19. The knowledge of the Arab world was shared through the crusades
Medical knowledge from the Islamic world filtered its way into the Christian societies of Europe, carried back from the Arab lands by the soldiers and pilgrims of the Crusades. It was substantial. Geoffrey Chaucer cited Arab physicians in his prologue to the Canterbury Tales. Many of the texts written by ancient Greeks were first encountered in Arabic translations, and the Islamic physicians expanded upon them, especially in areas such as anatomy. In the ancient Arab world, mosques served as centers where learning and the sharing of acquired knowledge was essential part of culture. Through the eighth century, Islamic thought included the belief that the cure for all human ailments had been provided by God.
In the early tenth century, a Persian physician, Muhammad ibn Zakariya al-Razi, developed what became the medical discipline of pediatrics, producing The Diseases of Children. He was the first physician to determine that fever was in fact a defense of the body against infection. He was also the first known to have written on the subject of immunology. The works of al-Razi and other Islamic physicians were influential in the training of physicians in Europe by the thirteenth century, though their work had little impact on the barber-surgeons and apothecaries who by and large treated the general public.