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Warm diseases in the four seasons are mostly similar to cold damage (Shanghan); however, while cold damage originates in the Foot-Taiyang channel (Foot-Taiyang Jing), it is now stated that warm diseases originate in the Hand-Taiyin channel (Hand-Taiyin Jing). Why does the Hand-Taiyin channel also govern external contraction? Why do the clinical manifestations of the Hand-Taiyin channel roughly resemble those of the Foot-Taiyang channel? There is a distinction between upper and lower for hand and foot channels, and a meaning of direct and reverse for yin and yang; how can they be confused! The *Suwen* (Plain Questions) · Pingren Qixiang Lun states: "The true qi of the zang organs is higher than the lung, which circulates Ying and Wei and yin and yang." In the *Shanghan Lun* (Treatise on Cold Damage), Ying and Wei are distinguished, and yin and yang are discussed, because at the initial stage of external contraction, one must necessarily proceed from Wei to Ying, and from Yang to Yin. The Foot-Taiyang channel is like the main gate of a house, governing the interior from the exterior, primarily managing Ying, Wei, yin, and yang; the Hand-Taiyin channel serves as the Huagai (Canopy, referring to the Lung as the highest organ), representing Heaven among the Three Powers, governing the lower from the upper, and also encompassing the interior from the exterior, similarly managing Ying, Wei, yin, and yang. Therefore, they are largely similar. Although largely similar, the details ultimately differ. What are the differences? For instance, the orifices of the Taiyang channel mainly govern excretion, whereas the orifices of the Taiyin channel govern both entry and exit; the orifices of the Taiyang channel open downwards, while those of the Taiyin channel open upwards, etc. Practitioners must seek differences within similarities, verify similarities within differences, and cross-reference sameness and difference, so that the true essence will naturally become apparent.

The dryness qi described in the previous three Jiao chapters all refer to syndromes where heat transformation injures fluids, treated with acrid-sweet slightly cool herbs (Metal overcomes Wood; when Wood is overcome, its son takes revenge for its mother, and Fire comes to restore balance). This did not cover cold transformation. Generally, the cold transformation of dryness qi represents the normal state of dryness, as stated in the *Suwen*: "What arrives via Yangming is clear and vigorous." The *Suwen* also states: "Dryness is urgent yet moist" (Earth is the mother of Metal, Water is the son of Metal). This treatise often categorizes such cases under the headings of latent damp-heat and cold-dampness, such as abdominal pain and vomiting. As the classics state: "When dryness qi prevails excessively, people suffer from frequent vomiting, heart and hypochondriac pain, and inability to turn their bodies." These are treated with bitter-warm methods, which is the correct method for treating dryness according to the *Neijing*. Previous scholars held the view that among the six qi, only dryness does not cause disease. This is likely because dryness is subsumed under cold (Wu's commentary on the *Suwen* states: Cold governs dryness and dampness, Summer-heat governs wind and fire, hence 'Cold and Summer-heat enter six'), and is close to cold. Thus, all dryness diseases were merely considered as cold, without recognizing them as dryness. Viewing the six qi collectively, all others govern life/growth, but dryness alone governs killing/destruction; could it not be a pathogenic factor? One would know this by carefully reading the *Suwen*. Furthermore, the previous three chapters were originally designed for warm diseases, yet they also include summer-heat warmth and damp-warmth. Special attention must be paid to the sections on latent summer-heat and damp-warmth, because in autumn, dampness resides internally while new cool dryness qi attacks externally. When dryness and dampness arrive simultaneously, it is most difficult to delineate clear boundaries. If the differentiation is slightly inaccurate, the disastrous consequences are incalculable. The classics state: "Incompetent physicians treat diseases; when dampness syndromes have not resolved, dryness syndromes arise again," which refers to this situation (Dampness may combine with heat or cold; Summer-heat may combine with wind or dryness; Dryness may undergo cold or heat transformation. First separate summer-heat, dampness, and dryness, then clearly differentiate cold and heat, and there will be a standard).