Xú Yánzuò 徐延祚 (zì Língchén 齡臣), late-Qīng physician of late nineteenth-century Beijing (fl. 1860s–1890s by internal evidence in KR3eq060). Originally trained as a Confucian scholar; abandoned the examination track and shifted to medicine. Settled in Beijing for over twenty years of clinical practice, becoming one of the principal northern (Beijing) clinical-theoretical synthesizers of the late-Qīng. Author of the Yī cuì jīng yán 醫粹精言 (KR3eq060, preface 1896) — a four-juǎn synthesis of twenty years’ Beijing practice. Native province likely Anhui (the prefacer Máo Zéyào 毛澤曜 of Wǎnjiāng 皖江 / Anhui calls him “wú yǒu” 吾友). Not in CBDB.