知母∶味苦，性寒，液浓而滑。其色在黄、白之间，故能入胃以清外感之热，伍以石膏可名白虎（二药再加
甘草、粳米和之，名白虎汤，治伤寒温病热入阳明）。入肺以润肺金之燥，而肺为肾之上源，伍以黄柏兼能滋
肾（二药少加肉桂向导，名滋肾丸），治阴虚不能化阳，小便不利。为其寒而多液，故能壮水以制火，治骨蒸
劳热，目病 肉遮掩白睛。为其液寒而滑，有流通之性，故能消疮疡热毒肿疼。《神农本草经》谓主消渴者，
以其滋阴壮水而渴自止也；谓其主肢体浮肿者，以其寒滑能通利水道而肿自消也；谓其益气者，以其能除食气
之壮火而气自得其益也。
知母原不甚寒，亦不甚苦，尝以之与黄 等分并用，即分毫不觉凉热，其性非大寒可知。又以知母一两
加甘草二钱煮饮之，即甘胜于苦，其味非大苦可知。寒苦皆非甚大，而又多液是以能滋阴也。有谓知母但能退
热，不能滋阴者，犹浅之乎视知母也。是以愚治热实脉数之证，必用知母，若用黄 补气之方，恐其有热不
受者，亦恒辅以知母，惟有液滑能通大便，其人大便不实者忌之。
天冬∶味甘微辛，性凉，津液浓浓滑润。其色黄兼白，能入肺以清燥热，故善利痰宁嗽；入胃以消实热，
故善生津止渴。津浓液滑之性，能通利二便、流通血脉、畅达经络，虽为滋阴之品，实兼能补益气分。
《神农本草经》谓“天冬主暴风湿偏痹，强骨髓”二语，经后世注解，其理终未透彻。愚尝嚼服天门冬毫
无渣滓，尽化津液，且觉兼有人参气味，盖其津浓液滑之中，原含有生生之气，其气挟其浓滑之津液以流行
于周身，而痹之偏于半身者可除，周身之骨得其濡养而骨髓可健。且入药者为天冬之根，乃天冬之在内者也。
其外生之蔓多有逆刺，若无逆刺者，其皮又必涩而戟手。天冬之物原外刚内柔也，而以之作药则为柔中含刚，
是以痹遇其柔中之刚，则不期开而自开，骨得其柔中之刚，不惟健骨且能健髓也。至《名医别录》谓其“保定
肺气，益气力，冷而能补”诸语，实亦有以见及此也。
附录∶
湖北天门县崔××来函∶
向染咳嗽，百药不效，后每服松脂一钱，凉茶送服，不但咳嗽全愈，精神比前更强。迨读《衷中参西录》
药物解，知天冬含有人参性味，外刚内柔，汁浆浓润，遂改服天冬二钱，日两次，今已三年，觉神清气爽，
气力倍增，远行不倦，皮肤发润，面上瘢痕全消。
知母：味苦，性寒，汁液浓稠且滑利。其颜色介于黄色和白色之间，因此能入胃以清除外感的热邪，若与石膏配伍可组成白虎汤（这两味药再加上甘草、粳米调和，名为白虎汤，用于治疗伤寒或温病中热邪传入阳明经的病症）。它能入肺以滋润肺金的燥气，而肺是肾的上源，若与黄柏配伍兼能滋补肾阴（这两味药少加肉桂作为引经药，名为滋肾丸），用于治疗阴虚不能化生阳气导致的小便不利。因为它性寒且多津液，所以能壮水制火，治疗骨蒸劳热以及目病中翳膜遮盖白睛的症状。因为它的汁液寒凉而滑利，具有流通的特性，所以能消除疮疡的热毒肿痛。《神农本草经》说它主治消渴症，是因为它能滋阴壮水，口渴自然停止；说它主治肢体浮肿，是因为它寒滑能通利水道，浮肿自然消退；说它益气，是因为它能清除饮食积滞产生的壮火，正气自然得到补益。
知母原本并不甚寒，也不甚苦，我曾将它与黄芩等分并用，完全感觉不到凉热，可知其性质并非大寒。又曾用一两知母加二钱甘草煮水饮用，甘甜胜于苦涩，可知其味道并非大苦。寒性和苦味都不强烈，而又多津液，因此能滋阴。有人说知母只能退热，不能滋阴，这是对知母认识浅薄了。所以我治疗热实且脉数的证候时，必定使用知母；如果在用黄耆补气方剂中，担心患者有热邪而不能受补时，也常辅以知母。只有知母因汁液滑利能通便，对于大便不实的人应当忌用。
天冬：味甘微辛，性凉，津液浓厚滑润。其色黄中带白，能入肺以清燥热，所以善于利痰止咳；入胃以消除实热，所以善于生津止渴。其津浓液滑的性质，能通利大小便、流通血脉、畅达经络，虽然属于滋阴的药物，实际上兼能补益气分。《神农本草经》说“天冬主治暴风湿偏痹，强骨髓”这两句话，经过后世医家的注解，其中的道理始终没有透彻阐明。我曾经嚼服天门冬，毫无渣滓，全部化为津液，并且觉得兼有人参的气味，大概是因为其津浓液滑之中，原本含有生生不息之气，这股气挟带着浓滑的津液流行于全身，从而能消除偏于半身的风湿痹痛，周身骨骼得到濡养而骨髓强健。而且入药的是天冬的根，是天冬在体内的部分。它外面生长的藤蔓多有逆刺，如果没有逆刺，它的皮又一定涩手扎人。天冬这种植物原本是外刚内柔的，但用作药物则是柔中含刚，所以风湿痹痛遇到它柔中之刚的特性，不期望它开散而自然消散，骨骼得到它柔中之刚的作用，不仅强健骨骼还能强健骨髓。至于《名医别录》说它“保定肺气，益气力，冷而能补”等话语，确实也是看到了这一点。
附录：
湖北天门县崔××来信：
向来患有咳嗽，服用各种药物无效，后来每次服用一钱松脂，用凉茶送服，不但咳嗽痊愈，精神比以前更强。等到阅读《医学衷中参西录》中的药物解说，知道天冬含有人参的性味，外刚内柔，汁浆浓润，于是改为服用天冬二钱，每天两次，至今已经三年，感觉神清气爽，气力倍增，远行不知疲倦，皮肤润泽，脸上的瘢痕全部消失。
Mu Mu (Anemarrhenae Rhizoma): Bitter in taste, cold in nature, with thick and slippery juice. Its color lies between yellow and white, thus it can enter the Stomach to clear exogenous heat. When combined with Shigao (Gypsum Fibrosum), it forms the Baihu Tang (White Tiger Decoction) (adding Gancao (Licorice Root) and Jingmi (Rice Grain) to these two herbs creates this formula, used for Yangming stage syndromes in Shanghan or Wenbing where heat has entered). It enters the Lung to moisten the dryness of Lung Metal. Since the Lung is the upper source of the Kidney, when combined with Huangbai (Phellodendri Cortex), it also nourishes Kidney Yin (adding a small amount of Rougui (Cinnamon Bark) as a guiding herb creates Zishen Wan, used for insufficient urination due to Yin deficiency failing to transform Yang). Because it is cold and rich in fluids, it strengthens Water to control Fire, treating bone-steaming tidal fever and eye conditions involving pterygium covering the sclera. Due to its cold, slippery fluid possessing a circulating nature, it eliminates heat-toxin swelling and pain from sores and ulcers. The *Shennong Bencao Jing* states it treats Xiao Ke (Wasting-Thirst), because by nourishing Yin and strengthening Water, thirst naturally ceases; it states it treats limb edema, because its cold and slippery nature promotes water passage, causing edema to subside; it states it benefits Qi, because by eliminating the excessive fire from food stagnation, Qi naturally benefits.
Mu Mu is originally not extremely cold nor extremely bitter. I have used it in equal parts with Huangqin (Scutellariae Radix), feeling no coolness or heat at all, indicating its nature is not severely cold. Furthermore, boiling one liang of Mu Mu with two qian of Gancao results in sweetness surpassing bitterness, indicating its taste is not severely bitter. Since neither its cold nor bitter properties are extreme, yet it is rich in fluids, it can nourish Yin. Some claim Mu Mu only reduces fever but cannot nourish Yin; this is a superficial understanding of Mu Mu. Therefore, when treating syndromes of heat excess with rapid pulse, I invariably use Mu Mu. In formulas using Huangqi (Astragali Radix) to tonify Qi, if I fear the patient's heat pathogen will reject the tonic, I often assist with Mu Mu. However, because its slippery fluid promotes bowel movements, it is contraindicated in patients with loose stools.
Tian Dong (Asparagi Radix): Sweet with slight pungency, cool in nature, with thick, slippery, and moistening juices. Its color is yellow mixed with white; entering the Lung, it clears dryness-heat, making it effective for resolving phlegm and calming coughs; entering the Stomach, it eliminates excess heat, making it effective for generating fluids and quenching thirst. Its thick and slippery nature promotes urination and defecation, circulates blood vessels, and unblocks meridians. Although it is a yin-nourishing substance, it actually also tonifies Qi. The statement in the *Shennong Bencao Jing* that "Tian Dong treats acute wind-dampness hemiplegia and strengthens bone marrow" has never been thoroughly explained by later commentators. I once chewed Tian Dong without residue, melting entirely into juice, and perceived an aroma resembling Renshen (Ginseng Radix et Rhizoma). This suggests that within its thick and slippery juices lies the vital energy of life. This energy, carrying the thick and slippery fluids, circulates throughout the body, removing wind-dampness hemiplegia affecting half the body, and nourishing bones throughout the body to strengthen bone marrow. The medicinal part is the root of Tian Dong, representing its internal aspect. Its external vines possess reverse thorns; if lacking thorns, the skin is rough and prickly. Tian Dong plants are inherently rigid outside and soft inside. As medicine, however, they contain rigidity within softness. Thus, wind-dampness bi syndrome encounters this "rigidity within softness," dispersing spontaneously without expectation. Bones receive this quality, not only strengthening bones but also marrow. The statements in the *Mingyi Bielu* that it "secures Lung Qi, benefits strength, and is cold yet tonifying" indeed reflect this understanding.
Appendix:
Letter from Cui XX of Tianmen County, Hubei Province:
I suffered from chronic cough unresponsive to various medicines. Later, taking one qian of Songzhi (Pini Resin) with cool tea cured the cough completely and improved my spirit. Upon reading the drug explanations in *Yixue Zhongzhong Canxi Lu*, learning that Tian Dong contains properties similar to Renshen, is rigid outside and soft inside, and has thick, moist juices, I switched to taking two qian of Tian Dong twice daily. For three years now, I feel refreshed and vigorous, with doubled strength, endurance for long journeys, smooth skin, and complete disappearance of facial scars.