张仲景八味丸用泽泻。寇宗 本草衍义云。不过接引桂附等归就肾经。别无他意。而王海藏
韪之。愚谓八味丸以地黄为君。而以余药佐之。非止为补血之剂。盖兼补气也。气者。血之
母。东垣所谓。阳旺。则能生阴血者。此也。若果专为补肾。而入肾经。则地黄。山茱萸。
白茯苓。牡丹皮。皆肾经之药。固不待夫泽泻之接引。而后至也。其附子官桂。虽非足少阴
经本药。然附子乃右肾命门之药。况浮中沉无所不至。又为通行诸经引用药。官桂能补下焦
相火不足。是亦右肾命门药也。易老亦曰补肾用肉桂。然则。桂附亦不待夫泽泻之接引。
而
后至矣。唯干山药。虽独入手太阴经。然其功亦能强阴。且手太阴为足少阴之上原。原既有
滋。流岂无益。夫其用地黄为君者。大补血虚不足。与补肾也。用诸药佐之者。山药之强阴
益气。山茱萸之强阴益精。而壮元气。白茯苓之补阳长阴。而益气。牡丹皮之泻阴火。而
治神志不足。泽泻之养五脏。益气力。起阴气。而补虚损。五劳。桂附之补下焦火也。由此
观之。则余之所谓兼补气者。非臆说也。且泽泻也。虽曰咸以泻肾。乃泻肾邪。非泻肾之本
也。故五苓散用泽泻者。讵非泻肾邪乎。白茯苓亦伐肾邪。即所以补正耳。是则八味丸之用
泽泻者。非他。盖取其泻肾邪。养五脏。益气力。起阴气。补虚损。五劳。之功而已。寇氏
何疑其泻肾。而为接引桂附等之说乎。且泽泻固能泻肾。然从于诸补药群众之中。虽欲泻之
。而力莫能施矣。故当归从于参 。则能补血。从于大黄牵牛。则能破血。从于桂附茱萸。
则热。从于大黄芒硝。则寒。此非无定性也。夺于群众之势。而不得不然也。虽然。或者又谓
。八味丸以附子为少阴之向导。其补自是地黄为主。盖取其健脾走下之性。以行地黄之滞。
可致远耳。窃意如此。则地黄之滞。非附子不能及下矣。然钱仲阳六味地黄丸。岂有附子
乎。夫八味丸。盖兼阴火不足者设。六味地黄丸。则惟阴虚者用之也。
Zhang Zhongjing uses Ze Xie (Rhizoma Alismatis) in Ba Wei Wan (Eight-Ingredient Pill with Rehmannia). Kou Zongshi, in *Bencao Yan Yi* (Supplement to Materia Medica), stated that its function is merely to guide Gui Zhi (Cinnamon Twig) and Fu Zi (Prepared Aconite Root) etc. into the Kidney Meridian, with no other intention. Wang Haicang endorsed this view. I argue that in Ba Wei Wan, Di Huang (Rehmannia Root) serves as the Sovereign herb, assisted by the remaining herbs; it is not merely a formula for nourishing blood, but also one that tonifies Qi. Qi is the mother of Blood. As Li Dongyuan stated, "When Yang is vigorous, it can generate Yin-Blood," which refers to this principle. If the formula were solely intended to tonify the Kidney and enter the Kidney Meridian, then Di Huang, Shan Zhu Yu (Cornus Fruit), Bai Fu Ling (Poria), and Mu Dan Pi (Moutan Cortex) are all herbs entering the Kidney Meridian; they would naturally reach the Kidney without needing Ze Xie as a guide. Although Fu Zi and Guan Gui (Cassia Bark) are not originally herbs of the Foot-Shaoyin (Kidney) Meridian, Fu Zi is an herb for the Right Kidney and Mingmen (Gate of Vitality); furthermore, it penetrates floating, middle, and deep levels without restriction, serving as a guiding herb for all meridians. Guan Gui can tonify the deficiency of Minister Fire in the Lower Jiao, making it also an herb for the Right Kidney and Mingmen. Yilao (Zhang Yuansu) also stated that Rou Gui (Cassia Bark) is used to tonify the Kidney. Thus, Gui and Fu Zi do not require Ze Xie's guidance to arrive. Only Gan Shan Yao (Dioscorea Rhizome), although acting on the Hand-Taiyin (Lung) Meridian alone, has the efficacy of strengthening Yin. Moreover, the Hand-Taiyin is the upper source of the Foot-Shaoyin; if the source is nourished, how could the flow not benefit?
The use of Di Huang as the Sovereign herb is primarily to greatly tonify Blood deficiency, which relates to tonifying the Kidney. The use of other herbs as Assistants is because: Shan Yao strengthens Yin and tonifies Qi; Shan Zhu Yu strengthens Yin, benefits Essence, and fortures Yuan Qi; Bai Fu Ling tonifies Yang, promotes Yin growth, and benefits Qi; Mu Dan Pi drains Yin-Fire and treats insufficiency of Spirit and Mind; Ze Xie nourishes the Five Zang organs, benefits Qi strength, raises Yin-Qi, and tonifies deficiency injuries and Wu Lao (Five Exhaustions); Gui and Fu Zi tonify the Fire of the Lower Jiao. From this perspective, my statement that it "also tonifies Qi" is not a baseless assertion.
Regarding Ze Xie, although it is said that Salty flavor drains the Kidney, it drains Kidney Pathogens (Xie), not the Kidney's true substance. Therefore, the use of Ze Xie in Wu Ling San (Five-Ingredient Powder with Poria) is indeed to drain Kidney Pathogens. Bai Fu Ling also attacks Kidney Pathogens, which is precisely how it tonifies Healthy Qi. Thus, the use of Ze Xie in Ba Wei Wan is for no other reason than to utilize its functions of draining Kidney Pathogens, nourishing the Five Zang organs, benefiting Qi strength, raising Yin-Qi, and tonifying deficiency injuries and Wu Lao. Why should Kou doubt that it drains the Kidney and instead claim it guides Gui and Fu Zi? Furthermore, although Ze Xie can drain the Kidney, amidst the multitude of tonifying herbs, even if it wished to drain, its force could not be exerted. Thus, Dang Gui (Angelica Sinensis), when accompanying Ren Shen (Ginseng Root), can tonify Blood; when accompanying Da Huang (Rhubarb Root) and Qian Niu Zi (Pharbitis Seed), it can break Blood stasis; when accompanying Gui, Fu Zi, and Zhu Yu, it becomes hot; when accompanying Da Huang and Mang Xiao (Mirabilite), it becomes cold. This is not due to lack of inherent nature, but rather being overwhelmed by the momentum of the group, leaving no choice but to conform.
Although so, some might say: "In Ba Wei Wan, Fu Zi acts as the guide for the Shaoyin Meridian; the tonification naturally relies mainly on Di Huang. It likely takes advantage of Fu Zi's property of strengthening the Spleen and descending to move the stagnation of Di Huang, allowing it to reach distant areas." I suspect that if this were true, then the stagnation of Di Huang could not reach the lower part without Fu Zi. However, where is Fu Zi in Qian Zhongyang's Liu Wei Di Huang Wan (Six-Ingredient Pill with Rehmannia)? Ba Wei Wan is established for cases involving insufficient Yin-Fire, whereas Liu Wei Di Huang Wan is used exclusively for Yin deficiency.