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Pulse floating generally indicates the need for sweating therapy, and pulse sinking generally indicates the need for purgation; this is indeed appropriate. However, even if the pulse is floating, there are cases where purgation may be used; this refers to pathogenic heat entering the Fu organs, causing difficulty in defecation. If defecation is not difficult, how could one dare to use purgation? Even if the pulse is sinking, there are cases where sweating therapy may be used; this refers to Shaoyin disease (Disease of the Lesser Yin) presenting with fever in the body. If there were no fever, how could one dare to use sweating therapy? This approach prioritizes symptoms over pulse diagnosis.

Generally, wind pathogens damage Wei Qi (Defensive Qi), while cold pathogens damage Ying Blood (Nutritive Blood). This is because Qi belongs to Yang, and wind also belongs to Yang; like attracts like, so it damages Wei Qi. Yang governs opening and dispersing, leading to spontaneous sweating; therefore, Guizhi Tang (Cinnamon Twig Decoction), a pungent-sweet-warm formula, is used to strengthen the exterior. Blood belongs to Yin, and cold also belongs to Yin; like attracts like, so it damages Ying Blood. Yin governs closure and storage, leading to an absence of sweat; therefore, Mahuang Tang (Ephedra Decoction), a light and ascending formula, is used to release the exterior. This is precisely what is meant by "water flows to wetness, fire moves toward dryness; clouds follow dragons, wind follows tigers"—each following its own kind.

Medicines used to release the exterior are typically warm; medicines used to purge the interior are typically cold; medicines used to warm the interior are typically hot. When pathogens are on the exterior, it signifies deficiency of Yang and excess of Yin. Using warm medicines aids Yang; as Yang grows with assistance, the Yin pathogen is thereby eliminated. Hence, pungent-sweet-warm formulas are used. Dispersal is Yang; thus, it is clear that exterior-releasing medicines should be warm. When pathogens are in the interior, it signifies deficiency of Yin and excess of Yang. Using cold medicines assists Yin and suppresses Yang; as Yang is suppressed and becomes weak, True Yin is thereby nourished. Hence, sour-bitter formulas are used. Purging and vomiting are Yin; thus, it is clear that interior-purging medicines should be cold. When the Yin meridians directly contract cold pathogens, it results in Zang organ disease, characterized primarily by insufficient Yang and excess Yin. Therefore, pungent-hot medicines are used to assist Yang and suppress Yin; thus, it is clear that meridian-warming medicines should be hot. If pathogens on the exterior are not released via sweating, from where will they depart? If pathogens in the interior are not expelled via purgation, from where will they exit? If cold in the Zang organs is not warmed, from where will it be removed? These three aspects constitute the distinction in using cold, warm, and hot medicines.

The term "Shanghan" (Cold Damage) generally refers to the severe cold weather in winter, which creates a lethal qi due to frozen water and ice. When humans encounter this and fall ill immediately, it is called Zheng Shanghan (True Cold Damage), presenting with aversion to cold, headache, and fever. Therefore, Mahuang (Ephedrae Herba) and Guizhi (Cinnamomi Ramulus) are used to disperse cold pathogens from the exterior and interior, naturally resulting in the subsidence of fever and cooling of the body. What complications would arise? If the exterior symptoms such as headache and aversion to cold are resolved, but instead delirium, fear of heat, irritability, thirst, and constipation appear, purgation should be applied according to the method. Once defecation is achieved and heat further subsides, what strange symptoms remain? In spring, summer, and autumn, although there may be mild aversion to cold, fever, and headache, these are merely Gaomao Bishi Baohan (Casual Cold Exposure due to Non-seasonal Cold), which are mild compared to the severity of True Cold Damage in winter. If cold is contracted in winter but does not manifest immediately, it lies latent in the skin and muscles. By spring or summer, this latent cold transforms into Warm Disease (Wenbing) or Heat Disease according to the seasonal qi. Because Warmth and Summerheat are about to emerge, and sudden cold is encountered, spring changes become Warm Disease. Once transformed, it can no longer be referred to as cold. Thus, Zhang Zhongjing stated: "Fever without aversion to cold and with thirst" indicates Warm Disease. Summerheat disease is similar but more intense than Warm Disease. Lack of aversion to cold indicates the pathogen is not external; thirst indicates heat radiating from within to the exterior, confirming the absence of exterior syndrome. Treatment for Warm and Summerheat diseases generally avoids sweating, as diseases occurring after the season are no longer on the exterior. Latent cold reaching summer, combined with sudden cold exposure, transforms into Summerheat disease. Summerheat disease is essentially Heat Disease; the term "Summerheat" is derived from the dominance of Fire in summer. Since both Warm and Summerheat conditions originate from latent winter cold and are collectively termed Cold Damage, their different timing of onset necessitates distinct treatments. It is incorrect to claim that all seasons involve True Cold Damage. For these three types (Warm, Summerheat, and latent cold transformation), acrid-cool formulas should be used. Using winter True Cold Damage medicines universally would certainly cause death. Acrid-cool formulas, such as Qianghuo Chonghe Tang (Qianghuo Harmonizing Decoction), can substitute for Da Qinglong Tang (Major Green Dragon Decoction), treating Cold Damage complicated by wind or Wind Strike complicated by cold, providing utmost stability. One formula substitutes for three, turning dangerous drugs into safe ones, which is truly miraculous! The common people are unaware of this. If the exterior is resolved but interior symptoms prevail, purgation should be applied without hesitation. Furthermore, if Cold Damage persists beyond the usual course despite sweating and purgation, it is also considered Warm Disease. Having undergone sweating and purgation, the pathogen is no longer on the exterior; treatment must adapt to the specific condition. For individuals engaged in hard labor who suffer from headache, aversion to cold, fever, soreness of bones and legs, slight thirst, spontaneous sweating, and a floating but large and forceless pulse, this is Cold Injury due to Labor (Laoli Ganhan). Bu Zhong Yi Qi Tang (Tonify the Middle and Augment the Qi Decoction) combined with acrid-warm medicines is beneficial. The classic states, "Warmth can eliminate great heat," referring precisely to this. If harmonization is indicated, Xiao Chaihu Tang (Minor Chaihu Decoction) with modifications should be used. If purgation indications appear, add Rhei Radix et Rhizoma (Rhubarb) to the base formula for mild purgation; do not overuse harsh medicines, as the harm would be significant. If the initial illness presents without fever or headache, but with aversion to cold, cold limbs, abdominal pain, vomiting, diarrhea, and a deep, slow, and forceless pulse, this is Direct Invasion of Cold Syndrome (Zhizhong Hanzheng). It requires warming and prohibits sweating and purgation. Epidemic Plagues (Yili) are caused by abnormal seasonal qi, spreading identically among old and young. Avoiding foul odors prevents damage to True Qi. Proximity to foul odors damages True Qi, leading to contagion. Just as a solid wall prevents thieves from entering, robust Righteous Qi prevents Pathogenic Qi from invading. When Righteous Qi is deficient, Pathogenic Qi takes advantage. This differs from the treatment of Warm and Summerheat diseases. For exterior syndromes, Ren Shen Bai Du San (Ginseng Decoction for Overcoming Toxins) is used. For half-exterior/half-interior syndromes, Xiao Chaihu Tang is used. For full interior syndromes, Da Chaihu Tang (Major Chaihu Decoction) is used for purgation. Without pulse diagnosis, aim for equilibrium. Conditions such as malaria and dysentery are also epidemic diseases and should be treated according to standard methods.