XXX. A brief examination of the construction of our bodies from a medical point of view.
32 For we say that those things are alive which spring up and grow, and no one would deny that all things that participate in life and natural motion are animate, yet at the same time one cannot say that such life partakes of a perfect soul—for though a certain animate operation exists in plants, it does not attain to the motions of sense; and on the other hand, though a certain further animate power exists in the brutes, neither does this attain perfection, since it does not contain in itself the grace of reason and intelligence.
33. And even so we say that the true and perfect soul is the human soul, recognized by every operation; and anything else that shares in life we call animate by a sort of customary misuse of language, because in these cases the soul does not exist in a perfect condition, but only certain parts of the operation of the soul, which in man also (according to Moses' mystical account of man's origin) we learn to have accrued when he made himself like this sensuous world. Thus Paul, advising those who were able to hear him to lay hold on perfection, indicates also the mode in which they may attain that object, telling them that they must “put off the old man,” and put on the man “which is renewed after the image of Him that created him.”
34. Now may we all return to that Divine grace in which God at the first created man, when He said, “Let us make man in our image and likeness”; to Whom be glory and might for ever and ever. Amen.
Source: On the Making of Man (New Advent)