In his commentary on Aristotle’s Physics,
Aquinas writes of natural minima that,
“although a body,
considered mathematically,
is divisible to infinity,
the natural body is not divisible to infinity.
For in a mathematical body nothing but quantity is considered.
And in this there is nothing repugnant to division to infinity.
But in a natural body the form also is considered,
which form requires a determinate quantity and also other accidents.
Whence it is not possible for quantity to be found in the species of flesh except as determined within some termini.”
https://en.wikipedia.org/wiki/Minima_naturalia