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independently； one might devote close consideration and inquiry。 At
the same time it becomes plain from them that as the eye ＇in seeing＇
is affected ＇by the object seen＇； so also it produces a certain effect
upon it。 If a woman chances during her menstrual period to look into a
highly polished mirror； the surface of it will grow cloudy with a
blood…coloured haze。 It is very hard to remove this stain from a new
mirror； but easier to remove from an older mirror。 As we have said
before； the cause of this lies in the fact that in the act of sight
there occurs not only a passion in the sense organ acted on by the
polished surface； but the organ； as an agent； also produces an action；
as is proper to a brilliant object。 For sight is the property of an
organ possessing brilliance and colour。 The eyes； therefore； have
their proper action as have other parts of the body。 Because it is
natural to the eye to be filled with blood…vessels； a woman's eyes；
during the period of menstrual flux and inflammation； will undergo a
change； although her husband will not note this since his seed is of
the same nature as that of his wife。 The surrounding atmosphere；
through which operates the action of sight； and which surrounds the
mirror also； will undergo a change of the same sort that occurred
shortly before in the woman's eyes； and hence the surface of the
mirror is likewise affected。 And as in the case of a garment； the
cleaner it is the more quickly it is soiled； so the same holds true in
the case of the mirror。 For anything that is clean will show quite
clearly a stain that it chances to receive； and the cleanest object
shows up even the slightest stain。 A bronze mirror； because of its
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
similarity is required to give rise to these illusory impressions。
Thus too； both in fits of anger； and also in all states of appetite；
all men become easily deceived； and more so the more their emotions
are excited。 This is the reason too why persons in the delirium of
fever sometimes think they see animals on their chamber walls； an
illusion arising from the faint resemblance to animals of the markings
thereon when put together in patterns； and this sometimes
corresponds with the emotional states of the sufferers； in such a
way that； if the latter be not very ill； they know well enough that it
is an illusion； but if the illness is more severe they actually move
according to the appearances。 The cause of these occurrences is that
the faculty in virtue of which the controlling sense judges is not
identical with that in virtue of which presentations come before the
mind。 A proof of this is； that the sun presents itself as only a
foot in diameter； though often something else gainsays the
presentation。 Again； when the fingers are crossed； the one object
＇placed between them＇ is felt ＇by the touch＇ as two； but yet we deny
that it is two； for sight is more authoritative than touch。 Yet； if
touch stood alone； we should actually have pronounced the one object
to be two。 The ground of such false judgements is that any appearances
whatever present themselves； not only when its object stimulates a
sense； but also when the sense by itself alone is stimulated； provided
only it be stimulated in the same manner as it is by the object。 For
example； to persons sailing past the land seems to move； when it is
really the eye that is being moved by something else ＇the moving ship。＇
3
From this it is manifest that the stimulatory movements based upon
sensory impressions； whether the latter are derived from external
objects or from causes within the body； present themselves not only
when persons are awake； but also then； when this affection which is
called sleep has come upon them； with even greater impressiveness。 For
by day； while the senses and the intellect are working together；
they （i。e。 such movements） are extruded from consciousness or
obscured； just as a smaller is beside a larger fire； or as small
beside great pains or pleasures； though； as soon as the latter have
ceased； even those which are trifling emerge into notice。 But by night
＇i。e。 in sleep＇ owing to the inaction of the particular senses； and
their powerlessness to realize themselves； which arises from the
reflux of the hot from the exterior parts to the interior； they
＇i。e。 the above 'movements'＇ are borne in to the head quarters of
sense…perception； and there display themselves as the disturbance
（of waking life） subsides。 We must suppose that； like the little
eddies which are being ever formed in rivers； so the sensory movements
are each a continuous process； often remaining like what they were
when first started； but often； too； broken into other forms by
collisions with obstacles。 This ＇last mentioned point＇； moreover；
gives the reason why no dreams occur in sleep immediately after meals；
or to sleepers who are extremely young； e。g。 to infants。 The
internal movement in such cases is excessive； owing to the heat
generated from the food。 Hence； just as in a liquid； if one vehemently
disturbs it； sometimes no reflected image appears； while at other
times one appears； indeed； but utterly distorted； so as to seem
quite unlike its original； while； when once the motion has ceased； the
reflected images are clear and plain； in the same manner during
sleep the phantasms； or residuary movements； which are based upon
the sensory impressions； become sometimes quite obliterated by the
above described motion when too violent； while at other times the
sights are indeed seen； but confused and weird； and the dreams
＇which then appear＇ are unhealthy； like those of persons who are
atrabilious； or feverish； or intoxicated with wine。 For all such
affections； being spirituous； cause much commotion and disturbance。 In
sanguineous animals； in proportion as the blood becomes calm； and as
its purer are separated from its less pure elements； the fact that the
movement； based on impressions derived from each of the organs of
sense； is preserved in its integrity； renders the dreams healthy；
causes a ＇clear＇ image to present itself； and makes the dreamer think；
owing to the effects borne in from the organ of sight； that he
actually sees； and owing to those which come from the organ of
hearing； that he really hears； and so on with those also which proceed
from the other sensory organs。 For it is owing to the fact that the
movement which reaches the primary organ of sense comes from them；
that one even when awake believes himself to see； or hear； or
otherwise perceive； just as it is from a belief that the organ of
sight is being stimulated； though in reality not so stimul