which can be accounted for only if they are held to derive from a
'higher source'. Goethe means experiences with coloured after-images.
This will be confirmed by our own discussion of the subject.

What we first need, however, is a closer insight into the physiological
process in the eye which causes the after-images as such. Wherever
Goethe speaks of a simple activity of the retina, we are in fact
concerned with a co-operation of the retina with other parts of our
organ of sight. In order to make this clear, let us consider how the
eye adapts itself to varying conditions of light and darkness.

It is well known that if the eye has become adjusted to darkness it is
dazzled if suddenly exposed to light, even though the light be of no
more than quite ordinary brightness. Here we enter a border region
where the seeing process begins to pass over into a pathological
condition.4 A 'secret' of the effect of light on the eye is here
revealed which remains hidden in ordinary vision, for normally the
different forces working together in the eye hold each other in
balance, so that none is able to manifest separately. This equilibrium
is disturbed, however, when we suddenly expose the eye to light while
it is adapted to darkness. The light then acts on the eye in its usual
way, but without the immediate counter-action which normally restores
the balance. Under these conditions we notice that the sudden dazzling
has a painful influence on the eye - that is, an influence in some way
destructive. This will not seem surprising if we remember that when
light strikes on the background of the eye, consciousness is quickened,
and this, as we know, presupposes a breaking down of substance in some
part of the nervous system. Such a process does in fact occur in the
retina, the nerve-part of the eye, when external light falls upon it.
If the eye were solely a structure of nerves, it would be so far