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Zhu Ling (Polyporus), Fu Ling (Poria), and Ze Xie (Alisma) are all substances with a bland taste and diaphoretic-draining properties; their primary function lies entirely in promoting urination. In Zhang Zhongjing's Wu Ling San (Five-Ingredient Powder with Poria) and Zhu Ling Tang (Polyporus Decoction), these three herbs are used together without concern for redundancy. I believe this reason was derived from the *Shennong Bencao Jing* (Divine Farmer's Materia Medica) and the *Huangdi Neijing* (Yellow Emperor's Inner Canon). The *Bencao Jing* states that Zhu Ling promotes water pathways, Fu Ling promotes small urination, and Ze Xie eliminates water retention. The *Neijing* indicates that the San Jiao (Triple Burner) is the pathway for water metabolism, the Bladder is the reservoir of water, and the Kidney is the master of the San Jiao and Bladder. Observing both texts together, does it not imply that Zhu Ling drains water from the San Jiao, Fu Ling drains water from the Bladder, and Ze Xie drains water from the Kidney?

Zhu Ling is formed from the residual qi of the Maple tree. By late autumn, the maple leaves turn red like fire; they move spontaneously without wind and stop when it rains. In heavy rain, they grow secretly by two or three chi. Its mechanism of action is identical to that of Shaoyang Ministerial Fire (Shaoyang Xiang Huo). The Bladder stores body fluids, which cannot be excreted without Qi transformation. Fu Ling, being white and entering the Lung meridian, can circulate Lung Qi to facilitate this transformation. Generally, aquatic plants and stones belong to the Kidney. Ze Xie grows in shallow water and has a salty taste; its entry into the Kidney meridian is unquestionable. These three herbs possess a subtle efficacy in draining water through the distribution and discharge of Qi.

In conditions where water and heat are bound together, such as in Wu Ling San and Zhu Ling Tang, if these three herbs are not administered together, the water may not be eliminated. If water is not eliminated, heat will not be removed. Polydipsia caused by heat can occur in the Upper and Middle Jiao. It may result from Yin deficiency and fluid depletion, from fluids scorched by heat, or from heat bound with water. These three herbs merely eliminate heat by promoting urination; they do not possess the ability to generate fluids and tonify Yin like Ren Shen (Ginseng Root) or Gua Lou Gen (Trichosanthes Root). Li Shi-zhen argued that bland-draining substances must first ascend before descending to remove water. However, examining how Zhang Zhongjing uses these three herbs, such high praise for this theory is unnecessary.

Nevertheless, among these three herbs, only Ze Xie is suitable for stopping thirst. Why? Although the *Bencao Jing* lacks records of Ze Xie "raising Yin Qi," the *Mingyi Bielu* (Record of Famous Physicians) explicitly contains this property. Ze Xie raises Yin Qi. Although it is not as direct as Ge Gen (Kudzu Root) drawing stomach fluids to nourish the Heart and Lungs, it obtains Qi transformation from water. With its single stem growing straight upward, it can send generating Qi to the highest point. Zhang Zhongjing has clearly revealed this to us. For symptoms of dizziness, palpitations, and vertigo, credit is often given to Fu Ling. However, in Ze Xie Tang (Alisma Decoction) treating Mao Xuan (vertigo with a sensation of heaviness/obscuration), Fu Ling is notably absent. Mao Xuan arises from Zhi Yin (branching fluid retention) obstructing the epigastrium, preventing lower Yin from assisting upper Yang. Consequently, Yang flares upward, causing a sensation of being covered and leading to vertigo. Ze Xie not only expels fluid retention but also raises Yin Qi, calling the floating Yang back to its root. Bai Zhu (Atractylodes Macrocephala Rhizome) fortifies Earth (Spleen/Stomach) merely to provide assistance. Li Shizhen's indication for dizziness and tinnitus likely derives from this insight of Zhang Zhongjing. Furthermore, Shen Qi Wan (Kidney Qi Pill) treats polydipsia using Kidney-tonifying herbs. Although Fu Ling is used, it is only borrowed to assist Gui Zhi (Cinnamon Twig) and Fu Zi (Aconite Lateral Root) in transforming Kidney Yang. Yu Jin (Cornus Fruit) and Di Huang (Rehmannia Root) nourish Yin but cannot raise it. If Kidney Yin does not circulate throughout the chest, thirst will persist. In such cases, Zhu Ling may be omitted, but Ze Xie must be included. Therefore, it is said that for stopping thirst, Ze Xie is the most appropriate.