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The *Huangdi Neijing* (Yellow Emperor's Inner Canon) distinguishes between "Chuan" (Wheezing/Dyspnea) and "Xiao" (Asthma/Wheezing with sound). By the Han Dynasty, medical texts began to discuss asthma and wheezing together. The origins of dyspnea are diverse, whereas the origin of asthma is solely due to cold phlegm entering the orifices of the lung. The lung is a delicate organ, possessing a clear and empty nature, allowing no slightest obstruction to remain suspended in the chest. Its orifices face upward; once an pathogen enters, it cannot exit. If a person drinks ice water or eats raw fruits, cold phlegm accumulates and permeates internally, becoming the mother of phlegm (Tan Mu). External factors interacting with internal pathogens trigger the disease. Once the phlegm surges upward like a tide, the lung orifices become blocked, and respiration becomes chaotic. When respiration is chaotic, the twenty-seven pulse positions exhibit mixed and alternating manifestations without limit. In cases triggered by cold, external cold interacts with internal cold, causing phlegm to surge upward due to this interaction; in cases triggered by heat, internal cold is steamed by heat, causing phlegm to surge upward due to this steaming. Recovery occurs only when pent-up qi reaches its extreme, and a substance resembling fish brain mucus is coughed out, at which point the symptoms subside and the pulse returns to normal. According to materia medica teachings, among herbs with potent properties, only Ephedrae Herba (Mahuang, 麻黄) and Realgar (Pishi, 砒石) can open the blocked orifices and forcibly expel the phlegm. Mahuang induces sweating, but in cases of asthma, its diaphoretic function is not utilized even in midsummer. Pishi is toxic and harmful, but in cases of asthma, it does not harm the patient even if their constitution is frail. If there is a corresponding symptom and herb, yet the root cause cannot be eradicated, it is because Mahuang can clear the pathways blocked by phlegm but cannot uproot the nest where phlegm resides; Pishi can eliminate the associates of phlegm but cannot annihilate the chief leaders of latent phlegm. This explains why symptoms resolve immediately after medication but recur later. I have observed elderly patients suffering from consumptive cough with hemoptysis, emaciation, and rapid pulses, exhibiting signs of terminal decline. Upon inquiry, they were found to have a history of asthma. Since the consumption was incurable, treating the asthma with these two herbs led to recovery in several cases. I have also observed elderly patients with rebellious qi, cough, asthmatic oppression, rapid pulses, and insomnia, in extreme exhaustion. Upon inquiry, they had a history of asthma. Since the rebellious qi was deemed incurable, treating the asthma with these two herbs resulted in recovery in several cases. The saying "Ancient ice and snow of Yaochi" refers to a method for treating cold phlegm in the lungs, which is quite accurate.

Method for preparing Pishi pills: Take one liang of dried and powdered Fermented Soybean (Danshidou, 淡豆豉), one qian of Realgar (Pishi, 砒石), mix with rice paste, and form into pills.
(Mr. Jie'an of the Cishi family served as an official for forty years. After resigning and returning home, he was seventy years old. He suffered from asthma and insomnia and recovered after taking Mahuang. To repay the kindness of a close relative, he invited various friends, established a bond of three lifetimes, and eagerly awaited insightful advice, requesting that I write this article.)