潮热者。不恶寒。但恶热。其来如潮之至。不失其时。谓之潮热。其证属里而不属表。
凡恶
寒发热属太阳。至少阳则往来寒热。此之潮热则属阳明。往往发于日晡。日晡未申之时。阳
明居中土。王于未申。邪入中土。无所复传。
故郁为实热。随王而潮。经云。日晡所发潮热者。属阳明也。惟其属阳明。则胃实为可
下之证。故曰潮热者实也。
潮热固可下而下法要有次第。经云。太阳病三日。发汗不解。蒸蒸发热者属胃也。调胃
承气
汤主之。此因胃已实而热未潮。故但用调胃承气。微利之而已。又云。阳明病脉迟。虽汗出
不恶寒者。其身必重。短气腹满而喘。有潮热者。此外欲解可攻里也。手足
然汗出者。此大便已硬也。大承气汤主之。若汗多微发热恶寒者。外未解也。其热不潮。未
可与承气汤。若腹大满不通者。可与小承气汤。微和胃气。勿令大泄下。按三承气俱用大黄
。大承气重用枳朴。兼以芒硝。上承邪热而下。用以攻坚破结。荡涤肠胃。乃峻下之剂。小
承气去芒硝而轻用枳朴。止取通利肠胃。其下较轻。调胃承气。佐以甘草。又于下中兼和。
三承气各有所主。仲景下法。不敢妄施。其慎细如此。又云。太阳病。重发汗而复下之。舌
上燥而渴。日晡小有潮热。从心下至少腹。硬满而痛不可近者。大陷胸汤主之。夫病至心下
及少腹硬满而痛不可近。则势已剧甚。此又非大承气所能胜任。宜兼破胸膈之结。以下通于
肠胃。则必主以大陷胸汤而无疑矣。
其有
阳明病潮热未去。而已趋入少阳者。经云。阳明病。发潮热。大便溏。小便自可。胸胁满不
去者。小柴胡汤主之。此非小柴胡汤之能治潮热也。胸胁满不去。已具少阳证。且大便已溏
。虽潮热未罢。未可再攻也。
更有瘅疟者。但热不寒。发作有时。此亦阳明经热。其热止在于经。未入于府。且病不从
伤寒来。故名之曰瘅疟。仲景不立方。而但曰以饮食消息之。
要之甘寒彻热。与治阳明经热同法也。
潮热，是指不恶寒，只怕热。其发作像潮水一样定时到来，不失时机，所以称为潮热。这种证候属于里证，而不属于表证。
凡是恶寒发热，属于太阳病；到了少阳病，则是往来寒热。而这里的潮热则属于阳明病，往往在日晡时分（下午3点到5点）发作。因为阳明经居中土，在未时和申时（下午1点到5点）当令。邪气进入中土后，没有地方再传变，所以郁结成为实热，随着经气旺盛的时间而如潮汐般发作。经典中说：“日晡所发潮热者，属阳明也。”正因为属于阳明病，所以胃家实是可以用下法治疗的证候，因此说“潮热者实也”。
潮热虽然可以用下法，但下法要有次第。经典中说：“太阳病经过三天，发汗后病不解，出现蒸蒸发热的，属于胃家实证，用调胃承气汤主治。”这是因为胃已经结实但热势尚未形成潮热，所以只用调胃承气汤，轻微通利大便即可。又说：“阳明病脉迟，虽然出汗但不恶寒，身体必定沉重，短气、腹满且喘，如果有潮热，说明表证已解，可以攻里了。如果手足濈然汗出，说明大便已经坚硬，用大承气汤主治。如果出汗多，伴有轻微发热恶寒，说明表证未解，此时热势不呈潮状，不可给予承气汤。如果腹部胀满不通的，可以给予小承气汤，轻微调和胃气，不要让它剧烈泻下。”
按三首承气汤都使用大黄。大承气汤重用枳实、厚朴，兼用芒硝，上承邪热而下，用来攻坚破结，荡涤肠胃，是峻下的方剂。小承气汤去掉芒硝，轻用枳实、厚朴，只取通利肠胃的作用，其泻下力量较轻。调胃承气汤佐以甘草，在下法中兼有调和作用。这三首承气汤各有所主，张仲景运用下法不敢妄加施用，谨慎细致到了如此地步。
又说：“太阳病，重发汗后又误用下法，导致舌上干燥而渴，日晡时有轻微潮热，从心下直到小腹硬满疼痛，甚至不能触碰的，用大陷胸汤主治。”病势发展到心下及少腹硬满疼痛且不能触碰，说明病情已经非常严重，这又不是大承气汤所能胜任的，应当兼破胸膈的结滞，以下通于肠胃，那么必然要用大陷胸汤无疑了。
还有那种阳明病潮热未去，而病势趋向少阳的情况。经典中说：“阳明病，发潮热，大便溏，小便正常，胸胁满闷不去的，用小柴胡汤主治。”这并不是小柴胡汤能治疗潮热，而是因为胸胁满闷不去，已经具备少阳病的证候，且大便已经溏薄，虽然潮热未罢，但不可再用攻下法。
更有瘅疟这种病，只发热不恶寒，发作有定时，这也是阳明经的热证。其热仅在于经，未入于腑，且病不是从伤寒传变而来，所以命名为瘅疟。张仲景没有给出具体方剂，只是说通过饮食调养来观察病情变化。
总之，甘寒清热的方法，与治疗阳明经热的方法是相同的。
Tidal fever refers to a condition where there is no aversion to cold, only aversion to heat. Its onset occurs like the tide, arriving at regular intervals without missing its time, hence it is called tidal fever. This syndrome belongs to the interior (Li) and does not belong to the exterior (Biao).
Generally, aversion to cold accompanied by fever belongs to Taiyang disease; when it reaches Shaoyang, it presents as alternating chills and fever. However, this type of tidal fever belongs to Yangming disease. It often occurs during the "Ribuxia" period (Shen hour, 3:00 PM to 5:00 PM). Since the Yangming meridian governs the central Earth element and is prosperous during the Wei (1:00 PM to 3:00 PM) and Shen hours, pathogenic factors entering the central Earth have nowhere else to transmit. Consequently, they stagnate and transform into excess heat, surging like the tide in accordance with the prosperity of the meridian qi. The Classic states: "Tidal fever occurring at Ribuxia belongs to Yangming." Because it belongs to Yangming, stomach excess (Wei Shi) is an indication for purgation, hence it is said that "tidal fever indicates excess."
Although tidal fever can be treated with purgation, the method must follow a sequence. The Classic states: "In Taiyang disease, after three days, if sweating fails to resolve the condition and steaming-hot fever appears, it belongs to the Stomach; Tiaowei Chengqi Tang should be used." This is because the Stomach is already full/excess but the heat has not yet formed tidal patterns, so only Tiaowei Chengqi Tang is used to mildly promote bowel movement. It also states: "In Yangming disease, if the pulse is slow, although there is sweating and no aversion to cold, the body will feel heavy, with shortness of breath, abdominal fullness, and wheezing. If there is tidal fever, it indicates that the exterior has resolved and the interior can be attacked. If sweat oozes continuously from the hands and feet, it indicates that the feces have hardened; Dachengqi Tang should be used. If there is much sweating with slight fever and aversion to cold, the exterior has not resolved. If the heat is not tidal, Chengqi Tang should not be given. If the abdomen is severely full and obstructed, Xiao Chengqi Tang may be given to mildly harmonize the Stomach Qi, avoiding severe purgation."
All three Chengqi Decoctions use Rhubarb (Dahuang). Dachengqi Tang heavily uses Immature Bitter Orange (Zhishi) and Magnolia Bark (Houpo), combined with Mirabilite (Mangxiao), to carry pathogenic heat downward, breaking hard accumulations and clearing the intestines and stomach; it is a harsh purgative. Xiao Chengqi Tang removes Mirabilite and uses lighter doses of Immature Bitter Orange and Magnolia Bark, aiming only to facilitate intestinal movement, thus having a milder purgative effect. Tiaowei Chengqi Tang adds Licorice Root (Ganzcao) to harmonize while purging. Each of the three Chengqi Decoctions has its specific indications. Zhang Zhongjing did not dare to apply purgation recklessly, showing such caution and detail.
It also states: "In Taiyang disease, if excessive sweating is followed by mistaken purgation, leading to dryness and thirst on the tongue, slight tidal fever at Ribuxia, and hardness, fullness, and pain from the epigastrium down to the hypogastrium that cannot be touched, Daxiexiong Tang should be used." When the disease progresses to hardness, fullness, and pain in the epigastrium and hypogastrium that cannot be tolerated to touch, the condition is severe. This exceeds the capacity of Dachengqi Tang; one must break the knot in the chest and diaphragm to connect downwards to the intestines and stomach, making the use of Daxiexiong Tang unquestionable.
There are cases where Yangming tidal fever persists while the pathology trends toward Shaoyang. The Classic states: "In Yangming disease, if there is tidal fever, loose stools, normal urination, and persistent fullness in the chest and hypochondrium, Xiaochaihu Tang should be used." This does not mean Xiaochaihu Tang treats tidal fever directly; rather, the persistent chest and hypochondriac fullness indicates Shaoyang syndrome. Furthermore, since the stools are already loose, even if tidal fever persists, further purgation is contraindicated.
Additionally, there is Dan Nue (Hot Malaria), characterized by fever without chills and regular paroxysms. This is also heat in the Yangming meridian. The heat remains only in the meridian and has not entered the fu organs. Moreover, it does not originate from Cold Damage transmission, hence it is named Dan Nue. Zhang Zhongjing provided no specific formula but stated that it should be managed through dietary adjustments.
In summary, the method of using sweet-cold herbs to clear heat is the same as treating Yangming meridian heat.