金代 · 张元素创立 · 李杲发展出补土派
Jin dynasty · Founded by Zhang Yuansu · Developed by Li Gao into the Earth-supplementing branch
张元素（约1131–约1234）提出脏腑辨证与药物归经理论，强调「古今异轨」，主张根据脏腑虚实与药物归经用药。其弟子李杲进一步提出「内伤脾胃，百病由生」，形成补土派，成为易水学派最重要的分支。
Zhang Yuansu (c. 1131–c. 1234) developed visceral pattern differentiation and the theory of channel entry for medicinals, stressing that ancient and modern conditions differ. His disciple Li Gao further argued that internal damage to the spleen and stomach is the root of many diseases, forming the Earth-supplementing branch—the most influential offshoot of the Yishui school.
张元素（易州人）→ 李杲（东垣）。二人构成易水学派的核心传承线。
Zhang Yuansu (of Yizhou) → Li Gao (Dongyuan). The two form the core transmission line of the Yishui school.