The Yellow Emperor's Classic of Internal Medicine, specifically Chapter 39, explores the nature of pain. A dialogue between the Yellow Emperor and Qi Bo investigates the causes of various pains, attributing them to imbalances of qi (vital energy) and the influence of cold and heat on the body's meridians. Diagnosis is discussed through observation of color and palpation of the pulse. Finally, the text links different emotional states to specific qi disturbances, explaining how these emotional imbalances can manifest as various illnesses.