616 
ME.  J.  LISTEE  ON  THE  PAETS  OF  THE  NEETOHS  SYSTEM 
that  influence  through  the  branches  which  connect  them  with  the  sympathetic,  but 
only  through  the  roots  of  the  nerves  given  off  from  the  more  posterior  parts  of  the 
cord. 
On  the  2nd  of  June,  a large  frog  having  been  put  under  the  influence  of  chloroform, 
the  vertebral  arches  were  removed,  from  the  sacrum  to  the  posterior  edges  of  the  sca- 
pulse,  and  at  0^  30“  p.m.  the  cord  was  divided  immediately  behind  the  latter  situation, 
e.  a little  behind  its  middle.  The  left  foot  being  examined  shortly  after,  the  arteries 
were  seen  to  be  considerably  constricted ; one  of  them,  which  appeared  to  be  a principal 
trunk,  permitting  single  corpuscles  to  pass  with  difficulty,  and  the  contraction  became 
extreme  after  irritation  of  the  posterior  segment  of  the  cord  with  a needle.  The  whole 
of  the  exposed  part  of  the  cord  and  the  cauda  equina,  including  the  chief  branches  of 
nerves  for  the  hind  legs,  were  then  removed  (at  0*“  56“),  and  when  the  foot  was  again 
looked  at,  at  I*"  10“,  the  circulation,  which  had  been  previously  entirely  arrested  by  the 
contraction  of  the  vessels,  was  going  on  rapidly  through  dilated  arteries,  the  one  before 
mentioned  now  measuring  3°.  This,  however,  proved  not  to  be  the  exHeme  degree  of 
dilatation  of  which  the  vessel  was  capable ; for  a stream  of  water  at  about  120°  Fahk., 
thrown  for  perhaps  a second  upon  the  foot,  induced,  after  brief  imperfect  contraction,  an 
expansion  to  nearly  4°,  which  again  was  followed  after  a few  minutes  by  a return  to  3°. 
This  experiment  was  several  times  repeated.  In  the  right  foot,  which  had  not  been 
subjected  to  the  hot  water,  though  necessarily  equally  affected  uith  the  other  by  the 
removal  of  the  portion  of  cord,  the  arteries  were  found  of  moderate  size  at  3**  45“, 
having  evidently  recovered,  to  a considerable  extent  at  least,  their  contractile  power 
during  the  2f  hours  which  had  elapsed  since  the  operation.  One  which  at  this  time 
measured  lf°,  became  dilated  on  the  application  of  hot  water  to  3°,  and  afteiTrards  con- 
tracted spontaneously  to  2°. 
At  4^^  15“  an  additional  portion  of  the  cord  was  removed,  so  as  to  clear  the  spinal 
canal  as  far  forward  as  the  anterior  third  of  the  scapulae.  The  arteries  became  at  once 
dilated  to  some  extent,  notwithstanding  that  the  heart’s  action  was  greatly  enfeebled 
by  this  operation ; and  at  6'^  45“  they  had  attained  nearly  the  fidl  diameters  that  the 
hot  water  had  before  induced,  while  the  cnculation  had  someAvhat  recovered.  Next 
momuig  the  arteries  of  the  two  feet,  the  dimensions  of  which  were  before  given, 
measured  4°  and  3°  respectively,  and  they  continued  without  the  slightest  vai’iation  until 
5h  25°i  pjyj  j the  circulation  meanwhile  had  continued  to  improve,  and  was  healthy, 
though  still  languid.  I then  removed  the  remainder  of  the  cord  and  the  entire  brain 
without  producing  any  effect  whatever  on  the  size  of  the  arteries,  and  they  still  measured 
precisely  the  same  at  10''  45“  p.m.  The  following  morning  the  frog  was  dead,  and  the 
tissues  of  the  web  had  become  opaque  by  the  imbibition  of  water. 
In  this  case  the  arteries  recovered  their  contractile  power  after  the  removal  of  the 
greater  part  of  the  posterior  half  of  the  cord,  together  with  the  chief  roots  of  the  nerves 
for  the  hind  legs ; but  when  the  part  which  furnishes  branches  to  the  posterior  extremi- 
ties had  been  completely  removed,  the  arteries  became  permanently  dilated ; and,  though 
