寒为阴，热为阳。发热，阳也，由阴气不和于阳而发热也。夫阴气不和于阳，是为阴虚。然阴在内，为阳
之守，阴虚则阳无所守，阳无所守则阳气亦虚，是发热有属阴虚者，有属阳虚者。阴虚发热，宜养血滋阴，阳
虚发热，当养气助阳。人身阴阳和则无热，阴阳不和则发热，揆其常理，但当和阴阳、调气血也。然而热之发
也，有微暴不同。微热者，热而和缓，阴血内虚也；暴热者，热之燔灼，阳气亢害也。阴血内虚而热，当以
滋养之药治之；阳气亢害而热，宜以温热之药治之。盖微热者，有根之热也∶热暴者，无根之热也。无根之热，
是为脱热；脱热者，阳气外脱而热也。如是之热，当求其属以衰之，故曰甘温除大热也。凡病而发热者什之九，
是身虽发热，必有本证。医者当视其色，诊其脉，察其表里，揆其虚实，合本证而详论之，得其要矣。
热，阳气也；寒，阴气也。恶寒者，周身毛窍不得阳气之卫外，故皮毛啬啬然而洒淅也。人周身八万四
千毛窍，太阳卫外之气也。若病太阳之气，则通体恶寒。从头项而至背膂，太阳循行之经也∶若病太阳之经，
则其背恶寒。恶寒之外，又有身寒。身寒者，着衣重复而身常寒，乃三焦火热之气不能外温肌肉也。《伤寒论》
云∶形冷恶寒者，此三焦伤也。形冷恶寒，即身寒之谓也。凡伤寒初起，身必发寒，盖寒乃太阳之本气也。
经云∶太阳之上，寒气主之。是太阳以寒为本，以热为标也。恶寒之外，又有恶风。经云∶厥阴之上，风气
主之。人身通体皮毛，太阳之气所主也。皮毛之内，肌腠之间，则有热肉充肤之血，厥阴之气所主也。病太
阳之本气，而皮毛不利，则恶寒；病厥阴之本气，而肌腠不利，则恶风。风、寒难以分别，从皮毛、肌腠而有
别也。病在皮毛，则皮毛闭拒而无汗；病在肌腠，则皮毛开发而有汗。盖凝敛闭拒则为寒，鼓动开发则为风。
风也，寒也，皆正气内虚，而淫气随生也。有身虽发热，发热之中，仍兼恶寒，法当辛温以治其热。经云∶病
未反本，治当从本。此之谓也。
寒属于阴，热属于阳。发热，属于阳证，是由于阴气不能与阳气和谐协调而导致发热。所谓阴气不能与阳气和谐协调，这就是阴虚（阴液不足）。然而，阴在内，是阳的守持者，如果阴虚，那么阳就失去了守持的对象；阳失去守持，阳气也会随之虚弱。因此，发热有的属于阴虚，有的属于阳虚。阴虚导致的发热，适宜采用养血滋阴的方法治疗；阳虚导致的发热，应当采用补气助阳的方法治疗。人身阴阳调和就没有热象，阴阳不调和就会发热，推究其常理，只应当调和阴阳、调理气血罢了。然而热的发作，有轻微和暴急的不同。微热，是指热势和缓，这是阴血内部亏虚所致；暴热，是指热势猛烈灼人，这是阳气亢盛为害所致。因阴血内部亏虚而发热，应当用滋养的药物来治疗；因阳气亢盛为害而发热，适宜用温热性质的药物来治疗。大概微热，是有根的热；暴热，是无根的热。无根的热，称为脱热（阳气外脱所致的假热）；脱热，是阳气向外脱逸而产生的热象。像这样的热，应当寻求其根本属性以使其衰退，所以说“甘温除大热”。凡是生病发热的占十分之九，这说明身体虽然发热，但一定有本质的证候。医生应当观察患者的面色，诊察脉象，考察表里状况，揣度虚实情况，结合本质证候详细论述，就能抓住关键了。
热，是阳气；寒，是阴气。恶寒（怕冷），是因为周身毛孔得不到阳气的卫护于外，所以皮肤感到寒冷战栗。人周身有八万四千个毛孔，由太阳经的卫外之气所主司。如果病在太阳经的气分，则全身都怕冷。从头项到背部脊柱，是太阳经循行的路线；如果病在太阳经的经脉，则背部怕冷。除了恶寒之外，还有身寒（自觉身体寒冷）。身寒，是指穿着多层衣服仍然觉得身体寒冷，这是因为三焦的火热之气不能向外温煦肌肉的缘故。《伤寒论》说：“形体寒冷且恶寒的，这是三焦受伤。”形体寒冷且恶寒，就是所说的身寒。凡是伤寒初起，身体必定发冷，因为寒是太阳经的本气。经文说：“太阳之上，寒气主之。”这说明太阳以寒为本，以热为标。除了恶寒之外，还有恶风（怕风）。经文说：“厥阴之上，风气主之。”人体全身的皮毛，由太阳之气所主司。皮毛之内，肌腠之间，则有充养肌肤的血，由厥阴之气所主司。病在太阳的本气，导致皮毛功能不利，则出现恶寒；病在厥阴的本气，导致肌腠功能不利，则出现恶风。风和寒难以区分，从皮毛和肌腠的区别来看便清楚了。病在皮毛，则毛孔闭塞拒邪而无汗；病在肌腠，则毛孔开张而有汗。大概收敛闭拒的性质属于寒，鼓动开发的性质属于风。风、寒，都是因为正气内部虚弱，而邪气随之产生的。有的病人虽然发热，但在发热的同时仍兼有恶寒，治法应当用辛温药来治疗这种热。经文说：“病未反本，治当从本。”说的就是这个道理。
Cold belongs to Yin, and heat belongs to Yang. Fever is a manifestation of Yang, arising from the disharmony between Yin Qi and Yang Qi. The disharmony of Yin Qi with Yang Qi constitutes Yin Deficiency (deficiency of Yin fluids). However, Yin resides within and serves as the anchor for Yang; if Yin is deficient, Yang has no anchor, and if Yang lacks an anchor, Yang Qi also becomes deficient. Thus, fever may be attributed to either Yin Deficiency or Yang Deficiency. For fever due to Yin Deficiency, nourishing blood and enriching Yin is appropriate; for fever due to Yang Deficiency, tonifying Qi and assisting Yang is indicated. When Yin and Yang are in harmony within the body, there is no heat; when they are disharmonious, fever occurs. According to general principles, one should merely harmonize Yin and Yang and regulate Qi and Blood. However, the onset of heat varies in intensity. Mild heat refers to a gentle and gradual fever, caused by internal deficiency of Yin Blood; sudden or violent heat refers to intense burning fever, caused by hyperactive and harmful Yang Qi. Fever resulting from internal deficiency of Yin Blood should be treated with nourishing herbs; fever resulting from hyperactive Yang Qi should be treated with warm-natured herbs. Generally, mild heat is "rooted" heat, whereas sudden/violent heat is "unrooted" heat. Unrooted heat is termed "Tuore" (fever due to collapse/escape of Yang); Tuore is heat generated by the external escape of Yang Qi. For such heat, treatment should seek its underlying nature to subdue it, hence the saying: "Sweet-warm [herbs] eliminate great heat." In nine out of ten cases of disease involving fever, although the body presents with fever, there must be an underlying fundamental syndrome. Physicians must observe the complexion, palpate the pulse, examine the exterior-interior status, assess deficiency-excess conditions, and analyze thoroughly in conjunction with the fundamental syndrome to grasp the essence.
Heat is Yang Qi; Cold is Yin Qi. Aversion to cold (fear of cold) occurs because the pores throughout the body fail to receive the protective function of Yang Qi on the exterior, resulting in shivering and chilliness. The eighty-four thousand pores throughout the human body are governed by the defensive Qi of the Taiyang (Greater Yang) channel. If the pathology affects the Qi aspect of Taiyang, the entire body will experience aversion to cold. From the head and neck down to the back and spine lies the pathway of the Taiyang channel; if the pathology affects the Taiyang meridian itself, aversion to cold will be localized to the back. Beyond aversion to cold, there is also "shen han" (generalized sensation of coldness). Shenhhan is characterized by feeling constantly cold despite wearing multiple layers of clothing, caused by the inability of the fire-heat Qi of the Sanjiao (Triple Burner) to warm the muscles externally. The *Shanghan Lun* states: "When the form is cold and there is aversion to cold, this indicates injury to the Sanjiao." Form being cold with aversion to cold is synonymous with shenhhan. In the initial stage of Shanghan (cold damage), the body invariably feels cold, because cold is the intrinsic nature (Ben Qi) of the Taiyang channel. The classics state: "Above Taiyang, Cold Qi governs." This indicates that Taiyang takes Cold as its root and Heat as its branch. Besides aversion to cold, there is also aversion to wind. The classics state: "Above Jueyin (Terminal Yin), Wind Qi governs." The skin and hair of the whole body are governed by Taiyang Qi. Within the skin and hair, in the interstices of the muscles and fascia, lie the blood that nourishes the flesh, which are governed by Jueyin Qi. Pathology affecting the root Qi of Taiyang leads to dysfunction of the skin and hair, resulting in aversion to cold; pathology affecting the root Qi of Jueyin leads to dysfunction of the muscle interstices, resulting in aversion to wind. Wind and cold are difficult to distinguish; differentiation lies in whether the pathology involves the skin/hair or the muscle interstices. When the pathology is in the skin and hair, the pores close and resist, leading to anhidrosis (absence of sweating); when the pathology is in the muscle interstices, the pores open, leading to sweating. Generally, contraction and closure characterize Cold, while stirring and opening characterize Wind. Both Wind and Cold arise because the healthy Qi is internally deficient, allowing pathogenic Qi to follow. In some cases, although the patient has fever, aversion to cold persists during the fever; the treatment method should employ acrid-warm herbs to address the heat. The classics state: "If the disease has not returned to its root, treatment should follow the root." This is what is meant.