The earliest medical book in China was the Yellow Emperor's Internal Classic. The Yellow Emperor's Internal Classic was one of the ancient medical classics in China and was known as the Holy Bible of Chinese Medicine. It was a comprehensive book on human biology, pharmacology, treatment, psychology, etc. It mainly talked about the internal operating mechanism of the human body, the occurrence and treatment of diseases, and so on. The Yellow Emperor's Internal Classics believed that the physiological and pathological changes of human beings were caused by changes in the internal and external environment, and the internal operation mechanism of the human body was composed of five elements: spirit, qi, blood, yin, and yang. Therefore, the method of treating human diseases was to adjust the operation of these five elements to achieve the purpose of curing diseases.