程氏曰∶经者径也，行于皮之内，肉之中者也。腑者器也，所以盛水谷者也。伤寒诸书，以经为腑，以
腑为经，混同立言，惑人滋甚，今特辨之。夫邪之在三阳也，有太阳之经，有阳明之经，有少阳之经，凡三
阳在经之邪，未入腑者，可汗而已。邪之在三阴也，有太阴之经，有少阴之经，有厥阴之经，凡三阴之邪，
已入腑者，可下而已。所谓入腑之腑，指阳明胃腑而言也。三阳三阴之邪，一入胃腑，则无复传矣。胃者土
也，万物归土之义也。《伤寒论》云∶有太阳阳明，有正阳阳明，有少阳阳明，此阳明即胃腑，非阳明之经
也。假令邪在太阳，不传阳明经，而径入胃腑，曰太阳阳明。邪在阳明经，不传少阳，而自入本腑，曰正阳阳
明。邪在少阳经，不传三阴，而径入胃腑，曰少阳阳明。凡三阳之邪，已入胃腑，俱下之勿疑矣。虽然三
阳入腑，人所共知，三阴入腑，鲜或能识。夫三阳之经，去腑尚远，三阴之经，与腑为近。然既曰经，则犹
在径路之间，未尝归并于一处也。《伤寒论》云∶太阴病，脉浮者，可发汗，宜桂枝汤。少阴中风，脉阳微
阴浮者，为欲愈。厥阴中风，脉微浮为欲愈，不浮为未愈。俱言邪在于经，故有还表向汗之时。若既入腑，则
无外出之路，惟有通其大便，令邪从内出也，此大、小承气，调
胃承气所由设也。然则以白虎汤治腑病，何谓也？以三阳之邪，初入胃腑，表里皆热，邪未结聚，热势散漫，
而无胃实不大便之症，故用白虎汤，内清胃腑，外透肌肤，令表里两解。若邪已结聚，在太阴之实痛，少阴
之咽干口燥，下利清水，心下硬，厥阴之烦满囊缩，白虎不中与也，惟急下之而已。此无他，经腑明，则施
治不致舛错矣。然则太阳之邪，自入本腑，何谓也？太阳之腑，膀胱也，膀胱主盛溺，太阳病盛，则移邪于腑，
而为口渴溺赤，外现太阳病，而兼有此症者，名曰太阳传本，当五苓散，以桂枝解外邪，以猪苓、泽泻利小便
而愈也。或问阳邪入阴，复有还表向汗之时，其信然乎？予曰∶古人之言，岂欺我哉！夫经者径也，犹径路然。
三阳之邪，既有路以达三阴，三阴之邪，即有路以返三阳，此循环之至理，非若邪入胃腑，更无外出之路也。
尝见病患体质素浓，有传经尽而自愈者，皆由汗解也。《伤寒论》云∶其不再传经，不加异气者，七日太阳病
衰，头痛稍愈。八日阳明病衰，身热稍歇。九日少阳病衰，耳聋微闻。十日太阴病衰，腹减思食。十一日少阴
病衰，渴止，舌干，已而嚏也。十二日厥阴病衰，囊纵，少腹微下，大气已去，病患精神爽慧也。由是观之，
岂非经尽而愈，还表向汗之明验乎。或曰∶阴不得有汗，今太阴脉浮，用桂枝汤，然则三阴亦可汗解乎？桂枝
汤将为太阴正药乎？曰∶不然，读仲景书，当会而通之。夫邪已入里，而复发其表，是增其热矣，故曰，阴
不得有汗。邪虽入里，而复返乎表，是邪外出矣，故曰，还阳而向汗。夫桂枝汤，太阳伤风药也，今太阴用桂
枝汤者，由太阳伤风，为医误下而传入太阴者也。太阴脉当沉，今反浮，是症在太阴，脉在太阳，太阳之邪，
未尽入于阴，太阴之邪，大有还阳向汗之势，故用桂枝汤以彻散之，令其从太阳来者，仍自太阳出也。推而论
之，若从太阳伤寒来，得伤寒脉，则桂枝可易麻黄，仲景麻黄石膏汤之意可推也。若从阳明来，得阳明脉，
则桂枝可易葛根，仲景葛根黄连黄芩汤之意可推也。若从少阳来，得少阳脉，则桂枝可易柴胡，是以大柴胡汤，
为少阳传入太阴之的方也。然必腹中实痛，乃为脾邪干胃，甫用大黄下之，否则只于本方加芍药以和之而已。《伤
寒论》云∶本太阳症，为医误下，传入太阴而腹痛者，桂枝汤加芍药，大实痛者桂枝汤加大黄，亦此意也。
太阴如此，少阴、厥阴何独不然。仲景少阴篇内，以四逆散治阳厥，方用柴胡、黄芩、甘草、枳实，岂少阴亦
用柴胡散之欤？诚以热邪传里，游行于少阴经络之间，尚未结聚成实，内陷于胃腑中，则用黄芩、甘草以
清传经之热邪，用枳实以导胃中之宿滞，使邪气不得乘机而内合，以作胃实不大便之症。更用柴胡疏通三阳
之路，俾其从此来者，仍从此出，不必扰动中宫，而病势已解，此仲景用药之微权也。愚遇阳邪入阴，犹未结
实之症，仿古人三黄解毒之意，而加以石膏，以守阳明之中路，加柴胡者，亦望其返之故道，而还阳向汗
也。大抵伤寒治法，急于解表，而缓于攻里，非惟三阳之邪，务从表散，即三阴未结之邪，且冀其还阳而之表，
必俟邪气结实，乃用承气汤攻下之。且戒曰∶欲行大承气，先与小承气，腹中转矢气者，方与大承气；若不
转失气，慎未可再攻，兢兢然不苟下也有如此。仲景又曰∶病发于阳而反下之，热入因作结胸；病发于阴而
下之，因作痞。热入者，言入胃也。三阴下早，虽不至成结胸，而已不免为痞气矣。噫！经腑之间，其可不
辨哉。
程氏说：经，就是路径的意思，运行在皮肤之内、肌肉之中的通道。腑，就是容器，用来盛装水谷的器官。治疗伤寒的各类书籍，常常把“经”当作“腑”，把“腑”当作“经”，混淆二者立论，极大地迷惑了世人，今天我特意对此加以辨析。
邪气侵犯三阳经时，有太阳经（足太阳膀胱经）、阳明经（足阳明胃经）、少阳经（足少阳胆经）。凡是三阳经的邪气，尚未传入腑的，可以通过发汗的方法治愈。邪气侵犯三阴经时，有太阴经（足太阴脾经）、少阴经（足少阴肾经）、厥阴经（足厥阴肝经）。凡是三阴经的邪气，已经传入腑的，可以通过泻下的方法治愈。所谓传入的“腑”，特指阳明胃腑而言。三阳和三阴的邪气，一旦进入胃腑，就不再传变其他经络了。因为胃属土，万物归于土的缘故。《伤寒论》说：有太阳阳明病，有正阳阳明病，有少阳阳明病，这里的“阳明”指的是胃腑，而不是阳明经。假如邪气在太阳经，不传入阳明经，而直接传入胃腑，称为太阳阳明。邪气在阳明经，不传入少阳经，而自行传入本腑，称为正阳阳明。邪气在少阳经，不传入三阴经，而直接传入胃腑，称为少阳阳明。凡是三阳的邪气，已经进入胃腑的，都应当毫不犹豫地采用泻下法。
虽然三阳邪气入腑是众所周知的，但三阴邪气入腑，很少有人能识别。三阳经距离腑尚远，三阴经与腑较为接近。然而既然称为“经”，说明邪气仍在路径之中，未曾归并汇聚于一处。《伤寒论》说：太阴病，脉象浮的，可以发汗，适宜用桂枝汤。少阴中风，脉象寸微尺浮的，是即将痊愈的表现。厥阴中风，脉象微浮为将愈，不浮则为未愈。这些都是说邪气停留在经，所以有回归体表通过发汗解邪的时候。如果邪气已经入腑，就没有外出的途径了，只有通导大便，让邪气从体内排出，这就是大承气汤、小承气汤、调胃承气汤设立的原因。
那么，为什么用白虎汤治疗腑病呢？这是因为三阳的邪气初入胃腑时，表里皆热，邪气尚未结聚，热势散漫，且没有胃实不大便的症状，所以使用白虎汤，在内清泄胃腑之热，在外透达肌肤之热，使表里两解。如果邪气已经结聚，出现太阴的剧烈腹痛、少阴的咽干口燥、下利清水、心下硬满，或者厥阴的烦闷胀满、阴囊收缩等症状，白虎汤就不适用了，只能紧急采用泻下法。这没有别的原因，只要分清经和腑，施治就不会出错。
那么，太阳的邪气自行传入本腑，是怎么回事呢？太阳的腑是膀胱，膀胱主要盛装尿液。太阳病严重时，邪气移入腑中，导致口渴、小便短赤。外表呈现太阳病的症状，同时兼有这些症状的，称为太阳传本证，应当用五苓散治疗，以桂枝解除外部邪气，以猪苓、泽泻利小便而痊愈。
有人问：阳邪传入阴经后，还有回归体表通过发汗解邪的时候吗？真的如此吗？我说：古人的话，难道会欺骗我们吗！经，就是路径，就像道路一样。三阳的邪气，既有路通向三阴；三阴的邪气，也有路返回三阳，这是循环往复的大道理，不像邪气进入胃腑那样，再也没有外出的路了。我曾经见到患者体质原本强盛，有的传经完毕而自愈的，都是通过发汗解决的。《伤寒论》说：不再传经、不夹杂其他邪气的，第七日太阳病衰退，头痛稍好；第八日阳明病衰退，身热稍歇；第九日少阳病衰退，耳聋稍能听见；第十日太阴病衰退，腹部变软思食；第十一日少阴病衰退，口渴停止，舌干好转，随后打喷嚏；第十二日厥阴病衰退，阴囊松弛，少腹轻微下坠，大气已去，患者精神清爽。由此看来，难道不是经尽而愈、回归体表通过发汗的明显证据吗？
有人说：阴经不能有汗，现在太阴脉浮，用桂枝汤，那么三阴也可以发汗解邪吗？桂枝汤将成为太阴的正药吗？我说：不是这样，读仲景的书，应当融会贯通。邪气已经入里，却再次发汗解表，这会增加内热，所以说“阴不得有汗”。邪气虽然入里，但又返回到体表，这是邪气向外排出的表现，所以说“还阳而向汗”。桂枝汤本是治疗太阳伤风（中风）的药，现在太阴病用桂枝汤，是因为太阳伤风被医生误用下法，导致邪气传入太阴。太阴病的脉象应当沉，现在反而浮，这是症候在太阴，脉象却在太阳，说明太阳的邪气未尽入于阴，太阴的邪气大有回归阳经通过发汗解邪的趋势，所以用桂枝汤来疏散它，让它从太阳来的，仍从太阳出。
推而言之，如果是从太阳伤寒来的，得到伤寒脉象，则桂枝可换成麻黄，可以推知仲景麻黄石膏汤的用意。如果是从阳明来的，得到阳明脉象，则桂枝可换成葛根，可以推知仲景葛根黄连黄芩汤的用意。如果是从少阳来的，得到少阳脉象，则桂枝可换成柴胡，因此大柴胡汤是少阳传入太阴的确切方剂。但是必须腹中实痛，才是脾邪干扰胃，才刚刚用大黄泻下，否则只在本方中加入芍药来调和即可。《伤寒论》说：原本是太阳病症，被医生误下，传入太阴而出现腹痛的，用桂枝汤加芍药；大实痛的，用桂枝汤加大黄，也是这个意思。太阴是这样，少阴、厥阴为何唯独不是这样呢？仲景少阴篇中，用四逆散治疗阳厥，方中用柴胡、黄芩、甘草、枳实，难道少阴也用柴胡散邪吗？确实是因为热邪传入里部，游行在少阴经络之间，尚未结聚成实，也没有内陷到胃腑中，所以用黄芩、甘草清泄传入经的热邪，用枳实导除胃中的宿滞，使邪气不能乘机内合，造成胃实不大便的症状。再用柴胡疏通三阳的路径，让它们从此处来，仍从此处出，不必扰动中焦脾胃，病情就已经解除，这是仲景用药的精妙权变。
我遇到阳邪入阴， yet 尚未结实的病症，仿效古人三黄解毒的意思，加上石膏，以守住阳明经的中路；加入柴胡，也是希望邪气返回故道，回归阳经通过发汗解邪。大抵治疗伤寒的方法，急于解表，而缓于攻里。不仅是三阳的邪气务必从表散发，即使是三阴未结的邪气，也期望其回归阳经进而至表。必须等到邪气结实，才用承气汤攻下。并且告诫说：想要用大承气汤，先用小承气汤试探，如果腹部转矢气（放屁），才给大承气汤；如果不转矢气，谨慎地不可再攻下，小心翼翼不敢轻易攻下到了这种程度。仲景又说：病发于阳而反用下法，热邪内入因而形成结胸；病发于阴而下之，因而形成痞证。所谓“热入”，是指邪气进入胃腑。三阴病过早攻下，虽然不至于形成结胸，但也难免形成痞气了。唉！经与腑之间，怎么能不加以辨别呢？
Cheng stated: "Jing" (Meridian) refers to a path, running within the skin and among the muscles. "Fu" (Hollow Organ) refers to a vessel, used to hold food and fluids. Various books on treating Cold Damage often confuse "Jing" with "Fu" and vice versa, establishing theories that mix them up, which greatly confuses people. I hereby specifically clarify this distinction.
When pathogens invade the Three Yang meridians, there are the Taiyang Meridian, Yangming Meridian, and Shaoyang Meridian. For pathogens in the Three Yang Jing that have not entered the Fu organs, sweating therapy can resolve them. When pathogens invade the Three Yin meridians, there are the Taiyin Meridian, Shaoyin Meridian, and Jueyin Meridian. For pathogens in the Three Yin Jing that have already entered the Fu organs, purgative therapy can resolve them. The "Fu" referred to as entering implies the Yangming Stomach Fu organ. Once pathogens from the Three Yang or Three Yin enter the Stomach Fu, transmission ceases. This is because the Stomach belongs to Earth, symbolizing where all things return. The *Shanghan Lun* states: There is Taiyang-Yangming, Zhengyang-Yangming, and Shaoyang-Yangming. Here, "Yangming" refers to the Stomach Fu, not the Yangming Meridian. If pathogens are in the Taiyang Meridian but do not transmit to the Yangming Meridian, instead directly entering the Stomach Fu, it is called Taiyang-Yangming. If pathogens are in the Yangming Meridian but do not transmit to the Shaoyang Meridian, instead entering its own Fu organ, it is called Zhengyang-Yangming. If pathogens are in the Shaoyang Meridian but do not transmit to the Three Yin, instead directly entering the Stomach Fu, it is called Shaoyang-Yangming. For any pathogens of the Three Yang that have entered the Stomach Fu, one should unhesitatingly use purgation.
Although it is common knowledge that Three Yang pathogens enter the Fu, few can recognize when Three Yin pathogens enter the Fu. The Three Yang Jing are far from the Fu organs, while the Three Yin Jing are closer to the Fu organs. However, since they are called "Jing," the pathogens remain on the pathway and have not converged into a single location. The *Shanghan Lun* states: In Taiyin disease, if the pulse is floating, sweating may be applied, preferably using Guizhi Tang (Cinnamon Twig Decoction). In Shaoyin wind-strike, if the radial pulse is slightly weak and the cunial pulse is floating, recovery is imminent. In Jueyin wind-strike, a slightly floating pulse indicates impending recovery, while a non-floating pulse indicates no recovery. These statements imply that pathogens reside in the Jing, allowing for a return to the exterior via sweating. If pathogens have entered the Fu, there is no route for external exit; only by unblocking the bowels can pathogens exit internally. This explains the establishment of Dachengqi Tang (Major Order the Qi Decoction), Xiaochengqi Tang (Minor Order the Qi Decoction), and Tiaowei Chengqi Tang (Regulate the Stomach Order the Qi Decoction).
Then, why use Baihu Tang (White Tiger Decoction) to treat Fu diseases? This is because when Three Yang pathogens first enter the Stomach Fu, both interior and exterior are hot, but the pathogens have not yet condensed, and the heat is diffuse without symptoms of gastric excess and constipation. Thus, Baihu Tang is used to clear heat internally from the Stomach Fu and vent heat externally through the skin, resolving both layers. If pathogens have condensed, presenting with severe abdominal pain in Taiyin, dry throat and mouth with water diarrhea and epigastric hardness in Shaoyin, or irritability, fullness, and penile retraction in Jueyin, Baihu Tang is contraindicated; urgent purgation is required. This is simply because distinguishing between Jing and Fu prevents therapeutic errors.
What about Taiyang pathogens entering their own Fu organ? The Fu of Taiyang is the Bladder, which stores urine. When Taiyang disease is severe, pathogens shift to the Fu, causing thirst and dark urine. Presenting with Taiyang disease symptoms alongside these signs is called "Taiyang transmitting to its own Fu." It should be treated with Wuling San (Five-Ingredient Powder with Poria), using Guizhi (Cinnamon Twig) to release exterior pathogens and Zhuling (Polyporus) and Zexie (Alisma) to promote urination for cure.
A question arises: Can yang pathogens transmitted to yin meridians still return to the exterior for sweating? Is this true? I say: Do not doubt the ancients' words. "Jing" means path, like a road. Just as there is a path for Three Yang pathogens to reach Three Yin, there is a path for Three Yin pathogens to return to Three Yang. This is a principle of cyclic transformation, unlike pathogens entering the Stomach Fu, which have no exit route. I have observed patients with strong constitutions who recovered after completing meridian transmission, all resolved through sweating. The *Shanghan Lun* states: For those whose disease does not transmit further nor acquire mixed pathogens, on the seventh day, Taiyang disease declines, headache improves slightly; on the eighth day, Yangming disease declines, body heat subsides slightly; on the ninth day, Shaoyang disease declines, deafness improves slightly; on the tenth day, Taiyin disease declines, abdomen softens, appetite returns; on the eleventh day, Shaoyin disease declines, thirst stops, tongue dryness resolves, followed by sneezing; on the twelfth day, Jueyin disease declines, scrotum relaxes, lower abdomen feels slightly heavy, vital qi has departed, and the patient's spirit is refreshed. Does this not prove that completion of meridian transmission leads to recovery via returning to the exterior and sweating?
Someone asks: Yin meridians should not sweat. Now, Taiyin presents with a floating pulse, and Guizhi Tang is used. Can Three Yin meridians also be resolved by sweating? Will Guizhi Tang become the primary medicine for Taiyin? I reply: Incorrect. One must interpret Zhang Zhongjing's works comprehensively. If pathogens have entered the interior but sweating is induced again, internal heat increases; hence, "Yin should not sweat." However, if pathogens enter the interior but then return to the exterior, this represents pathogens exiting outward; hence, "returning to Yang to sweat." Guizhi Tang is originally for Taiyang wind-strike. Its use in Taiyin occurs because Taiyang wind-strike was mistakenly treated with purgation, transmitting pathogens to Taiyin. Taiyin pulse should be deep; a floating pulse indicates the syndrome is in Taiyin but the pulse reflects Taiyang. This shows Taiyang pathogens have not fully entered Yin, and Taiyin pathogens have a strong tendency to return to Yang for sweating. Thus, Guizhi Tang is used to disperse them, allowing pathogens coming from Taiyang to exit via Taiyang.
By extension, if originating from Taiyang cold-injury with a cold-injury pulse, Guizhi can be replaced by Mahuang (Ephedra), inferring the logic of Zhang Zhongjing's Mahuang Shigao Tang (Ephedra and Gypsum Decoction). If originating from Yangming with a Yangming pulse, Guizhi can be replaced by Gegen (Kudzu Root), inferring the logic of Gegen Huanglian Huangqin Tang (Kudzu, Coptis, and Scutellaria Decoction). If originating from Shaoyang with a Shaoyang pulse, Guizhi can be replaced by Chaihu (Bupleurum), making Daxiehu Tang (Major Bupleurum Decoction) the specific formula for Shaoyang transmitting to Taiyin. However, only if there is solid abdominal pain, indicating Spleen pathogens interfering with the Stomach, should Dahuang (Rhubarb) be used for purgation; otherwise, just add Shaoyao (Peony) to the base formula to harmonize. The *Shanghan Lun* states: Original Taiyang syndrome, mistakenly purged by physicians, transmitting to Taiyin with abdominal pain, uses Guizhi Tang plus Shaoyao; for severe solid pain, Guizhi Tang plus Dahuang. This aligns with the above logic. If Taiyin follows this pattern, why not Shaoyin and Jueyin? In the Shaoyin chapter, Zhang Zhongjing uses Sixni San (Four-Reversal Powder) to treat Yang reversal, containing Chaihu, Huangqin (Scutellaria), Gancao (Licorice), and Zhishi (Immature Bitter Orange). Does Shaoyin also use Bupleurum to scatter pathogens? Indeed, because heat pathogens transmit to the interior, roaming between Shaoyin meridians without condensing into excess, and not sinking into the Stomach Fu, Huangqin and Gancao are used to clear transmitted heat, while Zhishi guides away stomach stagnation, preventing pathogens from combining internally to cause gastric excess constipation. Chaihu is added to unblock the Three Yang pathways, allowing pathogens to exit as they entered, without disturbing the Middle Jiao, resolving the disease. This demonstrates Zhang Zhongjing's subtle manipulation of herbs.
In my practice, for yang pathogens entering yin without condensation, I imitate the ancient Sanhuang Jiedu Tang (Three Yellows Detoxification Decoction) concept, adding Shigao (Gypsum) to guard the Yangming mid-pathway, and adding Chaihu to hope for a return to the original path and sweating resolution. Generally, treating Cold Damage prioritizes releasing the exterior over attacking the interior. Not only should Three Yang pathogens be dispersed from the exterior, but even Three Yin pathogens without condensation are hoped to return to Yang and the exterior. Only when pathogens condense is Chengqi Tang used for purgation. A warning is given: Before using Dachengqi Tang, try Xiaochengqi Tang first. If intestinal gas passes, administer Dachengqi Tang; if not, cautiously avoid further purgation. One must be extremely careful not to purge lightly. Zhang Zhongjing also said: Disease starting in Yang, if mistakenly purged, heat enters forming Jie Xiong (Chest Binding); disease starting in Yin, if purged, forms Pi (Glomus/Fullness). "Heat entering" means entering the Stomach. Premature purgation in Three Yin, while not forming Chest Binding, inevitably results in Pi syndrome. Alas! How can one fail to distinguish between Jing and Fu?