EEGULATINa  THE  CONTEACTIONS  OF  THE  AETEEIES. 
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The  first  experiment  which  I performed  with  reference  to  this  subject  (October  27, 
1856),  namely,  division  of  the  sciatic  nerve  on  one  side,  gave  somewhat  puzzling  results. 
Knowing  how  difficult  it  is  to  judge  correctly  of  differences  of  calibre  in  the  vessels  by 
mere  inspection,  I tied  out  both  feet  of  a frog  (under  chloroform),  so  that  a slight  move- 
ment of  the  stage  of  the  microscope  would  bring  either  into  view,  and  thus,  after  per- 
formance of  the  operation  in  one  limb,  the  other  foot  might  serve  as  a standard  of  com- 
parison. I then  selected  a particular  artery  of  the  left  foot  for  measurement  with  the 
eyepiece  micrometer,  and,  having  noted  the  limits  between  which  its  calibre  varied 
during  half  an  hour,  isolated  the  nerve  from  surrounding  parts  by  dissection,  with- 
out any  material  change  taking  place  in  the  diameter  of  the  vessel.  I next  tied  a piece 
of  thread  tightly  round  the  nerve,  with  the  efiect  of  causing  within  the  first  few  seconds 
distinct  constriction  of  the  artery,  which  then  gradually  expanded,  and  within'  two 
minutes  had  a larger  measurement  than  I had  previously  observed.  In  other  words, 
the  effect  of  the  ligature  had  been  constriction  speedily  followed  by  dilatation.  But  on 
examining  the  web  half  an  horn’  later,  I found  the  artery  had  contracted  again  to  about 
its  usual  proportions ; after  a few  minutes  the  amount  of  constriction  was  very  consider- 
ably greater,  and  continued  so  after  division  of  the  nerve  above  the  ligature,  and  on 
looking  at  the  other  foot  I found  the  arteries  there  similarly  contracted.  During  the 
next  twenty-four  hours  I made  frequent  careful  comparisons  of  the  conditions  of  the 
arteries  in  the  two  feet,  and  found  that  they  presented  exactly  the  same  variations 
in  calibre ; being  sometimes  closely  constricted,  at  other  times  fully  dilated  in  both. 
The  constrictions  generally  commenced  a very  short  time  before  a struggle  of  the  animal, 
and  gradually  subsided  when  it  had  become  quiet.  It  was  thus  evident  that  the  arteries 
had  experienced  no  permanent  dilatation  whatever  from  the  division  of  the  sciatic  nerve, 
a result  quite  at  variance  with  the  experience  of  previous  observers. 
The  explanation  of  this  will  shortly  appear.  On  the  8th  of  April,  1857,  I laid  open 
the  spinal  canal  of  a frog  in  its  entire  length,  and  divided,  as  I supposed,  all  the  roots 
of  the  nerves  coming  off  from  the  left  side  of  the  cord  from  the  occiput  to  the  sacrum, 
and  immediately  examined  the  webs  of  both  feet,  the  frog  being  under  the  influence  of 
chloroform.  In  the  right  limb  the  circulation  was  almost  entirely  arrested,  while  in  the 
left  it  was  going  on  freely.  My  attention  was  then  diverted  for  half  an  hour,  when  the 
arteries  of  the  right  foot  were  found  of  medium  size ; but  in  all  the  three  webs  of  the 
left  foot  they  were  extremely  dilated,  appearing  to  have  two  or  three  times  the  diameter 
of  those  of  the  right  limb  *.  This  observation  was  of  itself  sufficient  to  prove  that  the 
performed  by  PflUger.  Operating  upon  the  large  edible  frog  of  the  continent  {liana  esculenta),  he 
succeeded  in  applying  the  galvanic  stimulus  to  the  anterior  roots  of  the  sciatic  nerve  within  the  spinal 
canal,  with  the  effect  of  causing  complete  constriction  of  the  arteries  of  the  webs.  Division  of  the  same 
roots  on  the  other  hand  was  followed  by  full  dilatation  of  the  vessels  (see  Henle  and  Meissner’s  Bericht, 
18.57).  Clear  proof  had  thus  been  given,  before  my  investigation  of  the  subject  commenced,  that  the  spinal 
system  does  influence  the  arteries  of  the  frog’s  foot. 
* In  this  and  other  cases  of  division  of  roots  of  the  spinal  nerves,  I observed  that  the  skin  of  the  limbs 
supplied  by  the  nerves  cut  became  perfectly  smooth,  instead  of  being,  as  usual,  rough  with  minute  papiUse. 
This  appears  to  show  that  the  unstriped  muscular  tissue  of  the  skin  is  under  the  control  of  the  spinal  system. 
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