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In the treatment of Cold Damage (Shanghan) disease, nothing is more primary than distinguishing between Exterior (Biao) and Interior (Li) patterns; in treating Exterior and Interior patterns, nothing is more primary than distinguishing between Sweating (Han) and Purging (Xia) methods. A single error in sweating or purging can lead to hundreds of complications; therefore, predecessors discussing the treatment of Cold Damage stated that "Sweating herbs should be used early, and Purging herbs should be used late." Although these two phrases serve as a general principle, they are also crucial therapeutic rules.

The phrase "should be used early" refers to the fact that when Wind-Cold pathogens enter from the exterior, one should promptly release the Exterior pathogen. This aligns with Zhang Zhongjing's saying: "Once the disease is perceived, even for an instant, it should be treated early, regardless of morning or night." The phrase "should be used late" refers to the principle that when Wind-Cold pathogens have transmitted into the Interior, purging must only be performed when there is excess heat in the Yang Ming Fu organs (Stomach and Intestines). This aligns with Zhang Zhongjing's warning: "Purging too early may lead to Pi Qi (Glomus/Epigastric fullness) or Jie Xiong (Chest Binding)." Here, "early and late" discuss the principles of therapeutic timing, not specific clock hours.

However, the book *Ci Shi Nan Zhi* (Difficulties of Certain Matters) argues that this "early" does not mean preemptive early, but rather the "morning" of the day, suggesting that sweating should occur before noon during the Yang phase; and this "late" does not mean waiting for a long time, but suggests that purging should occur after the Si hour (9-11 AM) during the Yin phase. Interpreting the characters "late" and "early" as referring to the sequence of days causes great confusion among people and must be urgently corrected.

The transmission of the Six Channels (Liu Jing) in Cold Damage proceeds from the Exterior to the Interior. The Three Yang channels belong to the Exterior, and the Three Yin channels belong to the Interior, progressing from shallow to deep. Once the Six Channels have been fully transmitted through, there is no logical possibility of further transmission outward. Cheng Wuji claimed that after six days, the transmission through the Jue Yin channel is complete, and healing should occur on the seventh day; if not healed by the seventh day, it transmits again starting from the Tai Yang channel, repeating until reaching Jue Yin; if not healed by the thirteenth day, it is termed "Guo Jing Huai Bing" (Disease beyond the period with deterioration). These annotations are extremely erroneous. Ma Yuantai refuted this, stating that transmission from Tai Yang to Jue Yin is like entering a house, ascending to the hall, and then entering the inner room. Tai Yang is the First Yang, located furthest outward; Yang Ming is the Second Yang, inside Tai Yang; Shao Yang is the Third Yang, inside Yang Ming. These Three Yang channels are at the Exterior. Tai Yin is the First Yin, inside Shao Yang; Shao Yin is the Second Yin, inside Tai Yin; Jue Yin is the Third Yin, inside Shao Yin. These Three Yin channels are at the Interior. Thus, on the first day, the disease begins in Tai Yang; on the second day, it transmits to Yang Ming; on the third day, to Shao Yang; on the fourth day, to Tai Yin; on the fifth day, to Shao Yin; and on the sixth day, to Jue Yin. The canonical text's discussion of sequential transmission merely outlines the general trend. The statement about "transmitting again if not healed by the seventh day" implies that within seven days, the course of transmission was incomplete, and the pathogen remained solely in the Tai Yang channel. As Zhang Zhongjing stated: "Tai Yang disease with headache heals spontaneously after seven days because the course of the channel has been completed." If one wishes for it to transmit to another channel, needling the Foot Yang Ming channel can prevent transmission and result in cure. This demonstrates that Tai Yang can persist for more than seven days; similarly, Yang Ming and Shao Yang may also linger beyond their periods without resolving. Therefore, needling the Earth element of Yang Ming (Spleen/Stomach) prevents transmission, indicating that the course of transmission was incomplete, not that the transmission cycle had finished. If one claims that after the Six Channels are fully transmitted, the pathogen exits from Jue Yin and re-transmits to Tai Yang, it would have to pass through barriers of Two Yin, Three Yin, One Yang, and Two Yang. How could there be a logic where the pathogen enters from outside to inside, and then directly jumps out to the exterior? When Wind-Cold pathogens invade the Zang-Fu organs, how could they, having reached the depth of the Two Yin channels, return from the skin and hair to invade Tai Yang again to cause harm? Cheng Wuji's error represents a profound misunderstanding throughout history, which I shall now clarify.