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The sequence of transmission in Shanghan (Cold Damage) disease typically proceeds from the Taiyang channel, then to Yangming, Shaoyang, Taiyin, Shaoyin, and finally Jueyin; this is the normal pattern. However, Wind-Cold pathogens may also directly invade the Yangming channel. Zhang Zhongjing stated: In Yangming Wind-strike, symptoms include bitter taste in the mouth, dry throat, abdominal fullness, slight wheezing, fever, aversion to cold, and a floating and tight pulse. Similarly, in Shaoyang Wind-strike, symptoms include hearing loss in both ears, red eyes, chest fullness with irritability. This applies not only to Yangming and Shaoyang but also to the Three Yin channels. For instance, when Shaoyin disease first occurs, the presence of fever and a deep pulse indicates that Shaoyin has initially been affected by Cold pathogens. In Taiyin Wind-strike, painful and uncomfortable limbs with a pulse that is faint at the Cun position, choppy at the Chi position, and long indicate that Taiyin has initially been affected by Wind pathogens. In Jueyin Wind-stroke, a slightly floating pulse suggests impending recovery, while a non-floating pulse indicates no recovery; this is the pulse manifestation when Jueyin is initially affected by Wind pathogens. These three scenarios differ from "Direct Invasion" (Zhi Zhong) of the Three Yin channels. Direct invasion implies pathology within the Zang organs, whereas here the pathology is within the Channels. Therefore, all Six Channels can independently contract Wind-Cold; it is not necessary for the pathogen to transmit exclusively from Taiyang. Even if transmitted from Taiyang, it does not necessarily follow a sequential order through the channels. Zhang Yuansu (Hanghai) discussed this in detail, so it will not be repeated here.

The notion that Shanghan transmits only to the Foot channels and not the Hand channels arises because Cold pathogens first attach to the skin. The Foot-Taiyang Bladder channel is located on the outermost layer, thus receiving the pathogen first. As the pathogen penetrates deeper, moving from skin into muscle, it affects the Foot-Yangming Stomach channel, which governs the muscle layer. Further penetration places the pathogen inside the body shell but outside the Zang-Fu organs, where the Foot-Shaoyang Gallbladder channel resides in the half-exterior half-interior region, thus being affected next. When the pathogen moves from exterior to interior, leaving the Yang channels to enter the Yin channels, the dynamics are governed by Taiyin as the opening, Jueyin as the closing, and Shaoyin as the pivot. Consequently, the pathogen enters Taiyin first, then Shaoyin, and finally Jueyin. Generally speaking, Yang governs the exterior and Yin governs the interior; the exterior corresponds to the Fu organs and the interior to the Zang organs. Thus, when the pathogen is in the exterior, the Foot-Yang channels are affected; when in the interior, the Foot-Yin channels are affected. Although the Hand-Yang channels also govern the exterior, the Hand-Taiyang Small Intestine, Hand-Shaoyang Sanjiao, and Hand-Yangming Large Intestine channels run from hand to head, occupying higher positions with shorter vessel paths, unlike the Foot channels which ascend from below to above and support the entire body. Although the Hand-Yin channels also govern the interior, the Hand-Taiyin Lung, Hand-Shaoyin Heart, and Hand-Jueyin Pericardium are located in the Upper Jiao, unlike the Liver, Spleen, and Kidney which reside firmly in the Yin positions. Therefore, although the Hand-Yang channels are Yang, their Qi is constrained relative to the exterior, making the Foot-Yang channels the sole governors of the Yang exterior; although the Hand-Yin Zang organs are Yin, their location is not purely Yin, making the Foot-Yin channels the sole governors of the Yin interior. Hence, why do Shanghan pathogens often affect the Foot channels rather than the Hand channels? The claim that Shanghan affects only people in the Northwest and not the Southeast is an arbitrary interpretation. It is true that pathogens may spread from Foot to Hand channels. As mentioned in the *Yu Ji* chapter, when Foot channels are excess and Hand channels are deficient, "Yuan Re" (stagnant heat) can occur. This aligns with Zhang Yuansu's (Jiegou) theory of Ren transmitting to Bing, and Bing transmitting to Ding. However, unless there are errors in sweating or purging therapies, or causes related to Seven Emotions and fatigue/overwork, how could the pathogen transmit to the Hand channels?