经曰。重阴必阳。重阳必阴。瘴病之作。天气热而人身亦热。上多燥渴。心胸烦热。是重阳也。
而鼻尖凉。腰足冷痛。是阴寓于其中也。又寒极生热。热极生寒。故瘴之始作也。必大热。及其病
退也。身无尺寸之肤下如冰冷。医者不知此理。见其发热烦躁舌黑面红目赤脉数便以为大热之症。
用苦寒降药。如黄芩黄连栀子黄柏知母之属。愈投愈剧。连服数剂。则上热未降。中寒作。或变
。或痰滞。或发哕。或手足梢冷厥而泄。诸症一起。百无一生。又有甚者。见其烦躁引饮。而用
白虎汤石膏汤见其舌。黑大便秘小便赤。而用大柴胡汤承气汤。此药下咽或即发狂而毙。或即痰
滞而卒。顷刻危亡。是知瘴病未必遽能危人。医危之也。苦寒降药。如天花粉木通滑石车前子元
参连翘元明粉
生地黄之类。亦不可轻用。医者审之。庶不误人。
或曰。瘴病因于脾胃虚寒。外感乖戾之气而成。而治法必先正气和解。所用正气散养胃汤
不换金和解散诸方。俱有平胃散在内。盖平胃散古人用以治脾胃敦阜。有削平之义。故曰平胃。
非补脾胃药。何又用之。况瘴病脉弦。脉弦而服平胃散。又犯东垣虚虚之戒何也。予曰发瘴之地。
其地多山。其土卑薄。方其晴明。天气热蒸。地下生水。及其阴雨。地下多湿。人生其间。常
履于湿土之上。经曰谷气通于脾。湿伤脾内。故脾胃之虚。多由阳气浮于上。阴湿之气伤于下而然。
非若内伤之主于饮食劳倦也。用平胃以去脾湿。胡为不可。中有苍术之燥湿。不闭腠理。使汗易出。
陈皮之消痰下气。川朴温中下气理痰消食。甘草之调中气。益脾胃。故李待制选。以为治瘴要药也。
若谓脉弦在
内伤。谓肝木克脾土。宜补脾抑肝。不宜去湿。故犯虚虚之戒。不知瘴病脉弦。是疟脉自弦之弦。
为邪在半表半里。因湿生痰而作。故不禁平胃。正欲其温中去湿也。
《黄帝内经》说：阴气重到极点就会转化为阳，阳气重到极点就会转化为阴。瘴病发作时，天气炎热，人体内部也发热，上部多见燥渴、心胸烦热，这是“重阳”的表现；而鼻尖发凉，腰部和足部冷痛，说明阴寒之邪潜伏在其中。另外，寒气极盛则生热，热势极盛则生寒。所以瘴病刚开始发作时，必定是大热；等到病情看似减退时，全身皮肤摸起来却像冰一样冷。医生如果不明白这个道理，看到患者发热、烦躁、舌苔黑、面色红、眼睛红赤、脉搏快，就认为是大热证，使用黄芩、黄连、栀子、黄柏、知母等苦寒性质的降火药。结果越用药病情越严重，连续服用几剂后，上部的热邪没有降下来，中焦的寒邪却产生了，或者出现变证，或者痰湿停滞，或者发生呃逆（打嗝），或者手足末端冰冷厥逆并伴有腹泻。各种症状一起出现，病人几乎没有存活的希望。更有甚者，看到患者烦躁且大量饮水，就使用白虎汤或石膏汤；看到患者舌苔黑、大便秘结、小便赤黄，就使用大柴胡汤或承气汤。这些药物服下后，有的立即发狂而死，有的立即因痰湿阻滞而猝死，顷刻间危及生命。由此可见，瘴病未必能立刻致命，是医生治死了它。天花粉、木通、滑石、车前子、玄参、连翘、元明粉、生地黄等苦寒降火药，也不可轻易使用。医生们务必审慎，以免误人性命。
有人问：瘴病是因为脾胃虚寒，外感乖戾不正之气而形成的。治疗法则应当先扶助正气、调和机体。所用的正气散、养胃汤、不换金正气散等方剂，都含有平胃散在内。大概平胃散是古人用来治疗脾胃敦厚壅滞（指脾胃运化失常导致的痞满）的，有削平壅滞的意思，所以叫“平胃”，它并不是补益脾胃的药，为什么又要用它呢？况且瘴病患者脉象弦，脉弦而服用平胃散，又犯了李东垣所说的“虚虚”（使虚者更虚）的禁忌，这是为什么呢？我回答说：发生瘴病的地区，多山，地势低洼，土壤卑湿。在晴朗的时候，天气炎热蒸腾，地下湿气上升；到了阴雨天气，地下更加潮湿。人生活在这样的环境中，经常踩在湿土之上。《内经》说：“谷气通于脾”，湿气内伤脾脏。所以脾胃的虚弱，大多是由于阳气浮越于上，阴湿之气损伤于下所致，不像内伤病主要是由饮食不节和劳倦过度引起的。使用平胃散来去除脾湿，有什么不可以的呢？方中苍术能燥湿，且不闭塞腠理，使汗液容易排出；陈皮能消痰下气；厚朴（川朴）能温中下气、理痰消食；甘草能调和中气、益补脾胃。所以李待制选取它们作为治疗瘴病的重要药物。如果说脉弦属于内伤病，认为是肝木克制脾土，应该补脾抑肝，不宜祛湿，从而犯了“虚虚”的禁忌。却不知道瘴病的脉弦，是疟疾病脉自有的弦象，是因为邪气在半表半里之间，因湿生痰而发作。因此不禁用平胃散，正是要利用它温中祛湿的作用。
The *Huangdi Neijing* (Yellow Emperor's Inner Canon) states: "When Yin reaches its extreme, it transforms into Yang; when Yang reaches its extreme, it transforms into Yin." In the onset of miasma disease (Zhang Disease), the weather is hot, and the human body also becomes hot. There is often dryness and thirst in the upper jiao, with irritability and heat in the chest and heart; this represents "redundant Yang" (excessive Yang). However, the tip of the nose feels cool, and the waist and feet suffer from cold pain, indicating that Yin is hidden within. Furthermore, extreme cold generates heat, and extreme heat generates cold. Therefore, at the initial stage of miasma disease, there is invariably high fever; but as the disease appears to recede, the skin over the entire body feels as cold as ice. If physicians do not understand this principle, and seeing fever, irritability, black tongue coating, red face, red eyes, and a rapid pulse, they diagnose it as a major heat syndrome, they will use bitter-cold descending herbs such as Huangqin (Scutellariae Radix), Huanglian (Coptidis Rhizoma), Zhizi (Gardeniae Fructus), Huangbai (Phellodendri Cortex), and Zhimu (Anemarrhenae Rhizoma). The more these are administered, the worse the condition becomes. After taking several doses, the heat in the upper jiao has not descended, while cold in the middle jiao arises. This may lead to transformation of symptoms, phlegm stagnation, hiccups, or cold extremities with diarrhea. With all these symptoms appearing simultaneously, survival rates are virtually zero. Even worse, seeing irritability and excessive drinking, some use Baihu Tang (White Tiger Decoction) or Shigao Tang (Gypsum Decoction); seeing black tongue coating, constipation, and dark urine, some use Daxiehu Tang (Major Bupleurum Decoction) or Chengqi Tang (Order the Qi Decoction). Upon swallowing these medicines, patients may immediately go mad and die, or suddenly die due to phlegm obstruction, facing imminent peril within moments. Thus, it is known that miasma disease does not necessarily kill people instantly; rather, the physician causes death. Bitter-cold descending herbs such as Tianhuafen (Trichosanthis Radix), Mutong (Akebiae Caulis), Huashi (Talcum), Cheqianzi (Plantaginis Semen), Xuanshen (Scrophulariae Radix), Lianqiao (Forsythiae Fructus), Yuanmingfen (Natrii Sulfas), and Shengdihuang (Rehmanniae Radix) should also not be used lightly. Physicians must exercise caution to avoid harming patients.
Someone asked: "Miasma disease arises from deficiency-cold of the Spleen and Stomach combined with external contraction of aberrant pathogenic factors. The treatment method must first support the righteous Qi and harmonize the body. The formulas used, such as Zhengqi San (Righteous Qi Powder), Yangwei Tang (Stomach-Nourishing Decoction), and Buhuanjin Hejie San (Non-Exchanging Gold Harmonizing Powder), all contain Pingwei San (Pingwei Powder). It is said that Pingwei San was used by ancients to treat 'Dunfu' (thickening and accumulation) of the Spleen and Stomach, implying the meaning of 'leveling' or 'flattening,' hence the name 'Pingwei.' It is not a tonic for the Spleen and Stomach. Why is it used? Moreover, the pulse in miasma disease is wiry (Xian). Using Pingwei San when the pulse is wiry seems to violate Dongyuan’s (Li Dongyuan) warning against 'making deficiency more deficient.' Why is this so?" I replied: "In regions where miasma occurs, there are many mountains, and the terrain is low and thin. During clear weather, the hot air steams upward, generating moisture from the ground; during rainy seasons, the ground is damp. Humans living here frequently walk on wet soil. The *Neijing* states: 'Grain Qi connects to the Spleen.' Dampness injures the interior of the Spleen. Therefore, Spleen and Stomach deficiency is mostly caused by Yang floating upwards and Yin-dampness injuring downwards, unlike internal injury diseases which are primarily caused by improper diet and fatigue. Using Pingwei San to remove Spleen dampness is appropriate. Cangzhu (Atractylodis Rhizoma) in the formula dries dampness without closing the interstices, facilitating sweating; Chenpi (Citri Reticulatae Pericarpium) resolves phlegm and directs Qi downward; Chunghoupo (Magnoliae Officinalis Cortex) warms the middle, directs Qi downward, regulates phlegm, and aids digestion; Gancao (Glycyrrhizae Radix et Rhizoma) harmonizes the middle Qi and benefits the Spleen and Stomach. Therefore, Li Daizhi selected them as essential herbs for treating miasma. If one argues that a wiry pulse indicates internal injury, specifically Liver Wood overacting on Spleen Earth, suggesting tonification of the Spleen and suppression of the Liver without removing dampness, thus violating the 'make deficiency more deficient' rule, they fail to realize that the wiry pulse in miasma disease is the natural wiry pulse of malaria-type conditions, indicating pathogens in the half-exterior and half-interior, arising from phlegm generated by dampness. Therefore, using Pingwei San is not contraindicated; precisely, we wish to utilize its ability to warm the middle and dispel dampness."