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Treats blood accumulation (Xuè Xù) in Shanghan (Cold Damage), as well as zheng zha (masses and accumulations); it is highly effective for expelling parasites and attacking toxins.
Shuizhi (Leech, *Hirudo nipponica*) (stir-fried) 30 pieces; Mengchong (Blue Bottle Fly Larva, *Chrysomya megacephala*) (stir-fried, remove head and feet) 30 pieces; Dahuang (Rhubarb Root and Rhizome, *Rhei Radix et Rhizoma*) 3 liang; Taoren (Peach Seed, *Persicae Semen*) (remove skin and sharp ends) 30 pieces. The above four ingredients are ground into a powder. Add five sheng of water, boil to three sheng, strain the dregs, and take one sheng warm. If no effect, administer again. Stop when bowel movement occurs.
Shuizhi (Leech, *Hirudo nipponica*) (stir-fried) 20 pieces; Mengchong (Blue Bottle Fly Larva, *Chrysomya megacephala*) (stir-fried, remove wings) 25 pieces; Taoren (Peach Seed, *Persicae Semen*) (remove skin and sharp ends) 20 pieces; Dahuang (Rhubarb Root and Rhizome, *Rhei Radix et Rhizoma*) 3 liang. The above four ingredients are pounded and divided into four pills. Add one sheng of water, boil one pill until seven he remains, and take the decoction. Blood should be expelled within twenty-four hours (Zui Shi). If not expelled, administer again.

[Collected Annotations] Ke Qin stated: The Bladder (Pang Guang) is the fu-organ of water, and blood has no place to accumulate therein. The Shaofu (Lower Abdomen) is the chamber of the Bladder. If heat accumulation causes hardness and fullness, urination should be difficult. However, if urination is actually free, it indicates that the disease is not inside the Bladder but within the Shaofu. It can be deduced that the Ying-blood (Nutritive Blood) traveling along the meridians has coagulated due to stasis-heat in the interior of the Shaofu, rather than in the interior of the Bladder. Therefore, although urination is free, the hardness, fullness, and urgency in the Shaofu indicate that accumulated blood remains stasis in the Shaofu. When pathogenic heat floods internally, the Shen-spirit becomes unsettled, leading to mania (Fa Kuang). When blood stasis obstructs flow, Ying-blood cannot circulate, resulting in a pulse that is faint and deep (Wei Er Chen). Since Ying-blood does not circulate, Qi mechanism fails to diffuse, causing the pulse to be deep and knotted (Chen Er Jie). When Ying-Qi fails to circulate throughout the body, jaundice (Huang) may appear. Excessive hunger after eating (Xiao Gu Shan Ji) indicates blazing Stomach-fire (Wei Huo Chi Sheng). Bowel movements being unusually easy suggests lubrication by blood; black stool color indicates that accumulated blood has seeped into the intestines. Forgetfulness (Shan Wang) results from blood failing to nourish and intelligence becoming unclear. These are all subtle signs of blood stasis. Only potent agents are sufficient to reach their nest; thus, Didang Tang (Resist-and-Attack Decoction) was established for this heavy responsibility. Leeches are insects skilled at drinking blood and thrive in water; fly larvae are insects skilled at sucking blood and are fiercer on land. By combining these two creatures skilled at extracting blood from water and land, seeking resonance with similar energies, and assisting with the bitter-sweet nature of Taoren (Peach Seed) to push out the old and generate the new, and the bitter-cold nature of Dahuang (Rhubarb) to cleanse pathogenic heat, the formula is named Didang. If heat is severe but mania has not yet occurred, and the Shaofu is full but not hard, the dosage should be reduced, and pills should be used for slow treatment. If exterior symptoms have resolved, there is urgency and knotting in the Shaofu, and the patient resembles mania, this indicates transformation into Yangming disease. In such cases, Tiaowei Chengqi Tang (Regulate-the-Stomach Purge-Decoction) combined with Taoren (Peach Seed) and Guizhi (Cinnamon Twig) to promote blood circulation is used to induce mild purgation. When Stomach harmony is restored, recovery occurs. This represents the milder approach of Tao Ren Cheng Qi Tang (Peach Kernel Purge-Decoction).