We now pass to the opinions of (Zeno and the other Stoic)
philosophers,[61] who assert that two bodies which make up a mixture
mutually interpenetrate each other totally. They support this view
by observing that when the bodies interpenetrate totally, they are
divided without the occurrence of a continuous division (which would
make their molecules lose their magnitude). Indeed, perspiration
issues from the human body without its being divided or riddled with
holes. To this it may be objected that nature may have endowed our
body with a disposition to permit perspiration to issue easily. To
this (the Stoics) answer that certain substances (like ivory[62]),
which when worked into thin sheets, admit, in all their parts, a liquid
(oat-gruel) which passes from one surface to the other. As these
substances are bodies, it is not easy to understand how one element
can penetrate into another without separating its molecules. On the
other hand, total division must imply mutual destruction (because
their molecules would lose all magnitude whatever). When, however, two
mingled bodies do not together occupy more space than either of them
separately (the Stoics) seem forced to admit to their adversaries that
this phenomenon is caused by the displacement of air.