周禹载曰。疫之行于天地间久矣。而人之治之者。未之知也。治之而适奏其效者。
亦未知之也。观周礼方相氏所掌。难以逐疫。则疫者气为之也。惟气故为害。从口
鼻入。虽然。六淫之气皆气也。而风寒暑湿燥火之病。不闻有沿门阖境相染。触发
者何也。六淫之气。日留于天地之间。偏胜则病。且人之病之者。每因于己之所不
胜。以淫于所胜。而不独天地之气。足以害之也。若疫则古今来虽有是证。而天地
间实无是气。或因天之风雨不时地之湿浊蒸动。又因 骼掩埋不浓。遂使大陵
积尸之气。随天地之升降者。飘泊远近。人在气交中。无可逃避。感之而病而死。于
是更增一种病气尸气。流行其间。复相渐染。至久弥甚矣。故从来疫疠行于兵荒
之后居多。不但人之中气先弱也。良由所积之秽气特甚耳。乃数千年来。说鬼说
梦。赖嘉言先生。援经据古。特标蕴义。我北海林夫子。引伸触类。指点治法。岂非功
在万世者乎。但嘉言自诩于平脉篇中。已见一斑。谓清邪中于上焦。浊邪中于下
焦云云。以为此即是仲景论疫。予未之信也。天下秽恶之气。至疫则为毒极矣。人
犯之者。三焦混淆。内外无间。不分表里。直行中道。然究竟古今恒变。未有定情。而
中上中下之说。仲景实论湿气之脉如是。而后入腑入脏。游行经络。便有种种危
证。只因三焦相混。内外不通等语。有似乎疫。而实无涉也。此嘉言善读书处。能开
发人之聪明。譬之茫无畔岸。借为指南。则可。谓竟为疫之脉证。则甚谬矣。然则如
世俗所称大头瘟者。下非不病也。特甚于上耳。所称疙瘩瘟者。内非不病也。特现
于外耳。所称虾蟆瘟者。腹非不病也。特痹于喉耳。其他证显多端。要以寒凉解毒
则一。施治之法。先上先下。从内从外。可以因证起悟。予惟奉吴又可先生书为主
治。余采集诸方。以相裨佐。俾后之学人。豁然心目云。
周禹载说：疫病在天地间流行已经很久了，但人们治疗它的方法，却很少有人知晓。那些治疗恰好奏效的人，也很少知道其中的原理。观察《周礼》中记载的方相氏所掌管的内容，难以用来驱逐疫病，那么疫病是由“气”造成的。正因为是气，所以通过口鼻侵入人体造成危害。虽然如此，六淫之气（风、寒、暑、湿、燥、火六种外感病邪）都是气，但对于风寒暑湿燥火引起的疾病，并没有听说有沿着门户、遍及整个地区相互传染、触发的情况。这是什么原因呢？六淫之气，每天停留在天地之间，偏盛则致病，而且人患病，往往是因为自身不能克制邪气，反而被邪气所侵凌，并不仅仅是天地之气足以伤害人。至于疫病，从古至今虽然有这种病症，但天地间实际上并没有这种特定的“疫气”。或许是因为天时风雨不按时令，地之湿浊蒸腾涌动，再加上尸骨掩埋不深，于是使得大陵山堆积尸体的秽气，随着天地的升降变化，飘泊到远近各处。人在气交之中，无法逃避，感受了这种气而生病甚至死亡。于是又增加了一种病气和尸气，在人群中流行，相互逐渐传染，时间越久越严重。所以自古以来，疫病多在战乱饥荒之后流行，不仅是因为人的中气（脾胃之气）先虚弱，确实是由于积累的秽气特别严重罢了。
几千年来，人们谈论鬼神、做梦呓语，幸好有嘉言先生，引用经典依据古义，特别标举出深层的含义；我的北海林夫子，引申触类旁通，指点治疗方法，这难道不是功在万世的壮举吗？但是嘉言先生在《平脉篇》中自夸已经见到一斑，说“清邪中于上焦，浊邪中于下焦”等等，认为这就是张仲景论述疫病的内容，我并不相信。天下的秽恶之气，到了疫病就毒极厉害了，人触犯它，三焦混淆，内外没有间隙，不分表里，直行中道。然而终究古今情况恒常变化，没有固定的情状，而上中下三焦的说法，张仲景实际上是论述湿气脉象时的说法，而后邪气入腑入脏，游行经络，便会有种种危重证候。只是因为“三焦相混，内外不通”等话语，似乎与疫病有关，但实际上并无关联。这是嘉言先生善于读书的地方，能够启发人的聪明才智，好比面对茫茫无边无际的情况，借它作为指南，是可以的；如果说这就是疫病的脉证，那就非常谬误了。
那么像世俗所称的大头瘟，下部并非不病，只是上部特别严重而已；所称的疙瘩瘟，内部并非不病，只是表现在外部而已；所称的虾蟆瘟，腹部并非不病，只是痹阻于咽喉而已。其他症状表现多种多样，但总归都要用寒凉解毒的方法。施治的方法，有的先治上部，有的先治下部，有的从内治，有的从外治，可以根据症状来领悟。我唯独奉行吴又可先生的著作作为主要治疗依据，其余采集各种方剂，用来辅助补充，使后来的学习之人，豁然开朗，心目明澈。
Zhou Yu Zai said: Epidemic diseases have been circulating in the world for a long time, yet few people know how to treat them. Even those whose treatments happen to be effective rarely understand the underlying principles. Observing the duties of the Fang Xiang Shi (a ritual official responsible for exorcism) recorded in the *Rites of Zhou* (Zhou Li), it is difficult to use these methods to drive away epidemics; thus, epidemics are caused by "Qi" (vital energy/pathogenic factors). Precisely because it is Qi, it enters through the mouth and nose to cause harm. Although the Six Excesses (Liu Yin, 六淫) — Wind, Cold, Summerheat, Dampness, Dryness, and Fire — are all forms of Qi, we do not hear that diseases caused by Wind, Cold, Summerheat, Dampness, Dryness, or Fire spread from door to door or infect entire regions. Why is this? The Qi of the Six Excesses remains in the heaven and earth daily; when one pathogen becomes excessive, disease occurs. Moreover, human illness often arises because one's own body cannot overcome the pathogen, allowing the pathogen to invade, rather than solely due to the harmful nature of heavenly and earthly Qi.
As for epidemic diseases, although such conditions have existed since ancient times, there is no specific "Epidemic Qi" in the natural environment. Perhaps due to irregular winds and rains, and the steaming and rising of damp turbidity from the earth, combined with shallow burial of corpses, the foul Qi accumulated from piles of dead bodies on large hills rises and falls with the heaven and earth, drifting to distant places. Humans, existing within the intersection of Qi, cannot escape it. Contracting this Qi leads to illness and death. Consequently, a new type of pathological Qi and corpse Qi emerges, circulating among people, gradually infecting each other, becoming more severe over time. Therefore, historically, epidemics mostly occur after wars and famines. This is not only because the Middle Qi (Spleen and Stomach Qi) is initially weak, but primarily because the accumulated foul Qi is particularly intense.
For thousands of years, people have spoken of ghosts and dreams. Fortunately, Mr. Jiayan cited classics and ancient texts to highlight profound meanings. My teacher, Master Lin of Beihai, extended these concepts and pointed out treatment methods. Is this not a merit benefiting ten thousand generations? However, Jiayan boasted in his commentary on the *Ping Mai Pian* (Treatise on Pulse Diagnosis) that he had glimpsed the essence, stating that "Clear pathogens attack the Upper Jiao, while Turbid pathogens attack the Lower Jiao," etc., and believed this referred to Zhang Zhongjing's discussion on epidemics. I do not agree. The foul and evil Qi in the world reaches extreme toxicity in epidemics. When humans contract it, the Three Jiaos become confused, with no distinction between interior and exterior, nor between surface and deep levels; it travels directly along the central pathway. Nevertheless, circumstances change constantly across eras, lacking fixed patterns. The theory of Upper, Middle, and Lower Jiao was actually Zhang Zhongjing's description regarding the pulse of Dampness. Subsequently, pathogens entering the Fu and Zang organs and traveling through meridians lead to various critical syndromes. Phrases like "Three Jiaos mixed, interior and exterior blocked" seem related to epidemics but are actually irrelevant. This shows Jiayan's skill in reading, which can enlighten others' intelligence, serving as a compass in vast uncertainty. However, claiming this definitively describes epidemic pulses and syndromes is highly erroneous.
Regarding what secular society calls "Big Head Plague" (Da Tou Wen), the lower body is not unaffected, but the upper part is severely affected. Regarding "Nodule Plague" (Ge Da Wen), the interior is not unaffected, but symptoms manifest externally. Regarding "Toad Plague" (Xia Ma Wen), the abdomen is not unaffected, but obstruction occurs in the throat. Other symptoms are diverse, but generally require cold-natured herbs to clear heat and detoxify. Treatment methods vary: some target the upper part first, some the lower; some treat from the interior, some from the exterior. One must deduce strategies based on specific syndromes. I primarily follow the book by Mr. Wu You Ke (Wu Youxing) for treatment, collecting other formulas to supplement it, so that future students may achieve sudden clarity of mind and vision.