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(The treatment principle is primarily to warm and disperse.)
Some cases result from sudden exposure to the cold qi of heaven and earth, while others arise from consuming raw or cold foods orally.
Dai Yun [Dai Yuanli] stated: Here, "Shanghan" (Cold Damage) refers to the body being affected by the austere and killing cold qi, and the mouth ingesting ice water, melons, fruits, and other cold substances. Patients will necessarily present with a deep and fine pulse, cold hands and feet, weak respiration, and physical fatigue. Even if there is fever, there is no thirst, and speech is limited due to fatigue. If this method is mistakenly applied to heat diseases, mild cases may become severe, and severe cases may lead to death. Any case with a rapid pulse, desire for drinking water, or restlessness and agitation indicates a heat disease. Cold and heat syndromes are like water and fire; they cannot be treated identically. Misdiagnosis leads to death. Students must exercise caution.

True "Shanghan" (Cold Damage) occurs only when the body has been exposed to cold qi and cold foods have been ingested. In such cases, dispersing herbs should be added to Buzhong Yiqi Tang (Spleen-Boosting Qi-Regulating Decoction). Cases belonging to internal injury account for eight or nine out of ten. The method is as follows: Wherever pathogenic factors gather, the healthy qi must be deficient. One should use only Buzhong Yiqi Tang (Spleen-Boosting Qi-Regulating Decoction) and modify it according to the observed syndrome. If there is qi deficiency with severe fever, a small amount of Fuzi (Aconite Lateral Root) should be used to facilitate the action of Ginseng-containing formulas. This method can only be used if there is indeed qi deficiency. The above Shanghan (Cold Damage) treatment methods are applicable in the South but not suitable for the North.

Dai Yun [Dai Yuanli] said: Shu (Summerheat) is the intense heat of summer that adheres to the human body. It is categorized into Mao Shu (Mild Summerheat), Shang Shu (Damaging Summerheat), and Zhong Shu (Stroke-like Summerheat), which differ in severity and distinction between excess and deficiency. Abdominal pain and watery diarrhea indicate involvement of the Stomach and Large Intestine; nausea indicates phlegm-fluid retention in the stomach region. These two conditions constitute Mao Shu (Mild Summerheat). Huanglian Xiangru Yin (Coptis and Elsholtzia Decoction) can be used. Coptis clears summerheat-heat, while Elsholtzia resolves accumulated water-dampness. Fever, headache, irritability, and restlessness, or a sensation of needle-pricks in the body, indicate heat damaging the muscle interspaces. Jiedu Baihu Tang (Detoxifying White Tiger Decoction) with Chaihu (Bupleurum Root) should be administered. If qi is deficient, Renshen (Ginseng Root) should be added. Cough, alternating chills and fever, unremitting night sweats, and a rapid pulse indicate heat in the Lung Meridian. Qingfei Tang (Lung-Clearing Decoction) or Chaihu Tianshui San (Bupleurum and Heavenly Water Powder) should be used. Timely treatment allows for cure; delay renders it incurable. If Fire pathogen attacks Metal (Lung), this is termed Zhong Shu (Stroke-like Summerheat). In treating diseases, one must clearly differentiate and avoid confusing treatments. It may also occur during spring and autumn; do not adhere rigidly to one pattern. Prescribing according to the specific disease is the best approach.
In Huanglian Xiangru Yin (Coptis and Elsholtzia Decoction), add Banxia (Pinellia Tuber) if phlegm is involved; add Renshen (Ginseng Root) and Huangqi (Astragalus Root) if attacking through deficiency; or use Qingshu Yiqi Tang (Summerheat-Clearing Qi-Boosting Decoction) with modifications.