伤寒治法先要明表里虚实。能明此四字。则仲景三百九十七法。可坐而定也。何以言之。有表实。有表虚。
有里实。有里虚。有表里俱实。有表里俱虚。予于表里虚实歌中。尝论其事矣。仲景麻黄汤类。为表实而设
也。桂枝汤类。为表虚而设也。里实则承气之类。里虚则四逆理中之类是也。表里俱实。所谓阳盛阴虚。下
之则愈也。表里俱虚。所谓阳虚阴盛。汗之则愈者也。尝读魏志华佗传。有府吏倪寻、李延共止。俱头痛身
热。所苦正同。佗曰。寻当下之。延当发汗。或难其异。佗曰。寻外实。延内实。故治之宜殊。此所谓能明表里虚
实者也。
仲景桂枝汤。用桂枝者。盖取桂之枝梢细薄者尔。非若肉桂之肉浓也。盖肉桂浓实。治五脏用之者。取其
镇重也。桂枝轻扬。治伤寒用之。取其发散也。今人例用之。是以见功寡。
仲景云。翕、奄沉。名曰滑。沉为纯阴。翕为正阳。阴阳和合。故名曰滑。古人论滑脉。虽云往来前却。流利展转。
替替然与数相似。曾未若仲景三语而足也。翕、张也。言脉升而开张也。忽焉而沉。言脉降而复也。奄、言奄
忽之间。与奄观 艾同义。仲景论滑脉。可谓谛当矣。然其言雅。恐浅识者未易晓。
大黄虽为将军。然荡涤蕴热。推陈致新。在伤寒乃为要药。但欲用之当尔。大柴胡汤中不用。诚脱误也。王
叔和云。若不加大黄。恐不名大柴胡。须是酒洗生用为有力。昔后周姚僧坦名善医。帝因发热。欲服大黄。
僧坦曰。大黄乃是快药。然至尊年高不宜轻用。帝弗从。遂至危笃。及元帝有疾。召诸医。咸谓至尊至贵。不
可轻脱。宜用平药。可渐宣通。僧坦曰。脉洪而实。此有宿食。非用大黄。必无差理。元帝从之。果下宿食而愈。
此明夫用与不用之异也。
伤寒的治疗法则，首要在于辨明表、里、虚、实。能够明白这四个字，那么张仲景的三百九十七种治法，就可以安坐而确定其要领了。为什么这样说呢？因为有表实证，有表虚证；有里实证，有里虚证；有表里俱实证，有表里俱虚证。我在《表里虚实歌》中，曾经论述过这些情况。张仲景的麻黄汤类方剂，是为表实证而设立的；桂枝汤类方剂，是为表虚证而设立的。里实证则用承气汤之类；里虚证则用四逆汤、理中汤之类。表里俱实证，就是所谓的阳盛阴虚，采用攻下法就能痊愈；表里俱虚证，就是所谓的阳虚阴盛，采用发汗法就能痊愈。
我曾读《三国志·魏书·华佗传》，记载府吏倪寻、李延一同求医，两人都头痛身热，所受的痛苦完全相同。华佗说：“倪寻应当用攻下法治疗，李延应当用发汗法治疗。”有人对此提出疑问，认为两人的症状相同为何治法不同。华佗说：“倪寻是外实（体表邪气盛），李延是内实（体内积滞实），所以治疗方法应该不同。”这就是所谓能辨明表里虚实的人。
张仲景的桂枝汤中使用桂枝，是选取桂树枝条梢部细薄的那部分，不像肉桂那样肉质厚实。因为肉桂质地浓重坚实，用于治疗五脏疾病时，是取其镇重的作用；桂枝性质轻扬升散，用于治疗伤寒时，是取其发散的作用。现在的人通常不加区分地混用，因此见效很少。
张仲景说：“脉象忽而浮起，忽而沉下，称为滑脉。沉脉代表纯阴，浮起代表正阳，阴阳调和，所以称为滑脉。”古人论述滑脉，虽然也说脉来往来流利，辗转自如，像连珠一样与数脉相似，但都不如张仲景这三句话概括得精当。“翕”意为张开，指脉气上升而开张；“奄沉”指忽然下沉，指脉气下降而复归。“奄”表示忽然之间，与“奄观艾”意义相同。张仲景对滑脉的论述，可以说是非常精当的了。然而他的言辞高雅深奥，恐怕见识浅薄的人不容易理解。
大黄虽然是将军之药，但能荡涤蕴结的热邪，推陈出新，在伤寒病中是重要的药物。只是使用它必须恰当。在大柴胡汤中如果不加大黄，确实是失误。王叔和说：“如果不加大黄，就不能称为大柴胡汤。”大黄必须经过酒洗并生用才有力。以前后周名医姚僧坦为例，皇帝因发热，想服用大黄。姚僧坦说：“大黄是峻猛之药，但陛下年事已高，不宜轻易使用。”皇帝没有听从，结果病情危重。等到元帝生病时，召集众医生，大家都说陛下尊贵，不可轻易攻伐，宜用平和的药物，慢慢宣通。姚僧坦说：“脉象洪大而实，这是有宿食停滞，不用大黄，一定无法痊愈。”元帝听从了他的建议，果然排出宿食而痊愈。这说明了用与不用的区别。
The treatment principles for Shanghan (Cold Damage) first require clarifying the exterior, interior, deficiency, and excess. Once these four concepts are understood, the three hundred and ninety-seven methods of Zhang Zhongjing can be determined with ease. Why is this so? Because there are exterior excess patterns, exterior deficiency patterns; interior excess patterns, interior deficiency patterns; patterns where both exterior and interior are in excess, and patterns where both exterior and interior are deficient. I have discussed these matters in my "Song on Exterior, Interior, Deficiency, and Excess." The Ma Huang Tang (Ephedra Decoction) category established by Zhang Zhongjing is designed for exterior excess patterns. The Gui Zhi Tang (Cinnamon Twig Decoction) category is designed for exterior deficiency patterns. For interior excess, formulas such as Cheng Qi Tang (Order the Qi Decoction) are used; for interior deficiency, formulas such as Si Ni Tang (Four Reversal Decoction) and Li Zhong Tang (Regulate the Middle Decoction) are used. In cases of simultaneous exterior and interior excess, it is referred to as Yang hyperactivity and Yin deficiency, and the condition can be cured by purgation (downward-draining). In cases of simultaneous exterior and interior deficiency, it is referred to as Yang deficiency and Yin hyperabundance, and the condition can be cured by diaphoresis (sweating).
I once read the Biography of Hua Tuo in the Records of Wei (Sanguozhi), which records that officials Ni Xun and Li Yan sought medical attention together. Both suffered from headache and fever, and their distress was identical. Hua Tuo said, "Ni Xun should be treated with purgation, while Li Yan should be treated with diaphoresis." Someone questioned this difference. Hua Tuo replied, "Ni Xun has exterior excess [pathogenic qi abundant at the surface], while Li Yan has interior excess [accumulation within]. Therefore, their treatments must differ." This exemplifies one who can clearly distinguish between exterior/interior and deficiency/excess.
In Zhang Zhongjing's Gui Zhi Tang (Cinnamon Twig Decoction), the use of Gui Zhi (Ramulus Cinnamomi) refers to selecting the thin, slender twigs of the cinnamon tree, not the thick bark like Rou Gui (Cortex Cinnamomi). Rou Gui is dense and substantial; when treating diseases of the five Zang organs, its heavy, sedative nature is utilized. Gui Zhi is light and ascending; when treating Shanghan (Cold Damage), its dispersing and diffusing properties are utilized. Nowadays, people often use them interchangeably without distinction, resulting in few therapeutic successes.
Zhang Zhongjing stated: "When the pulse rises suddenly and then sinks, it is called a Slippery Pulse (Hua Mai). Sinking represents pure Yin, rising represents positive Yang. When Yin and Yang harmonize, it is named Slippery." Ancient discussions on the Slippery Pulse described it as flowing smoothly back and forth, turning freely, resembling a string of pearls and similar to the Rapid Pulse (Shu Mai). However, none matched the sufficiency of Zhang Zhongjing's three words. "Xi" means opening or spreading, indicating the pulse rising and expanding. "Yan chen" means sinking suddenly, indicating the pulse descending and returning. "Yan" denotes a sudden moment, having the same meaning as in "Yan Guan Ai." Zhang Zhongjing's discussion of the Slippery Pulse can be considered highly accurate. However, his language is elegant and profound, making it difficult for those with shallow understanding to easily comprehend.
Although Da Huang (Radix et Rhizoma Rhei) is known as the "General," it sweeps away accumulated heat, eliminates the old, and generates the new. It is a crucial herb in the treatment of Shanghan (Cold Damage). However, its application must be appropriate. Its omission in Da Chai Hu Tang (Major Bupleurum Decoction) is indeed an error. Wang Shuhe stated, "If Da Huang is not added, it cannot be called Da Chai Hu Tang." Da Huang must be washed with wine and used raw to be effective.
Consider Yao Sengtan, a famous physician of the Later Zhou dynasty. The Emperor, suffering from fever, wished to take Da Huang. Yao Sengtan said, "Da Huang is a potent purgative, but Your Majesty is advanced in age and should not use it lightly." The Emperor did not heed this advice and became critically ill. Later, when the Yuan Emperor fell ill, all physicians were summoned. They argued that His Majesty is supreme and noble, and should not be subjected to harsh depletion; mild herbs should be used to gradually promote circulation. Yao Sengtan said, "The pulse is surging and excess, indicating retained food stagnation. Without using Da Huang, recovery is unlikely." The Yuan Emperor agreed and recovered after passing the retained food. This illustrates the difference between using and not using the herb.