久寒下伏。有因新感风寒而触发。有因春月时阳上升而触发。有因饮食劳倦而触发。新感触发。外证与伤寒
相似。而不同者。上焦伤寒。恶寒发热。遍身筋络。拘急疼痛。而头项为甚。脉象沉紧而数。呼吸稍促。而不甚粗。
常欲仰卧。展布四体。伏寒虽已发热。心常凛凛畏寒。筋骨诸节。 胀痛。而两髀以下。膝胫为甚。脉象浮弦而
大。重按反小。起伏应指战栗。呼吸喘粗。身热足冷。胸虽烦躁。而两足常欲蜷曲。不能伸展。时阳与饮食劳倦
触发。外证与冬温春温相似。而不同者。时温。大热气粗。久抚肌里灼手。脉象洪缓而数。来疾去迟。舌苔满黄。
渴欲冷冻饮料。时时欲呕。筋骨微胀而不痛。神识不清。不待胸满。即不思食。伏寒微热。动即气喘。寒热往来。久抚
肌里不热。或反冷如冰。脉象洪缓而迟。其来不盛。而去甚疾。沉候与尺后反紧。舌苔前黄后白。表黄里白。渴不
欲饮。或欲热饮。少腹气冲。暴大呕吐。筋骨疼胀。神识清明。食稍减而易饥。以上皆初起见证也。血气尚未浊
乱。邪正尚未混淆。是伤寒温病。与伏寒之最要关头。入手辨症不差。施治不误。刻期可已。过此失治。变证蜂涌。
高下相引。表里相攻。斑疹隐见。而痰嗽频仍。口烂龈蚀。而脐痛腹泻。寒热之真假难明。虚实之浅深莫辨。心慌
手乱。顾此失彼。鲜不败者。
旧说辨伤寒温病有曰。温病从里。伤寒从表。又曰。温病分三焦。伤寒分六经。予更续之曰。伤寒重证。自下
而上。温病重证。自上而下。伤寒死证。自上而下。温病死证。自下而上。伤寒在下而不上。轻证也。在上而不下。
轻之轻也。温病在上而不下。轻证也。在下而不上。轻重之间。未可知也。夫温病发于伏气者。由口鼻吸受。伏于
膈上膜原。侵淫三焦血分。其即病者。亦由口鼻散布肺胃。消灼津液。血分浊恶也。伤寒发于伏气者。由足胫浸受。
伏于筋络骨节。侵淫肌膜气分。其即病者。乃由腠理布于上焦。闭遏阳气气分搏激也。伤寒伏气变为温病者。非寒
能化温也。其人本体气血多热。寒伏于下。阳气不得下通。三焦菀热。日积月盛。及至发病。只见三焦热证。不见
下焦寒象。且有清利上热。自能借逐下寒者。故虽有髀胫 胀痛诸证。前人往往皆强属于温。而不敢议其为寒也。
若下寒太盛。上热不及借逐者。当俟热势半减后。加药分治之。须得内经病所远而中道气味之者。食而过之之义。
否则温去寒存。上呕下利。中焦隔塞。有合偏死下虚人之说矣。其实非下虚也。乃下寒而失治耳。
深伏于体内的寒邪，可能因新近感受风寒而诱发；也可能因春季阳气上升而诱发；还可能因饮食不节或过度劳累而诱发。由新感风寒诱发的病症，其外在表现与伤寒相似，但不同之处在于：上焦受伤寒邪，会出现恶寒发热，全身筋络拘急疼痛，以头颈部最为严重；脉象沉紧且数，呼吸稍促但并不粗重；患者常想仰卧，舒展四肢。
由伏寒诱发的病症，虽然已经发热，但心中常常感到凛冽畏寒；筋骨各个关节胀痛，以大腿以下、膝盖和小腿部位最为严重；脉象浮弦且大，重按反而变小，脉搏起伏时手指感到战栗；呼吸喘促粗重；身体发热但脚冷；胸部虽烦躁，但双脚常想蜷曲，不能伸展。
由时令阳气及饮食劳倦诱发的病症，其外在表现与冬温、春温相似，但不同之处在于：时温病表现为高热、气息粗重，长时间触摸肌肤感觉灼手；脉象洪缓且数，来势急而去势慢；舌苔满布黄色，口渴想喝冷冻饮料，时常想呕吐；筋骨轻微胀但不痛；神志不清，尚未出现胸满症状时就已不想进食。
伏寒引发的病症表现为微热，活动后即气喘，寒热往来，长时间触摸肌肤并不热，甚至反冷如冰；脉象洪缓且迟，来势不盛而去势极疾，沉取及尺部后方反而紧；舌苔前黄后白，表黄里白，口渴但不欲饮水，或想喝热饮；少腹部有气冲逆感，突发剧烈呕吐，筋骨疼胀，神志清醒，食欲稍减但容易饥饿。以上这些都是疾病初起时的见证。此时气血尚未浑浊混乱，邪气与正气尚未混淆。这是辨别伤寒、温病与伏寒的最关键关口。若能在此时准确辨证施治，可迅速痊愈。若错过此时机失治，变证将蜂拥而至，上下相互牵引，表里相互攻伐，出现隐现的斑疹和频繁的痰嗽，口腔溃烂牙龈腐蚀，脐部疼痛腹泻。寒热的真假难以辨明，虚实的深浅无法区分。医生心慌手乱，顾此失彼，很少有不失败的。
旧说在辨别伤寒与温病时说：温病从里发起，伤寒从表发起；又说：温病分三焦，伤寒分六经。我在此基础上补充说：伤寒的重证，病势自下而上发展；温病重证，病势自上而下发展。伤寒的死证，病势自上而下；温病的死证，病势自下而上。伤寒病位在下而不向上蔓延，属于轻证；病位在上而不向下蔓延，属于最轻之证。温病病位在上而不向下蔓延，属于轻证；病位在下而不向上蔓延，则处于轻重之间，尚不可知。
凡是温病由伏气引发，是由口鼻吸入，潜伏于膈上膜原，浸淫三焦血分。如果是即发者，也是由口鼻散布至肺胃，消灼津液，导致血分浊恶。伤寒由伏气引发，是由足胫浸受寒邪，潜伏于筋络骨节，浸淫肌膜气分。如果是即发者，则是从腠理布散至上焦，闭遏阳气，气分搏激所致。
伤寒伏气转化为温病，并非寒邪能化为温邪，而是患者本体气血多热，寒邪伏于下部，导致阳气不得下行通达，三焦郁热，日积月累日益旺盛。等到发病时，只见三焦的热证，不见下焦的寒象。而且只要清利上部的热邪，自然能借助药力驱逐下部的寒邪。因此，即使有大腿和小腿胀痛等症状，前人往往都强行将其归属于温病，而不敢议论其为寒邪所致。如果下部寒邪太盛，上部热邪不足以借药力驱逐时，应当等待热势减半后，再加药分别治疗。必须遵循《内经》中“病所远而中道气味之者，食而过之”的意义。否则，温邪去而寒邪存，会导致上呕下利，中焦隔塞，这就符合了“偏死下虚”人的说法了。其实这并不是下焦虚弱，而是下焦寒邪未得到正确治疗罢了。
Deep-seated cold lurking within the body may be triggered by a recent contraction of wind-cold; it may also be triggered by the rising of seasonal yang in spring; or it may be triggered by improper diet and overexertion. The external manifestations of cases triggered by recent wind-cold contraction are similar to those of Shanghan (Cold Damage), but differ in that: when the Upper Jiao is affected by Shanghan pathogen, there is aversion to cold and fever, stiffness and pain throughout the meridians and collaterals of the body, most severe in the head and neck; the pulse is deep, tight, and rapid; respiration is slightly accelerated but not coarse; the patient often desires to lie supine with limbs extended.
In cases triggered by latent cold, although fever has already appeared, the heart often feels piercingly cold; the bones, muscles, and joints ache and distend, most severely below the thighs, specifically at the knees and shins; the pulse is floating, wiry, and large, but becomes smaller upon heavy pressure, with a trembling sensation against the fingers during its rise and fall; respiration is panting and coarse; the body is hot while the feet are cold; although the chest is irritable, the feet constantly desire to curl up and cannot extend.
Cases triggered by seasonal yang, improper diet, and overexertion present externally similarly to Dongwen (Winter Warmth) and Chunwen (Spring Warmth), but differ in that: Shiwarm presents with high fever and coarse breath; prolonged palpation of the skin reveals burning heat; the pulse is surging, slow, and rapid, coming swiftly and departing slowly; the tongue coating is entirely yellow; thirst drives the desire for frozen beverages; nausea occurs intermittently; the bones and muscles feel slightly distended but not painful; mental clarity is impaired; appetite is lost even before chest fullness appears.
Latent cold triggers mild fever; exertion immediately induces panting; alternating chills and fever occur; prolonged palpation of the skin reveals no heat, or even coldness like ice; the pulse is surging, slow, and delayed, lacking vigor on arrival but swift on departure, becoming tight upon deep palpation and at the Chi position posteriorly; the anterior tongue coating is yellow and the posterior is white, indicating exterior yellow and interior white; thirst exists without desire to drink, or desire for hot drinks; Qi rushes from the lower abdomen, causing sudden violent vomiting; bones and muscles ache and distend; mental clarity remains intact; appetite is slightly reduced but hunger arises easily. These are all initial manifestations. At this stage, Qi and Blood have not yet become turbid and chaotic; pathogenic factors and healthy Qi have not yet confused each other. This is the critical juncture for distinguishing between Shanghan, Wenbing (Warm Diseases), and latent cold. If syndrome differentiation is accurate and treatment is administered correctly at this point, recovery can be expected promptly. If this opportunity is missed and treatment is neglected, complications will swarm forth, upper and lower regions influencing each other, exterior and interior attacking each other, resulting in hidden macules and papules, frequent phlegm and cough, oral ulcers and gum erosion, umbilical pain, and diarrhea. The truth and falsehood of cold and heat become difficult to clarify; the depth and superficiality of deficiency and excess become impossible to distinguish. Physicians may panic and act hastily, attending to one aspect while neglecting another, rarely avoiding failure.
Old theories on distinguishing Shanghan and Wenbing state: Wenbing originates from the interior, Shanghan from the exterior; furthermore, Wenbing is differentiated by the Three Jiao, while Shanghan is differentiated by the Six Channels. I add to this: In severe cases of Shanghan, the pathology moves upward from below; in severe cases of Wenbing, the pathology moves downward from above. In fatal cases of Shanghan, the pathology moves downward from above; in fatal cases of Wenbing, the pathology moves upward from below. When Shanghan pathology remains below and does not move upward, it is a mild case; when it remains above and does not move downward, it is the mildest case. When Wenbing pathology remains above and does not move downward, it is a mild case; when it remains below and does not move upward, it lies between mild and severe, uncertain.
Wenbing arising from latent Qi enters through the nose and mouth, lurks in the Diaphragm and Mo Yuan (Membrane Source), and infiltrates the Blood level of the Three Jiao. If it manifests immediately, it spreads via the nose and mouth to the Lung and Stomach, consuming fluids and causing turbidity in the Blood level. Shanghan arising from latent Qi enters through immersion of the lower legs, lurks in the sinews, collaterals, and bone joints, and infiltrates the Qi level of the muscle membranes. If it manifests immediately, it spreads from the Cou Li (Pores) to the Upper Jiao, obstructing Yang Qi and causing agitation in the Qi level.
When latent Shanghan transforms into Wenbing, it is not that cold transforms into warmth, but rather that the individual's constitution possesses abundant Heat in Qi and Blood. Cold lurks below, preventing Yang Qi from descending and communicating. The Three Jiao accumulates stagnant heat, growing day by day and month by month. Upon manifestation, only Heat syndromes of the Three Jiao are seen, with no signs of Cold in the Lower Jiao. Moreover, clearing and draining the Heat in the Upper Jiao naturally aids in expelling the Cold in the Lower Jiao. Therefore, despite symptoms such as thigh and shin distension and pain, predecessors often forcibly attribute these to Wenbing and dare not discuss them as caused by Cold. If the Cold in the Lower Jiao is too severe for the Heat in the Upper Jiao to assist in expulsion, one should wait until the Heat intensity reduces by half, then add medications to treat separately. One must follow the principle in the Neijing (Inner Canon): "When the disease site is distant, utilize the flavor and qi of food to reach it." Otherwise, the removal of Warmth leaves Cold behind, leading to vomiting above and diarrhea below, with obstruction in the Middle Jiao, fitting the description of a person with "partial death and Lower Deficiency." In reality, this is not Lower Deficiency, but rather Lower Cold due to mismanagement.