二阳者，足阳明胃、手阳明大肠也。其病发于心脾，盖因思为脾志，而实本于心。其始也，有不得于隐曲之事，于
是思则气结，郁而为火，以致心营暗耗，既不能下交于肾，脾土郁结，又转而克肾，是以男予少精，女子不月，无非肾
燥而血液干枯也。且夫脾有郁火，则表里相传，胃津亦涸；大肠为胃之传道，故并大肠而亦病也。此二阳之病，当以燥
火之证言，在胃则为消、为格，在肠则为闭、为鞭；至于胃腑既燥，而脾无以行其津液，则为风消。风消者、火甚而生
风，脾惫而肌肉消削也。大肠之燥传入于肺，则为息奔。息奔者，息有音而上奔不下也。四脏二腑交相燔灼，阴液尽耗，
故直断为“死不治”。昔王安道以肠胃有病，延及心、脾，颠倒其说，于“不得隐曲”之故，阙而未洋。喻嘉言阐发稍明，
亦但言其所当然，而未穷其所以然，故更详之。
《二十九难》曰∶“阳维为病苦寒热，阴维为病苦心痛”。越人但有是说，而无治法，后人以桂枝汤为治，可谓中肯。
盖“阳维维于阳”，属于卫也，故为寒热；“阴维维于阴”，属于营也，故为心痛。桂枝汤有和营卫，调阴阳之力，适合比
例以治也。
自有轩、岐、越人以来，着书立说者，不下数百家，而久推张、刘、李、朱为四大家者，盖以仲景首论伤寒，立法
立方，实为医祖。守真复以春温夏热立言，补仲景之未备。东垣详辨脾胃内伤，与外感悬殊，又补张、刘之未备。丹溪
又专论补阴，再补东垣之未备。各有见地，迭为补阀，已有李士材论之晓畅矣。而余谓言外感者张、刘，言内伤者李、
朱，似乎备矣，而实有未尽。明之薛立斋，谓十三科一理，慨外科固执成方，不穷病本，特发内外合一之论；又以风会
不齐，今人虚薄，痛戒寒凉，多行温补，此又补丹溪之未备，而扩人胸臆者。由是张景岳、李士材辈，着述颇行，实皆
立斋之余韵也。虽然，内伤诸症，脾胃独详于李氏，阴阳分擅于朱、薛，可谓无遗蕴矣。而外感风寒温热之外，尚有夏
月直受暑邪者，虽洁古、东垣辈以动静分阴阳，似属近理，自有张凤逵申明伤暑之理蕴，特着《全书》，可云见老。复有
喻嘉言，不独从仲景书中悟出冬温、春温、伏气为病，于千百年无人道破之书，一旦揭其微义，诚为暗中一大炬；更悟
出秋燥一门，指破《内经》秋伤于湿”之误，可称千古只眼，至此而天之六气，方云大备。更有不关六气，而亦属外受
之疫邪，诸书中虽亦有所阐发，而莫如吴又可直穷变态，反复详明，此又于讲求外感诸家，补其未备者也。其外载
籍充栋，纵各有可采之论，可传之方，无论醇于此者疵于彼，难称完壁，即有腹筒广博，卷帙充盈者，要不及薛、张、
吴、喻四先生，各开生面，以补张、刘、李、朱之阙也，读其书，不敢没其功，故特以八大家推之。
二阳，指的是足阳明胃经和手阳明大肠经。这两条经络的病变发源于心和脾，这是因为“思”是脾的情志表现，但其根本实际上在于心。起初，是因为在隐秘曲折的事情上有所不得志，于是产生思虑导致气机郁结，郁久化火，致使心之营血暗中消耗，既不能下行与肾相交，脾土因郁结而反过来克制肾水，因此男子出现精少，女子月经闭止，无非是肾燥而血液干枯所致。况且脾有郁火，就会表里相传，导致胃津枯竭；大肠作为胃传导糟粕的腑，所以也一并发病。这种二阳的病变，应当从燥火的证候来论述：在胃则表现为消渴、格拒（饮食不下），在肠则表现为便秘、大便干硬；至于胃腑已经干燥，脾无法运化输布津液，就会形成风消。所谓风消，就是火势极盛而生风，脾脏疲惫而导致肌肉消瘦。大肠的燥热传入肺脏，就会形成息奔。所谓息奔，就是呼吸有声且气逆上冲而不能下行。五脏中的四脏与两个腑相互燔灼，阴液完全耗竭，所以直接断定为“死不治”。过去王安道认为肠胃有病延及心、脾，颠倒了因果关系，对于“不得隐曲”的原因，遗漏而未阐明。喻嘉言阐发得稍为明白，但也只说了其必然性，而没有穷究其所以然的原因，所以我对此进行更详细的阐述。
《难经·二十九难》说：“阳维脉为病使人恶寒发热，阴维脉为病使人心中疼痛。”越人（扁鹊）只有这一说法，而没有治疗方法，后人用桂枝汤来治疗，可以说切中肯綮。因为“阳维维系于阳”，属于卫分，所以表现为寒热；“阴维维系于阴”，属于营分，所以表现为心痛。桂枝汤具有调和营卫、调理阴阳的功效，比例适宜，适合用来治疗。
自从轩辕、岐伯、扁鹊以来，著书立说的人，不下数百家，而长久推崇张仲景、刘完素、李东垣、朱丹溪为四大家，大概是因为仲景首先论述伤寒，确立法则和方剂，实为医学始祖。守真（刘完素）又根据春温夏热的理论立论，补充了仲景未完备之处。东垣（李杲）详细辨析脾胃内伤与外感病的显著差异，又补充了张、刘二人未完备之处。丹溪（朱震亨）又专门论述补阴，再次补充了东垣未完备之处。他们各有见解，互相补充阙漏，已有李士材论述得清晰透彻了。然而我认为，如果说谈论外感的是张、刘，谈论内伤的是李、朱，似乎已经很完备了，但实际上仍有未尽之处。明代的薛立斋，认为十三科医理相通，感慨外科医生固执于成方，不探究疾病本源，特别提出了内外合一的理论；又因为风气不同，现代人身体虚弱单薄，痛斥寒凉药物，多采用温补疗法，这又补充了丹溪未完备之处，开阔了人们的视野。由此张景岳、李士材等人，著作颇为流行，其实都是薛立斋学说的余绪。虽然如此，在内伤诸症方面，脾胃病唯独李氏论述详尽，阴阳辨证分别擅长于朱、薛两家，可以说是没有遗漏了。但是在外感风寒温热之外，还有夏季直接感受暑邪的情况，虽然洁古（张元素）、东垣等人以动静区分阴阳，似乎合乎道理，但自有张凤逵申明伤暑的道理，特意撰写《全书》，可以称为见识老练。又有喻嘉言，不仅从仲景书中领悟出冬温、春温、伏气致病，在千百年无人点破的书籍中，一旦揭示其微妙的义理，诚如黑暗中的一大火炬；更领悟出秋燥这一门类，指出《内经》中“秋伤于湿”的错误，可称为千古独到的眼光，至此，天的六气理论才算大大完备。此外，有不涉及六气，但也属于外受疫邪的疾病，各种书籍中虽有阐发，但不如吴又可直接穷究其变化，反复详明，这又在研究外感的各家之中，补充了其未完备之处。其余典籍堆积如山，纵然各有可取的理论和可传的方剂，无论在此处精醇则在彼处有瑕疵，难以称为完美无缺，即使有学识广博、卷帙浩繁者，总不如薛、张、吴、喻四位先生，各自开创局面，以补充张、刘、李、朱四大家的阙漏，阅读他们的书籍，不敢埋没他们的功劳，所以特别将他们推举为八大家。
Er Yang (Two Yangs), refers to the Foot-Yangming Stomach Meridian and the Hand-Yangming Large Intestine Meridian. Diseases of these two meridians originate from the Heart and Spleen, because "pensive thinking" (Si) is the emotional manifestation of the Spleen, yet its root actually lies in the Heart. Initially, it stems from frustration regarding matters that are difficult to disclose or resolve privately. Consequently, pensive thinking causes Qi stagnation, which condenses into Fire, leading to the secret consumption of Ying Blood (Nutritive Blood) of the Heart. This prevents the Heart Fire from descending to interact with the Kidney Water. Meanwhile, Spleen Earth becomes stagnant and counter-attacks Kidney Water. Thus, men suffer from scanty essence, and women experience amenorrhea (absence of menstruation). This is essentially due to Kidney dryness and the desiccation of blood and fluids. Furthermore, if the Spleen has stagnant Fire, it transmits between the interior and exterior, causing Stomach Jin Ye (Body Fluids) to dry up. Since the Large Intestine serves as the conduit for the Stomach's transmission of waste, it also becomes diseased. These Er Yang diseases should be discussed in terms of Dryness-Fire syndromes: in the Stomach, they manifest as Xiao Ke (Wasting-Thirst/Consumption) and Ge Ju (Regurgitation/Inability to swallow); in the Intestines, they manifest as Bi Mi (Constipation) and Bian Bian (Hard stools). When the Stomach Fu organ is already dry, and the Spleen cannot transport and distribute Jin Ye, Feng Xiao (Wind Consumption) occurs. Feng Xiao means that excessive Fire generates Wind, exhausting the Spleen and causing muscle emaciation. If the Dryness of the Large Intestine transmits to the Lung, Xi Ben (Panting with Rushing Breath) occurs. Xi Ben refers to breathing accompanied by sounds and upward rushing of Qi that fails to descend. With four Zang organs and two Fu organs burning each other mutually, Yin fluids are completely exhausted; therefore, it is directly judged as "incurable death." In the past, Wang Andao argued that diseases of the intestines and stomach extended to the Heart and Spleen, reversing the causal relationship, and omitted an explanation for the cause of "frustration regarding private matters." Yu Jiayan elucidated this somewhat clearly but only stated what must happen, without exploring the underlying reasons; thus, I elaborate further here.
The *Nan Jing* (Classic of Difficult Issues), Difficulty 29, states: "Diseases of the Yang Wei Mai (Yang Linking Vessel) cause aversion to cold and fever; diseases of the Yin Wei Mai (Yin Linking Vessel) cause heart pain." Yue Ren (Bian Que) provided only this description without treatment methods. Later practitioners used Gui Zhi Tang (Cinnamon Twig Decoction) for treatment, which can be considered hitting the mark accurately. Because "Yang Wei links with Yang," it belongs to the Wei Qi (Defensive Qi) level, hence presenting with chills and fever; "Yin Wei links with Yin," it belongs to the Ying Qi (Nutritive Qi) level, hence presenting with heart pain. Gui Zhi Tang possesses the power to harmonize Ying and Wei Qi and regulate Yin and Yang, making it suitable for treating this condition when used in appropriate proportions.
Since the times of Xuanyuan (Yellow Emperor) and Qibo, there have been hundreds of authors writing books and establishing theories. Long revered as the Four Great Masters are Zhang Zhongjing, Liu Wansu, Li Dongyuan, and Zhu Danxi. This is largely because Zhongjing first discussed Shang Han (Cold Damage), establishing laws and formulas, truly serving as the Ancestor of Medicine. Shouzhen (Liu Wansu) further established theories based on Spring Warmth and Summer Heat, supplementing what Zhongjing left incomplete. Dongyuan (Li Gao) detailed the distinction between Pi Wei (Spleen and Stomach) internal injury and external contraction, supplementing what Zhang and Liu left incomplete. Danxi (Zhu Zhenheng) specialized in tonifying Yin, again supplementing what Dongyuan left incomplete. Each had their own insights, complementing each other's omissions, a point already clearly explained by Li Shicai. However, I argue that while saying Zhang and Liu discuss external contractions, and Li and Zhu discuss internal injuries, seems comprehensive, it is not entirely so. Xue Lizhai of the Ming Dynasty asserted that the principles of thirteen medical departments are unified. He lamented that surgeons stubbornly adhered to fixed prescriptions without investigating the root of diseases, specifically proposing the theory of unity between internal and external medicine. Furthermore, noting that conditions vary and modern people are physically weak and deficient, he strongly criticized cooling drugs and advocated warm tonification. This supplemented what Danxi left incomplete and broadened perspectives. Consequently, works by Zhang Jingyue and Li Shicai became popular, being essentially extensions of Xue Lizhai's legacy. Although internal injury syndromes were detailed uniquely by Li regarding the Spleen and Stomach, and by Zhu and Xue regarding Yin-Yang differentiation, leaving little unexplored, there remains the issue of direct summer heat pathogenic factors contracted in summer. Although Jiegu (Zhang Yuansu) and Dongyuan distinguished Yin and Yang via movement and stillness, which seemed reasonable, it was Zhang Fengkui who clarified the principles of summer heat damage, specifically authoring the *Quan Shu*, demonstrating profound insight. Additionally, Yu Jiayan not only deduced winter warmth, spring warmth, and latent qi diseases from Zhongjing's texts, revealing hidden meanings in books untouched for millennia like a torch in the dark, but also identified the category of Autumn Dryness, pointing out the error in the *Nei Jing*'s statement "Autumn damages with Dampness." This can be called a unique vision through the ages; thus, the theory of Heaven's Six Qi became fully complete. Moreover, beyond the Six Qi, there are epidemic pathogens contracted externally. While various books elaborated on these, none explored their transformations as thoroughly and explicitly as Wu Keyou, thereby supplementing the deficiencies of previous scholars studying external contractions. Other literature is piled high like beams; although each contains valuable theories and effective prescriptions, no work is perfect without flaws elsewhere. Even those with vast knowledge and numerous volumes do not surpass the four masters—Xue, Zhang, Wu, and Yu—who each opened new avenues to fill the gaps of Zhang, Liu, Li, and Zhu. Reading their works, one dare not overlook their merits; therefore, I specifically promote them as the Eight Great Masters.