Lecture 2 : It focuses on introducing the basic theories in TCM. The Theory of Essence and Qi, the Theory of Yin and Yang and the Theory of Five Elements constitute the thinking method system of TCM, and they are a sum of processes and methods reflecting the rational recognition and understanding of TCM to life, health, disease and other major medical issues of human body. It specifically explains what the essence, yin and yang and five elements theories are and the application of these theories in TCM diagnosis and treatment. The last part introduces the meridians and collaterals of TCM and the running course of the twelve main meridians and their indications.