d that
the species of bread is lost, as when the continuity of its parts is
destroyed, and the taste, color, and other accidents are changed;
hence the body of Christ may not be made from such matter. But
sometimes there is not such corruption as to alter the species, but
merely disposition towards corruption, which a slight change in the
savor betrays, and from such bread the body of Christ may be made:
but he who does so, sins from irreverence towards the sacrament. And
because starch comes of corrupted wheat, it does not seem as if the
body of Christ could be made of the bread made therefrom, although
some hold the contrary.
_______________________

FOURTH ARTICLE [III, Q. 74, Art. 4]

Whether This Sacrament Ought to Be Made of Unleavened Bread?

Objection 1: It seems that this sacrament ought not to be made of
unleavened bread. Because in this sacrament we ought to imitate
Christ's institution. But Christ appears to have instituted this
sacrament in fermented bread, because, as we have read in Ex. 12, the
Jews, according to the Law, began to use unleavened bread on the day
of the Passover which is celebrated on the fourteenth day of the
moon; and Christ instituted this sacrament at the supper which He
celebrated "before the festival day of the Pasch" (John 13:1, 4).
Therefore we ought likewise to celebrate this sacrament with
fermented bread.

Obj. 2: Further, legal observances ought not to be continued in the
time of grace. But the use of unleavened bread was a ceremony of the
Law, as is clear from Ex. 12. Therefore we ought not to use
unfermented bread in this sacrament of grace.

Obj. 3: Further, as stated above (Q. 65, A. 1; Q. 73, A. 3), the
Eucharist is the sacrament of charity just as Baptism is the
sacrament of faith. But the fervor of charity is signified by
fermented bread, as is declared by the gloss on Matt. 13:33: "The
kingdom of heaven is like unto leaven," etc. Therefore this sacrament
ought to be made of leavened bread.

Obj. 4: Further, leavened or unleavened are mere accidents of bread,
which do not vary the species. But in the matter for the sacrament of
Baptism no difference is observed regarding the variation of the
accidents, as to whether it be salt or fresh, warm or cold water.
Therefore neither ought any distinction to be observed, as to whether
the bread be unleavened or leavened.

_On the contrary,_ According to the Decretals (Extra, De Celebr.
Miss.), a priest is punished "for