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The *Neijing* (Inner Canon) states: Febrile diseases occurring after the Summer Solstice are termed *Shu* (Summerheat). Summerheat pathogens should be expelled through sweating; do not forcibly stop perspiration. Upon contracting Summerheat and sweating, if restlessness occurs, there is panting and thirst; if calm, there is excessive talking. The body feels as hot as a burning charcoal, and the heat dissipates once sweat is released. A deficient pulse with febrile sensation indicates injury by Summerheat (*Shangshu*).

The *Nanjing* (Classic of Difficult Issues) states: Injury by Summerheat results from direct pathogenic invasion, where Fire acts as the disease itself. Patients may exhibit an aversion to foul odors. Symptoms include febrile sensation, restlessness, heart pain, and a floating, large, and scattered pulse.

The *Shanghan Lun* (Treatise on Cold Damage) states: *Taiyang Zhongre* (Summerheat in the Taiyang channel), also referred to as *Zhonghe*, manifests with sweating, aversion to cold, febrile sensation, and thirst. *Taiyang Zhongye* (Yin-summerheat/Cold-summerheat in the Taiyang channel) presents with febrile sensation, painful heaviness, and a weak pulse; this is caused by exposure to cold water in summer, leading to water-dampness residing in the skin. Another presentation of *Taiyang Zhongye* includes fever, aversion to cold, bodily heaviness, and pain, with a wiry-thin, knotted-empty, or slow pulse. After urination, one feels chilly with shivering and piloerection; the hands and feet are cold. Slight exertion causes immediate heat; the mouth opens, and the anterior teeth appear dry. If diaphoresis (sweating-inducing treatment) is applied, aversion to cold worsens; if warm needle therapy is used, fever intensifies; if purgation is repeatedly applied, strangury (dysuria) worsens.

Commentary: Xu Xueshi (Xu Shuni) asks: Why is the pulse in injury by Summerheat wiry-thin, knotted-empty, or slow? The *Neijing* states: "Cold damages the form; Heat damages the Qi." Since only Qi is damaged and not the form, Qi becomes depleted, resulting in a weak pulse. Therefore, wiry-thin, knotted-empty, and slow pulses are all deficient pulses. Zhang Zhongjing considers the wiry pulse as Yin, and Zhu Gong also states that the pulse in Summerheat is fine and weak; thus, these are all deficient pulses, which can be deduced.

Jiegou (Zhang Yuansu) states: Contracting illness while at rest is termed *Zhongshu* (Summerstroke/Yin-summerheat); contracting illness during activity is termed *Zhonger* (Heatstroke/Yang-summerheat). *Zhongshu* is a Yin syndrome; *Zhonger* is a Yang syndrome.

Dongyuan (Li Dongyuan) states: During the season of Summerheat, healthy individuals who seek coolness in deep halls and large buildings to avoid the heat contract what is named *Zhongshu*. Their symptoms necessarily include headache, aversion to cold, stiff and rigid body, joint pain, and restlessness. The skin and muscles feel hot, but there is no sweat. This is because the yin-cold of the rooms suppresses the body's Yang Qi, preventing it from extending and dispersing. Treatment primarily uses *Dashun San* (Great Harmony Powder) to disperse heat, which is correct. However, for porters or farmers who labor under the sun and contract the disease, it is named *Zhonger*. Their symptoms necessarily include severe headache, irritability, heat sensation, aversion to heat, scorching-hot skin upon touch, extreme thirst with desire to drink, profuse sweating, and lethargy due to lack of Qi. This is caused by heavenly heat externally injuring Lung Qi. Treatment uses cooling agents such as *Cangzhu Baihu Tang* (Atractylodes White Tiger Decoction).

Annotation: The *Zhongshu* discussed here corresponds to Zhang Zhongjing’s *Zhongye* (Yin-summerheat). Here, the distinction is made solely based on Summerheat, revealing two syndromes of Yin and Yang with different etiologies. However, in summer illnesses, those suppressed by yin-cold preventing the extension of whole-body Yang Qi, treated with *Dashun San*, are called *Zhongshu*, analogous to how febrile diseases in winter are called *Shanghan* (Cold Damage). Yet, although the treatment for *Zhonger* mentions using *Cangzhu Baihu Tang*, methods for clearing Summerheat and benefiting Qi are also prescribed. Furthermore, *Dashun San* is originally a formula from Zhang Zhongjing’s Taiyang chapter. Li Dongyuan’s application of this formula likely involved more than just this; there must have been elaborations on cases similar to *Ruogaiqi Tang*, but unfortunately, these were not transmitted, causing doubt among later generations. See further discussions below. Moreover, *Zhongshu* can also result from labor and activity, while *Zhonger* can result from seeking coolness and rest. Generally, because individuals’ Yuan Qi (Original Qi) varies in deficiency or excess, the contracted pathology differs accordingly. How can the treatment methods remain without variation?