It has been suggested that this exclusion of monks and religious from the study of medicine by Church ordinance practically shut out all the clerics, that is, all the educated men of the medieval period, from the medical profession. Any such idea, however, could only have occurred to one who does not realize that at any given time there are only a comparatively few religious and a great many secular clergymen. Practically all those who could read and write in the Middle Ages were known as clerks, that is clerics, and were under the protection of the Church, most of them indeed receiving minor orders, and if all the clergy were to have been excluded from the medical profession this contention would be true.
So far is it from the truth, however, that a number of the great physicians and surgeons of the thirteenth and fourteenth centuries belonged to the clerical orders, not a few of them were priests and some of the greatest of them, like Theodoric, were actually bishops. It was only the religious, that is the men who had specially devoted their lives to monasticism, who were forbidden to take up the study of medicine because it did not comport with their monastic vocation.
James J. Walsh, The Popes and Science (1908)