夫《内经》之所谓未满三日者，可汗而已；其满三日者，可泄而已。盖谓热病而言也，故篇名《热论》。
热病者，寒邪在于表之三阳，寒已化热，故可汗而已；在不从汗解，则热邪已入于里阴，故可下而已。若寒
邪在表而不能化热，及表阳虚脱者，太阳经有四逆汤之寒证，寒邪直中于里阴，感君、相二火之热化者，
少阴经有急下之火证，厥阴经有便脓血之热证。此皆从人身中之气化也。故邪在三阳曰阳证，能化热曰热
证，不能化热曰寒证；在三阴曰阴证，病阴寒曰寒证，得火化曰热证。又不可以病在阳而定为热病，在阴而必为寒也。
阳剧似阴者，谓厥深热亦深也。《厥阴篇》曰∶伤寒一二日至四五日，厥者必发热，前热者后必厥，
厥深者热亦深，厥微者热亦微。所谓伤寒一二日者，谓一日病在太阳，二日病在阳明，寒已化热，至四五
日而后传入于里阴，故曰必发热。言伤寒一二日必前发热，至四五日而后厥也。深重微轻也，盖热邪深入，
而里气不能外达，故热深而厥亦深也。如此者，当知一二日之间，邪在表阳，曾发热，而后传入于里
阴也。（一日必见太阳之头痛。）所谓阴剧似阳者，乃寒邪直中于里，阴盛而格阳于外，是以喜寒恶热，
揭去衣被，欲卧凉处。如此者，其人必躁，其脉沉细，或虚浮而
乱，其舌必滑，其面色必清；或赤浮于外，其肤必凉，或发热者，必先凉而后热，以手按之，始觉壮热，久
之反凉。此二者，先详审其因证，而假象自露矣。若犹恐阳剧似阴，阴剧似阳，先以此摇惑于心中，则反有差误。
《内经》所说的“未满三日者，可汗而已；其满三日者，可泄而已”，是专指热病而言的，所以该篇名为《热论》。
所谓热病，是因为寒邪在体表的三阳经（太阳、阳明、少阳），寒邪已经转化为热邪，所以可以通过发汗的方法治愈；如果未能通过汗法解除，那么热邪就已经传入体内的阴经，所以可以通过泻下的方法治疗。如果寒邪在体表但不能转化为热邪，以及表阳虚脱的情况，太阳经会出现四逆汤证（一种寒性证候）；寒邪直接中伤于体内的阴经，感受君火与相火的火热转化之气，少阴经会出现急需泻下的火热证候，厥阴经会出现大便带脓血的火热证候。这些情况都是根据人体内部的气化功能而变化的。因此，邪气在三阳经称为阳证，能够化热的称为热证，不能化热的称为寒证；在三阴经称为阴证，表现为阴寒性质的称为寒证，得到火化作用的称为热证。又不能因为病位在阳部就一定定为热病，在阴部就一定是寒证。
阳气极盛而似阴证的情况，是指厥逆越深重，内热也越深重。《厥阴篇》说：“伤寒一二日至四五日，出现厥逆的必然伴有发热，先前发热的后来必然出现厥逆，厥逆深重的内热也深重，厥逆轻微的内热也轻微。”所谓伤寒一二日至四五日，是指第一天病在太阳经，第二天病在阳明经，寒邪已经化热，到了第四五日才传入体内的阴经，所以说必然发热。意思是伤寒一二日时必然先有发热，到了第四五日才出现厥逆。“深”代表严重，“微”代表轻微。这是因为热邪深入体内，而里气不能向外通达，所以内热越深重，四肢厥逆也越深重。遇到这种情况，应当知道在一二日之间，邪气在体表的阳经，曾经有过发热，而后才传入体内的阴经。（第一天必定会出现太阳经的头痛症状。）所谓阴寒极盛而似阳证的情况，乃是寒邪直接中伤于体内，阴寒过盛将阳气格拒于外，所以患者喜欢寒冷厌恶热气，掀开衣服被子，想要睡在凉快的地方。遇到这种情况，其人必定烦躁，脉象沉细，或者虚浮且紊乱，舌苔必定滑润，面色必定清冷；或者红色浮现在表面，皮肤必定凉爽，或者有发热的，必定先感到凉然后才发热，用手按压时，才开始觉得壮热，时间久了反而变凉。这两种情况，只要详细审察病因和证候，假象自然就会暴露出来。如果还担心阳盛似阴、阴盛似阳的情况，预先在心中产生动摇迷惑，反而会导致诊断错误。
The statement in the *Neijing* (Inner Canon) that "if less than three days have passed, sweating may suffice; if three days or more have passed, purgation may suffice" refers specifically to heat diseases, which is why the chapter is titled "Discussion on Heat" (*Re Lun*).
Heat disease occurs when cold pathogenic factors are located in the exterior San Yang meridians (Taiyang, Yangming, Shaoyang), and the cold has transformed into heat; thus, it can be resolved by inducing sweating. If it does not resolve through sweating, the heat pathogen has entered the interior Yin organs/meridians, and thus can be treated by purgation. However, if the cold pathogen remains in the exterior without transforming into heat, or in cases of collapse of exterior Yang, the Taiyang meridian presents a cold syndrome treatable with Sini Tang (Four Reversal Decoction). When cold pathogenic factors directly strike the interior Yin, influenced by the thermal transformation of Ministerial Fire (Xiang Huo) and Sovereign Fire (Jun Huo), the Shaoyin meridian presents a fire syndrome requiring urgent purgation, and the Jueyin meridian presents a heat syndrome manifesting as pus and blood in the stool. These variations depend entirely on the Qi transformation within the human body. Therefore, pathogens in the San Yang meridians are called Yang syndromes; those capable of transforming into heat are called heat syndromes, while those unable to transform into heat are called cold syndromes. Pathogens in the San Yin meridians are called Yin syndromes; those characterized by Yin-cold are called cold syndromes, while those undergoing fire transformation are called heat syndromes. One cannot definitively classify a disease as a heat disease simply because it is located in the Yang, nor assume it must be a cold disease because it is located in the Yin.
A condition where Yang excess mimics Yin is described as "the deeper the Jue (cold extremities), the deeper the heat." The *Jueyin Chapter* states: "In cold damage, from one to two days up to four or five days, if Jue occurs, there must be fever; if there was fever previously, Jue will follow later. The deeper the Jue, the deeper the heat; the milder the Jue, the milder the heat." The phrase "one to two days up to four or five days" means that on the first day, the pathology is in the Taiyang meridian, and on the second day, it is in the Yangming meridian, where the cold has transformed into heat. By the fourth or fifth day, it transmits to the interior Yin, hence it is said that fever must occur. This implies that in the first two days of cold damage, fever necessarily precedes, and by the fourth or fifth day, Jue follows. "Deep" indicates severity, and "mild" indicates lightness. This is because the heat pathogen has penetrated deeply, and the interior Qi cannot reach the exterior; thus, the deeper the internal heat, the deeper the Jue. In such cases, one should understand that during the first two days, the pathogen was in the exterior Yang and had previously presented with fever before transmitting to the interior Yin. (On the first day, headache characteristic of the Taiyang meridian must be present.) Conversely, a condition where Yin excess mimics Yang occurs when cold pathogenic factors directly strike the interior, causing Yin-cold to become excessive and repel Yang to the exterior. Consequently, the patient prefers cold and dislikes heat, removes clothing and bedding, and desires to lie in cool places. In such cases, the person is likely irritable, the pulse is deep and fine, or deficient, floating, and chaotic; the tongue coating is slippery; the facial complexion is pale/clear; or redness floats on the surface while the skin feels cool. If there is fever, it typically begins with a sensation of cold followed by heat; upon palpation, intense heat is felt initially, but after a while, it feels cool again. For both these scenarios, if the etiology and symptoms are carefully examined, the false manifestations will naturally be revealed. If one harbors doubts about Yang mimicking Yin or Yin mimicking Yang beforehand, causing confusion in the mind, it will lead to diagnostic errors.