destroyed by the impact of light that it could not be restored even by
sleep, as are the more inward parts of the nervous system. But the eye
receives also a flow of blood, and we know that throughout the
threefold human organism the blood supplies the nervous system with
building-up forces, polarically opposite to the destructive ones. In
sleep, as we have already seen, the interruption of consciousness
allows the blood to inundate the nervous system, as it were, with its
healing, building-up activity. It is not necessary, however, for the
whole of the body to pass into a condition of sleep before this
activity can occur. It functions to some extent also in the waking
state, especially in those parts of the organism which, like the eye,
serve in the highest degree the unfolding of consciousness.

Having established this, we have a basis for an understanding of the
complete process of vision. We see that it is by no means solely the
nerve part of the eye which is responsible for vision, as the
spectator-physiology was bound to imagine. The very fact that the place
where the optic nerve enters the eye is blind indicates that the
function of mediating sight cannot be ascribed to the nerve alone. What
we call 'seeing' is far more the result of an interplay between the
retina carrying the nerves, and the choroid carrying the blood-vessels.
In this interplay the nerves are the passive, receptive organ for the
inworking of external light, while the blood-activity comes to meet the
nerve-process with a precisely correlated action. In this action we
find what Goethe called the 'inner light'.

The process involved in adaptation now becomes comprehensible. The
cause of the dazzling effect of light of normal intensity on an eye
adapted to the dark, is that in such an eye the blood is in a state of
rest, and this prevents it from exercising quickly enough the necessary