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.
He has a singular theory of respiration for which he accounts
solely by the movement of the air in and out of the body; he does
not attribute any part of the process to the action of the body
itself. The air has a double ingress and a double exit, through
the mouth or nostrils, and through the skin. When exhaled through
the mouth or nostrils, it leaves a vacuum which is filled up by
other air finding a way in through the pores, this air being
thrust out of its place by the exhalation from the mouth and
nostrils. There is also a corresponding process of inhalation
through the mouth or nostrils, and of exhalation through the
pores. The inhalation through the pores appears to take place
nearly at the same time as the exhalation through the mouth; and
conversely. The internal fire is in either case the propelling
cause outwards—the inhaled air, when heated by it, having a
natural tendency to move out of the body to the place of fire;
while the impossibility of a vacuum is the propelling cause
inwards.
Thus we see that this singular theory is dependent on two
principles largely employed by Plato in explaining the operations
of nature, the impossibility of a vacuum and the attraction of
like to like. To these there has to be added a third principle,
which is the condition of the action of the other two,—the
interpenetration of particles in proportion to their density or
rarity. It is this which enables fire and air to permeate the
flesh.
Plato’s account of digestion and the circulation of the blood is
closely connected with his theory of respiration. Digestion is
supposed to be effected by the action of the internal fire, which
in the process of respiration moves into the stomach and minces
the food. As the fire returns to its place, it takes with it the
minced food or blood; and in this way the veins are replenished.
Plato does not enquire how the blood is separated from the
faeces.
Of the anatomy and functions of the body he knew very
little,—e.g. of the uses of the nerves in conveying motion and
sensation, which he supposed to be communicated by the bones and
veins; he was also ignorant of the distinction between veins and
arteries;—the latter term he applies to the vessels which conduct
air from the mouth to the lungs;—he supposes the lung to be
hollow and bloodless; the spinal marrow he conceives to be the
seed of generation; he confuses the parts of the body with the
states of the body—the network of fire and air is spoken of as a
bodily organ; he has absolutely no idea of the phenomena of
respiration, which he attributes to a law of equalization in
nature, the air which is breathed out displacing other air which
finds a way in; he is wholly unacquainted with the process of
digestion. Except the general divisions into the spleen, the
liver, the belly, and the lungs, and the obvious distinctions of
flesh, bones, and the limbs of the body, we find nothing that
reminds us of anatomical facts. But we find much which is derived
from his theory of the universe, and transferred to man, as there
is much also in his theory of the universe which is suggested by
man. The microcosm of the human body is the lesser image of the
macrocosm. The courses of the same and the other affect both;
they are made of the same elements and therefore in the same
proportions. Both are intelligent natures endued with the power
of self-motion, and the same equipoise is maintained in both. The
animal is a sort of ‘world’ to the particles of the blood which
circulate in it. All the four elements entered into the original
composition of the human frame; the bone was formed out of smooth
earth; liquids of various kinds pass to and fro; the network of
fire and air irrigates the veins. Infancy and childhood is the
chaos or first turbid flux of sense prior to the establishment of
order; the intervals of time which may be observed in some
intermittent fevers correspond to the density of the elements.
The spinal marrow, including the brain, is formed out of the
finest sorts of triangles, and is the connecting link between
body and mind. Health is only to be preserved by imitating the
motions of the world in space, which is the mother and nurse of
generation. The work of digestion is carried on by the superior
sharpness of the triangles forming the substances of the human
body to those which are introduced into it in the shape of food.
The freshest and acutest forms of triangles are those that are
found in children, but they become more obtuse with advancing
years; and when they finally wear out and fall to pieces, old age
and death supervene.
As in the Republic, Plato is still the enemy of the purgative
treatment of physicians, which, except in extreme cases, no man
of sense will ever adopt. For, as he adds, with an insight into
the truth, ‘every disease is akin to the nature of the living
being and is only irritated by stimulants.’ He is of opinion that
nature should be left to herself, and is inclined to think that
physicians are in vain (Laws—where he says that warm baths would
be more beneficial to the limbs of the aged rustic than the
prescriptions of a not over-wise doctor). If he seems to be
extreme in his condemnation of medicine and to rely too much on
diet and exercise, he might appeal to nearly all the best
physicians of our own age in support of his opinions, who often
speak to their patients of the worthlessness of drugs. For we
ourselves are sceptical about medicine, and very unwilling to
submit to the purgative treatment of physicians. May we not claim
for Plato an anticipation of modern ideas as about some questions
of astronomy and physics, so also about medicine? As in the
Charmides he tells us that the body cannot be cured without the
soul, so in the Timaeus he strongly asserts the sympathy of soul
and body; any defect of either is the occasion of the greatest
discord and disproportion in the other. Here too may be a
presentiment that in the medicine of the future the
interdependence of mind and body will be more fully recognized,
and that the influence of the one over the other may be exerted
in a manner which is not now thought possible.