And I shall now show that the fluid parts may, in like manner, by the same fermentation, be drawn out from the internal to the external parts of our bodies. For seeing that wheresoever the fluid medium is contiguous to the body of any living creature, there the parts of that medium are, by perpetual change of place, separated from one another; the contiguous parts of the living creature must, of necessity, endeavour to enter into the spaces of the separated parts. For otherwise those parts, supposing there is no vacuum, would have no place to go into. And therefore that, which is most fluid and separable in the parts of the living creature which are contiguous to the medium, will go first out; and into the place thereof will succeed such other parts as can most easily transpire through the pores of the skin. And from hence it is necessary that the rest of the parts, which are not separated, must altogether be moved outwards, for the keeping of all places full. But this motion outwards of all parts together must, of necessity, press those parts of the ambient air which are ready to leave their places; and therefore all the parts of the body, endeavouring at once that way, make the body swell. Wherefore a possible cause is given of heat from the sun; which was to be done. [Sidenote: The generation of fire from the sun.] 4. We have now seen how light and heat are generated; heat by the simple motion of the medium, making the parts perpetually change places with one another; and light by this, that by the same simple motion action is propagated in a strait line. But when a body hath its parts so moved, that it sensibly both heats and shines at the same time, then it is that we say fire is generated. Now by fire I do not understand a body distinct from matter combustible or glowing, as wood or iron, but the matter itself, not simply and always, but then only when it shineth and heateth. He, therefore, that renders a cause possible and agreeable to the rest of the phenomena, namely, whence, and from what action, both the _shining_ and _heating_ proceed, may be thought to have given a possible cause of the generation of _fire_.