EEG-ULATING  THE  CONTEACTIONS  OF  THE  AETEEIES. 
617 
the  circulation  was  then  feeble,  soon  attained  the  full  calibre  which  hot  water  had 
induced  at  a time  when  the  heart  was  in  powerful  action. 
The  perfect  constancy  with  which  the  vessels  observed  maintained  these  dimensions 
for  more  than  thirty  hours  after  the  operation,  implied  that  they  were  not  then  at  all 
acted  on  by  the  nervous  system ; and  hence  I was  led  at  first  to  infer  that  there  existed 
no  other  ganglionic  apparatus  for  the  arteries  of  the  feet  than  that  contained  in  the 
cerebro-spinal  axis*. 
I have  since  witnessed  in  other  frogs  the  permanence  of  the  dilatation  of  the  arte- 
ries after  removal  of  the  brain  and  cord.  The  following  case,  however,  appeared  at 
first  inconsistent  with  these  observations.  On  the  23rd  of  October  the  brain  and  cord 
of  a large  frog  were  completely  removed,  and  an  operation  was  performed  upon  the 
right  thigh,  which,  as  it  turned  out,  tended  to  interfere  with  the  freedom  of  the  cir- 
culation in  the  webs ; so  that  after  twelve  hours,  the  blood,  though  not  presenting  the 
appearances  of  inflammation,  was  almost  motionless  in  that  foot.  At  the  same  time, 
two  arteries  in  one  of  the  webs,  which  had  till  then  remained  perfectly  constant  in 
calibre,  as  determined  by  micrometer,  began  to  exhibit  variations,  and  during  the 
next  twenty-four  hours  continued  to  change  their  diameter  occasionally.  There  were, 
however,  certain  peculiarities  about  these  changes  such  as  I had  never  before  seen. 
Generally  speaking,  all  the  arteries  of  a web  are  found  in  the  same  degree  of  contrac- 
tion at  any  one  time ; but  here,  one  of  the  vessels  under  observation  was  sometimes 
small,  when  the  other,  though  in  the  same  web,  was  large ; and  not  only  was  there  no 
proportion  between  the  degrees  of  contraction  in  the  two  vessels,  but  in  one  and  the 
same  artery  the  amount  of  constriction  was  very  different  at  different  parts.  The 
unusual  character  of  these  contractions  implied  that  they  were  caused  by  some  unwonted 
circumstances ; and  from  their  coincidence  with  the  almost  total  arrest  of  the  blood,  as 
well  as  from  the  fact  that  in  the  left  foot,  where  the  circulation  continued  free,  the 
arteries  remained  of  full  size  till  the  animal  was  destroyed,  I was  led  to  conclude  that 
the  puzzling  appearances  in  question  must  be  in  some  way  or  other  dependent  on  the 
cessation  of  the  flow  of  the  -vital  fluid  through  the  vessels.  If  this  were  so,  it  seemed 
probable  that  the  mechanism  by  which  these  irregular  contractions  were  induced  might 
be  as  local  as  their  exciting  cause,  in  which  case  they  would  be  seen  to  occur  in  an 
amputated  limb.  In  order  to  determine  this  point  I made  the  following  experiment. 
On  the  2nd  of  April,  1858,  having  passed  a knife  between  the  brain  and  cord  of  a large 
frog  so  as  to  render  the  legs  insensible,  and  having  ascertained  that  the  arterial  con- 
striction resulting  from  that  operation  had  subsided,  I placed  a ligature  round  one  of 
the  thighs,  and  then  amputated  the  limb  at  a higher  point.  The  application  of  the 
ligature  not  only  prevented  the  blood  from  escaping,  but  produced  considerable  tension 
in  the  soft  parts  of  the  thigh ; and  on  examining  the  webs,  I found  the  arteries  fully 
dilated,  one  which  I selected  for  special  observation  measuring  4|°  in  diameter.  At 
* This  was  the  -new  expressed  in  the  original  manuscript,  but  it  has  been  since  modified  by  further  expe- 
riments mentioned  in  the  text,  made,  as  their  dates  imply,  subsequently  to  the  reading  of  the  paper. 
4 M 2 
