The *Suwen* (Basic Questions) states: The disease is the root (*ben*), and the physician is the branch (*biao*). If the root and branch do not correspond, the pathogenic factor cannot be subdued.

It further states: If the root and branch have corresponded, then the pathogenic factor can be subdued. What is meant by "root" and "branch" is a matter of the beginning and end of a single entity. Today, the patient and the physician are not one entity; why speak of them as root and branch? It is said that a specific disease constitutes the root, and thus the physician who treats that specific disease constitutes the branch. By following the root to treat the branch, the physician and the disease become integrated into one system.

For instance, in a case of *Shanghan* (Cold Damage), *Shanghan* is the root, and the physician capable of treating *Shanghan* is the branch. This is what is meant by "the root and branch have corresponded, and the pathogenic factor is subdued." If *Shanghan* is taken as the root, but a physician skilled in treating *Bishan* (Bi syndrome and hernia) is chosen as the branch, then the root and branch do not correspond; how could the pathogenic factor possibly be subdued? The *Suwen* discusses this in terms of correspondence or non-correspondence, revealing the intent of the sages.

Moreover, diseases vary in severity, and physicians vary in skill. Severe diseases require highly skilled physicians, which refers to the correspondence of root and branch. Bian Que said: "What people worry about is the multiplicity of diseases; what physicians worry about is the paucity of medical principles." When principles are few and diseases many, it is difficult for the root and branch to correspond.

All diseases are indeed difficult, but *Shanghan* is particularly severe. Human ailments may reside in the skin, muscles, bone marrow, or the five zang and six fu organs. Once pathogens attach, they linger and do not depart; normally, they do not enter the meridians and circulate with the meridian qi. Only the toxin of *Shanghan* can enter the major meridians and contend with the meridian qi. If the meridian qi cannot overcome it, it instead utilizes the meridians to attack the body recklessly, leaving the person helpless and awaiting death. The meridians once known for circulating blood and qi and nourishing life have now become pathways for cold, heat, and warm toxins that endanger life. How can this be compared to other diseases?

Therefore, since ancient times, it has been considered a difficult disease to treat. At the onset of the illness, the pathogen transmits through one meridian each day. During the initial transmission, symptoms may be hard to distinguish, and medication choices remain uncertain; at this time, the physician's key lies in clarity (*ming*). When the transmitted symptoms begin to manifest, urgency in medication is required; hesitation leads to error, so the physician's key lies in decisiveness (*duan*). After one meridian stage passes, transmission to another begins, mixing new and old symptoms; here, the physician's key lies in careful examination (*shen*).

A physician must have a clear, pre-judged understanding of the six-day transmission cycle; otherwise, responses will likely be inadequate. The changes of the Three Yin and Three Yang meridians are swift like a gale or a galloping horse, passing without pause. To chase after them and attack is erroneous. Furthermore, when heterogeneous pathogens invade intermittently, variations emerge spontaneously, sometimes in the exterior, sometimes in the interior, transcending normal constraints like spirits. How should one respond?

Thus, Zhang Zhongjing stated: "The interweaving of Yin-Yang deficiency and excess presents subtle signs; the opposition of sweating, vomiting, and purging methods brings rapid disaster." Believing this statement, unless one possesses profound insight, extensive learning, and infinite adaptability, one will inevitably hit a wall and act counterproductively. This emphasizes the importance of the root and branch corresponding, so that the pathogenic factor may be subdued.

Because it is the most difficult to treat, attention has been specially focused on it since Zhang Changsha (Zhang Zhongjing). Analyzing minute details, writing tens of thousands of words to instruct future generations. Among current medical theories and formulas, none are more detailed regarding *Shanghan*. A disease once considered difficult to treat is now clearly visible and easy to understand. The problem lies in ordinary people being negligent and failing to study these books. Thus, the benefit of these books to posterity is indeed vast.

Therefore, Tao Hongjing praised Zhang Zhongjing's book as the ancestor of all formulas, and Sun Simiao sighed at its miraculous efficacy, both having valid reasons. My second brother, courtesy name Ziyan, served as acting governor of Yiling and Zigui commanderies. Suffering from frequent illnesses since childhood, he favored medical prescriptions and visited famous physicians extensively. He was able to meet figures such as Chang Qizhi and Kang Chundao. Consequently, he realized that the art of medicine, having been passed down for a long time, deeply embodies Zhang Zhongjing's theories. He often lamented that this learning is extremely difficult to exhaust and that its lineage is nearing extinction, frequently speaking of this to me.

I initially obtained Zhang Zhongjing's book but did not fully grasp it. Through gradual study over time, I came to love it deeply in my old age, sighing that I had started too late. Formerly, Zhang Zhongjing lamented the loss of past classics and mourned those who died prematurely without rescue, leading him to compile the *Shanghan Zabing Lun* (Treatise on Cold Damage and Miscellaneous Diseases). My intention is the same. Although my knowledge is sparse and lacking in superior insights, every word and deed must have an upper source and inner conviction before I dare record it in writing. I discard worldly absurdities and deceptive techniques, always feeling as if Heaven, Earth, and parents are watching from above. I hope that someone like Yang Xiong will appear in later generations to confirm that my words are not erroneous.

The discussions compiled here range from Qibo and Huangdi to recent works. All debates, Q&A, symptom analysis, and treatments total over 1,500 entries, amounting to 50,000 characters, divided into over 70 categories, forming 20 volumes of theoretical discourse and 5 volumes of formulas and herbs. I have heard that medical scholars who enjoy writing may take thirty years for essays or twenty years for books. Their focused effort allows their work to endure. I am now eighty years old, with the sun setting and the road far; my ambition is quick completion. How can I linger long in this path? Therefore, within a year, I have outlined the main points. Since predecessors' accounts are already complete, subsequent works rely merely on letter-writing efforts and cannot avoid omissions and contradictions. Future gentlemen may pity my senile confusion, correct my errors, and perfect this work, which is indeed hoped for.

Alas! I was born in an ill-fated time. I cannot see Zhang Changsha or Sun Zhenren to bow and ask for instruction; nor can I approach Pang Anshi and Zhu Gong. Alone holding lost texts, groaning in deep mountains and remote valleys, drinking bean soup and water without weariness, finding joy therein. Confucius mastered many humble skills; Zixia said even minor arts must be observed. Even sages did not abandon them, let alone later generations. I hope I am not rejected for my clumsiness and stinginess.

In the eighth year of Chunxi, Xin Chou year, late spring month, Guo Yong of Henan respectfully records this.

Recent scholarly works on *Shanghan*, such as Gao Wenzhuang's *Shanghan Leyao*, I have not obtained the original. The works of Pang Anshi and Zhu Gong have been transmitted for a long time. Chang Qizhi's *Bu Zhi Lun* has slight circulation but no good edition. Where text is missing, I supplement it; where errors exist, I correct them; where doubts persist, I remove them, hoping not to tarnish their reputations. Among later authors, only Wang Zhonggong's monograph shows significant innovation. Where predecessors were deficient, I adopt his views. Below this point, nothing else is suitable for recording. Even if transmitted, they are insufficient to serve as unchangeable doctrines for posterity.