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[Flavor and Nature]
Bitter, cold, non-toxic. The medicinal property is sinking and descending, belonging to Yin. It enters the Foot-Shaoyin (Kidney) meridian and serves as a guiding herb for the Foot-Taiyang (Bladder) meridian.

[Indications]
It clears accumulated heat in the five Zang organs and the intestines and stomach. It promotes the free flow of the lower orifices. It drains latent fire and rescues Kidney Water (nourishes Kidney Yin). It treats rebellious Qi of the Chong vessel without thirst, accompanied by dysuria. When combined with Anemarrhenae Rhizoma (Zhimu, 知母), it nourishes Yin and descends fire; when combined with Atractylodis Rhizoma (Cangzhu, 苍术), it removes dampness and clears heat; when combined with Asari Radix (Xixin, 细辛), it drains Bladder fire and treats sores in the mouth and tongue. In cases where excessive indulgence in rich food leads to accumulated heat damaging Kidney Water, causing the Bladder to become dry over time, resulting in the failure of urine transformation, and fire rebelling upward causing vomiting and hiccups, this corresponds to the "Guan" (closure leading to inability to urinate) and "Ge" (regurgitation leading to vomiting) described in the *Nan Jing* (Classic of Difficult Issues). This condition is suitable for treatment with the bitter-cold nature of Phellodendri Cortex (Huangbai, 黄柏) to drain dryness and replenish water. Furthermore, if heat pathogens accumulate in the Blood level of the Lower Jiao, causing dysuria without thirst, this aligns with the principle in the *Su Wen* (Chapter on Basic Questions): "Without Yin, Yang has no basis to generate; without Yang, Yin has no basis to transform." The Bladder is referred to as the "Official of the Metropolis," the organ storing body fluids. When fire lodges in water, Yang Qi fails to ascend. In such cases, the bitter-cold nature of Phellodendri Cortex (Huangbai, 黄柏) should be used to suppress fire and thereby raise Yang, allowing Yin and Yang to mutually generate. Thus, there are two types of fire: Jun Fire (Monarch Fire), which is Human Fire, specifically Heart Fire. It can be subdued by dampness, extinguished by water, or directly折 (broken/clamped down). Therefore, herbs like Anemarrhenae Rhizoma (Zhimu, 知母) and Phellodendri Cortex (Huangbai, 黄柏) are considered appropriate agents for nourishing Yin and descending fire. However, Xiang Fire (Minister Fire), also known as Heavenly Fire, Dragon-Lei Fire, or Yin Fire, cannot be subdued by water or dampness. Why? Dragon-Lei Fire erupts in the fifth and sixth lunar months and hides in the ninth and tenth. This is because in winter, Yang Qi resides beneath the water and earth, and Dragon-Lei follows this warmth to stay below; in summer, Yin Qi is below, forcing Dragon-Lei to rise above. Using Phellodendri Cortex (Huangbai, 黄柏) to subdue it would be like trying to restrain the momentum of thunder and lightning during a sudden heavy rain—is this feasible? No. Only when the sun shines does the fire naturally vanish. This is clear evidence that this fire thrives with water and is extinguished by fire. Recently, individuals with deficiency consumptive diseases or those who indulge in sexual activity often use Anemarrhenae Rhizoma (Zhimu, 知母) and Phellodendri Cortex (Huangbai, 黄柏) as the chief ingredients in yin-nourishing prescriptions, taking them daily. This excessive descending action damages the Spleen and Stomach, secretly depletes True Yang, causes the essence and Qi to lose warmth, and leads to other illnesses. One should realize that the bitter-cold, slippery, and draining nature of Huangbai and Zhimu, if taken long-term, may cause harm by following the fire path upwards. How can one not be cautious? Understanding this, it is acceptable to refer to Huangbai and Zhimu as "Descending Mothers" to nourish Yin. However, to simply label them as "Nourishing Yin and Descending Fire" is highly contradictory.