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Leech (Shuizhi), with a salty and bitter taste, and a neutral to slightly cold nature, is toxic. It should be used after being stir-fried until yellowish-black. It excels at dispelling accumulated blood stasis and hard masses (Zhijia). Master Zhang Zhongjing employed it in Didang Tang (Cistanche Pill) and Didang Wan (Pill) to treat jaundice caused by blood stasis in Cold Damage diseases. It is also an essential herb for treating traumatic injuries, promoting urination, regulating menstruation, and inducing abortion. When blood accumulation fails to resolve, what other means could remove it but this herb?

A question arises: Why must leech be used for blood accumulation syndromes? The reason is that blood accumulation differs from qi stagnation. Although both are heat syndromes, qi stagnation involves heat binding in the Bladder, whereas blood accumulation involves heat binding in the Intestines and Stomach. Diseases of qi stagnation can be dispersed by qi-regulating herbs into formlessness. However, blood accumulation cannot be dispersed into formlessness without using blood-invigorating substances. Leech is precisely such a tangible substance, used to dissipate tangible blood stasis. Why fear it excessively? (Commentary: Blood accumulation syndromes cannot be eliminated without leech or horsefly.)

Another question: Leech is the leech found in rice paddies, which feeds on human blood and is the most detestable creature. Why did Master Zhang Zhongjing specifically use it to treat blood stasis in Cold Damage? Is there any herb that can substitute for it? The answer is: When blood is stagnant and accumulated without dispersing, there is truly no other herb to replace leech. If leech is unavailable, one must use a larger dose of horsefly (Mengchong) as a substitute. However, horsefly ultimately falls short of the efficacy of leech. People today fear it and dare not use it; who knows that this creature does not harm humans?

Yet another question: Leech is extremely difficult to kill and possesses great transformative abilities, seemingly able to multiply from one body into thousands. It is understandable that people doubt and dare not use it. Yet you claim it does not harm humans, which is hard to believe. The response is: If leech is processed improperly, it may survive and remain alive; if processed correctly, it will die permanently and lose its vitality. Take dried leech, slice it finely with an iron knife into pieces the size of millet grains, and stir-fry over gentle heat until yellowish-black. Remove when smoke rises. Do not place it on the ground to avoid absorbing earth qi; otherwise, how could it regenerate and transform? (Commentary: In processing leech, it is best to prevent contact with earth qi. Once stir-fried thoroughly, it loses its vital energy and cannot regenerate.) Thus, when administered together with blood stasis, it is completely expelled through the bowels, yielding the fastest therapeutic effect. How could it possibly cause harm?

Someone asks: If the stir-frying process of leech is improper and its properties remain active, leaving it in the intestines and abdomen would surely be harmful. The reply is: Why fear so excessively? I have a method to counteract this. By adding two qian of loess (Huangtu) to the decoction of leech and taking them together, even if the leech survives, it will certainly cause no harm. (Commentary: Another ingenious method.) Since leech regards earth as its mother, it cannot sustain itself without earth. Used together with earth, while effectively resolving blood stasis, it moves along with the earth and eliminates any concern about lingering in the abdominal intestines.