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
every animal the hottest part is that which is around the blood
and veins; it is in a manner on internal fountain of fire, which
we compare to the network of a creel, being woven all of fire and
extended through the centre of the body, while the-outer parts
are composed of air. Now we must admit that heat naturally
proceeds outward to its own place and to its kindred element; and
as there are two exits for the heat, the out through the body,
and the other through the mouth and nostrils, when it moves
towards the one, it drives round the air at the other, and that
which is driven round falls into the fire and becomes warm, and
that which goes forth is cooled. But when the heat changes its
place, and the particles at the other exit grow warmer, the
hotter air inclining in that direction and carried towards its
native element, fire, pushes round the air at the other; and this
being affected in the same way and communicating the same
impulse, a circular motion swaying to and from is produced by the
double process, which we call inspiration and expiration.
The phenomena of medical cupping-glasses and of the swallowing
of drink and of the projection of bodies, whether discharged in
the air or bowled along the ground, are to be investigated on a
similar principle; and swift and slow sounds, which appear to be
high and low, and are sometimes discordant on account of their
inequality, and then again harmonical on account of the equality
of the motion which they excite in us. For when the motions of
the antecedent swifter sounds begin to pause and the two are
equalised, the slower sounds overtake the swifter and then propel
them. When they overtake them they do not intrude a new and
discordant motion, but introduce the beginnings of a slower,
which answers to the swifter as it dies away, thus producing a
single mixed expression out of high and low, whence arises a
pleasure which even the unwise feel, and which to the wise
becomes a higher sort of delight, being an imitation of divine
harmony in mortal motions. Moreover, as to the flowing of water,
the fall of the thunderbolt, and the marvels that are observed
about the attraction of amber and the Heraclean stones,-in none
of these cases is there any attraction; but he who investigates
rightly, will find that such wonderful phenomena are attributable
to the combination of certain conditions-the non-existence of a
vacuum, the fact that objects push one another round, and that
they change places, passing severally into their proper positions
as they are divided or combined
Such as we have seen, is the nature and such are the causes of
respiration-the subject in which this discussion originated. For
the fire cuts the food and following the breath surges up within,
fire and breath rising together and filling the veins by drawing
up out of the belly and pouring into them the cut portions of the
food; and so the streams of food are kept flowing through the
whole body in all animals. And fresh cuttings from kindred
substances, whether the fruits of the earth or herb of the field,
which God planted to be our daily food, acquire all sorts of
colours by their inter-mixture; but red is the most pervading of
them, being created by the cutting action of fire and by the
impression which it makes on a moist substance; and hence the
liquid which circulates in the body has a colour such as we have
described. The liquid itself we call blood, which nourishes the
flesh and the whole body, whence all parts are watered and empty
places filled.
Now the process of repletion and evacuation is effected after
the manner of the universal motion by which all kindred
substances are drawn towards one another. For the external
elements which surround us are always causing us to consume away,
and distributing and sending off like to like; the particles of
blood, too, which are divided and contained within the frame of
the animal as in a sort of heaven, are compelled to imitate the
motion of the universe. Each, therefore, of the divided parts
within us, being carried to its kindred nature, replenishes the
void. When more is taken away than flows in, then we decay, and
when less, we grow and increase.
The frame of the entire creature when young has the triangles
of each kind new, and may be compared to the keel of a vessel
which is just off the stocks; they are locked firmly together and
yet the whole mass is soft and delicate, being freshly formed of
marrow and nurtured on milk. Now when the triangles out of which
meats and drinks are composed come in from without, and are
comprehended in the body, being older and weaker than the
triangles already there, the frame of the body gets the better of
them and its newer triangles cut them up, and so the animal grows
great, being nourished by a multitude of similar particles. But
when the roots of the triangles are loosened by having undergone
many conflicts with many things in the course of time, they are
no longer able to cut or assimilate the food which enters, but
are themselves easily divided by the bodies which come in from
without. In this way every animal is overcome and decays, and
this affection is called old age. And at last, when the bonds by
which the triangles of the marrow are united no longer hold, and
are parted by the strain of existence, they in turn loosen the
bonds of the soul, and she, obtaining a natural release, flies
away with joy.
