火为热病，是固然矣。然火得其正，即为阳气，此火之不可无，亦不可衰。衰则阳气之
虚也。火失其正，是以邪热，此火之不可有，尤不可甚。甚则真阴伤败也。然阳以元气言。
火以病气言，故凡病在元气者，不得以火论。何也？盖人之元气止于充足，焉得有余？既非有
余，则何以言火？所谓无形者其化虚，即此是也。惟病在形体者，乃可以察火证，盖其不在
气即在血，所谓有形者其化实，即此是也。故凡火之为病，其在外者，必见于皮肉筋骨；其
在内者，必见于脏腑九窍。若于形质之间，本无热证可据，而曰此火也。此热也，则总属莫
须有之妄谈也。矧如火证悉具，而犹有虚实之殊，真假之异，其可不为详辨乎。若果有火病
，则火性急烈，诚可畏也。然实火止随形质，余因谓之凡火，又谓之邪火。火之为病，病之
标耳，洗之涤之，又何难哉。惟虚火之病，则本于元气，元气既虚，而再攻其火，非梃即刃
矣。是以诸病之杀人，而尤惟火病为最者，正以凡火未必杀人，而以虚作实，则无不杀之矣
，不忍见也。
一、凡五脏之火，肺热则鼻干，甚则鼻涕出。肝热则目眵浓。心热则言笑多。脾热则善
饥善渴。肾热则小水热痛。凡此之类，宜从清也。诸所不尽，详一卷寒热篇。
一、凡察火证，必须察其虚实。虽其元气本虚，然必虚中挟实者，乃为易治。何以见之
？如或大便干结，或善饥多食，或神气精明，或声音强壮，而脉见有力，此皆虚中有实也，
俱可随证清解之。若或内外俱热，而反见溏泄，或饮食少进，或声微气短，诸虚皆见，而反
不利温补者。此其胃气已败，生意已穷，非吉兆也。
火证属于热病，这是理所当然的。然而，当火保持其正常状态时，它就是阳气，这种火是不可缺少且不可衰弱的。如果衰弱了，那就是阳气的虚损。如果火失去了它的正常状态，就会变成邪热，这种火是不应该存在且尤其不能过盛的。如果过盛，就会导致真阴受损败坏。这里的“阳”是从元气角度而言的，“火”则是从病气角度而言的，所以凡是涉及元气的疾病，不能简单地用“火”来论述。为什么呢？因为人的元气只要充足就可以了，哪里会有多余呢？既然不是有余，那么为什么说会有“火”呢？所谓“无形者其化虚”，指的就是这种情况。只有当疾病发生在形体层面时，才可以观察火证，因为此时病不在气就在血，所谓“有形者其化实”，指的就是这种情况。因此，凡是火引起的疾病，在体表的，必然表现在皮肉筋骨；在体内的，必然表现在脏腑和九窍。如果在形质之间，本来没有热证的依据，却说是火、是热，那总归是无中生有的妄谈。况且即使火证完全具备，还有虚实之分、真假之别，难道不值得详细辨别吗？如果真的患有火病，火的性质急烈，确实令人畏惧。但是，实火只随形体质地而存在，我因此称它为凡火，又叫做邪火。火引起的疾病，只是疾病的表象，清洗它、涤荡它，又有什么难的呢？只有虚火引起的疾病，根源在于元气，元气既然已经虚弱，如果再攻伐它的火，无异于用棍棒或刀刃伤害病人。因此，在各种致人死亡的疾病中，尤以火病最为严重，正是因为凡火未必杀人，但如果把虚证当作实证来处理，那就无不导致死亡的，这真是令人不忍目睹。
一、凡是五脏之火：肺热则鼻干，严重时鼻涕流出；肝热则眼屎浓稠；心热则言语多且爱笑；脾热则容易饥饿且口渴；肾热则小便灼热疼痛。凡是这类情况，适宜采用清热的方法。其他未尽的情况，详见第一卷《寒热篇》。
一、凡是诊察火证，必须辨别其虚实。虽然元气本已虚弱，但如果是虚中挟实的情况，就容易治疗。怎么知道呢？比如大便干结，或者容易饥饿多吃，或者精神精明，或者声音强壮，而且脉象有力，这些都是虚中有实的情况，都可以根据症状进行清热解表处理。如果内外都热，反而出现腹泻，或者饮食减少，或者声音微弱气息短促，各种虚象都出现了，却不适宜温补。这说明胃气已经败坏，生机已尽，不是吉兆。
Fire syndromes belong to heat diseases, which is indeed the case. However, when fire maintains its proper state, it constitutes Yang Qi (Yang Energy), a type of fire that is indispensable and must not be deficient. Deficiency indicates a depletion of Yang Qi. Conversely, when fire deviates from its proper state, it becomes pathogenic heat (Evil Heat); such fire should not exist and certainly must not be excessive. Excessiveness leads to the damage and failure of True Yin (True Essence). Here, "Yang" refers to Yuan Qi (Original Qi), whereas "fire" refers to pathogenic qi. Therefore, diseases involving Yuan Qi cannot simply be discussed in terms of "fire." Why? Because human Yuan Qi needs only to be sufficient; how could there ever be an excess? Since it is not an excess, why speak of "fire"? The concept that "formless transformations become deficiency" refers precisely to this situation. Only when disease manifests in the physical form can one observe fire syndromes, as the pathology resides either in Qi or Blood. The concept that "formed transformations become excess" refers to this scenario. Thus, for any disease caused by fire, if located externally, it must manifest in the skin, flesh, sinews, and bones; if located internally, it must manifest in the Zang-Fu organs and the nine orifices. If there are no heat symptoms evident in the physical structure, yet one claims it is "fire" or "heat," this is entirely baseless speculation. Moreover, even when all signs of fire syndrome are present, distinctions between deficiency and excess, and between true and false, must be carefully differentiated. If one truly suffers from a fire disease, the nature of fire is urgent and fierce, which is indeed formidable. However, excess fire follows the physical form; I therefore call it ordinary fire (Fan Huo) or evil fire (Xie Huo). Fire-induced diseases represent merely the branch manifestations of illness; cleansing and purging them is hardly difficult. It is only deficiency fire (Xu Huo) that originates from Yuan Qi. Since Yuan Qi is already deficient, attacking the fire further would be akin to striking with a club or blade. Therefore, among various fatal diseases, fire diseases are particularly lethal precisely because ordinary fire may not kill, but treating deficiency as excess invariably leads to death—a sight too heartbreaking to witness.
1. Regarding fire in the five Zang organs: Lung heat causes dryness of the nose, and severely, nasal discharge; Liver heat results in thick eye discharge; Heart heat leads to excessive talking and laughing; Spleen heat causes frequent hunger and thirst; Kidney heat results in hot and painful urination. For such cases, clearing heat (Qing Re) is appropriate. Details on other instances can be found in Volume 1, Chapter on Cold and Heat.
2. When examining fire syndromes, one must distinguish between deficiency and excess. Although Yuan Qi is inherently deficient, cases where deficiency is complicated by excess (Xu Zhong Jia Shi) are easier to treat. How can this be identified? For instance, if there is dry and constipated stool, or frequent hunger with increased food intake, or mental clarity, or strong voice, accompanied by a forceful pulse, these indicate excess within deficiency. Such cases can be treated by clearing heat and resolving pathogens according to symptoms. Conversely, if there is internal and external heat but accompanied by loose stools, reduced appetite, weak voice, and shortness of breath—manifesting various deficiency signs—if warm tonification is contraindicated, this indicates that Stomach Qi has failed and vitality is exhausted, which is an ominous sign.