伤寒恶寒。何以明之。恶寒者。风寒客于荣卫之中也。惟其风寒客于荣卫。则洒淅
然恶寒也。惟其荣卫之受风寒。则啬啬然不欲舒也。其恶寒者。非寒热之寒也。又
非恶风也。且恶风者见风至则恶矣。得以居密室之内。帏帐之中。则坦然自舒也。
至于恶寒者。则不待风而寒。虽身大热而不欲去衣者是也。寒热之热。谓寒热更
作。热至则寒无矣其恶寒虽发热而不欲去衣也甚则至于向火被覆而犹不能
遏其寒也。所以然者。由阴气上入阳中。或阳微。或风虚相搏之所致也。恶寒一切
属表。虽里证悉具。而微恶寒者。亦是表未解也。犹当先解其外。俟不恶寒为外解。
乃可攻里也。经曰。发热而恶寒者。发于阳也。无热而恶寒者。发于阴也。谓如伤寒。
或已发热。或未发热。必恶寒者。谓继之以发热。此则发于阳也。若恶寒而蜷。脉沉
细而紧者。此则发于阴也在阳者可发汗。在阴者可温里。恶寒虽悉属表。而在表
者亦有虚实之别。若汗出而恶寒者。则为表虚。无汗而恶寒者。则为表实。表虚可
解肌。表实可发汗。又有止称背恶寒者。背者胸中之府。诸阳受气于胸中。而转行
于背。内经曰。人身之阴阳者。背为阳。腹为阴。阳气不足。阴寒气盛。则背为之恶寒。
若风寒在表而恶寒者。则一身尽寒矣。但背恶寒者。阴寒气盛可知也。经所谓少
阴病一二日。口中和而背恶寒者。当灸之。处以附子汤者是矣。又或乘阴气不足。
阳气内陷入阴中。表阳新虚。有背微恶寒者。经所谓伤寒无大热。口燥渴心烦。背
微恶寒者。白虎加人参汤主之者是也。二者一为阴寒气盛。一为阳气内陷。又何
以明之也。且阴寒气盛。岂又能消耗津液。故于少阴病则曰口中润。如阳气内陷。
则热烁津液为干。故于太阳病。则口燥舌干而渴也。二者均是背恶寒。要辨阴阳
寒热不同者。亦于口中润燥可知。
伤寒病中的恶寒症状。如何阐明其机理？恶寒，是因为风寒邪气侵袭于营卫之中。正因为风寒客居于营卫，所以身体感到如冷水洒身般的寒冷（洒淅然）。正因为营卫受到风寒侵袭，所以身体蜷缩、畏缩不敢舒展（啬啬然）。这种恶寒，并不是指寒热交替发作中的“寒”，也不是指怕风。所谓怕风，是见到风吹来就感到厌恶，如果能待在密室之内、帷帐之中，就会感到坦然舒适。至于恶寒，则不需要有风吹袭也会感到寒冷，即使身体发高热也不愿脱去衣服，就是这种情况。所谓的“寒热”之热，是指寒与热交替发作，当热来的时候，寒的感觉就没有了；而恶寒的人，虽然也发热，却不愿意脱去衣服。严重时甚至靠近火源、盖上被子仍不能遏制寒冷感。之所以这样，是由于阴气上入阳分，或者是阳气微弱，或者是风邪与虚证相互搏结所致。恶寒一概属于表证，即使具备所有的里证表现，只要还有轻微的恶寒，就说明表证尚未解除。仍然应当先解表，等到不再恶寒，表示表证已解，才可以攻治里证。经典说：发热而恶寒的，是发于阳经；不发热而恶寒的，是发于阴经。例如伤寒病，或者已经发热，或者尚未发热，但必定伴有恶寒，这预示着随后会发热，这就是发于阳经。如果恶寒且身体蜷缩，脉象沉细而紧的，这就是发于阴经。病在阳经的可以发汗，病在阴经的可以温补里虚。恶寒虽然都属于表证范畴，但在表证中也有虚实之分。如果出汗而恶寒的，属于表虚；不出汗而恶寒的，属于表实。表虚证可以用解肌法治疗，表实证可以用发汗法治疗。又有仅表现为背部恶寒的情况。背为胸中之府，诸阳之气受于胸中，转而运行于背部。《内经》说：人身之阴阳，背为阳，腹为阴。如果阳气不足，阴寒气盛，就会导致背部恶寒。如果是风寒在表引起的恶寒，那么全身都会感到寒冷。如果只是背部恶寒，可以知道是阴寒气盛。经典所说的少阴病一二日，口中平和而不渴，仅背部恶寒的，应当用灸法治疗，并处以附子汤，就是这个道理。又或者因阴气不足，阳气内陷入阴分，表阳刚刚虚弱，出现背部轻微恶寒的情况。经典所说的伤寒没有大热，口燥渴，心烦，背部轻微恶寒的，用白虎加人参汤主治，就是这个道理。这两种情况，一种是阴寒气盛，一种是阳气内陷，又该如何阐明区别呢？况且阴寒气盛，难道又能消耗津液吗？所以在少阴病中说口中湿润；如果是阳气内陷，则热邪灼烧津液导致干燥，所以在太阳病中说口燥舌干而渴。两者都是背部恶寒，要辨别阴阳寒热的不同，也可以通过观察口中润燥的情况得知。
Aversion to cold in Shanghan disease. How is its mechanism explained? Aversion to cold occurs when wind-cold pathogens invade the Ying (Nutrient) and Wei (Defensive) levels. Because wind-cold resides in the Ying and Wei, one feels a shivering sensation of cold (saxi ran). Because the Ying and Wei are affected by wind-cold, one feels shrinking and unwilling to stretch out (sesse ran). This aversion to cold is not the "cold" phase of alternating chills and fever, nor is it fear of wind. Fear of wind means feeling aversion only when exposed to wind; if staying within a sealed room or behind curtains, one feels relaxed and comfortable. In contrast, aversion to cold involves feeling cold even without wind exposure; even with high body temperature, the patient does not wish to remove clothing. The term "alternating chills and fever" refers to the cycle where heat replaces cold; when heat arrives, the chill disappears. However, patients with aversion to cold feel cold despite fever and refuse to remove clothes. In severe cases, they may lean towards fire or cover themselves with quilts yet still cannot suppress the cold sensation. This happens because Yin qi ascends into the Yang regions, or due to deficient Yang, or the interaction between wind pathogen and deficiency. Aversion to cold generally belongs to Exterior syndromes. Even if Interior symptoms are fully present, slight aversion to cold indicates that the Exterior syndrome has not yet resolved. One should first resolve the Exterior; only after aversion to cold ceases, indicating the Exterior is resolved, can one attack the Interior. The Classics state: Fever accompanied by aversion to cold indicates onset from Yang channels; absence of fever with aversion to cold indicates onset from Yin channels. For example, in Shanghan disease, whether fever has appeared or not, the presence of inevitable aversion to cold suggests fever will follow, indicating onset from Yang. If there is aversion to cold with curling up, and the pulse is deep, fine, and tight, this indicates onset from Yin. Cases in Yang channels can be treated with sweating methods; cases in Yin channels can be treated with warming the Interior. Although aversion to cold belongs to the Exterior, there are Deficiency and Excess distinctions within Exterior syndromes. Sweating accompanied by aversion to cold indicates Exterior Deficiency; absence of sweating with aversion to cold indicates Exterior Excess. Exterior Deficiency can be treated with muscle-releasing methods; Exterior Excess can be treated with sweating methods. There is also a condition described merely as aversion to cold in the back. The back is the mansion of the chest; all Yang Qi receives energy in the chest and circulates to the back. The Neijing states: In the human body, the back is Yang, and the abdomen is Yin. When Yang Qi is insufficient and Yin-cold Qi is excessive, aversion to cold in the back occurs. If aversion to cold were caused by wind-cold at the Exterior, the entire body would feel cold. Therefore, isolated aversion to cold in the back indicates excess of Yin-cold Qi. As stated in the Classics regarding Shaoyin disease: On the first or second day, if the mouth is normal (not dry/thirsty) but there is aversion to cold in the back, moxibustion should be applied, and Fuzi Tang (Aconite Decoction) prescribed. Alternatively, due to insufficiency of Yin Qi, Yang Qi may sink internally into the Yin, causing new deficiency of Exterior Yang, leading to slight aversion to cold in the back. As stated in the Classics: In Shanghan, if there is no significant fever, but dry mouth, thirst, irritability, and slight aversion to cold in the back, Baihu Jia Renshen Tang (White Tiger Decoction plus Ginseng) is the primary treatment. These two conditions differ: one is excess of Yin-cold Qi, the other is sinking of Yang Qi. How can they be distinguished? Excess Yin-cold Qi does not consume body fluids; thus, in Shaoyin disease, the mouth is described as moist. Conversely, sinking Yang Qi generates heat that scorches body fluids, causing dryness; thus, in Taiyang disease, the mouth is dry, the tongue is parched, and thirst is present. Both involve aversion to cold in the back, but the distinction between Yin/Cold and Yang/Heat can be determined by observing the moisture or dryness of the mouth.