach yang. Thus, can we still say "seeing one symptom is sufficient" for Chai Hu Tang? Or that if Chai Hu syndrome persists after purgation, Chai Hu Tang can be reused?

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Six or seven days into Shanghan, if there is fever, slight aversion to cold, painful joints, slight vomiting, subcostal binding, and unresolved exterior signs, Chaihu Guizhi Tang should be administered.

[Note]
Six or seven days into Shanghan, fever, slight aversion to cold, painful joints, slight vomiting, and subcostal binding indicate Taiyang pathogens transmitting to Shaoyang. Half of Guizhi Tang is used to disperse remaining Taiyang pathogens; half of Chai Hu Tang is used to disperse Shaoyang vomiting and binding. It is not named Guizhi Chai Hu Tang because although exterior signs persist, the pathology manifests in the Shaoyang interior. Placing Chai Hu before Guizhi emphasizes treating Shaoyang primarily and Taiyang secondarily. "Zhi" means side or small. "Zhi Jie" refers to small binding on the side of the epigastrium.

[Collected Notes]
Fang Youzhi said: "Zhi Jie" refers to limb joints. "Zhi Jie" (binding) refers to fluid retention gathering and binding. From fever to slight vomiting are Taiyang exterior signs, hence "exterior signs unresolved."
Cheng Zhi said: This is pathogens entering Shaoyang while Taiyang signs persist. Fever, chills, and joint pain are Taiyang signs, but chills are slight, and pain is limited to joints without neck stiffness, indicating slightly reduced Taiyang signs. Vomiting and binding are Shaoyang signs, but vomiting is slight and binding is lateral in the epigastrium, not between both hypochondria, indicating shallow Shaoyang involvement. In such cases, Chai Hu Tang should harmonize Shaoyang, supplemented by Guizhi Tang to release Taiyang. This is an unchangeable method.