of pleasure and pain,
not sensations, but emotions.[91]

Since in this vague interpretation of bodily sensation the actual
impression is obscured, and not taken up as an integral part into the
percept, it is evident that we cannot, strictly speaking, call the
process an imitation of an act of perception, that is to say, an
illusion. And since, moreover, the visual image by which the sensation
is thus displaced appears as a present object, it would, of course, be
allowable to speak of this as an hallucination. This substitution of a
more or less analogous visual image for that appropriate to the
sensation forms, indeed, a transition from dream-illusion, properly so
called, to dream-hallucination.

_Dream-Hallucinations._

On the physical side, these hallucinations answer to cerebral
excitations which are central or automatic, not depending on movements
transmitted from the periphery of the nervous system. Of these
stimulations some appear to be direct, and due to unknown influences
exerted by the state of nutrition of the cerebral elements, or the
action of the contents of the blood-vessels on these elements.

_Effects of Direct Central Stimulation._

That such action does prompt a large number of dream-images may be
regarded as fairly certain. First of all, it seems impossible to account
for all the images of dream-fancy as secondary phenomena connected by
links of association with the foregoing classes of sensation. However
fine and invisible many of the threads which hold together our ideas may
be, they will hardly explain the profusion and picturesque variety of
dream-imagery. Secondly, we are able in certain cases to infer with a
fair amount of certainty that a dream-image is due to such central
stimulation. The common occurrence that we dream of the more stirring
events, the anxieties and enjoyments of the preceding day, appears to
show that when the cerebral elements are predisposed to a certain kind
of activity, as they are after having been engaged for some time in this
particular work, they are liable to be excited by some stimulus brought
directly to bear on them during sleep. And if this is so, it is not
improbable that many of the apparently forgotten images of persons and
places which return with such vividness in dreams are excited by a mode
of stimulation which is for the greater part confined to sleep. I say
"for the greater part," because even in our indolent, listless moments
of waking exist