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The Treatise on Heatstroke states: Shu (Summerheat) is the scorching heat of summer, a pathogenic factor of intense heat invading the human body. It is categorized into three types: Mao (Superficial Exposure), Shang (Injury), and Zhong (Stroke/Severe Attack). These three types differ in severity and can be distinguished by deficiency or excess patterns. If abdominal pain and watery diarrhea occur, it indicates that the Stomach and Large Intestine are affected; if nausea occurs, it indicates phlegm-fluid retention at the stomach opening. These two conditions belong to Mao Shu (Superficial Summerheat). Huanglian Xiangru Yin (Coptis and Elsholtzia Decoction) or Qingshu Yiqi Tang (Clear Summerheat and Boost Qi Decoction) may be used, as Huanglian (Coptidis Rhizoma) clears summerheat-heat, and Xiangru (Moslae Herba) resolves retained water-dampness. If there is fever, headache, restlessness, or a sensation like needle pricks in the body, this indicates heat injuring the muscle layer (Roufen). Jiedu Tang (Detoxification Decoction) or Baihu Tang (White Tiger Decoction) with Chaihu (Bupleuri Radix) should be used. For those with Qi deficiency, Renshen (Ginseng Radix et Rhizoma) is added; this constitutes Shang Shu (Summerheat Injury). If cough, alternating chills and fever, night sweats that do not stop, and a rapid pulse occur, this indicates heat in the Lung Meridian. Qingfei Tang (Clear Lung Decoction), Chaihu Tang (Bupleuri Decoction), or Tiansan San (Heavenly Water Powder) and similar formulas should be used. Prompt treatment leads to recovery, while delayed treatment is incurable, because excessive Fire overacts on Metal (Lung); this constitutes Zhong Shu (Summerheat Stroke). In treating diseases, one must clearly differentiate and distinguish, never confusing them for treatment. They may also occur during spring and autumn; one must not adhere rigidly to one pattern but prescribe according to the specific condition.

Commentary: Summerheat disease inherently has degrees of severity, so dividing it into Mao, Shang, and Zhong is correct. However, all illnesses caused by contracting summerheat stem from contracting fire-heat and are collectively termed Shang Shu. Only when the contraction of fire is heavy and the heat is severe is it called Zhong Shu. Assigning various internal and external miscellaneous syndromes to the Five Zang Organs is reasonable. However, assigning the Three Types (Mao, Shang, Zhong) to the Five Zang Organs is erroneous. Although these miscellaneous syndromes have degrees of severity, they all originate from the Zang-Fu organs. To assign these three syndromes specifically would be rigid and biased. Even renowned physicians have made this error; how then can they dispel the confusion of later generations?

Danyu stated: During the time of summerheat, healthy individuals who seek relief from the heat by staying in deep halls, large mansions, cool terraces, or cold pavilions, or by using large fans and wind-charts, contract illness through stillness. This is a Yin syndrome obtained through stillness. The symptoms necessarily include headache, aversion to cold, stiffness and rigidity of the body, pain in the limbs and joints, irritability, high skin temperature, and absence of sweating. This is because Yin-cold constrains the body, preventing the Yang Qi of the whole body from extending and venting. It is appropriate to use acrid-warm agents to release the exterior and disperse cold, such as Houpo (Magnoliae Officinalis Cortex), Zisu (Perillae Folium), Genge (Puerariae Lobatae Radix), Huoxiang (Agastaches Herba), Qianghuo (Notopterygii Rhizoma et Radix), and Cangzhu (Atractylodis Rhizoma). If there is external cold contraction combined with internal injury from ice water, raw fruits, and vegetables, add Ganjiang (Zingiberis Rhizoma), Suosha (Amomi Fructus Rotundus), and Shenqu (Massa Medicata Fermentata) to the previous formula. These are not treatments for Summerheat itself, but treatments for diseases caused by the summer season.

Commentary: Distinguishing Zhong Shu and Shang Shu by stillness and movement originates from Zhang Jiegu, and later generations followed this theory. In the height of summer, the blazing sun is like roasting, everywhere being thus. Therefore, ancients spoke of avoiding summerheat but did not speak of avoiding cold. Deep halls and large mansions were indeed for avoiding summerheat; how could entering them lead to invasion by pathogens? Moreover, cool rooms protect Yang Qi; how could they constrain and injure it? Even in the depths of wealthy households, one inevitably encounters summerheat. One should interact with those suffering from Shang Shu, which is contracted through movement. Laozi said: "If man can maintain constant clarity and stillness, Heaven and Earth will return to him." One stillness can dispel summerheat; from where does the invasion come? As for ice water and fruits, consuming too many naturally damages the Spleen and Stomach and generates miscellaneous syndromes. It is acceptable to say that dysentery and miscellaneous syndromes involve the accumulation of these foods, but it is incorrect to say they specifically cause summerheat disease. If one insists that oral intake of cold substances and physical exposure to cold should be treated like winter cold diseases, the error would be thousands of miles off.

Lin commented: Jiegu’s discussion of sudden onset distinguishing Yin and Yang by stillness and movement is highly inappropriate and has provoked criticism from later generations, yet it was done out of necessity. Why? The character "Shu" contains "Sun" (Day). Saying Shu rather than Fire invites reflection. It implies that the Yang heat of the heavenly sun steams the earth's Qi upward. Humans exist in the intersection of these Qi; contracting it causes Summerheat disease. The *Suwen: Wuyun Liuda Lun* states that Summerheat is steaming; the *Liji: Yue Ling* describes "moist and muggy heat" as an example. At the Summer Solstice, Yin Qi begins to grow. The Yin Qi latent in the human body corresponds to this. Summerheat belongs to Junhuo (Ministerial Fire) among the Six Qi, corresponds to the Heart among the Zang Organs, and corresponds to the Li Trigram among the Eight Trigrams. Since the Li Trigram is hollow in the middle, Summerheat, though Yang-heat, contains Yin characteristics, which can be verified. Therefore, Zhang Zhongjing established three methods for treating Summerheat, standing together. Jiegu feared that physicians of his time did not understand this principle, so he established the names Yin Shu and Yang Shu to differentiate treatment. Danyu extended Jiegu’s meaning, stating, "This is not treating Summerheat, but treating diseases caused by the summer season." How clear and thorough! Initially, he did not expect to be criticized by later generations.

What Jiegu called "Yang Shu obtained through movement" refers to common people who run long distances or labor in fields, suddenly exposed to the midday sun. This is Yang Shu, representing movement within movement. What he called "Yin Shu obtained through stillness" refers to wealthy individuals living in large mansions using fans, indulging excessively, damaging their True Yang, causing Yin-dampness to accumulate internally and Cold to attack externally. This is Yin Shu, representing movement within stillness. If one truly practices non-action and maintains inner Truth-Qi, no pathogen can invade, let alone just Summerheat disease.