Pleasure and pain are attributed in the Timaeus to the suddenness
of our sensations—the first being a sudden restoration, the
second a sudden violation, of nature (Phileb.). The sensations
become conscious to us when they are exceptional. Sight is not
attended either by pleasure or pain, but hunger and the appeasing
of hunger are pleasant and painful because they are
extraordinary.
Section 6.
I shall not attempt to connect the physiological speculations of
Plato either with ancient or modern medicine. What light I can
throw upon them will be derived from the comparison of them with
his general system.
There is no principle so apparent in the physics of the Timaeus,
or in ancient physics generally, as that of continuity. The world
is conceived of as a whole, and the elements are formed into and
out of one another; the varieties of substances and processes are
hardly known or noticed. And in a similar manner the human body
is conceived of as a whole, and the different substances of
which, to a superficial observer, it appears to be composed—the
blood, flesh, sinews—like the elements out of which they are
formed, are supposed to pass into one another in regular order,
while the infinite complexity of the human frame remains
unobserved. And diseases arise from the opposite process—when the
natural proportions of the four elements are disturbed, and the
secondary substances which are formed out of them, namely, blood,
flesh, sinews, are generated in an inverse order.
Plato found heat and air within the human frame, and the blood
circulating in every part. He assumes in language almost
unintelligible to us that a network of fire and air envelopes the
greater part of the body. This outer net contains two lesser
nets, one corresponding to the stomach, the other to the lungs;
and the entrance to the latter is forked or divided into two
passages which lead to the nostrils and to the mouth. In the
process of respiration the external net is said to find a way in
and out of the pores of the skin: while the interior of it and
the lesser nets move alternately into each other. The whole
description is figurative, as Plato himself implies when he
speaks of a ‘fountain of fire which we compare to the network of
a creel.’ He really means by this what we should describe as a
state of heat or temperature in the interior of the body. The
‘fountain of fire’ or heat is also in a figure the circulation of
the blood. The passage is partly imagination, partly fact.