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The pulse of epidemic rash (Yizhen) is invariably rapid (Shu). There are those that are floating, large, and rapid; those that are deep, fine, and rapid; those that are neither floating nor deep but rapid; and those that seem to appear and disappear when pressed. This is what the *Ling Shu* refers to as the manifestation of Yang toxin hiding and lying dormant. By examining the pulse, one can know the auspiciousness or inauspiciousness of the disease. If the pulse is floating, large, and rapid, the toxin is disseminating, representing a superficial heat syndrome in one meridian, and the illness will naturally resolve quickly. If the pulse is deep, fine, and rapid, the toxin has penetrated deeply; with large doses of clearing and resolving agents, it is still easy to subdue. As for pulses that seem to appear and disappear, or are completely hidden, the toxin is severe, and the symptoms are critical. Such pulses are occasionally seen at the onset of the disease but are quite common on the seventh or eighth day. Why? Because physicians initially mistake it for Cold Damage (Shanghan), heavily using diaphoretic (Fabiao) methods, which first depletes Yang Qi; when the exterior syndrome does not dissipate, they subsequently use purgatives, further depleting Yin fluids. Little do they know that if Cold Damage persists beyond the fifth or sixth day, the method should indeed be purgation, but one must carefully examine whether the pulse is forceful before applying it. Epidemic diseases are caused by pathogenic qi (Li Qi) that deviates from the four seasons. Pathogenic qi is an invisible toxin; those with deficient Stomach Qi contract it. The clinical presentation may resemble excess syndromes, yet the pulse is fine, rapid, and weak. To confront invisible pathogenic qi with the fierce potency of Rhubarb (Dahuang) and Mirabilite (Mangxiao), how could the evil toxin not enter through the deficiency? For those with weak constitutions, either Yang collapse or Yin collapse will occur; even those whose Qi and Blood can somewhat withstand it will inevitably see the pulse turn deep and hidden, with complications arising like swarms of bees: cold extremities, coma with delirious speech, oppression and dizziness with fixed gaze, enuresis, or involuntary stool discharge. In extreme cases, there is tongue retraction and testicular contraction, picking at bedclothes, and other various malignant symptoms that closely resemble Cold Damage. Physicians fail to realize that this is inviting evil inward, where extreme Yang resembles Yin, yet they claim it has transformed into a Yin syndrome, recklessly administering Ginseng (Renshen) and Cinnamon Twig (Guizhi). Patients die as if poisoned, turning blue-purple all over, with bleeding from the nose and mouth. For those who have not taken hot medicines, immediate administration of a large dose of Baidu Yin (Poison-Resolving Decoction) with heavy additions of Gypsum (Shigao) might possibly save them. Having saved many people in this manner, I record this for publication.

In the Wuzi year of the Qianlong reign, epidemic rash prevailed in my county. One person contracting the disease would infect the whole family. Among mild cases, eight or nine out of ten survived; among severe cases, only one or two out of ten survived. This pattern was generally observed throughout the region. At the onset, patients first experienced aversion to cold followed by fever, splitting headache, back pain as if beaten by a club, abdominal pain as if intestines were being twisted, accompanied by simultaneous vomiting and diarrhea. Adults and children suffered the same symptoms, following the same course in thousands of people. Some physicians treated it as a Three-Yang disease, others as a Two-Gan disease, and others as Cholera-like disorder (Huluan). By the second day, ominous signs arose in swarms, and various critical symptoms were too numerous to enumerate. Deaths resulting from such presentations were countless. This seasonal pathogenic qi is something people cannot avoid. The root cause lies in the theory of Five Movements and Six Qi (Yunqi). The human body is a microcosm; just as Heaven and Earth have such pathogenic qi, humans suffer corresponding epidemics. In the Wuzi year, Shaoyin Junhuo (Ministerial Fire) governed the Tian (Heavenly Qi), dominating the Great Movement. Between the fifth and sixth lunar months, Shaoyin Junhuo combined with Shaoyang Xianghuo (Ministerial Fire) to dominate the Small Movement. The Second Qi and Third Qi acted together in their functions. How could the single-year Qi of the human body withstand such rampant fire? Physicians who ignore Yunqi and rigidly adhere to ancient prescriptions achieve virtually no efficacy. When questioned, they recite old theories to justify themselves. Ultimately, persisting in treating epidemics with Cold Damage methods leads inevitably to death. These people do not die from the disease itself, but from medicine; not merely from medicine, but specifically from the prescriptions of physicians who rigidly cling to ancient formulas. Through understanding Yunqi, I realized that epidemic disease involves the Stomach suffering from exogenous excessive heat, which can only be effectively treated with Gypsum (Shigao)! Moreover, medical practice relies on intuitive understanding. Gypsum corresponds to Cold Water; using cold to overcome heat, and water to control fire, this approach yields consistent success. In May, I myself contracted the epidemic. For those who invited me for treatment, unable to visit personally, I inquired about symptoms, recorded prescriptions, and transmitted them mutually, saving many lives. In the Guichou year, epidemics were prevalent in the capital. Even Vice-Censor-in-Chief Wang and Herald Feng transmitted my prescriptions. Those who had failed with other medicines recovered instantly. Therefore, I wrote this down, naming the formula Qingwen Baidu Yin (Clear Plague and Resolve Toxin Decoction), with modifications based on symptoms, detailed below, along with case records.