刘河间阐发素问元机。 热病凡三十有三证。此泛言热因之病机。而伤寒例中所称之热
病。
却不系此。此亦犹伤寒例中之中风。不与金匮中风历节病一例看者同义。凡风寒之病。一
经传变之后。大率转成热证。其最难辨者。莫如太阳病初起时。此伤寒例中之热病。却要在
初
见头痛项强恶寒发热之太阳病时辨起。按仲景云。太阳中热者 是也。其人汗出恶寒身热而
渴也。仲景分明指此为 病。则合之内经热病论。所云先夏至日为病温。后夏至日为病暑者
。即从此例矣。同一太阳病。温病渴而不恶寒。热病渴而恶寒。中风汗出而不渴。热病汗出
而渴。伤寒不渴而恶寒无汗。热病汗出恶寒而渴。仲景辨证。如此明确。其主治不与风寒温
湿同法。又可推矣。盖热则伤寒。故反恶寒。热则耗津。故见口渴。至于汗出身热。罔非阳
邪怫郁之状。金匮明设人参白虎汤之制。取其益气生津。涤除烦热。此又显示人以可循之矩
。后世之用六一散。即祖此意。设遇此等病而妄行解肌发汗。其不致贻误者几希。谁谓同一
头项强痛恶寒之太阳病。而可不辨之于微哉。
问曰。病热而反恶寒者。何也。答曰。此义内经明言之。经云。恶寒战栗者。皆属于热。
又
云禁栗如丧神守。皆属于火。故河间云。病热甚而反觉其寒。此为病热。实非寒也。夫火郁
于
内。逼阴向外。阳盛拒阴。往往见外寒之证。且恶寒而渴。自与中风伤寒之恶寒不同。但当直
彻其热。则恶寒之表证自罢。又难经云。热病之脉。阴阳俱浮。浮之而滑。沉之散涩。此病
机之常。然以今人当夏月盛暑。或坐卧当风。或恣啖生冷。内热被外寒所束。热益郁而不得
泄。因反病热。故仲景于太阳中 。别出脉弦细芤迟脉微弱两条。以尽病情之变。此又仲景
当日之圆机活法。以牖后人临症之灵心善悟。遇此等证。便不宜用寒凉直折。后贤治夏月暑
病。有用大顺散。香薷饮者。正自此义。且内经云。人伤于寒。则为病热。正惟热病中亦见头
项强痛恶寒之太阳病。故得类于伤寒之例。夫上古圣人。夏三月养长之道。夜卧早起。无厌
于日。使气得泄。若所受在外。热固欲其外泄。不欲其内壅也。旨深哉。
刘河间阐发了《素问·玄机原病式》中的理论。热病总共有三十三种证候，这是泛指由热邪致病的基本病机。然而，《伤寒例》中所称的“热病”，却并不属于这一范畴。这其中的道理，也如同《伤寒例》中的“中风”不与《金匮要略》中的“中风历节病”混为一谈是一样的意思。大凡风寒之病，一经传变之后，大多会转化为热证。其中最难辨别的时候，莫过于太阳病初起之时。因此，《伤寒例》中的“热病”，却要在初见头痛、项强、恶寒、发热等太阳病症状时就开始辨别。
按照张仲景的说法：“太阳中热者，是谓暍（yē）病。”其表现为汗出、恶寒、身热而口渴。张仲景明确将此指认为暍病，这与《内经·热病论》所说的“先夏至日为病温，后夏至日为病暑”是一致的。同样是太阳病，温病表现为口渴而不恶寒；热病（此处指伤暑/暍）表现为口渴且恶寒；中风表现为汗出但不渴；伤寒表现为不渴、恶寒且无汗；热病则表现为汗出、恶寒且口渴。张仲景的辨证如此明确，其主治方法不与风寒湿同法，是可以推知的。因为热邪导致类似伤寒的症状，所以反而出现恶寒；热邪耗伤津液，所以出现口渴。至于汗出、身热，无不都是阳邪怫郁在里的表现。《金匮要略》明确设立了人参白虎汤的方制，取其益气生津、清除烦热的作用。这又向人们展示了可以遵循的法度。后世使用六一散，就是承袭了这个意旨。如果遇到这类疾病而妄行解肌发汗的方法，不造成延误误治的情况就太少了。谁说同样是头项强痛、恶寒的太阳病，却不在细微之处加以辨别呢？
有人问：患热病反而恶寒，是什么原因？回答说：这个意义《内经》讲得很明白。经文说：“恶寒战栗者，皆属于热。”又说：“禁栗如丧神守，皆属于火。”所以刘河间说：病热很严重反而觉得寒冷，这是因为病热，实际上并不是寒邪。火热郁结于内，逼迫阴气向外；阳气盛极拒阴，往往表现出外寒的证候。而且恶寒伴有口渴，自然与中风、伤寒的恶寒不同。只要直接清彻其热，那么恶寒的表证自然就会消除。
另外，《难经》说：热病的脉象，阴阳俱浮，轻取而滑，重按而散涩。这是病机的常理。然而，以今人而言，在盛夏酷暑时节，或坐卧当风，或恣意吃生冷食物，内热被外寒所束缚，热更加郁结而不能宣泄，因此反而患上热病。所以张仲景在论述太阳中暍时，特别列出脉弦细芤迟、脉微弱两条，以穷尽病情的变化。这又是张仲景当时灵活圆通的治法，用来启发后人临证时的灵心善悟。遇到这类证候，就不宜用寒凉药物直折其热。后世治疗夏季暑病，有用大顺散、香薷饮的，正是基于这个道理。
况且《内经》说：“人伤于寒，则为病热。”正因为热病中也见到头项强痛、恶寒的太阳病表现，所以得以类比于伤寒的法则。上古圣人在夏季三个月养长的道理，是晚睡早起，不厌恶日光，使气机得以宣泄，就像受之于外的热气一样。热固然希望它向外宣泄，不希望它向内壅滞。旨意深远啊。
Liu Hejian elucidated the theories in *Suwen: Yuanji* (Basic Principles of the Yellow Emperor's Inner Canon). There are thirty-three types of heat diseases in total; this is a general statement regarding the pathogenesis of diseases caused by heat pathogens. However, the "heat disease" mentioned in the *Shanghan Li* (Treatise on Cold Damage Examples) does not belong to this category. The principle here is similar to how the "wind strike" in the *Shanghan Li* is not viewed in the same manner as the "wind strike and joint pain diseases" in the *Jingui Yaolue*. Generally speaking, after transmission and transformation, wind-cold diseases mostly turn into heat syndromes. The most difficult time to distinguish them is at the initial stage of Taiyang disease (diseases affecting the Taiyang channel). Therefore, the "heat disease" in the *Shanghan Li* must be distinguished starting from the initial appearance of Taiyang disease symptoms such as headache, stiffness of the neck and nape, aversion to cold, and fever.
According to Zhang Zhongjing: "Taiyang heat strike is called Ye disease." Its manifestations include sweating, aversion to cold, body heat, and thirst. Zhang Zhongjing clearly identifies this as Ye disease, which aligns with what is stated in the *Neijing: Rebing Lun* (Treatise on Heat Diseases): "Diseases occurring before the Summer Solstice are called Warm diseases; those occurring after the Summer Solstice are called Summerheat diseases." For the same Taiyang disease, Warm diseases present with thirst but no aversion to cold; heat diseases (here referring to summerheat/Ye) present with both thirst and aversion to cold; wind strike presents with sweating but no thirst; cold damage presents with no thirst, aversion to cold, and absence of sweating; whereas heat disease presents with sweating, aversion to cold, and thirst. Zhang Zhongjing's differentiation of syndromes is so clear that it can be inferred his main treatment methods differ from those for wind, cold, dampness, etc. Because heat pathogens cause symptoms resembling cold damage, aversion to cold occurs conversely; because heat consumes body fluids, thirst appears. As for sweating and body heat, these are all signs of Yang pathogens being constrained and depressed. The *Jingui Yaolue* explicitly establishes the prescription of Renshen Baihu Tang (Ginseng White Tiger Decoction), utilizing its functions to benefit Qi, generate fluids, and eliminate irritability and heat. This provides a standard for people to follow. The later use of Liuyi San (Six-to-One Powder) inherits this intent. If one were to recklessly apply muscle-relaxing and diaphoretic methods to such diseases, few would avoid causing harm or delay. How can one fail to distinguish between different conditions presenting with the same Taiyang symptoms of head and neck stiffness, pain, and aversion to cold?
Question: Why does a patient with a heat disease experience aversion to cold? Answer: This meaning is clearly stated in the *Neijing*. The classic says: "Aversion to cold and shivering all belong to heat." It also states: "Trembling as if losing spiritual control all belong to fire." Thus, Liu Hejian said: When heat is severe, the patient may feel cold; this is due to heat disease, not actual cold. Fire constrained internally forces Yin outward; excessive Yang repels Yin, often manifesting as exterior cold syndromes. Moreover, aversion to cold accompanied by thirst is naturally different from the aversion to cold seen in wind strike or cold damage. One should directly clear the heat, and the exterior syndrome of aversion to cold will naturally resolve.
Furthermore, the *Nanjing* states: In heat diseases, the pulse is floating at both Yin and Yang positions; superficially it is slippery, deeply it is scattered and choppy. This is the normal pattern of pathogenesis. However, considering modern people, during the peak of summer heat, sitting or lying in drafts, or indulging in raw and cold foods, internal heat is bound by external cold. The heat becomes more constrained and cannot vent, thus leading to heat disease. Therefore, when discussing Taiyang summerheat strike, Zhang Zhongjing specifically lists two pulse patterns—string-taut, fine, hollow, slow; and weak—to exhaustively cover variations in disease presentation. This represents Zhang Zhongjing's flexible and adaptive methods of his time, intended to inspire the intuitive understanding of later practitioners. When encountering such syndromes, one should not use bitter-cold herbs to directly suppress the heat. Later generations treating summerheat diseases have used Dasun San (Great Harmony Powder) and Xiangru Yin (Elsholtzia Drink), precisely based on this principle.
Moreover, the *Neijing* states: "When humans are injured by cold, they develop heat diseases." Precisely because heat diseases also present with Taiyang symptoms like head and neck stiffness, pain, and aversion to cold, they can be analogized to the principles of cold damage. The ancient sages taught the method of nourishing growth during the three months of summer: go to bed late and rise early, do not dislike the sun, allow Qi to vent, just as heat received from outside should be allowed to dissipate externally. Heat certainly desires to vent outward and not be obstructed internally. The purport is profound.