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. For that which takes place according to nature is
pleasant, but that which is contrary to nature is painful. And
thus death, if caused by disease or produced by wounds, is
painful and violent; but that sort of death which comes with old
age and fulfils the debt of nature is the easiest of deaths, and
is accompanied with pleasure rather than with pain.