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1. The exposition of this book specifically categorizes "Zhonghan" (Cold Damage from Exogenous Cold) as an independent discipline. Contemporary medical texts occasionally mention Zhonghan within the context of miscellaneous diseases but lack detail; conversely, while the *Shanghan Lun* (Treatise on Cold Damage) discusses Zhonghan extensively, it often mixes content with other conditions, causing confusion for later learners and leading to misdiagnosis and mistreatment of both categories. Therefore, after completing my annotated commentary on the *Shanghan Lun*, I compiled this book to elucidate the profound principles of Zhang Zhongjing.

2. This book is divided into three volumes: Upper, Middle, and Lower. The first two volumes consist exclusively of the formulas and theories of Zhang Zhongjing, enabling students to identify the orthodox foundation. The final volume appends formulas and theories from later virtuous physicians, allowing students to master adaptive variations. By integrating ancient wisdom with contemporary practice, one can ensure accuracy in syndrome differentiation and formula prescription.

3. Under each syndrome entry, annotations are provided followed by detailed analysis to confirm its classification as Zhonghan. Under each formula, the properties of individual herbs are meticulously noted to demonstrate the formula's appropriateness for the specific syndrome. If a syndrome appears slightly inconsistent or if dosage adjustments raise doubts, detailed analysis is provided to warn against rigid adherence to ancient or modern formulas. Flexible application based on clinical reality will surely yield remarkable results.

4. Novice practitioners must first study my annotated version of Zhang Zhongjing’s *Shanghan Lun*. This ensures they know how to administer medication for heat syndromes and enter the school of Zhang Zhongjing. Subsequently, studying this book allows them to penetrate the inner sanctum of Zhang’s teachings. Consequently, true cold syndromes will be immediately recognizable, enabling accurate use of warming and tonifying formulas with high success rates. Mastery of cooling and purging methods for Shanghan heat diseases will also become effortless. Beginners should proceed systematically.

5. Among the general population, nine out of ten cases are Shanghan (Cold Damage), while only one in ten is Zhonghan. Thus, physicians using cooling medicines often achieve more successes, whereas those using heating medicines succeed less frequently. Some renowned physicians, specializing in Shanghan and reciting Zhang Zhongjing’s texts, mistakenly classify complications of Shanghan as Zhonghan, recklessly administering heating medicines and repeatedly failing. These individuals admire Zhang Zhongjing excessively but fail to adapt his principles. Students who read this book with an open mind will naturally acquire effective therapeutic methods.

6. The various commentaries collected herein include Cheng Wuji’s original explanation of the *Shanghan Lun*, Fang Youzhi’s *Tiaobian*, Yu Chang’s *Shanglun Pian*, Cheng Zhi’s *Hou Tiaobian*, Chen Shi of Wuling’s annotation of the *Six Channels of Shanghan*, as well as texts such as *Neitai Fangyi*, *Waitai Miyao*, *Buwang Lun*, and *Huoren Shu*. (A separate bibliography lists these citations.) These were synthesized to form this book. Fearing that later learners might not fully grasp the material, I have repeatedly expounded upon my own insights. For borrowed commentaries, I explicitly cite the source author and text to avoid plagiarism. Personal observations are marked with phrases such as "Hu An" (Commentary by Hu), "Yu An" (My Commentary), "Yu Wei" (I believe), or "Yu Yi" (In my opinion), or presented as Q&A sections where I provide answers.

7. My work on annotating this book began during the Mid-Autumn Festival of the Jiazi year of the Kangxi reign and concluded on the first day of the second lunar month of the Bingyin year. During periods of leisure amidst social engagements, I would sometimes dedicate a full day to annotating one or two syndrome entries or one or two formulas. If delayed for ten days or half a month, finding only half a day free allowed me to annotate one syndrome or one formula. Occasionally, accumulating two or three days of free time resulted in the annotation of merely one syndrome or one formula. The total working time amounted to only five months. However, for over twenty years, I had been diligently collecting, copying, and studying medical texts from various masters, while simultaneously treating difficult and critical cases. All insights gained over these two decades were poured into this book. Although written in five months, it was not produced hastily. Having completed it, I dared not keep it hidden at home; thus, I copied it for dissemination among colleagues nationwide.