仲景以为冬伤于寒，中而即病者，名曰伤寒。盖初感即发，无蕴积之毒瓦斯，虽为伤寒，而其病亦轻。仲景又曰∶不
即病，寒毒藏于肌肤，至春变为温病，至夏变为热病。是则既伤于寒，又感于温，两邪相搏合为一病，如人遇盗，又有
同恶济之者，何可支也？故伤寒冬不即发，遇春而发者，比于冬之伤寒为重也。又有夏至而发者，盖寒毒浅近在肤腠，
正气易胜，故难久留，是以即发。其毒稍深，则入于肌肉，正气不能胜，必假春温之气，开疏腠理，而后可发，是以出
为温病。又其毒之盛者，经时既久，深入骨髓，非假大暑消烁，则其毒不可动，此冬伤于寒，至夏为热病者，所以又重
于温也。故古人谓冬伤于寒，轻者夏至以前发为温病，甚者夏至以后发为暑病也。此三者其为伤寒本一也。惟有即发不
即发之异，随脉变动，遂大不同。又有冬不伤寒，至春感不正之气而病，其病无寒毒之气为根，虽名温病，又比冬伤于
寒，至春再感温气为病轻。然春温、冬寒之病，乃由自感自致之病也。若夫一乡、一邦、一家皆同患者，是则温之为疫
者然也，非冬伤于寒，自感自致之病也。盖以春时应暖而反寒，夏热反凉，秋凉反热，冬寒反暖，气候不正，盛强者感
之必轻，衰弱者得之必重，故名温疫，亦曰天行时行也。设在冬寒之日，而一方、一乡、一家皆同此病者，亦时行之寒
疫也。大抵冬伤于寒，经时而后发者，有寒毒为根，再感四时不正之气而病，则其病安得不重。如冬病伤寒，春病温气，
与夫时行温疫之类，才感即发，中人浅薄，不得与寒毒蕴蓄有时而发者，同论也。（《伤寒温疫论》）
张仲景认为，冬季感受寒邪，随即发病的，称为伤寒。这是因为初次感邪即刻发作，体内没有蕴积的毒气，虽然属于伤寒，但病情较轻。张仲景又说：如果不立即发病，寒毒潜伏在肌肤之间，到了春天就转变为温病，到了夏天就转变为热病。既然已经受了寒邪，又感染了温邪，两种邪气相互搏结合并成为一种疾病，就像人遇到强盗，又有同伙助恶，这怎么能承受得住呢？所以，冬季受寒而没有立即发病，等到春季才发作的，比冬季直接患伤寒的病证要严重。又有在夏至时发作的，这是因为寒毒浅近位于皮肤腠理之间，正气容易战胜邪气，所以难以长久停留，因此会立即发作。如果寒毒稍微深重一些，就会进入肌肉层，正气不能战胜它，必须借助春季温热的风气，疏泄腠理，然后才能发作，因此表现为温病。还有那些寒毒特别盛行的，经过很长时间，深入骨髓，不借助大暑天的酷热消烁，其毒邪就不能发动，这就是冬季受寒，到了夏天变为热病的原因，所以病情又比温病更重。因此古人说，冬季受寒，轻的在夏至以前发作称为温病，重的在夏至以后发作称为暑病。这三种情况，其本源都是伤寒。只是有立即发作和不立即发作的区别，随着脉象的变化，病情就大大不同了。又有冬季没有受寒，到了春天感受不正之气而发病的，这种病没有寒毒作为根本，虽然也称为温病，但比冬季受寒到春天再感受温邪而发病的要轻。然而，春温和冬寒的疾病，都是由自身感受、自身导致的疾病。如果在一个乡里、一个国家、一个家庭中都有相同患者，这就是温邪转化为疫病的状况，不是冬季受寒、自身感受导致的疾病。大概是因为春季应该温暖却反而寒冷，夏季炎热却反而凉爽，秋季凉爽却反而炎热，冬季寒冷却反而温暖，气候不正，体质强壮的人感染它必然病情轻，体质衰弱的人感染它必然病情重，所以称为温疫，也称为天行时行。如果在寒冷的冬日，而一个地方、一个乡里、一个家庭都患有同样的病，这也是时行之寒疫。大抵冬季受寒，经过一段时间后才发作的，以寒毒为根本，再感受四时不正之气而发病，那么病情怎能不重呢？如冬天得伤寒病，春天得温气病，以及像时行温疫之类，刚感受邪气就立即发作，侵入人体较浅，不能与寒毒蕴蓄一段时间后才发作的情况相提并论。（《伤寒温疫论》）
Zhang Zhongjing believed that those who contracted cold pathogenic factors in winter and fell ill immediately were diagnosed with Shanghan (Cold Damage). Since the onset occurs upon initial infection, there is no accumulation of toxic qi within the body; although classified as Shanghan, the pathology is relatively mild. Zhang Zhongjing further stated: If the illness does not manifest immediately, the cold toxin hides within the skin and muscles (Fufu), transforming into Wenbing (Warm Disease) in spring and Rebing (Heat Disease) in summer. Having been injured by cold and subsequently infected by warmth, the two pathogens contend and merge into a single disease. This is akin to encountering a robber with accomplices aiding the evil; how can one withstand it? Therefore, injuries from cold in winter that do not manifest immediately but erupt in spring are more severe than direct Shanghan contracted in winter. Cases manifesting at the Summer Solstice occur because the cold toxin is shallow and located near the skin and pores; since the Healthy Qi (Zhengqi) can easily overcome it, it cannot remain long, thus manifesting quickly. If the toxin is slightly deeper, entering the muscles, the Healthy Qi cannot overcome it alone. It requires the warming Qi of spring to open and vent the pores before it can manifest, resulting in Wenbing. For cases where the toxin is particularly vigorous, after a long duration, it penetrates deeply into the bone marrow. Without the scorching heat of midsummer to dissipate it, the toxin cannot be activated. This explains why cold injury in winter leading to Heat Disease in summer is even more severe than Warm Disease. Thus, ancients stated that for winter cold injury, mild cases manifesting before the Summer Solstice are called Warm Disease, while severe cases manifesting after are called Shubing (Summerheat Disease). These three types share the same origin in Shanghan. The difference lies only in immediate versus delayed onset; following changes in pulse patterns, the clinical presentations become vastly different. Additionally, there are cases where one does not contract cold in winter but falls ill in spring due to abnormal Qi. These illnesses lack cold toxin as their root; although named Warm Disease, they are milder than those caused by winter cold injury followed by secondary warmth infection in spring. However, Spring Warmth and Winter Cold diseases are conditions contracted and caused by oneself. If a village, region, or family all suffer from the same illness simultaneously, this indicates that Warm Pathogens have transformed into Yi (Epidemic) diseases, which are not self-contracted from winter cold. Generally, when spring should be warm but is cold, summer hot but cool, autumn cool but hot, and winter cold but warm, the climate is abnormal. Those with strong constitutions contracting it will have mild symptoms, while those with weak constitutions will suffer severely. Hence, it is named Wenyi (Warm Epidemic), also known as Tianxing (Heavenly Transmission) or Shixing (Seasonal Transmission). If during a cold winter day, a specific area, village, or family all suffer from the same illness, this is also considered a seasonal Cold Epidemic. In general, cold injuries in winter that manifest after a period of time have cold toxin as their root. When combined with the contraction of abnormal Qi from the four seasons, the pathology inevitably becomes severe. Conditions such as Shanghan contracted in winter, Warm Qi diseases in spring, and seasonal Warm Epidemics, which manifest immediately upon infection and affect the exterior superficially, cannot be discussed on the same level as those involving the accumulation of cold toxin over time before manifestation. (From *Shanghan Wenyi Lun*)