伤寒之病，莫先于分经表里，治表里之法，莫先于分汗下缓急，汗下迟早一差，变
症百出，是以前人论治伤寒，有曰汗药宜早，下药宜迟，此二语紧要法也。曰宜早
者，谓风寒之邪自表而入，即当速为发表，邪从表解，免其传里而病，即仲景所谓，觉
病须臾，即宜早治，不避晨夜是也。曰宜迟者，谓风寒之邪，传入于里，攻下必须在正
阳阳明之腑。俟邪热壅盛于里，下之则去其邪热而愈，所谓应犯而犯似乎无犯。若邪热
未盛于里而早下之，则正气受伤，傍流阴寒之气乘虚痞聚，即仲景所谓下早恐成痞气与
结胸是也。此云迟早，论治法之先后，非论时刻之早晚也。奈有以发汗当在午前阳分，
攻下当在午后阴分，以早迟一字，竟以日候之早晚论之，支离穿凿，莫此为甚。且有既
不明伤寒治法，又不识杂证类伤寒，往往妄投汗下之药，以致虚人元气，变证丛生，未
有不因之而毙者矣。
《经》曰∶中满者，泻之于内；又曰∶土郁夺之。谓下之令其疏泄也。然欲攻病邪
之标，必先审正气之本。如伤寒寸脉弱而无力者，切忌发吐，尺脉弱而无力者，切忌汗
下，俱宜小柴胡汤和之。若小便数而赤，大便结而脉沉实者，日数虽少，邪已传里，病
宜下之，失下则聚热不散，无黄、发狂等症生焉。如脉浮大，小便清长，日数虽多，病
未传里，未成热结，不可下也，下之则虚其阴，阴气弱于中，阳邪攻于内，所谓引贼破
家也。并宿滞未熟，表邪未尽，亡血溃疡，动气恶心，六脉无力，睡卧安宁，虚结年
高，病久产后，均忌大下。内伤元气不足，有食停滞，当补泻兼施，补中益气，加熟大
黄润而行之。更有太阳、少阳并病，是半表半里之症，宜和之者也。若误下之，则太阳
表邪入里，而为结胸，少阳里邪攻于肠、胃而为脏结，或开肠洞泄，便溺不禁而死，故
身热恶寒，邪在表也，可汗不可下。发热恶热，热在里也，可下不可汗。邪在半表半
里，汗下俱禁之人，皆曰汗多亡阳，不知下多亦亡阳，以亡阴中之阳，故曰亡阴耳。若
不呕不渴，睡卧安宁，身无大热，惟心下觉痛，时欲进食，下痢频频，舌有白苔者，是
寒在胸中，热聚丹田，此谓脏结，因邪结于中，气不得通于下，故心下觉痛也。至若白
苔不退，是上焦寒盛，寒盛则其结愈固，伤寒以阳盛为顺，阴盛者，逆候也。如至五六
日间，胸无结滞，但日中烦躁不眠，至夜微能安静者，是过下过汗而阴阳亡也。盖昼主
阳，在昼则阳气欲复，因虚不胜邪，故烦躁不宁也。夜稍安静者，阳虚不能与之争，邪
热遇阴，故少解也。如阴阳未脱者，至夜而阴复之，至日而阳复之，则数日阴阳渐复，
邪气自当潜退矣。如逐日更甚者，此正气散乱于内，邪气纵横于中也，不治。然伤寒汗
下之后，不可便用参 大补，宜用小柴胡汤加减和之。若即加大补，则邪气得补，而热
复盛，所以谓伤寒无补法此也。惟挟虚类伤寒，脉见无力者，并劳力伤寒者，不在禁补
之例，更宜须分阴阳二症，阴症者，身静重语无声，气难布息，口鼻气冷身凉，水浆不
入，二便不禁，面上恶寒是也。阳症者，身动轻语有声，口鼻气热身烙是也。更当以脉
之有力无力辨之。
伤寒这一类疾病，没有比区分经络、表里更优先的了；治疗表证和里证的方法，没有比区分发汗与攻下的缓急更优先的了。发汗与攻下的时机早晚只要有一个差错，就会变生百种病症。因此前人论述治疗伤寒时，曾说“发汗药宜早用，攻下药宜迟用”，这两句话是至关重要的法则。
所谓“宜早”，是指风寒之邪从体表侵入，就应当迅速使用发表药物，使邪气从体表解除，避免其传入体内而致病。这正是张仲景所说的：“发觉病证须臾之间，就应当尽早治疗，不分早晨夜晚。”
所谓“宜迟”，是指风寒之邪传入体内后，攻下法必须等到“正阳阳明”腑实热盛的时候才能使用。要等待邪热在体内壅盛，此时使用下法可以去除邪热而痊愈，这就是所谓的“应该犯下的时候才去攻下，表面上看似乎没有妄加攻下”。如果邪热在体内尚未盛实就过早使用下法，就会损伤正气，旁流的阴寒之气会乘虚痞塞聚集，这正是张仲景所说的“过早攻下恐怕会导致痞气和结胸证”。
这里说的“迟早”，讨论的是治疗方法的先后顺序，而不是指一天中时刻的早晚。然而，有些人认为发汗应当在午前（阳分时段），攻下应当在午后（阴分时段），仅仅因为“早迟”这两个字，竟然以一天中日候的早晚来论断，这种说法支离破碎、穿凿附会，没有比这更严重的了。
况且，有的人既不明白伤寒的治疗法则，又不认识那些类似伤寒的杂病，往往胡乱投用发汗或攻下的药物，导致体质虚弱者的元气受损，变证丛生，没有不因此死亡的。
《黄帝内经》说：“胸腹胀满的，要从内部疏导泻下；又说：土气郁结的，要用夺法（攻下）。”这是指通过攻下使其疏泄。然而，想要攻治病邪的标象，必须先审察正气的根本。例如，伤寒患者寸脉弱而无力的，切忌使用催吐法；尺脉弱而无力的，切忌使用发汗或攻下法，这些都适宜用小柴胡汤调和。
如果小便频数且颜色红赤，大便干结且脉象沉实，虽然患病天数不多，但邪气已经传入体内，病情适宜使用下法。如果失于攻下，则聚积的热邪无法消散，会产生发黄、发狂等症状。
如果脉象浮大，小便清长，虽然患病天数较多，但病邪未传入体内，也未形成热结，不可使用下法。如果使用下法，则会耗伤阴液，导致阴气在中焦虚弱，阳邪在内进攻，这就是所谓的“引贼破家”（招致祸患）。
此外，宿食停滞未熟、表邪未尽、亡血、溃疡、动气、恶心、六脉无力、睡卧安宁、虚性便秘且年事已高、久病之后、产后等情况，均忌讳使用峻烈的攻下法。如果是内伤导致元气不足，又有食物停滞，应当补泻兼施，使用补中益气汤，加入熟大黄润燥通便而行。
更有太阳病与少阳病并见的情况，这是半表半里的证候，适宜使用和解法。如果误用下法，则太阳表的邪气会陷入体内，形成结胸证；少阳里的邪气会攻冲肠、胃，形成脏结证，或者导致肠道洞泄、大小便失禁而死。
所以，身体发热且恶寒，说明邪气在表，可发汗不可攻下。发热且恶热，说明热邪在里，可攻下不可发汗。邪气在半表半里，发汗和攻下都禁忌。人们都说“发汗过多会亡阳”，却不知道“攻下过多也会亡阳”，这是因为攻下过多会亡失阴中之阳，所以称为亡阴。
如果不呕吐、不口渴、睡卧安宁、身体没有高热，只是心下部感觉疼痛，时常想吃东西，频繁腹泻，舌苔白腻的，这是寒邪在胸中，热邪聚集在下焦丹田，这叫做脏结。因为邪气结滞在中焦，气机不能通达于下，所以心下部感觉疼痛。至于白苔不退，说明上焦寒盛，寒盛则结滞更加牢固。伤寒病以阳气旺盛为顺证，阴气旺盛则是逆证。
如果到了五六天，胸部没有结滞，只是白天烦躁不眠，到了晚上稍微能安静一些，这是过度攻下和过度发汗导致阴阳两虚的缘故。白天主阳，在白天阳气试图恢复，但因为正气虚弱不能抗御邪气，所以烦躁不宁。晚上稍微安静，是因为阳气虚弱不能与邪气抗争，邪热遇到阴气，所以稍得缓解。
如果阴阳之气尚未脱绝，到了晚上阴气来复，到了白天阳气来复，那么几天后阴阳逐渐恢复，邪气自然会潜退。如果每天症状都加重，这是正气在内散乱，邪气在中纵横肆虐，属于不治之症。
然而，伤寒经过发汗或攻下治疗后，不可以立即使用人参等大补药物，适宜用小柴胡汤加减进行调和。如果立即加大剂量使用补药，则邪气得到补益，热势会更加炽盛，所以说“伤寒无补法”就是这个道理。只有夹杂虚证的类似伤寒病，脉象无力的，以及劳力所致伤寒的，不在禁止使用补法的范围内。另外，还必须区分阴证和阳证两种情况。
阴证的表现是：身体静重、说话声音低微、气息难以布达、口鼻气息冷、身体凉、水浆不入、二便失禁、面部怕冷。
阳证的表现是：身体轻动、说话有声、口鼻气息热、身体烫手。
更应当通过脉象的有力或无力来辨别。
In the disease of Shanghan (Cold Damage), nothing is more primary than distinguishing the meridians and the levels of exterior and interior. In treating exterior and interior conditions, nothing is more urgent than distinguishing the urgency of sweating (diaphoresis) and purging methods. If there is even a slight error in the timing of sweating or purging, hundreds of complications will arise. Therefore, predecessors discussing the treatment of Shanghan stated that "sweating medicines should be used early, and purging medicines should be used late." These two phrases constitute a crucial principle.
"Sweating should be early" means that when wind-cold pathogens enter from the exterior, one should promptly use exterior-releasing methods to resolve the pathogen from the surface, preventing it from transmitting inward and causing internal disease. This aligns with Zhang Zhongjing's saying: "Once a disease is detected, it must be treated immediately, regardless of morning or night."
"Purging should be late" means that when wind-cold pathogens have transmitted into the interior, purging methods must only be employed when the "Zheng Yang Yang Ming" (Positive Yang Bright Yang) fu-organ syndrome is established. One must wait until the pathogenic heat is abundant and congested within the interior; only then can purging remove the pathogenic heat and achieve recovery. This is referred to as "acting when action is required, which appears as not acting rashly." If purging is applied prematurely before the pathogenic heat has become abundant in the interior, it will damage the healthy qi. The cold qi from paralogous diarrhea will take advantage of the deficiency to cause stagnation and accumulation. This corresponds to Zhang Zhongjing's warning that premature purging may lead to Pi Qi (stagnation syndrome) or Jie Xiong (chest binding syndrome).
The mention of "early and late" here refers to the sequence of therapeutic strategies, not the specific time of day. However, some individuals mistakenly believe that sweating should occur during the morning (yang phase) and purging during the afternoon (yin phase), interpreting "early and late" solely based on the time of day. Such interpretations are fragmented and far-fetched, none being more egregious than this.
Furthermore, those who neither understand the treatment principles of Shanghan nor recognize miscellaneous diseases that mimic Shanghan often administer sweating or purging drugs recklessly. This damages the yuan qi (original qi) of constitutionally weak patients, leading to a proliferation of complications, invariably resulting in death.
The *Classic* states: "For fullness in the chest and abdomen, drain from within"; and again, "When earth qi is stagnant, use the method of seizure (purging)." This implies using purging to promote drainage and dispersion. However, to attack the branch manifestations of pathogenic factors, one must first examine the root of healthy qi. For instance, in Shanghan, if the cun pulse at the wrist is weak and powerless, emetic therapy is strictly contraindicated; if the chi pulse is weak and powerless, sweating and purging are strictly contraindicated. In such cases, Xiao Chai Hu Tang (Minor Bupleurum Decoction) should be used to harmonize.
If urination is frequent and red, stool is constipated, and the pulse is deep and solid, although the number of days since onset is small, the pathogen has already transmitted to the interior, and purging is indicated. Failure to purge will result in the accumulation of heat that cannot dissipate, leading to symptoms such as jaundice and mania.
If the pulse is floating and large, and urination is clear and profuse, although many days have passed, the pathogen has not transmitted to the interior, and heat consolidation has not formed. Purging is contraindicated. Applying purging would deplete yin fluids. With yin qi weakened in the middle, yang pathogenic factors will attack internally, a situation described as "inviting thieves to break up the household."
Additionally, conditions involving unripe food retention, incomplete resolution of exterior pathogens, blood loss, ulcers, moving qi, nausea, powerless pulses across all positions, peaceful sleep, constipation due to deficiency in the elderly, prolonged illness, and postpartum states are all contraindications for harsh purging. In cases of internal injury with insufficient yuan qi accompanied by food stagnation, tonification and purging should be combined. Use Bu Zhong Yi Qi Tang (Tonify the Middle and Augment the Qi Decoction) with cooked Da Huang (Rhei Radix et Rhizoma) added to moisten and promote movement.
Moreover, concurrent Taiyang and Shaoyang diseases represent half-exterior, half-interior syndromes, which require harmonization. Misapplication of purging will cause Taiyang exterior pathogens to sink into the interior, forming Jie Xiong (chest binding); Shaoyang interior pathogens will attack the intestines and stomach, forming Zang Jie (z visceral binding), or cause intestinal洞泄 (profuse watery diarrhea) and incontinence of urine and feces, leading to death.
Therefore, fever with aversion to cold indicates the pathogen is in the exterior; sweating is permissible, purging is not. Fever with aversion to heat indicates heat is in the interior; purging is permissible, sweating is not. When the pathogen is in the half-exterior, half-interior region, both sweating and purging are prohibited. People often say that excessive sweating leads to the loss of yang, but they do not realize that excessive purging also leads to the loss of yang. This is because purging excessively depletes the yang within yin, hence it is termed the loss of yin.
If there is no vomiting, no thirst, peaceful sleep, no high fever, but only pain in the epigastrium, occasional desire to eat, frequent dysentery, and a white tongue coating, this indicates cold in the chest and heat aggregated in the lower dantian. This is called Zang Jie (visceral binding). Because pathogenic factors are bound in the middle, qi cannot circulate downward, causing epigastric pain. If the white coating persists, it indicates excess cold in the upper jiao. Excess cold makes the binding more solid. In Shanghan, abundance of yang is a favorable sign, while abundance of yin is an unfavorable prognosis.
If, on the fifth or sixth day, there is no congestion in the chest, but restlessness and insomnia during the day, with slight calmness at night, this results from excessive purging and sweating leading to the depletion of yin and yang. Daytime governs yang; during the day, yang qi attempts to recover, but due to deficiency, it cannot resist the pathogen, causing restlessness. Slight calmness at night occurs because deficient yang cannot contend with the pathogen, and the pathogenic heat encounters yin, providing slight relief.
If yin and yang have not yet collapsed, yin recovers at night and yang recovers during the day. After several days, yin and yang gradually recover, and the pathogenic qi will naturally retreat. If symptoms worsen daily, this indicates that healthy qi is scattered internally and pathogenic qi is rampant in the middle; this is incurable.
However, after sweating or purging in Shanghan, one must not immediately use strong tonics like Ren Shen (Ginseng Root). Instead, Xiao Chai Hu Tang (Minor Bupleurum Decoction) modified should be used to harmonize. If strong tonics are added immediately, the pathogenic qi receives nourishment, and heat becomes more vigorous. This is why it is said that "there is no tonification method in Shanghan." Only in cases of Shanghan-like diseases complicated by deficiency with powerless pulses, or Shanghan caused by overexertion, is tonification not prohibited. Furthermore, one must distinguish between yin and yang syndromes.
Yin syndromes manifest as: stillness and heaviness of the body, silent speech, difficulty in breathing, cold breath from mouth and nose, cool body, inability to swallow liquids, incontinence of urine and feces, and aversion to cold on the face.
Yang syndromes manifest as: restlessness and lightness of the body, audible speech, hot breath from mouth and nose, and a burning-hot body.
Differentiation must further rely on whether the pulse is powerful or powerless.