外科之法，最重外治，而外治之中，尤当围药。凡毒之所最得，散大而顶不高。盖人之
一身
，岂能无七情六欲之伏火，风寒暑湿之留邪，食饮痰涎之积毒？身无所病，皆散处退藏，气
血一聚而成痈肿，则诸邪四面皆会。惟围药能截之，使不并合，则周身之火毒不至矣。其已
聚之毒，不能透出皮肤，势必四布为害，惟围药能束之使不散漫，则气聚而外泄矣。如此，
则形小顶高，易脓易溃矣。故外治中之围药，较之他药为特重，不但初起为然，即成脓收口
，始终赖之，一日不可缺。若世医之围药，不过三黄散之类，每试不效，所以皆云围药无用
。如有既破之后，而仍用围药者，则群然笑之。故极轻之毒往往至于散越，而不可收拾者，
皆不用围药之故也。至于围药之方，亦甚广博，大段以消痰拔毒、束肌收火为主，而寒热攻
提、和平猛厉，则当随症去取。世人不深求至理，而反轻议围药之非，安望其术之能工也？
《难经》，非经也。以经文之难解者，设为问难以明之，故曰《难经》。言以经文以难
而释
之也。是书之旨，盖欲推本经旨，发挥至道，剖晰疑义，垂示后学，真读《内经》之津梁也
。但其中亦有未尽善者，其问答之词，有即引经文以释之者。经文本目明显，引之或反遗其
要，以至经语反晦，或则无所发明，或则与两经相背，或则以此误彼，此其所短也。内中有
自出机杼，发挥妙道，未尝见于《内经》，而实能显《内经》之奥义，补《内经》之所未发
。此盖别有师承，足与《内经》并垂千古。不知创自越人乎？抑上古亦有此书，而越人引以
为证乎？自隋唐以来，其书盛着尊崇之者固多，而无能驳正之者。盖业医之辈，读《难经》
而识其大义，已为医道中杰出之流，安能更深考《内经》，求箕 异同得失乎？古今流传之载
籍，凡有舛误，后人无敢议者，比比然也，独《难经》乎哉？余详余所着《难经经释》中。
外科治疗的方法，最重视外治法，而在外治法中，尤其重要的是围药。凡是毒邪聚集之处，往往呈现散漫而顶部不高的特点。因为人的全身，难道没有七情六欲潜伏的火邪、风寒暑湿滞留的病邪、饮食痰涎积聚的毒素吗？身体如果没有生病，这些邪气都分散处于退藏状态；一旦气血凝聚而成痈肿，那么各种邪气就会从四面汇聚而来。只有围药能够拦截它们，使邪气不相互合并，那么周身之火毒就不会蔓延了。那些已经凝聚的毒邪，如果不能透出皮肤，势必会向四周扩散造成危害，只有围药能够束缚它使其不散漫，那么气机就能聚拢并向外宣泄。这样，疮形就会变小且顶部高耸，容易化脓也容易溃破。所以外治法中的围药，比其他药物更为重要，不仅初起阶段是这样，即使到了成脓和收口阶段，始终都依赖它，一天都不能缺少。如果世间的医生所用的围药，不过是三黄散之类的方剂，每次使用都不见效，所以大家都说围药无用。如果有在疮疡已经破溃之后，仍然使用围药的，众人都会嘲笑他。因此，极轻微的毒邪往往因为不使用围药而导致散越失控、无法收拾。至于围药的方剂，也非常广泛博大，大体上以消痰拔毒、束肌收火为主，而寒热攻提、和平猛厉等性质，则应当根据症状去选取。世人如果不深入探究其中的至理，反而轻率地议论围药的不对，怎么指望他们的医术能精湛呢？
《难经》，并不是真正的“经”。它是针对《内经》中难以理解的经文，设立问答来阐明其义，所以称为《难经》。意思是凭借经文之难来解释它。这本书的宗旨，大概是想要追溯《内经》的根本旨意，发挥至高之道，剖析疑难之义，留给后世学者学习，确实是研读《内经》的门径。但是其中也有不够完善的地方，它的问答言辞，有的直接引用《内经》经文来解释。经文原本目次明显，引用它反而可能遗漏要点，以至于经文语意反而晦涩；或者没有什么发明创造，或者与两经相违背，或者以此误彼，这是它的短处。其中有自己独创见解，发挥妙道，未曾见于《内经》，但确实能彰显《内经》深奥义理，补充《内经》所未阐发的内容。这大概是有别的师承，足以与《内经》并传千古。不知道是秦越人（扁鹊）所创，还是上古时期已有此书，而秦越人引用它作为证据呢？自隋唐以来，这本书盛行，尊崇它的人固然很多，但没有能驳正它错误的人。大概是因为从事医学的人，读了《难经》而识得其大义，就已经算是医道中的杰出人物，怎么能再深入考究《内经》，探求两者的异同得失呢？古今流传的书籍，凡是有错谬错误的，后人不敢议论的情况，比比皆是，难道只有《难经》如此吗？我在自己所著的《难经经释》中有详细论述。
The methods of external medicine (Waike) place the greatest emphasis on external treatment, and among external treatments, "Wei Yao" (surrounding medicine) is particularly important. Wherever pathogenic toxins accumulate, they tend to spread widely with a low or flat apex. After all, can the human body be devoid of latent fire from the seven emotions and six desires, lingering pathogens such as wind, cold, summer-heat, and dampness, or accumulated toxins from food, drink, phlegm, and saliva? If the body is not diseased, these pathogens remain dispersed and hidden; however, once Qi and Blood condense to form an abscess or swelling, various pathogens converge from all sides. Only Wei Yao can intercept them, preventing their merger, thereby stopping the fire toxins throughout the body from spreading. For toxins that have already condensed but cannot penetrate the skin, they will inevitably spread in all directions causing harm; only Wei Yao can bind them to prevent dispersion, allowing the Qi to gather and vent externally. In this way, the lesion becomes smaller with a high apex, facilitating pus formation and ulceration. Therefore, within external treatments, Wei Yao is more critical than other medicines. This applies not only to the initial stage but also to the stages of pus formation and wound healing; it is indispensable at all times. However, the Wei Yao used by contemporary physicians often consists merely of formulas like Sanhuang San (Three Yellows Powder), which frequently prove ineffective, leading people to claim that Wei Yao is useless. If Wei Yao is still applied after the lesion has ruptured, it is met with ridicule. Thus, even mild toxic conditions often become uncontrollable and irretrievable due to the lack of Wei Yao. The prescriptions for Wei Yao are extensive and broad, primarily focusing on resolving phlegm, extracting toxins, binding the muscle tissue, and containing fire. Properties ranging from cold, hot, purgative, lifting, to mild and potent should be selected according to the specific symptoms. People who do not deeply seek the underlying principles but instead lightly criticize Wei Yao cannot hope to achieve medical proficiency.
"Nan Jing" (Classic of Difficult Issues) is not a true "Jing" (Classic). It sets up questions and answers to clarify the difficult-to-understand passages in the original classics, hence the name "Nan Jing." It means explaining the difficulties through the classics. The purpose of this book is to trace the fundamental principles of the "Nei Jing" (Inner Canon), expound upon the supreme Dao, analyze doubtful meanings, and provide guidance for future students; it is truly a bridge for studying the "Nei Jing." However, there are imperfections within it. Some of its Q&A responses directly quote the "Nei Jing" to explain concepts. Since the original texts are clear, quoting them may sometimes omit key points, making the meaning obscure, or fail to offer new insights, or contradict other classics, or confuse one classic with another; these are its shortcomings. There are also parts where the author offers original insights and elucidates profound truths not found in the "Nei Jing," yet effectively revealing its deep mysteries and supplementing what was left unexpressed in the "Nei Jing." This likely stems from a different lineage of transmission, worthy of being handed down alongside the "Nei Jing" for millennia. It remains unknown whether it was created by Yue Ren (Bian Que) or if it existed in ancient times and was cited by Yue Ren as evidence. Since the Sui and Tang dynasties, the book has been popular, and while many have revered it, few have dared to correct its errors. Perhaps those engaged in medicine, having grasped the main ideas of the "Nan Jing," consider themselves outstanding figures in the field, lacking the motivation to further investigate the "Nei Jing" to explore the similarities, differences, merits, and faults between the two. Throughout history, books with errors have rarely been criticized by later generations; this is common everywhere, not just with the "Nan Jing." I discuss this in detail in my own work, "Nan Jing Jing Shi" (Explanation of the Nan Jing).