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Mr. Zhang Yuansu, courtesy name Jiegu, was a native of Yishui. At the age of eight, he took the examination for children's classics; at twenty-seven, he passed the imperial examination due to his mastery of classical interpretations. However, he was dismissed from office because his name offended the taboo of Emperor Zhang's ancestral temple. Consequently, he lost interest in official career advancement and devoted himself to medicine. For over twenty years, although his memorization was extensive, his medical skills in treating people were no better than those of others.

One night, he dreamed that someone used a large axe and a long chisel to open a cavity in his heart, placing several volumes of books inside. He saw the title inscribed as *Jingnei Zhuzhi Beiyao* (Essentials of Indications from the Inner Canon). Startled awake by fear, he felt heart pain upon waking and considered it an ominous sign, so he dared not tell anyone. From then on, his mind and vision became clear and penetrating, and he resolved to transmit the medical teachings of Xuanyuan and Qibo, wielding medical prowess comparable to that of Qin Yue (Bian Que). Liu Shouzhen of Hejian had a medical reputation that spanned the world, but Zhang initially regarded him with disdain.

Later, Liu Shouzhen contracted cold damage (*Shanghan*) for eight days and was mistakenly treated with purgatives. He suffered from headache, tight pulse, vomiting, nausea, and inability to eat. His disciples, attending to their sick teacher, did not know what to do and requested Zhang Jiegu to examine him. Upon arrival, Liu turned his back to the wall and ignored him. Zhang said, "Why do you regard me with such contempt?" After examining the pulse, he said, "The pulse and condition are indeed severe. Did you initially take a certain medicine that conflicted with another?" Liu replied, "Yes." Zhang said, "The error is very serious." Liu suddenly rose and asked, "What do you mean?" Zhang explained, "That medicine is cold in nature and descending, affecting the Taiyin channel, leading to the loss of Yang qi and incomplete sweating. Given the current pulse, you should take [a specific] medicine." Liu was deeply convinced by Zhang's ability. After one dose, he recovered, and Zhang's fame spread throughout the world.

When treating diseases, Zhang did not use ancient prescriptions, stating instead, "Ancient prescriptions for new diseases are highly inappropriate and can harm people." He always formulated prescriptions according to the specific illness, ensuring efficacy within a set timeframe. The medicine acted swiftly, like grasping something, and people of the time called him a Divine Physician. In his leisure time, he compiled materials on the Five Movements and Six Qi from the *Suwen*, essential treatments from the *Inner Canon*, and drug properties from the *Bencao*, naming the work *Yixue Qiyuan* (Origin of Medicine) to teach his disciples. Additionally, thirty volumes of *Medical Prescriptions* (*Yifang*) were transmitted to the world. [Lost during the Renchen year, only *Yixue Qiyuan* remains]. Li Mingzhi of Zhengding, a senior disciple of Zhang, requested me to write a preface, so I have written these words. Preface by Zhang Jifu, the Old Man of Lanquan.