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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.