Chapter 18 — Part II: The Sacraments — The Holy Eucharist
Section 57. The words: This is the chalice of my blood, are to be understood to mean: This is my blood, which is contained in this chalice. The mention of the chalice made at the consecration of the blood is right and appropriate, inasmuch as the blood is the drink of the faithful, and this would not be sufficiently signified if it were not contained in some drinking vessel.