From the Bull "Exsultate Deo" of Eugene IV and the Council of
Its matter is wheat bread and wine from the vine, to which a very little water is added before the consecration. Water is added thus because it is believed, in accordance with the testimony of holy fathers and doctors of the church manifested long ago in disputation, that the Lord himself instituted this sacrament in wine mixed with water, and because it befits the representation of the Lord's passion. For the blessed pope Alexander, fifth after blessed Peter, says: "In the oblations of the sacraments which are offered to the Lord within the solemnities of masses, only bread and wine mixed with water are to be offered in sacrifice. There should not be offered in the chalice of the Lord either wine only or water only but both mixed together, because both blood and water are said to have flowed from Christ's side'; also because it is fitting to signify the effect of this sacrament, which is the union of the christian people with Christ. For, water signifies the people according to those words of the Apocalypse: many waters, many peoples. And Pope Julius, second after blessed Silvester, said: The chalice of the Lord, by a precept of the canons, should be offered mixed of wine and water, because we see that the people is understood in the water and the blood of Christ is manifested in the wine; hence when wine and water are mingled in the chalice, the people are made one with Christ and the mass of the faithful are linked and joined together with him in whom they believe. Since, therefore, both the holy Roman church taught by the most blessed apostles Peter and Paul and the other churches of Latins and Greeks, in which the lights of all sanctity and doctrine have shone brightly, have behaved in this way from the very beginning of the growing church and still do so, it seems very unfitting that any other region should differ from this universal and reasonable observance. We decree, therefore, that the Armenians should conform themselves with the whole christian world and that their priests shall mix a little water with the wine in the oblation of the chalice, as has been said.
The form of this sacrament are the words of the Saviour with which he effected this sacrament. A priest speaking in the person of Christ effects this sacrament. For, in virtue of those words, the substance of bread is changed into the body of Christ and the substance of wine into his blood. In such wise, however, that the whole Christ is contained both under the form of bread and under the form of wine, under any part of the consecrated host as well as after division of the consecrated wine, there is the whole Christ. (Emphasis supplied)
The effect of this sacrament, which is produced in the soul of one who receives it worthily, is the union of him or her with Christ. Since by grace a person is incorporated in Christ and is united with his members, the consequence is that grace is increased by this sacrament in those who receive it worthily, and that every effect that material food and drink produce for corporal life -- sustaining, increasing, repairing and delighting -- this sacrament works for spiritual life. For in it, as Pope Urban said, we recall the gracious memory of our Saviour, we are withdrawn from evil, we are strengthened in good and we receive an increase of virtues and graces.