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. EXPLANATION OF MIXTURE THAT OCCUPIES MORE SPACE THAN ITS ELEMENTS. In the case where the compound occupies more space than each element separately, it might (though with little probability), be asserted, that, since every body, along with its other qualities, implies size, a local extension must take place. No more than the other qualities could this increase perish. Since, out of both qualities, arises a new form, as a compound of the mixture of both qualities; so also must another size arise, the mixture combining the size out of both. Here (the Peripatetics) might answer (the Stoics): "If you assert a juxtaposition of substances, as well as of the masses which possess extension, you are actually adopting our opinions. If however one of the masses, with its former extension, penetrate the entire mass of the other, the extension, instead of increasing, as in the case where one line is added to another by joining their extremities, will not increase any more than when two straight lines are made to coincide by superimposing one on the other." CASE OF MIXTURE OF UNEQUAL QUANTITIES.