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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.