Book 4; Thought 22

If souls continue to exist, how does the air contain them from eternity?- But how does the earth contain the bodies of those who have been buried from time so remote? For as here the mutation of these bodies after a certain continuance, whatever it may be, and their dissolution make room for other dead bodies; so the souls which are removed into the air after subsisting for some time are transmuted and diffused, and assume a fiery nature by being received into the seminal intelligence of the universe, and in this way make room for the fresh souls which come to dwell there.

And this is the answer which a man might give on the hypothesis of souls continuing to exist. But we must not only think of the number of bodies which are thus buried, but also of the number of animals which are daily eaten by us and the other animals. For what a number is consumed, and thus in a manner buried in the bodies of those who feed on them! And nevertheless this earth receives them by reason of the changes of these bodies into blood, and the transformations into the aerial or the fiery element.