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Wind, summerheat (Shu), dampness, dryness, and cold are the manifestations of the Qi of Heaven and Earth moving through the four seasons. Only summer belongs to Fire, when sunlight is most intense. The *Neijing* states: "When the annual Fire is excessive, blazing summerheat prevails." This explicitly refers to the fire of the scorching sun. However, the warmth in spring, autumn, and winter is nothing but the light and heat of the sun, and thus cannot be called "summerheat." Therefore, Qibo (Xuanqi) added a "Fire" character below the five Qi. Moreover, regarding summerheat, he clearly stated: "In Heaven it is Heat, on Earth it is Fire, its nature is Summerheat." This indicates that summerheat is merely Heat and Fire; the canonical meaning is already profound and clear. The reason why people suffer predominantly from Fire diseases is that wind, cold, summerheat, and dampness can all transform into Fire, and excessive movement of the Five Emotions invariably generates Fire. This is the great source where heavenly Qi and human nature intersect to generate Fire.

Ye (暍) is summerheat. Referring to summerheat disease as Ye is because summerheat disease is attributed to latent cold, named as Zhong Ye (Heatstroke/Summerheat Stroke) when it manifests after the Summer Solstice. To prevent confusion between the two, this is the method of Zhang Zhongjing.

Shaoyang Cold (Shanghan) cannot be resolved without sweating, and favors inducing sweat; Wind Strike (Shangfeng) also cannot be resolved without sweating, but strongly forbids inducing sweat, only permitting the release of the muscle layer (Jie Ji). This difference in treatment between Mahuang Tang (Ephedra Decoction) and Guizhi Tang (Cinnamon Twig Decoction) lies in their differing methods. Warm diseases (Wenbing) also favor resolution through sweating, but strongly forbid forced sweating; they only permit the use of Acrid-Cool herbs to release the muscle layer, while Acrid-Warm herbs must not be used. The subtlety lies in guiding the pathogen outwards. When Ying and Wei, Qi and Blood harmonize, sweat occurs naturally; there is no need to force sweating. However, for Summerheat-Warmth (Shuwen) and Dampness-Warmth (Shiwen), this is not the case. Summerheat cannot be resolved without sweating, and Xiangru (Moslae Herba) can be used to disperse it. After inducing sweat, if profuse sweating continues, one should revert to the Baihu Tang (White Tiger Decoction) method. This is certainly different from the unceasing leakage of sweat in Shanghan or Shangfeng, which requires Guizhi (Cinnamomi Ramulus) and Fuzi (Aconiti Lateralis Radix Praeparata) to protect Yang and consolidate the exterior. One must not repeatedly weaken the exterior, leading to Jue Tuo (cold limbs and collapse). Observing the ancients' approach in the Summerheat category, the prescription of Shengmai San (Pulse-Generating Powder: Renshen, Maidong, Wuweizi) reveals its rationale.

Exogenous pathogens do not exceed the Six Evils (Liu Yin); people's illnesses should be divided according to the Four Qi. Physicians treating Shanghan blindly adhere to established formulas for releasing the exterior and purging the interior, disregarding the harm caused by Acrid-Warm and Bitter-Cold herbs, thereby obscuring the principles of Warm diseases. I, though untalented, have read extensively and suddenly realized the necessity of studying Warm diseases. The *Neijing* says: "If one does not store essence in winter, one will inevitably contract Warm diseases in spring." This implies that during the severe cold of winter, Yang Qi is internalized. If one conforms to the heavenly timing and remains secure, Kidney Qi fills internally, and Mingmen (Gate of Life), acting as the special envoy of Sanjiao (Triple Burner), also consolidates the Cou Li (pores and interstices) and protects the skin and hair. Even during the ascending and dispersing phase of spring, one's True Qi permeates internally and externally, not depleting with the ascending dispersal. Thus, even if exogenous pathogens exist, how can they invade internally? This is how the *Neijing* clarifies the origin of disease. However, it mentions only "not storing essence in winter" and omits other seasons because winter is the time when Water is prosperous, belonging to the transformation of Northern Cold Water. In terms of season, it is Winter; in terms of the person, it is the Kidney. Well water is warm while hard ice forms; Yin is outside and Yang is inside, embodying the meaning of the Kan hexagram. Hence, the statement emphasizes winter, not implying that only winter is suitable for storing essence while other seasons allow neglect. Even the phrase "spring will inevitably see Warm diseases" is a proximal pointer. Ultimately, it shows that those with interior deficiency have insecure exteriors, making them susceptible to all seasonal pathogens. Students can thereby comprehend the diseases caused by the Six Qi of the four seasons. The *Nanjing* states: There are five types of Shanghan: Shanghan, Fengzhong (Wind Strike), Fengwen (Wind-Warmth), Rebing (Heat Disease), and Shiwen (Dampness-Warmth). Grouping these Wind, Cold, Dampness, and Heat pathogens under the name Shanghan is because, early on, it was recognized that when the Cold Zang organs are injured, exogenous pathogens can enter. Thus, investigating the root, they are all called Shanghan. Generally, in the northwest, winds are high and soil is dry, so Wind-Cold diseases are predominant; in the southeast, the terrain is wet, so Damp-Heat harms people particularly severely. Traditionally, Wind-Cold injures the Form (Xing), and injuries to Form always enter from the exterior; Damp-Heat injures Qi, and injuries to Qi do not necessarily enter from the exterior. When Wind pathogen binds the exterior, it is called Fengwen; when Damp pathogen invades internally, it is called Shiwen. Even if slight cold accompanies it, it differs from the biting severity of freezing cold. Therefore, releasing the exterior should use Acrid-Cool, not Acrid-Warm; clearing the interior should drain Heat, not purge Heat aggressively. If one indiscriminately applies methods such as "releasing the exterior without avoiding Heat" and "purging the interior without avoiding Cold," death would follow in succession.