The decadence of the early Middle Ages was due to the natural shifting of masses of population of this time, while the salvation of scientific and literary traditions was due to the one stable element in all these centuries--the Church. Far from Christianity inhibiting culture, it was the most important factor for its preservation, and it provided the best stimulus and incentive for its renewed development just as soon as the barbarous peoples were brought to a state of mind to appreciate it. Bearing this in mind, it is easier to understand the course of medical traditions through the Middle Ages, and especially in the earlier period, with regard to which our documents are comparatively scanty, and during which the disturbed conditions made medical developments impossible, and anything more than the preservation of the old authors out of the question. The torch of medical illumination lighted at the great Greek fires passes from people to people, never quenched, though often burning low because of unfavorable conditions, but sometimes with new fuel added to its flame by the contributions of genius. The early Christians took it up and kept it lighted, and, with the Jewish physicians, carried it through the troublous times of the end of the old order, and then passed it on for a while to the Arabs. Then, when favorable conditions had developed again, Christian schools and scholars gave it the opportunity to burn brightly for several centuries at the end of the Middle Ages. This medieval age is probably the most difficult period of medical history to understand properly, but it is worth while taking the trouble to follow out the thread of medical tradition from the Greeks to the Renaissance medical writers, who practically begin modern medicine for us. It is easy to understand that Christianity's influence on medicine, instead of hampering, was most favorable. The Founder of Christianity Himself had gone about healing the sick, and care for the ailing became a prominent feature of Christian work. One of the Evangelists, St. Luke, was a physician. It was the custom a generation ago, and even later, when the Higher Criticism became popular, to impugn the tradition as to St. Luke having been a physician, but this has all been undone, and Harnack's recent book, "Luke the Physician," makes it very clear that not only the Third Gospel, but also the Acts, could only have been written by a man thoroughly familiar with the Greek medical terms of his time, and who had surely had the advantage of a training in the medical sciences at Alexandria. This makes such an important link in medical traditions that a special chapter has been devoted to it in the Appendix.