Q. 878.  How do we know that it is possible to change one substance into another?  A. We know that it is possible to change one substance into another, because (1) God changed water into blood during the plagues of Egypt; (2) Christ changed water into wine at the marriage of Cana; (3) Our own food is daily changed into the substance of our flesh and blood; and what God does gradually, He can also do instantly by an act of His will.

Q. 879.  Are these changes exactly the same as the changes that take place in the Holy Eucharist?  A. These changes are not exactly the same as the changes that take place in the Holy Eucharist, for in these changes the appearance also is changed, but in the Holy Eucharist only the substance is changed while the appearance remains the same.

Q. 880.  How do we show that Christ did change bread and wine into the substance of His body and blood?  A. We show that Christ did change bread and wine into the substance of His body and blood:  (1) From the words by which He promised the Holy Eucharist; (2) From the words by which He instituted the Holy Eucharist; (3) From the constant use of the Holy Eucharist in the Church since the time of the Apostles; (4) From the impossibility of denying the Real Presence in the Holy Eucharist, without likewise denying all that Christ has taught and done; for we have stronger proofs for the Holy Eucharist than for any other Christian truth.

Q. 881. {243} Is Jesus Christ whole and entire both under the form of bread and under the form of wine?  A. Jesus Christ is whole and entire both under the form of bread and under the form of wine.

Q. 882.  How do we know that under the appearance of bread we receive also Christ’s blood; and under the appearance of wine we receive also Christ’s body?  A. We know that under the appearance of bread we receive also Christ’s blood, and under the appearance of wine we receive also Christ’s body; because in the Holy Eucharist we receive the living body of Our Lord, and a living body cannot exist without blood, nor can living blood exist without a body.

Q. 883.  Is Jesus Christ present whole and entire in the smallest portion of the Holy Eucharist, under the form of either bread or wine?  A. Jesus Christ is present whole and entire in the smallest portion of the Holy Eucharist under the form of either bread or wine; for His body in the Eucharist is in a glorified state, and as it partakes of the character of a spiritual substance, it requires no definite size or shape.

Q. 884. {244} Did anything remain of the bread and wine after their substance had been changed into the substance of the body and blood of our Lord?  A. After the substance of the bread and wine had been changed into the substance of the body and blood of Our Lord, there remained only the appearances of bread and wine.

Q. 885. {245} What do you mean by the appearances of bread and wine?  A. By the appearances of bread and wine I mean the figure, the color, the taste, and whatever appears to the senses.