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[Harm] The nature of Ejiao (Donkey-hide Gelatin) is sticky and cloying; it should not be taken by those with weak stomachs who experience vomiting. It is also contraindicated for those with Spleen deficiency leading to indigestion.

[Benefit] Sweet, salty, and neutral in nature. It clears the Lungs, nourishes the Liver, tonifies the Kidney, and supplements Yin. It stops bleeding, removes blood stasis, dispels wind, and transforms phlegm.
Donkey skin primarily treats Wind pathogens and is effective in regulating excessive Wind pathogenic factors. Its black color corresponds to Water in the Five Elements, embodying the principle of using Water to control Heat and thereby extinguish Wind. It moistens dryness, calms asthma, promotes urination and bowel movements, regulates menstruation, and calms the fetus. It also treats diarrhea and dysentery; it is essential for cases of dysentery caused by summerheat injury or latent heat. It is particularly suitable for bloody dysentery during pregnancy. Generally, it is a crucial herb for tonifying Blood and body fluids, and serves as an important medicine for diseases of the Lung and Large Intestine.
Gelatin from black donkey skin has similar functions.
Huangming Jiao (Cow-hide Gelatin), which is gelatin made from cow skin, is sweet and neutral. It tonifies Yin, moistens dryness, and invigorates blood circulation. Its efficacy is similar to that of Ejiao and can be used as a substitute when necessary. Use cow-hide gelatin to tonify deficiency, and donkey-skin gelatin to dispel wind. When boiled together with scallion white, it can unblock the Large Intestine. For early-stage carbuncles and sores, taking four taels stewed in wine can prevent toxic pathogens from attacking inward.

[Processing] In Dong'e County, Shandong Province, there is the A Well located sixty li to the northeast. From the tenth month to the second or third month of the following year, black donkey skins are collected. They are soaked for four to five days until thoroughly permeated using pure Yang water from the Yelang Creek River, then de-haired, washed, and scraped clean. The skins are placed in a copper pot and boiled with the extreme Yin water from the A Well, stirred occasionally, with water frequently added until the mixture becomes extremely soft. Surface impurities and dregs are skimmed off. Once boiled to a clear consistency into a paste, it is held up to the light; true Ejiao appears amber-colored or glossy black like wall lacquer, has a fresh fragrance, lacks any leathery odor, does not soften in summer, and is best when aged. This constitutes genuine Ejiao.
Donkey-hide gelatin is made by soaking and boiling black donkey skins. Huangming Jiao is made by soaking and boiling yellow cow hides. Their odors are turbid and foul, lacking freshness. Modern commercial gelatins are often poorly manufactured and thus unsuitable for use. Current medical prescriptions sometimes stir-fry gelatin with flour until it forms beads to transform phlegm; stir-fry with clam shell powder to stop bleeding; or stir-fry with Polygoni Multiflori Caulis (or dissolve with child's urine) to mitigate its cloying nature. Genuine Ejiao possesses a descending and tranquilizing nature. For conditions where Heat in the Blood causes turbulent, reckless hemorrhage, various bleeding disorders will cease upon encountering this substance. Therefore, dissolving it in water is preferred. Stir-frying into beads may disrupt its natural properties. The A Well is fed by the Ji River. Using well water to boil gelatin demonstrates that stirring turbid water with it clarifies the water. Similarly, when ingested by humans, it descends through the diaphragm, disperses phlegm, and stops vomiting. This is because the waters of the Ji River are clear and heavy, possessing a descending nature, making it effective for treating blood stasis, turbidity, and rebellious phlegm.