did not act, the streams of the mouth as well were replenished
through the nose. With the other cavity (i.e. of the greater weel) he
enveloped the hollow parts of the body, and at one time he made all this
to flow into the lesser weels, quite gently, for they are composed of
air, and at another time he caused the lesser weels to flow back again;
and the net he made to find a way in and out through the pores of the
body, and the rays of fire which are bound fast within followed the
passage of the air either way, never at any time ceasing so long as the
mortal being holds together. This process, as we affirm, the name-giver
named inspiration and expiration. And all this movement, active as
well as passive, takes place in order that the body, being watered and
cooled, may receive nourishment and life; for when the respiration is
going in and out, and the fire, which is fast bound within, follows
it, and ever and anon moving to and fro, enters through the belly and
reaches the meat and drink, it dissolves them, and dividing them into
small portions and guiding them through the passages where it goes,
pumps them as from a fountain into the channels of the veins, and makes
the stream of the veins flow through the body as through a conduit.

Let us once more consider the phenomena of respiration, and enquire into
the causes which have made it what it is. They are as follows:--Seeing
that there is no such thing as a vacuum into which any of those things
which are moved can enter, and the breath is carried from us into the
external air, the next point is, as will be clear to every one, that
it does not go into a vacant space, but pushes its neighbour out of its
place, and that which is thrust out in turn drives out its neighbour;
and in this way everything of necessity at last comes round to that
place from whence the breath came forth, and enters in there, and
following the breath, fills up the vacant space; and this goes on like
the rotation of a wheel, because there can be no such thing as a vacuum.
Wherefore also the breast and the lungs, when they emit the breath,
are replenished by the air which surrounds the body and which enters
in through the pores of the flesh and is driven round in a circle; and
again, the air which is sent away and passes out through the body forces
the breath inwards through the passage of the mouth and the nostrils.
Now the origin of this movement may be supposed to be as follows. In the
interior of