〔害〕胶性粘腻，胃弱作呕吐者勿服。脾虚食不消者，亦忌之。
〔利〕甘咸平，清肺养肝，滋肾补阴，止血去瘀，除风化痰。
驴皮主风，善理风淫。取其乌色属水，以制热则息风之义。润燥定喘，利大小肠，调经安胎
，又兼治利，伤暑伏热成痢者必用。妊娠血痢尤宜。大抵补血与液，为肺、大肠要药。
乌驴皮胶。功用略同。
黄明胶，即牛皮胶。甘平补阴，润燥活血，功同阿胶，可以权代。补虚用牛皮胶，去风
用驴
皮胶，同葱白煮服，可通大肠，痈疽初起，酒炖分服四两，则毒不内攻。
〔修治〕山东东阿县，东北六十里有阿井。自十月至二三月，收取乌驴皮。用野狼溪河纯
阳水
，浸四五日透，去毛洗刮洁净，入铜锅内，用阿井至阴之水熬煮，时时搅之，恒添水至极烂
。提去浮面渣秽，待极清熬成膏，对光明透照，如琥珀色或光如壁漆黑色气味清香，并无
皮臭臊气，夏月亦不温软，陈者良，此真阿胶也。
驴皮胶，取乌驴皮，浸消熬胶。黄明胶，用黄牛皮，浸消熬膏。其气浊臭，而不清香。
今市中胶物，制作不精，故不堪用。今方法用面炒成珠，化痰，蛤粉炒止血，蒲黄炒或
童便
和化，以解其气。如真阿胶，得趋下至静之性，凡血热则沸郁妄行，诸见血症，遇此即止。
故用水溶化为佳。炒珠，恐乱其性也。井乃济水所注，取井水煮胶，用搅浊水则清，故人服
之，下膈疏痰止呕，盖济水清而重，其性趋下，故治瘀浊及上逆之痰也。
【危害】阿胶性质粘腻，脾胃虚弱、容易呕吐的人不要服用。脾虚导致食物不消化的人，也应禁忌服用。
【功效】味甘、咸，性平。能清肺、养肝、滋肾、补阴，具有止血、祛瘀、除风、化痰的作用。
驴皮主治风邪，善于调理风邪过盛（风淫）的病症。取其黑色对应五行中的水，以水制热从而平息风邪的道理。能润燥定喘，通利大小肠，调和月经、安胎，又兼治腹泻痢疾，因伤暑或伏热导致痢疾者必须使用。妊娠期间患血痢尤为适宜。大体上，阿胶是补血和补津液的要药，也是治疗肺和大肠疾病的关键药物。
乌驴皮胶的功效大致相同。
黄明胶，即牛皮胶。味甘，性平，能补阴、润燥、活血，功效与阿胶相同，可以酌情替代。补虚损用牛皮胶，祛风邪用驴皮胶；若与葱白同煮服用，可通利大肠；痈疽初起时，用酒炖服四两，则毒邪不会内攻入里。
【炮制方法】山东东阿县东北六十里有阿井。从十月到二三月期间，采集乌驴皮。用野狼溪河的纯阳之水浸泡四五日，直至透心，去毛后洗净刮干净，放入铜锅中，用阿井的至阴之水熬煮，不时搅拌，经常加水直到熬至极烂。撇去浮面的渣滓污秽，待熬得极清后制成膏状，对着光亮透视，呈琥珀色或像壁漆一样黑亮，气味清香，没有皮革的腥臊气，夏季也不变软，陈久的为佳，这才是真正的阿胶。
驴皮胶，取乌驴皮浸泡消解后熬胶。黄明胶，用黄牛皮浸泡消解后熬膏。它们的气味浑浊发臭，并不清香。如今市面上的胶类制品，制作不精细，所以不堪使用。现在医方中常用面炒成珠状，用于化痰；用蛤粉炒用于止血；或用蒲黄炒，或用童便烊化，以解除其粘滞之气。如果是真正的阿胶，具有趋下、至静的特性，凡是血热导致的沸腾郁结、妄行出血，各种血症遇到它就能停止。因此用水溶化服用为佳。炒成珠状，恐怕会扰乱其药性。阿井是济水注入的地方，取井水煮胶，用它来搅动浊水可使水变清，所以人服用后，能下行膈间、疏泄痰饮、止呕，这是因为济水清澈且沉重，其性质趋下，所以能治疗瘀浊及上逆的痰饮。
[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.