REGULATING  THE  CONTRACTIONS  OE  THE  ARTERIES. 
613 
and  transmitting  rapid  streams  of  blood,  were  found  completely  contracted,  so  that  the 
wehs  appeared  bloodless  except  in  the  veins,  and  continued  so  for  some  minutes.  At 
3'’  10“  an  artery  selected  for  special  observation  was  dilating,  having  already  attained 
to  a diameter  of  1^°,  and  the  circulation  was  returning  in  the  web.  At  3**  15“  the 
vessel  measured  3°,  but  two  minutes  later  was  2^°,  and  half  an  hour  afterwards 
exhibited  the  spontaneous  changes  in  calibre  commonly  seen  in  arteries  in  health,  the 
limits  observed  being  1^°  and  2°.  It  thus  appeared  that  the  removal  of  the  brain  had 
had  no  further  etfect  upon  the  arteries  than  the  temporary  constriction  induced  by  the 
irritation  of  the  anterior  part  of  the  cord  in  the  operation,  followed  by  a brief  period  of 
dilatation.  At  4^,  a small  part  of  the  spinal  canal  having  been  laid  open,  the  anterior 
sixth  of  the  cord  was  removed,  corresponding  to  the  anterior  third  of  the  scapulae. 
At  4*’  3“,  when  the  web  was  first  looked  at,  the  artery  was  contracted  to  absolute 
closure,  and  the  web  exsanguine ; and  this  state  of  things  continued  till  4^  7“,  when  the 
vessel  began  to  dilate.  At  4'^  8“  it  measured  2^°,  and  at  4*^  13“,  3°.  Four  minutes  later 
it  was  short  of  3°,  and  after  five  minutes  more  it  was  observed  to  be  undergoing  spon- 
taneous variations  of  calibre  from  2^°  to  2-|°.  Finally,  at  5^  30“  its  condition  was  just 
as  it  was  before  the  experiment  was  performed,  varying  from  1^°  to  2°,  without  any 
struggle  on  the  part  of  the  creature,  the  blood  at  the  same  time  flowing  rapidly  through 
it*.  At  6*",  another  vertebral  arch  having  been  taken  away,  the  subjacent  portion 
of  cord  was  removed,  the  canal  being  thus  cleared  as  far  back  as  the  level  of  the  mid- 
scapulae, corresponding  to  rather  more  than  a quarter  of  the  cord.  The  operation 
caused  contraction  of  the  artery  to  1° ; but  this  passed  off  in  half  a minute,  and  was 
followed  by  no  further  dilatation  than  to  1^°,  and  a few  minutes  later  the  artery  was 
again  spontaneously  varying  from  1°  to  1^° ; at  the  same  time  the  heart’s  action  was 
somewhat  enfeebled.  At  15“  the  portion  of  cord  corresponding  to  another  vertebral 
arch  was  cut  away.  The  operation  induced  contraction  from  to  5°,  followed  by 
gradual  dilatation  (in  fifteen  seconds)  up  to  1-|°,  and  this,  in  a few  seconds,  gave  place  to 
spontaneous  contraction  to  1^°.  By  this  last  operation  the  vertebral  canal  had  been 
cleared  as  far  back  as  the  posterior  third  of  the  scapulae,  corresponding  to  between  one- 
third  and  one-half  of  the  length  of  the  cord. 
At  G**  30“,  having  removed  another  vertebral  arch,  I divided  the  cord  imperfectly,  as 
far  back  as  it  was  exposed,  namely,  at  the  level  of  the  posterior  edges  of  the  scapulae, 
which  is  in  the  commencement  of  the  posterior  half  of  the  cord ; and  on  looking  at 
the  web  twenty  seconds  later,  found  the  artery  undergoing  oscillations  in  calibre,  such 
as  had  never  before  been  seen  in  it,  contracting  and  dilating  distinctly  five  times  in 
a minute,  from  1°  to  or  1-1°.  At  6^  32“  20^  the  cord  was  cut  fairly  through  at 
the  point  indicated,  without  removal  of  the  segment  from  the  canal,  and  at  6**  34“  the 
* The  transient  character  of  the  efi’ects  produced  upon  the  arterial  calibre  by  these  operations,  led  me  at 
first  to  conclude  that  the  anterior  parts  of  the  cerebro-spinal  axis  did  not  contain  any  nervous  centre  for  the 
arteries,  and  this  view  was  expressed  in  the  original  manuscript.  My  opinions  on  this  point  have,  however, 
been  altered  by  the  results  of  subsequent  experiments,  as  wdl  appear  at  the  conclusion  of  the  paper. 
