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According to the *Zhubing Yuanhou Lun* (Treatise on the Pathogenesis of All Diseases): The climate in spring is mild, in summer it is hot and humid, in autumn it is cool, and in winter it is icy cold. This constitutes the normal sequence of the four seasons' righteous qi (normal climatic conditions).

During the severe cold of winter, all things lie deep in concealment. If a gentleman (one who understands health preservation) maintains his exterior defenses tightly, he will not be injured by cold. However, if one exposes himself to the cold, he contracts Shanghan (Cold Damage).

Contracting the qi of the four seasons can lead to disease. However, Shanghan is considered the most toxic because it is the most lethal pathogenic factor. If illness occurs immediately upon contraction, it is named Shanghan; if it does not occur immediately, the cold toxin hides within the skin and muscles. By spring, it transforms into Wenbing (Warm Disease); by summer, it transforms into Shubing (Summerheat Disease). Shubing involves extreme heat and is more severe than Wenbing. Therefore, among those who engage in hard labor, warm-heat diseases are common in spring and summer, caused by exposure to cold qi during winter. (The above content is consistent with the *Shanghan Lun*).

Those who contract Shanghan and subsequently develop Wenbing: those who fall ill before the Summer Solstice are diagnosed as having "Wen" (Warmth); those who fall ill after the Summer Solstice are diagnosed as having "Shu" (Summerheat). Thus, it is said that during the three months of winter, one should sleep early and rise late, waiting for sunlight. One's mind should be like something hidden or concealed, as if harboring private thoughts or having already attained satisfaction. One should avoid cold and seek warmth, preventing the skin from sweating to avoid frequent depletion of qi. Furthermore, due to the influence of cold, one's movements should be like the turning of a door pivot. Hence, injury by cold in winter leads to Wen disease in spring.

Additionally, injury by unseasonable warmth in winter creates a toxicity known as "Dongwen Zhi Du" (Winter Warmth Toxicity), which is vastly different from Shanghan. Those suffering from Wen disease are actually victims of Tianxing Bing (Epidemic Disease). When the weather is unusually warm in winter, people contract abnormal qi contrary to the season. Illness does not manifest immediately; by spring, accumulated cold may suppress the body, preventing the toxin from being excreted. Only when the weather becomes warm does the Wen Du (Warmth Toxin) erupt, causing muscle rot and macules/rashes.

The Classics state: "Avoid empty evils and thieving winds at the proper time; maintain tranquility and emptiness so that True Qi follows naturally; keep spirit and essence guarded within, and how could disease arise?" Therefore, if a person remains pure and quiet, the flesh and couli (skin pores) close and resist pathogens. Even strong winds and harsh toxins cannot harm them.

It is also stated: "The yin and yang of the four seasons are the root of all things. Thus, the sages nourish Yang in spring and summer, and nourish Yin in autumn and winter, following their root." Following yin and yang ensures life; opposing them leads to death. Therefore, "Essence is the root of the body; those who preserve essence will not suffer from Wen disease in spring."

If a patient with Wen disease sweats but fever returns immediately, with a rapid and restless pulse that does not subside with sweating, accompanied by delirium and inability to eat, what is this disease called? It is called "Yin Yang Jiao" (Interaction of Yin and Yang). In cases of Jiao, death ensues. Sweating originates from grain (food/nutrients), which generates essence. Now, if pathogenic qi contends with essence between the bones and flesh, and sweating occurs, it indicates that the pathogen is retreating and essence is victorious. If essence is victorious, the patient should be able to eat and the fever should cease. Heat represents pathogenic qi; sweat represents essential qi. If sweating is followed immediately by recurrent heat, the pathogen is victorious. Inability to eat means essence receives no benefit. If the disease lingers, life expectancy is imminent. If sweating is followed by a still vigorous and rapid pulse, death occurs. The current pulse does not correspond with the sweating, indicating the body cannot overcome the disease; death is evident. Delirium indicates loss of Zhi (Will/Shen); loss of Zhi leads to death. Seeing three signs of death and no sign of life, even if recovery seems apparent, death is inevitable.

For any case where the skin is hot and the pulse is full and rapid, it is Wen disease; if the pulse is full and slippery, sweat is about to appear.

In general, for patients with Wen disease: if on the second or third day the body is hot, the pulse is rapid, there is headache, but eating and drinking remain normal, yet the pulse is straight and rapid, death occurs on the eighth day. If on the fourth or fifth day there is headache, rapid pulse, and a desire to vomit, and the pulse is fine/thin, death occurs on the twelfth day.

If this disease is untreated: after eight or nine days, if the pulse is not rapid, the body is not painful, the eyes are not red, the complexion is unchanged, but diarrhea occurs instead, and the pulse feels weak/flaccid (Die Die), lacking resilience upon pressure, occasionally becoming large, with hardness below the heart, death occurs on the seventeenth day.

If within three or four days of onset, there is no sweating, and the pulse is large and rapid, survival is possible; if the pulse is small, thin, and difficult to feel, death is certain and untreatable. If accompanied by diarrhea and abdominal pain, death is certain and untreatable.