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The *Classic of Medicine* (Huangdi Neijing) states: "In the heaven, it manifests as heat; in the earth, it manifests as fire." Shu (Summerheat) is the Qi of fire and heat. Just as Heaven possesses this Qi of fire and heat, so does humanity. Regardless of the seasons' cold or heat, any disease involving the Three Yang channels (Taiyang, Yangming, Shaoyang) that presents with symptoms of fire and heat can be termed Shu disease. Thus, Cold and Shu are simply the Qi of Yin and Yang. Today's people do not understand the principles of physiological luck transformation; when encountering diseases during scorching summer heat, they either diagnose it as "Shangshu" (injury by summerheat) or "Zhongshu" (struck by summerheat), indiscriminately administering herbs such as Xiangru (Moslae Herba), Shigao (Gypsum Fibrosum), Zhuye (Bambusae Folium), Huangqin (Scutellariae Radix), and Lianzi (Nelumbinis Semen). This reckless prescribing has caused countless deaths! In summer, everyone knows of Summerheat, and using cold-cooling medicines is considered appropriate. If the patient does not recover after taking them, more is given; if still no recovery, frequent doses are administered. Even if death ensues, there is no complaint. However, if a skilled physician identifies the root cause and prescribes warm medicines, people will say it is inappropriate. If ineffective, they stop taking it, thinking anxiously: "This is a Shu disease; can one take hot medicines?" People recklessly administer cooling medicines until death occurs, yet still blame the hot medicines for being wrong. Thus, deaths caused by cold-cooling medicines in summer are inevitable. To seek avoidance of this inevitability, should one listen to shallow opinions?

Shu is merely one of the Four Seasons' Qi; how can Shu itself harm humans? If Shu inevitably harmed people, then during Changxia (Late Summer), everyone would fall ill. Why do those laboring under the blazing sun remain healthy, while those avoiding heat in high halls and large buildings fall ill? One must realize that human illness is self-inflicted. If one's Five Movements (Wuyun) are harmonious and Six Qi (Liuqi) are balanced, one will not fall ill even amidst constant summerheat. Conversely, if Wuyun is deficient and Liuqi fails to flourish, Yin deficiency leads to Yang excess and heat syndromes arise; Yang deficiency leads to Yin excess and cold syndromes emerge. Cold and Shu diseases are generated according to the body's Yin-Yang Qi transformation. For instance, if Cold pathogen damages Yang and transforms into pathology, Cold can become Heat; if Shu pathogen damages Yin and transforms into pathology, Shu can become Cold. If one does not rely on the body's internal Qi transformation regarding cold/heat, but instead rigidly adheres to external weather conditions, it is truly killing without weapons! Moreover, in summer, the human body often presents with upper heat and lower cold, similar to how the air is hot but the ground is cool, as seen in extremely cold well water. The Qi of the Dantian in the human body is analogous to underground water. In treating diseases, one must attend to the root. In summer illnesses, approximately 70-80% require warm tonification, while only 20-30% are suitable for cooling purgation. For individuals with abundant Kidney Qi and unexhausted physical strength, who merely contract Wind-Shu transforming into heat disease, formulas like Xiangru Tang (Mosla Decoction) or Baihu Tang (White Tiger Decoction) can cure in one dose; watermelon and cold water may also suffice. Physicians, seeing these recoveries, apply these same remedies to cases of Shu pathogen entering the Zang organs, resulting in frequent deaths after a single dose. During intense summer heat, some die from morning to evening; people attribute this to epidemic Qi, but it is actually due to Shu pathogen entering the Zang organs. Those dying after five or six days do so because Yang Qi has been entirely exhausted externally, Grain Qi cannot enter, Kidney Qi is depleted, and True Qi collapses internally. Such conditions can only be treated with Renshen (Ginseng Radix et Rhizoma), Ganjiang (Zingiberis Rhizoma), Guizhi (Cinnamomi Ramulus), and Fuzi (Aconiti Lateralis Radix Praeparata). If treatment succeeds and all recover, people may believe it; if occasional failures occur, people will doubt and criticize it. I once reflected on Zichan's discussion on governance: "Fire is fierce; people fear it, so few die in it. Water is weak; people play with it, so many die in it." Today, people fear hot medicines and prefer cold ones; is it surprising that they die frequently? (This warns that during summer, one must recognize mixed deficiency-cold syndromes and avoid reckless use of cooling dispersants. Although the statement may seem extreme, readers should grasp the main intent and not let literal wording obscure the deeper meaning.)