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The Thirty-Third Difficulty states: "The liver is green and symbolizes Wood; the lung is white and symbolizes Metal. The liver sinks in water, while Wood floats in water; the lung floats in water, while Metal sinks in water. What is the meaning of this?" The response uses concepts such as the Five Tones (Wuyin), Gang-Rou (Hardness and Softness), and Xi-Shou (Absorption and Reception) to explain this. This serves to inspire later learners to recognize the profound mysteries of the creation and transformation of the Five Elements (Wuxing). However, commentators have further invoked terms like Changsheng (Long Life), Linguan (Approaching Office), and Diwang (Imperial Prosperity), without thoroughly investigating the theory based on the specific nature of the Liver and Lung. This seems overly profound and abstruse. All things possess the attributes of the Five Elements; if we follow the commentators' explanation, the Heart, Spleen, and Kidney would also sink in water. How should this be interpreted? In my humble opinion, it is better to explain it plainly, which will naturally be clear and accessible, and can also help develop the learner's understanding of the principle of Yin-Yang mutual interaction. Although not explicitly stated, the rationale is implied therein.

Although the Lung belongs to Metal, its position is above the diaphragm, where Yang Qi circulates more abundantly. Its meridian is the Hand-Taiyin (Lung Meridian), which governs Qi. From the perspective of form/substance (Ti), it is Metal; from the perspective of function/application (Yong), it is Qi. Furthermore, because it belongs to the Hand meridians, it is light and floats. When the lung is cooked, the Qi of the Hand meridian dissipates, leaving only the substance of Metal, so it sinks after cooking.

Although the Liver belongs to Wood, its position is below the diaphragm, where Yin Qi circulates more abundantly. Its meridian is the Foot-Jueyin (Liver Meridian), which governs Blood. From the perspective of form/substance (Ti), it is Wood; from the perspective of function/application (Yong), it is Blood. Furthermore, because it belongs to the Foot meridians, it sinks. When the liver is cooked, the Blood of the Foot meridian dissipates, leaving only the substance of Wood, so it floats after cooking. This reflects the principle of returning to the root. The theories of Linguan and Diwang seem somewhat forced; students should examine this carefully.

Shengshengzi said: The Seventy-Fifth Difficulty states: "The classic says: 'The East is excess (Liver/Wood), the West is deficient (Lung/Metal); drain the South (Heart/Fire), tonify the North (Kidney/Water). What does this mean?'... Therefore, by draining Fire and tonifying Water, one intends to prevent Metal from directly leveling Wood. The classic says: 'If you cannot treat the deficiency, why ask about the rest?' This is what it means." Hua Borun (Hua Tuo's descendant/commentator) said: "The character 'Bu' (Not) is likely a superfluous character (yanwen)." Chen Shiming (Chen Wuze) said: Zhang Zhongjing stated that when Wood overacts on Metal, it is called 'Heng' (Horizontal/Rebellious). The *Neijing* states: 'When Qi is in excess, it controls what it normally overcomes and insults what it normally cannot overcome.' With Wood excess and Metal deficiency, Wood is rebellious and insults Metal, insulting what it cannot normally overcome. Normally, Metal should level Wood. However, since Wood's Qi is strong and rebellious, if Metal attempts to level it, they will struggle against each other. In this struggle, both the excess condition and the deficiency condition suffer. Metal deficiency originally relies on Earth for support, but at that time, Earth is also constrained and insufficient to support Metal. Therefore, Water is selected as the son of Metal and the mother of Wood. By draining Fire and tonifying Water, Water overcomes Fire. Consequently, Fire becomes weak and draws Qi from Wood, causing Wood to decrease and fail to restore its excess. Since Water is the mother of Wood, this follows the principle that 'the mother can make the child deficient.' Once Wood is no longer excessive, its Qi becomes balanced. Being balanced, Metal is spared from being insulted by Wood and ceases to be deficient. Since Water is the son of Metal, this follows the principle that 'the child can make the mother substantial.' The phrase 'Metal does not level Wood' means that Metal should not directly level Wood. Instead, one must treat indirectly by draining Fire and tonifying Water, allowing the Qi of Wood and Metal to naturally become balanced.

Hua Borun further stated: "Chen's interpretation has its own merit, but it is entangled by the single character 'Bu', appearing forced and verbose. It would be better to regard 'Bu' as a superfluous character." I say: "'Bu' is not a superfluous character. The 'Bu' in the *Nan Jing* implies a concept of forbearance or indirect action, meaning Metal does not directly level Wood, hence the treatment of draining Fire and tonifying Water. Consider Bian Que (Yue Ren) stating: 'Metal, Wood, Water, Fire, and Earth should mutually and alternately level each other.' The character 'Geng' (Alternate/Mutual) and the character 'Bu' (Not) are the key points of this chapter. This 'Geng' shares the same meaning as the 'Geng' in the Twentieth Difficulty ('mutually overcoming, mutually subduing'), indicating mutual regulation, rather than directly letting Metal level Wood. Observing Zhang Zhongjing's use of 'Heng' (Rebellious) for Wood overacting on Metal, we know that Metal's deficiency is not trivial. Even if rapidly tonified, it might not even sustain itself, let alone level Wood. The scenario where Metal levels Wood refers to the normal sequence of Five Elements control. Here, it refers to the mutual and alternate regulation of the Five Elements. 'Geng' (Alternate) and 'Shun' (Sequential) must be distinct. Otherwise, why did Bian Que not simply say 'Tonify Metal to allow it to level Wood,' but instead said 'Drain the South, Tonify the North'? Bian Que's subtle intent was precisely to drain Fire to vent the surplus of Wood, and tonify Water to fill the deficiency of Metal. The Five Elements nourish each other in turn, overcoming and subduing each other alternately, embodying the principle of the child avenging the mother. Hence, it says 'intending to let Metal not [directly] level Wood.' This is akin to the strategy of 'Besieging Wei to Rescue Han'; an apparent imbalance is used to achieve true balance. Chen's interpretation of 'Bu' is indeed correct, but he failed to elucidate 'Geng', thus inevitably arousing doubt among later learners. Hua Borun, whose medical knowledge was extremely refined, regarded 'Bu' as a superfluous character. I do not understand his reasoning."