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The transmission of Shanghan (Cold Damage) involves pathogenic heat gradually penetrating deeper, with the Six Channels (Six Meridians) affected in sequence. Once the transmission through all Six Channels is completed, there is no mechanism for it to restart from Taiyang and transmit through again. To understand the beginning of this transmission, one must first distinguish the hierarchy of the Six Channels in the human body. Foot-Taiyang belongs to the "Three Yang" and is located most externally; Yangming belongs to the "Two Yang" and is internal to Taiyang; Shaoyang belongs to the "One Yang" and is internal to Yangming. These three Yang channels belong to the Exterior level, and their numerical order (3-2-1) reflects a counting from interior to exterior layers, though anatomically Taiyang is outermost. Thus, the sequence is as follows: Shanghan moves from the exterior to the interior, with pathogenic qi deepening gradually. By the sixth or seventh day, it reaches Jueyin. This describes the normal pattern. However, if variations occur, one cannot rigidly adhere to this sequence or specific day counts. When the pathogen reaches Jueyin, the transmission process is complete, and it will not continue further.

Cheng Wuji stated: "On the sixth day, transmission reaches Jueyin, completing the cycle. On the seventh day, recovery should occur. If not recovered by the seventh day, it is called 'secondary transmission' (Zai Chuan), meaning it transmits again from Taiyang to Jueyin. This completion is termed 'transmission exhausted.' Recovery should occur on the thirteenth day. If not recovered by the thirteenth day, it is called 'passing the channel' (Guo Jing), implying passing through the Taiyang channel again and transmitting sequentially." This view is erroneous.

Ma Zhonghua argued: "Moving from Taiyang to Jueyin is like entering a house from the gate, then to the hall, and finally to the inner room. For Jueyin to transmit back to Taiyang, it would have to bypass Shaoyin, Taiyin, Shaoyang, and Yangming. How could it suddenly jump out to transmit to Taiyang?" This refutation of 'secondary transmission' is indeed a definitive judgment for the ages. Unfortunately, his explanation of 'pathogenic decline on the seventh day' remains unclear, causing confusion among later practitioners regarding channel transmission.

So, is it true that pathogenic qi never exits from the interior to the exterior? In the Taiyang Chapter, it is stated: "For self-resolution, vexation (Fan) must precede sweating, which leads to resolution. How do we know this? Because the pulse is floating, indicating that sweating and resolution are imminent." This uses the floating pulse to identify that pathogenic qi has returned to the exterior, signaling a trend toward health, requiring no further herbal decoctions. Pathogens dispersing from the exterior have nowhere else to transmit once dispersed. One must understand that interior pathogens, if they do not exit, remain static; if they exit, they seek resolution, not transmission.

Some ask: "The Taiyang Chapter states: 'Taiyang disease with headache resolves spontaneously after seven days because the channel's course is completed.' If it is about to enter the next stage ('Zuo Zai Jing'), needling the Foot-Yangming channel prevents transmission and ensures cure. Does this not imply that from day 1 to 6, the Three Yang channels are transmitted through, and by day 7, recovery is expected? If not cured, does the Taiyang pathogen transmit again to Yangming?"

The response is: "Shanghan begins in Taiyang and proceeds sequentially until Jueyin, marking the completion of transmission. Any channel disease resolving within seven days indicates the completion of that specific channel's cycle. Headache in Taiyang resolving on day 7 signifies the completion of the Taiyang channel's course. The pathogen's journey starts and ends within Taiyang alone, accounting for the seven-day recovery period. The Taiyang Chapter states: 'Diseases originating in Yang resolve in seven days because seven is the number of Yang.' If symptoms persist beyond seven days, intending to exceed the Taiyang channel, one should needle the Foot-Yangming channel to intercept and prevent transmission to Yangming. Examining the phrase 'moving through the channel,' without using 'transmission exhausted' (referring to all six channels), Zhang Zhongjing’s intent becomes clear. Cheng Wuji mistakenly interpreted 'completing its own channel' as 'transmitting through all six channels,' suggesting Jueyin transmits to Taiyang, then Taiyang to Yangming. If this were true, one should needle Taiyang before Jueyin transmits to it, rather than waiting until transmission to Yangming is anticipated to needle Yangming.

Another query: "The Huoluan Chapter mentions recovery on the thirteenth day due to 'channel exhaustion.' Does this refer to the transmission of Three Yin and Three Yang, followed by another six days of transmission, totaling thirteen days? The Taiyang Chapter also says: 'Shanghan unresolved for thirteen days, with delirium after passing the channel, is due to heat and requires purgative decoctions.' Does this mean twelve days of secondary transmission exhausted, and non-recovery on day thirteen is 'passing the channel'? Similar to the concept of Taiyang completing its course? Inferring from Taiyang (day 1 to 7 completes Taiyang), other channels follow suit. Yangming disease (day 2 to 8) resolves as Yangming's course is completed. Shaoyang disease (day 3 to 9) resolves as Shaoyang's course is completed. Then, moving to the Three Yin channels around days 4-5, reaching day 12 resolves as Jueyin's course is completed. Day 13 is when vital qi fully recovers and spirit clarifies; thus, if unresolved past day 13 with sunken pulses at Cun and Chi, it is critical. 'Unresolved after thirteen days, delirium after passing the channel' means failing to resolve at the expected time causes the pathogen to exceed the channel and enter the interior, creating interior excess with heat binding internally, requiring purgatives. This is a general term for 'exceeding the channel,' not specific to any single channel. There is no principle stating 'secondary transmission exhausted is called passing the channel.'

Examining 'Guo Jing' (Passing/Exceeding the Channel): Some refer to exceeding Taiyang to form interior syndromes; some specify Taiyang; others use it generally. The Yangming Chapter states: 'Sweating and delirium indicate dry feces in the stomach due to wind. Purging is only appropriate after passing the channel.' This means if dry feces cause delirium and wind-pathogen causes sweating, purging is permissible only after the Taiyang channel phase has passed, exterior signs are absent, and the pathogen is bound in the interior. This refers to becoming an interior syndrome after exceeding Taiyang. If Cheng’s view (13 days = secondary transmission exhausted = Guo Jing) were correct, one would wait until day 13 to purge dry feces. However, the note says 'must pass Taiyang, no exterior signs, then purge,' contradicting the 'secondary transmission' theory.

The Taiyang Chapter states: 'After more than ten days of Taiyang disease, following two or three purgations, if four to five days later Shaoyang symptoms persist, administer Xiao Chaihu Tang first.' This implies Taiyang exterior signs are gone, but interior signs are insufficient for direct purgation. After purgations, Shaoyang symptoms emerge, requiring Xiao Chaihu Tang. This specifically discusses exceeding Taiyang.

The Huoluan Chapter states: 'After dysentery, hard stool with appetite indicates recovery. Inability to eat suggests transmission to the next channel. Appetite returning after passing a channel indicates recovery in one day; otherwise, it is not Yangming.' This follows the previous text on fluid loss causing hard stool. Hard stool with appetite indicates harmonious Yangming Stomach Qi. Inability to eat suggests transmission to the subsequent channel. Slight appetite here is due to sudden heat, not Yangming harmony. This is a general use of 'passing the channel.' Where is the idea of 'secondary transmission exhausted equals passing the channel'? Moreover, pathogen transmission through Six Channels logically allows only one cycle, not three. Zhu’s commentary elucidates profound principles but falls short on transmission, leading to forced interpretations. *Yiyong Zuyao* inherits Cheng’s errors, annotating 'unresolved after passing the channel' by claiming Zhang Zhongjing never said 'thirteen days unresolved is passing the channel,' thereby elevating Cheng’s notes to classic status. His 'Six Channel Transmission Theory' claims 'unresolved after passing the channel is a damaged disease (Huai Bing).' Zhang Zhongjing defined 'Huai Bing' as damage caused by improper treatment. *Yiyong Zuyao*’s view is error upon error. Tao Shangwen claimed: 'Shanghan unresolvable after sweating and passing the channel, with persistent symptoms, is also Warm Disease.' This is equally incomprehensible.