For it cannot be said that the
substance of the bread or wine is dissolved gradually into the
original matter, or that it successively quits the species, for if
this began to be done in the last instant of its consecration, then
at the one time under part of the host there would be the body of
Christ together with the substance of bread, which is contrary to
what has been said above (A. 2). But if this begin to come to pass
before the consecration, there will then be a time in which under one
part of the host there will be neither the substance of bread nor the
body of Christ, which is not fitting. They seem indeed to have taken
this into careful consideration, wherefore they formulated their
proposition with an alternative viz. that (the substance) may be
annihilated. But even this cannot stand, because no way can be
assigned whereby Christ's true body can begin to be in this
sacrament, except by the change of the substance of bread into it,
which change is excluded the moment we admit either annihilation of
the substance of the bread, or dissolution into the original matter.
Likewise no cause can be assigned for such dissolution or
annihilation, since the effect of the sacrament is signified by the
form: "This is My body." Hence it is clear that the aforesaid opinion
is false.

Reply Obj. 1: The substance of the bread or wine, after the
consecration, remains neither under the sacramental species, nor
elsewhere; yet it does not follow that it is annihilated; for it is
changed into the body of Christ; just as if the air, from which fire
is generated, be not there or elsewhere, it does not follow that it
is annihilated.

Reply Obj. 2: The form, which is the term _wherefrom,_ is not
changed into another form; but one form succeeds another in the
subject; and therefore the first form remains only in the
potentiality of matter. But here the substance of the bread is
changed into the body of Christ, as stated above. Hence the
conclusion does not follow.

Reply Obj. 3: Although after the consecration this proposition is
false: "The substance of the bread is something," still that into
which the substance of the bread is changed, is something, and
consequently the substance of the bread is not annihilated.
_______________________

FOURTH ARTICLE [III, Q. 75, Art. 4]

Whether Bread Can Be Converted into the Body of Christ?

Objection 1: It seems that bread cannot be converted into the body of
Christ. For conversion is