水蛭、虻虫，同为吮血之品，能逐瘀破结。而仲圣抵当汤、抵当丸，必二味并用；桃核
承气汤、下瘀血汤，又二味并不用。其所以然之故，有可得而言焉。成氏云∶咸胜血，血蓄
于下，胜血者必以咸为主，故以水蛭为君。苦走血，血结不行，破血者必以苦为助，故以虻
虫为臣。张隐庵、张令韶云∶虻虫水蛭，一飞一潜。在上之热，随经而入，飞者抵之；在下
之血，为热所瘀，潜者当之。按此论水蛭虻虫精矣。而抵当汤所佐之大黄桃仁，亦非泛而不
切。盖四物皆血药，而桃为肺果，桃仁气微向表，协虻虫为走表逐瘀；大黄涤热下行，协水
蛭为走里破结；而同归于抵少腹下血。抵当丸之证，与抵当汤尽同，惟少腹满，则尚不至于
硬矣。小便本不利而今反利，则蓄血必暂而未久矣。用汤方减少其数，又捣丸煮服者，以随
经之热留于表分者多，用峻药轻取之法，使热邪尽入网罗，而瘀不复聚，正不少伤也。若桃
核承气汤证，则与抵当悬绝矣。太阳病不解至下者愈为一截，言蓄血而血自下者不必攻也，
血自下者亦自愈也。其外不解者至当先解外为一截，言血不自下则宜攻，然太阳传本有表邪
未罢者，当先解其外，未可以下有蓄血而遂攻之也。外解已至宜桃核承气汤为一截，外解曰
已，少腹急结曰但，可见表证已无，不必顾表；少腹急结而非硬满，其人亦不如狂，洄溪所
谓瘀血将结之时也。桃核承气汤，即调胃承气汤加桃仁桂枝，加桃仁桂枝而仍名承气，明示
此证之有关于阳明。盖太阳病汗解之后，原有阳明腑实之虑，今不腑实而少腹急结，未始非
肠胃之热下迫膀胱，以桃仁协调胃承气，则下逐膀胱之血瘀，亦上清阳明之热迫。加桂枝者，
膀胱寒水之腑，热结初萌，骤以黄硝折之，气必先郁，故以桂枝化膀胱之气。且桂枝协甘草，
能散结缓急，又为少腹急结之要药。观桂枝茯苓丸之下症，温经汤之瘀血在少腹不去，土瓜
根散之少腹满痛，皆用桂枝，即可知此之非为解表矣。彼用桂枝敛以芍药，此用桂枝引以黄
硝，桂枝所以能抵少腹也。下瘀血汤，瘀血在脐下不在少腹，不曰蓄而曰着，是其血瘀未久，
腹痛亦新著之故。况在产后，岂宜峻攻。既服枳实芍药散而不愈，其为血被热灼而不行无疑
矣。治以大黄桃仁涤热逐瘀， 虫导血通络，蜜丸和药而不伤液，酒煮行药而不疾下，合之
则共成脐下去着之功。此与抵当汤丸之用虻蛭，顾可以同年语乎。
桃核承气汤之治，愚既辨之详矣，惟此条热结膀胱四字，前人多看作太阳传本之公共语，
谓热邪随经入于膀胱，有水结，有血结，五苓散所以治水结，桃核承气汤抵当汤丸所以治血
结。不知热结膀胱，但有血结，并无水结。盖膀胱为津液之腑，气化则能出，故小便不利，
是气病非血病。按巢氏病源，淋病至于热甚则变尿血，何尝非膀胱之热由气入血。而外台治
血淋诸方，无用桃仁虻蛭者，以尿血而非蓄血也。血不蓄，则热可谓之盛，不可谓之结。且
五苓散之不治膀胱热结，固显有可证者。观仲圣用五苓散诸证，不曰脉浮微热，则曰水逆。
须末服而又多饮暖水出汗，是欲使邪从表解。若热结膀胱，何能逆挽而出。其所以渴与小便
不利者，太阳之标，为寒邪所迫。热将传本，遂与少阴水脏均不得施化，即三焦之水道亦滞
而不鬯，于是上不济以肾阴而渴，下则水欲泄而不利，服五苓散而诸弊俱祛，以热不在膀胱
也。且五苓之利小便，乌得与滑石乱发白鱼戎盐瞿麦之属，等量齐观。为问桂枝利小便乎？
而桂枝非四两不利小便，今只半两。桂枝茯苓合而利小便乎？而防己茯苓汤桂苓并用，则治
水气在皮肤。桂枝茯苓泽泻合而利小便乎？而茯苓泽泻汤桂苓泽泻并用，则治胃反吐。茯苓
猪苓白术合而利小便乎？而猪苓散二苓白术并用，则治思水呕吐。白术泽泻合而利小便乎？
而泽泻汤术泻并用，则治支饮苦冒眩。善夫柯氏之论五苓散也，曰重在脉浮微热，不重在小
便不利，真得仲圣立方之旨矣。
水蛭和虻虫，都是吸食血液的药物，能够驱逐瘀血、破除结块。然而张仲景的抵当汤（Diding Decoction）和抵当丸（Diding Pill），必须这两味药并用；而桃核承气汤（Taohé Chengqi Decoction）和下瘀血汤（Xiayuxue Decoction），却这两味药都不用。其中之所以有这样的区别，是有道理可以说的。
成无己说：咸味能胜血，瘀血蓄积在下焦，要战胜血邪必须以咸味为主，所以用水蛭作为君药。苦味走血分，血结滞不通，破血必须以苦味为辅助，所以用虻虫作为臣药。
张隐庵和张令韶说：虻虫和水蛭，一个在空中飞，一个在水中潜行。在上部的热邪，随经脉传入，由飞的虻虫去抵挡它；在下部的瘀血，被热邪所阻滞，由潜的水蛭去承担它。按这种论述，对水蛭和虻虫的分析非常精妙。而抵当汤中辅佐的大黄（Rhei Radix et Rhizoma）和桃仁（Persicae Semen），也不是泛泛而不贴切的。大概这四味药都是血分药，但桃是肺之果，桃仁气味微向表，协助虻虫走向体表以驱逐瘀血；大黄涤荡热邪下行，协助水蛭走向体内以破除结块；最终都归于消除少腹下的瘀血。
抵当丸的证候，与抵当汤完全相同，只是少腹胀满，还不至于坚硬。小便本来不利，现在反而通利，说明蓄血的时间短暂且不久。使用汤剂减少药量，又制成丸剂煮服，是因为随经传入的热邪留在表分的较多，采用峻猛药物轻取的方法，使热邪全部落入网罗，而瘀血不再聚集，确实不会造成损伤。
至于桃核承气汤的证候，则与抵当汤截然不同了。“太阳病不解至下者愈”是一层意思，是说蓄血而血自下行的，不必攻下，血自下行也能自愈。“其外不解者至当先解外”是一层意思，是说血不自下则应当攻下，但如果太阳病传变至本经，有表邪未罢的情况，应当先解除表邪，不可以因为有蓄血就立即攻下。“外解已至宜桃核承气汤”是一层意思，表证已解曰“已”，少腹急结曰“但”，可见表证已无，不必顾护表邪；少腹急结而不是硬满，病人也不像发狂那样，正如洄溪所说的瘀血将结之时。
桃核承气汤，就是调胃承气汤（Tiaowei Chengqi Decoction）加上桃仁和桂枝（Guizhi, Cinnamon Twig）。加了桃仁和桂枝却仍然名叫承气汤，明确显示此证与阳明腑实有关。大概太阳病汗解之后，原本就有转为阳明腑实的顾虑，现在不是腑实而是少腹急结，未必不是肠胃的热邪下迫膀胱，用桃仁配合调胃承气汤，就能向下驱逐膀胱的瘀血，也能向上清泄阳明的热迫。加桂枝的原因在于，膀胱是寒水之腑，热结刚刚萌发，如果骤然用大黄、芒硝（Mangxiao, Natrii Sulfas）来折损热势，气机必然郁滞，所以用桂枝来化行膀胱的气机。而且桂枝配合甘草，能散结缓急，又是治疗少腹急结的要药。观察桂枝茯苓丸（Guizhi Fuling Pill）的下症，温经汤（Wenjing Decoction）中瘀血在少腹不去，土瓜根散（Tuguagen San）中的少腹满痛，都用桂枝，就可以知道此处用桂枝不是为了发表。那些方子用桂枝配伍芍药（Shaoyao, Paeoniae Radix Alba），这里用桂枝引导大黄、芒硝，桂枝之所以能抵达少腹，正在于此。
下瘀血汤，瘀血在脐下而不在少腹，不叫“蓄”而叫“着”，说明血瘀时间不长，腹痛也是新近形成的。况且是在产后，岂宜峻猛攻下。既然服用枳实芍药散（Zhishi Shaoyao San）后没有痊愈，那肯定是血被热邪灼烧而不能运行无疑了。治疗上用大黄、桃仁涤荡热邪、驱逐瘀血，䗪虫（Eupolyphaga seu Steleophaga）引导血脉通畅经络，蜜丸调和药性而不伤津液，酒煮行药而不致急速泻下，合起来共同成就消除脐下着瘀的功效。这与抵当汤丸中使用虻虫、水蛭，怎么可以相提并论呢？
关于桃核承气汤的治疗，我已经辨析得很详细了，只是这一条中“热结膀胱”四个字，前人大多看作太阳病传变至本经的通用语，认为热邪随经脉进入膀胱，有水结，也有血结，五苓散（Wuling San）用来治水结，桃核承气汤、抵当汤、抵当丸用来治血结。却不知道“热结膀胱”，只有血结，并没有水结。因为膀胱是津液之腑，气化功能正常才能排出尿液，所以小便不利，是气病而非血病。
按巢元方的《诸病源候论》，淋病到了热盛的时候变成尿血，这难道不是膀胱的热从气分进入血分吗？而《外台秘要》治疗血淋的各种方剂，没有用桃仁、虻虫、水蛭的，因为这是尿血而不是蓄血。血不蓄积，那么热可以说很盛，但不能说是结。而且五苓散不治膀胱热结，也是有明显证据的。看张仲景使用五苓散的各个证候，不是说脉浮微热，就是说水逆。需要服药后多饮暖水出汗，是想让邪气从表解除。如果是热结膀胱，怎么能逆挽而出呢？
之所以出现口渴和小便不利，是因为太阳的标气，被寒邪所逼迫。热将要传入本经，于是与少阴水脏都不能发挥气化作用，就连三焦的水道也停滞不畅，于是上面得不到肾阴的滋润而口渴，下面想排尿却排出不利，服用五苓散后各种弊端都消除了，这是因为热不在膀胱的缘故。
而且五苓散利小便的作用，怎能与滑石（Huaishi, Talcum）、乱发（Luanfa, Crinis Carbonisatus）、白鱼（Baiyu, Lepisma saccharina）、戎盐（Rongyan, Natrium Chloratum）、瞿麦（Qumai, Herba Siegesbeckiae）等药物等同看待呢？试问桂枝能利小便吗？桂枝不用到四两就不能利小便，而五苓散中只用了半两。桂枝和茯苓一起能利小便吗？防己茯苓汤（Fangji Fuling Tang）中桂枝和茯苓并用，却是治疗水气在皮肤。桂枝、茯苓、泽泻一起能利小便吗？茯苓泽泻汤（Fuling Zexie Tang）中桂枝、茯苓、泽泻并用，却是治疗胃反呕吐。茯苓、猪苓、白术一起能利小便吗？猪苓散（Zhuling San）中猪苓、茯苓、白术并用，却是治疗思水呕吐。白术、泽泻一起能利小便吗？泽泻汤（Zexie Tang）中白术、泽泻并用，却是治疗支饮引起的头目苦冒眩晕。柯琴对五苓散的评论真好啊，他说五苓散重在脉浮微热，不重在小便不利，真正得到了张仲景立方的宗旨。
Shuizhi (Leech) and Mengchong (Horsefly) are both substances that suck blood; they can expel blood stasis and break up accumulations. However, in Zhang Zhongjing's Diding Tang (Diding Decoction) and Diding Wan (Diding Pill), these two herbs must be used together; whereas in Taohé Chengqi Tang (Peach Kernel Modulating the Stomach Decoction) and Xiayuxue Tang (Expelling Blood Stasis from Below Decoction), neither of these two herbs is used. The reason for this difference is worth discussing.
Cheng Wuji stated: "Salty flavor overcomes blood." When blood accumulates in the lower jiao, one must primarily use salty substances to overcome the blood pathogen; therefore, Shuizhi (Leech) is used as the sovereign herb. "Bitter flavor travels to the blood aspect." When blood is knotted and does not flow, one must assist with bitter substances to break the blood stasis; therefore, Mengchong (Horsefly) is used as the minister herb.
Zhang Yinan and Zhanglingshao stated: "Mengchong and Shuizhi, one flies and one dives. Heat in the upper part enters via the meridians; the flying insect targets it. Blood stasis in the lower part is obstructed by heat; the diving creature addresses it." This analysis of Shuizhi and Mengchong is exquisite. Furthermore, the Da Huang (Rhei Radix et Rhizoma) and Tao Ren (Persicae Semen) assisting in Diding Tang are not generic but precise. Generally, all four ingredients are blood-acting herbs. However, the peach is a fruit corresponding to the Lung; Tao Ren has a slight qi directed outward, cooperating with Mengchong to travel to the exterior and expel blood stasis. Da Huang purges heat downward, cooperating with Shuizhi to travel inward and break up knots; ultimately, they converge to eliminate blood stasis below the hypogastrium.
The syndrome treated by Diding Wan is identical to that of Diding Tang, except that there is fullness in the hypogastrium but no hardness. Urination was previously difficult but is now free, indicating that the blood accumulation is recent and not long-standing. Using a decoction with reduced dosage, and preparing it as pills boiled for administration, is because the heat traveling along the meridians remains largely in the exterior aspects. By using potent drugs lightly, the heat pathogen is fully captured, preventing the re-aggregation of stasis, without causing injury.
In contrast, the syndrome of Taohé Chengqi Tang is completely different. "If Taiyang disease is not resolved and leads to bleeding which resolves itself, no attack is needed" is one point: if blood stasis expels itself through bleeding, no purgation is required, and self-resolution will occur. "If the exterior is not resolved, one must first resolve the exterior" is another point: if blood does not expel itself, attack is indicated; however, if Taiyang disease has transmitted to its interior yet the exterior pathogen remains unresolved, one must first resolve the exterior. One cannot immediately purge simply because there is blood accumulation. "Once the exterior is resolved, Taohé Chengqi Tang is appropriate" is the third point. "Exterior resolved" implies the end of the condition; "hypogastric urgency and knotting" implies exclusivity. Thus, the exterior syndrome is gone, and there is no need to protect the exterior. Hypogastric urgency without hardness, and the patient not exhibiting mania-like behavior, corresponds to Hui Xi's description of the time when blood stasis is about to form.
Taohé Chengqi Tang is essentially Tiaowei Chengqi Tang (Modulating the Stomach Decoction) plus Tao Ren (Persicae Semen) and Guizhi (Cinnamon Twig). Adding these two yet retaining the name "Chengqi" clearly indicates this syndrome relates to Yangming. After sweating resolves Taiyang disease, there is originally a concern of Yangming Fu organ excess. Now, instead of Fu excess, there is hypogastric urgency. This may well be due to heat in the intestines and stomach pressing down on the Bladder. Using Tao Ren to coordinate with Tiaowei Chengqi Tang allows for the downward expulsion of Bladder blood stasis and the upward clearing of Yangming heat pressure. The reason for adding Guizhi is that the Bladder is an organ of cold water. When heat knot begins, abruptly using Da Huang and Mangxiao (Natrii Sulfas) to suppress heat would cause Qi stagnation; thus, Guizhi is used to transform Bladder Qi. Moreover, Guizhi combined with Gancao (Licorice Root) can dissipate knots and relieve urgency, making it a key herb for hypogastric urgency. Observing the indications for Guizhi Fuling Pill (Cinnamon Twig and Poria Pill), Wenjing Tang (Warming the Meridians Decoction) for persistent blood stasis in the hypogastrium, and Tuguagen San (Trichosanthes Root Powder) for hypogastric fullness and pain, all use Guizhi. This confirms that here, Guizhi is not used for releasing the exterior. In those formulas, Guizhi is constrained by Shaoyao (White Peony Root); here, Guizhi guides Da Huang and Mangxiao. It is precisely this function of Guizhi that allows it to reach the hypogastrium.
Xiayuxue Tang treats blood stasis located below the umbilicus, not in the hypogastrium. It uses the term "zhuo" (adhering/clinging) rather than "xu" (accumulating), indicating the stasis is not long-standing, and the abdominal pain is newly formed. Furthermore, since this occurs postpartum, harsh purgation is inappropriate. Since Zhishi Shaoyao San (Immature Bitter Orange and White Peony Powder) failed to cure, it is undoubtedly that the blood was scorched by heat and ceased to flow. Treatment employs Da Huang and Tao Ren to purge heat and expel stasis, Eupolyphaga seu Steleophaga (Ground Beetle) to guide blood and unblock collaterals. Honey pills harmonize the medicine without damaging fluids, and wine-boiling promotes drug action without causing rapid purging. Together, they achieve the effect of removing adherent stasis below the umbilicus. How can this be compared to the use of Mengchong and Shuizhi in Diding Tang and Wan?
Regarding the treatment of Taohé Chengqi Tang, I have analyzed it in detail. However, the phrase "heat knot in the Bladder" in this clause has often been viewed by predecessors as a common expression for Taiyang transmitting to its interior. They believed heat pathogens enter the Bladder via meridians, causing either water accumulation or blood accumulation: Wuling San (Five-Ingredient Powder with Poria) treats water accumulation, while Taohé Chengqi Tang, Diding Tang, and Diding Wan treat blood accumulation. They did not realize that "heat knot in the Bladder" involves only blood accumulation, with no water accumulation. The Bladder is the organ of body fluids; it functions through Qi transformation to excrete urine. Therefore, difficulty in urination is a Qi disorder, not a Blood disorder.
According to Chao Yuanfang's *General Treatise on Epidemic Diseases*, strangury turning into hematuria when heat is severe is indeed heat entering the blood level from the Qi level in the Bladder. Yet, in *Waitai Miyao* (Essential Prescriptions Worth a Thousand Gold for Emergencies), formulas treating bloody strangury do not use Tao Ren, Mengchong, or Shuizhi, because hematuria is not blood accumulation. If blood does not accumulate, heat can be described as abundant, but not as "knotted." Moreover, the fact that Wuling San does not treat Bladder heat knot is evident. Looking at Zhang Zhongjing's various indications for Wuling San, he mentions either "floating pulse with slight fever" or "water reversal." The instruction to drink warm water after taking the powder to induce sweating aims to resolve the pathogen from the exterior. If there were heat knot in the Bladder, how could it be reversed and expelled outward?
The reasons for thirst and difficulty in urination are that the superficial aspect of Taiyang is forced by cold pathogens. As heat prepares to transmit to the interior, both the Shaoyin Water Organ and the Bladder fail to perform their transformations. Consequently, the waterways of the Triple Burner also become stagnant. Thus, the upper body lacks Kidney Yin nourishment, leading to thirst; the lower body desires to excrete water but fails to do so. Taking Wuling San removes all these drawbacks because the heat is not in the Bladder.
Furthermore, the diuretic effect of Wuling San cannot be equated with herbs like Huashi (Talcum), Luanfa (Carbonized Human Hair), Baiyu (Silverfish), Rongyan (Rock Salt), and Qumai (Herba Siegesbeckiae). Does Guizhi promote urination? Guizhi requires a dosage of four liang to promote urination, yet Wuling San uses only half a liang. Do Guizhi and Fuling (Poria) promote urination together? In Fangji Fuling Tang (Stephania and Poria Decoction), Guizhi and Fuling are used together to treat water qi in the skin. Do Guizhi, Fuling, and Zexie (Rhizoma Alismatis) promote urination together? In Fuling Zexie Tang (Poria and Rhizoma Alismatis Decoction), these three are used together to treat gastric regurgitation and vomiting. Do Fuling, Zhuling (Polyporus), and Baizhu (Atractylodis Macrocephalae Rhizoma) promote urination together? In Zhuling San (Polyporus Powder), these three are used together to treat vomiting triggered by desire for water. Do Baizhu and Zexie promote urination together? In Zexie Tang (Rhizoma Alismatis Decoction), these two are used together to treat vertigo and dizziness caused by fluid retention (Zhiyin). Ke Qin's commentary on Wuling San is excellent: he states that Wuling San focuses on the floating pulse and slight fever, not on difficulty in urination. This truly captures the essence of Zhang Zhongjing's formula creation.