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Dihuang (dried Rehmanniae Radix) is bitter, slightly sweet, and cold in nature, with no toxicity. Those produced in Huaiqing have a shape resembling a nail head and rat's tail, with rough skin and firm texture; those weighing seven or eight qian per plant possess superior efficacy. Those produced in Bozhou are thick at both ends, with fine skin and soft texture; although large in size, their medicinal power is weak. Those produced in Jiangsu and Zhejiang are thin, soft, and powerless, suitable only for clearing heat, and should not be used in tonifying prescriptions. Regardless of origin, if they are withered, shriveled, and light in weight, they are called "Tianhuang" and are unsuitable for decoctions.

Invention: The purple heart of Dihuang enters the Heart to promote circulation; the yellow middle part enters the Spleen; the black skin returns to the Kidney. It has a strong flavor but faint aroma. Internally, it specializes in cooling blood and nourishing Yin; externally, it moistens the skin and promotes luster. It is suitable for patients who are deficient and have internal heat. Dai Yuanli stated: When Yin is slight and Yang is abundant, and ministerial fire is blazing and strong, invading the Yin positions, causing gradual consumption leading to syndromes of Yin deficiency and hyperactive fire, raw Dihuang (Shengdihuang) should be used to nourish Yin and retreat Yang. Combined with Renshen (Ginseng), Fuling (Poria), and Shimi (Rock Sugar), it is named Qiongyu Gao (Jade Dew Paste), treating consumptive coughing and hemoptysis. Combined with Tianmendong (Asparagi Radix), Maidong (Ophiopogonis Radix), Shudihuang (Prepared Rehmanniae Radix), and Renshen (Ginseng), it is named Guben Wan (Root-Firming Pill), treating elderly patients with withered essence and blood. Adding Gouqi (Lycium Fruit) to Guben Wan and boiling it into a paste creates Jiling Gao (Collection of Spirits Paste), treating emaciation, wheezing, coughing, and fatigue. Although Qiongyu Gao uses fresh Dihuang crushed for juice and boiled with mulberry wood branches, containing retention within dispersion, it is no different from the dried form. Both Guben Wan and Jiling Gao use dried Dihuang, but Jiling Gao changes pills to paste, which is slightly superior to Guben Wan. *Yijian Fang* states: Men often suffer from Yin deficiency and should use Shudihuang (Prepared Rehmanniae Radix); women often suffer from blood heat and should use Shengdihuang (Raw Rehmanniae Radix). Yu Tun said: Shengdihuang cools blood, but may hinder digestion in those with weak Stomach Qi; Shudihuang tonifies blood, but may cause stagnation in those with excessive phlegm-fluids. Some say that wine-frying Shengdihuang does not harm the Stomach, and ginger-processing Shudihuang does not cause stagnation, yet one must carefully examine the depth of the patient's Yuan Qi (Primary Qi) and pathogenic factors before use. In cases of postpartum aversion to food and diarrhea, lower abdominal binding pain, consumptive disease, weak Spleen and Stomach, loose stools, excessive phlegm in chest and abdomen, unsmooth air pathways, and obstructed ascending and descending movements, this herb must be avoided. Dihuang from Zhejiang specializes in cooling blood and moistening dryness. For patients whose Yuan Qi is originally deficient, but due to heat-pathogen obstruction leading to a dry, scorched-black tongue, and constipation of both urine and stool, who cannot tolerate purgative methods, using this among heat-clearing herbs to unblock constipation is most excellent, as it possesses the function of moistening dryness without the drawback of being cloying. I observe: Although *Benjing* lists Dihuang in the Upper Grade, its actual nature is yin-soft, similar to a hypocrite. Like a villain hiding secrets inside while showing tolerance outside, all renowned experts rely on it as a premier herb for nourishing Yin and a divine pill for stopping bleeding. Even if used inappropriately, it can slightly clear excessive Qi, allowing temporary relief after ingestion. Unlike Renshen (Ginseng), whose nature belongs to Yangming and resembles a gentleman, where faults are known to all, doctors hesitate to use it, and patients dare not taste it. Only when critically ill and desperate do they use it, often resulting in death upon swallowing. Thus, everyone blames Renshen, unaware that this is caused by previous medication errors. Medicinal hazards occur frequently, none more so than Dihuang and Mendong (Ophiopogonis Radix), which are extremely yin-soft, remaining unaware of their error even until death. Therefore, I do not shy away from triviality and specifically highlight this for awareness.