Historical Chinese medical book. The Chinese medical tradition is based on the theory of a universal life force known as Chi. Chi manifests itself in the body as two complementary forces known as yin and yang. Chinese medicine dictates that yin and yang must be balanced to be able to restore the flow of Chi. Traditional Chinese treatments aim to restore the yin-yang balance to cure illness. Various techniques such as herbalism, acupuncture and T'ai-chi have evolved to restore yin-yang balance. Photographed in Korea.