疫者，役也。犹徭役之谓，多见于旱潦兵燹之余，烈日郁蒸，尸骸之气，与亢胜之气，混
合化而为厉毒，散漫于天地之间，受之者大则一郡一城，小则一村一镇，互相传染，所感之
因虽同，所患之证不一。如东坡所论寒湿之疫也，东垣所论虚疫也，吴又可所论湿热相搏之
疫也，余师愚所论暑燥之疫也，故刘温舒《素问遗篇》有五疫之刺，庞安常《总病论》有五色
之治，然不可泥也。越人《五十八难》言，伤寒有五，其中风，伤寒，湿温，热病，证脉委曲详
尽，行在诸经，不知何经之动也。盖随其经所在而取之。盖天地 厉之气，不可以常理测，
不得以常法治。彼见温病，动手发汗，是误以伤寒法治温病。每遇疫病，往往失下，则又是
以温病法施治于疫，更误之甚矣。
发热
寒证发热恶寒者，病发于太阳也。无热恶寒者，病发于少阴也。温疫发热是潮热，非若
伤寒壮热，初起间有恶风，及次日即口渴畏热。而疫证憎寒壮热，有如瘅疟是已。
呕利
少阳胆木，挟火披猖，呕是上冲，利由下迫，此谓风温之呕利也。中虚始利，聚饮而呕，
此湿温之呕利也。若夫胃气不降，肺气不和之呕利，疫多有之。盖或温或疫，凡呕利者，是其
邪之出路，不可遽止，寒病反是。
诸痛
头痛目痛，太阳阳明伤寒者不至侧倾难举，温与疫则头痛如劈，两目昏瞀，势若难支，
骨烦疼，腰如被杖。寒病责在伤阳，温疫责在亏阴。
肢冷
在寒证是肾阳不通，在温证、疫证是肝阳不宣，所以寒踞少阴，与热伏厥阴有别。
鼻衄
寒证见之是邪气之将退，温疫见之乃邪气之正进。
蓄血
寒证当汗不汗，热结膀胱，温疫当下失下，火郁膜原，均有此证。凡发热不退，小便自
利，其人如狂，而喜忘者皆是。
疫病，所谓“役”，如同徭役一般。多见于旱灾、水灾或战乱之后的时期，烈日闷热蒸腾，尸骸之气与亢盛之气混合，化生为厉毒，弥漫散播于天地之间。感染此邪者，重的波及一郡一城，轻的波及一村一镇，互相传染。虽然感受的病因相同，但所患的症状却不一。如苏东坡所论述的寒湿之疫，李东垣所论述的虚疫，吴又可所论述的湿热相搏之疫，余师愚所论述的暑燥之疫。因此刘温舒在《素问遗篇》中记载了五疫的刺法，庞安常在《总病论》中记载了五色病的治法，然而不可拘泥于此。越人（扁鹊）在《难经·五十八难》中说，伤寒有五种类型，其中中风、伤寒、湿温、热病，其证候和脉象详尽曲折地描述出来，病邪行走在各条经脉之中，不知道是哪条经脉受动。大概随着病邪所在的经脉而选取相应的治疗方法。天地间的厉气，不能用常理来推测，不能用常规方法来治疗。那些见到温病就动手发汗的，是错误地用治疗伤寒的方法去治疗温病。每当遇到疫病，往往该用下法而失于使用下法，这又是用治疗温病的方法来施治于疫病，更是错上加错。
发热
寒证出现发热且恶寒的，病发于太阳病（太阳经受邪所致的病证）。无发热仅恶寒的，病发于少阴病（少阴心肾阳虚或阴虚所致的病证）。温疫引起的发热是潮热（定时发热或定时热甚），不像伤寒那样壮热（高热），初起时偶尔有恶风，到了第二天就会口渴畏热。而疫病表现为憎寒（极度怕冷）壮热，就像瘅疟（一种以高热为主症的疟疾）一样。
呕利
少阳胆木（指少阳胆经及其功能），挟带火势猖獗，呕吐是气机上冲，腹泻是由于气机下迫，这称为风温之呕利。中焦虚弱导致先腹泻，停聚的水饮导致呕吐，这称为湿温之呕利。至于胃气不降、肺气不和导致的呕利，疫病中多有发生。大概无论是温病还是疫病，凡是出现呕利的，这是邪气外出的途径，不可急于止住，寒病则相反。
诸痛
头痛目痛，如果是太阳阳明伤寒，不至于侧身困难、难以举头；温病与疫病则头痛如劈裂，两眼昏花视物不清，病情势态若难以支撑，骨骼烦疼，腰部像被棍棒打过一样疼痛。寒病责在于损伤阳气，温疫责在于亏损阴液。
肢冷
在寒证中是肾阳不通畅，在温证、疫证中是肝阳不宣通，所以寒邪踞守少阴，与热邪伏藏厥阴是有区别的。
鼻衄
寒证出现鼻衄（鼻出血），是邪气将要退去的征兆；温疫出现鼻衄，则是邪气正在深入进展的表现。
蓄血
寒证应当发汗而未发汗，导致热结膀胱；温疫应当攻下而失于攻下，导致火郁结于膜原（半表半里之隙），均有蓄血这一证候。凡是发热不退，小便自利，其人神志狂乱，且喜忘事的，都是蓄血证。
Epidemic diseases, termed "Yi" (役), are akin to corvée labor. They often occur in the aftermath of droughts, floods, or wars, where intense heat and humidity evaporate, causing the qi of corpses to mix with excessive pathogenic qi, transforming into virulent toxins that spread diffusely between heaven and earth. Those infected may suffer on a large scale affecting a commandery or city, or on a small scale affecting a village or town, transmitting mutually among themselves. Although the cause of infection is the same, the resulting symptoms vary. For instance, Su Dongpo discussed cold-damp epidemics; Li Dongyuan discussed deficiency-type epidemics; Wu Youke discussed epidemics caused by the struggle between dampness and heat; and Yu Shiyu discussed summer-heat and dryness epidemics. Therefore, Liu Wenshu recorded acupuncture methods for five types of epidemics in the *Suwen Yipian* (Lost Chapters of the Yellow Emperor's Inner Canon), and Pang Anchang recorded treatments for five-colored diseases in the *Zongbing Lun*. However, one must not adhere rigidly to these texts. Yue Ren (Bian Que) stated in the *Nan Jing* (Classic of Difficult Issues), Chapter 58, that "Shanghan" (Cold Damage) encompasses five categories: wind strike, cold damage, damp-warmth, heat disease, etc., describing their syndromes and pulses in detail. The pathogen travels through various meridians, making it unclear which specific meridian is affected. Treatment should generally be selected based on the location of the pathogen within the meridians. The virulent qi of heaven and earth cannot be predicted by ordinary principles nor treated by routine methods. Those who initiate sweating therapy upon seeing warm diseases are erroneously applying Shanghan treatment methods to warm diseases. Conversely, when encountering epidemic diseases, physicians often fail to use purgative methods when indicated; this is applying warm disease treatment methods to epidemics, which is an even greater error.
Fever
In cold syndromes, fever accompanied by aversion to cold indicates the disease has originated in the Taiyang syndrome (diseases of the Taiyang channel). Fever absent but aversion to cold present indicates the disease has originated in the Shaoyin syndrome (diseases of the Shaoyin organ system). Fevers in warm epidemics manifest as tidal fever (fever that occurs at regular intervals or worsens at specific times), unlike the high fever seen in Shanghan. Initially, there may be occasional aversion to wind, but by the next day, thirst and aversion to heat appear. Epidemic syndromes present with severe aversion to cold combined with high fever, resembling Dan Nue (a type of malaria characterized by high fever).
Vomiting and Diarrhea
When the Wood of the Shaoyang Gallbladder is rampant with fire, vomiting results from upward rushing of qi, and diarrhea results from downward pressure of qi; this is termed vomiting and diarrhea due to Wind-Warmth. If middle-jiao deficiency leads to diarrhea first, followed by vomiting due to retained fluids, this is termed vomiting and diarrhea due to Damp-Warmth. Regarding vomiting and diarrhea caused by failing descent of Stomach Qi and disharmony of Lung Qi, these are common in epidemics. Generally, whether in Warm Diseases or Epidemics, the presence of vomiting and diarrhea represents an exit route for the pathogen and should not be abruptly stopped; this contrasts with cold diseases.
Various Pains
Headache and eye pain in Taiyang-Yangming Shanghan do not typically cause difficulty in turning the head or lifting it. In contrast, Warm Diseases and Epidemics cause headaches as if splitting, blurred vision, and a condition so severe it seems unbearable, accompanied by bone distress and pain, and waist pain as if beaten by a stick. Cold diseases are attributed to injury of Yang Qi, whereas Warm Epidemics are attributed to depletion of Yin Fluids.
Cold Limbs
In cold syndromes, cold limbs result from the obstruction of Kidney Yang. In Warm Syndromes and Epidemic Syndromes, they result from the failure of Liver Yang to circulate freely. Thus, cold pathogens occupying the Shaoyin differ from heat pathogens latent in the Jueyin.
Epistaxis
In cold syndromes, epistaxis indicates that the pathogen is about to retreat. In Warm Epidemics, epistaxis indicates that the pathogen is advancing.
Blood Accumulation
If a cold syndrome requires sweating but does not receive it, heat becomes bound in the Bladder. If an epidemic requires purgation but fails to receive it, fire becomes stagnant in the Membrane Source (Moyuan). Both scenarios can lead to Blood Accumulation. Any case presenting with persistent fever, free urination, mental restlessness resembling mania, and forgetfulness constitutes Blood Accumulation.