Chapter 18 — Part II: The Sacraments — The Holy Eucharist
Section 44. These very elements serve also somewhat to suggest to men the truth of the Real Presence of the body and blood of the Lord in the Sacrament. Observing, as we do, that bread and wine are every day changed by the power of nature into human flesh and blood, we are led the more easily by this analogy to believe that the substance of the bread and wine is changed, by the heavenly benediction, into the real flesh and real blood of Christ.