（８）辨主次兼夹：六经辨证，往往从错综复杂的病候中，突出最关紧要之处，分清疾病中的主要矛盾和次要矛盾，从而制定合理的治疗措施及相适应的方药。此种例子，在合并病中，尤为显见。例如“太阳与阳明合病者，必自下利，葛根汤主之”（３２条）。“太阳与阳明合病，不下利但呕者，葛根加半夏汤主之”（３３条）。太阳与阳明合病，涉及阳明，但以方测证，必有头项（背部）强痛、恶寒发热无汗等主证在内，是病之重心主要在表，故用葛根汤以解表发汗为主，而主药葛根升发清阳，调理胃气，实有兼治下利的作用。若下条合病不下利而呕逆，自是承接上条文意，故仍主葛根汤解表，而加半夏以降逆止呕。再有合并病之名，而无合并病之实者。如“三阳合病，腹满身重，难以转侧，口不仁，面垢，谵语，遗尿……若自汗出者，白虎汤主之”（２２４条）。因太阳主背，少阳主侧，阳明主腹，今热邪弥散于表里，充斥于全身，故腹满身重，难以转侧。其口不仁，面垢，谵语遗尿，自汗出，是高热熏蒸，神积昏蒙，为阳明燥热独盛之象，故主用白虎汤以直清里热。亦有无合并病之名，而有合并病之实者。如“伤寒四五日，身热恶风，颈项强，胁下满，手足温而渴者，小柴胡汤主之”（９９条）。此证身热恶风项强属太阳之表；手足温而渴，病已涉及阳明；其胁下满，颈强等则属少阳，故以和解为大法，而主用小柴胡汤。但病已涉及他经，治法似以兼顾为宜。故柯琴谓“当用小柴胡去参、夏加桂枝、瓜蒌根以两解之”是也。
少阳病有“或渴”（９６条）证，治法照加减法如小柴胡去半夏加人参、瓜蒌根之例。若少阳病有渴不止，审为阳明热盛伤津之证，则白虎加人参汤，清里热，益元气，生津液，又为必用之法。如“服柴胡汤已，渴者属阳明，以法治之”（９７条）。是同一为渴，有以渴为主证者，有作为其次者，主次不同，治法有别。又如“太阳病，外证未除，而数下之，遂协热而利，利下不止，心下痞硬，表里不解者，桂枝人参汤主之”（１６８条）。此病在初期阶段，自以表证为主。今因数下损伤脾胃之阳，遂见协热下利，表里不解，方用桂枝人参汤，是以温里为主，而又兼治其表。综上所述，是第三卷１７３辨证之主次中，治法有针对主证，而又隐括治其次者。有用一法治其主证，而于方中略作加减，可以兼治次者。更有突出治其主证，而不问其余者。亦有疾病矛盾转化，次证转为主证，又应以主证治之者。盖病机变化纷纭复杂，故治法亦应适合病情，随证而变。
六经分证，每一主证立一主方。若有兼证，可于方中随证加减，如太阳病中风，以发热汗出恶风脉缓为主证。主方用桂枝汤，治法是取其解肌祛风，调和营卫。兼项背强则加葛根以疏通太阳经俞；兼微喘加厚朴、杏仁以平喘降逆；兼漏汗恶风，小便难，四肢微急，难以屈伸，则加附子以温经复阳；兼大实痛则加芍药、大黄以通下里实，缓和腹痛。又如下后脉促胸满，则去芍药以避中寒；若微（脉）恶寒，又宜加附子以复阳等等。又如少阳病有五主证七或然证，其或然证亦当属于兼证范畴，故小柴胡汤多加减法。然需与上段辨主次之证合看。
水血痰食气郁等病，为杂病中常见之证。六经病中，有挟痰饮挟宿食挟瘀血等为患者，故论中具备有消水气、涤痰饮、去宿滞、活瘀血、疏郁理气等法。此类相挟之证，有因外感热病而致者，亦有属于宿疾因外感触发而加剧者。例如蓄血：有“以太阳随经郁热在里故也”（１２４条），亦有“本有久瘀血”（２３７条）。其他如水气、痰饮、宿食等亦然，可以仿此类推。
（９）辨轻重缓急：《伤寒论》在六经的前提下，审其病候有轻重，病势有缓急，则治法有差异，而制方有大小以适应治之。例如“太阳中风，脉浮紧，发热恶寒，身疼痛，不汗出而烦躁者，大青龙汤主之”（３８条）。“伤寒表不解，心下有水气，干呕发热而咳，……或喘者，小青龙汤主之”（４０条）。此两条一为表寒里热证。寒实于表，阳郁于里，产生内热而引起神志不安，以“不汗出而烦躁”为主证。因表证偏重，故治法表里双解而偏重于表。用大青龙汤，方即麻黄汤倍麻黄，减杏仁，合姜枣以解表寒；用石膏以清内热。一则属于表寒里饮证，以伤寒表不解，心下有水气，干呕咳喘等为主证。用小青龙汤，取麻桂芍草，解表散寒，以调和营卫；姜辛夏味，温中降逆，而温化水饮。是其太阳表证自较大青龙为轻矣。又如“阳明病，脉迟，虽汗出不恶寒者，其身必重，短气，腹满而喘，有潮热者，此外欲解。可攻里也，手足然汗出者，此大便已硬也。大承气汤主之。……若腹满不通者，可与小承气汤，微和胃气，勿令致大泄下”（２０８条）。此是阳明腑热燥结成实，下证全具，自可用大承气汤以峻下热结。若潮热、手足然汗出等燥实证未全具，只有阳明腑实腹满不通之证存在，则应用小承气汤以和下为宜。
此外，同一表病，其发病原因、机理略同，因所续发证候中有轻重之殊，则治法自有缓急之异。如“伤寒，医下之，续得下利清谷不止，身疼痛者，急当救里；后身疼痛，清便自调者，急当救表。救里，宜四逆汤；救表，宜桂枝汤”（９１条）。“太阳病，外证未除，而数下之，遂协热而利，利下不止，心下痞硬，表里不解者，桂枝人参汤主之”（１６３条）。以上两者同为表病误下而表证不解，下利不止。但前者病为脾阳衰微，火不燠土，已属少阴虚寒重证。虽有表证，亦当先救其里，后解其表。是里急治里之治法。后者下利不止，心下痞硬，是下后脾阳受伤，不能转输水谷运化精微所致。病情略轻而病势稍缓，故主用桂枝人参汤温里解表。此法虽偏于治里，但仍属表里双解之治法。
又有同一种类病，亦有轻重缓急之异。例如太阳蓄血：“其人如狂”，“少腹急结”（１０６条），同是蓄血轻证。故当先解其外，后用桃核承气汤以下其瘀热。若“少腹硬满”，或疼痛，“其人发狂”，则是蓄血重证而病势甚急，虽“表证仍在”（１２４条），亦宜急用抵当汤以破血消瘀。若蓄血证“少腹满”（１２６条），此条以方括证，当伴有神志失常或发狂或喜忘等证，但病势略缓，或属久病瘀血，不能一下而使病悉除，故用抵当丸缓而攻之。
第三卷１７４少阴三急下证用大承气汤后，紧接“少阴病，脉沉者，急温之，宜四逆汤”（３２３条）一条，殊有深意存焉。盖少阴病属里虚，热证宜急消亢阳以救阴液，寒证宜急温阳气以祛阴寒。救阴救阳，其用皆不可缓。从上所举大承气、四逆汤之例，又可说明同一经方，其所主证候与治法，亦有轻重缓急之殊。此即伤寒注家所谓法中之法、方外之方欤，值得深入研究。
（１０）辨预后：六经辨证，首在利用正确的诊断，分析病机变化的全过程，增强对疾病的预见性，决定可治与否的程度，殊有必要。故少阴虚寒证，《伤寒论》中分为自愈、可治、难治、不治、死亡等各种不同证型：如“少阴病，脉紧，至七八日，自下利，脉暴微，手足反温，脉紧反去者，为欲解也，虽烦下利，必自愈”（２８７条）。少阴脉紧下利，是阴寒内盛。脉暴微正指脉紧反去说；是七八日后病邪向衰。手足温而烦，为阳气来复之证，与太阴病手足温暴烦下利必自止（见２７８条）的病机略同，故断其欲愈。又“少阴病，下利，若利自止，恶寒而卧，手足温者，可治”（２８８条）；“少阴病，恶寒而，时自烦，欲去衣被者，可治”（２８９条）。少阴下利，恶寒卧，是阴寒内盛；若利止，手足温自烦，是里阳欲复。故此二条均属可治之例。再有“少阴病，吐利，手足不逆冷，反发热者，不死。脉不至者，灸少阴七壮”（２９２条）。少阴病，吐利，脉不至，此是阴寒暴中，吐利交作，一时正气不相接续所致。手足不逆冷，反发热，是阳气未至衰竭程度，并有来复之象，故断其不死。但须急以药物与温灸并用，以回阳气，而祛阴寒为妥。若“少阴病，但厥无汗，而强发之，必动其血，未知从何道出，或从口鼻，或从目出者，是为下厥上竭，为难治”（２９４条）。少阴但厥无汗，是少阴虚寒，阴阳气血并损。不可认为表证而用汗法。若误用辛温发汗之剂，则激动营血，冲激阳络，使血上出而上竭；更虚下焦阳气而为下厥。虚虚之患，故称难治。
然而育阴液，益阳气，阴阳气血兼顾之剂，又当急用以治矣。若“少阴病，恶寒身而利，手足逆冷者，不治”（２９５条），则是少阴虚寒，纯阴无阳，病趋危重，故曰不治。但从病情细致分析，尚未达到阳越阴竭的程度。治宜急投辛甘温热之剂，如参附并用，回阳救逆，扶正祛邪，庶可望其好转。其“少阴病，吐利躁烦，四逆者死”（２９６条）。“少阴病，下利止而头眩。时时自冒息，死”（２９７条）。“少阴病，四逆，恶寒而身。脉不至，不烦而躁者，死”（２９８条）。“少阴病，六七日，息高者，死”（２９７条）。“少阴病，脉微细沉，但欲卧，汗出不烦，自欲吐；至五六日自利，复烦躁不得卧寐者，死”（３００条）。这五条，病属少阴虚寒，已至末期阶段。呈现“阴阳离决，精气乃绝”之危候，故直断为死证。
又有热证，有实热、虚热之分，亦当审辨其预后。如“伤寒，若吐若下后不解，不大便五六日，上至十余日，日晡所发潮热，不恶寒，独语如见鬼状；若剧者，发则不识人，循衣摸床，惕而不安，微喘直视，脉弦者，生，涩者死。微者，但发热谵语者，大承气汤主之。若一服利，则止后服”（２１７条）。此是阳明燥热腑实之证。阳热亢极，阴液潜消，病情相当严重，脉弦是病属热实，津液未至枯竭，正邪犹能相争，若得泻热去实之剂，尚可回生；脉涩是津液已竭，故曰死证。此外，虚热之证，《伤寒论》载于少阴篇，然简略而不详。若太阳火逆证，似可窥其底蕴，如“太阳病中风，以火劫发汗，邪风被火热，血气流溢，失其常度。两阳相熏灼，其身发黄，阳盛则欲衄，阴虚小便难，阴阳俱虚竭，身体则枯燥，但头汗出，剂颈而还，腹满微喘，口干咽烂，或不大便。久则谵语，甚则至哕，手足躁扰，捻衣摸床，小便利者，其人可治”（１１１条）。此条所载手足躁扰、捻衣摸床、发黄、哕逆等，多属热病坏证常见的症状。仲景如实描写，实为后人研究病机变化规律的宝贵资料。其谓“小便利者，其人可治”，是以津液之存亡，决病情之生死。故治热病当明救津液的重要。
第三卷１７５综上所述，是知诊外感热病，对于决病情的生死，审预后的顺逆，多取决于病邪的轻重，正气的强弱，以及与治疗适当与否有关。从此可以说明《伤寒论》六经有扶阳气存阴液两大重要法门，救阳救阴，均需图之于早，不可稍缓。若证候严重，病情已到危险程度，又必须尽力抢救，不可因循推诿不治。
２论六经之病与证中医历来就讲究按照其本身的理论体系既辨证，又辨病。这一辨证、辨病相结合的辨证思想，在《伤寒论》中体现得尤为突出。
何谓病？即《伤寒论》中之太阳病、阳明病、少阳病、太阴病、少阴病、厥阴病是也。三阳为阳；三阴为阴。揆以《内经》治病必求于本之义。盖所谓三阳病者，邪入未深，病势尚浅，病位在上在表，正气抗邪能力较强，营卫气血流行之机，充盛有力，病多属实，故于三阳病多见发热证，即“病有发热恶寒者，发于阳也”。若三阴病邪入较深，病势沉重，病位在里在下，正气抗邪能力不足，阳气反应迟滞，病多属虚，故三阴病多无发热证，所谓“无热恶寒者，发于阴也”。是其所谓病者，盖仲景固从纷纭复杂千变万化之病候中，根据邪气之微甚，正气之强弱，脏腑经络营卫气血之反应。三因、四诊、八纲、八法之具体运用，始厘定此三阳三阴，亦即六经病，治伤寒如是，治杂病亦如是也。
《内经》谓“百疾之始期也，必生于风雨寒暑，循毫毛而入腠理”（《灵枢·五变篇》）。凡外感疾病发生、发展的一般规律，多由表而深入及里。太阳主人身在外一层，总六经而统摄营卫，故外邪犯表，阳气被遏，在表营卫不和，则表现为太阳之为病，或简称太阳病。“太阳之为病，脉浮，头项强痛而恶寒”为太阳表病总纲。外邪束表，阳气失宣，反映出太阳病本质，则恶寒。然太阳病必有发热，因躯体阳气反应有迟速不同，如太阳伤寒。有“或已发热，或未发热”，但不发热一般则非表病，因表病初则阴盛而寒，继则阳盛而热也，太阳经气受病，病机逆而上行，故头痛项强，太阳病势反映向外向上，故脉象应之而浮。
阳明主三阳之里，故阳明病偏重于里，以“胃家实”为提纲。又因阳明主燥热之化，故以“身热，汗自出，不恶寒，反恶热”为外证，以“脉大”为主脉。阳明之腑属胃与大肠，故阳明病既有腑实燥结证，又有气分大热证。
（8）辨别主次与兼夹证候：六经辨证，往往从错综复杂的病候中，突出最关紧要之处，分清疾病中的主要矛盾和次要矛盾，从而制定合理的治疗措施及相适应的方药。这种例子，在合并病中，尤为明显。例如“太阳病与阳明病同时发病者，必然出现自发性腹泻，用葛根汤主治”（第32条）。“太阳病与阳明病同时发病，不腹泻而呕吐的，用葛根加半夏汤主治”（第33条）。太阳病与阳明病合病，虽然涉及阳明经，但以方剂推测证候，必然包含头项强痛、恶寒发热无汗等主要证候在内，这是疾病的重心主要在表，所以用葛根汤以解表发汗为主，而主药葛根升发清阳，调理胃气，实际上有兼治腹泻的作用。如果下一条合病不腹泻而呕吐，自然是承接上一条条文的意思，所以仍以葛根汤解表，并加入半夏以降逆止呕。还有只有合并病的名称，而没有合并病的实质的情况。如“三阳合病，腹部胀满，身体沉重，难以翻身侧卧，口舌麻木不知味，面部油垢，胡言乱语，遗尿……如果有自汗出的，用白虎汤主治”（第224条）。因为太阳经主背部，少阳经主身侧，阳明经主腹部，现在热邪弥散于表里，充斥于全身，所以腹部胀满身体沉重，难以翻身侧卧。其口舌麻木不知味，面部油垢，胡言乱语，遗尿，自汗出，是高热熏蒸，神志昏蒙，是阳明燥热独盛的征象，所以主用白虎汤以直清里热。也有没有合并病的名称，而有合并病的实质的情况。如“伤寒四五日，身体发热怕风，颈项强直，胁下胀满，手足温暖而口渴的，用小柴胡汤主治”（第99条）。此证身体发热怕风项强属于太阳之表；手足温暖而口渴，病情已涉及阳明；其胁下胀满，颈项强直等则属于少阳，所以以和解为大法，而主用小柴胡汤。但病情已涉及他经，治法似乎应当兼顾为宜。所以柯琴说“应当用小柴胡汤去掉人参、半夏，加入桂枝、瓜蒌根以两解之”，是正确的。
少阳病有“或然渴”（第96条）的证候，治法按照加减法如小柴胡汤去掉半夏加入人参、瓜蒌根的例证。如果少阳病有口渴不止，审察认为是阳明热盛伤津的证候，那么白虎加人参汤，清里热，益元气，生津液，又是必用的方法。如“服用柴胡汤后，出现口渴的属于阳明病，按法治之”（第97条）。同样是口渴，有的以口渴为主要证候，有的作为次要证候，主次不同，治法有别。又如“太阳病，外证未除，却多次攻下，于是导致协热下利，腹泻不止，心下痞塞坚硬，表里同病的，用桂枝人参汤主治”（第168条）。此病在初期阶段，自然以表证为主。如今因多次攻下损伤脾胃之阳气，于是见到协热下利，表里不解，方用桂枝人参汤，是以温里为主，而又兼治其表。综上所述，是第三卷173页辨证之主次中，治法有针对主证，而又隐含治理其次者的。有用一法治其主证，而在方中略作加减，可以兼治次者的。更有突出治其主证，而不问其余的。也有疾病矛盾转化，次证转为主证，又应以主证治之的。盖病机变化纷纭复杂，故治法亦应适合病情，随证而变。
六经分证，每一主证立一主方。若有兼证，可在方中随证加减，如太阳病中风，以发热汗出恶风脉缓为主证。主方用桂枝汤，治法是取其解肌祛风，调和营卫。兼见项背强急则加葛根以疏通太阳经俞；兼见微喘加厚朴、杏仁以平喘降逆；兼见漏汗恶风，小便难，四肢微急，难以屈伸，则加附子以温经复阳；兼见大实痛则加芍药、大黄以通下里实，缓和腹痛。又如下法后脉促胸满，则去芍药以避免中寒；若微恶寒，又宜加附子以复阳等等。又如少阳病有五主证七或然证，其或然证亦当属于兼证范畴，故小柴胡汤多加减法。然而需与上段辨主次之证合看。
水、血、痰、食、气郁等病，为杂病中常见之证。六经病中，有挟痰饮、挟宿食、挟瘀血等为患的患者，故论中具备有消水气、涤痰饮、去宿滞、活瘀血、疏郁理气等法。此类相挟之证，有因外感热病而致者，亦有属于宿疾因外感触发而加剧者。例如蓄血：有“因太阳随经郁热在里故也”（第124条），亦有“本有久瘀血”（第237条）。其他如水气、痰饮、宿食等亦然，可以仿此类推。
（9）辨别轻重缓急：《伤寒论》在六经的前提下，审其病候有轻重，病势有缓急，则治法有差异，而制方有大小以适应治之。例如“太阳中风，脉浮紧，发热恶寒，身体疼痛，无汗而烦躁的，用大青龙汤主治”（第38条）。“伤寒表不解，心下有停水之气，干呕发热而咳，……或者喘的，用小青龙汤主治”（第40条）。这两条，一条为表寒里热证。寒实于表，阳郁于里，产生内热而引起神志不安，以“无汗而烦躁”为主证。因表证偏重，故治法表里双解而偏重于表。用大青龙汤，方即麻黄汤倍用麻黄，减少杏仁，合姜枣以解表寒；用石膏以清内热。另一条属于表寒里饮证，以伤寒表不解，心下有停水之气，干呕咳喘等为主证。用小青龙汤，取麻黄、桂枝、芍药、甘草，解表散寒，以调和营卫；生姜、细辛、半夏、五味子，温中降逆，而温化水饮。是其太阳表证自然比大青龙汤证较轻了。又如“阳明病，脉迟，虽有汗出不恶寒者，其身必重，短气，腹满而喘，有潮热的，这是表证欲解，可攻里也，手足濈然汗出的，这是大便已硬也。用大承气汤主治。……如果腹满不通的，可给予小承气汤，微和胃气，勿令导致大泄下”（第208条）。这是阳明腑热燥结成实，下证全具，自然可用大承气汤以峻下热结。如果潮热、手足濈然汗出等燥实证未全具，只有阳明腑实腹满不通之证存在，则应用小承气汤以下和为宜。
此外，同一表病，其发病原因、机理略同，因所续发证候中有轻重之殊，则治法自有缓急之异。如“伤寒，医生误用下法，随后出现下利清谷不止，身体疼痛的，急当救里；后来身体疼痛，大便正常者，急当救表。救里，宜四逆汤；救表，宜桂枝汤”（第91条）。“太阳病，外证未除，却多次攻下，于是导致协热下利，腹泻不止，心下痞塞坚硬，表里同病的，用桂枝人参汤主治”（第163条）。以上两者同为表病误下而表证不解，下利不止。但前者病为脾阳衰微，火不燠土，已属少阴虚寒重证。虽有表证，亦当先救其里，后解其表。是里急治里之治法。后者下利不止，心下痞硬，是下后脾阳受伤，不能转输水谷运化精微所致。病情略轻而病势稍缓，故主用桂枝人参汤温里解表。此法虽偏于治里，但仍属表里双解之治法。
又有同一种类病，亦有轻重缓急之异。例如太阳蓄血：“其人如狂”，“少腹急结”（第106条），同是蓄血轻证。故当先解其外，后用桃核承气汤以下其瘀热。若“少腹硬满”，或疼痛，“其人发狂”，则是蓄血重证而病势甚急，虽“表证仍在”（第124条），亦宜急用抵当汤以破血消瘀。若蓄血证“少腹满”（第126条），此条以方括证，当伴有神志失常或发狂或喜忘等证，但病势略缓，或属久病瘀血，不能一下而使病悉除，故用抵当丸缓而攻之。
第三卷174页少阴三急下证用大承气汤后，紧接“少阴病，脉沉者，急温之，宜四逆汤”（第323条）一条，殊有深意存焉。盖少阴病属里虚，热证宜急消亢阳以救阴液，寒证宜急温阳气以祛阴寒。救阴救阳，其用皆不可缓。从上所举大承气、四逆汤之例，又可说明同一经方，其所主证候与治法，亦有轻重缓急之殊。此即伤寒注家所谓法中之法、方外之方欤，值得深入研究。
（10）辨别预后：六经辨证，首在利用正确的诊断，分析病机变化的全过程，增强对疾病的预见性，决定可治与否的程度，非常有必要。故少阴虚寒证，《伤寒论》中分为自愈、可治、难治、不治、死亡等各种不同证型：如“少阴病，脉紧，到了七八日，自发性下利，脉突然变微弱，手足反而温暖，脉紧反而消失的，为欲解也，虽然有烦闷下利，必定自愈”（第287条）。少阴脉紧下利，是阴寒内盛。脉暴微正指脉紧反去说；是七八日后病邪向衰。手足温而烦，为阳气来复之证，与太阴病手足温暴烦下利必自止（见第278条）的病机略同，故断其欲愈。又“少阴病，下利，如果利自止，恶寒而蜷卧，手足温暖的，可治”（第288条）；“少阴病，恶寒而蜷卧，时常自烦，想要脱去衣被的，可治”（第289条）。少阴下利，恶寒蜷卧，是阴寒内盛；如果利止，手足温自烦，是里阳欲复。故此二条均属可治之例。再有“少阴病，吐利，手足不逆冷，反而发热的，不死。脉不至的，灸少阴穴七壮”（第292条）。少阴病，吐利，脉不至，这是阴寒暴中，吐利交作，一时正气不相接续所致。手足不逆冷，反而发热，是阳气未至衰竭程度，并有来复之象，故断其不死。但须急以药物与温灸并用，以回阳气，而祛阴寒为妥。若“少阴病，仅厥冷无汗，而强行发汗的，必然动其血，未知从何道出，或从口鼻，或从目出者，是为下厥上竭，为难治”（第294条）。少阴仅厥冷无汗，是少阴虚寒，阴阳气血并损。不可认为表证而用汗法。若误用辛温发汗之剂，则激动营血，冲激阳络，使血上出而上竭；更虚下焦阳气而为下厥。虚虚之患，故称难治。
然而育阴液，益阳气，阴阳气血兼顾之剂，又当急用以治矣。若“少阴病，恶寒身体蜷卧而下利，手足逆冷的，不治”（第295条），则是少阴虚寒，纯阴无阳，病趋危重，故曰不治。但从病情细致分析，尚未达到阳越阴竭的程度。治宜急投辛甘温热之剂，如参附并用，回阳救逆，扶正祛邪，庶可望其好转。其“少阴病，吐利躁烦，四肢厥逆者死”（第296条）。“少阴病，下利止而头眩。时时自冒息，死”（第297条）。“少阴病，四肢厥逆，恶寒而身体蜷卧。脉不至，不烦而躁者，死”（第298条）。“少阴病，六七日，呼吸高远的，死”（第297条）。“少阴病，脉微细沉，只想睡觉，汗出不烦，自己想要呕吐；到了五六日自利，又烦躁不得卧寐者，死”（第300条）。这五条，病属少阴虚寒，已至末期阶段。呈现“阴阳离决，精气乃绝”之危候，故直断为死证。
又有热证，有实热、虚热之分，亦当审辨其预后。如“伤寒，如果用吐法或用下法后病不解，不大便五六日，上至十余日，日晡时发潮热，不恶寒，独语如见鬼状；如果严重的，发作时不认识人，循衣摸床，惊恐而不安，微喘直视，脉弦的，生，涩的，死。轻微的，只是发热谵语的，用大承气汤主治。如果服一次有利，则停止后服”（第217条）。这是阳明燥热腑实之证。阳热亢极，阴液潜消，病情相当严重，脉弦是病属热实，津液未至枯竭，正邪犹能相争，若得泻热去实之剂，尚可回生；脉涩是津液已竭，故曰死证。此外，虚热之证，《伤寒论》载于少阴篇，然简略而不详。若太阳火逆证，似可窥其底蕴，如“太阳病中风，用火劫发汗，邪风被火热，血气流溢，失其常度。两阳相熏灼，其身发黄，阳盛则欲衄，阴虚小便难，阴阳俱虚竭，身体则枯燥，但头汗出，齐颈而还，腹满微喘，口干咽烂，或不大便。久则谵语，甚则至哕，手足躁扰，捻衣摸床，小便利的，其人可治”（第111条）。此条所载手足躁扰、捻衣摸床、发黄、哕逆等，多属热病坏证常见的症状。仲景如实描写，实为后人研究病机变化规律的宝贵资料。其谓“小便利的，其人可治”，是以津液之存亡，决病情之生死。故治热病当明救津液的重要。
第三卷175页综上所述，是知诊外感热病，对于决病情的生死，审预后的顺逆，多取决于病邪的轻重，正气的强弱，以及与治疗适当与否有关。从此可以说明《伤寒论》六经有扶阳气存阴液两大重要法门，救阳救阴，均需图之于早，不可稍缓。若证候严重，病情已到危险程度，又必须尽力抢救，不可因循推诿不治。
2. 论六经之病与证中医历来就讲究按照其本身的理论体系既辨证，又辨病。这一辨证、辨病相结合的辨证思想，在《伤寒论》中体现得尤为突出。
何谓病？即《伤寒论》中之太阳病、阳明病、少阳病、太阴病、少阴病、厥阴病是也。三阳为阳；三阴为阴。揆以《内经》治病必求于本之义。盖所谓三阳病者，邪入未深，病势尚浅，病位在上在表，正气抗邪能力较强，营卫气血流行之机，充盛有力，病多属实，故于三阳病多见发热证，即“病有发热恶寒者，发于阳也”。若三阴病邪入较深，病势沉重，病位在里在下，正气抗邪能力不足，阳气反应迟滞，病多属虚，故三阴病多无发热证，所谓“无热恶寒者，发于阴也”。是其所谓病者，盖仲景固从纷纭复杂千变万化之病候中，根据邪气之微甚，正气之强弱，脏腑经络营卫气血之反应。三因、四诊、八纲、八法之具体运用，始厘定此三阳三阴，亦即六经病，治伤寒如是，治杂病亦如是也。
《内经》谓“百疾之始期也，必生于风雨寒暑，循毫毛而入腠理”（《灵枢·五变篇》）。凡外感疾病发生、发展的一般规律，多由表而深入及里。太阳主人身在外一层，总六经而统摄营卫，故外邪犯表，阳气被遏，在表营卫不和，则表现为太阳之为病，或简称太阳病。“太阳之为病，脉浮，头项强痛而恶寒”为太阳表病总纲。外邪束表，阳气失宣，反映出太阳病本质，则恶寒。然太阳病必有发热，因躯体阳气反应有迟速不同，如太阳伤寒。有“或已发热，或未发热”，但不发热一般则非表病，因表病初则阴盛而寒，继则阳盛而热也，太阳经气受病，病机逆而上行，故头痛项强，太阳病势反映向外向上，故脉象应之而浮。
阳明主三阳之里，故阳明病偏重于里，以“胃家实”为提纲。又因阳明主燥热之化，故以“身热，汗自出，不恶寒，反恶热”为外证，以“脉大”为主脉。阳明之腑属胃与大肠，故阳明病既有腑实燥结证，又有气分大热证。
(8) Distinguishing between Primary and Secondary/Concurrent Syndromes: Six-Channel differentiation often highlights the most critical aspects from complex and intertwined clinical manifestations, distinguishing the primary and secondary contradictions in the disease, thereby formulating appropriate treatment measures and corresponding formulas. Such examples are particularly evident in concurrent diseases (concurrent involvement of multiple channels). For instance, "When Taiyang and Yangming channels are concurrently involved, spontaneous diarrhea will inevitably occur; Gegen Tang (Pueraria Decoction) is the primary formula" (Clause 32). "When Taiyang and Yangming channels are concurrently involved, without diarrhea but with vomiting, Gegen Jia Banxia Tang (Pueraria Decoction with Pinellia) is the primary formula" (Clause 33). Although Taiyang-Yangming concurrent involvement involves the Yangming channel, inferring the syndrome from the formula implies that primary symptoms such as stiffness and pain in the head and neck (back), aversion to cold, fever, and absence of sweating must be present. The focus of the disease lies primarily in the exterior; therefore, Gegen Tang is used mainly to release the exterior and induce sweating. Its chief herb, Ge Gen (Radix Puerariae Lobatae), raises clear yang and regulates stomach qi, effectively having a dual action of treating diarrhea. If the subsequent clause mentions concurrent involvement without diarrhea but with vomiting, it naturally follows the previous text's intent; thus, the exterior is still released using Gegen Tang, with Ban Xia (Rhizoma Pinelliae Preparatum) added to descend rebellious qi and stop vomiting. There are also cases where there is the name of concurrent involvement but not the reality. For example, "In concurrent involvement of the Three Yang channels, there is abdominal fullness, heaviness of the body, difficulty in turning over, numbness of the mouth, greasy face, delirium, and urinary incontinence... If there is spontaneous sweating, Baihu Tang (White Tiger Decoction) is the primary formula" (Clause 224). Since the Taiyang channel governs the back, Shaoyang governs the sides, and Yangming governs the abdomen, now heat pathogens diffuse throughout the interior and exterior, filling the whole body, causing abdominal fullness, body heaviness, and difficulty in turning. The numbness of the mouth, greasy face, delirium, urinary incontinence, and spontaneous sweating are due to high heat steaming and clouding the spirit, indicating an image of excessive dry-heat in Yangming alone; hence, Baihu Tang is primarily used to directly clear interior heat. Conversely, there are cases with the reality of concurrent involvement but not its name. For example, "After four or five days of Shanghan (Cold Damage), with fever, aversion to wind, stiff neck, fullness under the hypochondrium, warm hands and feet, and thirst, Xiaochaihu Tang (Minor Bupleurum Decoction) is the primary formula" (Clause 99). This syndrome's fever, aversion to wind, and stiff neck belong to the Taiyang exterior; warm hands and feet and thirst indicate involvement of Yangming; fullness under the hypochondrium and stiff neck belong to Shaoyang. Therefore, harmonization is the major method, and Xiaochaihu Tang is primarily used. However, since the disease involves other channels, the treatment should ideally address them simultaneously. Thus, Ke Qin stated that "Xiaochaihu Tang should be used with Ren Shen (Radix Ginseng) and Ban Xia removed, and Gui Zhi (Ramulus Cinnamomi) and Gua Lou Gen (Radix Trichosanthis) added to resolve both," which is correct.
Shaoyang disease has the "possible symptom of thirst" (Clause 96). The treatment method follows the modification principle, such as removing Ban Xia and adding Ren Shen and Gua Lou Gen to Xiaochaihu Tang. If Shaoyang disease presents with persistent thirst, and upon examination it is determined to be a syndrome of excessive Yangming heat damaging fluids, then Baitu Jia Renshen Tang (White Tiger Decoction with Ginseng) to clear interior heat, benefit primal qi, and generate fluids becomes a necessary method. As stated, "After taking Chaihu Tang, if thirst occurs, it belongs to Yangming; treat according to the method" (Clause 97). Thirst can be either a primary symptom or a secondary one; depending on whether it is primary or secondary, the treatment differs. Furthermore, "In Taiyang disease, if external signs persist but purgatives are administered repeatedly, leading to concurrent heat diarrhea that does not cease, epigastric hardness, and unresolved exterior and interior conditions, Guizhi Renshen Tang (Cinnamon Twig and Ginseng Decoction) is the primary formula" (Clause 168). In the early stage, this disease is primarily an exterior syndrome. However, repeated purgation damages the spleen and stomach yang, resulting in concurrent heat diarrhea and unresolved exterior-interior conditions. Guizhi Renshen Tang is used, focusing on warming the interior while simultaneously addressing the exterior. In summary, regarding the differentiation of primary and secondary aspects in Volume 3, page 173, treatment methods may target the primary symptom while implicitly treating the secondary one. One method may treat the primary symptom, with slight modifications to the formula to concurrently treat the secondary aspect. There are also cases where the primary symptom is emphasized, ignoring others. Additionally, when disease contradictions transform, secondary symptoms may become primary, requiring treatment based on the new primary symptom. Given the complex and varied changes in pathogenesis, treatment methods must adapt to the condition and change with the syndrome.
Six-Channel differentiation establishes a primary formula for each primary syndrome. If concurrent symptoms exist, modifications can be made within the formula. For example, in Taiyang Wind Strike disease, the primary symptoms are fever, sweating, aversion to wind, and a slow pulse. The primary formula is Guizhi Tang (Cinnamon Twig Decoction), whose treatment method aims to release the muscle layer, dispel wind, and harmonize Ying and Wei (Nutritive and Defensive levels). If accompanied by stiffness in the neck and back, Ge Gen is added to unblock the Taiyang channel acupoints; if accompanied by mild asthma, Hou Po (Cortex Magnoliae Officinalis) and Xing Ren (Semen Armeniacae Amarum) are added to calm asthma and direct rebellious qi downward; if accompanied by leakage of sweat, aversion to wind, difficult urination, slight stiffness in the four limbs, and difficulty in flexion and extension, Fu Zi (Radix Aconiti Lateralis Preparata) is added to warm the channels and restore yang; if accompanied by severe painful constipation, Shao Yao (Radix Paeoniae Alba/Rubra) and Da Huang (Radix et Rhizoma Rhei) are added to purge interior excess and relieve abdominal pain. Furthermore, after purgation, if there is a rapid pulse and chest fullness, Shao Yao is removed to avoid middle jiao cold; if there is slight aversion to cold, Fu Zi should be added to restore yang, etc. Similarly, Shaoyang disease has five primary symptoms and seven possible symptoms; these possible symptoms also fall under the category of concurrent syndromes, hence Xiaochaihu Tang has many modifications. However, this must be viewed in conjunction with the aforementioned differentiation of primary and secondary syndromes.
Pathogens such as water, blood, phlegm, food stagnation, and qi stagnation are common in miscellaneous diseases. In Six-Channel diseases, patients may suffer from complications involving phlegm-fluid retention, retained food, or blood stasis. Thus, the Treatise contains methods to eliminate water qi, wash away phlegm-fluids, remove retained stagnation, invigorate blood and resolve stasis, and soothe depression to regulate qi. These complicated syndromes may result from exogenous febrile diseases or be pre-existing conditions exacerbated by exogenous triggers. For example, Blood Accumulation: some cases are due to "Taiyang following the channels with stagnant heat in the interior" (Clause 124), while others are due to "pre-existing long-term blood stasis" (Clause 237). The same applies to water qi, phlegm-fluids, and retained food, which can be inferred by analogy.
(9) Distinguishing Severity and Urgency: Under the premise of Six-Channel differentiation, *Shanghan Lun* assesses the severity of clinical manifestations and the urgency of the disease progression, leading to differences in treatment methods and the formulation of large or small formulas to suit the treatment. For example, "Taiyang Wind Strike, with floating-tight pulse, fever, aversion to cold, body pain, no sweating, and irritability, is treated with Da Qinglong Tang (Major Blue-Green Dragon Decoction)" (Clause 38). "Shanghan with unresolved exterior, fluid retention in the heart region, dry heaving, fever, and cough... or wheezing, is treated with Xiao Qinglong Tang (Minor Blue-Green Dragon Decoction)" (Clause 40). The first case is an exterior-cold interior-heat syndrome. Cold excess in the exterior and yang constraint in the interior generate internal heat causing mental unrest, with "no sweating and irritability" as the primary symptom. Since the exterior syndrome is predominant, the treatment resolves both exterior and interior, emphasizing the exterior. Da Qinglong Tang is used, which is Mahuang Tang (Ephedra Decoction) with doubled Mahuang (Herba Ephedrae), reduced Xing Ren, combined with Sheng Jiang (Rhizoma Zingiberis Recens) and Da Zao (Fructus Jujubae) to release exterior cold; Shi Gao (Gypsum Fibrosum) is used to clear internal heat. The second case is an exterior-cold interior-fluid retention syndrome, with unresolved exterior, fluid retention in the heart region, dry heaving, cough, and wheezing as primary symptoms. Xiao Qinglong Tang uses Ma Huang, Gui Zhi, Bai Shao (Radix Paeoniae Alba), and Gan Cao (Radix Glycyrrhizae Preparata) to release the exterior and dispel cold, harmonizing Ying and Wei; Sheng Jiang, Xi Xin (Herba Asari), Ban Xia, and Wu Wei Zi (Fructus Schisandrae Chinensis) warm the middle, direct rebellious qi downward, and warm-transform fluid retention. Thus, the Taiyang exterior syndrome here is lighter than in Da Qinglong Tang syndrome. Furthermore, "Yangming disease, with a slow pulse, sweating without aversion to cold, heavy body, shortness of breath, abdominal fullness and wheezing, tidal fever indicates the exterior is resolving and interior can be purged. Sweating on the hands and feet indicates hardened stool. Da Chengqi Tang (Major Order to Yield Decoction) is the primary formula... If there is abdominal fullness and obstruction, Xiao Chengqi Tang (Minor Order to Yield Decoction) may be given to mildly harmonize stomach qi, avoiding severe purgation" (Clause 208). This is a Yangming fu-organ heat-dryness accumulation syndrome with all lower indications present, suitable for Da Chengqi Tang to vigorously purge heat accumulation. If tidal fever and sweating on hands and feet are not fully present, and only Yangming fu-organ excess with abdominal fullness and obstruction exists, Xiao Chengqi Tang is appropriate for mild purgation.
Additionally, for the same exterior disease, although the cause and mechanism are similar, differences in the severity of subsequent symptoms lead to differences in the urgency of treatment. For example, "In Shanghan, if the physician incorrectly uses purgation, followed by continuous diarrhea with undigested food and body pain, urgent rescue of the interior is required; later, if body pain persists and bowel movements normalize, urgent rescue of the exterior is required. To rescue the interior, Sini Tang (Frigid Extremities Decoction) is suitable; to rescue the exterior, Guizhi Tang is suitable" (Clause 91). "In Taiyang disease, if external signs persist but purgatives are administered repeatedly, leading to concurrent heat diarrhea that does not cease, epigastric hardness, and unresolved exterior and interior conditions, Guizhi Renshen Tang is the primary formula" (Clause 163). Both cases involve unresolved exterior syndrome and continuous diarrhea due to incorrect purgation of an exterior disease. However, the former involves decline of spleen yang and failure of fire to warm earth, constituting a severe Shaoyin deficiency-cold syndrome. Despite the exterior syndrome, the interior must be rescued first, followed by releasing the exterior. This is the method of treating urgency in the interior. The latter involves continuous diarrhea and epigastric hardness due to spleen yang injury from purgation, impairing the transport of grain and essence. The condition is slightly milder and less urgent, so Guizhi Renshen Tang is primarily used to warm the interior and release the exterior. Although this method leans towards treating the interior, it still belongs to the method of resolving both exterior and interior.
There are also variations in severity and urgency among the same type of disease. For example, in Taiyang Blood Accumulation: "The person acts like a madman, with acute binding in the lower abdomen" (Clause 106) represents a mild syndrome. Thus, the exterior should be resolved first, followed by Taohe Chengqi Tang (Peach Kernel and Major Order to Yield Decoction) to purge blood-heat. If there is "hardness and fullness in the lower abdomen," or pain, and "the person goes mad," this is a severe blood accumulation syndrome with urgent progression. Even if "exterior signs remain" (Clause 124), Didang Tang (Di Dang Decoction) should be urgently used to break blood and resolve stasis. If the blood accumulation syndrome presents with "fullness in the lower abdomen" (Clause 126), inferring the syndrome from the formula suggests accompanying mental aberrations, madness, or forgetfulness. However, the progression is slower, possibly due to long-term blood stasis that cannot be completely eliminated in one dose; thus, Didang Wan (Di Dang Pill) is used for a slow attack.
Following the use of Da Chengqi Tang for the three urgent Shaoyin purgation syndromes on page 174 of Volume 3, the immediate next clause states, "In Shaoyin disease, if the pulse is deep, urgently warm it; Sini Tang is suitable" (Clause 323). This holds profound meaning. Shaoyin disease belongs to interior deficiency. In heat syndromes, it is urgent to subdue hyperactive yang to save yin fluids; in cold syndromes, it is urgent to warm yang qi to dispel yin cold. Saving yin and saving yang are both urgent. The examples of Da Chengqi Tang and Sini Tang illustrate that even the same classic formula has variations in the severity of its indicated syndromes and treatment urgency. This is what Shanghan commentators refer to as "methods within methods" and "formulas beyond formulas," worthy of in-depth study.
(10) Distinguishing Prognosis: Six-Channel differentiation prioritizes accurate diagnosis to analyze the entire process of pathogenesis changes, enhancing predictability of the disease and determining the degree of treatability, which is highly necessary. Therefore, Shaoyin deficiency-cold syndromes in *Shanghan Lun* are divided into various types: self-healing, treatable, difficult to treat, untreatable, and death. For example, "In Shaoyin disease, with a tight pulse, after seven or eight days, spontaneous diarrhea occurs, the pulse suddenly becomes weak, hands and feet become warm, and the tight pulse disappears; this indicates impending resolution. Although there is irritability and diarrhea, it will surely heal itself" (Clause 287). Tight pulse and diarrhea in Shaoyin indicate excessive interior yin-cold. The sudden weakness refers to the disappearance of the tight pulse; after seven or eight days, the pathogen declines. Warm hands and feet with irritability indicate the return of yang qi, similar to the pathogenesis in Taiyin disease where warm hands and feet, sudden irritability, and diarrhea will stop spontaneously (see Clause 278); thus, it is judged as impending healing. Also, "In Shaoyin disease, with diarrhea, if the diarrhea stops, there is aversion to cold and curling up, and warm hands and feet; this is treatable" (Clause 288); "In Shaoyin disease, with aversion to cold and curling up, occasional irritability, and desire to remove clothing and blankets; this is treatable" (Clause 289). Diarrhea, aversion to cold, and curling up in Shaoyin indicate excessive interior yin-cold; if diarrhea stops, hands and feet are warm, and there is spontaneous irritability, it indicates the recovery of interior yang. Thus, these two clauses are examples of treatable conditions. Furthermore, "In Shaoyin disease, with vomiting and diarrhea, if hands and feet are not cold, but rather warm, there is no death. If the pulse is absent, moxa seven moxibustions on Shaoyin points" (Clause 292). Vomiting and diarrhea with absent pulse in Shaoyin disease are caused by sudden invasion of yin-cold, alternating vomiting and diarrhea, and temporary discontinuity of righteous qi. Hands and feet not being cold and instead being warm indicate that yang qi has not reached exhaustion and shows signs of recovery; thus, death is ruled out. However, urgent combination of medication and warm moxibustion is required to restore yang qi and dispel yin-cold. If "In Shaoyin disease, there is only cold extremities and no sweat, and forced sweating causes bleeding, unknown from which orifice it exits, either from nose/mouth or eyes, this is lower cold and upper depletion, which is difficult to treat" (Clause 294). Only cold extremities and no sweat in Shaoyin indicate deficiency-cold, with damage to yin, yang, qi, and blood. It should not be mistaken for an exterior syndrome treated with sweating. If mistakenly treated with acrid-warm sweating agents, it agitates Ying blood and attacks yang collaterals, causing blood to exit upwards leading to upper depletion; further depleting lower jiao yang leads to lower cold. The harm of depleting the depleted makes it difficult to treat.
However, formulas that nourish yin fluids, benefit yang qi, and balance yin, yang, qi, and blood should be urgently used. If "In Shaoyin disease, with aversion to cold, body curling, diarrhea, and cold extremities; this is untreatable" (Clause 295), it indicates Shaoyin deficiency-cold, pure yin without yang, approaching critical danger, hence termed untreatable. However, detailed analysis shows it has not yet reached the stage of yang floating and yin exhaustion. Treatment should urgently administer acrid-sweet-warm formulas, such as combining Renshen and Fu Zi to restore yang and rescue from collapse, support righteous qi and dispel pathogens, hoping for improvement. "In Shaoyin disease, with vomiting, diarrhea, restlessness, irritability, and cold extremities; death" (Clause 296). "In Shaoyin disease, diarrhea stops but dizziness occurs. Frequent feeling of faintness in breathing; death" (Clause 297). "In Shaoyin disease, cold extremities, aversion to cold, and body curling. Absent pulse, no irritability but restlessness; death" (Clause 298). "In Shaoyin disease, after six or seven days, high breathing; death" (Clause 297). "In Shaoyin disease, pulse is micro-fine-deep, desire to sleep, sweating without irritability, desire to vomit; after five or six days, spontaneous diarrhea, again irritable and unable to lie down; death" (Clause 300). These five clauses represent Shaoyin deficiency-cold reaching the terminal stage, presenting the critical sign of "separation of yin and yang, exhaustion of essence and qi," thus directly judged as fatal.
Heat syndromes are also divided into excess-heat and deficiency-heat, and their prognosis must be assessed. For example, "In Shanghan, if after vomiting or purgation the disease is unresolved, no bowel movement for five or six days, up to ten or more days, tidal fever at dusk, no aversion to cold, talking alone as if seeing ghosts; if severe, during episodes inability to recognize people, grasping at clothes and bed, fearful and uneasy, slight asthma, fixed gaze, if the pulse is wiry, survival; if choppy, death. Mild cases, only fever and delirium, are treated with Da Chengqi Tang. If one dose results in relief, stop subsequent doses" (Clause 217). This is a Yangming dry-heat fu-organ excess syndrome. Extreme yang heat and latent consumption of yin fluids make the condition serious. A wiry pulse indicates heat-excess, fluids not yet exhausted, and struggle between righteous and pathogenic qi; with heat-purging and excess-resolving agents, recovery is possible. A choppy pulse indicates exhausted fluids, hence death. Additionally, deficiency-heat syndromes are recorded in the Shaoyin chapter of *Shanghan Lun*, but briefly. The Sun Fire Reversal syndrome offers insight, e.g., "In Taiyang Wind Strike, using fire to force sweating, evil wind combined with fire, blood and qi overflow, losing normal rhythm. Two yangs scorch each other, body turns yellow, excess yang leads to nasal hemorrhage, yin deficiency leads to difficult urination, yin and yang both deficient and exhausted, body becomes dry, only head sweats up to the neck, abdominal fullness, slight asthma, dry mouth and rotten throat, or no bowel movement. Long term leads to delirium, severely to hiccups, restless hands and feet, grasping at clothes and bed, if urine flows freely, the person is treatable" (Clause 111). Symptoms such as restless hands and feet, grasping at clothes and bed, jaundice, and hiccups described in this clause are common in deteriorated heat diseases. Zhongjing's realistic description is valuable data for studying pathogenesis changes. Stating "if urine flows freely, the person is treatable" determines life and death based on the presence or absence of fluids. Thus, in treating heat diseases, the importance of preserving fluids must be understood.
In summary on page 175 of Volume 3, diagnosing exogenous heat diseases to determine life/death and favorable/unfavorable prognosis depends largely on the severity of pathogens, strength of righteous qi, and appropriateness of treatment. This illustrates that the Six Channels in *Shanghan Lun* have two important principles: supporting yang qi and preserving yin fluids. Rescuing yang and yin must be planned early and not delayed. If syndromes are severe and the condition is critical, every effort must be made to rescue, without procrastination or neglect.
2. On the Disease and Syndrome of Six Channels: Traditional Chinese Medicine has always emphasized differentiating both syndrome and disease according to its own theoretical system. This integrated thinking of syndrome and disease differentiation is particularly prominent in *Shanghan Lun*.
What is a disease? It refers to Taiyang disease, Yangming disease, Shaoyang disease, Taiyin disease, Shaoyin disease, and Jueyin disease in *Shanghan Lun*. The Three Yang are yang; the Three Yin are yin. Referring to the *Neijing* principle that "in treating disease, one must seek the root." Generally speaking, in Three Yang diseases, pathogens have not penetrated deeply, the disease trend is shallow, the location is upper and exterior, the ability of righteous qi to resist pathogens is strong, the mechanism of Ying, Wei, Qi, and Blood circulation is vigorous, and the disease is mostly excess. Therefore, fever syndromes are common in Three Yang diseases, i.e., "Diseases with fever and aversion to cold originate from yang." If in Three Yin diseases, pathogens penetrate deeper, the disease trend is heavy, the location is interior and lower, the ability of righteous qi to resist pathogens is insufficient, yang response is sluggish, and the disease is mostly deficiency. Therefore, Three Yin diseases mostly lack fever syndromes, i.e., "Diseases without fever but with aversion to cold originate from yin." Thus, the so-called disease refers to Zhang Zhongjing clarifying these Three Yang and Three Yin, i.e., Six-Channel diseases, from complex and changing clinical manifestations based on the depth of pathogens, strength of righteous qi, reactions of zang-fu organs, meridians, Ying, Wei, Qi, and Blood. Through the specific application of Three Causes, Four Diagnostic Methods, Eight Principles, and Eight Methods, these were established. Treating Shanghan is like this, and treating miscellaneous diseases is also like this.
The *Neijing* states, "The beginning of all diseases must arise from wind, rain, cold, and summer heat, entering through hair follicles into interstices" (*Ling Shu: Wu Bian Pian*). The general law of occurrence and development of exogenous diseases mostly progresses from exterior to interior. Taiyang governs the outermost layer of the body,统领 (leads) the Six Channels and controls Ying and Wei. Thus, when exogenous pathogens invade the exterior, yang qi is constrained, and Ying and Wei are disharmonious at the exterior, manifesting as Taiyang disease, or simply Taiyang disease. "Taiyang disease is characterized by floating pulse, stiffness and pain in the head and neck, and aversion to cold" is the general outline of Taiyang exterior disease. Exogenous pathogens binding the exterior and loss of yang qi dissemination reflect the essence of Taiyang disease, hence aversion to cold. However, Taiyang disease must have fever, as the body's yang response varies in speed. For example, in Taiyang Cold Damage, there is "either already fever, or not yet fever," but generally, no fever is not an exterior disease, because initially exterior disease involves yin excess and cold, followed by yang excess and heat. When Taiyang channel qi is diseased, the pathogenesis reverses and moves upward, causing headache and stiff neck. The trend of Taiyang disease reflects outward and upward, so the pulse corresponds by being floating.
Yangming governs the interior of the Three Yang, so Yangming disease focuses on the interior, with "Stomach-Fu excess" as the outline. Also, because Yangming governs dry-heat transformation, "body heat, spontaneous sweating, no aversion to cold, but aversion to heat" are external signs, and "large pulse" is the main pulse. The fu-organs of Yangming belong to the Stomach and Large Intestine, so Yangming disease includes both fu-organ excess-dryness accumulation syndromes and qi-level excessive heat syndromes.