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Shortness of breath and deficiency. The Ren Mai (Conception Vessel) and Du Mai (Governing Vessel) run along the midline of the abdomen and back, having distinctions between blood and qi; thus, their afflictions manifest in this manner. Stiffness of the spine with internal knotting indicates differences between pathology in the Yang meridians and Yin meridians. The Chong Mai (Penetrating Vessel) is the sea of the twelve regular meridians; when pathogenic factors invade it, rebellious qi becomes particularly severe. The Dai Mai (Girdle Vessel) is located at the costal margin and horizontally binds all meridians; therefore, when diseased, it causes flaccidity and a sensation of looseness in the waist region. Its meridian connects to the Foot-Shaoyang Gallbladder Meridian; thus, when the Yang within Yin loses its guardianship, there is a shortage of qi, resembling the feeling of sitting in water. Generally, the pathological manifestations of these eight extraordinary vessels are scattered across various chapters of the *Neijing* (*Inner Canon*) without unified classification. Therefore, Yue Ren (Qin Yueren/Bian Que) raised questions collectively to elucidate them. From the Twenty-Seventh Difficulty through these three sections, the discussion covers the extraordinary vessels comprehensively and thoroughly. (The Thirtieth Difficulty is identical to the old text.)

Question: Does the movement of Ying Qi (Nutritive Qi) always accompany Wei Qi (Defensive Qi)?
Answer: The classics state that humans derive Sheng Qi (Vital Qi) from grain. When grain enters the stomach, it is transmitted to the Zang organs and Fu organs. All Zang and Fu organs receive this Qi (the essence of water and grain). The clear portion (Yang) becomes Ying Qi (blood component circulating within vessels), while the turbid portion (Yin) becomes Wei Qi (defensive qi circulating outside vessels). Ying Qi circulates within the vessels, and Wei Qi circulates outside the vessels. Ying Qi flows continuously, completing fifty cycles before reconvening at the Cun Kou (Cun position) of the Hand-Taiyin Lung Meridian. Yin and Yang meridians interconnect like an endless circle; thus, we know that Ying Qi and Wei Qi move together.

Commentary: This dialogue is based on the text of the *Lingshu* chapter "Ying Wei Sheng Hui" to clarify the principle that Ying and Wei Qi do not separate. However, the meaning of Wei Qi varies. In the chapters "Wei Qi" and "Wei Qi Xing," it refers to Wei Qi that moves independently; in the chapter "Ying Wei Sheng Hui," it refers to Wei Qi that moves concurrently. All pathogenic factors located outside the vessels belong to this category of Wei Qi. Hence, it is said that "Ying Qi moves within the vessels, and Wei Qi moves outside the vessels," each having its specific meridian distribution. Otherwise, how could one explain statements such as "Wind-stroke is a disease of the Taiyang Wei aspect, treated with Guizhi Tang (Cinnamon Twig Decoction); Cold damage is a disease of the Taiyang Ying aspect, treated with Mahuang Tang (Ephedra Decoction)"? As for the floating and dispersed Wei Qi, it travels through the Yang meridians during the day and the Yin meridians at night. The main point of this Difficulty focuses specifically on the variations of two diseases within one vessel to illustrate the accompanying nature of Ying and Wei Qi. The two types of diseases mentioned in the previous section, namely "Shi Dong" (Is-Moving) and "Suo Sheng" (So-Produced), can also be deduced from this reasoning. Previous annotations regarding the clarity and turbidity of Ying and Wei Qi are already quite detailed; their theory is essentially based on the principle of mutual root between Blood and Qi.