甘草（二两，炙） 干姜（一两半） 附子（一枚，生用去皮破八片） 上三味，以水三升，煮取一升二合，去渣，
分温再服。强人可大附子一枚，常人则取中者，小者可知。干姜三两。按∶方名四逆，必以之治厥逆。《论》
云∶厥者，阴阳气不顺接，手足逆冷是也。凡《论》中言“脉沉、微、迟、弱”者，则厥冷不待言而可知，此
方温中散寒，故附子用生者。
四逆、理中，皆温热之剂，而四逆一类，总不离干姜，以通阳也，治宜下焦；理中一类，总不离白术，
以守中也，治宜中焦。余药皆相同，而功用迥别。
伤寒脉浮，自汗出，小便数，心烦，微恶寒，脚挛急，反与桂枝汤，欲攻其表，此误也，得之便厥，
咽中干，烦躁吐逆者，作甘草干姜汤与之，以复其阳。若厥愈足温者，便作芍药甘草汤与之，其脚即伸，若
胃气不和谵语者，少与调胃承气汤。以上义详杂方条内。若重发汗，复加烧针者，四逆汤主之。阴阳两
虚之后，又复竭其阳，非此汤不能挽回阳气。
伤寒医下之，续得下利清谷不止，身疼痛者，急当救里；后身疼痛，清便自调者，急当救表。救里宜
四逆汤；救表宜桂枝汤。说详前桂枝条内。
病发热头疼，此乃表邪。脉反沉，见里脉。若不瘥，身体疼痛，当救其里，宜四逆汤。身体疼痛，阴
阳二症皆有之。今脉沉而疼痛，虽发热，亦是里寒外热之症，故用四逆。
脉浮而迟，表热浮。里寒，迟。下利清谷者，四逆汤主之。
自利不渴者，属太阴，以其脏有寒故也。明所以不渴之故，当温之，宜四逆辈。有寒则不渴。则知
渴者，皆当作热治。不曰四逆汤，而曰四逆辈，凡温热之剂，皆可选用。
少阴病，脉沉者，急温之，病与脉相合，则温不可迟。宜四逆汤。
少阴病，饮食入口则吐，心中温温欲吐，复不能吐，此二句指不食之时言。此与少阳之呕，当有分别，
宜以他症验之。始得之，手足寒，脉弦迟者，此胸中实，“始得”言病方起；“脉弦”则有力，故知为实。不
可下也，欲吐则病在上焦，下之为逆。当吐之。在上者因而越之，此少阴宜吐之法。若膈上有寒饮干呕者，
干呕无物，则知其为饮矣。不可吐也，当温之。寒饮无实物，温之则寒散，而饮亦去矣，凡治饮皆用温法。
宜四逆汤。大汗出，热不去，内拘急，四肢疼，以上皆外症，其疼亦属阴疼。又下利清谷，厥逆而恶寒者，
三者皆虚寒内症。四逆汤主之。按∶此条诸症，皆属阴寒，因为易辨，惟“热不去”三字，则安知非表邪
未尽。即恶寒，亦安知非太阳未罢之恶寒。惟下利厥逆，则所谓急当救里，不论其有表无表，而扶阳不可
缓矣。
大汗，若大下利，而厥冷者，四逆汤主之。汗下后而厥冷，则虚寒极矣。
呕而脉弱，小便复利，身有微热，见厥者难治亦外热内虚寒之故。四逆汤主之。
吐利汗出，发热恶寒，四肢拘急，手足厥冷者，
四逆汤主之。
既吐且利，小便复利而大汗出，下利清谷，内寒外热，脉微欲绝者，四逆汤主之。
以上五条，皆系汗下之后，阳气大虚，故虽外有微热，而总以扶阳为急，大小便俱利，则内阳亦尽矣。
不仅手足逆冷为阳微之验也。
Gancao (Licorice Root, *Glycyrrhizae Radix et Rhizoma*, 2 liang, honey-fried), Ganjiang (Dried Ginger, *Zingiberis Rhizoma*, 1.5 liang), Fuzi (Prepared Aconite Root, *Aconiti Lateralis Radix Praeparata*, 1 piece, raw, skin removed, broken into eight pieces). The above three ingredients are boiled in 3 sheng of water to obtain 1.2 he of decoction. Strain the dregs, and divide into two doses for warm administration. For robust individuals, a large Fuzi may be used; for ordinary people, a medium-sized one is chosen; for smaller ones, it goes without saying. Ganjiang should be 3 liang. Note: The formula is named Si Ni Tang (Four Reversals Decoction) because it must be used to treat Jue Ni (Reversal Cold/Extremity Cold). The *Shanghan Lun* states: "Jue" refers to the failure of Yin and Yang Qi to connect smoothly, manifesting as cold extremities. Whenever the *Lun* mentions "pulse deep, faint, slow, or weak," Jue Leng (Cold Extremities) is implied without need for further explanation. This formula warms the middle and disperses cold, hence raw Fuzi is used.
Si Ni Tang and Lizhong Tang are both warming and heat-dispelling formulas. However, formulas in the Si Ni category invariably contain Ganjiang to unblock Yang Qi, targeting the Lower Jiao (Lower Burner); formulas in the Lizhong category invariably contain Baizhu to secure the Middle, targeting the Middle Jiao. Although the other herbs are identical, their functions are vastly different.
In Shaoyin disease presenting with floating pulse, spontaneous sweating, frequent urination, vexation, slight aversion to cold, and cramped/tight calves, administering Guizhi Tang (Cinnamon Twig Decoction) to attack the exterior is an error. This leads to Jue (cold extremities), dryness in the throat, irritability, vomiting, and reflux. In such cases, provide Gancao Ganjiang Tang (Licorice and Dried Ginger Decoction) to restore Yang Qi. If the Jue resolves and feet become warm, administer Shaoyao Gancao Tang (Peony and Licorice Decoction), after which the legs will extend. If stomach Qi disharmony leads to delirious speech, administer a small amount of Tiaowei Chengqi Tang (Regulate the Stomach and Direct Downward Decoction). The principles detailed above are explained in the miscellaneous formulas section. If excessive sweating is followed by cauterization (burning needle therapy), Si Ni Tang is indicated. After both Yin and Yang are depleted, if Yang is further exhausted, only this formula can rescue the Yang Qi.
In Shanghan (Cold Damage), if a physician erroneously uses purgatives, leading to continuous diarrhea with undigested food and body pain, urgent treatment of the Interior is required. Later, if body pain persists but bowel movements normalize, urgent treatment of the Exterior is required. Treatment of the Interior suits Si Ni Tang; treatment of the Exterior suits Guizhi Tang. See the Guizhi Tang section for details.
If a patient has fever, headache, and body pain, this indicates Exterior pathogenic factors. However, if the pulse is unexpectedly deep (indicating Interior pattern), and symptoms persist, treat the Interior with Si Ni Tang. Body pain occurs in both Yin and Yang patterns. Here, with a deep pulse and pain despite fever, it is a pattern of Interior Cold with Exterior Heat, thus Si Ni Tang is used.
If the pulse is floating and slow, floating indicates Exterior Heat, while slow indicates Interior Cold. In cases of diarrhea with undigested food, Si Ni Tang is indicated.
Spontaneous diarrhea without thirst belongs to Taiyin disease due to Interior Cold. Understanding the cause of non-thirst dictates warming treatment, suitable for Si Ni Tang and similar formulas. Cold implies no thirst; thus, thirst indicates Heat patterns requiring heat-clearing treatment. The text says "Si Ni Lei" (Si Ni category/formulas) rather than just Si Ni Tang, implying that any warming and heat-dispelling formula may be selected.
In Shaoyin disease, if the pulse is deep, urgent warming is required, as the disease matches the pulse, leaving no room for delay. Si Ni Tang is indicated.
In Shaoyin disease, if food is vomited immediately upon entering the mouth, and there is a sensation of warmth and nausea in the heart/chest but inability to vomit (referring to loss of appetite), this differs from Shaoyang vomiting and should be differentiated by other symptoms. If at onset, hands and feet are cold with a wiry and slow pulse, this indicates Excess in the Chest (Upper Jiao). "At onset" means the disease has just begun; "wiry pulse" indicates strength, confirming Excess. Purging is contraindicated as the pathology is in the Upper Jiao; purging would be contrary to treatment principles. Vomiting methods should be used ("Those in the upper should be vented"). This is the method for using emetics in Shaoyin. However, if there is dry retching due to Cold-Fluid retention above the diaphragm (dry retching without substance indicating fluid retention), emetics are contraindicated. Warming is required. Since Cold-Fluid lacks solid matter, warming disperses the cold and eliminates the fluid. All treatments for Fluid retention use warming methods. Si Ni Tang is indicated.
Profuse sweating with persistent heat, internal cramping, and limb pain are exterior signs, and the pain is Yin-type pain. Combined with diarrhea of undigested food, Jue Ni (reversal cold), and aversion to cold, these are Interior Deficiency-Cold signs. Si Ni Tang is indicated. Note: These symptoms belong to Yin-Cold and are easy to identify. The phrase "heat does not go away" raises the question of whether Exterior pathogens remain. Similarly, "aversion to cold" might suggest unresolved Taiyang syndrome. However, diarrhea and Jue Ni necessitate urgent Interior rescue. Regardless of the presence of Exterior signs, rescuing Yang cannot be delayed.
Profuse sweating, or severe purgation leading to cold extremities, is treated with Si Ni Tang. Jue Ni after sweating or purging indicates extreme Deficiency-Cold.
Vomiting with a weak pulse, free urination, slight body heat, and Jue are difficult to treat, resulting from Exterior Heat and Interior Deficiency-Cold. Si Ni Tang is indicated.
Vomiting, diarrhea, sweating, fever, aversion to cold, limb cramping, and cold extremities are treated with Si Ni Tang.
Simultaneous vomiting and diarrhea, free urination, profuse sweating, diarrhea with undigested food, Interior Cold with Exterior Heat, and a faint pulse nearly imperceptible are treated with Si Ni Tang.
The above five cases all follow sweating or purging, resulting in massive Yang deficiency. Thus, although there is slight Exterior Heat, rescuing Yang is the priority. Free urination and defecation indicate exhaustion of Interior Yang. Cold extremities are not the only sign of weak Yang.