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Du Zhong (Eucommiae Cortex) tastes pungent, sweet, and slightly bitter. Its nature is neutral and warm. Its qi is thin while its flavor is dense, and it has a descending property. It enters the Foot-Shaoyin Kidney Meridian and the Foot-Jueyin Liver Meridian. It is a herb that acts on the Qi level of the Liver Meridian.

It mainly treats pain in the lower back and knees. It tonifies the Middle Jiao, benefits Essence and Qi, strengthens sinews and bones, and fortifies the will. It eliminates itching and dampness in the genital area. It treats urinary dribbling. It treats kidney labor causing spasms of the lower back and spine, soreness and pain in the feet, and an unwillingness to tread on the ground. (This occurs when Yin fails to be transported by Yang.) It eliminates cold in the kidney. (Li Dongyuan stated it can make sinews and bones adhere closely together.) (Ma Shicai stated that although it is warm, it does not aid fire.) Its color is purple and lustrous; its temperature is neutral and harmonizes Yang; its pungent and sweet flavors enrich Yin. Therefore, it can achieve effects from benefiting the Kidney to nourishing the Liver. (Li Shizhen noted this.) The Kidney dislikes dryness and urgently needs pungent foods to moisten it; the Liver dislikes tension and urgently needs sweet foods to relax it. Du Zhong possesses both pungent and sweet flavors, perfectly resolving the distress of the Liver and Kidney and supplementing their deficiencies.

When used with Niuxi (Achyranthis Bidentatae Radix), Gouqizi (Lycii Fructus), Xuduan (Dipsaci Radix), Baijiao (Ejiao, Donkey-hide Gelatin), Dihuang (Rehmanniae Radix), Shanyao (Dioscoreae Rhizoma), Wuweizi (Schisandrae Fructus), Tusizi (Cuscutae Semen), and Huangbai (Phellodendri Cortex), it treats lumbar pain due to Kidney deficiency and weakness in the lower body. For those prone to habitual miscarriage at three or four months of pregnancy, two months prior to conception, take eight taels of Du Zhong, soak it thoroughly in decoction made from glutinous rice, stir-fry to remove silk fibers, add two taels of Xuduan soaked in wine and dried over low heat, grind into powder, mix with five or six taels of Shanyao powder to form pills the size of wutong seeds, and swallow with rice water on an empty stomach. A young man who recently married suffered from severe leg weakness and pain. Treatment for Hongxiangjiao (Gout/Lower limb swelling and pain) was ineffective. Using one tael of Du Zhong, decocted with half wine and half water, he recovered.

[Discussion] Du Zhong's taste begins with pungency, followed by sweetness, and finally bitterness. Sweetness does not overpower pungency, while bitterness is slight. Beginning with pungency and ending with bitterness indicates that bitterness is the destination of pungency and sweetness, and it is bitterness that guides their efficacy. Bitterness belongs to Fire; the downward-moving fire associated with bitterness is Yuan Qi (Original Qi). This herb transitions from pungent and sweet to bitter, returning to the central Earth's harmonious Qi, thereby sinking and densely nurturing Yang within Yin. Its purple color is also evidence of its affinity with Ministerial Fire. The Yuan Qi of the Sanjiao (Triple Burner) coils up and down throughout the body. (Fire within Water refers to the Yuan Qi of the Kidney, distributed by the Sanjiao.) Why does this herb exert its effect primarily in the lower part? Presumably because the sweetness of Central Earth transforms and returns to the Kidney, and the pungency of Heaven's Qi, via Central Earth, also returns to the Kidney. Thus, the functions of benefiting Yuan Yang and generating fluids converge here. The efficacy of this herb relies entirely on Yuan Qi as its foundation. (The lower half of the body, including the waist, knees, and feet, relies on the Yuan Yang within Yin as the master of tension and relaxation. Regarding treating miscarriage, it relies primarily on Qi transformation, not merely on physical support.) The *Shennong Bencao Jing* states it benefits Essence and Qi and strengthens the will, all referring to Yuan Qi. It generates Yang within Yin and contains Yin within Yang; it is not biased toward Yang alone. (It is not biased toward tonifying Yang, so this herb focuses on benefiting Essence and Qi; when Essence and Qi are benefited, sinews and bones naturally strengthen.) Hence, it is said to have a neutral nature, and Li Shi-zhen also noted it is warm without aiding fire. Furthermore, since the Yuan Qi of the Sanjiao is the Qi of the Kidney, why is it described as acting on the Qi level of the Liver Meridian? Because the Liver originates from the Kidney, and conversely helps the Kidney facilitate its generative functions. Considering Li Dongyuan's statement that it "makes sinews and bones adhere," we see that the origin of Liver transformation lies in the Kidney, and the Kidney's supplementation comes from the Liver. This herb benefits the Liver through the Kidney, and thus the Kidney is supported by the Liver, resulting in adherent sinews and bones. This is how the Liver utilizes Qi transformation. It does not mean it directly enters the Liver meridian in a separate sense. (To benefit the Yuan Qi of the Kidney is to act on the Qi level of the Liver Meridian, meaning it is a herb that tonifies Wind-Deficiency and moistens Liver Dryness. What is Liver Dryness? It is when Yuan Yang is deficient and the true Qi of Wind-Wood fails to reach, causing dryness and tension.) If it were not based on the Yuan Qi of the Sanjiao, generating Yang within Yin and containing Yin within Yang, could it benefit Wind-Deficiency and Liver Dryness? As for itching and dampness in the genital area and urinary dribbling, these are manifestations of Yang failing to circulate fully into Yin. Although its lipid richness is valued, its utility lies in the bark, which invites deep thought. Understanding this, for lumbar pain caused by Yin deficiency, one should still exercise discretion in its use. Zhen Quan treated lumbar pain due to Kidney Cold; Ri Huazi treated lumbar and spinal spasms due to Kidney Labor. Cold and Labor both belong to Kidney Qi deficiency. Deficiency of Yuan Yang in the Kidney leads to symptoms of lumbar pain and spinal spasms, which are also signs of Wind pathology due to Yang deficiency. When Yang is deficient and combined, it cannot reach Yin, leading to Wind pathology, known as Haizang's "Wind-Deficiency." Also, "Liver Dryness" means Yang cannot reach the Liver, nor can Yin follow it. The principle of the unity of Yin and Yang can be glimpsed in this herb. However, benefiting the Liver through the Kidney differs from Shizao (Corni Fructus), which first warms the Liver to assist the Kidney.

It is not suitable for cases of Kidney deficiency with blazing Fire. If used, it should be combined with Zhimu (Anemarrhenae Rhizoma) and Huangbai (Phellodendri Cortex). (Chen Shigong stated this.)

[Processing] Scrape off the rough bark. For every jin (500g), mix with one liang of Su (Butyrum) and three liang of Mi (Honey), apply evenly, and roast over fire until completely processed. Another method: stir-fry with wine to break the silk fibers, then gradually crush into powder to avoid burning. Those that are dense and solid can strengthen sinews and bones. Stir-fry with flour to remove silk fibers, soak in Tongbian (Child's Urine) for seven days, dry on new tile tiles, and grind into powder.