undergo a direct, or "automatic," mode of excitation, being roused into
activity independently of an incoming nervous impulse. This automatic
stimulation has been plausibly referred to the action of the products of
decomposition accumulating in the cerebral blood-vessels.[77] It is
possible that there is something in the nature of this stimulation to
account for the force and vividness of its conscious results, that is to
say, of dreams.

_The Dream State._

Let us now turn to the psychic side of these conditions, that is to say,
to the general character of the mental states known as dreams. It is
plain that the closing of the avenues of the external senses, which is
the accompaniment of sleep, will make an immense difference in the
mental events of the time. Instead of drawing its knowledge from
without, noting its bearings in relation to the environment, the mind
will now be given over to the play of internal imagination. The activity
of fancy will, it is plain, be unrestricted by collision with external
fact. The internal mental life will expand in free picturesque
movement.

To say that in sleep the mind is given over to its own imaginings, is to
say that the mental life in these circumstances will reflect the
individual temperament and mental history. For the play of imagination
at any time follows the lines of our past experience more closely than
would at first appear, and being coloured with emotion, will reflect the
predominant emotional impulses of the individual mind. Hence the saying
of Heraclitus, that, while in waking we all have a common world, in
sleep we have each a world of our own.

This play of imagination in sleep is furthered by the peculiar attitude
of attention. When asleep the voluntary guidance of attention ceases;
its direction is to a large extent determined by the contents of the
mind at the moment. Instead of holding the images and ideas, and
combining them according to some rational end, the attention relaxes its
energies and succumbs to the force of imagination. And thus, in sleep,
just as in the condition of reverie or day-dreaming, there is an
abandonment of the fancy to its own wild ways.

It follows that the dream-state will not appear to the mind as one of
fancy, but as one of actual perception, and of contact with present
reality. Dreams are clearly illusory, and, unlike the illusions of
waking life, are complete and persistent.[78] And the reason of this
ought now to be cle