Mass of Saint Gregory

The Mass of Saint Gregory is a subject in Roman Catholic art which first appears in the late Middle Ages and was still found in the Counter-Reformation. Pope Gregory I (c. 540-604) is shown saying Mass just as a vision of Christ as the Man of Sorrows has appeared on the altar in front of him, in response to the Pope's prayers for a sign to convince a doubter of the doctrine of transubstantiation.
History of the story and the image
The earliest version of the story is found in the 8th century biography of Gregory by Paul the Deacon, and was repeated in the 9th Century one by John the Deacon. In this version, the Pope was saying mass when a woman present started to laugh at the time of the Communion, saying to a companion that she could not believe the bread was Christ, as she herself had baked it. Gregory prayed for a sign, and the host turned into a bleeding finger.
In the popular 13th century compilation the Golden Legend...