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Zhu Ling (Polyporus), with bitter, sweet, and bland flavors, has a neutral nature. It descends and belongs to Yang; it is non-toxic. It enters the Kidney Meridian and the Bladder Meridian. It promotes urination to alleviate strangury, reduces swelling and fullness, removes dampness, facilitates urination, unblocks stagnation, assists Yang in opening orifices, and its efficacy is specifically dedicated to promoting water metabolism. Whenever water-dampness pathogens reside in the intestines, stomach, bladder, limbs, or skin, Zhu Ling must be used to promote urination and drain dampness. However, water-dampness syndromes vary into Yang, Yin, Deficiency, and Excess types; one cannot indiscriminately apply diuretic methods. If a Yin-deficiency syndrome occurs, using Zhu Ling lightly to drain water will cause the loss of Yin along with the water, inevitably leading to symptoms such as dry mouth and tongue. Moreover, if there is no original water-dampness pathology, forcing diuresis will severely deplete body fluids, exacerbating Yin deficiency. In severe cases, patients may find themselves unable to pass even a few drops of urine despite the urge, which is clear evidence of misusing diuretics. Although water-dampness pathogens exist in the body, should treatment be abandoned simply because Yin deficiency is difficult to treat? When using Zhu Ling, a water-draining herb, it should be combined with Yin-nourishing herbs. This way, Yin remains intact, and dampness is naturally drained. Thus, Zhu Ling can indeed be used.

One might ask: Why does Zhu Ling sometimes fail to promote urination effectively, resulting in urinary retention accompanied by urgent oppression that cannot be relieved? This is due to Fire accumulation in the Bladder, preventing the Qi of the Upper Jiao from ascending, and causing the Lung Metal's descending and purifying function to fail in reaching the Lower Jiao. The Bladder excretes water, but this requires the Lung Metal's Qi to descend purely and heavily for water to flow out through the genitalia. Zhu Ling only drains water but cannot raise the Qi of the Upper Jiao. If Fire exists in the Upper Jiao, it excessively suppresses Lung Metal, preventing its purifying function from reaching the Lower Jiao. If one does not use herbs to descend Fire but focuses solely on draining water, Zhu Ling will prove ineffective. This inefficacy is not due to Zhu Ling's inability to drain water, but rather improper differentiation and treatment.

One might ask: Zhu Ling guides water, allowing Fire pathogens to exit via urination, which is guiding Fire downward. However, Master Zhang Zhongjing often uses Zhu Ling Tang (Polyporus Decoction) to disperse pathogens. Why? The nature of Zhu Ling not only travels downward to the yin orifices but also extends to the pores of the skin. Master Zhang Zhongjing uses Zhu Ling Tang because he fears pathogens moving from the Bladder to the skin, worrying about Yang collapse syndromes. Therefore, he uses it to guide Fire pathogens outward through the skin. Thus, Zhu Ling not only guides water downward for excretion but also guides Fire outward for discharge.

One might ask: How does Zhu Ling's diuretic action explain the symptom of "no thirst"? Frequent urination without thirst indicates Fire accumulation in the Bladder. Accumulated Fire boils the water, creating heat, which causes thirst. Using Zhu Ling to drain water is essentially to purge Fire. Once Fire is purged, water remains, allowing body fluids to circulate freely and moisten the mouth and tongue. Thus, Zhu Ling is not merely a diuretic but also a fluid-generating herb.

Some doubt whether Zhu Ling can truly generate fluids, considering it inappropriate as a standard principle. I reply: If Zhu Ling drains all water, the mouth becomes drier, making fluid generation difficult. The term "generating fluids" applies only to conditions with excessive water (dampness), not to conditions lacking water (fluid depletion). In fluid-depletion conditions, draining water leads to exhaustion of water and rising Fire; in dampness-excess conditions, draining water lowers Fire and raises Water. Once Water rises, body fluids naturally moisten the teeth and mouth. Therefore, Zhu Ling generates fluids by draining water to remove Fire, not by indiscriminate diuresis.

Some question why I distinguish the functions of Zhu Ling and Ze Xie (Alisma Rhizome), given both are diuretics, suggesting curiosity for its own sake. I answer: Zhu Ling and Ze Xie have different applications and principles. Differences should be stated as differences, similarities as similarities. There is nothing curious about this distinction.