病疫之由昔以為非其時有其氣春應温而反大寒夏應熱而反大涼秋應涼而反大熱冬應寒而反大温得非時之氣長幼之病相似以為疫 余論則不然夫寒熱温涼乃四時之常因風雨隂晴稍為損益假令秋熱必多晴春寒因多雨較之亦天地之常事未必多疫也 傷寒與中暑感天地之常氣疫者感天地之厲氣在歳運有多寡在方隅有厚薄在四時有盛衰此氣之來無論老少强弱觸之者即病 邪自口鼻而入則其所客内不在藏府外不在經絡舍於夾脊之内去表不遠附近於胃乃表裏之分界是為半表半裏即緘經所謂横連膜原是也胃為十二經之海十二經皆都會於胃故胃氣能敷布於十二經中而榮養百骸毫髪之間靡所不貫 凡邪在經為表在胃為裏今邪在膜原者正當經胃交闗之所故為半表半裏其熱淫之氣浮越於某經即能顯某經之證如浮越於太陽則有頭項痛腰痛如折如浮越於陽明則有目痛眉稜骨痛鼻乾如浮越於少陽則有脇痛耳聾寒熱嘔而口苦大㮣觀之邪越太陽居多陽明次之少陽又其次也 邪之所著有天受有傳染所感雖殊其病則一凡人口鼻之氣通乎天氣本氣充滿邪不易入本氣適逢虧欠呼吸之間外邪因而乘之昔有三人冐霧早行空腹者死飲酒者病飽食者不病疫邪所著又何異耶若其年氣來之厲不論强弱正氣稍衰者觸之即病則又不拘于此矣 其感之深者中而即發感之淺者邪不勝正未能頓發或遇饑飽勞碌憂思氣怒正氣被傷邪氣始得張溢榮衞運行之機乃為之阻吾身之陽氣因而屈曲故為熱其始也格陽於内不及於表故先凛凛惡寒甚則四肢厥逆陽氣漸積鬱極而通則厥回而中外皆熱至是但熱而不惡寒者因其陽氣之通也 此際應有汗或反無汗者存乎邪結之輕重也即使有汗乃肌表之汗若外感在經之邪一汗而解今邪在半表半裏表雖有汗徒損真氣邪氣深伏何能得解必俟其伏邪已潰表氣潛行於内乃作大戰精氣自内由膜原以逹表振戰止而後熱此時表裏相通故大汗淋漓衣被濕透邪從汗解此名戰汗當即脉靜身涼神清氣爽霍然而愈然有自汗而解者但出表為順即不藥亦自愈也 伏邪未潰所有之汗止得衞氣暫通熱亦暫減逾時復熱午後潮熱者至是鬱甚陽氣與時消息也自後加熱而不惡寒者陽氣之積也其惡寒或微或甚因其人之陽氣盛衰也其發熱或短或長或晝夜純熱或黎明稍減因其感邪之輕重也 疫邪與瘧彷彿但瘧不𫝊胃惟疫乃𫝊胃始則皆先凛凛惡寒既而發熱又非若傷寒發熱而兼惡寒也 至於伏邪動作方有變證其迹或從外解或從内陷從外解者順從内陷者逆更有表裏先後不同有先表而後裏者有先裏而後表者有但表而不裏者有但裏而不表者有表裏偏勝者有表裏分𫝊者有表而再表者有裏而再裏者從外解者或發斑或戰汗狂汗自汗盜汗從内陷者胸膈痞悶心下脹滿或腹中痛或燥結便秘或熱結㫄流或協熱下利或嘔吐惡心譫語舌黄舌黒胎刺等證因證而知變因變而知治此言其大略詳見脉證治法諸條

As for the cause of epidemic sickness, people used to say it came from a qi that arrives out of its season. Spring should be warm, but it turns very cold; summer should be hot, but it turns very cool. Autumn should be cool, but it turns very hot; winter should be cold, but it turns very warm. People catch this out-of-season qi, and young and old fall sick in the same way. That, they said, is an epidemic. I do not agree. Cold, heat, warmth, and coolness are the regular course of the four seasons. Wind and rain, cloud and sun make them a little stronger or weaker. If autumn is hot, it must have had many clear days; if spring is cold, that comes from much rain. These too are ordinary events of Heaven and Earth, and they do not necessarily bring many epidemics. Cold Damage and heatstroke come from the regular qi of Heaven and Earth. An epidemic comes from the pestilential qi of Heaven and Earth. From year to year there is more or less of it; from place to place it is thicker or thinner; through the four seasons it rises and falls. When this qi comes, old or young, strong or weak, whoever touches it falls ill at once. The harmful qi enters through the mouth and nose. It does not lodge inside, in the organs, or outside, in the channels. It settles beside the spine, not far from the surface of the body and close to the stomach. This is the border between the outside and the inside of the body, so it is called “half outside, half inside.” It is what the classic calls “stretching across to the membrane source.” The stomach is the sea of the twelve channels, and all twelve channels meet at the stomach. So the qi of the stomach can spread through all twelve channels and nourish every bone of the body. There is no place, down to the root of a hair, that it does not reach. When harmful qi is in the channels, [the illness] is on the outside; when it is in the stomach, it is on the inside. Harmful qi in the membrane source sits just where the channels and the stomach meet, and so it is half outside, half inside. When its hot, excessive qi floats out into one of the channels, it shows that channel’s signs. If it floats out into the Greater Yang, the head and neck ache, and the lower back aches as if it were broken. If it floats into the Yang Brightness, the eyes hurt, the bone of the brow hurts, and the nose is dry. If it floats into the Lesser Yang, the ribs hurt, the ears go deaf, there are chills and fever, and vomiting with a bitter taste in the mouth. On the whole, it floats out most often into the Greater Yang, next into the Yang Brightness, and least into the Lesser Yang. The harmful qi takes hold in two ways. Some people receive it from the sky, and some catch it by contagion. The ways differ, but the illness is the same. The qi of a person’s mouth and nose is open to the qi of the sky. When a person’s own qi is full, harmful qi cannot easily get in. When it happens to be low, the harmful qi from outside seizes its chance in the space of a breath. Once three men set out early through a fog. The one with an empty stomach died, the one who had drunk wine fell ill, and the one who had eaten well stayed healthy. How is it any different when the epidemic qi takes hold? But in a year when the qi comes fiercely, strong or weak makes no difference. Anyone whose healthy qi is even a little weak falls ill as soon as he touches it, and then this rule no longer holds. Those who catch it deeply fall ill as soon as it strikes. Those who catch it lightly do not fall ill at once, because the harmful qi cannot overcome the healthy qi. But if they meet with hunger or overeating, hard work, worry, or anger, the healthy qi is harmed, and the harmful qi can at last spread. Then the flow of the nourishing and defensive qi is blocked, and the yang qi of the body is bent back on itself. That is why there is fever. At first the yang is shut up inside and does not reach the surface. So first there is shivering and a dread of cold, and at worst the hands and feet go cold. The yang qi slowly builds up, and when it is pent up to the limit it breaks through. Then the hands and feet warm again, and the body is hot inside and out. From then on there is only fever, without the dread of cold, because the yang qi has broken through. At this point there should be sweating. If instead there is none, that depends on how tightly the harmful qi is knotted. Even if there is sweat, it is only sweat of the skin. When harmful qi caught from outside is in the channels, one sweat clears it. But here the harmful qi is half outside, half inside. Even if the surface sweats, this only wastes the true qi. The harmful qi lies deep in hiding, so how can it be cleared? One must wait until the hidden harmful qi has broken up. Then the qi of the surface slips inward, and there is a great shaking. The vital qi comes from within, through the membrane source, and reaches the surface. When the shaking stops, fever follows. Now the outside and inside are open to each other, and a great sweat pours out, soaking clothes and bedding. The harmful qi leaves with the sweat. This is called “the shaking sweat.” At once the pulse is calm and the body cool, the mind is clear and the breath easy, and the patient suddenly recovers. Some, though, are cleared by sweating on their own. As long as [the harmful qi] goes out through the surface, all is well, and they will recover even without medicine. While the hidden harmful qi has not yet broken up, any sweat only lets the defensive qi through for a while. The fever drops for a while too, and after a time it returns. A fever that rises like a tide in the afternoon comes when the blockage is at its worst, and the yang qi waxes and wanes with the hours. When the fever then grows without any dread of cold, that is because the yang qi is building up. The dread of cold may be slight or severe, depending on whether the person’s yang qi is strong or weak. The fever may be short or long; it may last day and night, or ease a little at dawn. That depends on how heavily the person caught the harmful qi. Epidemic qi is much like malaria, except that malaria does not pass into the stomach, and only an epidemic does. Both begin with shivering and a dread of cold, and then fever follows. This is not like Cold Damage, where fever and the dread of cold come together. Only when the hidden harmful qi starts to move do the changing signs appear. It either clears outward or sinks inward. Clearing outward is a good sign; sinking inward is a bad one. The order of outside and inside also differs. In some it goes first outside, then inside; in others first inside, then outside. In some it stays outside only, in others inside only. In some one side is stronger; in some it divides between outside and inside; in some it goes outside again and again, or inside again and again. When it clears outward, there may be blotches on the skin, or the shaking sweat, a raving sweat, sweating without cause, or night sweats. When it sinks inward, there is tightness in the chest, swelling below the heart, or pain in the belly; hard, dry stools and constipation; hard stools with watery leakage around them; diarrhea with fever; or vomiting and nausea, raving speech, a yellow or black tongue, a prickly coating on the tongue, and other signs. From the signs one knows the changes; from the changes one knows the treatment. This is only an outline. Details are given under each heading on the pulse, the signs, and the treatment.