by nature, the conception is
not formed; but from a certain secretion of the pure blood which by a
process of elimination is prepared for conception, being, as it were,
more pure and more perfect than the rest of the blood. Nevertheless,
it is tainted with the impurity of lust in the conception of other
men: inasmuch as by sexual intercourse this blood is drawn to a place
apt for conception. This, however, did not take place in Christ's
conception: because this blood was brought together in the Virgin's
womb and fashioned into a child by the operation of the Holy Ghost.
Therefore is Christ's body said to be "formed of the most chaste and
purest blood of the Virgin."
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SIXTH ARTICLE [III, Q. 31, Art. 6]

Whether Christ's Body Was in Adam and the Other Patriarchs, As to
Something Signate?

Objection 1: It would seem that Christ's body was in Adam and the
patriarchs as to something signate. For Augustine says (Gen. ad lit.
x) that the flesh of Christ was in Adam and Abraham "by way of a
bodily substance." But bodily substance is something signate.
Therefore Christ's flesh was in Adam, Abraham, and the other
patriarchs, according to something signate.

Obj. 2: Further, it is said (Rom. 1:3) that Christ "was made . . . of
the seed of David according to the flesh." But the seed of David was
something signate in him. Therefore Christ was in David, according to
something signate, and for the same reason in the other patriarchs.

Obj. 3: Further, the human race is Christ's kindred, inasmuch as He
took flesh therefrom. But if that flesh were not something signate in
Adam, the human race, which is descended from Adam, would seem to
have no kindred with Christ: but rather with those other things from
which the matter of His flesh was taken. Therefore it seems that
Christ's flesh was in Adam and the other patriarchs according to
something signate.

_On the contrary,_ Augustine says (Gen. ad lit. x) that in whatever
way Christ was in Adam and Abraham, other men were there also; but
not conversely. But other men were not in Adam and Abraham by way of
some signate matter, but only according to origin, as stated in the
First Part (Q. 119, A. 1, A. 2, ad 4). Therefore neither was Christ
in Adam and Abraham according to something signate; and, for the same
reason, neither was He in the other patriarchs.

_I answer that,_ As stated above (A. 5, ad 1), the matter of Christ's
body was not the flesh and bones