In 610 Chao Yuanfang，an imperial court physician, discovered that some diseases were epidemic and infectious. He thought they were triggered by so-called “epidemic pathogens”, along with abnormal climatic factors. He was the predecessor to the later theory of warm-disease in the Ming and Qing dynasties (1368-1911). He also developed etiology and symptomatology in his book Zhu Bing Yuan Hou Lun (Treatise on Causes and Symptoms of Diseases), where he discussed the causes and symptoms of diseases in various branches of medicine, such as internal medicine, external medicine, gynecology , pediatrics, stomatology , bone disorders and traumatology.