The particle of the Eucharistic bread sent by the bishop of Rome to the bishops of other churches as a symbol of unity and intercommunion. According to Eusebius this custom was already known to Irenaeus as a longstanding tradition (Hist. eccl. 5.24.16; Die griechischen christlichen Schriftsteller der ersten drei Jahrhunderte, 9.1:497). In the 4th century the Council of Laodicea forbade sending the Eucharist abroad. In Rome, however, at the time of Innocent I (402–417), acolytes brought the fermentum to the priests of the titular churches every Sunday. This too was a symbol of the unity between the bishop and his priests. For the same reason, the officiating priest, who represented the pope at the stational Mass, also received the fermentum. When this custom finally fell into disuse, every priest nonetheless continued to drop a particle of consecrated Host into the chalice at the commingling, but the Host was the one consecrated in the same Mass.
Bibliography: j. a. jungmann, The Mass of the Roman Rite, tr. f. a. brunner, 2 v. (New York 1951–55) 2:312–313; "Fermentum …," Colligere fragmenta: Festschrift Alban Dold, ed. b. fischer and v. fiala (Beuron 1952) 185–190.
[j. p. de jong]