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The leaves of *Rheum palmatum* (Dahuang, 大黄) are green and the stems are red; it inherits the qi of Wood and Fire. Its vines spread with short internodes. Its taste is bitter and its nature is neutral. It can unblock and benefit the Sanjiao (Triple Burner), searching out and eliminating damp-heat pathologies hidden in subtle areas. Therefore, *Jingui Yaolue* (Essential Prescriptions from the Golden Cabinet) states: "For impetigo (Imjin Chuang, 浸淫疮), if it starts from the mouth and flows to the four limbs, it is treatable; if it starts from the four limbs and flows into the mouth, it is untreatable." This is because the mouth is the orifice of the Spleen. When the pathology flows to the four limbs, the damp-heat does not invade the Spleen Earth. With the Spleen Earth having authority, it becomes treatable. The spreading vines and short internodes of *Rheum*, along with flowers blooming at every node, could this not be considered a manifestation of damp-heat flowing to the four limbs?

Zou believed that Dahuang has a central channel connecting its interior, resembling brocade patterns, with a deep purple color and texture, representing Fire penetrating through Earth. He greatly admired Lu Zhiyuan's phrase "executing the function of Fire." I privately ponder that while Lu's discussion on the meaning of control and generation in *Suwen* (Plain Questions) is indeed profound, shallow learners may find it difficult to comprehend. Although Dahuang's yellow color and central channel might support Spleen Yang, this refers only to its physical substance. Its taste is intensely bitter, and its nature is intensely cold. Furthermore, the red veins running through the yellow indicate that for the Fire constrained within the Earth in the Blood aspect of the Spleen, it naturally acts to extinguish it. Once the constrained Fire in Earth is extinguished, the Fire generated by the Heart Sovereign to produce Earth will inevitably act upon it. This is why it bears the title of "General," capable of executing the Sovereign's orders, quelling chaos, and expanding territory.

Dahuang is yellow and fragrant, its nature aligning with Earth, making it highly suitable for treating Spleen and Stomach diseases. Its ability to execute the function of Fire throughout the upper and lower, exterior and interior, is often overlooked. However, one sentence can summarize it: it sweeps away excess and purges heat. In cases where Heat and Excess coexist, such as using Da Chengqi Tang (Major Order the Qi Decoction) to purge dry feces, Da Xiexiong Tang/Wan (Major Trap the Chest Decoction/Pill) to treat chest binding, Didang Tang/Wan (Arrive at Blood Decoction/Pill) to purge blood stasis, and Dahuang Fuzi Tang (Rhubarb and Aconite Decoction) to treat unilateral hypochondriac pain; in cases where there is Heat but no Excess, such as using Linggan Wuwei Jiangxin Banxia Dahuang Tang (Poria, Cinnamon Twig, Licorice, Ginger, Asarum, Pinellia, and Rhubarb Decoction) for facial heat resembling drunkenness, Yinchenhao Tang (Artemisia Capillaris Decoction) for grain jaundice, and Xiexin Tang (Drain the Epigastrium Decoction) for insufficiency of Heart Qi; these two categories show distinct differences. Extending this logic, conditions like Biejia Jian Wan (Turtle Shell Building-Up Pill) for abdominal masses, Dahuang Zhechong Wan (Rhubarb and Ground Beetle Pill) for consumptive disease with emaciation, Dahuang Mudan Tang (Rhubarb and Moutan Decoction) for intestinal abscess, and Dahuang Huanglian Xiexin Tang (Rhubarb, Coptis, and Scutellaria Drain the Epigastrium Decoction) for Qi痞 (Qi obstruction), although not strictly Heat-Excess, are treated similarly to Heat-Excess. They merely borrow the sweeping and purging properties to expand miraculous applications. Zhang Zhongjing's method of formulating prescriptions goes even further. Ji Jiao Li Huang Wan (Stephania, Piper, Descurainia, and Rhubarb Pill) treats water qi in the intestines. Water is a soft/fluid substance; Dahuang can sweep Excess but cannot crush deficiency/water. Since Fangji (Stephania) and Tinglizi (Descurainia) already drain water, what is the purpose of adding Dahuang? Some claim it drains blood closure and lowers heat; others suggest it disperses via the large intestine. These are speculative guesses lacking credibility. Only the modern scholar Tang Rongchuan stated: The Sanjiao is the official responsible for irrigation, where water passages emerge. The Sanjiao corresponds to the diaphragmatic fatty network. Water seeps from the stomach through tiny pores into this network, then enters the Bladder. If water enters the intestines, it becomes stagnant water. If water stagnates and does not circulate through the Sanjiao, it fails to transform into Qi, leading to a lack of Jin-Ye (Body Fluids), causing dry mouth and tongue. The treatment should guide water that has not yet entered the intestines back to the Sanjiao pathway; and for water already stagnant in the intestines, it should be drained downward from the intestines. Based on the Western medical concept of the fatty network and verifying it against the *Neijing*'s description of the Sanjiao, this matches the syndrome and prescription perfectly, surpassing old interpretations. Fangji (Stephania) has veins like wheel spokes, yellow inside and white outside, possessing the ability to pivot the Sanjiao water pathways between the Spleen and Lung. Jiaomu (Piper Seed) warms the Kidney to evaporate Spleen Yang, removing abdominal fullness and promoting urination, similar to how Fuzi (Aconite) and Guizhi (Cinnamon Twig) function in Shenqi Wan (Kidney Qi Pill). Thus, the original pathway of the Sanjiao can be restored. Regarding the water in the intestines, should Dahuang be used to drain it downward? Or is it not yet time? The Large Intestine is the residence of waste. If there is water in the Large Intestine, it exits with the waste. Even if not dry feces, Dahuang still has a role. However, its jurisdiction lies primarily in the intestines and stomach, lacking power to reach the Lung. The Lung pairs with the Large Intestine; without the Lung's governance and regulation, water and food cannot descend together. Tinglizi (Descurainia Seed) is a herb moving from Lung to Spleen (according to Zou's commentary); it benefits water passages and breaks accumulations. Thus, it is added to assist Dahuang's insufficiency. Moreover, Jiaomu combined with Dahuang balances Cold and Warmth. Diseases of the intestines and stomach require the Fire function to operate before healing.

As an object, Dahuang has fixed characteristics, but the methods of using it are variable. Without Zhang Zhongjing's methods, Dahuang fails to fulfill its potential, leading to many instances of failing Dahuang. Conversely, misuse leads to Dahuang being blamed frequently. *Suwen: Zhi Zhen Yao Da Lun* discusses prescription formulation extensively, covering speed/slowness, odd/even combinations, intensity of flavors/natures, small/large formulations, and numerical variations. These intricate combinations offer infinite applications. Zhang Zhongjing formulated based on this principle, refusing single-dimensional interpretation. Dahuang has strong flavor and nature, originally a harsh purgative. By slightly altering its nature due to its harshness, different effects are achieved. For example, in Da Chengqi Tang and Didang Tang, Dahuang is washed/soaked in wine to address residual Shaoyang pathogens; in Dahuang Huanglian Xiexin Tang, Dahuang is steeped in boiling water without boiling to retain its action in the epigastrium; in Dahuang Fuzi Tang, combining with Fuzi changes cold purging to warm purging; in Yinchenhao Tang, combining with Yinchen and Zhizi directs action to urination rather than defecation. Such is the variability of Dahuang usage. Regarding formulas, You Shi argued that Xiaochengqi Tang (Minor Order the Qi Decoction) lacks Mangxiao (Mirabilite) and contains only Zhishi (Immature Bitter Orange) and Zhi Ke (Aurantium), resulting in a slower descending force, hence "Minor." However, Xiaochengqi Tang has less Zhishi and Zhi Ke than Da Chengqi Tang. The distinction between Major and Minor lies in the dosage/formulation, not merely the presence of Mangxiao. Mangxiao does not solely act to descend. In Tiaowei Chengqi Tang (Regulate the Stomach Order the Qi Decoction), Mangxiao combined with Gancao (Licorice) regulates the Stomach; in Da Xiexiong Tang, combined with Gansui (Kansui Root), it traps the Chest. Da Chengqi Tang uses only 3 he of Mangxiao, whereas Tiaowei and Da Xiexiong use up to half a sheng or one sheng. Didang Tang/Wan lacks Mangxiao entirely. Clearly, Mangxiao's function is not limited to descending. Ke Yunbo stated that raw herbs have sharp Qi acting first, while cooked herbs have pure Qi acting gently. Thus, in Da Chengqi Tang, Mangxiao dissolves dry feces, Dahuang follows to open the earthy pathway, then Zhishi and Zhi Ke remove fullness. Zou agreed, but this is partially correct yet fundamentally flawed. As mentioned, Mangxiao does not seek rapid purging. Longer boiling yields stronger flavor and earlier purging; shorter boiling yields weaker flavor and later purging. Zhishi and Zhi Ke are boiled first to descend directly; Dahuang is added later to assist in purging heat, not to delay intentionally. Thus, Dahuang is added last, and Mangxiao is boiled briefly. Xiaochengqi Tang boils all together because Zhishi/Zhi Ke are scant and there is no Mangxiao. Da Chengqi Tang boils Zhishi/Zhi Ke in 10 dou of water to get 5 sheng, adds Dahuang, and reduces to 2 sheng. Xiaochengqi Tang boils 4 sheng of water to get 1.2 sheng. Even if boiled together, Dahuang's strength is not intense, so separating order is unnecessary. Zou claimed that in Da Xiexiong Tang, using the sharpness of Gansui and Mangxiao risks temporary relief followed by re-obstruction, so Dahuang is boiled first to handle aftermath. Ignoring holistic formula synergy, focusing only on boiling order is misguided. Gansui and Mangxiao treat heat/water binding in the chest; thus Mangxiao is boiled briefly and Gansui is taken as powder. Dahuang, a gastrointestinal herb, acts as a vanguard for Gansui, hence boiled first. Zou also claimed that in Yinchenhao Tang, Dahuang and Zhizi are the vanguard, and Yinchen is the rear guard. This is incorrect. Yinchen promotes aromatic dispersion, inheriting Taiyang Cold-Water Qi, resolving muscle-surface damp-heat. To drive pathogens out via urine, it must be boiled longer to intensify its power, similar to Guizhi requiring larger doses for diuresis. Dahuang (only 2 liang) is added late, blending with Yinchen's surface-moving Qi and promoting downward movement. Since Yinchen and Zhizi direct to urination, Dahuang naturally avoids the large intestine. This reflects Zhang Zhongjing's formulation...