1261–1264 · Thomas Aquinas, Of God and His Creatures: An Annotated Translation (With some Abridgement) of the Summa contra Gentiles 4.63
This then is one reason for the accident of bread remaining, that something may be found permanent under the conversion. Another reason is this. If the substance of bread was converted into the Body of Christ, and the accidents of bread also passed away, there would not ensue upon such conversion the being of the Body of Christ in substance where the bread was before: for nothing would be left to refer the Body of Christ to that place. But since the dimensions of bread (quantitas dimensiva panis), whereby the bread held this particular place, remain after conversion, while the substance of bread is changed into the Body of Christ, the Body of Christ comes to be under the dimensions of bread, and in a manner to occupy the place of the bread by means of the said dimensions.