the Five Phases (五行)
Wood, fire, earth, metal, and water: five linked stages that Chinese thinkers used to explain change in nature and in the body.
Preface to the Treatise on Cold Damage
Zhang Zhongjing, Treatise on Cold Damage and Miscellaneous Diseases, preface · c. 200–206 (within ten years of the start of the Jian'an era, 196)
[15]
夫天布五行以運萬類人禀五常以有五藏經絡府俞隂陽㑹通玄冥幽㣲變化難極
Heaven spreads out the Five Phases to keep all things moving. People receive the five constants, and so they have the five organs. The channels and the acupoints, and the ways yin and yang meet and flow together, are dark, deep, and subtle, and their changes are almost impossible to fathom.