To resist the attacks of renewed heresies against the Holy Eucharist and to revive in the Church a zeal which had somewhat grown cold, the Holy Ghost inspired, at the beginning of the thirteenth century, the solemnity of Corpus Christi.
In 1208 the blessed Juliana of Mount Cornillon, near Liege, saw in a vision the full moon with an indentation indicating that a feast was missing in the liturgical cycle. The Eucharist, instituted on Maundy-Thursday, had not in effect been celebrated with all the desired pomp, the Church's thoughts being absorbed by the passion of the Saviour. It was thought that immediately after Paschaltide a feast with an octave should be established. As the Last Supper took place on Thursday, the Bishop of Liege instituted in 1246 this solemnity in his diocese on the Thursday which follows the octave of Pentecost. In 1264, Pope Urban IV extended this feast to the whole world. Let us venerate the Eucharist, the greatest of the miracles performed by the Holy Ghost.
Mass as on the day of the feast.
Cibavit eos ex adipe frumenti, alleluia: et de petra, melle saturavit eos, alleluia, alleluia, alleluia. * Exsultate Deo adjutorio nostro; jubilate Deo Jacob.
He fed them with the fat of wheat, alleluia; and filled them with honey out of the rock, alleluia, alleluia, alleluia. * Rejoice unto God our helper; sing aloud to the God of Jacob.
(Psalm 80:17,2 from the Introit of Mass)
Deus, qui nobis sub Sacramento mirabili passionis tuae memoriam reliquisti: tribue, quaesumus, ita nos Corporis et Sanguinis tui sacra mysteria venerari; ut redemptionis tuae fructum in nobis jugiter sentiamus.
O God, who in this wonderful sacrament has left us a memorial of Thy passion, grant us, we beseech Thee, so to venerate the sacred mysteries of Thy Body and Blood, that we may ever perceive within us the fruit of Thy redemption.
St Juliana of Liege: http://en.wikipedia.org/wiki/Juliana_of_Li%C3%A8ge