On Dreams   

shininess, is especially sensitive to any sort of contact (the

movement of the surrounding air acts upon it like a rubbing or

pressing or wiping); on that account, therefore, what is clean will

show up clearly the slightest touch on its surface. It is hard to

cleanse smudges off new mirrors because the stain penetrates deeply

and is suffused to all parts; it penetrates deeply because the

mirror is not a dense medium, and is suffused widely because of the

smoothness of the object. On the other hand, in the case of old

mirrors, stains do not remain because they do not penetrate deeply,

but only smudge the surface.

From this therefore it is plain that stimulatory motion is set up

even by slight differences, and that sense-perception is quick to

respond to it; and further that the organ which perceives colour is

not only affected by its object, but also reacts upon it. Further

evidence to the same point is afforded by what takes place in wines,

and in the manufacture of unguents. For both oil, when prepared, and

wine become rapidly infected by the odours of the things near them;

they not only acquire the odours of the things thrown into or mixed

with them, but also those of the things which are placed, or which

grow, near the vessels containing them.

In order to answer our original question, let us now, therefore,

assume one proposition, which is clear from what precedes, viz. that

even when the external object of perception has departed, the

impressions it has made persist, and are themselves objects of

perception: and [let us assume], besides, that we are easily

deceived respecting the operations of sense-perception when we are

excited by emotions, and different persons according to their

different emotions; for example, the coward when excited by fear,

the amorous person by amorous desire; so that, with but little

resemblance to go upon, the former thinks he sees his foes

approaching, the latter, that he sees the object of his desire; and

the more deeply one is under the influence of the emotion, the less