occupied our attention meanwhile, it will yet return suddenly to our
consciousness with all the force and freshness of the original
sensation. A whole group of sensations is sometimes reproduced in
its due sequence as regards time and space, with so much reality that
it illudes us, as though things were actually present which have long
ceased to be so. We have here a striking proof of the fact that
after both conscious sensation and perception have been extinguished,
their material vestiges yet remain in our nervous system by way of a
change in its molecular or atomic disposition, {69} that enables the
nerve substance to reproduce all the physical processes of the
original sensation, and with these the corresponding psychical
processes of sensation and perception.

Every hour the phenomena of sense-memory are present with each one of
us, but in a less degree than this. We are all at times aware of a
host of more or less faded recollections of earlier impressions,
which we either summon intentionally or which come upon us
involuntarily. Visions of absent people come and go before us as
faint and fleeting shadows, and the notes of long-forgotten melodies
float around us, not actually heard, but yet perceptible.

Some things and occurrences, especially if they have happened to us
only once and hurriedly, will be reproducible by the memory in
respect only of a few conspicuous qualities; in other cases those
details alone will recur to us which we have met with elsewhere, and
for the reception of which the brain is, so to speak, attuned. These
last recollections find themselves in fuller accord with our
consciousness, and enter upon it more easily and energetically; hence
also their aptitude for reproduction is enhanced; so that what is
common to many things, and is therefore felt and perceived with