function of brain substance, whose results, it is true, fall, as
regards one part of them, into the domain of consciousness, while
another and not less essential part escapes unperceived as purely
material processes.

The perception of a body in space is a very complicated process. I
see suddenly before me, for example, a white ball. This has the
effect of conveying to me more than a mere sensation of whiteness. I
deduce the spherical character of the ball from the gradations of
light and shade upon its surface. I form a correct appreciation of
its distance from my eye, and hence again I deduce an inference as to
the size of the ball. What an expenditure of sensations, ideas, and
inferences is found to be necessary before all this can be brought
about; yet the production of a correct perception of the ball was the
work only of a few seconds, and I was unconscious of the individual
processes by means of which it was effected, the result as a whole
being alone present in my consciousness.

The nerve substance preserves faithfully the memory of habitual
actions. {72} Perceptions which were once long and difficult,
requiring constant and conscious attention, come to reproduce
themselves in transient and abridged guise, without such duration and
intensity that each link has to pass over the threshold of our
consciousness.

We have chains of material nerve processes to which eventually a link
becomes attached that is attended with conscious perception. This is
sufficiently established from the standpoint of the physiologist, and
is also proved by our unconsciousness of many whole series of ideas
and of the inferences we draw from them. If the soul is not to ship