dynasty, a more intense investigation of domestic herbs took place: The result was the publication of numerous books on domestic herbs. Medical theories at this time were based on the medicine of Song dynasty, but prescriptions were based on the medicine of the Unified Silla period such as the medical text First Aid Prescriptions Using Native Ingredients or Hyangyak Gugeupbang (향약구급방), which was published in 1236. Other medical journals were published during this period like Introductory Guide to Medicine for the General Public or Jejungiphyobang (제중입효방). Medicine flourished in the period of the Joseon. For example, the first training system of nurses was instituted under King Taejong (1400–1418), while under the reign of King Sejong the Great (1418–1450) measures were adopted to promote the development of a variety of Korean medicinal ingredients. These efforts were systematized and published in the Hyangyak Jipseongbang (향약집성방, 1433), which was completed and included 703 Korean native medicines, providing an impetus to break away from dependence on Chinese medicine. The medical encyclopaedia named Classified Collection of Medical Prescriptions (醫方類聚, 의방유취), which included many classics from traditional chinese medicine, written by Kim Ye-mong (金禮蒙, 김예몽) and other Korean official doctors from 1443 to 1445, was regarded as one of the greatest medical texts of the 15th century. It included more than 50,000 prescriptions and incorporated 153 different Korean and Chinese texts, including the Concise Prescriptions of Royal Doctors (御醫撮要方, 어의촬요방) which was written by Choi Chong-jun (崔宗峻, 최종준) in 1226. Classified Collection of Medical Prescriptions has very important research value, because it keeps the contents of many ancient Korean and Chinese medical books that had been lost for a long time. After this, many books on medical specialties were published. There are three physicians from the Joseon Dynasty (1392–1910) who are generally credited with further development of traditional Korean medicine—Heo Jun, Saam, and Yi Je-ma. After the Japanese invasion in 1592, Dongeui Bogam (동의보감) was written by Heo Jun, the first of the major physicians. This work further integrated the Korean and Chinese medicine of its time and was influential to Chinese, Japanese and Vietnamese medicine. In the late period of Joseon, Yi Je-ma's “unique system of constitutional medicine” illustrates the “nature of” the medicine that has been traditionally developed in Korea by example. Medical treatments were based upon yin and yang principles “and the five elements." A warm treatment would treat a person who is