urther, what is the term _wherefrom_ in every change exists
no longer, except in the potentiality of matter; e.g. when air is
changed into fire, the form of the air remains only in the
potentiality of matter; and in like fashion when what is white
becomes black. But in this sacrament the substance of the bread or of
the wine is the term _wherefrom,_ while the body or the blood of
Christ is the term "whereunto": for Ambrose says in De Officiis (De
Myster. ix): "Before the blessing it is called another species, after
the blessing the body of Christ is signified." Therefore, when the
consecration takes place, the substance of the bread or wine no
longer remains, unless perchance dissolved into its (original) matter.

Obj. 3: Further, one of two contradictories must be true. But this
proposition is false: "After the consecration the substance of the
bread or wine is something." Consequently, this is true: "The
substance of the bread or wine is nothing."

_On the contrary,_ Augustine says (Q. 83): "God is not the cause of
tending to nothing." But this sacrament is wrought by Divine power.
Therefore, in this sacrament the substance of the bread or wine is
not annihilated.

_I answer that,_ Because the substance of the bread and wine does not
remain in this sacrament, some, deeming that it is impossible for the
substance of the bread and wine to be changed into Christ's flesh and
blood, have maintained that by the consecration, the substance of the
bread and wine is either dissolved into the original matter, or that
it is annihilated.

Now the original matter into which mixed bodies can be dissolved is
the four elements. For dissolution cannot be made into primary
matter, so that a subject can exist without a form, since matter
cannot exist without a form. But since after the consecration nothing
remains under the sacramental species except the body and the blood
of Christ, it will be necessary to say that the elements into which
the substance of the bread and wine is dissolved, depart from thence
by local motion, which would be perceived by the senses. In like
manner also the substance of the bread or wine remains until the last
instant of the consecration; but in the last instant of the
consecration there is already present there the substance of the body
or blood of Christ, just as the form is already present in the last
instant of generation. Hence no instant can be assigned in which the
original matter can be there.