A. First Way

60. Those who state that the sin is contracted because of infected flesh, which is sown in concupiscence [Bonaventure, Aquinas, Giles of Rome], say that the whole flesh of Mary was sanctified and thus what was assumed to form the body of Christ was sanctified before it was assumed, so that there was no infection there at the moment of the soul’s infusion.

61. But the argument against this is first that, if the blood of the blessed Virgin were what the body of Christ was formed from (according to Damascene ch.46), then consequently, since this blood was never animated with the soul of the whole body [sc. of the Virgin] or of any human being, it never contracted the stain from a sinful soul, and no reason for the stain can be assigned on the part of it nor can any sanctification be assigned for the body generated from it.

62. But if it be said that the active power that formed the body from the blood was infected in the parents, and so the generated body was infected - this does not seem true if the Holy Spirit immediately formed the body from that blood.

63. Further, it does not seem probable that there was corruption without generation of any kind; but if the sanctification and cleansing of the flesh were the corruption of the diseased quality and yet there was no generation of any other positive quality, then there was no generation of grace, because that flesh was not capable of sanctity.