燥湿相对，燥湿所对应的气当然也应该相对。阳气聚敛收藏，则天气逐渐变冷；阳气聚敛收藏，则水不蒸腾，湿不氤氲，燥便随之而生。因此，燥的本性为凉，或者说燥气为凉。秋为什么主燥？秋气为什么会凉？道理就在这里。而整个春夏，阳气散发蒸腾，天气随之变温变热；而随着这个阳气的散发蒸腾，带着阴水往上走，这就形成了湿。所以，湿在《中基》里虽然定为阴邪，但，究其本性而言它是与温热相关的。这个道理大家不能不清楚，不能不明白。前面曾经说过，任何一个事物，你只要思考到了阴阳这个份上，那你就抓住了本质，你就不会动摇。任何人来你都不会动摇，就是黄帝、岐伯亲自来说你这个思考有问题，你也不会动摇！当然，要是黄帝、岐伯真的能够亲临，他看到你这个后生小子能够这样来思考问题，他会觉得孺子可教，他会赞叹都来不及。春夏为什么多湿？东南为什么多湿？根本的原因就在这里。以上我们说湿性本热，燥性本凉，这是从很根本的角度讲。从这个角度看，我们对苦何以燥湿，辛何以润燥，就能很好地理解。辛苦之性，《内经》已经作了很明确的定论，就是辛开苦降。开者开发阳气，降者降敛阳气。过去读本科的时候，学《中药》学到黄连、黄芩、黄柏的时候，这三味药都有一个共同的功用，就是“燥湿”。学《中药》是大学一年级的事，因此，这个问题在我脑海中一直困扰了十多年。《中基》明确告诉我们湿为阴邪，那么，祛除这个阴邪就必定要依靠阳的东西，这才符合治寒以热，治热以寒，治阳以阴，治阴以阳的基本原则。三黄是最苦寒的药，其性至阴，用这个三黄加在湿邪上，只能是雪上加霜，怎么能起到燥湿的作用呢？确实是百思不得其解。直到后来，十多年后，我开始学会用阴阳来思考问题，用阴阳来思考六气，这才发现困扰我十多年的问题原来是这么简单，这么清楚明白。苦寒不就是清热泻火吗？不就是降阳吗？不就是为了形成秋冬的这个格局吗？不就是为了拿掉湿的这个“显”旁吗？火热泻掉了，阳气敛降了，秋冬的格局形成了，显旁没有了，还有什么湿气可言。这才想到苦寒乃是治湿的正法。这才想到《素问》的“阴阳者，天地之道也，万物之纲纪，变化之父母，生杀之本始，神明之府也”是真正的“真实语”。这才感受到辛翁的“众里寻他千百度。蓦然回首，那人却在灯火阑珊处”是一个什么样的境界。苦寒燥湿的问题解决了，辛以润之就不再会成为困难。辛温何以润燥呢？辛温不就是为了鼓动阳气，蒸发阳气；辛温不就是为了形成春夏的格局；辛温不就是为了还湿的这个“显”傍。阳气鼓动了，蒸发了；春夏的格局产生了；显傍还原了，湿润自然产生，还有什么燥气可言。吴鞠通有一首治燥名方，叫杏苏散。这个方大家肯定学过，而且临床上会经常用到它。该方由苏叶，半夏，茯苓，前胡，桔梗，枳壳，甘草，生姜，大枣，橘皮，杏仁等十一味药组成。本科的时候背方歌，至今对前两句还有记忆，就是“杏苏散用夏陈前，枳桔苓甘姜枣研”，从杏苏散的这个组成，除了杏仁质润以外，其他的药物看不出什么润燥的成分，而且偏于辛温，可吴鞠通说它是润燥的。对杏苏散的这个方义，过去我也不甚理解，从《方剂》书去看，写《方剂》，讲《方剂》的这些人也未必就真正弄通了这个方润燥的实义。到后来燥的道理真正弄明白了，就知道这个方的确是一个润燥的方。杏苏散与小青龙汤，一为时方，一为经方，一者性缓，一者性猛，然二者有异曲同工之妙。记得先师在日曾治过一例咳嗽病人，患者女性，起病三年，每逢秋季即作咳嗽，咳则一二月方罢，西药中药皆不济事。至第四年上，患者到先师处求治，先师诊罢即云：此燥咳也，当守辛润之法，径处小青龙汤。服一剂咳止，连服三剂，随访数年皆未作秋咳。小青龙汤怎么润燥？我们只知道它是辛温之剂，我们只知道它能够治疗水气病，说它润燥，着实费解。然而一旦将它与燥的本义联系起来，就知道小青龙治燥一点也不足为奇。为什么叫青龙呢？青龙是兴云布雨的。云雨兴布以后，天还会燥吗？郑钦安于《医法圆通》一书中云：“阴阳务求实据，不可一味见头治头，见咳治咳，总要探求阴阳盈缩机关，与夫用药之从阴从阳变化法窍，而能明白了然，经方、时方，俱无拘执。久之，法活圆通，理精艺熟，头头是道，随拈二三味，皆是妙法奇方。”观先师以小青龙治燥咳，便知什么是“头头是道”了。学医贵乎明理，理精方能艺熟。大家在这个问题上应该很清楚，不要瞧不起基础理论，不要我们讲阴阳你就打瞌睡，而讲某某方治某某病你就来精神。理不精，艺怎么熟？理不精就不可能有活法圆通，就不可能头头是道。
前面我们讲燥与湿的本性，这个应该容易理解。因为你一把它放到自然的背景里，就很容易感受到。《素问》里面把燥邪又叫做清邪，治清以温；《难经》的广义伤寒在谈湿的时候它讲湿热而不讲寒湿，这就是从本性上言。本性是大局，是整体。但是，燥与湿还有另外的一个方面，这就是燥热与寒湿的问题。《易经》乾卦里有一句话叫“火就燥”，而《说卦》则云：“燥万物者莫熯乎火。”燥字的形符为什么用火呢？看来是与这个意义相应。本来我们前面说得好好的，是凉就燥，阳气收聚，天气转凉，气候就随之干燥。秋冬你到北方走一走，就知道这个“凉（寒）就燥”真实不虚。怎么现在突然转到“火就燥”，突然转到“燥万物者莫熯乎火”呢？这一点看起来很矛盾，看起来不容易说清。但，其实这是两回事，说开了还是能够弄清。火就燥，这个在我们日常生活中会经常碰到。潮湿的东西往火上一烤就慢慢变干了，因此，火就燥拿到生活经验中是很容易理解的。潮湿的东西放到火上很快就变干燥了，那么，这个东西里原有的水分、原有的湿到哪里去了呢？是不是火把它消灭掉了？我想火还没有这个功能。我们在农村烧湿柴的时候就会发现，火一烧水就出来了，所以，火本身并不能把水湿消灭掉，只是把水蒸走而已。我们要是把一件刚刚洗过的湿衣用火烤干，就会看到湿气在蒸腾，如果这个时候我们把门窗都关闭起来，过不了多久，就会发现窗户上的串串水珠。因此，火的功能只是把这个水，把这个潮湿转移了，转移到另外的地方，转移到离火远一些的地方。所以，这个地方干了，那个地方就会潮湿。火就燥，就者近也，离火近的地方干燥，那必然离火远的地方潮湿。因此，燥热我们应该这样来理解，它讲的是局部的情况，它讲的是标，不是本。从这个火就燥亦使我们联想到一个全球关注的问题，现在全球的气温不断升高，北极的冰川以前所未有的速度在日渐融化，是什么原因造成这个现状呢？很显然与温室气体的日益大量地排放有关。我们现在的空调，我们现在的制冷设备，是不是真能将热变冷呢？完全不是这么回事。它只不过是将此地的热转到彼地去了，转到大气中去了。这绝对是一种拆东墙补西墙的做法。所以，空调冷气越多，大气温度必然越高。而大气温度越高，使用空调冷气的时候就会越多。因此，这是一个难以避免的恶性循环。从上面这个火就燥我们应该知道，火热到哪里，燥就到哪里。温病讲卫气营血辨证，热一入营到血，就会引起血热，血热就会导致血燥，血燥就要生风。这是就血这个局部而言，火热不入血，血燥必定不会发生，必须有血热这个前提，血燥才能发生。因此，血燥这个概念不是随便就能用的，血虚并不等于血燥，这一点大家要弄清楚。前面讲治燥我们提到一个杏苏散，与杏苏散相对应的还有一个桑杏汤。桑杏汤由桑叶，杏仁，沙参，浙贝，豆豉，栀子，梨皮等药组成。该方的气味正好与杏苏散相反，它所对治的就是这个“火就燥”，这个燥热。对付这个燥比较简单，首先就是要拿掉火，让物远离火，不就火，自然就没有燥，这就需要清热。另外一个方面，已经被火蒸干了的水分我们需要补充，所以，还要养阴。一个清火，一个养阴，这就达到了润燥的目的。一个辛温润燥，一个甘寒润燥，虽然都是润燥，但方法却截然相反。这个问题很值得我们细心地去琢磨，细心地去思考。思考清楚了，琢磨清楚了，那我们在阴阳的思维里又大大地前进了一步。
接下来我们看寒湿的问题，前面我们已经讨论过湿性本热，所以，要祛湿就必须清热。温病讲湿去热孤，其实这个问题我们完全可以反过来看，热去湿亦孤。在春夏的回南天里，空气非常闷热，地下都是湿兮兮的，用什么办法防潮都不济事，可是一旦天气转北，北风一吹，气转凉爽，地面便立马变干。为什么北风一刮便干，南风越吹越湿呢？因为北风带来的是寒是降，南风带来的是热是升。从这个角度我们很容易理解湿，很容易理解如何燥湿。可现在一转到寒湿上来，治湿不但不能用苦寒，反过来还要用苦温苦热，这个弯好像一下转不过来。其实这个问题要与前面的燥热联系起来看，既然燥与湿是相对的，这个相对是从本性上言。那么，在标性上燥湿也应该相对。燥的标性是热，湿的标性是寒。所以，燥热与寒湿亦相对应。这个对应关系一建立，我们就知道潮湿的东西一近火就变干燥，这个过程就是燥湿的过程。这个潮湿就是寒湿。火就燥，火味苦，其性热。因此，以苦温苦热来化湿燥湿，其实就是讲的这个“火就燥”的过程。“火就燥”其实谈的是两个问题，一个是燥热形成的过程，一个是寒湿的治疗过程。对于燥热与寒湿应该可以这样来思考。
（5）阳明病之燥
Dryness and dampness are relative concepts; therefore, the Qi corresponding to dryness and dampness must also be relative. When Yang Qi converges and stores, the weather gradually becomes cold; when Yang Qi converges and stores, water fails to evaporate, and dampness fails to permeate, so dryness arises accordingly. Thus, the intrinsic nature of dryness is cool, or one may say that Dryness Qi is cool. Why does Autumn govern dryness? Why is the Qi of Autumn cool? The reason lies here. In contrast, throughout Spring and Summer, Yang Qi disperses and evaporates, causing the weather to become warm and hot; with this dispersion and evaporation of Yang Qi, Yin Water is carried upward, thus forming dampness. Therefore, although Dampness is classified as a Yin pathogen in Basic Theory of Traditional Chinese Medicine (TCM), its intrinsic nature is actually related to warmth and heat. Everyone must clearly understand this principle. As mentioned earlier, for any phenomenon, once you contemplate it at the level of Yin and Yang, you grasp its essence and will not be shaken. No matter who questions you, even if Huangdi (Yellow Emperor) and Qibo personally come to say your thinking is flawed, you will not waver! Of course, if Huangdi and Qibo were truly present, seeing a young scholar think in this manner, they would find him teachable and unable to express their praise enough. Why are there many cases of dampness in Spring and Summer? Why is the Southeast region prone to dampness? The root cause lies here. Above, we discussed from a fundamental perspective that the nature of dampness is warm/heat, while the nature of dryness is cool. From this perspective, we can well understand why "Bitter flavors can dry dampness" and "Acrid flavors can moisten dryness." The Neijing (Classic of Internal Canon) has already made a clear conclusion regarding the properties of Acrid and Bitter flavors: "Acrid opens, Bitter descends." Opening refers to developing Yang Qi; descending refers to gathering/converging Yang Qi. During my undergraduate studies, when learning Materia Medica about Coptis Rhizome (Huanglian), Scutellaria Root (Huangqin), and Phellodendron Bark (Huangbai), these three herbs shared a common function: "drying dampness." Since studying Materia Medica was a first-year university activity, this issue troubled me for over ten years. Basic Theory explicitly tells us that dampness is a Yin pathogen; therefore, dispelling this Yin pathogen must rely on Yang substances, which conforms to the basic principles of "treating cold with heat, treating heat with cold, treating Yang with Yin, and treating Yin with Yang." Sanhuang (the Three Yellows: Coptis Rhizome, Scutellaria Root, and Phellodendron Bark) are the most bitter and cold herbs, possessing extreme Yin nature. Using these three herbs against a damp pathogen would only add frost to snow; how could they achieve the effect of drying dampness? I indeed pondered this endlessly without solution. It was only later, more than ten years after, when I began to learn to think using Yin and Yang, and to consider the Six Qi through the lens of Yin and Yang, that I discovered the problem troubling me for over a decade was actually so simple and clear. Is Bitter-Cold not clearing heat and purging fire? Is it not descending Yang? Is it not aiming to form the pattern of Autumn and Winter? Is it not removing the "Xian" radical from the character for dampness? Once fire-heat is purged, Yang Qi gathers and descends, the pattern of Autumn and Winter is formed, and the "Xian" radical disappears, what dampness remains? Only then did I realize that Bitter-Cold is indeed the orthodox method for treating dampness. Only then did I feel that the statement in Suwen (Basic Questions): "Yin and Yang are the Way of Heaven and Earth, the general discipline of all things, the parents of changes, the origin of life and death, and the mansion of spiritual brilliance" is true truth. I also came to appreciate the realm described by Sun Ranweng: "I searched for her in the crowd a thousand times. Suddenly looking back, there she was, where the lantern light was dim." With the problem of Bitter-Cold drying dampness resolved, Acrid moistening dryness no longer poses a difficulty. How can Acrid-Warmth moisten dryness? Is Acrid-Warmth not meant to stir and evaporate Yang Qi? Is it not meant to form the pattern of Spring and Summer? Is it not meant to restore the "Xian" radical to the character for dampness? When Yang Qi is stirred and evaporated; when the pattern of Spring and Summer is generated; when the "Xian" radical is restored, moisture naturally arises, and what dryness remains? Wu Jutong created a famous formula for treating dryness called Xing Su San (Apricot and Perilla Powder). Everyone must have studied this formula, and it is frequently used in clinical practice. This formula consists of eleven herbs: Perilla Leaf (Zi Su Ye), Pinellia Tuber (Ban Xia), Poria (Fu Ling), Peucedanum Root (Qian Hu), Platycodon Root (Jie Geng), Aurantium Fruit (Zhi Ke), Licorice Root (Gan Cao), Fresh Ginger (Sheng Jiang), Jujube (Da Zao), Tangerine Peel (Chen Pi), and Apricot Seed (Xing Ren). During undergraduate studies, memorizing the formula song, I still remember the first two lines: "Xing Su San uses Ban Xia, Chen Pi, and Qian Hu; Zhi Ke, Jie Geng, Fu Ling, Gan Cao, Sheng Jiang, and Da Zao are ground together." Looking at the composition of Xing Su San, except for the moistening quality of Apricot Seed, other herbs show no obvious moistening components and lean towards Acrid-Warmth, yet Wu Jutong claims it moistens dryness. I previously did not fully understand the rationale of Xing Su San; those who wrote and taught Formulae (Fang Ji) might not have truly grasped the actual meaning of its moistening action either. Later, once I truly understood the principle of dryness, I knew this formula was indeed a moistening one. Xing Su San and Xiao Qing Long Tang (Minor Green Dragon Decoction), one being a contemporary formula and the other an ancient classic formula, one having a mild nature and the other a fierce nature, nevertheless share similar efficacy through different methods. I recall my late master once treated a female patient suffering from cough for three years, which occurred every autumn and lasted for one or two months before subsiding; neither Western nor Chinese medicines were effective. In the fourth year, she sought treatment from my master. After diagnosis, he said: "This is dryness-cough; adhere to the method of Acrid-Moistening, prescribe Xiao Qing Long Tang directly." One dose stopped the cough; after three consecutive doses, follow-up over several years showed no recurrence of autumn cough. How does Xiao Qing Long Tang moisten dryness? We only know it is an Acrid-Warm formula and that it treats fluid retention diseases; claiming it moistens dryness is indeed puzzling. However, once linked to the intrinsic meaning of dryness, it is not surprising that Xiao Qing Long Tang treats dryness. Why is it called Qing Long (Azure Dragon)? The Azure Dragon brings clouds and rain. Once clouds and rain are generated, can the sky still be dry? Zheng Qin'an stated in Yi Fa Yuan Tong (Round Communication of Medical Methods): "Regarding Yin and Yang, seek real evidence; do not merely treat the head when there is a headache or the cough when there is a cough. Always explore the mechanisms of Yin-Yang fullness and emptiness, and the techniques of medication following Yin or Yang transformations. Once understood clearly, both classic and contemporary formulas can be applied without rigid adherence. Over time, methods become flexible and comprehensive, principles refined and skills mature, everything proceeds logically, and picking just two or three herbs constitutes a wonderful and miraculous prescription." Observing my master use Xiao Qing Long Tang for dryness-cough reveals what "everything proceeding logically" means. Learning medicine values understanding principles; only with refined principles can skills mature. Everyone should be clear on this issue: do not look down on basic theory. Do not fall asleep when discussing Yin and Yang but perk up when hearing about specific formulas treating specific diseases. If principles are not refined, how can skills mature? Without refined principles, there can be no flexible application of methods, nor can one achieve logical consistency.
(4) Dryness-Heat and Cold-Dampness
Previously, we discussed the intrinsic nature of dryness and dampness, which should be easy to understand. Placing them in a natural context makes them easily perceptible. In Suwen, the Dryness pathogen is also called Clear Qi (Qing Xie), and "treat Clear with Warmth"; in Nan Jing (Classic of Difficult Issues), when discussing dampness in the context of generalized Shanghan (Cold Damage), it mentions Damp-Heat rather than Cold-Dampness. This speaks to the intrinsic nature. Intrinsic nature refers to the big picture, the whole. However, dryness and dampness have another aspect: Dryness-Heat and Cold-Dampness. A sentence in the Qian Gua of Yi Jing (Book of Changes) says "Fire approaches dryness," and Shuo Gua Zhuan (Commentary on the Trigrams) states: "Nothing dries things more fiercely than Fire." Why does the radical for the character "dry" use Fire? It seems corresponding to this meaning. Previously, we stated well that coolness leads to dryness; Yang Qi gathers, weather turns cool, and climate becomes dry accordingly. Traveling north in Autumn and Winter confirms that "cool/cold leads to dryness" is truly valid. Why suddenly shift to "Fire approaches dryness" and "Nothing dries things more fiercely than Fire"? This appears contradictory and difficult to explain. Yet, these are two different matters; explained clearly, they can be understood. "Fire approaches dryness" is commonly encountered in daily life. Wet items placed near fire slowly become dry; thus, "Fire approaches dryness" is easily understood through empirical experience. Wet items placed on fire quickly become dry; so, where do the original moisture and dampness go? Did fire destroy them? I doubt fire has such a function. Burning wet firewood in rural areas shows that when fire burns, water emerges; thus, fire itself cannot eliminate water/dampness but merely evaporates it. If we dry a freshly washed wet garment with fire, we see moisture steaming off. If windows and doors are closed, water droplets will soon appear on the glass. Therefore, fire's function is merely to transfer this water/moisture to another place, further away from the fire. Consequently, where it is dry, elsewhere becomes damp. "Fire approaches dryness": "approaches" means near. Places near fire become dry; necessarily, places far from fire become damp. Thus, Dryness-Heat should be understood as describing local conditions, the manifestation (Biao), not the root (Ben). From "Fire approaches dryness," we also associate with a globally concerned issue: global temperatures are rising, and Arctic glaciers are melting at unprecedented rates. What causes this? Clearly, it relates to the increasing emission of greenhouse gases. Do our current air conditioners and refrigeration equipment truly convert heat to cold? Not at all. They merely transfer heat from one place to another, into the atmosphere. This is absolutely a case of robbing Peter to pay Paul. Therefore, the more air conditioning cold air produced, the higher the atmospheric temperature becomes. And the higher the atmospheric temperature, the more air conditioning is used. Thus, this is an unavoidable vicious cycle. From "Fire approaches dryness," we should know: wherever fire-heat goes, dryness follows. In Warm Disease theory, regarding Wei-Qi-Ying-Blood differentiation, once heat enters Ying and Blood levels, it causes Blood Heat; Blood Heat leads to Blood Dryness; Blood Dryness generates Wind. This refers to the local aspect of blood. If fire-heat does not enter the blood, Blood Dryness will certainly not occur; Blood Heat is a prerequisite for Blood Dryness. Therefore, the concept of Blood Dryness cannot be used casually; Blood Deficiency does not equal Blood Dryness; everyone must clarify this. Earlier, when discussing treating dryness, we mentioned Xing Su San; corresponding to it is Sang Xing Tang (Mulberry Leaf and Apricot Kernel Decoction). Sang Xing Tang consists of Mulberry Leaf (Sang Ye), Apricot Seed (Xing Ren), Glehnia Root (Shashen), Zhejiang Fritillary Bulb (Zhe Bei Mu), Fermented Soybean (Dou Chi), Gardenia Fruit (Zhi Zi), and Pear Skin (Li Pi). Its aroma and flavor are exactly opposite to Xing Su San, and it treats this "Fire approaches dryness," i.e., Dryness-Heat. Treating this type of dryness is relatively simple: first, remove the fire, keep objects away from fire, do not approach fire, and naturally there is no dryness; this requires clearing heat. Secondly, we need to replenish the moisture evaporated by fire, so nourishing Yin is necessary. One clears fire, one nourishes Yin; this achieves the goal of moistening dryness. One uses Acrid-Warmth to moisten dryness, the other uses Sweet-Cold to moisten dryness; although both moisten dryness, the methods are diametrically opposed. This issue deserves careful consideration and contemplation. Thinking it through thoroughly represents a significant advance in Yin-Yang thinking.
Next, let us look at Cold-Dampness. We previously discussed that the intrinsic nature of dampness is warm/heat; therefore, dispelling dampness requires clearing heat. Warm Disease theory states "when dampness is removed, heat stands alone"; conversely, "when heat is removed, dampness stands alone." During the humid "return of the south wind" days in Spring and Summer, the air is muggy and the ground is wet; no anti-dampness measure works. However, once the weather shifts northward and the North Wind blows, bringing cooler air, the ground dries immediately. Why does the North Wind bring dryness while the South Wind increases dampness? Because the North Wind brings Cold and descent, while the South Wind brings Heat and ascent. From this angle, it is easy to understand dampness and how to dry it. But now turning to Cold-Dampness, treating dampness requires not Bitter-Cold but Bitter-Warmth and Bitter-Heat; this turn seems hard to accept. Actually, this issue should be viewed in connection with Dryness-Heat. Since dryness and dampness are relative, this relativity is based on intrinsic nature. Then, on the level of manifested nature (Biao), dryness and dampness should also be relative. The manifested nature of dryness is Heat; the manifested nature of dampness is Cold. Thus, Dryness-Heat and Cold-Dampness correspond. Establishing this correspondence, we know that wet things become dry when near fire; this process is drying dampness. This wetness is Cold-Dampness. Fire approaches dryness; Fire tastes Bitter and is Hot in nature. Therefore, using Bitter-Warmth and Bitter-Heat to transform and dry dampness essentially describes the process of "Fire approaches dryness." "Fire approaches dryness" actually discusses two issues: one is the formation process of Dryness-Heat, and the other is the treatment process of Cold-Dampness. Dryness-Heat and Cold-Dampness can be contemplated in this manner.
(5) Dryness in Yangming Disease