发明曰伤寒受病之由皆出热论一篇而已皆传足经不传手经何也盖伤寒病冬月得之足太阳
膀胱
经为首次至足厥阴肝经为尾此病惟伤北方与东方及戌土上有足阳明胃湿之专位兼丑上有足太
阴脾土之专位盖足之六经皆在东北之方经云冬伤于寒即发者为伤寒春发为温病夏发为温疫为
病最重此之谓也仲景云无奇经则无伤寒缘奇经皆附足六经不附手经寒邪只伤足经者为有奇经
故
也长夏为大热病者夏火既王火之方与秋之分皆手经居之水方与春之分皆足经不足及夏火王客
邪助于手经则不足者愈不足矣故所用之药皆泄有余而非足经药何者泄有余则不足者补矣此伤
寒只先足经而不言手经也大大意如此至于传手经者亦有之矣
此事难知曰伤寒传至五六日间渐变神昏不语或睡中独语一二句目赤唇焦舌干不饮水稀粥
与之
则咽终日不与则不思六脉细数而不洪大心下不痞腹中不满大小便如常或传至十日以来形貌如
醉人虚见神昏不已多用承气汤下之则误矣盖不知此热传手少阴心经也然而又未知自何经而来
答曰本太阳经伤风风为阳邪阳邪伤卫阴血自燥热蓄膀胱壬病逆传于丙丙丁兄妹由是传心心火
自
上迫而熏肺所以神昏也谓肺为清虚之藏内有火邪致令神昏宜栀子黄芩黄连汤若脉在丙者导赤
散脉在丁者泻心汤若误用凉膈散乃气中之血药也在左手寸脉沉滑有力者则可用之或用犀角地
黄
汤近于是也本方所说若无犀角以升麻代之是阳明经药也此解阳明经血中热药若脉浮沉俱有力
者是丙丁中俱有热也可以导赤泻心各半服之则宜矣此证膀胱传丙足传手经也下传上也丙传丁
也表传里也壬传丁者艮传离也越经传也又谓腑传脏也活人云伤寒只传足经不传手经此言不
尽
意也有从足经而传手经者何以知之经云传寒或止传一经或间传三经不可一途而取之但凭其脉
与外证治之此活法也与食则咽者邪不在胃也不与则不思者以其神昏故热邪既不在胃误与承气
汤下之其死也必矣
谨按伤寒本只传足经以上又例传手经之义可谓发病机之秘矣盖只是邪蕴日久因足经实手
经虚
故冤热尔有因汗下差误而传有因七情或劳倦等而致者有之大抵传于经必有所因所以古人有救
逆复脉等法岂但切中病情实启后人之意例尔
【发明】
关于伤寒病因的论述，都出自《热论》一篇。其核心观点是：伤寒只传足经，不传手经。为什么呢？因为伤寒病是在冬季感受邪气而得的。足太阳膀胱经是发病的首经，足厥阴肝经是发病的尾经。这种病主要损伤北方（肾）和东方（肝），以及戌土位置上有足阳明胃湿气的专位，丑土位置上有足太阴脾土气的专位。大概足部的六条经脉都位于东北方向。经文说：“冬天感受寒邪随即发病的叫伤寒，春天发病的叫温病，夏天发病的叫温疫”，这是病情最重的情况，说的就是这类病。张仲景说：“如果没有奇经，就没有伤寒。”这是因为奇经都依附于足部的六条经脉，而不依附于手部的经脉。寒邪只伤害足部经脉，是因为有奇经的缘故。长夏季节发生的大热病，是因为夏季火气旺盛，火的方位与秋季的分界处都是手经所在；水的方位与春季的分界处都是足经所在。如果夏季火气旺盛，客邪帮助手经，那么原本不足的经脉就会更加不足。所以所用的药物都是泻有余之邪，而不是针对足经的药物。为什么说是泻有余呢？因为泻了有余的部分，不足的部分也就得到了补益。这就是伤寒只先传足经而不提手经的原因。大意大致如此。至于传入手经的情况，也是有的。
【此事难知】
有人问：伤寒传到五六天之间，逐渐出现神志昏迷、不说话，或者在睡梦中独自说一两句胡话，眼睛发红，嘴唇焦裂，舌头干燥但不想喝水。给喝稀粥就能咽下，整天不给喝就不想吃。脉象细数而不洪大，心下没有痞满感，腹部没有胀满感，大小便正常。或者传到十天以后，形貌像醉酒的人，虚性神志昏迷不止。这时候如果用承气汤攻下，就错了。这是不知道热邪已经传入手少阴心经。然而又不知道是从哪条经脉传来的。
回答：原本是太阳经受风邪侵袭。风是阳邪，阳邪伤害卫气，阴血自然燥热。热邪蓄积在膀胱（壬水），逆传于丙火（小肠）。丙丁如同兄妹，由此传于心。心火从上向下逼迫并熏蒸肺脏，所以导致神志昏迷。肺是清虚的脏器，内有火邪，导致神志昏迷。适宜用栀子黄芩黄连汤。如果脉象显示病在丙（小肠），用导赤散；脉象显示病在丁（心），用泻心汤。如果误用凉膈散，那是治疗气分中的血药。如果在左手寸脉沉滑有力的情况下，可以使用它。或者使用犀角地黄汤，也接近这个意思。原方所说如果没有犀角，可以用升麻代替，这是阳明经的药物，是解除阳明经血中热邪的药。如果脉象浮取沉取都有力，说明丙（小肠）和丁（心）都有热，可以各半服用导赤散和泻心汤，这样就适宜了。这个证候是膀胱传丙，足经传手经，下传上，丙传丁，表传里。壬传丁，相当于艮卦传离卦，这叫越经传，也叫腑传脏。朱肱（活人）说“伤寒只传足经不传手经”，这话表达得不够全面。也有从足经传到手经的情况。怎么知道的呢？经文说：“传变寒邪，有时只传一经，有时隔经传三经”，不能拘泥于一种途径来取值。只要根据脉象和外证来治疗，这才是灵活的方法。吃东西能咽下，说明邪气不在胃；如果不给吃就不想吃，是因为神志昏迷。既然热邪不在胃，误用承气汤攻下，病人一定会死。
【谨按】
按语：伤寒本来只传足经，以上又举例说明了传手经的道理，可以说是揭示了发病机理的秘密。这大概是因为邪气蕴结日久，因为足经实而手经虚，所以冤热（郁热）产生。有的是因为发汗或攻下失误而传变，有的是因为七情或劳倦等原因导致。大体上传变到某条经脉必然有所原因。所以古人有救逆、复脉等方法，岂止是切中病情，实际上是开启了后人的思路罢了。
[Invention]
Regarding the etiology of Shanghan (Cold Damage), all arguments stem from a single chapter titled "Re Lun" (Discourse on Heat). The core viewpoint is that Shanghan transmits only through the Foot meridians and not the Hand meridians. Why is this? Because Shanghan disease is contracted in winter. The Foot Taiyang Bladder Meridian is the initial meridian affected, and the Foot Jueyin Liver Meridian is the terminal one. This disease primarily injures the North (Kidney) and East (Liver), as well as specific positions associated with Dampness of the Foot Yangming Stomach at Xu Earth and Spleen Earth at Chou Earth. Generally, the six Foot meridians are located in the Northeast direction. The classic states: "If cold is injured in winter and manifests immediately, it is called Shanghan; if it manifests in spring, it is called Warm Disease; if it manifests in summer, it is called Warm Epidemic." This represents the most severe form of illness. Zhang Zhongjing stated, "Without the Extraordinary Vessels, there would be no Shanghan," because the Extraordinary Vessels attach to the six Foot meridians but not the Hand meridians. Cold pathogens only injure the Foot meridians due to the presence of the Extraordinary Vessels. In late summer, major heat diseases occur because Fire Qi dominates in summer. The direction of Fire and the boundary with Autumn are where the Hand meridians reside; the direction of Water and the boundary with Spring are where the Foot meridians reside. If Summer Fire Qi is dominant, external pathogens assist the Hand meridians, causing the already deficient meridians to become even more deficient. Therefore, the medications used are those that drain excess rather than targeting the Foot meridians. Why drain excess? Because draining the excess replenishes the deficiency. This explains why Shanghan is described as transmitting first through the Foot meridians without mentioning the Hand meridians. The general idea is as above. However, transmission to the Hand meridians does occur.
[Ci Shi Nan Zhi - Difficulties in Understanding This Matter]
Question: When Shanghan reaches the fifth or sixth day, symptoms gradually change to mental confusion, muteness, or speaking alone in sleep for one or two sentences. The eyes are red, lips are cracked, tongue is dry, yet there is no desire to drink water. Thin porridge can be swallowed if offered, but if not offered all day, there is no desire to eat. The pulse is fine and rapid but not surging. There is no epigastric fullness or abdominal distension, and urination and defecation are normal. Or, after ten days, the patient appears intoxicated, suffering from persistent false mental confusion. Using Chengqi Tang (Gut-Draining Decoction) to purge in such cases is an error. This is due to ignorance that the heat has transmitted to the Hand Shaoyin Heart Meridian. Furthermore, it is unknown which meridian it came from.
Answer: Originally, the Taiyang meridian was injured by Wind. Wind is a Yang pathogen; Yang pathogens injure Wei (Defensive) Qi, causing Yin Blood to naturally dry up. Heat accumulates in the Bladder (Ren Water) and reversely transmits to Bing Fire (Small Intestine). Bing and Ding are like siblings, thus transmitting to the Heart. Heart Fire presses down from above and steams the Lung, causing mental confusion. The Lung is a clear and empty organ; internal fire causes this confusion. It is appropriate to use Zhizi Huangqin Huanglian Tang (Gardenia, Scutellaria, and Coptis Decoction). If the pulse indicates pathology in Bing (Small Intestine), use Daochi San (Guide Out Red Powder); if in Ding (Heart), use Xiexin Tang (Drain the Heart Decoction). If mistakenly using Liangge San (Cooling the Chest Powder), which treats blood within the Qi level, it would be incorrect. If the Cun position on the left hand is deep, slippery, and forceful, it may be used. Alternatively, Xijiao Dihuang Tang (Rhinoceros Horn and Rehmannia Decoction) is also close to this indication. The original formula states that if Rhinoceros Horn is unavailable, Shengma (Cimicifugae Rhizoma) can substitute it; this is a Yangming meridian herb that clears heat from the blood in the Yangming meridian. If the pulse is forceful in both floating and deep positions, it indicates heat in both Bing and Ding. Taking half doses of Daochi San and Xiexin Tang together would be appropriate. This syndrome involves transmission from Bladder to Bing, from Foot to Hand meridians, from lower to upper, from Bing to Ding, from exterior to interior. Ren transmitting to Ding is analogous to Gen transmitting to Li, known as transcending meridian transmission, or Fu (Hollow Organ) transmitting to Zang (Solid Organ). Zhu Gong (author of Huo Ren) stated, "Shanghan transmits only through Foot meridians, not Hand meridians." This statement is incomplete. There are cases of transmission from Foot to Hand meridians. How do we know? The classics state: "Transmission of cold may affect only one meridian or skip three meridians." One cannot rely on a single rigid method. Treatment must depend on the pulse and external symptoms; this is the flexible approach. Swallowing food indicates the pathogen is not in the Stomach; lack of desire to eat when not offered is due to mental confusion. Since the heat is not in the Stomach, mistakenly using Chengqi Tang to purge will inevitably lead to death.
[Commentary]
Comment: Shanghan originally transmits only through the Foot meridians; the above examples illustrate the principle of transmission to Hand meridians, revealing the secrets of pathogenesis. This generally occurs because pathogens accumulate over time; since the Foot meridians are full/excess and the Hand meridians are deficient,郁热 (stagnant heat) arises. Transmission may result from errors in sweating or purging, or from emotional disturbances or fatigue. Generally, transmission to a specific meridian always has a cause. Thus, ancient physicians employed methods such as Niujie (Rescuing Reversal) and Fumai (Restoring Pulse), not merely addressing symptoms but also inspiring future generations' understanding.