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Zhou Yu Zai said: Epidemic diseases have been circulating in the world for a long time, yet few people know how to treat them. Even those whose treatments happen to be effective rarely understand the underlying principles. Observing the duties of the Fang Xiang Shi (a ritual official responsible for exorcism) recorded in the *Rites of Zhou* (Zhou Li), it is difficult to use these methods to drive away epidemics; thus, epidemics are caused by "Qi" (vital energy/pathogenic factors). Precisely because it is Qi, it enters through the mouth and nose to cause harm. Although the Six Excesses (Liu Yin, 六淫) — Wind, Cold, Summerheat, Dampness, Dryness, and Fire — are all forms of Qi, we do not hear that diseases caused by Wind, Cold, Summerheat, Dampness, Dryness, or Fire spread from door to door or infect entire regions. Why is this? The Qi of the Six Excesses remains in the heaven and earth daily; when one pathogen becomes excessive, disease occurs. Moreover, human illness often arises because one's own body cannot overcome the pathogen, allowing the pathogen to invade, rather than solely due to the harmful nature of heavenly and earthly Qi.

As for epidemic diseases, although such conditions have existed since ancient times, there is no specific "Epidemic Qi" in the natural environment. Perhaps due to irregular winds and rains, and the steaming and rising of damp turbidity from the earth, combined with shallow burial of corpses, the foul Qi accumulated from piles of dead bodies on large hills rises and falls with the heaven and earth, drifting to distant places. Humans, existing within the intersection of Qi, cannot escape it. Contracting this Qi leads to illness and death. Consequently, a new type of pathological Qi and corpse Qi emerges, circulating among people, gradually infecting each other, becoming more severe over time. Therefore, historically, epidemics mostly occur after wars and famines. This is not only because the Middle Qi (Spleen and Stomach Qi) is initially weak, but primarily because the accumulated foul Qi is particularly intense.

For thousands of years, people have spoken of ghosts and dreams. Fortunately, Mr. Jiayan cited classics and ancient texts to highlight profound meanings. My teacher, Master Lin of Beihai, extended these concepts and pointed out treatment methods. Is this not a merit benefiting ten thousand generations? However, Jiayan boasted in his commentary on the *Ping Mai Pian* (Treatise on Pulse Diagnosis) that he had glimpsed the essence, stating that "Clear pathogens attack the Upper Jiao, while Turbid pathogens attack the Lower Jiao," etc., and believed this referred to Zhang Zhongjing's discussion on epidemics. I do not agree. The foul and evil Qi in the world reaches extreme toxicity in epidemics. When humans contract it, the Three Jiaos become confused, with no distinction between interior and exterior, nor between surface and deep levels; it travels directly along the central pathway. Nevertheless, circumstances change constantly across eras, lacking fixed patterns. The theory of Upper, Middle, and Lower Jiao was actually Zhang Zhongjing's description regarding the pulse of Dampness. Subsequently, pathogens entering the Fu and Zang organs and traveling through meridians lead to various critical syndromes. Phrases like "Three Jiaos mixed, interior and exterior blocked" seem related to epidemics but are actually irrelevant. This shows Jiayan's skill in reading, which can enlighten others' intelligence, serving as a compass in vast uncertainty. However, claiming this definitively describes epidemic pulses and syndromes is highly erroneous.

Regarding what secular society calls "Big Head Plague" (Da Tou Wen), the lower body is not unaffected, but the upper part is severely affected. Regarding "Nodule Plague" (Ge Da Wen), the interior is not unaffected, but symptoms manifest externally. Regarding "Toad Plague" (Xia Ma Wen), the abdomen is not unaffected, but obstruction occurs in the throat. Other symptoms are diverse, but generally require cold-natured herbs to clear heat and detoxify. Treatment methods vary: some target the upper part first, some the lower; some treat from the interior, some from the exterior. One must deduce strategies based on specific syndromes. I primarily follow the book by Mr. Wu You Ke (Wu Youxing) for treatment, collecting other formulas to supplement it, so that future students may achieve sudden clarity of mind and vision.