The Fourth General Council of the Lateran, in 1215, defined that "the Body and Blood of Christ are truly contained in the Sacrament of the Altar by Transubstantiation." Transubstantiation is a changing across from one substance to another. A transcontinental railroad will take a person from New York to San Francisco but it does not change New York into San Francisco. Take the word "transformation." A carpenter can transform a log of wood into all kinds of furniture. He gives the wood another form or shape. In Transubstantiation it is a question not of another form or shape, but of another substance. Hydrogen and oxygen are two gaseous substances, but we know that they can be changed into the substance of water. So also, Transubstantiation changes the substance of bread into the Substance of the Body of Christ. When hydrogen and oxygen are changed into water they lose their previous form or gaseous appearance whereas the bread retains its previous appearance, the substance alone being changed. The word "Transubstantiation," therefore, is used by the Catholic Church to show that the substance of bread, which was present before the consecration, has been changed into the Substance of Our Lord's Body, although the appearance of bread still remains.

Q. A. Eucharist: Quizzes to a Street Preacher
Fr. Chas. M. Carty & Dr. L. Rumble, M.S.C.