人有十二经仲景伤寒但立六经者从六气也少阴少阳阳明手经司气而足经从化者也厥阴太阴太阳足经司气而手经从化
者也伤寒六经皆言足经而不言手经以足经周遍于身其部大手经祗行两手其部小其实两经同气病则皆病主其大者以概小者
非足病而手安也诸言四肢厥逆疼痛则手亦在其内未尝不病也足太阳（膀胱）以寒水主令手太阳（小肠）之火从而化寒手
阳明（大肠）以燥金主令足阳明（胃）之土从而化燥手少阳（三焦）以相火主令足少阳（胆）之木从而化火足太阴（脾）
以湿土主令手太阴（肺）之金从而化湿手少阴（心）以君火主令足少阴（肾）之水从而化火足厥阴（肝）以风木主令手
厥阴（心包）之火从而化风此六经之常也病则太阳是寒阳明是燥少阳是火太阴是湿厥阴是风而惟少阴则不从热化而从寒
化以火胜则热水胜则寒病则水能胜火而火不胜水故从壬水而化寒不从丁火而化热也至于阳明阳盛则从庚金而化燥阴盛则
从己土而化湿不皆燥盛也（阳明上编是燥盛者阳明下编是湿盛者）至于少阳阳盛则火旺而传腑阳虚则火衰而传脏不皆火
胜也
六气和平则一气不至独胜诸气败北一气独胜故见一腑一脏之病阳莫盛于阳明阴莫盛于少阴曰阳明之为病是少阴之水
负而趺阳土盛者也曰少阴之为病是趺阳土负而少阴水胜者也土胜水负则为顺水胜土负则为逆阳明腑病是土胜之证三阴脏
病是水胜之证燮理阴阳补泻水土之奥仲景既没后世庸工一丝不解也
人有十二经脉，张仲景在《伤寒论》中只确立六经辨证体系，这是依据六气（风、寒、暑、湿、燥、火）的规律而言的。少阴、少阳、阳明这三经，由手经主管气化，而足经随之化生相应的病机；厥阴、太阴、太阳这三经，由足经主管气化，而手经随之化生相应的病机。
《伤寒论》中的六经都只谈论足经而不谈手经，是因为足经遍布全身，其循行部位广大；手经只在两手之间循行，其部位狭小。实际上这两类经脉的气血是相同的，发病时都会受累，所以主要论述广大的足经来概括狭小的手经。并不是说只有足经生病而手经不生病，凡是提到四肢厥冷、逆乱、疼痛等症状，手经也包含在其中，并未尝不发病。
足太阳膀胱经以寒水之气主令，手太阳小肠经的火气随之化为寒气；手阳明大肠经以燥金之气主令，足阳明胃经的土气随之化为燥气；手少阳三焦经以相火之气主令，足少阳胆经的木气随之化为火气；足太阴脾经以湿土之气主令，手太阴肺经的金气随之化为湿气；手少阴心经以君火之气主令，足少阴肾经的水气随之化为火气（注：此处原文逻辑似有倒置或特定语境，通常心火下交于肾，肾水上济于心，但依原文直译）；足厥阴肝经以风木之气主令，手厥阴心包络的火气随之化为风气。这是六经的正常生理常态。
一旦发病，则太阳表现为寒，阳明表现为燥，少阳表现为火，太阴表现为湿，厥阴表现为风，而唯独少阴不从热化，而从寒化。因为火胜则热水退，水胜则寒气盛。发病时，水能克火，而火不能克水，所以少阴从壬水（阳水/寒水）而化为寒，不从丁火（阴火/君火）而化为热。
至于阳明经，阳气旺盛则从庚金（阳金）而化为燥，阴气旺盛则从己土（阴土）而化为湿，并不都是燥气过盛。（《伤寒论》上编讲的是燥气过盛的阳明病，下编讲的是湿气过盛的阳明病）。至于少阳经，阳气旺盛则火旺并传入腑，阳气虚弱则火衰并传入脏，并不都是火气过胜。
The human body has twelve primary meridians. Zhang Zhongjing established only the Six Meridians (Liu Jing) differentiation system in *Shanghan Lun* (Treatise on Cold Damage), based on the laws of the Six Qi (Wind, Cold, Summer-heat, Dampness, Dryness, Fire). For the Shaoyin (Lesser Yin), Shaoyang (Lesser Yang), and Yangming (Greater Yang) meridians, the Hand meridians govern the Qi transformation, while the Foot meridians follow to transform accordingly. For the Jueyin (Terminal Yin), Taiyin (Greater Yin), and Taiyang (Greater Yang) meridians, the Foot meridians govern the Qi transformation, while the Hand meridians follow to transform accordingly.
In the Six Meridians of *Shanghan Lun*, only the Foot meridians are discussed, not the Hand meridians, because the Foot meridians circulate throughout the entire body and their domains are extensive, whereas the Hand meridians circulate only in the two arms and their domains are small. In reality, both sets of meridians share the same Qi; when disease occurs, both are affected. Therefore, the discussion focuses on the extensive Foot meridians to generalize the small Hand meridians. It is not that only the Foot meridians become diseased while the Hand meridans remain unaffected. Whenever symptoms such as cold limbs, reversal (Jue), pain, or numbness are mentioned, the Hand meridians are also included and do indeed become diseased.
The Foot-Taiyang Bladder Meridian (Taiyang) governs with Cold-Water Qi, and the Hand-Taiyang Small Intestine Meridian's Fire Qi transforms into Cold Qi accordingly. The Hand-Yangming Large Intestine Meridian governs with Dry-Metal Qi, and the Foot-Yangming Stomach Meridian's Earth Qi transforms into Dry Qi accordingly. The Hand-Shaoyang Sanjiao (Triple Burner) Meridian governs with Minister-Fire Qi, and the Foot-Shaoyang Gallbladder Meridian's Wood Qi transforms into Fire Qi accordingly. The Foot-Taiyin Spleen Meridian governs with Damp-Earth Qi, and the Hand-Taiyin Lung Meridian's Metal Qi transforms into Damp Qi accordingly. The Hand-Shaoyin Heart Meridian governs with Sovereign-Fire Qi, and the Foot-Shaoyin Kidney Meridian's Water Qi transforms into Fire Qi accordingly. The Foot-Jueyin Liver Meridian governs with Wind-Wood Qi, and the Hand-Jueyin Pericardium Meridian's Fire Qi transforms into Wind Qi accordingly. This is the normal physiological state of the Six Meridians.
When disease occurs, Taiyang manifests as Cold, Yangming as Dryness, Shaoyang as Fire, Taiyin as Dampness, and Jueyin as Wind. However, Shaoyin does not transform from Heat but rather from Cold. Because Fire prevailing causes Water to retreat, and Water prevailing causes Cold to flourish. In disease, Water can overcome Fire, but Fire cannot overcome Water. Therefore, Shaoyin transforms into Cold following Ren-Water (Yang Water/Cold Water), rather than transforming into Heat following Ding-Fire (Yin Fire/Sovereign Fire).
Regarding the Yangming meridian, when Yang Qi is abundant, it follows Geng-Metal (Yang Metal) to transform into Dryness; when Yin Qi is abundant, it follows Ji-Earth (Yin Earth) to transform into Dampness. It is not always excessive Dryness. (The upper volume of *Shanghan Lun* discusses Yangming diseases characterized by excessive Dryness, while the lower volume discusses those characterized by excessive Dampness). Regarding the Shaoyang meridian, when Yang Qi is abundant, Fire is vigorous and transmits to the Fu organs; when Yang Qi is deficient, Fire is weak and transmits to the Zang organs. It is not always excessive Fire.