旧说谓∶伤寒邪在阳经，其脉浮；邪入阴经，其脉沉。此浮表、沉里之大义也。其实寒
邪初感
在表，脉多沉紧而数，不见浮也。此事景岳已曾辨之矣。邪入阴经，惟寒邪直中者，脉见沉
紧；若由阳经化热传里者，脉多洪盛，未有转变沉细者。然则旧说非耶?曰∶所谓阳经脉在
浮者，非谓其脉之浮也，谓诊者当于浮分诊候其变象也；阴经脉在沉者，非谓其脉之沉也，
谓诊者当于沉分诊候其变象也。大抵初感外邪，如属风热，则脉浮，然风热之象，止见于浮
，若重按则不见也；如属风寒，则脉沉不能浮，然风寒之象，止在指力初到脉皮之上，若
重按至脉底，亦不见也，且其势有欲浮不得之意，即此可见寒邪据表，阳气不得外达矣。此
邪在阳经则脉浮之说也。邪入于里，若属沉寒，或寒湿从下受，直入阴经者，重按沉分，必
见细紧；若系热邪入里，外有寒束，则必见浮紧而沉滑矣。至伤寒由阳经化热传入阴经，只
是邪气内连，非邪气内移，表邪全罢也。其脉当较病在阳经时更觉洪实，其邪气之变象不止
见于浮分，连沉分亦如是矣。此邪在阴经则脉沉之说也。若表邪入里，而表分全退，只见里
证，此必内虚，而致邪气内陷也；或热结于胸，而为神昏、谵语，其脉必沉细而数；或寒陷
于中，而为下利、足冷，其脉必沉微欲绝，亦有沉紧而迟。邪盛正虚，比之邪气直中者，更
难挽回也。内连者，是邪气蔓延，而正气之力不敌也。内陷者，是正气全虚，而邪气据其巢
穴也。直中者，虽亦正气之虚，而邪气单刀
直入，尚未蔓延四布，盘踞未牢，故可急攻，稍迟亦无及矣。又有邪盛于表，正虚于里，如
所谓尺中微，不可发汗，尺中迟，不可下者。此犹虚处无邪，正当急补其虚，助正驱邪也，
稍迟邪即内陷矣。处处有邪，便难措手。
旧时的说法认为：伤寒邪气在阳经，脉象浮；邪气进入阴经，脉象沉。这是浮脉主表、沉脉主里的基本大义。其实寒邪初感于体表时，脉象多表现为沉紧而数，并不见浮象。此事景岳（张介宾）已经辨析过。邪气进入阴经，只有寒邪直中者，脉象才见沉紧；如果是从阳经化热传里者，脉象多洪盛，没有转变为沉细的。那么旧的说法不对吗？回答说：所谓阳经脉象在浮，并不是说脉象一定是浮的，而是指诊察者应当在浮分（轻取部位）诊察其变化之象；阴经脉象在沉，并不是说脉象一定是沉的，而是指诊察者应当在沉分（重按部位）诊察其变化之象。大抵初感外邪，如果属于风热，则脉象浮，但风热的征象只见于浮分，若重按则不见；如果属于风寒，则脉象沉不能浮，但风寒的征象只出现在指力刚接触到脉皮之上时，若重按至脉底，也不见，而且其势态有想要浮起却不得之意，由此可见寒邪占据体表，阳气不能向外通达了。这就是“邪在阳经则脉浮”的说法。邪气进入体内，如果属于沉寒，或者寒湿从下部受邪，直入阴经者，重按沉分，必定见到细紧；如果是热邪入里，外面有寒邪束缚，则必定见到浮紧而沉滑。至于伤寒由阳经化热传入阴经，只是邪气在内相连，并非邪气向内移动且表邪完全解除。其脉象应当比病在阳经时更觉洪实，其邪气的变象不仅见于浮分，连沉分也是如此。这就是“邪在阴经则脉沉”的说法。如果表邪入里，而表分完全消退，只见里证，这必定是内虚，导致邪气内陷；或者热结于胸，出现神昏、谵语，其脉必沉细而数；或者寒陷于中焦，出现下利、足冷，其脉必沉微欲绝，也有沉紧而迟的情况。邪盛正虚，比起邪气直中者，更难挽回。所谓“内连”，是邪气蔓延，而正气之力不敌；所谓“内陷”，是正气全虚，而邪气占据其巢穴。所谓“直中”，虽然也是正气之虚，但邪气单刀直入，尚未蔓延四布，盘踞未牢，所以可以急攻，稍迟就来不及了。又有邪盛于表，正虚于里，如所谓尺中微，不可发汗，尺中迟，不可下者。这种情况还是虚处无邪，正当急补其虚，助正驱邪，稍迟邪气就会内陷了。处处都有邪气，就难以着手治疗。
Old theories state: When pathogenic cold is in the Yang meridians, the pulse is floating; when pathogen enters the Yin meridians, the pulse is sinking. This represents the general principle that a floating pulse indicates exterior conditions and a sinking pulse indicates interior conditions. In reality, when cold pathogen is initially contracted at the exterior, the pulse is often deep (Chen), tight (Jin), and rapid (Shu), rather than floating. Zhang Jingyue has already clarified this matter. When pathogen enters the Yin meridians, only in cases of direct strike by cold pathogen does the pulse appear deep and tight; if heat transforms from the Yang meridians and transmits inward, the pulse is typically surging (Hong) and full, rarely transforming into a fine (Xi) and thin pulse. Then, are the old theories incorrect? The answer is: When it is said that the pulse of the Yang meridians lies in "floating," it does not mean the pulse itself must be floating, but rather that the practitioner should examine its variations at the superficial level (Fu fen, light pressure); when it is said that the pulse of the Yin meridians lies in "sinking," it does not mean the pulse itself must be sinking, but rather that the practitioner should examine its variations at the deep level (Chen fen, heavy pressure). Generally, upon initial contraction of external pathogen, if it belongs to wind-heat, the pulse floats, but the signs of wind-heat are only visible at the superficial level; if pressed heavily, they disappear. If it belongs to wind-cold, the pulse is deep and cannot float, but the signs of wind-cold are only present where the finger force first touches the skin surface of the pulse; if pressed heavily to the bottom of the pulse, they also disappear, and the momentum suggests an intention to float but inability to do so. From this, we can see that cold pathogen occupies the exterior, preventing Yang qi from reaching the outside. This explains the saying "pathogen in Yang meridians results in a floating pulse." When pathogen enters the interior, if it involves deep cold or cold-dampness received from below directly entering the Yin meridians, pressing deeply will definitely reveal a fine and tight pulse; if heat pathogen enters the interior while exterior cold binds, the pulse will likely be floating and tight with a slippery quality at the deep level. Regarding cold damage transforming into heat in the Yang meridians and transmitting to the Yin meridians, this is merely the internal connection of pathogen, not a complete shift of pathogen inward with the total resolution of exterior pathogen. The pulse should feel more surging and solid compared to when the disease was in the Yang meridians; the variations of the pathogen are seen not only in the superficial level but also in the deep level. This explains the saying "pathogen in Yin meridians results in a sinking pulse." If exterior pathogen enters the interior and the exterior completely recedes, showing only interior symptoms, this must be due to internal deficiency causing pathogen to sink inward; or if heat knots in the chest causing confusion and delirious speech, the pulse must be deep, fine, and rapid; or if cold sinks into the middle jiao causing diarrhea and cold feet, the pulse must be deep, faint, and nearly imperceptible, or deep, tight, and slow. With excess pathogen and deficient healthy qi, recovery is harder than in cases of direct strike by pathogen. "Internal connection" means pathogen spreads while healthy qi is insufficient to resist; "internal sinking" means healthy qi is entirely deficient, allowing pathogen to occupy its stronghold. "Direct strike" implies although there is also deficiency of healthy qi, the pathogen strikes directly without spreading widely or firmly establishing itself, so urgent attack is possible, but delay renders it ineffective. There are also cases where pathogen is excessive at the exterior and healthy qi is deficient at the interior, such as "if the chi position is faint, sweating is contraindicated; if the chi position is slow, purgation is contraindicated." In these cases, the deficient areas lack pathogen, so one should urgently tonify the deficiency to assist healthy qi in expelling pathogen; otherwise, pathogen will sink inward. If pathogen is everywhere, treatment becomes difficult to initiate.