THE second great stream which carried Greek medicine to modern days runs through the Eastern Empire. Between the third century and the fall of Constantinople there was a continuous series of Byzantine physicians whose inspiration was largely derived from the old Greek sources. The most distinguished of these was Oribasius, a voluminous compiler, a native of Pergamon and so close a follower of his great townsman that he has been called "Galen's ape." He left many works, an edition of which was edited by Bussemaker and Daremberg. Many facts relating to the older writers are recorded in his writings. He was a contemporary, friend as well as the physician, of the Emperor Julian, for whom he prepared an encyclopaedia of the medical sciences. Other important Byzantine writers were Aetius and Alexander of Tralles, both of whom were strongly under the influence of Galen and Hippocrates. Their materia medica was based largely upon Dioscorides. From Byzantium we have the earliest known complete medical manuscript, dating from the fifth century--a work of Dioscorides--one of the most beautiful in existence. It was prepared for Anicia Juliana, daughter of the Emperor of the East, and is now one of the great treasures of the Imperial Library at Vienna.(9) From those early centuries till the fall of Constantinople there is very little of interest medically. A few names stand out prominently, but it is mainly a blank period in our records. Perhaps one man may be mentioned, as he had a great influence on later ages--Actuarius, who lived about 1300, and whose book on the urine laid the foundation of much of the popular uroscopy and water-casting that had such a vogue in the sixteenth and seventeenth centuries. His work on the subject passed through a dozen Latin editions, but is best studied in Ideler's "Physici et medici Graeci minores" (Berlin, 1841). (9) It has been reproduced by Seatone de Vries, Leyden, 1905, Codices graeci et latini photographice depicti, Vol. X. The Byzantine stream of Greek medicine had dwindled to a very tiny rill when the fall of Constantinople (1453) dispersed to the West many Greek scholars and many precious manuscripts. ARABIAN MEDICINE THE third and by far the strongest branch of the Greek river reached the West after a remarkable and meandering course. The map before you shows the distribution of the Graeco-Roman Christian world at the beginning of the seventh century. You will notice that Christianity had extended far eastwards, almost to China. Most of those eastern Christians were Nestorians and one of their important centres was Edessa, whose school of learning became so celebrated. Here in the fifth century was built one of the most celebrated hospitals of antiquity.