Many terrible famines and plagues were caused by two grand wars against Japanese in the end of the sixteenth century and by the abnormally cold weather in the beginning of the seventeenth century. Especially, deficiency of immunity through famines made the death rate higher. The raging of famines and plagues in this period made the demographic size of Chosŏn dynasty smaller, and so people roved over the whole country and begged for food. Urgent relief policies of publishing of medical books were demanded. Knowledge of medicine and skill in it were introduced into Korea from the Yüan and Ming dynasties in the late Koryŏ period, and the early Chosŏn dynasty tried to establish the medical theory of her own. Problems, however, came up. There were contradictions and confusions between Yüan and Ming medical theories. The contemporary doctors had to solve these problems. First, Yang Yesu(楊禮壽), a doctor charged with Royal Hospital, solved these problems and wrote a medical book titled The Compact of Many Doctors' Skills and Theories (Ŭilim ch'walyo : 「醫林撮要」). Hŏ Chun, an apprentice of Yang, followed Yang's achievements and developed his own theory more systematically than his teacher's. Finally, accumulation of Hŏ's efforts produced in his sixties the great medical book, The Thesaurus of Doctors in Chosŏn (Tongŭi pogam : 「東醫寶鑑」). Tongŭi pogam has following characteristic features. First, it has stronger Taoistic character than any other medical book in the Chosŏn dynasty. In this period, a circle of scholars was formed, who were alienated from the orthodox Neo Confucianism, and leaned toward thoughts that did not conform to Confucianism. These scholars took part in writing The Thesaurus of Doctors in Chosŏn, and they and Hŏ exchanged visits with one another. Second, Hŏ Chun treated the humble social class of Chosŏn, and tried to enhance his social position. Third, he took positive steps to protect pregnant women and infants, because their body strength was weaker than other people's, and because famines and plagues struck them more fatally. As the result of these, demographic size decreased. The Government tried to diminish death rates of pregnant women and infants. Hŏ was sympathetic to these government policies and, above all, tried to increase effects of herb dispensary. Instead of expensive Chinese medicines, he used cheap Korea-born herbs for the poor. It lowered prices of medicines and enabled more people to take medicines. In the end of the sixteenth century and in the beginning of the seventeenth century, national project to publish and supply the medical books to alleviate the condition took its roots among the doctors in the provinces. As a result, the doctors in the provinces had augmentation in their skills and knowledge and wrote medical books for themselves. It can be said that these phenomena testify the popularization of medical knowledge that gave the doctors chances to grow up to the middle class in the late 18th century.