Zhū Zhènhēng 朱震亨 (zì Yànxiū 彥修, hào Dānxī 丹溪, 1281–1358), the fourth and last of the canonical JīnYuán “Four Masters” and founder of the Yīn-deficiency school (滋陰派) of Chinese medicine. Native of Wūshāng 烏傷 (modern Yìwū, Zhèjiāng); known as Dānxī wēng 丹溪翁 (the Old Man of the Cinnabar-Stream, after his home village). Originally a Confucian scholar, disciple of the Neo-Confucian Xǔ Qiān 許謙. After his mother’s illness left him concerned about medical knowledge, took up medical study in midlife. Initially studied the Héjì jú fāng commercial-formulary tradition; recognized the limitations of “ancient prescriptions for modern diseases” and traveled extensively through Jiāngnán seeking a teacher of the classical-textual tradition; finally apprenticed with Luō Zhītì 羅知悌 (a Tàiwú 太無 disciple in Hángzhōu, transmitting the Liú Wánsù school via Jīngshān 荊山 fútúshī 浮屠師), who only after Zhū’s tenfold visit-and-wait accepted him as a disciple. Major works: Gézhì yúlùn 格致餘論 (KR3e0060, 1 juan, doctrinal manifesto); Júfāng fāhuī 局方發揮 (KR3e0061, programmatic critique of the Héjì jú fāng); Běncǎo yǎnyì bǔyí 本草衍義補遺 (TBD); Jīnguì gōuxuán 金匱鉤玄 (a Jīnguì commentary). Doctrinal contribution: the yáng is always in surplus, the yīn is always deficient (陽常有餘陰常不足) — combined with strong moral admonitions against alcohol-and-sexual-excess and the development of yīn-tonifying / fire-clearing prescriptions. Dài Liáng’s Jiǔ líng shānfáng jí contains the principal contemporary biography (Dānxī wēng zhuàn).