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 thi