仲景书以伤寒命名。此伤寒乃外感病之统名也。而伤寒类中。专有一种太阳病。或已发
热
。或未发热。必恶寒体重呕逆。脉阴阳俱紧者。独名之曰伤寒。伤寒与中风。同见头项强痛
恶
寒之太阳病。同一浮脉。最易牵混。最宜分别。脉浮而缓。汗自出者。此属风因。脉浮而紧
。汗不出者。此属寒因。风则伤卫。寒则伤营。营卫界限綦严。丝毫不容错认。而叔和序例
。谓凡伤寒之病。多从风寒得之。风与寒尚混同无别。奚况温热耶。又谓冬时严寒。中而即
病者。名曰伤寒。无论仲景当日未有此说。即指定冬时发者始为正伤寒。设当严寒之时。遇
有头痛发热之太阳病。或其人脉缓汗自出。或但发热不恶寒而渴者。将概从仲景大发其汗之
例。其不误人者几希。然则从时乎。从证乎。惑滋甚矣。要之仲景之圆机活法。初未尝泥定
四
时言病。但教人从平脉辨证上认取。太阳病无论已未发热。必恶寒体重呕逆脉阴阳俱紧者。
即此便是真正寒伤营病。似此辨得真确。自不得以风混寒。并不至以热乱寒矣。
伤寒病有同一发热。其邪不在太阳而直入阴经者。按三阴经中。惟少阴一经。最易与太
阳病
牵混。以太阳膀胱。与少阴肾。一脏一腑。相为表里。其在阴精素虚之人。寒邪不俟由表传
经。径从膀胱之腑。袭入肾脏者有之矣。故仲景于大青龙汤一证。伤寒脉浮缓。身不疼。但
重乍有轻时。必辨其无少阴证。方予以大发其汗。若误施之少阴病。则肾中真阳。随汗飞腾
。可不慎欤。太阳伤寒。其脉浮紧。或兼风因。间有浮缓。若少阴病。其脉必沉而微细。仲
景于少阴病。始得之。反发热。脉沉者。特有麻黄附子细辛汤之制。盖必以附子镇摄肾中真
阳。而后麻黄细辛始得引少阴之邪驱之出表。其有寒邪初犯太阳。以次传经。渐入三阴者。
又多寒热错杂之证。不必尽属寒因。更有种种救逆诸法。或径从里解。或还从表解。随证施
治。又各不同矣。若寒邪直入三阴。绝不见一毫表证者。其证或吐利。或厥冷。或烦躁。种
种危候。死生之机。只争俄顷。则当急用回阳猛剂。直破重扃。收复真阳。迅扫阴霾。稍缓
须臾。即属不救。仲景大法。森森俱列。谁谓伤寒之病。可概从表散哉。
张仲景的著作以“伤寒”命名。这里的“伤寒”是外感病的统称。而在伤寒各类病证中，专门有一种称为“太阳病”。其症状表现为：或者已经发热，或者尚未发热，但必定伴有恶寒、身体沉重、呕吐逆气，且寸关尺三部脉象均呈紧象的，才单独称之为“伤寒”。
“伤寒”与“中风”，都可见到头痛项强、恶寒等“太阳病”表现，脉象也都见浮脉，最容易混淆，因此最应当加以区分。脉象浮而缓，汗自出的，这属于风邪致病；脉象浮而紧，无汗的，这属于寒邪致病。风邪伤害卫气，寒邪伤害营血，营与卫的界限非常严格，丝毫不容认错。然而王叔和在《序例》中说，凡是伤寒的病，多从风寒而来，将风与寒混同而无区别，更何况温热病呢？他又说，冬季严寒之时，受邪即发病的，名叫“伤寒”。无论张仲景当时是否有此说法，即使指定冬季发作的才是正宗的“伤寒”，假设在严寒之时，遇到有头痛发热的“太阳病”，如果其人脉缓汗自出，或者只发热不恶寒且口渴的，难道都要一概按照张仲景大发其汗的法则治疗吗？这样不误人的情况太少了。那么，是顺从时令呢，还是顺从证候呢？困惑更加深重了。总之，张仲景圆融机变、灵活运用的治法，起初并未拘泥于四季来谈论疾病，只是教导人们通过平脉辨证来识别病机。“太阳病”无论是否发热，只要必定伴有恶寒、身体沉重、呕吐逆气、脉阴阳俱紧的，这就是真正的寒伤营血病。像这样辨别得真确，自然就不会以风混同寒，也不会以热扰乱寒了。
伤寒病中有同样出现发热的，但其邪气不在太阳经，而是直接传入阴经的。在三阴经中，只有少阴经，最容易与太阳病相混淆。因为太阳膀胱与少阴肾，一脏一腑，互为表里。对于那些阴精素来亏虚的人，寒邪不必等待由表传经，径直从膀胱之腑袭入肾脏的情况是有的。所以张仲景在大青龙汤这一证候中，对于伤寒脉浮缓、身体不疼、只是沉重、偶尔有减轻的时候，必须辨别其没有少阴病证，才给予大发其汗的治疗。如果误施用于少阴病，那么肾中的真阳就会随着汗水飞散流失，能不谨慎吗？
太阳伤寒，其脉象浮紧，或兼有风邪因素，间或有脉浮缓的。若是少阴病，其脉象必定沉而微细。张仲景对于少阴病，初起时反而发热、脉沉的，特别制定了麻黄附子细辛汤。大概是因为必须用附子镇摄肾中的真阳，然后麻黄、细辛才能引导少阴的邪气驱除出体表。那些寒邪初犯太阳，依次传经，逐渐进入三阴经的，又多见寒热错杂的证候，不一定全属寒邪致病。更有各种种样的救逆方法，有的直接从里解，有的还从表解，随证施治，又各不相同了。如果寒邪直接传入三阴经，完全不见丝毫表证的，其症状或是吐利，或是四肢厥冷，或是烦躁，种种危重征候，死生的关键，只在顷刻之间，这时就应当急用回阳猛剂，直破重重阻碍，收复真阳，迅速扫除阴霾，稍微延缓片刻，就属于无法救治了。张仲景的大法，严谨地全部列出，谁说伤寒的病，可以一概从表散治疗呢？
Zhang Zhongjing’s classic is named "Shanghan" (Cold Damage). Here, "Shanghan" serves as a general term for external contraction diseases. Among the various categories of Shanghan, there is a specific type known as Taiyang disease (disease of the Taiyang channel). Its manifestations include: either fever has already appeared, or it has not yet appeared, but there must be aversion to cold, heaviness of the body, vomiting and regurgitation, and a tight pulse at both yin and yang positions (cun and guan). Only this specific presentation is uniquely termed "Shanghan."
Both "Shanghan" (Cold Damage) and "Zhongfeng" (Wind Strike) present with Taiyang disease symptoms such as headache, stiffness of the head and neck, and aversion to cold, and both exhibit a floating pulse. They are most easily confused and thus require careful differentiation. A pulse that is floating and slow, accompanied by spontaneous sweating, indicates an etiology of wind. A pulse that is floating and tight, without sweating, indicates an etiology of cold. Wind damages Wei Qi (Defensive Qi), while cold damages Ying Blood (Nutritive Blood). The boundary between Ying and Wei is extremely strict; errors in identification are inadmissible. However, Wang Shuhe, in his Preface to the Examples, stated that most Shanghan diseases arise from wind and cold, conflating wind and cold without distinction, let alone differentiating them from warm-heat diseases. He further stated that those who contract illness immediately during the severe cold of winter are named "Shanghan." Regardless of whether Zhang Zhongjing held this view at the time, even if one specifies that only winter-onset cases constitute true "Shanghan," consider a scenario during severe cold where a patient presents with Taiyang disease characterized by headache and fever. If this patient has a slow pulse with spontaneous sweating, or exhibits only fever without aversion to cold and with thirst, should they all be treated according to Zhang Zhongjing’s principle of inducing heavy sweating? In such cases, misdiagnosis would be nearly inevitable. Thus, should treatment follow the season or the syndrome? The confusion deepens. Ultimately, Zhang Zhongjing’s flexible and adaptive methods were never rigidly bound to seasonal discussions of disease. Instead, he instructed practitioners to identify pathogenesis through pulse analysis and syndrome differentiation. For Taiyang disease, regardless of whether fever is present, if there is aversion to cold, body heaviness, vomiting/regurgitation, and a tight pulse at both yin and yang positions, this constitutes true cold damaging Ying Blood. With such accurate differentiation, one will not confuse wind with cold, nor allow heat to disrupt the understanding of cold.
In Shanghan diseases, some present with fever, but the pathogen does not remain in the Taiyang channel but directly enters the Yin channels. Among the Three Yin channels, Shaoyin disease is most easily confused with Taiyang disease. This is because the Taiyang Bladder and the Shaoyin Kidney share a zang-fu exterior-interior relationship. In individuals with inherent deficiency of Yin essence, cold pathogens may bypass the transmittal process from the exterior to the interior and directly invade the Kidney from the Bladder fu-organ. Therefore, regarding the syndrome treated by Da Qing Long Tang (Major Green Dragon Decoction), where the Shanghan pulse is floating and slow, the body is not painful but feels heavy, occasionally alleviating, Zhang Zhongjing insisted on distinguishing the absence of Shaoyin syndrome before administering heavy sweating therapy. If mistakenly applied to Shaoyin disease, the True Yang within the Kidney would dissipate with the sweat; how can one not be cautious?
Taiyang Shanghan typically presents with a floating-tight pulse, or occasionally a floating-slow pulse if wind factors are involved. Conversely, Shaoyin disease presents with a sunken, thready, and fine pulse. For Shaoyin disease presenting with initial onset, counter-current fever, and a sunken pulse, Zhang Zhongjing specifically formulated Ma Huang Fu Zi Xi Xin Tang (Ephedra, Aconite, and Asarum Decoction). This is because Aconite is required to stabilize the True Yang in the Kidney, allowing Ephedra and Asarum to guide the Shaoyin pathogen out to the exterior. When cold pathogens initially attack Taiyang and gradually transmit through the channels into the Three Yin channels, the presentations often involve mixed cold and heat patterns, not necessarily attributable solely to cold etiology. Various rescue methods exist: some resolve from the interior, others from the exterior, each tailored to the specific syndrome. If cold pathogens directly enter the Three Yin channels without any exterior signs, symptoms may include vomiting and diarrhea, cold extremities, or restlessness—various critical conditions where the pivot of life and death hangs in the balance. In such cases, potent Yang-restoring decoctions must be urgently administered to break through obstructions, recover True Yang, and swiftly dispel yin-cold. Any delay renders the condition incurable. Zhang Zhongjing’s major principles are rigorously documented; who claims that Shanghan diseases can be universally treated by exterior-dispersing methods?