St. Ambrose was born at Trier (today in Germany) between 335 and 340. He became a lawyer and a Roman administrator in Milan. There he was chosen as bishop by popular acclamation, although he was only a catechumen. He thus received all the Sacraments of Initiation and the episcopate within one week. He died in Milan in 397. Ambrose, who may well be the first to refer to the Eucharistic Mystery as the Mass" (Ambrose, in Epistola, 20, 4 (PL, 16, 995), remarks, "I, however, remained at my task and began to offer the Mass"... Some would dispute this and say that he is merely speaking of the dismissal of the catechumens. An undisputed reference to the Eucharistic liturgy as "Mass" is found in Gregory of Tours (died 594), who writes of "celebrating daily the solemnity of the Mass"... , has left us two great works that deal with the Eucharist: the De Sacramentis and the De Mysteriis, both of them published around 390... (48) Now consider which is more excellent, the bread of angels [i.e., the manna] or the Flesh of Christ which is indeed the Body of life. That manna was from heaven, the latter from the Lord of the heavens; the former was subject to corruption if it was preserved for a second day, the latter foreign to all corruption so that whoever shall have piously tasted it will not be able to experience corruption. For the people of Israel water flowed from the rock; for you Blood flows from Christ. The water satisfied them for a while; Blood washes you for eternity. The Jew drinks and is thirsty again; when you drink you will not be able to thirst. The former was given as an image [in umbra]; the latter is given as the reality [in veritate]. (De Mysteriis)

The Hidden Manna: A Theology of the Eucharist
Fr. James T. O'Connor