From the Beginning to Plato

178 FROM THE BEGINNING TO PLATO
This is the way in which all things breathe in and out: they all have
channels of flesh which the blood leaves, stretched over the surface of the
body, and at the mouth of these the outside of the skin is pierced right
through with close-set holes, so that blood is contained, but a passage is
cut for the air to pass through freely. Then, when the smooth blood rushes
away from the surface, a wild surge of blustering air rushes through, and
when the blood leaps up, the air is breathed out again. It is like a girl
playing with a clepsydra…
(fr. 100.1–9)
The clepsydra was a common household utensil for transferring liquid from one
container to another, and for measuring. It had a narrow opening at the top,
which could be plugged by hand, and a perforated base. Empedocles compared
the movement of air into and out of the body through skin pores (and in human
and higher animals through the two large pores that are the nostrils) to that of
water into and out of the perforated base of the clepsydra. He used the clepsydra
as a model (comparable to Harvey’s use of a pump as a model for the heart), rather
than as a specific experimental device.
For the first time in extant Greek physiological theory respiration was here
connected with the movement of the blood. Empedocles recognized that the
blood is in continuous motion as air is breathed in and exhaled, not yet
understanding that the movement involves a circulation but taking it as
oscillatory, from the heart to and from the body’s surface in small-scale channels.
Taking the perforations in the clepsydra to correspond to these channels or pores,
Empedocles explained inhalation as blood moving inwards followed by air
entering the pores, and exhalation (comparable to the child unplugging the
clepsydra) as the blood returning to the surface as the air is expelled again into
the atmosphere. No void is involved, but, as is obvious, the heart and chest area
expands with the intake of air and returns to normal as the air goes back out
through the channels. The comparison is not exact in every detail for the blood
obviously does not pour out of the body into an external container, but
Empedocles did not claim an exact correlation. The model works admirably in
showing a mutual movement of air and blood in respiration, the corresponding
oscillation of the blood within the body, and the way in which it can be held in
the capillaries at the extremities by the pressure of the air outside.
Empedocles took these discoveries further in suggesting that the blood acts as
a kind of neural system between the individual sense organs (which in touch and
smell can include the whole of the body surface) and the centre of the cognitive
system which, like most Greek philosophers apart from Plato, he located in the
heart:
In seas of blood coursing to and fro, there above all is what men call
thought, because for humans blood around the heart is thought [noēma].
(fr. 105)