猪苓茯苓泽泻，三者皆淡渗之物，其用全在利水。仲圣五苓散猪苓汤，三物并用而不嫌
于复，此其故愚盖得之本经与内经矣，本经猪苓利水道，茯苓利小便，泽泻消水。内经三焦
为水道，膀胱为水府，肾为三焦膀胱之主。合二者观之，得非猪苓利三焦水，茯苓利膀胱水
，泽泻利肾水乎。猪苓者，枫之余气所结，枫至秋杪，叶赤如火，其无风自动，天雨则止，
遇豪雨则暗长二三尺，作用与少阳相火正复无异。膀胱藏津液，非气化不出，茯苓色白入肺
，能行肺气以化之。凡水草石草皆属肾，泽泻生浅水而味咸，入肾何疑。三物利水，有一气
输泻之妙。水与热结之证，如五苓散猪苓汤，若非三物并投，水未必去，水不去则热不除，
热不
消渴上中焦皆有之，或阴虚津亏而渴，或津被热烁而渴，或热与水结而渴。三物第利水
以除热，何尝如人参栝蒌根有生津补阴之能。李氏谓淡渗之物，其能去水，必先上行而后下
降，以仲圣用三物稽之，正不必过高其论也。
虽然，于三物中求止渴，惟泽泻其庶几耳。何则？本经无泽泻起阴气之文，而别录固有
之。泽泻起阴，虽不及葛根挹胃汁以注心肺，而得气化于水，独茎直上，即能以生气朝于极
上，仲圣又不啻明告我矣。凡眩悸颠眩，多归功于茯苓，而泽泻汤治冒眩，偏无茯苓。冒眩
者，支饮格于心下，下之阴不得济其上之阳，于是阳淫于上如复冒而眩以生。泽泻不特逐饮
，且能起阴气以召上冒之阳复返于本。白术崇土，第以资臂助耳。大明之主头旋耳鸣，殆得
仲圣此旨也。又肾气丸治消渴皆肾药。虽用茯苓，亦只借以协桂附化肾阳。萸地益阴而不能
升阴。肾阴不周于胸，则渴犹不止，此猪苓可不加，而泽泻不得不加。故曰止渴，惟泽泻为
庶几
猪苓、茯苓和泽泻，这三味药都是性质淡而具有渗利作用的药物，它们的主要功效全在于通利水道。张仲景在五苓散和猪苓汤中，将这三味药同时使用而不担心功效重复，这个原因我大概是从《神农本草经》和《黄帝内经》中领悟到的。《本经》记载猪苓通利水道，茯苓通利小便，泽泻消除水饮。《内经》指出三焦是水液运行的通道，膀胱是水液汇聚的府库，肾是三焦和膀胱的主宰。综合这两部经典来看，难道不是猪苓通利三焦的水湿，茯苓通利膀胱的水液，泽泻通利肾脏的水湿吗？
猪苓是枫树余气凝结而成的，枫树到了深秋，叶子红得像火一样，无风时自动摇动，下雨就停止，遇到大雨能暗长二三尺，其作用机理与少阳相火的特性完全一致。膀胱贮藏津液，必须经过气化才能排出，茯苓颜色白入肺经，能够宣行肺气从而促进气化。凡是生长在水中的草石都归属于肾，泽泻生长在浅水中且味道咸，归入肾经有什么可疑的呢？这三味药在利水方面，具有一种通过气机输布来排泄水湿的妙用。
对于水与热互结的病证，如五苓散证和猪苓汤证，如果不是三味药同时投用，水湿未必能去除；水湿不去则热邪不能清除。热邪导致的消渴症状在上焦和中焦都有可能出现，有的是因为阴虚津亏而口渴，有的是因为津液被热邪灼烧而口渴，有的是因为热与水互结而口渴。这三味药只是通过利水来清除热邪，哪里像人参、天花粉（栝蒚根）那样具有生津补阴的功效呢？李氏认为淡渗的药物，其去水的作用，一定是先上行然后再下降，但考察张仲景使用这三味药的情况，这种说法确实不必过分推崇。
虽然如此，在这三味药中寻求止渴的效果，只有泽泻比较接近。为什么呢？《本经》中没有泽泻“起阴气”的记载，但《名医别录》中确实有这一条。泽泻能升发阴气，虽然不如葛根汲取胃中津液以灌注心肺那样直接，但它得自于水的化生，独茎直立向上，能够以生气朝贡于极上之处，张仲景又不止一次明确地启示了我们。凡是眩晕、心悸、头重脚轻的症状，多归功于茯苓，但泽泻汤治疗冒眩（头目昏沉如物蒙蔽），方中偏偏没有茯苓。所谓冒眩，是因为支饮阻滞于心下，下方的阴气不能济助上方的阳气，于是阳气亢盛于上，如同被覆盖般产生眩晕。泽泻不仅能驱逐水饮，还能升发阴气，使上冒的阳气重新返回本源。白术培补脾土，只是起到辅助作用罢了。李时珍主治头晕耳鸣，大概是得到了张仲景这一旨意的启发。另外，肾气丸治疗消渴，用的都是补肾的药。虽然也用茯苓，也只是借助它来协助桂枝、附子化生肾阳。山茱萸、地黄滋补阴液但不能升提阴气。如果肾阴不能周流于胸部，那么口渴仍然不会停止，这种情况下猪苓可以不加，但泽泻不得不加。所以说，在止渴方面，只有泽泻最为适宜。
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.