ideas; what is continuous is the special disposition of nerve
substance in virtue of which this substance gives out to-day the same
sound which it gave yesterday if it is rightly struck. {71}
Countless reproductions of organic processes of our brain connect
themselves orderly together, so that one acts as a stimulus to the
next, but a phenomenon of consciousness is not necessarily attached
to every link in the chain. From this it arises that a series of
ideas may appear to disregard the order that would be observed in
purely material processes of brain substance unaccompanied by
consciousness; but on the other hand it becomes possible for a long
chain of recollections to have its due development without each link
in the chain being necessarily perceived by ourselves. One may
emerge from the bosom of our unconscious thoughts without fully
entering upon the stage of conscious perception; another dies away in
unconsciousness, leaving no successor to take its place. Between the
"me" of to-day and the "me" of yesterday lie night and sleep, abysses
of unconsciousness; nor is there any bridge but memory with which to
span them. Who can hope after this to disentangle the infinite
intricacy of our inner life? For we can only follow its threads so
far as they have strayed over within the bounds of consciousness. We
might as well hope to familiarise ourselves with the world of forms
that teem within the bosom of the sea by observing the few that now
and again come to the surface and soon return into the deep.

The bond of union, therefore, which connects the individual phenomena
of our consciousness lies in our unconscious world; and as we know
nothing of this but what investigation into the laws of matter teach
us--as, in fact, for purely experimental purposes, "matter" and the
"unconscious" must be one and the same thing--so the physiologist has
a full right to denote memory as, in the wider sense of the word, a