伤寒传变，不可以日数为拘，亦不可以次序为拘。如《内经》言一日太阳，二日阳明，三日少
阳之类，盖言传经之大概，非谓凡患伤寒者，必皆如此也。盖寒邪中人，本无定体，观陶节庵曰∶
风寒之国中人也无常，或入于阴，或入于阳，非但始太阳、终厥阴也。或自太阳始，日传一经，六
日至厥阴，邪气衰不传而愈者，亦有不罢再传者，或有间经而傅者，或有传至二三经而止者，或有
始终只在一经者，或有越经而传者，或有自少阳、阳明而入者，或有初入太阳，不作郁热，便入少
阴而成真阴证者。所以凡治伤寒，不可拘泥，但见太阳证，便治太阳，但见少阴证，便治少阴，但
见少阳、阳明证，便治少阳、阳明，此活法也。又有合病、并病之证。曰合病者，两经或三经齐病
，不传者为合病。并病者，一经先病未尽，又过一经者，为并病。所以有太阳阳明合病，有太阳少
阳合病，有阳明少阳合病，有三阳合病。三阳若与三阴合病，即是两感，所以三阴无合并例也。即
仲景亦曰∶日数虽多，但见表证而脉浮紧者，犹宜汗之；日数虽少，但见里证而脉沉实者，犹宜下
之，诚为不易之论。故不可执定日数，谓一二日宜发表，三四日宜和解，五六日即宜下，若或不知
通变，因致误人者多
矣。故必真知其表邪未解，则当汗之，真知其胃邪已实，方可下之，真知其阴寒邪胜，自宜温之，
真知其邪实正虚，客主不敌，必须补之。但能因机察变，原始要终而纤悉无遗者，方是活人高手。
仲景曰∶伤寒一日，太阳受之，脉若静者为不传；颇欲吐，若躁烦，脉数急者，为传也。伤寒
六七日，无大热，其人躁烦者，此为阳去入阴故也。伤寒二三日，阳明、少阳证不见者，为不传
也。伤寒三日，三阳为尽，三阴当受邪，其人反能食而不呕，此为三阴不受邪也。
伤寒病的传变规律，不能单纯以发病日数来拘泥判定，也不能机械地按照固定的次序来判断。例如《黄帝内经》中提到的“第一天太阳经，第二天阳明经，第三天少阳经”等说法，大概只是阐述邪气传入经络的一般情况，并非指凡是患伤寒病的人，病情发展必定完全如此。
寒邪侵袭人体，本来就没有固定的模式。观察陶节庵（陶华）的观点：在风寒之地，邪气侵入人体没有常规，有时进入阴经，有时进入阳经，并不一定是从太阳经开始，最终传到厥阴经。有的从太阳经开始，每天传变一经，六天传到厥阴经，此时邪气衰退不再传变而痊愈；也有邪气未罢继续传变的；有跳过某一经而传变的；有传至第二、第三经就停止的；有始终只停留在一经的；有跨越经络传变的；有直接从少阳经、阳明经开始的；也有初入太阳经，没有形成郁热，就直接传入少阴经而成真阴证（少阴寒化证）的。
所以，凡治疗伤寒病，不可拘泥固执，只要见到太阳经证候，就治疗太阳经；只要见到少阴经证候，就治疗少阴经；只要见到少阳经、阳明经证候，就治疗少阳经、阳明经，这才是灵活的方法。
又有合病、并病的证候。所谓合病，是指两经或三经同时发病，不经过传变过程的，称为合病。所谓并病，是指一经的病邪尚未痊愈，又波及另一经的，称为并病。因此有太阳经与阳明经合病，有太阳经与少阳经合病，有阳明经与少阳经合病，有三阳经合病。如果三阳经与三阴经合病，就是两感病（表里同病），所以三阴经没有合并的说法。
即张仲景也说：虽然发病日数较多，但只要见到表证且脉象浮紧的，仍然适宜用发汗法；虽然发病日数较少，但只要见到里证且脉象沉实的，仍然适宜用泻下法，这确实是不可改变的定论。所以不能固执地认定一二天适宜发表，三四天适宜和解，五六天就适宜泻下。如果不知道通权达变，因而导致误治害人的情况很多。
因此，必须真正确认表邪未解，才应当用发汗法；真正确认胃腑邪气已实，才可以采用泻下法；真正确认阴寒邪气盛，自然适宜用温补法；真正确认邪气盛而正气虚，客邪为主而主气不敌，必须采用补益法。只要能根据机宜观察变化，探究本源并推究结果，做到细致无遗漏的，才是救活病人的高手。
张仲景说：伤寒第一天，太阳经受邪，如果脉象平静，说明没有传变；如果病人频频想吐，或者烦躁不安，脉象数而急迫，说明已经传变。伤寒第六七天，身体没有大热，但病人烦躁不安，这是阳气去而转入阴经的缘故。伤寒二三天，如果没有出现阳明经和少阳经的证候，说明没有传变。伤寒三天，三阳经的病程已尽，三阴经应当受邪，如果病人反而能进食且不呕吐，这说明三阴经没有受邪。
The transmission and transformation of cold damage (Shanghan) should not be rigidly constrained by the number of days, nor mechanically bound by a fixed sequence. For instance, statements in the *Huangdi Neijing* (Yellow Emperor's Inner Canon), such as "Day 1: Taiyang; Day 2: Yangming; Day 3: Shaoyang," generally describe the broad patterns of meridian transmission, rather than implying that every case of cold damage follows this exact progression.
Cold pathogenic factors invading the human body have no fixed pattern. As Tao Jie'an (Tao Hua) observed: In regions with wind and cold, pathogenic invasion is irregular; it may enter the Yin meridians or the Yang meridians, and does not necessarily begin at Taiyang and end at Jueyin. Some cases start at Taiyang, transmitting one meridian per day, reaching Jueyin on the sixth day, where the pathogen weakens, stops transmitting, and the patient recovers. Other cases involve continuous transmission without cessation, skipping meridians during transmission, stopping after affecting two or three meridians, remaining confined to a single meridian throughout, jumping across meridians, starting directly from Shaoyang or Yangming, or entering Shaoyin directly from an initial Taiyang stage without forming stagnant heat, resulting in True Yin Syndrome (Shaoyin Cold Transformation).
Therefore, in treating cold damage, one must not be dogmatic. If Taiyang syndrome is present, treat Taiyang; if Shaoyin syndrome is present, treat Shaoyin; if Shaoyang and Yangming syndromes are present, treat Shaoyang and Yangming. This constitutes flexible treatment principles.
There are also conditions known as He Bing (Combined Disease) and Bing Bing (Concurrent Disease). He Bing refers to two or three meridians being affected simultaneously without prior transmission. Bing Bing refers to a condition where the pathogen in one meridian has not fully resolved before spreading to another meridian. Thus, there are Taiyang-Yangming Combined Disease, Taiyang-Shaoyang Combined Disease, Yangming-Shaoyang Combined Disease, and Three Yang Combined Disease. If Three Yang combines with Three Yin, it is termed Liang Gan (Simultaneous Exterior and Interior Infection); therefore, there is no concept of "combined disease" among the Three Yin meridians alone.
Zhang Zhongjing also stated: Even if many days have passed, if exterior signs are present and the pulse is floating and tight, sweating therapy is still appropriate. Conversely, even if few days have passed, if interior signs are present and the pulse is deep and excess, purgative therapy is still appropriate. This is indeed an unchangeable principle. One must not rigidly adhere to the notion that days 1-2 require exterior-releasing methods, days 3-4 require harmonizing methods, and days 5-6 require purgative methods. Failure to adapt flexibly often leads to misdiagnosis and harm.
Thus, one must truly confirm that exterior pathogens remain unresolved before employing sweating therapy; truly confirm that stomach pathogens are excess before employing purgative therapy; truly confirm that Yin-cold pathogens are predominant before employing warming therapy; and truly confirm that pathogen excess and righteous qi deficiency exist, where the guest pathogen overcomes the host, necessitating tonification therapy. Only those who can observe changes according to circumstances, trace origins to conclusions, and leave no detail overlooked are true masters of saving lives.
Zhang Zhongjing said: On the first day of cold damage, the Taiyang meridian receives the pathogen. If the pulse remains calm, transmission has not occurred. If the patient frequently desires to vomit, or exhibits restlessness and irritability with a rapid and urgent pulse, transmission has occurred. On the sixth or seventh day of cold damage, if there is no significant fever but the patient is restless, this indicates the departure of Yang and entry into Yin. If, on the second or third day, no Yangming or Shaoyang symptoms appear, transmission has not occurred. By the third day, the course of the Three Yang meridians is complete, and the Three Yin meridians should receive the pathogen. However, if the patient can eat and does not vomit, this indicates that the Three Yin meridians have not received the pathogen.