蜀漆，常山之苗也。常山不可用，而苗则可取。味苦，纯阴。散火邪错逆，破痈瘕症坚，
除
痞结积凝，辟蛊毒鬼疰，久疟兼治，咳逆且调。
或问蜀漆，即常山之苗，子删常山而取其苗，何谓也？盖常山性烈而功峻，虽取效甚速，
而
败坏元气亦最深。世人往往用常山治疟，一剂即愈，而身体野狼狈，将息半载，尚未还元。设
再不慎，疾一朝重犯，得免于死亡幸也。其不可轻用，亦明矣。蜀漆虽是常山之苗，不比根
之猛烈。盖苗发于春，其性轻扬，且得春气之发生，散邪既速，而破气亦轻，可借之以攻坚
，不必虑其损内。此所以舍常山而登蜀漆也。
白头翁，味苦，气温，可升可降，阴中阳也。无毒。一云味甘、苦，有小毒者，非。主
温疟
、阳狂、寒热，治症瘕积聚，逐血，愈金疮，祛风暖腰，疗血衄疝肿，并疗百节骨疼痛。赤
毒之痢，所必用也。
或问白头翁，人多错认是鸟名，谁知是《本草》之药耶。《本草》言其功效颇多，皆不
足深
信。惟伤寒中之下利，乃热毒也，芩、连、栀子不足以解其毒，必用白头翁，以化大肠之热
，而又不损脾气之阴，逐瘀积而留津液，实有奇功也。若胃虚寒，不思食，及下利完谷不化
，不由于湿毒者，俱宜忌之也。
牡丹皮，味辛、苦，气微寒，阴中微阳，无毒。种分赤、白，性味却同。入肾、肝二经，
兼
入心包络。凉骨蒸之热，止吐血、衄血、呕血、咯血，兼消瘀血，除症坚，定神志，更善调
经，止惊搐，疗痈肿，排脓住痛。亦臣、佐、使之药，而不可为君也。仲景张夫子入之八味
丸中，所以治汉武帝消渴之症也。消渴，本是热症，方中加入桂、附，以火治火，奇矣。盖
此火乃相火，而非火。相火者，虚火也。实火可泻，虚火必须滋补。阳火可以水折，阴火必
须火引。地黄汤中既用熟地、山药以滋阴，不用桂、附以引火，则火不归源，而渴终不可止
。但既用桂、附以引火，而火归于下焦，而上焦余热，何能顿清。吾恐命门之火已归于肾宫
，心包之火仍炎于心位，热必余焰尚存，而渴仍不止也。故方中又加入牡丹皮，调和于心、
肝、肾之际，滋肾而清其肝中之木，使木不助心包之火。而牡丹皮又自能直入于膻中，以凉
其热，下火既安，而上火亦静，火宅之中，不成为清凉之境乎。此仲景夫子制方之神，而亦
牡丹皮之功，实有如是者也。不特此也，牡丹皮在六味地黄丸中，更有奇议。肾有补无泻，
用熟地、山药以补肾，又何必用牡丹皮以滋其骨中之髓耶。若云泻火，则已有泽泻矣；若云
健脾，则已用茯苓矣。若云涩精，则已用山萸矣。然则何所取，而又用牡丹皮哉？不知
牡丹皮，所以佐五味之不足也。补阴之药过于寒，则阴不能生，而过于热，则阴亦不能生。
六味丸中不寒不热，全赖牡丹皮之力，调和于心、肝、脾、肾之中，使骨中之髓温和，而后
精闭于肾内，火泻于膀胱，水湿化于小便，肺气清肃，脾气健旺，而阴愈生矣。
或问地骨皮治有汗之骨蒸，牡丹皮治无汗之骨蒸，此前人之成说，吾子何略而不谈？岂
牡丹
皮非治无汗之骨蒸耶，铎所亟欲辨者也。夫地骨皮未尝不治无汗
之骨蒸，牡丹皮未尝不治有汗之骨蒸也。元素将二药分有汗、无汗，为骨蒸之法，余不知其
何所见而分。据其论，牡丹皮牡而不牝，其色丹，象离阳中之火，能泻，似乎牡丹皮乃阳中
之阴，亦宜治有汗之骨蒸，而不宜治无汗之骨蒸矣。总之，牡丹皮乃治骨蒸之圣药，原不必
分有汗、无汗也。
或问仲景张公制八味丸，经吾子之阐发奇矣，不知更有异闻乎？曰∶医道何尽，请于前
论而
再穷其义。夫火有上、下之分。下火非补不能归，其在上之火，非凉不能息。补其在下之火
，
则火安而上不炎；凉其在上之火，则火静而下亦戢。虽然牡丹皮补肾水，而不补肾火，似乎
下火之炎上，不能使其归于下也。然而，牡丹皮虽不能补肾中之火，实能补肾中之水，补水
之不足，即能制火之有余。火有所制，自然不敢沸腾，然后用附子、肉桂，引其下伏，则火
藏于至阴之肾矣。牡丹皮亦补肾以益心，而不能补肾以克心者也，似乎上火趋下，不能使其
静于上也。然牡丹皮虽不能补肾水克心，实能补肾水以益心气之不足。即能制心气之有余，
必有所养，自然常能宁定。然后用附子、肉桂导其上通，则暗交于至阴之心矣。此前论所未
及者，而阐发其奇又如此矣。
或又问仲景张公八味丸，已发异论，不识六味丸亦有异论乎？曰∶六味丸中，别有微义
也。
牡丹皮用之于六味丸中，岂独凉骨中之髓，以生阴水哉。夫独阴不生，独阳不长。六味丸中
，乃纯阴之药也，苟不用阴中微阳之药，入于群阴之内，虽以水济火，似亦为阴虚者之所喜
，然而孤阴无阳，仅能制火之有余，不能生水之不足。丹皮虽亦是阴药，入于肾经，但性带
微阳，入于六味丸，使阳气通于阴之中，而性亦微寒，但助阴以生水，而不助阳以动火。此
仲景夫子立方之本意，铎实有以窥其微而尽发之也。
或问牡丹皮阴中微阳，又入于群阴之内，恐阳气更微，虽各药亦有兼于阳者，毕竟阴重
而阳
微也。不知他药如茯苓、泽泻、山药之类，入于群阴之中，全忘乎其为阳矣。惟牡丹皮虽在
阴药之中，而阳之气不绝，子试将六味丸嗅之，牡丹皮之气未尝全消，不可以悟其微阳之独
存，不为群阴所夺之明验乎。惟牡丹皮于群阴之中，独全其微，且能使茯苓、泽泻、山茱萸
、熟地、山药之阳气不散，以助其生阴之速。故牡丹皮用之于地黄丸中，尤非无意也。
或问牡丹皮能退骨蒸之虚热，是亦地骨皮之流亚也，乃先生誉地骨皮之解骨蒸，而不及
牡丹
皮，岂别有意欤？夫牡丹皮之解骨蒸，虽同于地骨皮而微有异者，非解有汗与无汗也。牡丹
皮之解骨蒸，解骨中之髓热也；地骨皮之解骨蒸，解骨中之血热也。骨中不止髓，髓之外必
有血以裹之。骨中之髓热，必耗其骨中之血矣；骨外之血热，必烁其骨中之髓矣。故治骨蒸
者，二味必须兼用，不可以有汗用地骨皮、无汗用牡丹皮也。此等论，实前人所未谈，言之
必惊世人，然予实闻之吾师，非凿空而论也。髓中有血，斯亦何奇。余尝见人骨折者，骨中
流
血，与髓俱出，非明验乎。独是地骨皮凉骨中之血，牡丹皮凉骨中之髓，无人证吾言耳。
蜀漆，是常山的嫩苗。常山的根不可使用，但其嫩苗却可以取用。味苦，属性纯阴。能疏散火邪的错乱逆乱，破除痈肿、瘕聚和症坚等积聚病块，消除痞结和积凝，驱避蛊毒和鬼疰（一种传染病），久疟疾兼治，咳嗽气逆也能调理。
有人问：蜀漆就是常山的嫩苗，您删去了常山而选用其嫩苗，这是什么道理呢？大概常山药性猛烈且功效峻急，虽然见效很快，但对元气的败坏也最深重。世人往往用常山治疗疟疾，一剂药下去就痊愈了，但身体却变得非常狼狈，调养半年，元气尚未恢复。如果再不小心谨慎，疾病一旦重新发作，能够免于死亡已经是幸运的了。它不可以轻易使用，这也是显而易见的。蜀漆虽然是常山的嫩苗，但不像根部那样猛烈。因为嫩苗在春天萌发，其性质轻扬，并且得到了春天生发之气，所以疏散邪气既快速，又不会严重耗破正气，可以利用它来攻坚散结，不必担心损伤内脏。这就是舍弃常山而选用蜀漆的原因。
白头翁，味苦，气温，作用可升可降，属于阴中之阳。无毒。有一种说法说它味甘、苦，有小毒，这是不对的。主治温疟、阳狂（因热盛导致的狂躁）、寒热往来，治疗症瘕积聚，逐除瘀血，治愈金疮（刀箭创伤），祛风暖腰，治疗血衄（鼻出血）和疝肿，并治疗全身关节骨骼疼痛。对于赤色毒痢，是必须使用的药物。
有人问：白头翁，人们大多错误地把它当作鸟的名字，谁知道它是《本草》中的药物呢。《本草》中记载它的功效很多，都不值得深信。只有伤寒病中的下利（腹泻），属于热毒，黄芩、黄连、栀子不足以解除这种毒，必须使用白头翁，以化解大肠的热毒，而且又不损伤脾脏的阴气，逐除瘀积而保留津液，确实有奇特的功效。如果是胃虚寒，不想吃东西，以及下利完谷不化（腹泻排出未消化的食物），不是由湿毒引起的，都应当忌用。
牡丹皮，味辛、苦，气微寒，属于阴中微阳，无毒。种植分为赤丹皮和白丹皮，但药性和味道却相同。入肾、肝二经，同时入心包络。能凉解骨蒸潮热，止吐血、衄血、呕血、咯血，兼消瘀血，除症坚，安定神志，更善于调理月经，止惊搐，治疗痈肿，排脓止痛。它也是臣药、佐药、使药，但不能作为君药。张仲景先生将其加入八味丸中，用来治疗汉武帝的消渴症。消渴，本来是热症，方剂中加入桂枝、附子，以火治火，这很奇特。大概这种火是相火，而不是实火。相火，就是虚火。实火可以泻除，虚火必须滋补。阳火可以用水来折服，阴火必须用火来引导。地黄汤中既然用了熟地黄、山药来滋阴，如果不使用桂枝、附子来引火归元，那么火就不能回归本源，口渴最终无法停止。但是既然使用了桂枝、附子来引火，火归于下焦，那么上焦的余热，怎么能立刻清除呢？我恐怕命门之火已经归于肾宫，但心包之火仍然燃烧在心位，热势必然还有余焰尚存，而口渴仍然不能停止。所以方剂中又加入牡丹皮，调和于心、肝、肾之间，滋补肾水而清泄肝中的木火，使木不助长心包之火。而牡丹皮又能直接入于膻中，以凉解其中的热，下焦的火既已平息，上焦的火也随之安静，在如火宅般的体内，不就成了清凉的境界了吗？这是张仲景先生制方的神奇之处，也是牡丹皮的功劳，确实如此啊。不仅如此，牡丹皮在六味地黄丸中，更有奇妙的议论。肾脏只有补法没有泻法，用熟地黄、山药来补肾，又何必用牡丹皮来滋养骨中的髓呢？如果说为了泻火，则已有泽泻了；如果说为了健脾，则已用了茯苓了；如果说为了涩精，则已用了山茱萸了。那么究竟取什么，又要用牡丹皮呢？不知道牡丹皮，是用来辅助五味子的不足的。补阴的药物如果过于寒凉，则阴不能生成；如果过于温热，则阴也不能生成。六味丸中不寒不热，全赖牡丹皮的力量，调和于心、肝、脾、肾之中，使骨中的髓温和，然后精气闭藏于肾内，火泻于膀胱，水湿化为小便，肺气清肃，脾气健旺，从而阴气更加滋生。
有人问：地骨皮治疗有汗的骨蒸，牡丹皮治疗无汗的骨蒸，这是前人的定论，您为什么简略而不谈呢？难道牡丹皮不是治疗无汗骨蒸的药吗？这正是我急于辩明的问题。其实地骨皮并非不治疗无汗的骨蒸，牡丹皮也并非不治疗有汗的骨蒸。李元素将这两种药分为有汗和无汗两种骨蒸的治疗方法，我不知道他根据什么见解来划分的。根据他的论述，牡丹皮牡而不牝（属阳），其色红，象征离卦阳中之火，能泻，似乎牡丹皮乃是阳中之阴，也应该治疗有汗的骨蒸，而不宜治疗无汗的骨蒸了。总之，牡丹皮是治疗骨蒸的圣药，原本不必区分有汗和无汗。
有人问：张仲景先生制作八味丸，经过您的阐发很奇妙，不知道还有其他的奇闻吗？回答说：医道哪里会有尽头，请让我在前面的论述基础上再穷究其义理。火有上、下之分。下部的火不通过补益就不能回归，在上部的火不通过凉解就不能平息。补益下部的火，那么火安而上部就不炎；凉解上部的火，那么火静而下部也会收敛。虽然牡丹皮补肾水，而不补肾火，似乎不能让下部的火炎上回归到下焦。然而，牡丹皮虽然不能补肾中的火，实际上能补肾中的水，补充水的不足，就能制约火的有余。火有所制约，自然不敢沸腾，然后用附子、肉桂，引导其潜伏在下，那么火就藏在至阴的肾中了。牡丹皮也能补肾以益心，而不能补肾以克制心，似乎上火趋下，不能使其静于上部。然而牡丹皮虽然不能补肾水以克心，实际上能补肾水以益心气的不足。即能制约心气的有余，必定有所滋养，自然常常能够宁定。然后用附子、肉桂引导其上通，则暗中交合于至阴的心中了。这是前面论述所未涉及的，而阐发的奇妙又如此啊。
又有人问：张仲景先生的八味丸，已经发表了异论，不知道六味丸也有异论吗？回答说：六味丸中，别有微妙的义理。牡丹皮用在六味丸中，难道仅仅是凉解骨中的髓，以生阴水吗？孤阴不生，独阳不长。六味丸中，乃是纯阴的药物，假如不使用阴中带有微阳的药物，进入群阴之内，虽然以水济火，看似也为阴虚者所喜欢，然而孤阴无阳，只能制约火的有余，不能生水的不足。丹皮虽然也是阴药，入于肾经，但性质带有微阳，进入六味丸，使阳气通达于阴之中，而其性质微寒，只帮助阴以生水，而不帮助阳以动火。这是张仲景先生立方的本意，我确实窥探到了其中的微妙并完全阐发了出来。
有人问：牡丹皮阴中带有微阳，又进入群阴之内，恐怕阳气更微弱，虽然各药也有兼于阳的，毕竟阴重而阳微。不知道其他药如茯苓、泽泻、山药之类，进入群阴之中，完全忘记了它们为阳的性质。只有牡丹皮虽然在阴药之中，但阳的气机不绝，您试着闻一闻六味丸，牡丹皮的气味未曾完全消失，这不可以作为悟出其微阳独存，不被群阴所夺取的明显验证吗？只有牡丹皮在群阴之中，独自保全其微阳，且能使茯苓、泽泻、山茱萸、熟地黄、山药的阳气不散，以帮助其生阴的速度快。所以牡丹皮用在六味地黄丸中，尤其不是没有用意的。
有人问：牡丹皮能退骨蒸的虚热，也是地骨皮的同类，可是先生赞誉地骨皮解骨蒸的功效，却不提及牡丹皮，难道另有深意吗？其实牡丹皮解骨蒸，虽然与地骨皮相同但略有不同，并不是解有汗与无汗的区别。牡丹皮解骨蒸，是解骨中髓的热；地骨皮解骨蒸，是解骨中血的热。骨中不仅有髓，髓之外必有血包裹着。骨中的髓热，必然会耗伤骨中的血；骨外的血热，必然会灼烧骨中的髓。所以治疗骨蒸，这两味药必须兼用，不可以说有汗用地骨皮、无汗用牡丹皮。这样的论述，确实是前人所未曾谈论的，说出来必会让世人惊讶，但我确实听自我的老师，并非凭空而论。髓中有血，这有什么奇怪的呢。我曾经见过人骨折的人，骨中流血，与髓一起流出，这不是明显的验证吗？只是地骨皮凉骨中的血，牡丹皮凉骨中的髓，没有人证实我的话罢了。
Shuqi (Rhizoma Dichroae), the tender shoot of Changshan (Radix Dichroae). The root of Changshan should not be used, but its tender shoots can be taken. It tastes bitter and is purely Yin in nature. It disperses disordered and rebellious Fire pathogens, breaks up abscesses, masses, and hard accumulations; eliminates痞结 (glomus) and coagulated stagnations; wards off Gu poison (parasitic disease) and Gui Zhu (ghostly afflictions); treats chronic malaria and regulates cough with counterflow Qi.
Someone asked: "Shuqi is merely the tender shoot of Changshan. Why did you discard Changshan and select its shoot?" The answer is that Changshan has a fierce nature and峻急 (rapid/forceful) efficacy. Although it produces quick results, it severely damages Yuan Qi (Original Qi). People often use Changshan to treat malaria; one dose may cure it, but the body becomes extremely debilitated, requiring half a year of recuperation before Yuan Qi is restored. If one is not careful, the disease may relapse suddenly, and avoiding death would be mere luck. Thus, it is clear that it should not be used lightly. Although Shuqi is the shoot of Changshan, it is not as fierce as the root. Since the shoot emerges in spring, its nature is light and ascending, benefiting from the generating Qi of spring. It disperses pathogens quickly without severely breaking Qi, allowing it to be used for attacking hardness without worrying about damaging the interior. This is why Changshan is discarded in favor of Shuqi.
Baitouweng (Radix Pulsatillae), tastes bitter, has a warm temperature, and its action can ascend or descend; it belongs to Yang within Yin. It is non-toxic. Some claim it tastes sweet and bitter with slight toxicity, which is incorrect. It primarily treats Wen Malaria (warm-type malaria), Yang Kuang (mania due to heat), alternating chills and fever; treats masses and accumulations; expels blood stasis; heals metal wounds (traumatic injuries); dispels wind and warms the waist; treats epistaxis and hernia swelling; and treats pain in all joints and bones. It is essential for treating Chi Du Li (dysentery with bloody discharge).
Someone asked: "Many people mistakenly believe Baitouweng is a bird's name, unaware that it is a herb in the Ben Cao materia medica." The Ben Cao records many effects for it, which are not entirely trustworthy. However, regarding diarrhea in Shanghan (Cold Damage) diseases, which is caused by Heat toxin, Huang Qin (Scutellariae Radix), Lian Zi (Coptidis Rhizoma), and Zhi Zi (Gardeniae Fructus) are insufficient to resolve the toxin. One must use Baitouweng to transform Heat in the Large Intestine without damaging the Yin of the Spleen Qi, expelling stasis while preserving fluids, truly achieving miraculous results. If there is Stomach deficiency-cold with loss of appetite, or diarrhea with undigested food not caused by damp-heat toxins, it should be strictly contraindicated.
Mudanpi (Cortex Moutan), tastes pungent and bitter, has a slightly cold temperature, and belongs to slight Yang within Yin. It is non-toxic. It is cultivated into red and white varieties, but their nature and taste are identical. It enters the Kidney and Liver meridians, and also the Pericardium vessel. It cools bone-steaming heat, stops hematemesis, epistaxis, hematemesis, and hemoptysis; dissipates blood stasis; removes hard masses; calms the spirit; regulates menstruation effectively; stops convulsions; treats carbuncles and swellings; and promotes pus discharge while relieving pain. It serves as a minister, assistant, or courier herb, but cannot serve as the sovereign herb. Master Zhang Zhongjing included it in Ba Wei Wan (Eight-Ingredient Pill with Rehmannia) to treat Emperor Wu of Han's Xiao Ke (wasting-thirst) syndrome. Xiao Ke is essentially a Heat syndrome. Adding Gui Zhi (Cinnamomi Ramulus) and Fu Zi (Aconiti Lateralis Radix Praeparata) to treat fire with fire seems peculiar. This fire is actually Xiang Huo (Ministerial Fire), not excess fire. Xiang Huo is deficient fire. Excess fire can be purged, but deficient fire must be tonified. Yang fire can be subdued by water, but Yin fire must be guided by fire. In Di Huang Tang (Rehmannia Decoction), although Shu Di Huang (Prepared Rehmanniae Radix) and Shan Yao (Dioscoreae Rhizoma) are used to nourish Yin, if Gui Zhi and Fu Zi are not used to guide fire back to its source, the fire will not return to its origin, and thirst will not cease. However, once Gui Zi and Fu Zi are used to guide fire to the Lower Jiao, how can residual heat in the Upper Jiao be cleared instantly? I fear that although the Ming Men (Gate of Life) fire has returned to the Kidney palace, the Pericardium fire still burns in the Heart position. Residual heat will likely persist, and thirst will continue. Therefore, Mu Dan Pi is added to harmonize between the Heart, Liver, and Kidney, nourishing Kidney water and clearing Liver wood-fire, preventing Wood from assisting Pericardium fire. Mu Dan Pi also directly enters the Dan Zhong (Chest center) to cool heat there. With lower fire pacified and upper fire quieted, does the fiery dwelling not become a realm of coolness? This demonstrates the divine formulation skill of Master Zhang Zhongjing and the true merit of Mu Dan Pi.
Furthermore, in Liu Wei Di Huang Wan (Six-Ingredient Pill with Rehmannia), Mu Dan Pi holds another profound significance. The Kidney is only tonified, never purged. Using Shu Di Huang and Shan Yao to tonify the Kidney, why is Mu Dan Pi needed to nourish the marrow in the bones? If it were for purging fire, Ze Xie (Alismatis Rhizoma) is already present; if for strengthening the Spleen, Fu Ling (Poria) is used; if for astringing essence, Shan Zhu Yu (Corni Fructus) is employed. Then what is the purpose of using Mu Dan Pi? It is to assist where the other five herbs fall short. Tonifying Yin herbs that are too cold prevent Yin generation; those too hot also prevent Yin generation. Liu Wei Di Huang Wan is neither cold nor hot, relying entirely on Mu Dan Pi to harmonize among the Heart, Liver, Spleen, and Kidney. This keeps the bone marrow mild, allowing essence to be sealed in the Kidney, fire to be purged via the Bladder, and water-dampness to transform into urine. Lung Qi becomes clear and descending, Spleen Qi becomes robust, and Yin is further generated.
Someone asked: "Di Gu Pi (Lycii Cortex) treats bone-steaming with sweating, while Mu Dan Pi treats bone-steaming without sweating. This is a established view of predecessors. Why do you omit this discussion? Is Mu Dan Pi not for treating bone-steaming without sweating? This is precisely what I urgently wish to clarify." Actually, Di Gu Pi does treat bone-steaming without sweating, and Mu Dan Pi does treat bone-steaming with sweating. Li Dongyuan divided these two herbs based on sweating vs. non-sweating bone-steaming, but I do not know his basis. According to his theory, Mu Dan Pi is yang-like (male/unyielding), red in color, symbolizing the fire of Li Trigram (Yang within Yin), and capable of purging. It seems Mu Dan Pi is Yin within Yang, suitable for bone-steaming with sweating, not without. In summary, Mu Dan Pi is the supreme herb for bone-steaming and need not be distinguished by sweating status.
Someone asked: "Your exposition of Zhang Zhongjing's Ba Wei Wan was fascinating. Are there other insights?" I reply: Medicine has no end. Let me explore deeper based on previous discussions. Fire has upper and lower distinctions. Lower fire requires tonification to return; upper fire requires cooling to subside. Tonifying lower fire prevents upper flare-up; cooling upper fire prevents lower agitation. Although Mu Dan Pi nourishes Kidney Water but not Kidney Fire, seemingly unable to make lower fire return downward, it actually nourishes Kidney Water. Supplementing water controls excess fire. Once controlled, fire ceases to boil. Then, using Fu Zi and Rou Gui (Cinnamomi Cortex) guides it to hide in the extreme Yin of the Kidney. Mu Dan Pi benefits the Heart by nourishing the Kidney, though it doesn't suppress Heart via Kidney. It nourishes Heart Qi deficiency, calming it. Then Fu Zi and Rou Gui guide it upward, allowing secret interaction with the extreme Yin of the Heart. This deepens our understanding.
Regarding Liu Wei Di Huang Wan, there is also subtle meaning. Does Mu Dan Pi in Liu Wei Di Huang Wan only cool bone marrow to generate Yin Water? Solitary Yin does not generate; solitary Yang does not grow. Liu Wei Di Huang Wan consists purely of Yin herbs. Without an herb containing slight Yang entering the group of Yin herbs, although water supports fire, it might please yin-deficient patients, solitary Yin without Yang can only control excess fire but cannot generate deficient water. Although Mu Dan Pi is a Yin herb entering the Kidney meridian, its nature carries slight Yang. In Liu Wei Di Huang Wan, it allows Yang Qi to penetrate Yin. Its nature is slightly cold, aiding Yin to generate water without stirring Yang to move fire. This is Zhang Zhongjing's original intent, which I have fully elucidated.
Someone asked: "Mu Dan Pi has slight Yang within Yin and enters a group of Yin herbs. Won't its Yang become even weaker? Other herbs also have Yang aspects, but Yin is heavy and Yang is slight." Consider Fu Ling, Ze Xie, and Shan Yao; when entering the group of Yin herbs, their Yang nature is forgotten. Only Mu Dan Pi, amidst Yin herbs, retains its Yang Qi unbroken. Smell Liu Wei Di Huang Wan; the aroma of Mu Dan Pi remains, proving its unique survival of slight Yang, not conquered by Yin. Mu Dan Pi preserves its slight Yang among Yin herbs and prevents the Yang Qi of Fu Ling, Ze Xie, Shan Zhu Yu, Shu Di Huang, and Shan Yao from scattering, accelerating Yin generation. Thus, its use in Di Huang Wan is intentional.
Someone asked: "Mu Dan Pi clears deficiency heat of bone-steaming, similar to Di Gu Pi. Yet you praise Di Gu Pi for bone-steaming but neglect Mu Dan Pi. Is there another intention?" The difference lies not in sweating vs. non-sweating. Mu Dan Pi clears Heat in the Bone Marrow; Di Gu Pi clears Heat in the Bone Blood. Outside the marrow, blood wraps the bone. Heat in the marrow consumes bone blood; heat in the blood scorches bone marrow. Therefore, both herbs must be used together for bone-steaming; one cannot simply assign Di Gu Pi to sweating cases and Mu Dan Pi to non-sweating cases. This theory, unheard of by predecessors, may astonish the world, but I learned it from my master, not fabricating it. Marrow contains blood, as seen in fractured bones where blood flows out with marrow. Di Gu Pi cools bone blood; Mu Dan Pi cools bone marrow. Few verify these words.