^ f. UBBARV - JScholarship - Johns Hopkins University

INTRODUCTION 5
a theory of vision without a settled notion of the nature
of light, or of the anatomical structure of eye or brain.
They had to explain the Operation of hearing without
accurate knowledge of the structure of the inner ear, or
of the facts and laws of sound, or at least with only some
few mathematical ideas gleaned from the study of harmonics.
Physiology and anatomy, chemistry and physics,
as yet undifferentiated, lay within the body of vague floating
possibilities of knowledge studied by them under the
name of Nature. For want of a microscope their examination
of the parts of the sensory organs remained barren.
They had no conception of the minuteness of the scale on
which nature works in the accomplishment of sensory
processes and in the formation of sensory organs. The
retina, as well as the structure of the auditory apparatus,
was wholly unknown to them. The nerve-system had not
been discovered, and the notions formed of the mechanism
of Sensation and motion ^ were hopelessly astray. The
veins, with the blood or (as some thought) the air coursing
through them, were looked upon as discharging the functions
now attributed to the sensory and motor nerves. Even
Aristotle did not know the difference between veins and
arteries. When this difference was first perceived, it was
for a time still supposed that the veins conducted the blood,
the arteries the air. Perhaps the climax of our surprise is
reached when we find Plato of opinion that not only air,
but also drink, passed into the lungs ^. Yet in this opinion
Plato was at one with the best, or some of the best,
medical teaching of his time. As early as Alcmaeon of
Crotona the brain had been thought of as the central organ
of sentiency, and, in short, of mind ; and Plato held that it
was so. But Aristotle, again, declares this to be untrue,
and holds that the heart is the great organ of perception
^ Vide Galen, de Placit. Hipp, et Plat. §§ 644 seqq.; [especially
'Epao'iaTpaTos [294 B. c] liiv ovv, el Kai nfj npötrdiv, dXV iitX yfipws ye rqv
akriBrj tS>v vevpav äpxrjv KOTevörja-ev' 'Apia-T0Te\7]S 8e /«XP' toitöi dyvorjiras
(Ikotios anopei XP^^"" fweiv iyK€(j)aKov.
' Timcieus 70 c.