but　not　to　another；　then　an　animal　while　asleep　may　perceive　with
  the　latter；　but　this　is　impossible。
  Now；　since　every　sense　has　something　peculiar；　and　also　something
  common；　peculiar；　as；　e。g。　seeing　is　to　the　sense　of　sight；　hearing　to
  the　auditory　sense；　and　so　on　with　the　other　senses　severally；　while
  all　are　accompanied　by　a　common　power；　in　virtue　whereof　a　person
  perceives　that　he　sees　or　hears　（for；　assuredly；　it　is　not　by　the
  special　sense　of　sight　that　one　sees　that　he　sees；　and　it　is　not　by
  mere　taste；　or　sight；　or　both　together　that　one　discerns；　and　has
  the　faculty　of　discerning；　that　sweet　things　are　different　from
  white　things；　but　by　a　faculty　connected　in　common　with　all　the　organs
  of　sense；　for　there　is　one　sensory　function；　and　the　controlling
  sensory　faculty　is　one；　though　differing　as　a　faculty　of　perception　in
  relation　to　each　genus　of　sensibles；　e。g。　sound　or　colour）；　and
  since　this　＇common　sensory　activity＇　subsists　in　association　chiefly
  with　the　faculty　of　touch　（for　this　can　exist　apart　from　all　the　other
  organs　of　sense；　but　none　of　them　can　exist　apart　from　it…a　subject　of
  which　we　have　treated　in　our　speculations　concerning　the　Soul）；　it
  is　therefore　evident　that　waking　and　sleeping　are　an　affection　of　this
  ＇common　and　controlling　organ　of　sense…perception＇。　This　explains
  why　they　belong　to　all　animals；　for　touch　＇with　which　this　common
  organ　is　chiefly　connected＇；　alone；　＇is　common＇　to　all　＇animals＇。
  For　if　sleeping　were　caused　by　the　special　senses　having　each　and
  all　undergone　some　affection；　it　would　be　strange　that　these　senses；
  for　which　it　is　neither　necessary　nor　in　a　manner　possible　to
  realize　their　powers　simultaneously；　should　necessarily　all　go　idle
  and　become　motionless　simultaneously。　For　the　contrary　experience；
  viz。　that　they　should　not　go　to　rest　altogether；　would　have　been
  more　reasonably　anticipated。　But；　according　to　the　explanation　just
  given；　all　is　quite　clear　regarding　those　also。　For；　when　the　sense
  organ　which　controls　all　the　others；　and　to　which　all　the　others　are
  tributary；　has　been　in　some　way　affected；　that　these　others　should
  be　all　affected　at　the　same　time　is　inevitable；　whereas；　if　one　of　the
  tributaries　becomes　powerless；　that　the　controlling　organ　should
  also　become　powerless　need　in　no　wise　follow。
  It　is　indeed　evident　from　many　considerations　that　sleep　does　not
  consist　in　the　mere　fact　that　the　special　senses　do　not　function　or
  that　one　does　not　employ　them；　and　that　it　does　not　consist　merely
  in　an　inability　to　exercise　the　sense…perceptions；　for　such　is　what
  happens　in　cases　of　swooning。　A　swoon　means　just　such　impotence　of
  perception；　and　certain　other　cases　of　unconsciousness　also　are　of
  this　nature。　Moreover；　persons　who　have　the　bloodvessels　in　the　neck
  compressed　become　insensible。　But　sleep　supervenes　when　such
  incapacity　of　exercise　has　neither　arisen　in　some　casual　organ　of
  sense；　nor　from　some　chance　cause；　but　when；　as　has　been　just
  stated；　it　has　its　seat　in　the　primary　organ　with　which　one
  perceives　objects　in　general。　For　when　this　has　become　powerless　all
  the　other　sensory　organs　also　must　lack　power　to　perceive；　but　when
  one　of　them　has　become　powerless；　it　is　not　necessary　for　this　also　to
  lose　its　power。
  We　must　next　state　the　cause　to　which　it　is　due；　and　its　quality
  as　an　affection。　Now；　since　there　are　several　types　of　cause　（for　we
  assign　equally　the　'final'；　the　'efficient'；　the　'material'；　and　the
  'formal'　as　causes）；　in　the　first　place；　then；　as　we　assert　that
  Nature　operates　for　the　sake　of　an　end；　and　that　this　end　is　a　good；
  and　that　to　every　creature　which　is　endowed　by　nature　with　the　power
  to　move；　but　cannot　with　pleasure　to　itself　move　always　and
  continuously；　rest　is　necessary　and　beneficial；　and　since；　taught　by
  experience；　men　apply　to　sleep　this　metaphorical　term；　calling　it　a
  'rest'　＇from　the　strain　of　movement　implied　in　sense…perception＇：　we
  conclude　that　its　end　is　the　conservation　of　animals。　But　the　waking
  state　is　for　an　animal　its　highest　end；　since　the　exercise　of
  sense…perception　or　of　thought　is　the　highest　end　for　all　beings　to
  which　either　of　these　appertains；　inasmuch　as　these　are　best；　and
  the　highest　end　is　what　is　best：　whence　it　follows　that　sleep
  belongs　of　necessity　to　each　animal。　I　use　the　term　'necessity'　in　its
  conditional　sense；　meaning　that　if　an　animal　is　to　exist　and　have
  its　own　proper　nature；　it　must　have　certain　endowments；　and；　if
  these　are　to　belong　to　it；　certain　others　likewise　must　belong　to　it
  ＇as　their　condition。＇
  The　next　question　to　be　discussed　is　that　of　the　kind　of　movement　or
  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
  thei