EEGULATING  THE  CONTEACTIONS  OF  THE  AETEEIES. 
623 
the  “ vaso-motor  ” nerves  is  more  strikingly  illustrated  by  the  first  experiment  mentioned 
in  this  paper*,  in  which  it  may  be  remembered  that  the  arteries  of  the  webs  completely 
recovered  their  usual  powers  of  varying  their  calibre  within  half  an  hour  after  division 
of  the  sciatic,  although  this  is  an  operation  which  abolishes  for  days  at  least  all  sensation 
and  voluntary  motion  in  the  leg.  I have  since  seen  yet  more  remarkable  instances  of 
the  same  thing.  On  the  10th  of  October,  1857,  with  the  view  of  investigating  the  nature 
of  the  control  exercised  by  the  nervous  system  over  the  actions  of  the  pigment-cells  f,  I 
di'vided  all  the  soft  parts  in  the  middle  of  the  thigh  of  a frog,  except  the  main  artery 
and  vein.  The  first  effect  upon  the  arteries  was  full  dilatation ; but  about  twenty-four 
hours  later  they  were  again  of  moderate  size,  while  the  circulation  was  still  active. 
After  the  death  of  the  animal,  I examined  with  the  microscope  the  coats  of  the  artery 
and  vein,  and  also  the  periosteum,  together  with  a very  slight  amount  of  muscular  tissue 
adhering  to  it,  but  could  detect  no  nerves  in  any  of  them,  although  from  the  method  of 
examination  1 could  hardly  have  missed  branches  containing  more  than  very  few  nerve- 
tubes.  Comparing  the  result  in  this  case  with  the  permanent  dilatation  which  always 
occurred  after  removal  of  the  spinal  cord,  so  long  as  the  circulation  continued  active.,  it 
was  e\ident  that  the  slender  filaments  contained  in  the  coats  of  the  vessels,  or  possibly 
in  the  bone,  had  served  as  an  efficient  means  of  communication  between  the  cerebro- 
spinal axis  and  the  arteries  of  the  foot. 
On  the  13th  of  the  same  month  I repeated  the  experiment  upon  another  frog, 
operating  in  this  case  upon  both  thighs.  In  the  first  place,  I divided  thoroughly  all 
the  soft  parts  except  the  artery,  vein  and  nerve,  the  circulation  remaining  unaffected. 
The  nerves  were  then  successively  cut,  full  dilatation  of  the  arteries  and  rapid  flow 
through  the  capillaries  being  the  immediate  result.  An  hour  and  a half  later,  how- 
ever, the  flow  was  observed  to  be  less  rapid,  no  doubt  in  consequence  of  slight  contrac- 
tion of  the  arteries,  one  of  which,  in  the  left  foot,  measured  3°  by  micrometer,  and  after 
sixteen  hours  more  they  were  both  moderate  and  variable  in  calibre  in  both  feet ; that 
in  the  left  limb  before  noted  now  changing  between  and  2°,  and  a principal  artery 
in  the  right  foot  between  1°  and  1^°.  The  circulation  meanwhile  continued  active,  and 
remained  so  more  than  twelve  hours  longer ; from  which  circumstance,  as  well  as  from 
the  normal  appearance  of  the  contractions,  it  was  evident  that  the  arteries  were  still 
under  the  control  of  the  cord ; and  I may  add,  that  in  another  animal  in  which  the  same 
operation  was  performed  upon  the  thigh  after  removal  of  the  brain  and  cord,  the  arteries 
remained  of  full  size  and  without  variation  for  thirty-four  hours,  after  which  circulation 
ceased. 
From  these  facts  it  appears  that  there  exists  a very  remarkable  provision  for  ensuring 
the  proper  regulation  of  the  arterial  calibre  in  a part  in  spite  of  almost  complete  divi- 
* Vide  page  609. 
t Further  information  regarding  this  experiment,  as  respects  the  pigmentary  system,  will  be  found  in  the 
next  paper  in  these  Transactions. 
MDCCCLVIII.  4 N 
