Council of Trent: Session 13
Chapter 4
On Transubstantiation.
And because that Christ, our Redeemer, declared that which He offered under the species of bread to be truly His own body, therefore has it ever been a firm belief in the Church of God, and this holy Synod doth now declare it anew, that, by the consecration of the bread and of the wine, a conversion is made of the whole substance of the bread into the substance of the body of Christ our Lord, and of the whole substance of the wine into the substance of His blood; which conversion is, by the holy Catholic Church, suitably and properly called Transubstantiation.
Chapter 5
On the cult and veneration to be shown to this most holy Sacrament.
Wherefore, there is no room left for doubt, that all the faithful of Christ may, according to the custom ever received in the Catholic Church, render in veneration the worship of latria, which is due to the true God, to this most holy sacrament. For not therefore is it the less to be adored on this account, that it was instituted by Christ, the Lord, in order to be received: for we believe that same God to be present therein, of whom the eternal Father, when introducing him into the world, says; And let all the angels of God adore him; whom the Magi falling down, adored; who, in fine, as the Scripture testifies, was adored by the apostles in Galilee.
The holy Synod declares, moreover, that very piously and religiously was this custom introduced into the Church, that this sublime and venerable sacrament be, with special veneration and solemnity, celebrated, every year, on a certain day, and that a festival; and that it be borne reverently and with honour in processions through the streets, and public places. For it is most just that there be certain appointed holy days, whereon all Christians may, with a special and unusual demonstration, testify that their minds are grateful and thankful to their common Lord and Redeemer for so ineffable and truly divine a benefit, whereby the victory and triumph of His death are represented. And so indeed did it behove victorious truth to celebrate a triumph over falsehood and heresy, that thus her adversaries, at the sight of so much splendour, and in the midst of so great joy of the universal Church, may either pine away weakened and broken; or, touched with shame and confounded, at length repent.
Chapter 6
On reserving the Sacrament of the sacred Eucharist, and bearing it to the Sick.
The custom of reserving the holy Eucharist in the sacrarium is so ancient, that even the age of the Council of Nicaea recognised that usage. Moreover, as to carrying the sacred Eucharist itself to the sick, and carefully reserving it for this purpose in churches, besides that it is exceedingly conformable to equity and reason, it is also found enjoined in numerous councils, and is a very ancient observance of the Catholic Church. Wherefore, this holy Synod ordains, that this salutary and necessary custom is to be by all means retained.