阴阳大论云春气温和夏气暑热秋气清凉冬气冷冽此则四时正气之序也冬时严寒万类深藏
君子固密则不伤于寒触冒之者乃名伤寒耳其伤于四时之气皆能为病以伤为毒者以气而成杀厉
之患也中而即病者名曰伤寒不即病者寒毒藏于肌肤至春变为温病至夏变为暑病暑病者热极重
于温也是以辛苦之人春夏必多温热病皆由冬时触寒所致非时行之气也凡时行者春时应暖而反
寒夏时应大热而反大凉秋时应凉而反大热冬时应大寒而反温此非其时而有其气是以一岁之中
长幼之病多相似者此则时行疫厉之气也夫欲究知四时之气为病及时行疫气之法皆当按斗历以
占之九月霜降节后宜渐寒而冬大寒至正月雨水节后宜解也所以谓之雨水者以冰雪解而为雨水
故也至惊蛰节后气渐和暖向夏大热至秋便凉从霜降以后至春分以前凡有触冒霜露体中寒即病
者谓之伤寒也如冬有非节之暖者名曰冬温冬温之毒与伤寒大异冬温复有先后更相重沓亦有轻
重为治不同症如后章从立春节后其中无暴大寒又不冰雪而有人壮热为病者此属春时阳气发于
冬时伏寒变为温病从春分以后至秋分节前天有暴寒者皆为时行寒疫也三月四月或有暴寒其时
阳气尚弱为寒所折病热犹轻五月六月阳气已盛为寒所折病热则重七月八月阳气已衰为寒所折
病热亦微其寒病与温及暑病相似但治有殊耳
The *Yin Yang Da Lun* (Great Treatise on Yin and Yang) states: The Qi of spring is mild and harmonious, the Qi of summer is hot and sultry, the Qi of autumn is cool and clear, and the Qi of winter is cold and biting. This constitutes the normal sequence of the four seasons' Qi.
When winter arrives, the cold is extremely severe, and all things hide deeply.
A gentleman (one who understands health preservation), if he maintains solidity and warmth, will not be injured by cold; however, if he exposes himself to and offends against the cold, this is termed "Shanghan" (Cold Damage).
Any invasion by the Qi of the four seasons that deviates from the norm can cause disease. Regarding "injury" as toxic, it is because such Qi can bring about calamitous and lethal disasters.
If illness occurs immediately upon exposure, it is named "Shanghan" (Cold Damage); if illness does not occur immediately, the Cold Toxicity hides within the skin and muscles, transforming into "Wenbing" (Warm Disease) in spring, and into "Shubing" (Summerheat Disease) in summer. Shubing (Summerheat Disease) involves heat that is extremely severe, heavier than that of Wenbing (Warm Disease).
Therefore, people engaged in hard labor must frequently suffer from Warm-Heat diseases during spring and summer. These are all caused by offending cold during winter, and do not belong to the category of "Shixing Yiqi" (Seasonal Epidemic Qi).
Whenever there is "Shixing" (Epidemic occurrence), it refers to situations where spring should be warm but is instead cold, summer should be intensely hot but is instead very cool, autumn should be cool but is instead hot, and winter should be intensely cold but is instead warm. Because the climate appears contrary to the season, throughout the year, the illnesses affecting both young and old are often similar. This is what is called the Qi of seasonal epidemic pestilence.
To thoroughly understand the diseases caused by the Qi of the four seasons and the methods regarding seasonal epidemics, one must consult the Douli (ancient astronomical calendar used to determine solar terms) for divination and inference.
After the Frost Descent (Shuangjiang) solar term in the ninth month, the weather should gradually become cold until the Great Cold (Dahan) of winter arrives. After the Rain Water (Yushui) solar term in the first month, the weather should begin to thaw. It is called "Rain Water" because ice and snow melt to become rainwater.
After the Awakening of Insects (Jingzhe) solar term, the Qi gradually becomes mild and warm, becoming intensely hot towards summer, and turning cool in autumn. From after Frost Descent until before the Spring Equinox (Chunfen), anyone who offends and exposes themselves to frost and dew, causing internal cold and immediate illness, is suffering from Shanghan (Cold Damage).
If there is unseasonable warmth during winter, it is named "Dongwen" (Winter Warmth). The toxicity of Dongwen (Winter Warmth) is vastly different from Shanghan (Cold Damage). Dongwen (Winter Warmth) may also have sequential occurrences with overlapping symptoms, varying in severity, and requiring different treatments; symptoms are detailed in the following chapter.
After the Beginning of Spring (Lichun) solar term, if there is no sudden severe cold and no ice or snow, yet some individuals suffer from high fever, this belongs to the transformation of latent winter cold into Wenbing (Warm Disease) due to the movement of spring Yang Qi.
From after the Spring Equinox (Chunfen) until the Autumn Equinox (Qiufen) solar term, any sudden cold weather in the sky constitutes a seasonal Cold Epidemic (Han Yi).
In the third and fourth months, there may be sudden cold. At this time, Yang Qi is still weak; being restrained by cold, the resulting fever is relatively mild. In the fifth and sixth months, Yang Qi is already abundant; being restrained by cold, the resulting fever is heavy. In the seventh and eighth months, Yang Qi is declining; being restrained by cold, the resulting fever is also slight.
These Cold diseases resemble Warm diseases and Summerheat diseases in symptoms, but their treatment methods differ significantly.