少阳之气化于相火其经自头走足病则气逆而火炎升燎咽喉而上燔头目少阳之兼证不一而口苦咽干目眩则为主证以相
火之上郁故也病情递变而三者不变病状善移而三者不移缘相火不得下秘离本根而上浮故口苦咽干头目旋转而不宁也是则
少阳之他证皆在于或然之中而少阳之三者则处于必然之例提纲揭三证以概少阳少阳虽幻化无常然或有殊状而必无遁情矣
少阳之为病口苦咽干目眩也
足少阳之经起目锐 下颈合缺盆口咽目皆少阳经脉之所循少阳以下行为顺病则经气壅遏逆循头面相火燔腾故见证如
此苦者火之味炎上作苦也眩者相火离根升浮旋转之象也（素问标本病传论肝病头目眩肝胆同气也）
伤寒五六日中风寒热往来胸胁苦满嘿嘿不欲饮食心烦喜呕或心中烦而不呕或渴或腹中痛或胁下痞硬或心下悸小便不
利或不渴身有微热或咳者小柴胡汤主之
伤寒五六日又中风邪此在太阳即风寒双感桂麻各半证也风寒在表逼遏少阳经气于是少阳病作少阳经在太阳阳明之里
三阴之表表则二阳故为半表里则三阴故为半里半表者居二阳之下从阳化气而为热半里者居三阴之上从阴化气而为寒人之
经气不郁则不盛郁则阳盛而生热阴盛而生寒经气郁迫半表之卫欲发于外而营气束之不能透发故闭藏而生表寒半里之营欲
发于外而卫气遏之不能透发故郁蒸而生里热盖寒伤营则营束其卫而生表寒及其营衰则寒往而热又来矣风伤卫则卫遏其营
而生里热及其卫衰则热往而寒又来矣一往一来胜负不一此所以往来寒热也少阳经脉下胸贯膈由胃口而循胁肋病则经气郁
遏而克戊土戊土胀塞碍胆经降路经脉壅阻故胸胁苦满戊土被贼困乏堙瘀故嘿嘿不欲饮食甲木既逆相火上燔而戊土升填君
火又无下济之路是以心烦胃土上逆浊气不降是以喜呕或相火薰心而胃未甚逆是以心烦而不呕或相火刑肺是以渴生或土寒
木燥土木逼迫是以腹痛或经气盘塞而胁下痞硬或土湿木郁心下悸动而小便不利或肺津未耗而内不作渴太阳未罢而心有微
热或胃逆肺阻而生咳嗽凡此诸病总是少阳中郁表里不和之故小柴胡汤柴芩清半表而泄甲木参甘枣温半里而补己土生姜半
夏降胃逆而止呕吐也 少阳在半表半里之间半里之阴虚则自阳明之经而入于阳明之腑半里之阳虚则自太阴之经而入太阴
之脏小柴胡柴芩清泄半表使不入于阳明参甘温补半里使不入于太阴则邪解于本经而无入阴入阳之患是之谓和解表里也盖
木病则传土所谓病则传其所胜也（素问语）少阳与阳明太阴为邻防其克土而传阳明故以柴芩泄半表而清阳明防其克土而
传太阴故以参甘补半里而温太阴于是表里双解矣
少阳经的气化功能依赖于相火。其经脉从头向下行走至足部。患病时，气机逆乱而相火上炎，向上焚烧咽喉并灼烧头目。少阳病的兼证虽多，但口苦、咽干、目眩是其主要症状，这是因为相火郁结于上部的缘故。病情虽然不断演变，但这三个症状却保持不变；病状虽然善于变化，但这三个症状却固定不移。原因在于相火不能向下秘藏，脱离了根本而上浮，所以出现口苦、咽干、头目旋转不安的症状。因此，少阳病的其他证候都存在于“或然”（可能出现的）情况之中，而这三个症状则处于必然的规律中。提纲列出这三个症状以概括少阳病的特点。少阳病虽然变幻无常，但即使有特殊的表现，也一定有内在的情理可循。
足少阳胆经起于眼外角，下行经过颈部，汇合于缺盆穴。口、咽、目都是少阳经脉循行所经过的部位。少阳经气以下行为顺，患病时经气壅滞阻碍，逆向上行至头部，相火燔腾，所以出现上述症状。“苦”是火的味道，火性炎上故味苦。“眩”是相火脱离根本、升浮旋转的表现。（《素问·标本病传论》指出：肝病导致头目眩晕，因为肝胆同属一气。）
伤寒病程到了五六天，又感受了风邪。这原本属于太阳病，即风寒双重感应的桂枝麻黄各半汤证。风寒在体表，逼迫遏制少阳经气，于是少阳病发作。少阳经位于太阳、阳明之里，三阴之表。位于表侧，涉及二阳，所以称为“半表”；位于里侧，涉及三阴，所以称为“半里”。所谓“半表”，居于二阳之下，从阳化气而产生热；所谓“半里”，居于三阴之上，从阴化气而产生寒。人的经气如果不郁结，就不会亢盛；如果郁结，阳气亢盛就产生热，阴气亢盛就产生寒。经气郁结紧迫，半表层的卫气想要发散到体外，但被营气束缚，不能透发，所以闭藏而产生表寒；半里层的营气想要发散到体外，但被卫气遏制，不能透发，所以郁蒸而产生里热。大概寒邪伤及营分，营气束缚卫气而产生表寒，等到营气衰退，寒邪退去而热邪又来；风邪伤及卫分，卫气遏制营气而产生里热，等到卫气衰退，热邪退去而寒邪又来。一往一来，胜负不定，这就是所谓的“往来寒热”。
少阳经脉下行穿过胸部，贯通膈肌，经过胃口而沿胁肋循行。患病时经气郁结阻碍，克制胃土（戊土），胃土胀塞，阻碍胆经下降的道路，经脉壅阻，所以胸胁部感觉苦闷胀满。胃土被肝木克制而困乏淤滞，所以神情默默不欲饮食。甲木（胆）既已逆乱，相火上炎，而胃土（戊土）上升填塞，君火又没有下济的路径，所以心烦；胃土上逆，浊气不降，所以喜欢呕吐。或者相火熏心而胃气未严重上逆，所以心烦而不呕吐；或者相火刑克肺金，所以口渴；或者脾土寒而肝木燥，土木逼迫，所以腹痛；或者经气盘结阻塞而胁下痞硬；或者脾湿肝郁，心下悸动而小便不利；或者肺津未耗而内部不作渴；或者太阳表证未罢而心中微热；或者胃气上逆肺气阻滞而生咳嗽。凡是这些病症，总是由于少阳中郁、表里不和的缘故。小柴胡汤中，柴胡、黄芩清泄半表而疏泄甲木（胆）；人参、甘草、大枣温补半里而补益己土（脾）；生姜、半夏降胃逆而止呕吐。
少阳位于半表半里之间。如果半里的阴虚，病邪就会从阳明经进入阳明腑；如果半里的阳虚，病邪就会从太阴经进入太阴脏。小柴胡汤用柴胡、黄芩清泄半表，使病邪不进入阳明；用人参、甘草温补半里，使病邪不进入太阴。这样邪气在本经解除，而没有陷入阴经或阳经的祸患，这就叫做“和解表里”。大概木病会传变给土，即“病则传其所胜”（《素问》语）。少阳与阳明、太阴相邻，为了防止木克土而传变至阳明，所以用柴胡、黄芩泄半表而清阳明；为了防止木克土而传变至太阴，所以用人参、甘草补半里而温太阴。于是表里双解。
The Qi transformation of the Shaoyang (Lesser Yang) channel relies on the Ministerial Fire (Xiang Huo). Its meridian runs from the head down to the feet. When diseased, Qi rebels and the fire flares upward, scorching the throat and burning the head and eyes. Although Shaoyang diseases have various accompanying syndromes, bitter taste in the mouth (Kou Ku), dryness of the throat (Yan Gan), and vertigo/dizziness (Mu Xuan) are the principal manifestations, due to the stagnation of Ministerial Fire in the upper jiao. Although the clinical condition evolves continuously, these three symptoms remain unchanged; although the pathological signs shift frequently, these three remain fixed. This is because the Ministerial Fire fails to descend and secure itself, detaching from its root and floating upward, thus causing bitter taste, dry throat, and restless spinning of the head and eyes. Therefore, other syndromes of Shaoyang exist within the realm of "possible" (huoran) variations, whereas these three symptoms represent the necessary pattern. The outline presents these three symptoms to summarize Shaoyang disease. Although Shaoyang pathology is变幻无常 (changeable and unpredictable), even if there are unique presentations, there is always an underlying rationale.
Disease of the Shaoyang channel manifests as bitter taste in the mouth, dryness of the throat, and vertigo.
The Foot-Shaoyang Gallbladder Channel originates at the outer canthus of the eye, descends along the neck, and converges at the Quepen (LI 15) point. The mouth, pharynx, and eyes are all areas traversed by the Shaoyang meridians. The normal direction of Shaoyang Qi is downward; when diseased, the meridian Qi becomes obstructed and rebels upward toward the head, causing the Ministerial Fire to flare, resulting in the aforementioned symptoms. "Bitter" is the flavor associated with Fire, which has a flaming-upward nature. "Vertigo" is the manifestation of Ministerial Fire detaching from its root and floating/spinning upward. (Su Wen: Chapter on Origin, Terminal, and Transmission of Diseases states that Liver diseases cause dizziness of the head and eyes, as the Liver and Gallbladder share the same Qi.)
In Taiyang disease, after five or six days, if Wind-Cold strikes again, this originally belongs to the Taiyang stage, specifically the Guizhi Mahuang Banxia Decoction syndrome where both Wind and Cold are present. The pathogenic factors in the exterior constrain the Shaoyang meridian Qi, thereby triggering Shaoyang disease. The Shaoyang meridian lies interior to the Taiyang and Yangming, and exterior to the Three Yin channels. Being exterior involves the Two Yangs, hence it is called "Half-Exterior"; being interior involves the Three Yins, hence it is called "Half-Interior". The "Half-Exterior" resides below the Two Yangs, transforming Qi from Yang to generate Heat; the "Half-Interior" resides above the Three Yins, transforming Qi from Yin to generate Cold. If human meridian Qi does not stagnate, it does not become excessive; if it stagnates, Yang excess generates Heat, and Yin excess generates Cold. Due to the constraint and pressure of meridian Qi, the Wei (Defensive) Qi of the Half-Exterior desires to emit outward but is bound by Ying (Nutritive) Qi, preventing penetration, thus leading to closure and generating Exterior Cold. The Ying Qi of the Half-Interior desires to emit outward but is blocked by Wei Qi, preventing penetration, thus leading to stagnation and steaming, generating Interior Heat. Generally, when Cold injures the Ying, Ying constrains Wei, generating Exterior Cold; when Ying declines, Cold recedes and Heat returns. When Wind injures the Wei, Wei blocks Ying, generating Interior Heat; when Wei declines, Heat recedes and Cold returns. This back-and-forth fluctuation, with uncertain victory or defeat, is what is termed "alternating chills and fever" (Wanglai Hanre).
The Shaoyang meridian descends through the chest, pierces the diaphragm, passes through the stomach opening, and follows the costal region. When diseased, meridian Qi stagnates and obstructs, attacking the Stomach Earth (Wu Tu). The Stomach becomes distended and obstructs the descending pathway of the Gallbladder meridian, causing congestion, leading to fullness and distress in the chest and hypochondrium (Xiong Xie Ku Man). The Stomach Earth is weakened and congested by the Wood (Liver/Gallbladder), leading to listlessness and lack of desire for food (Heihei Buyu Yinzshi). Since Jia Wood (Gallbladder) has rebelled and Ministerial Fire scorches upward, while Wu Earth rises and fills, leaving no path for Jun Fire (Heart Fire) to descend, mental restlessness (Xin Fan) occurs. Stomach Qi rebels upward, turbid Qi fails to descend, leading to frequent vomiting (Xi Ou). Alternatively, if Ministerial Fire harasses the Heart but Stomach Qi does not severely rebel, there is mental restlessness without vomiting. If Ministerial Fire insults the Lung, thirst arises. If Spleen Earth is cold and Liver Wood is dry, the pressure between Wood and Earth causes abdominal pain. If meridian Qi is knotted and obstructed, there is epigastric hardness (Xia Piying). If Spleen Dampness and Liver Stagnation cause palpitations under the heart (Xin Xia Ji) and dysuria (Xiao Bian Bu Li). If Lung fluids are not yet depleted, there is no internal thirst. If the Taiyang exterior syndrome has not resolved, there may be slight heat in the heart/chest. If Stomach Qi rebels and Lung Qi is obstructed, coughing may occur. All these conditions stem from Shaoyang internal stagnation and disharmony between the interior and exterior. Xiao Chaihu Tang uses Chaihu (Bupleuri Radix) and Huangqin (Scutellariae Radix) to clear the Half-Exterior and drain Jia Wood; Renshen (Ginseng Radix), Gancao (Licorice Root), and Dazao (Jujubae Fructus) warm and tonify the Half-Interior and supplement Ji Earth (Spleen); Shengjiang (Zingiberis Rhizoma Recens) and Banxia (Pinelliae Tuber) descend Stomach Qi to stop vomiting.
Shaoyang resides between the Half-Exterior and Half-Interior. If Yin deficiency exists in the Half-Interior, pathogens enter the Yangming Meridian and then the Yangming Fu organs. If Yang deficiency exists in the Half-Interior, pathogens enter the Taichyin Meridian and then the Taichyin Zang organs. Xiao Chaihu Tang uses Chaihu and Huangqin to clear the Half-Exterior, preventing entry into Yangming; it uses Renshen and Gancao to warm and tonify the Half-Interior, preventing entry into Taichyin. Thus, the pathogen is resolved in the original channel without entering the Yin or Yang stages. This is termed "harmonizing the interior and exterior" (Hejie Biaoli). As stated in Su Wen: "When Wood is diseased, it transmits to Earth," meaning "disease transmits to what it overcomes." Since Shaoyang is adjacent to Yangming and Taichyin, to prevent Wood overcoming Earth and transmitting to Yangming, Chaihu and Huangqin are used to drain the Half-Exterior and clear Yangming. To prevent Wood overcoming Earth and transmitting to Taichyin, Renshen and Gancao are used to tonify the Half-Interior and warm Taichyin. Thus, both the exterior and interior are simultaneously resolved.