The Catechism of the Council of Trent
*Form To Be Used In The Consecration Of The Bread
*
We are then taught by the holy Evangelists, Matthew and Luke, and also by the Apostle, that the form consists of these words: This is my body; for it is written: Whilst they were at supper, Jesus took bread, and blessed it, and brake, and gave to his disciples, and said:
Take and eat, This is my body.
This form of consecration having been observed by Christ the Lord has been always used by the Catholic Church. The testimonies of the Fathers, the enumeration of which would be endless, and also the decree of the Council of Florence, which is well known and accessible to all, must here be omitted, especially as the knowledge which they convey may be obtained from these words of the Saviour: Do this for a commemoration of me. For what the Lord enjoined was not only what He had done, but also what he had said; and especially is this true, since the words were uttered not only to signify, but also to accomplish.
That these words constitute the form is easily proved from reason also. The form is that which signifies what is accomplished in this Sacrament; but as the preceding words signify and declare what takes place in the Eucharist, that is, the conversion of the bread into the true body of our Lord, it therefore follows that these very words constitute the form. In this sense may be understood the words of the Evangelist: He blessed; for they seem equivalent to this: Taking bread, he blessed it, saying: “This is my body”.
*Not All The Words Used Are Essential
*
Although in the Evangelist the words, Take and eat, precede the words (This is my body), they evidently express the use only, not the consecration, of the matter. Wherefore, while they are not necessary to the consecration of the Sacrament, they are by all means to be pronounced by the priest, as is also the conjunction for in the consecration of the body and blood. But they are not necessary to the validity of the Sacrament, otherwise it would follow that, if this Sacrament were not to be administered to anyone, it should not, or indeed could not, be consecrated; whereas,
no one can lawfully doubt that the priest, by pronouncing the words of our Lord according to the institution and practice of the Church, truly consecrates the proper matter of the bread, even though it should afterwards never be administered.
*Form To Be Used In The Consecration Of The Wine
*
With regard lo the consecration of the wine, which is the other element of this Sacrament, the priest, for the reason we have already assigned, ought of necessity to be well acquainted with, and well understand its form. We are then firmly to believe that it consists in the following words:
This is the chalice of my blood, of the new and eternal testament, the mystery of faith, which shall be shed for you and for many, to the remission of sins. Of these words the greater part are taken from Scripture; but some have been preserved in the Church from Apostolic tradition.
Thus the words, this is the chalice, are found in St. Luke and in the Apostle; but the words that immediately follow, of my blood, or my blood of the new testament, which shall be shed for you and for many to the remission of sins, are found partly in St. Luke and partly in St. Matthew. But the words, eternal, and the mystery of faith, have been taught us by holy tradition, the interpreter and keeper of Catholic truth.
Concerning this form no one can doubt, if he here also attend to what has been already said about the form used in the consecration of the bread. The form to be used (in the consecration) of this element, evidently consists of those words which signify that the substance of the wine is changed into the blood of our Lord. since, therefore, the words already cited clearly declare this, it is plain that no other words constitute the form.
Source:
cin.org/users/james/ebooks/master/trent/tsacr-e.htm
St Thomas Aquinas teaches the same:
newadvent.org/summa/4078.htm