【纲】仲景曰。伤寒五六日。中风。往来寒热。胸胁苦满。默默不欲饮食。心烦喜呕。或胸中
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。但见一症。便是。不必悉具。
【目】朱肱曰。寒热往来者。阴阳相胜也。阳不足。则先寒后热。阴不足。则先热后寒。然寒
热有三症。小柴胡汤、大柴胡汤、柴胡桂枝干姜汤。有表症而往来寒热者。用小柴胡。即本条是也。
有里症而往来寒热者。用大柴胡。即伤寒十余日。热结在里。往来寒热者。大柴胡主之一条是也。
或已表。或已下。而往来寒热者。皆用柴胡桂枝干姜汤。即伤寒五六日。已发汗。复下之。胸胁
满。小便不利。渴而不呕。头汗出。往来寒热。心烦。柴胡桂枝干姜汤主之一条是也。
刘完素曰。寒为阴。热为阳。里为阴。表为阳。邪客于表为寒邪。与阳相争则为寒矣。邪入于
里为热邪。与阴相争则为热矣。其邪半在表。半在里。外与阳争而为寒。内与阴争而为热矣。表
里不拘。出入不定。由是而寒热。且往且来也。是以往来寒热。属半表半里之症。邪居表多则多寒。
邪居里多则多热。邪在半表里则寒热亦半。小柴胡专主之也。又有病至十余日。热结在里。复往来
寒热者。亦可与大柴胡下之。不可不知也。
张介宾曰。寒热往来者。阴阳相争。阴胜则寒。阳胜则热也。盖热为阳。寒为阴。表为阳。里
为阴。邪之客于表者。为寒邪。与阳相争。则为寒栗。邪之传于里者为热邪。与阴相争。则为热躁。
其邪在半表半里之间者。外与阳争则为寒。内与阴争则为热。或表或里。或出或入。是以寒热往
来。为半表半里之症也。故凡寒胜者必多寒。热胜者必多热。但审其寒热之势。则可知邪气之浅深
也。
柯琴曰。往来寒热有三义。少阳自受寒邪。阳气衰少。既不能退寒。又不能发热。至五六日热
郁内发。始得与寒气相
争。而往来寒热。一也。若太阳受寒。过五六日。阳气始衰。余邪未尽。转属少阳。此往来寒热。
二也。风为阳邪。少阳为风脏。一中于风。便往来寒热。不必五六日而始见。三也。往来寒热。便
有不寒热时。此病情之见于外者。
【纲】仲景曰。血弱气尽。腠理开。邪气因入。与正相搏。结于胁下。正邪分争。往来寒热。
休作有时。默默不欲饮食。脏腑相连。其痛必下。邪高痛下。故使呕也。小柴胡汤主之。
【目】刘完素曰。邪气入。正气不争。则但热无寒。正与邪争。寒热作矣。争则气郁不发于外。
而寒热争焉。争甚。则愤然而热。故寒已而热作焉。兹乃寒热之理也。
魏荔彤曰。此总见妇人经来适断之时。血既出而必弱。血室中之气。亦随之尽矣。此际内虚则
表疏。腠理开。而邪气易乘以入。随与正气相搏。正气足。则邪入可拒。正气虚。则邪入相溷。凡
病皆然也。既属妇人血分之病。则肝为血之专司。其部位正在胁下。正气忽盛而拒。正气忽衰而迎。
与邪迎拒。遂作分争之势。且梗塞阻滞于阴阳升降道路之间。于是往来寒热。休作有时。兼见默不
欲饮食。纯为少阳之症。谁知此非伤寒由太阳而阳明而少阳递传之邪乎。盖热入血室。可以在太阳
即入。亦可以太阳罢而入。迥非伤寒传经。必由太阳阳明方入少阳也。此治法虽同于少阳。病之由
来。大不同于男子之得少阳病也。所以然者。肝木属脏。为厥阴。胆木属腑。为少阳。二木同气。
部位又相连。热入血室。肝既司血。肝必为邪所乘。胆附于肝。邪入肝分。必侵胆为患。一脏一腑。
体既相连。病则俱病。又不比于别脏腑表里之义矣。于是热入而血结。血结而为痛。痛则气沉。
气沉则痛愈下。然少阳之胆。毕竟属阳。其性上升。厥阴之肝。毕竟属阴。其性下降。胆有邪。自
高而上冲。斯作呕也。肝有邪。自下而沉结。斯作痛也。邪高痛下。故使呕也。何非热入血室。血结
少阳之所致乎。症固非伤寒之少阳。而妇人热入血室。邪在少阳之本位。法宁不从少阳为治耶。小柴
胡主之。其升清降浊之义。已言之矣。此申明妇人经来经断。热邪易入血室。与男子不同病之大旨
也。然男子有
病。即非伤寒之递传。其病原属少阳者。亦未尝不可。即其法以通治之也。此仲师专为妇人热入血
室。明其来自太阳。无关阳明。病结少阳。所以然之故也。再绎热入血室。即结于血室。亦能作寒
热往来如疟状。何也。亦是脏腑相连。邪高痛下之义。肝胆之血。与血室之血。一血也。结于下则
上亦不通。不通则不能升降矣。所以寒热作而如疟也。不必谓热入血室而血结于肝下也。
【纲】仲景曰。太阳病不解。转入少阳者。胁下硬满。干呕。不能食。往来寒热。尚未吐下。
脉弦细者。与小柴胡汤。若已吐下。发汗。温针。谵语。柴胡症罢。此为坏病。知犯何逆。以法治
之。
【目】陶华曰。小柴胡专主往来寒热。如寒多者。加桂。热多者。加大黄。此其大法也。
【纲】仲景曰。伤寒五六日。已发汗。而复下之。胸胁满微结。小便不利。渴而不呕。但头汗
出。往来寒热。心烦者。此为未解也。柴胡桂枝干姜汤。主之。初服微烦。复服汗出。则愈。
【目】魏荔彤曰。此亦三阳并见之症。宜从少阳治之。而少变其法也。盖已发汗而表未除。复
下之而里邪入。胸胁满微结。是太阳外感之邪。弥漫于三阳。胸满。太阳也。胁满。少阳也。因不专
满在胸。故其结较结胸也微。又可见阳明亦病。小便不利。渴而不呕。津液短而化气衰。胃病可知
矣。此所以三阳俱病也。未解者。不独阳明少阳。正太阳表邪未尽解也。太阳未解。似宜治表。然
阳明少阳已病。不可复发汗。法应三阳并治。而以太阳少阳为两路出邪之门户。盖少阳之邪。终亦
必由太阳透表。故治少阳。亦所以治太阳也。阳明更不必专治矣。本方以柴胡为主。意在少阳。入桂
枝。太阳之治寓焉。去人参加干姜。下药寒结可开。易半夏为栝蒌根。已伤之津液可复。牡蛎制水
安神。小柴胡升清降浊。使半表解。半里和者。是又小柴胡加减法外。神明之一法。一了百当者也。
柯琴曰。汗下后。柴胡症仍在。仍用柴胡汤加减。此因增微结一症。故变其方耳。
【纲】仲景曰。伤寒十余日。热结在里。往来寒热者。宜与大柴胡汤。
【目】柯琴曰。里者。对表而言。不是指胃。此热结气分。不属有形。故十余日复能往来寒热。
若结在胃。则蒸蒸发热。不复知有寒矣。
【纲要】张仲景说：患伤寒病五六天，又感受风邪，出现寒热交替发作的症状，胸胁部苦闷胀满，神情沉默，不想吃东西，心中烦躁，经常想呕吐。或者胸中烦闷但不呕吐，或者口渴，或者腹部疼痛，或者胁下痞塞硬满，或者心下悸动、小便不利，或者不渴但身体有轻微发热，或者咳嗽的，用小柴胡汤主治。只要见到其中一个症状，就可以使用此方，不必所有症状都具备。
【注释】朱肱说：寒热交替发作，是阴阳相互偏胜的结果。阳气不足，就先发冷后发热；阴气不足，就先发热后发冷。然而寒热交替有三种证型：小柴胡汤、大柴胡汤、柴胡桂枝干姜汤。如果有表证而寒热交替的，用小柴胡汤，就是本条所述的情况。如果有里证而寒热交替的，用大柴胡汤，就是“伤寒十余日，热结在里，往来寒热者，大柴胡主之”这一条所述的情况。如果已经发汗或已经攻下，仍然寒热交替的，都用柴胡桂枝干姜汤，就是“伤寒五六日，已发汗，复下之，胸胁满，小便不利，渴而不呕，头汗出，往来寒热，心烦，柴胡桂枝干姜汤主之”这一条所述的情况。
刘完素说：寒属于阴，热属于阳；里属于阴，表属于阳。邪气客居在表为寒邪，与阳气相争则表现为寒；邪气进入在里为热邪，与阴气相争则表现为热。当邪气一半在表、一半在里时，向外与阳争就产生寒，向内与阴争就产生热。此时表里界限不拘束，邪气出入不定，因此出现寒热交替，且往且来。所以寒热交替属于半表半里的证候。邪气在表多则寒多，邪气在里多则热多，邪气在半表半里则寒热各半。小柴胡汤专门主治这种情况。又有病情发展到十余日，热结在里，又出现寒热交替的，也可以给予大柴胡汤攻下，这一点不可不知道。
张介宾说：寒热交替，是阴阳相互争斗，阴胜则寒，阳胜则热。热属于阳，寒属于阴；表属于阳，里属于阴。邪气客居在表的，是寒邪，与阳相争，就会发生寒战；邪气传入在里的，是热邪，与阴相争，就会发生热躁。邪气在半表半里之间的，向外与阳争就产生寒，向内与阴争就产生热。无论在于表还是在于里，无论外出还是内入，因此寒热交替成为半表半里的证候。所以凡是寒胜的必然寒多，热胜的必然热多。只要审察寒热的趋势，就可以知道邪气的深浅。
柯琴说：寒热交替有三层含义。一是少阳直接感受寒邪，阳气衰少，既不能驱退寒气，又不能产生热量，到了第五六天，热气郁积在内爆发，才开始与寒气相争，从而出现寒热交替，这是第一种情况。二是太阳感受寒邪，过了第五六天，阳气开始衰退，余邪未尽，转属少阳，这也出现寒热交替，这是第二种情况。三是风为阳邪，少阳为风脏，一旦中风，便出现寒热交替，不一定等到第五六天才显现，这是第三种情况。寒热交替期间，也有不寒不热的时候，这是病情表现于外部的现象。
【纲要】张仲景说：气血虚弱，正气耗尽，腠理（皮肤毛孔及肌肉间隙）开放，邪气趁机侵入，与正气相搏结，结聚在胁下。正气与邪气分争，导致寒热交替发作，且有定时停止和发作的特点，神情沉默，不想吃东西。脏腑相连，疼痛部位往往在下部，邪气位置高而疼痛位置低，所以引起呕吐。用小柴胡汤主治。
【注释】刘完素说：邪气侵入，若正气不与邪气抗争，则只发热而不恶寒；正气与邪气相争，寒热才会发作。相争时，气机郁滞不能发散于外，于是寒热交争。相争剧烈时，愤然发热，所以寒退之后热才发作，这就是寒热的机理。
魏荔彤说：这里总括了妇女月经刚断之时，血液流失导致血虚，血室中的气也随之耗尽。此时内部空虚则体表疏松，腠理开放，邪气容易乘虚而入，随即与正气相搏。正气充足，就能抵御邪气入侵；正气虚弱，邪气入侵就会混杂其中。各种疾病都是这样。既然属于妇人血分的病，那么肝作为主管血液的脏器，其部位正在胁下。正气忽盛而抗拒，正气忽衰而迎受，与邪气形成迎拒之势，并且梗塞阻滞在阴阳升降的道路之间，于是出现寒热交替，有定时发作和停止，兼见神情沉默不想吃东西，纯粹是少阳病的症状。谁能想到这不是伤寒由太阳经传至阳明经再传至少阳经的递传邪气呢？其实热入血室，可以在太阳经阶段就进入，也可以在太阳经病罢之后进入，完全不同于伤寒传经必须经由太阳、阳明才进入少阳。这种治法虽然与少阳病相同，但病因来源，大大不同于男子得少阳病的原因。之所以这样，是因为肝木属于脏，为厥阴；胆木属于腑，为少阳。二者同气，部位又相连。热入血室，肝既主管血液，肝必然被邪气所乘，胆附于肝，邪气进入肝分，必然侵犯胆造成危害。一脏一腑，形体既相连，生病则一起生病，又不比于其他脏腑的表里关系了。于是热进入而血凝结，血凝结而产生疼痛，疼痛则气下沉，气下沉则疼痛更偏向下方。然而少阳之胆毕竟属阳，其性质上升，厥阴之肝毕竟属阴，其性质下降。胆有邪气，自然从高处向上冲逆，这就产生呕吐；肝有邪气，自然从低处下沉结聚，这就产生疼痛。邪气位置高而疼痛位置低，所以引起呕吐。这难道不是热入血室、血结少阳所致吗？症状固然不是伤寒的少阳病，但妇人的热入血室，邪气位于少阳的本位，治法怎能不从少阳入手呢？小柴胡汤主治，其升清降浊的意义，前面已经讲过了。这里申明妇人经期来潮或经血刚断时，热邪容易进入血室，与男子患病不同的大旨。然而男子有病，即使不是伤寒的递传，其病原属于少阳的，也未尝不可以用这种方法通治。这是仲景专门为妇人热入血室，阐明其来自太阳，无关阳明，病结于少阳，所以如此的原因。再推演热入血室，即结于血室，也能出现像疟疾一样的寒热交替。为什么呢？也是因为脏腑相连，邪高痛下的道理。肝胆之血与血室之血，是一股血。结聚在下部则上部也不通畅，不通畅就不能升降，所以寒热发作像疟疾一样。不必认为热入血室而血结在肝脏下方。
【纲要】张仲景说：太阳病未解，转入少阳的，胁下硬满，干呕，不能进食，寒热交替，尚未经过催吐或泻下治疗，脉象弦细的，给予小柴胡汤。如果已经经过催吐、泻下、发汗、温针等误治，谵语，柴胡证消失，这称为坏病，需查明犯了什么错误，根据具体情况进行治疗。
【注释】陶华说：小柴胡汤专门主治寒热交替。如果寒多者，加桂枝；热多者，加大黄，这是基本大法。
【纲要】张仲景说：伤寒五六天，已经发汗，却又攻下，胸胁满闷微有结滞，小便不利，口渴但不呕吐，只有头部出汗，寒热交替，心烦的，这是病未解除，用柴胡桂枝干姜汤主治。初服后微微心烦，再服后汗出，则痊愈。
【注释】魏荔彤说：这也是三阳经同时出现的症状，应当从少阳论治，但稍微改变一下方法。因为已经发汗而表证未除，又攻下导致里邪内入。胸胁满闷微结，是太阳外感之邪弥漫于三阳经。胸满是太阳病，胁满是少阳病，因为不满主要在胸部，所以其结滞比结胸证轻微，又可见阳明也病了。小便不利，口渴但不呕吐，说明津液短少而化气功能衰退，胃病可知。这就是三阳俱病。所谓“未解”，不仅指阳明、少阳，正指太阳表邪未尽解除。太阳未解，似乎应该治表，然而阳明、少阳已病，不可再次发汗，治法应三阳并治，而以太阳、少阳为两条排出邪气的门户。因为少阳的邪气，最终也必须通过太阳透达体表，所以治疗少阳，也就是治疗太阳。阳明更不必专门治疗了。本方以柴胡为主，意在少阳，加入桂枝，寓含太阳的治疗。去掉人参加上干姜，可以开通药下的寒结；将半夏换成栝蒌根，可以恢复已伤的津液；牡蛎制水安神。小柴胡汤升清降浊，使半表解、半里和，这是在小柴胡汤加减法之外，神妙变化的一种方法，一举两得。
柯琴说：发汗攻下后，柴胡证仍在，仍用柴胡汤加减。这是因为增加了“微结”这一症状，所以改变了方剂。
【纲要】张仲景说：伤寒十余日，热结在里，寒热交替的，宜给予大柴胡汤。
【注释】柯琴说：“里”是相对于“表”而言的，不是指胃。这是热结在气分，不属于有形实邪，所以十余日后仍能寒热交替。如果结在胃中，则是蒸蒸发热，不再知道有恶寒了。
[Outline] Zhang Zhongjing said: In the course of a cold damage disease, after five or six days, if wind pathogen is also contracted, alternating chills and fever occur. There is bitter fullness in the chest and hypochondrium, silence with loss of appetite, mental irritability, and frequent vomiting. Alternatively, there may be irritability in the chest without vomiting, thirst, abdominal pain, stuffiness and hardness under the hypochondrium, palpitations in the epigastrium with dysuria, absence of thirst but slight body heat, or coughing. Xiao Chai Hu Tang (Minor Bupleurum Decoction) is the primary treatment. If any single symptom is present, this formula can be used; it is not necessary for all symptoms to be present.
[Commentary] Zhu Gong said: Alternating chills and fever result from the mutual excess of Yin and Yang. When Yang Qi is insufficient, chills precede fever; when Yin Qi is insufficient, fever precedes chills. However, there are three patterns of alternating chills and fever treated by Xiao Chai Hu Tang, Da Chai Hu Tang, and Chai Hu Gui Zhi Gan Jiang Tang. If alternating chills and fever occur with exterior syndrome, Xiao Chai Hu Tang is used, as described in this section. If they occur with interior syndrome, Da Chai Hu Tang is used, corresponding to the case where "after ten or more days of cold damage, heat is knotted in the interior with alternating chills and fever," which Da Chai Hu Tang treats. If alternating chills and fever persist after sweating or purging have been performed, Chai Hu Gui Zhi Gan Jiang Tang is used, corresponding to the case where "after five or six days of cold damage, having already sweated and then purged, with fullness in the chest and hypochondrium, dysuria, thirst without vomiting, sweating only on the head, alternating chills and fever, and mental irritability," which Chai Hu Gui Zhi Gan Jiang Tang treats.
Liu Wansu said: Cold belongs to Yin, heat belongs to Yang; interior belongs to Yin, exterior belongs to Yang. Pathogenic factors lodging in the exterior are cold pathogens; struggling with Yang Qi, they manifest as cold. Pathogenic factors entering the interior are heat pathogens; struggling with Yin Qi, they manifest as heat. When pathogens are half in the exterior and half in the interior, struggling outward with Yang produces cold, and struggling inward with Yin produces heat. The boundaries between exterior and interior are not fixed, and the movement of pathogens is uncertain, leading to alternating chills and fever. Thus, alternating chills and fever belong to Shaoyang (Half-Exterior/Half-Interior) syndrome. If pathogens reside more in the exterior, chills predominate; if more in the interior, heat predominates; if in the half-exterior/half-interior, chills and heat are balanced. Xiao Chai Hu Tang specifically governs this condition. Furthermore, if the disease progresses for over ten days with heat knotted in the interior and recurring alternating chills and fever, Da Chai Hu Tang may be used to purge, a fact that must not be overlooked.
Zhang Jiebin said: Alternating chills and fever represent the struggle between Yin and Yang; Yin excess causes cold, Yang excess causes heat. Heat is Yang, cold is Yin; exterior is Yang, interior is Yin. Cold pathogens lodging in the exterior struggle with Yang, causing shivering. Heat pathogens transmitting to the interior struggle with Yin, causing restlessness and heat. Pathogens in the half-exterior/half-interior struggle outward with Yang to produce cold and inward with Yin to produce heat. Whether in the exterior or interior, moving out or in, alternating chills and fever constitute a half-exterior/half-interior syndrome. Therefore, cold excess leads to more chills, and heat excess leads to more heat. By examining the trend of chills and heat, one can determine the depth of the pathogen.
Ke Qin said: There are three meanings to alternating chills and fever. First, Shaoyang directly contracts cold pathogens; Yang Qi is weak, unable to dispel cold or generate heat. By the fifth or sixth day, internal heat stagnates and erupts, finally struggling with cold qi, resulting in alternating chills and fever. Second, Taiyang contracts cold; after five or six days, Yang Qi declines, residual pathogens remain, and the condition transfers to Shaoyang, presenting alternating chills and fever. Third, wind is a Yang pathogen, and Shaoyang is the Wind organ. Contracting wind immediately causes alternating chills and fever, not necessarily waiting until the fifth or sixth day. During alternating chills and fever, there are periods without chills or heat, which are external manifestations of the disease state.
[Outline] Zhang Zhongjing said: When blood is deficient and Qi is exhausted, the Cou Li (pores and interstices) open, allowing pathogenic factors to enter. They contend with healthy Qi and knot in the hypochondrium. The struggle between healthy Qi and pathogens causes alternating chills and fever, occurring at specific times. There is silence with loss of appetite. Because the Zang and Fu organs are connected, pain tends to occur lower down. The pathogen is high (in the chest/hypochondrium), while the pain is low (in the abdomen), thus causing vomiting. Xiao Chai Hu Tang is the primary treatment.
[Commentary] Liu Wansu said: If pathogens enter and healthy Qi does not struggle, there will be fever without chills. When healthy Qi struggles with pathogens, chills and fever arise. During the struggle, Qi stagnates and cannot disperse outward, leading to the contest of chills and heat. When the struggle is intense, heat suddenly rises; thus, after chills subside, heat appears. This is the mechanism of chills and fever.
Wei Litong said: This describes the situation when a woman's menstruation has just ceased. Blood loss leads to blood deficiency, and the Qi in the Blood Chamber is also depleted. Internal emptiness leads to surface laxity, opening the Cou Li, making it easy for pathogens to invade and contend with healthy Qi. If healthy Qi is sufficient, it repels invasion; if deficient, pathogens mix with it. This applies to all diseases. Since this involves the blood aspect in women, the Liver, which governs blood, is relevant, located in the hypochondrium. Healthy Qi fluctuates between sufficiency (resisting) and deficiency (yielding), creating a struggle with pathogens. This obstruction blocks the pathway of Yin-Yang ascent and descent, causing alternating chills and fever with regular intervals, along with silence and loss of appetite, purely indicating Shaoyang syndrome. One might wonder if this is not the sequential transmission of cold damage from Taiyang to Yangming to Shaoyang. Actually, heat entering the Blood Chamber can occur during Taiyang or after Taiyang resolves, differing significantly from the mandatory sequential transmission in men. Although the treatment is similar to Shaoyang disease, its origin differs greatly from how men contract Shaoyang disease. This is because the Liver Wood belongs to the Zang (Jueyin), and the Gallbladder Wood belongs to the Fu (Shaoyang). They share the same Qi and adjacent locations. When heat enters the Blood Chamber, the Liver, governing blood, is attacked. The Gallbladder, attached to the Liver, is invaded as pathogens enter the Liver branch. One Zang and one Fu, connected in structure, suffer together in disease, unlike other Zang-Fu pairs. Heat enters and knots the blood; blood knotting causes pain. Pain causes Qi to sink, and sinking Qi intensifies lower pain. However, the Shaoyang Gallbladder is Yang and tends to ascend, while the Jueyin Liver is Yin and tends to descend. Gallbladder pathology ascends from above, causing vomiting; Liver pathology sinks from below, causing pain. The pathogen is high, pain is low, hence vomiting. Is this not caused by heat entering the Blood Chamber and blood knotting in Shaoyang? Although the symptoms are not typical cold damage Shaoyang, the heat entering the Blood Chamber places pathogens in the Shaoyang domain, so treatment must follow Shaoyang principles. Xiao Chai Hu Tang is used, embodying the principle of ascending clear and descending turbid, as previously explained. This clarifies why heat easily enters the Blood Chamber during menstruation in women, differing from men. However, even in men, if the disease originates in Shaoyang without sequential transmission, this method can still be applied. Zhang Zhongjing specifically elucidates why heat entering the Blood Chamber comes from Taiyang, bypasses Yangming, and knots in Shaoyang. Furthermore, heat entering the Blood Chamber, knotting within it, can also cause alternating chills and fever resembling malaria. Why? Because of the connection between Zang and Fu, and the principle of high pathogen/low pain. The blood of the Liver/Gallbladder and the Blood Chamber is essentially the same. Knotting below obstructs flow above, preventing ascent and descent, thus causing malaria-like chills and fever. It should not be assumed that blood knots only below the Liver.
[Outline] Zhang Zhongjing said: If Taiyang disease does not resolve and transfers to Shaoyang, there is hardness and fullness in the hypochondrium, dry retching, inability to eat, and alternating chills and fever. If emesis or purgation has not yet been used, and the pulse is wiry and fine, Xiao Chai Hu Tang is given. If emesis, purgation, sweating, or warm needle therapy have already been performed, leading to delirium and the cessation of Chai Hu symptoms, this is termed a damaged disease (Huai Bing). One must identify the error and treat accordingly.
[Commentary] Tao Hua said: Xiao Chai Hu Tang primarily treats alternating chills and fever. If chills predominate, add Guizhi (Cinnamon Twig); if heat predominates, add Dahuang (Rhubarb Root). This is the general rule.
[Outline] Zhang Zhongjing said: After five or six days of cold damage, having already sweated and then purged, if there is mild knotting and fullness in the chest and hypochondrium, dysuria, thirst without vomiting, sweating only on the head, alternating chills and fever, and mental irritability, the disease is unresolved. Chai Hu Gui Zhi Gan Jiang Tang (Bupleurum, Cinnamon Twig, and Dried Ginger Decoction) is the primary treatment. Mild irritability upon initial administration, followed by sweating upon subsequent doses, indicates recovery.
[Commentary] Wei Litong said: This presents symptoms involving all three Yang meridians. Treatment should focus on Shaoyang with modifications. Sweating failed to remove the exterior, and purging allowed interior pathogens to enter. Chest and hypochondriac fullness with mild knotting indicates Taiyang exterior pathogens spreading across the three Yang meridians. Chest fullness relates to Taiyang; hypochondriac fullness to Shaoyang. Since fullness is not concentrated solely in the chest, the knotting is milder than in Jie Xiong (Chest Binding). Yangming involvement is also evident. Dysuria, thirst, and lack of vomiting indicate short fluid supply and declining Qi transformation, pointing to Stomach pathology. Thus, all three Yang meridians are affected. "Unresolved" means not only Yangming and Shaoyang but also incomplete resolution of Taiyang exterior pathogens. Although Taiyang is unresolved, re-sweating is contraindicated due to Yangming and Shaoyang involvement. The method should treat all three Yang meridians, using Taiyang and Shaoyang as dual pathways for expelling pathogens. Shaoyang pathogens ultimately exit via Taiyang; thus, treating Shaoyang also treats Taiyang. Yangming requires no specific treatment. The formula uses Chai Hu as the chief ingredient targeting Shaoyang, adding Guizhi to address Taiyang. Removing Renshen and adding Ganjiang opens cold knots from purgatives. Replacing Banxia with Gualougen restores damaged fluids. Muli calms the spirit and controls water. Xiao Chai Hu Tang ascends clear and descends turbid, resolving half-exterior and harmonizing half-interior. This is a flexible variation of Xiao Chai Hu Tang, achieving comprehensive results.
Ke Qin said: After sweating and purging, if Chai Hu symptoms persist, Chai Hu Tang variations are still used. The modification is due to the addition of the "mild knotting" symptom.
[Outline] Zhang Zhongjing said: After ten or more days of cold damage, if heat is knotted in the interior with alternating chills and fever, Da Chai Hu Tang (Major Bupleurum Decoction) is appropriate.
[Commentary] Ke Qin said: "Interior" is defined relative to "exterior," not referring specifically to the Stomach. This heat knots in the Qi level, not forming tangible solid masses, allowing alternating chills and fever to recur after ten days. If heat were knotted in the Stomach, it would manifest as steaming fever, and chills would no longer be perceived.