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The *Huangdi Neijing* (Yellow Emperor's Inner Canon) states: "For pathogens located in the upper region, induce vomiting to expel them; for those in the lower region, drain them through urination or defecation; for fullness in the middle, purge from within; for pathogens in the body, soak the form to induce sweating; for pathogens in the skin, disperse them through sweating." The subtlety of treating *Shanghan* (Cold Damage) involves flexibility, but ultimately does not exceed these few methods.

When pathogenic factors of *Shanghan* transmit from the exterior to the interior and remain in the chest, this constitutes pathogens at a high position, and thus emesis may be employed. This is the method of "inducing vomiting to expel" (*Yin Er Yue Zhi*). The indications for emesis vary. For instance, if no sweating or purgation has been performed, and pathogenic factors are constrained and stagnant in the diaphragm, it is termed "Diaphragmatic Excess" (*Ge Shi*), which should be treated with *Gua Di San* (Melon Seed Powder) to induce vomiting. *Gua Di San* is used to expel excess pathogens from the chest. If, after sweating, vomiting, or purging, pathogenic factors take advantage of the deficiency to remain in the chest, it is termed "Deficiency Irritability" (*Xu Fan*), which should be treated with *Zhizi Chi Tang* (Gardenia and Fermented Soybean Decoction) to induce vomiting. *Zhizi Chi Tang* is used to expel the irritability caused by deficiency-heat in the chest.

Zhi Zi (Fructus Gardeniae) is bitter and cold. The *Neijing* states: "Sour and bitter flavors have the effect of surging and draining, belonging to Yin." "Surging" refers to inducing vomiting. To surge and drain deficiency-irritability, one must primarily use bitter substances; therefore, Zhi Zi is used as the Sovereign herb (Jun). Irritability results from excessive heat. To surge and drain heat, bitter substances are required; to overcome heat, cold substances are required. Xiang Chi (Fermented Soybean) is bitter and cold, assisting Zhi Zi in vomiting out deficiency-irritability; therefore, Xiang Chi is used as the Minister herb (Chen). The *Neijing* states: "Qi has high and low positions; diseases have distant and near origins; syndromes have internal and external locations; treatments have light and heavy degrees." One must apply treatment appropriately according to the situation, following the principles, which constitutes good practice.

[Prescription Composition] Zhi Zi (Sovereign, 14 pods, broken open); Xiang Chi (Minister, 4 he, wrapped in silk cloth).

Take the above two ingredients, add four sheng of water, boil Zhi Zi until half of the water remains (2.5 sheng), remove the dregs, add Xiang Chi, and boil again until 1.5 sheng remains. Remove the dregs and divide into two doses. Take one dose warm. If rapid vomiting occurs, stop taking the remaining dose.

Hua Tuo stated: "On the fourth day, when pathogens enter the chest, emesis can be applied." This is the method of "meeting and seizing" (attacking the pathogen directly). The *Qianjin Fang* states: "When qi floats to the upper part, filling and blocking the heart and chest, causing chest fullness, emesis will cure it." This is the method of treating according to the syndrome. Generally, on the fourth or fifth day of *Shanghan*, this is when pathogens lodge in the chest. Additionally, if there is chest irritability and fullness, qi rushing up to the throat, and difficulty breathing, the indications for emesis are complete. At this point, administering various emetic drugs can ensure a perfect outcome.

Gua Di (Fructus Momordicae) is bitter and cold. The *Neijing* states: "Dampness in the upper region is treated with bitter emetics." Cold-dampness staying in the chest requires bitter substances as the primary agent; therefore, Gua Di is used as the Sovereign herb. Chi Xiao Dou (Semens Phaseoli Angularis) is sour and astringent. The *Neijing* states: "Sour and bitter flavors have the effect of surging and draining, belonging to Yin." To separate and drain diaphragmatic excess, sour substances must be used as Assistant herbs (Zuo); therefore, Chi Xiao Dou is used as the Minister herb. Xiang Chi is bitter and cold; bitterness induces surging and draining, and cold overcomes heat. To remove heat from the upper diaphragm, bitter-cold substances are necessary as Auxiliary herbs (Shi); therefore, Xiang Chi is used as the Envoy herb. When sour and bitter flavors combine, phlegm-heat in the chest will be surged and vomited out. For patients who have lost blood or are constitutionally deficient, this formula is contraindicated because *Gua Di San* is a harsh agent that severely depletes body fluids. Such patients require nourishment; further depletion of fluids would inevitably lead to failure to recover. Practitioners must study this carefully.

[Prescription Composition] Gua Di (Sovereign, 1 fen, roasted until yellow); Chi Xiao Dou (Minister, 1 fen).

The above two ingredients are separately pounded and sifted into powder, then mixed thoroughly. Take 1 qian 7 fen of the powder. Use 1 he of Xiang Chi and 7 he of boiled water, cook into a thin porridge, remove the dregs to obtain the juice, mix with the powder, and take warm in one dose. If vomiting does not occur, increase the dose slightly. Stop once rapid vomiting is achieved. All patients with blood loss or constitutional deficiency must not take *Gua Di San*.