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Fresh Rehmanniae Radix (Xian Dihuang): Its nature is cold, with a slightly bitter and sweet taste. It is most effective in clearing heat, cooling blood, resolving blood stasis, and generating new blood. It treats hemorrhage due to reckless bleeding from blood-heat, such as hematemesis (vomiting blood), epistaxis (nosebleed), and bleeding from the intestines or bladder due to heat. It contains iron substances; therefore, it turns black when sun-dried or steamed. Its ability to generate blood and cool blood also relies on the iron substances it contains.

Dried Rehmanniae Radix (Gan Dihuang) (i.e., Sheng Dihuang sold in pharmacies): After being dried by sun exposure, its nature becomes cool rather than cold. It generates blood vessels, benefits essence and marrow, improves hearing and vision, and treats bone-steaming tidal fever and internal heat generated by Kidney deficiency.

Prepared Rehmanniae Radix (Shu Dihuang) (made by steaming and drying fresh Rehmanniae Radix repeatedly with wine): Its nature is slightly warm, sweet without bitterness. It is the primary herb for nourishing Yin and tonifying the Kidney. It treats fever due to Yin deficiency, wheezing caused by Yin deficiency failing to grasp Qi, consumptive cough, edema resulting from the Kidney's failure to filter water leading to scanty urination, and deficiency damage to the Yin aspect of various Zang-Fu organs. Prepared Rehmanniae Radix can tonify all these conditions.

[Attached Cases] An elderly woman surnamed Li in the neighboring village, aged seventy, suffered severely from exhaustion-induced wheezing and had not been able to lie down and sleep for ten years. She was instructed to decoct Prepared Rehmanniae Radix daily and drink it as tea. Within a few days, she was able to lie down and sleep peacefully. Her family members were extremely frightened, believing that such a change from her usual state might be an ill omen, unaware that it indicated the recovery from illness.

The son of Mr. Hou, five years old, developed slow convulsions (Man Jing) due to excessive administration of cooling and purgative medicines. He presented with cold-stomach vomiting and diarrhea, frequent convulsions, mental confusion, upward deviation of the eyes, and appeared critical. A prescription was formulated using Prepared Rehmanniae Radix (2 liang), raw Dioscoreae Rhizoma (1 liang), Dried Zingiberis Rhizoma, Prepared Aconiti Lateralis Radix, and Cinnamomi Cortex (each 2 qian), cleaned Corni Fructus, and wild Codonopsis Radix (each 3 qian). The herbs were decocted to yield one and a half cups of liquid, which was administered slowly while warm. The vomiting, diarrhea, and convulsions ceased, and his spirit revived, though he showed signs of irritability. Dried Zingiberis Rhizoma was then removed, and raw Paeoniae Radix Alba (4 qian) was added. After one more dose, he fully recovered.

A boy, aged fourteen or fifteen, had passed ten days since the onset of Cold Damage (Shanghan). He suffered from incessant loose stools, severe palpitations, and a feeling of inability to sustain himself. His pulse beat seven times per respiration and felt empty upon pressure. Physicians declined to treat him. I prescribed Prepared Rehmanniae Radix, raw Dioscoreae Rhizoma, and raw Paeoniae Radix Alba (each 1 liang), Talcum (8 qian), and Glycyrrhizae Radix et Rhizoma (5 qian). Decocted into a large bowl, it was administered slowly while warm. He consumed the entire dose and recovered.

Reviewing these cases, Feng’s assertion that Rehmannia greatly tonifies the primal Qi of the Kidney is not baseless. Generally, Yin guards Yang, and Blood complements Qi. Rehmannia excels at nourishing Yin and nourishing Blood. When taken in large doses to ensure sufficient Yin and Blood, the body's primal Yang Qi will naturally not rise excessively or sink downward.

Using Prepared Rehmanniae Radix to treat Cold-Warm diseases is often criticized by physicians. However, in cases where true Yin is severely deficient and cannot withstand the heat of external pathogens, boldly adding Prepared Rehmanniae Radix to formulas treating Cold-Warm diseases to nourish true Yin can often save lives instantly. I once treated a young maiden who was constitutionally weak. After five or six days of Warm Disease, she suffered severe phlegm-wheezing. Treatment with Xiao Qing Long Tang (Minor Green Dragon Decoction) from *Jin Gui Yao Lue* plus Gypsum (Shi Gao) stopped the wheezing after one dose. At 8 PM, she slept peacefully through the night. In the Yin hour (3–5 AM), the wheezing recurred, less severely than before, but she appeared mentally vague and experienced palpitations. Re-examination of the pulse revealed it floating like hemp seeds on water, indistinguishable in rate, and vanishing upon pressure, indicating impending collapse. There was no time to fetch medicine. Fortunately, I had purchased some raw Dioscoreae Rhizoma earlier. It was quickly decocted and administered, leading to slight improvement. By this time, a prescription had already been written for pharmacy pickup: Prepared Rehmanniae Radix (4 liang), raw Dioscoreae Rhizoma (1 liang), and wild Codonopsis Radix (5 qian). However, the local pharmacy had no wild Codonopsis Radix, nor any other Ginseng species. Going elsewhere risked delay. Thus, I simply decocted Prepared Rehmanniae Radix and Dioscoreae Rhizoma for her to drink. Her condition improved significantly. Over the course of one day, three doses according to the original formula were administered consecutively, resulting in full recovery.

Note: This case originally required my formulated Lai Fu Tang, which heavily uses Corni Fructus to secure collapsing Qi. At that time, I was young, and the formula had not yet been devised, so I did not know to use heavy doses of Corni Fructus. From morning to evening, she consumed twelve liang of Prepared Rehmanniae Radix, which successfully saved this critical case. The efficacy of Prepared Rehmanniae Radix is indeed magnificent. Furthermore, the initial error in this case was failing to administer tonic herbs immediately after Xiao Qing Long Tang. After this experience, whenever I encounter patients suitable for Xiao Qing Long Tang but with a slightly weak pulse, I follow the decoction with tonic herbs. If I add Ginseng, fearing its heat, I increase the dosage of Gypsum.

*Zhang Shi Ba Zhen*, Zhao’s *Yi Guan*, and *Feng Shi Jin Nang* all favor heavy use of Prepared Rehmanniae Radix, even in external contraction cases. Their statements are indeed biased. However, they only wrote this after repeated clinical success. Zhang’s book records a case of an elderly man with Cold Damage who shivered but had no sweat. The next day, just as sweating was expected, a large dose of Ba Wei Di Huang Wan (Eight-Ingredient Rehmannia Pill) was given to assist sweating. After ingestion, profuse sweating occurred. Hours later, the whole body cooled, breath became faint, and sweating continued. Mental state was drowsy. Another dose of the original formula stopped the sweating and restored mental clarity. Using the same herb to induce and then stop sweating demonstrates profound skill. Zhao’s book claims Liu Wei Di Huang Wan (Six-Ingredient Rehmannia Pill) can clear excess heat in Cold-Warm diseases, inviting criticism. Yet, his words are not entirely invalid. Recalling the Cold-Warm epidemics during the Yi You and Bing Xu years, after heat entered the Yangming Fu organs, cases treated with clearing and resolving formulas supplemented with heavy doses of Prepared Rehmanniae Radix to nourish Yin all recovered. This was due to specific environmental factors and should not be codified as a fixed rule.

Additionally, Feng’s Materia Medica states that Prepared Rehmanniae Radix greatly tonifies the primal Qi of the Kidney, which is an accurate view. For lower Jiao deficiency with loose stools unresponsive to other drugs, single-use of Prepared Rehmanniae Radix can stop diarrhea. However, it must be used in large doses (four to five liang daily), decocted into a thick liquid. It does not cause chest tightness when used in large amounts (small amounts do cause tightness); small doses are ineffective. Chen Xiuyuan dismisses it entirely, deeming it unusable, showing a lack of understanding of Prepared Rehmanniae Radix. After Cold-Warm diseases transmit inward, if the lower Jiao is severely depleted, external pathogens often directly target the lower Jiao causing diarrhea, which cannot be cured without heavy doses of Prepared Rehmanniae Radix. In autumn of the Gui Si year, a thirty-year-old woman contracted a Warm Disease. After ten days, her condition became critical, and she was about to be carried out. A neighbor, Mr. Jia, knowing I practiced medicine, invited me to examine her. She suffered from day-and-night diarrhea, unconsciousness, unresponsiveness to calls, and a rapid pulse (seven beats per respiration) that vanished upon pressure. I prescribed Prepared Rehmanniae Radix (2 liang), raw Dioscoreae Rhizoma and raw Paeoniae Radix Alba (each 1 liang), and Glycyrrhizae Radix et Rhizoma (3 qian). Decocted into a large bowl, it was administered slowly while warm. She consumed the entire dose and recovered.