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action； taking place within their bodies； from which the affection
of waking or sleeping arises in animals。 Now； we must assume that
the causes of this affection in all other animals are identical
with； or analogous to； those which operate in sanguineous animals； and
that the causes operating in sanguineous animals generally are
identical with those operating in man。 Hence we must consider the
entire subject in the light of these instances ＇afforded by
sanguineous animals； especially man＇。 Now； it has been definitely
settled already in another work that sense…perception in animals
originates ill the same part of the organism in which movement
originates。 This locus of origination is one of three determinate
loci； viz。 that which lies midway between the head and the abdomen。
This is sanguineous animals is the region of the heart； for all
sanguineous animals have a heart； and from this it is that both motion
and the controlling sense…perception originate。 Now； as regards
movement； it is obvious that that of breathing and of the cooling
process generally takes its rise there； and it is with a view to the
conservation of the ＇due amount of＇ heat in this part that nature
has formed as she has both the animals which respire； and those
which cool themselves by moisture。 Of this ＇cooling process＇ per se we
shall treat hereafter。 In bloodless animals； and insects； and such
as do not respire； the 'connatural spirit' is seen alternately
puffed up and subsiding in the part which is in them analogous ＇to the
region of the heart in sanguineous animals＇。 This is clearly
observable in the holoptera ＇insects with undivided wings＇ as wasps
and bees； also in flies and such creatures。 And since to move
anything； or do anything； is impossible without strength； and
holding the breath produces strength…in creatures which inhale； the
holding of that breath which comes from without； but； in creatures
which do not respire； of that which is connatural （which explains
why winged insects of the class holoptera； when they move； are
perceived to make a humming noise； due to the friction of the
connatural spirit colliding with the diaphragm）； and since movement
is； in every animal； attended with some sense…perception； either
internal or external； in the primary organ of sense； ＇we conclude＇
accordingly that if sleeping and waking are affections of this
organ； the place in which； or the organ in which； sleep and waking
originate； is self…evident ＇being that in which movement and
sense…perception originate； viz。 the heart＇。
Some persons move in their sleep； and perform many acts like
waking acts； but not without a phantasm or an exercise of
sense…perception； for a dream is in a certain way a
sense…impression。 But of them we have to speak later on。 Why it is
that persons when aroused remember their dreams； but do not remember
these acts which are like waking acts； has been already explained in
the work 'Of Problems'。
3
The point for consideration next in order to the preceding
is：…What are the processes in which the affection of waking and
sleeping originates； and whence do they arise？ Now； since it is when
it has sense…perception that an animal must first take food and
receive growth； and in all cases food in its ultimate form is； in
sanguineous animals； the natural substance blood； or； in bloodless
animals； that which is analogous to this； and since the veins are
the place of the blood； while the origin of these is the heart…an
assertion which is proved by anatomy…it is manifest that； when the
external nutriment enters the parts fitted for its reception； the
evaporation arising from it enters into the veins； and there；
undergoing a change； is converted into blood； and makes its way to
their source ＇the heart＇。 We have treated of all this when
discussing the subject of nutrition； but must here recapitulate what
was there said； in order that we may obtain a scientific view of the
beginnings of the process； and come to know what exactly happens to
the primary organ of sense…perception to account for the occurrence of
waking and sleep。 For sleep； as has been shown； is not any given
impotence of the perceptive faculty； for unconsciousness； a certain
form of asphyxia； and swooning； all produce such impotence。 Moreover
it is an established fact that some persons in a profound trance
have still had the imaginative faculty in play。 This last point；
indeed； gives rise to a difficulty； for if it is conceivable that
one who had swooned should in this state fall asleep； the phantasm
also which then presented itself to his mind might be regarded as a
dream。 Persons； too； who have fallen into a deep trance； and have come
to be regarded as dead； say many things while in this condition。 The
same view； however； is to be taken of all these cases； ＇i。e。 that they
are not cases of sleeping or dreaming＇。
As we observed above； sleep is not co…extensive with any and every
impotence of the perceptive faculty； but this affection is one which
arises from the evaporation attendant upon the process of nutrition。
The matter evaporated must be driven onwards to a certain point；
then turn back； and change its current to and fro； like a tide…race in
a narrow strait。 Now； in every animal the hot naturally tends to
move ＇and carry other things＇ upwards； but when it has reached the
parts above ＇becoming cool＇； it turns back again； and moves
downwards in a mass。 This explains why fits of drowsiness are
especially apt to come on after meals； for the matter； both the liquid
and the corporeal； which is borne upwards in a mass； is then of
considerable quantity。 When； therefore； this comes to a stand it
weighs a person down and causes him to nod； but when it has actually
sunk downwards； and by its return has repulsed the hot； sleep comes
on； and the animal so affected is presently asleep。 A confirmation
of this appears from considering the things which induce sleep； they
all； whether potable or edible； for instance poppy； mandragora；
wine； darnel； produce a heaviness in the head； and persons borne
down ＇by sleepiness＇ and nodding ＇drowsily＇ all seem affected in
this way； i。e。 they are unable to lift up the head or the eye…lids。
And it is after meals especially that sleep comes on like this； for
the evaporation from the foods eaten is then copious。 It also
follows certain forms of fatigue； for fatigue operates as a solvent；
and the dissolved matter acts； if not cold； like food prior to
digestion。 Moreover； some kinds of illness have this same effect；
t