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(Zhang Zhongjing)
Treating Taiyang disease (Taiyang disease, a syndrome caused by pathogenic factors affecting the Taiyang channel) after six or seven days, where the exterior syndrome (biao zheng, symptoms such as fever and aversion to cold indicating pathogen at the surface) still persists, the pulse is faint and deep. There is no Jie Xiong (Jie Xiong, chest binding syndrome characterized by fullness and pain in the chest) formation. The patient exhibits mania (fa kuang, manic behavior due to heat disturbing the mind). This is because heat resides in the Lower Jiao (Lower Jiao, the lower part of the torso containing the bladder and intestines), and the lower abdomen should be hard and full. If urination is normal and free, there must be Blood Stasis accumulation (Xu Xue, accumulation of stagnant blood). This causes forgetfulness (shan wang). The reason for this is that the heat of the Taiyang channel follows the meridian into the interior, resulting in stasis-heat lodged within (Yu Re Zai Li). ("Exterior syndrome still persists" refers to the unresolved symptoms of fever, aversion to cold, headache, and neck stiffness. Taiyang governs the channels, and the Bladder is its associated organ. Here, Taiyang heat pathogens follow the meridians into the Bladder organ, where heat and blood contend, thus forming Blood Stasis accumulation. A deep pulse indicates an interior location. Since the exterior syndrome persists, the pathogen is still shallow; it does not bind in the chest but causes mania. The Classics state: "Heat binds in the Bladder, the person becomes like mad." Also: "Blood congregates below, causing disorder and forgetfulness." Hardness and fullness of the lower abdomen with difficulty in urination indicate urinary obstruction; hardness and fullness with free urination indicate Blood Stasis accumulation. *Zhun Sheng* states: Considering the words "still persists," the pathogen has not failed to enter the interior, nor is it merely shallow. The Bladder is the primary organ of the Taiyang channel. Statements regarding "heat binding in the Lower Jiao," "hardness and fullness of the lower abdomen," and "free urination" are all syndromes of the Bladder. Thus, it is summarized as "meridian-following stasis-heat." The term "in the interior" refers to the interior of the Bladder following the meridian, not the interior of the Three Yin channels. Note: Taiyang belongs to Yang and is at the exterior. Even if deep-tight or deep-slippery pulses appear, they cannot be named as Interior or Yin.)

Shuizhi (Leech, Hirudo nipponica - 30 pieces, fried black in Pig Fat [Zhu Zhi])
Mengchong (Dragonfly Larva, Odonata larvae - 30 pieces, remove head, feet, and wings)
Taoren (Peach Kernel, Persicae Semen - 20 seeds, remove skin and tips, grind)
Dahuang (Rhubarb Root, Radix et Rhizoma Rhei - 4 liang, soaked in wine)

This formula acts on the Foot-Taiyang Bladder Channel. Cheng Wuji stated: Bitter flavors move into the Blood level, salty flavors infiltrate the Blood. The bitter and salty properties of Mengchong and Shuizhi eliminate Blood Stasis accumulation; sweet flavors moderate tension, and bitter flavors drain heat. The sweet and bitter properties of Taoren and Dahuang descend and drain bound heat. (Cheng Jiaoqian stated: Exterior syndrome persists, pulse is faint and deep; this presents exterior symptoms without exterior pulse characteristics, indicating heat in the Lower Jiao. It cannot be dispersed by Guizhi Tang (Cinnamon Twig Decoction) nor attacked by Tao Ren Cheng Qi Tang (Peach Kernel and Magnolia Bark Decoction). Because heat binding in the Bladder differs from stasis-heat in the interior, the pathogen has varying depths of invasion. Therefore, the attack by Tao Ren Cheng Qi Tang and Didang Tang varies in speed and intensity.)

The original formula reduces Shuizhi by 10 pieces, and Mengchong and Taoren each by 5 pieces. These are divided into four pills. Each pill is decocted in water and taken orally. This is named Didang Wan (Didang Pill): It treats the same disease but in cases lacking symptoms of severe forgetfulness or mania. (Shuizhi is the leech, salty and cold, slightly toxic. It is an insect that feeds on blood, capable of unifying blood clots in the Liver Channel. It is extremely difficult to kill; even when roasted and powdered, it revives upon contact with water. If ingested alive, it may breed and cause harm; drinking mud-water can detoxify it. Mengchong is the horsefly/mosquito-like insect; since it feeds on blood, it is used to treat blood disorders. Both medicines are potent and dangerous, rarely used by common practitioners, hence the formulation of Dai Didang Tang (Substitute Didang Decoction). Wu Hegao stated: Ancients used horseflies and leeches to treat blood accumulations because they are adept at sucking blood. Tian Shu Shi (rat droppings, which eat mosquitoes) might also treat blood accumulations. Materia Medica states it expels dead fetuses...)

Appendix: Dai Didang Wan (Substitute Didang Pill):
Dahuang (Rhubarb Root, Radix et Rhizoma Rhei - 4 liang)
Shengdi (Rehmannia Root, Rehmanniae Radix)
Guiwei (Cassia Twig, Cinnamomi Ramulus - specifically the tail end)
Taoren (Peach Kernel, Persicae Semen)
Chuanshanjia (Pangolin Scale, Manis Squama)
Xuanmingfen (Mirabilite, Natrii Sulfas - 1 liang each)
Guixin (Cinnamon Heart, Cinnamomi Cortex - 3 qian)
Prepared as Honey Pills. (Taoren, Guiwei, and Shengdi moisten and unblock; Guixin warms and activates blood flow; Dahuang and Xuanmingfen use bitter-cold and salty-cold properties to push down and purge stagnation; Chuanshanjia is added to guide the medicine to the site of pathology...)