《活人书》云∶阳明证宜下，少阴证宜温。又曰∶少阴病，一二日，口中和，其背恶寒
者，宜着艾，并四逆汤。又云∶三阳证宜下，三阴证宜温。少阴病，发热，脉沉，麻黄附子细辛
汤主之，少阴病，二三日，当见少阴证，无阳者，宜麻黄附子甘草汤，皆阴证表药也。又云∶发
热而恶寒者，发于阳也，麻黄、桂枝汤主之。守真云∶夫辨伤寒阴阳之理者，邪热在表，腑病
为阳，邪热在里，脏病为阴。世俗妄谓有寒热阴阳之异，误人多矣。寒病固有，然非汗病之谓
也，止为杂病，不可与汗病同科。且造化为汗液之气者，乃阳热之气，非阴寒之所能也，观万物
热极而反出水液，明可知矣。况法曰身热为热在表，饮水为热在里，其伤寒病，本末身凉不渴，
及小便不黄，脉不数者，未之有也。虽仲景有四逆汤证，表热里和，误以寒药下之太早，表热
未入于里，里寒下利不止，及表热里寒自利，急以四逆汤温里，利止里和者，急于解表也。故仲
景四逆汤证后，复有承气汤寒药下热之说。由是伤寒汗病，经直言热，而不言其有寒也。经言三
阴证者、邪热在脏在里，以脏为里为阴，当下热者是也。按《素问》论伤寒热病三篇，皆名曰
热，竟无寒说，兼以《灵枢》诸经运气之说推之，则名为热病，诚非寒也。《素问·热论》云，
帝曰∶治之奈何？岐伯曰∶治之各通其脏脉，病日衰矣。其未满三日，可汗而已，其满三日，
可泄而已。此言表里之大体也。（注曰∶《正理伤寒论》脉大浮数，病在表，可发其汗，脉沉细数，
病在里，可下之。）由此，虽日数过多，但有表证，而脉浮数，犹宜发汗，日数虽少，即有里证，
犹宜下之，正应脉证而汗下之也。
《活人书》说：阳明证适宜用下法，少阴证适宜用温法。又说：少阴病，发病一二天，口中感觉平和（不苦不燥），背部怕冷的，适宜用艾灸，并用四逆汤。又说：三阳证适宜用下法，三阴证适宜用温法。少阴病，出现发热，脉象沉，由麻黄附子细辛汤主治；少阴病，二三天，应当见到少阴病的症状，没有阳气（指无太阳表证之发热等）的，适宜用麻黄附子甘草汤，这些都是治疗阴证兼有表邪的药物。又说：发热并且怕冷的，是发于阳经，由麻黄汤、桂枝汤主治。
刘守真（刘完素）说：辨别伤寒阴阳的道理，邪热在体表，腑病属于阳；邪热在体内，脏病属于阴。世俗之人错误地认为有寒热阴阳的区别，误导了很多人。寒病固然存在，但这并不是指需要发汗的病（即不是外感风寒表实证），仅属于杂病，不能与需要发汗的外感病归为一类。况且造化生成汗液的气，乃是阳热之气，不是阴寒之气所能产生的，观察万物在热极时反而出水液，就可以明显知道了。何况医法规定：身体发热说明热在体表，想喝水说明热在体内。那些伤寒病，从头到尾身体凉爽且不口渴，以及小便不黄，脉象不数的情况，是从来没有过的。虽然张仲景有使用四逆汤的证候，那是表热里和（内部平和），误用寒凉药过早攻下，导致表热未入里，而里寒导致腹泻不止，以及表热里寒导致的自发性腹泻，此时急需用四逆汤温补里气，待腹泻停止、里气调和后，再急于解除表邪。所以张仲景在四逆汤证之后，又有承气汤用寒凉药攻下热邪的说法。因此，伤寒的发汗病，经典直接论述的是热，而没有说它有寒。经典所说的三阴证，是指邪热在脏、在里，以脏为里、为阴，应当攻下热邪的情况。按《素问》讨论伤寒热病的三篇，都命名为“热”，竟然没有关于“寒”的说法，再加上《灵枢》中各经脉气运行的理论来推究，那么命名为热病，确实不是寒病。《素问·热论》说，黄帝问：怎么治疗？岐伯说：治疗要分别疏通其所属脏腑的经脉，病势就会一天天衰退。病程未满三天，可以通过发汗治愈；病程已满三天，可以通过泄下治愈。这是讲述表里治法的大致原则。（注释说：《正理伤寒论》指出，脉象大浮数，病在表，可以发汗；脉象沉细数，病在里，可以攻下。）由此看来，即使天数过多，只要有表证，且脉象浮数，仍然适宜发汗；即使天数很少，如果有里证，仍然适宜攻下，这正是顺应脉证进行发汗或攻下的道理。
The *Huoren Shu* (Book of Living People) states: Yangming syndrome is suitable for purgation, while Shaoyin syndrome is suitable for warming. It further states: In Shaoyin disease, if within one or two days the mouth feels normal (not bitter or dry) and there is aversion to cold in the back, moxibustion should be applied, along with Sini Tang (Four Reversal Decoction). It also says: San yang syndromes are suitable for purgation, while San yin syndromes are suitable for warming. In Shaoyin disease, if fever is present with a deep pulse, it is treated with Mahuang Fuzi Xixin Tang (Ephedra, Aconite, and Asarum Decoction); in Shaoyin disease, if after two or three days Shaoyin symptoms appear but there is no exterior heat (absence of Yang), Mahuang Fuzi Gancao Tang (Ephedra, Aconite, and Licorice Decoction) is suitable; these are all formulas treating interior Yin syndromes with exterior-resolving properties. It further states: Fever accompanied by aversion to cold indicates onset from the Yang meridians, treated with Mahuang Tang (Ephedra Decoction) or Guizhi Tang (Cinnamon Twig Decoction).
Liu Shouzhen (Liu Wansu) stated: To distinguish the principles of Yin and Yang in Shanghan (Cold Damage), when pathogenic heat is on the exterior, Fu-organ diseases belong to Yang; when pathogenic heat is on the interior, Zang-organ diseases belong to Yin. Laypeople erroneously believe there are distinct differences between cold and heat, Yin and Yang, which has misled many. Although Cold diseases do exist, they do not refer to conditions requiring sweating (exterior excess due to cold), but rather constitute miscellaneous diseases and should not be classified together with exterior syndromes requiring diaphoresis. Moreover, the Qi that generates sweat through natural creation is Yang-heat Qi, not Yin-cold Qi. Observing that all things produce fluids when heat reaches its extreme clearly demonstrates this. Furthermore, medical principles state: Body heat indicates heat in the exterior; desire for water indicates heat in the interior. In Shanghan disease, cases where the body remains cool throughout without thirst, urine is not yellow, and the pulse is not rapid, have never existed. Although Zhang Zhongjing described indications for Sini Tang (Four Reversal Decoction), this applies when there is exterior heat with an harmonious interior, and cold-purgatives were mistakenly used too early. This caused the exterior heat to fail to enter the interior, resulting in persistent diarrhea due to interior cold, or spontaneous diarrhea due to exterior heat and interior cold. In such urgent cases, Sini Tang is used to warm the interior; once diarrhea stops and the interior harmonizes, efforts should then focus on resolving the exterior. Thus, after the Sini Tang indications, Zhang Zhongjing discusses using Chengqi Tang (Descending the Qi Decoction) and other cold purgatives to clear heat. Therefore, regarding sweating treatments for Shanghan, the classics explicitly discuss Heat, not Cold. The classics mention San yin syndromes as cases where pathogenic heat resides in the Zang organs and the interior; since Zang organs represent the interior and Yin, purgation to clear heat is indicated. According to the three chapters in *Suwen* (Basic Questions) discussing Shanghan and heat diseases, all are named "Heat," with no mention of "Cold." Further inference from the theories of meridians and vital qi in *Lingnu* (Spiritual Pivot) confirms that naming them "Heat Diseases" indeed implies they are not Cold diseases. *Suwen·Re Lun* (Treatise on Heat Diseases) states: The Yellow Emperor asked, "How should they be treated?" Qibo replied, "Treatment involves unblocking the meridians of the respective Zang organs, and the disease will decline day by day. If less than three days have passed, sweating can cure it; if more than three days have passed, purgation can cure it." This outlines the general principles of exterior and interior treatment. (Note: *Zhengli Shanghan Lun* [Correct Principles of Shanghan Lun] states: If the pulse is large, floating, and rapid, the disease is in the exterior, and sweating is appropriate; if the pulse is deep, fine, and rapid, the disease is in the interior, and purgation is appropriate.) From this, even if many days have passed, if exterior signs are present and the pulse is floating and rapid, sweating is still appropriate; even if few days have passed, if interior signs are present, purgation is still appropriate. This precisely follows the pulse and signs to determine whether to sweat or purge.