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The human body is divided by the navel: the upper part is Yang, the lower part is Yin; the face is Yang, the back is Yin; the left side is Yang, the right side is Yin; the exterior is Yang, the interior is Yin; the Fu organs (Six Intestines/Gallbladder/Bladder) are Yang, the Zang organs (Five Viscera) are Yin; Qi is Yang, Blood is Yin; movement is Yang, stillness is Yin; speaking is Yang, silence is Yin; being awake is Yang, sleeping is Yin; exhaling is Yang, inhaling is Yin; Hun (Ethereal Soul) is Yang, Po (Corporeal Soul) is Yin. The *Huangdi Neijing* states that the back is Yang, which is said in contrast to the abdomen being Yin; it does not mean the back is Yang and the face is Yin. This is because the abdomen is situated below, while the back is positioned above; thus, what is above is considered Yang, and what is below is considered Yin. Later generations did not understand this explanation and misinterpreted "abdomen" as "face," which was an error. Observing the hexagrams of the *I Ching*, Yang Qi peaks at Wu hour (noon), and Yin Qi peaks at Zi hour (midnight). The back corresponds to the North; the North belongs to Yin. Yin is still, Yang is active; since the back is immobile, it clearly belongs to Yin. Furthermore, among those who drown, female corpses always float on their backs, indicating that women have heavy Yin Qi; male corpses always lie prone, indicating that men have heavy Yang Qi. Does this not further verify that the back belongs to Yin and the face belongs to Yang?

Yang Qi is most abundant at Wu hour, and Yin Qi is most abundant at Zi hour; this is the meaning behind the face being Yang and the back being Yin. From the Fu hexagram to the Qian hexagram, rising to the left constitutes Yang; from the Gou hexagram to the Kun hexagram, descending to the right constitutes Yin; this is the meaning behind the left being Yang and the right being Yin. Yang primarily governs Qi, and Yin primarily governs Blood; Yang is large, and Yin is small. However, Zhu Danxi stated: "There is more Blood in the left half and more Qi in the right half, hence a person's right hand and foot are larger than the left." Why is this? The answer is: Left and Right Yin and Yang are mutually opposing and originally very balanced, with no excess or deficiency. Yet, when Yang Qi peaks at Wu hour, it remains hot until You hour; when Yin Qi peaks at Zi hour, it remains cold until Mao hour. Is this not evidence that even after reaching peak intensity, residual energy remains vigorous? Therefore, although the left belongs to Yang, Yin actually prevails there; although the right belongs to Yin, Yang actually dominates there. This is evident. So why doubt that there is more Blood in the left half-body and more Qi in the right half-body, and that the right hand and foot are larger than the left? (*Yi Guan* states: "At Winter Solstice, one Yang Qi arises, so warmth should gradually increase; yet during the Great Cold of the twelfth lunar month, ice and snow become even more severe. This is because Yang Qi hides below, forcing Yin Qi upward, causing well water to steam while solid ice forms. At Summer Solstice, one Yin Qi arises, so coolness should gradually increase; yet during the Sanfu extreme heat, scorching heat becomes intense. This is because Yin Qi is abundant below, forcing Yang Qi upward, causing well water to be cold while thunder and lightning combine. These can corroborate each other.") I once suffered from eye heat; my right eye would always be affected first and severely, while the left eye was affected later and mildly. Thus, I knew the left belongs to Blood, and Fire pathogenic factors do not easily injure it. (This is like dry wood burning first and wet wood burning later.) I also once suffered from leg edema; my left foot swelled first and severely, while the right foot swelled later and mildly. Thus, I knew the right belongs to Qi, and Dampness pathogenic factors are relatively easy to transform. I once covered my right eye and used my left eye to view the moon, but it was not as clear as with my right eye, because the right eye has abundant Fire Qi and can illuminate distant objects. I covered my left eye and used my right eye to read books, but it was not as bright as with my left eye, because the left eye has abundant Water Qi and can inspect near objects. However, these cases show that each has its strengths. If comparing strength, the right eye must be stronger than the left. I once used a blowpipe to shoot at birds; aiming at a bird through the pipe seemed like pulling a tight rope, leading me to believe I would hit it, but I missed. This showed that the two eyes have different levels of power. Then, closing my right eye and using only my left eye to aim at the bird as if pulling a tight rope, and then opening both eyes to look together, the situation changed drastically; this indicated that the left eye was overpowered by the right eye. Conversely, closing my left eye and using only my right eye to aim at the bird as if pulling a tight rope, and then opening both eyes to look together, the image remained consistent; this indicated that the right eye was not overpowered by the left eye. Does this not prove that the right eye is strong and the left eye is weak? Therefore, I do not believe the statement in the Classics that the right ear and eye are less acute than the left.

The Fu organs are Yang, and the Zang organs are Yin. In finer detail, the Heart and Lung are located in the upper part and belong to Yang; the Liver and Kidney are located in the lower part and belong to Yin. Furthermore, comparing the Heart and Lung, the Lung belongs to Metal and is Yin, while the Heart belongs to Fire and is Yang. Comparing the Liver and Kidney, the Kidney belongs to Water and is Yin, while the Liver belongs to Wood and is Yang. Comparing the Lung and Liver, the Lung governs descending and is Yin, while the Liver governs ascending and is Yang. Moreover, the Kidney contains both Water and Fire; Kidney Fire is Yang, and Kidney Water is Yin. These distinctions are complex and variable, without fixed names. Medical texts often speak of Yin and Yang without specifically pointing out which category they refer to, which is very vague and should be clarified in detail. (For example, when stating "Yin Deficiency," it is unclear whether it refers to Blood Deficiency, Lung Deficiency, Kidney Water Deficiency, or Kidney Fire Deficiency. Why not specify explicitly as Blood Deficiency, Lung Deficiency, Kidney Water Deficiency, or Kidney Fire Deficiency for clarity? These have been analyzed one by one in this collection.)