636 
ME.  J.  LISTEE  ON  THE  CTTANEOrS 
the  truth  of  this  idea,  the  following  experiment  was  performed.  In  the  afternoon  of  the 
10th  of  October  1857  I divided  in  a pale  frog  all  the  soft  parts  in  the  middle  of  the 
right  thigh,  except  the  femoral  artery  and  vein  and  the  sciatic  nerve ; and  late  in  the 
evening,  having  ascertained  that  the  circulation  was  going  on  freely  in  the  webs,  I cut 
the  nerve  also,  no  effect  having  been  hitherto  produced  upon  the  colour-  of  the  limb. 
Next  morning  the  body  generally  was  stiQ  pale,  but  the  right  leg  was  black  from  the 
wound  downwards.  The  same  remarkable  appearance  continued  till  the  evening,  when 
circulation  ceased  in  the  limb.  On  the  13th  I pei-foi-med  the  same  experiment  upon 
both  thighs  of  another  large  pale  frog,  leaving  the  sciatic  trunks  entii-e  in  the  first 
instance,  until  I had  ascertained  that  the  circulation  in  the  feet  had  not  been  intei-fered 
with.  Three  hours  after  this  had  been  done  I divided  the  nei-r  e in  the  left  thigh,  and 
in  about  forty  minutes  observed  that  the  leg  was  decidedly  darker  below  the  seat  of 
operation.  After  another  hour  I found  the  pigment  stellate  in  the  left  webs,  whereas 
it  was  in  the  dotted  condition  in  the  right  foot.  I then  cut  the  nerve  in  the  right  limb, 
and  within  a quarter  of  an  hour  the  leg  was  already  considerably  darker  below  the 
wound,  and  the  pigment  in  the  webs  had  become  stellate.  Next  morning  the  body  was 
still  pale,  but  the  legs  were  very  dark,  and  they  continued  to  deepen  in  tint,  although 
the  animal  was  kept  in  a white  earthen  jar  covered  vrith  glass  in  a bright  light,  till  at 
about  3 p.M.  they  were  almost  absolutely  black,  while  the  pigment  was  diffused  in  the 
webs  to  the  extremest  degree,  the  body  meanwhile  and  the  upper  parts  of  the  thighs 
retaining  their  former  light  colour.  The  tint  of  the  legs  remained  unaltered  till  the 
death  of  the  animal,  which  took  place  several  hours  later. 
The  natural  interpretation  of  these  results  appeared  to  be,  that  there  exists  a con- 
stant tendency  to  difiusion  of  the  pigment  in  a limb  so  soon  as  it  is  liberated  riom 
the  influence  of  the  usually  recognised  nervous  centres.  It  afterwards  occuiTed  to  me. 
that  if  this  were  really  true,  diffusion  of  the  pigment  might,  by  proper  management, 
be  observed  in  an  amputated  limb  before  the  supervention  of  the  tendency  to  post 
mortem  concentration : for  I knew,  from  reasons  to  be  mentioned  hereafter,  that  this 
effect  of  death  depended  on  the  cessation  of  the  flow  of  blood  through  the  vessels,  and. 
from  what  I had  seen  of  arterial  contractions  in  the  frog’s  web,  and  vermicular  move- 
ments of  the  mammalian  intestine  from  a similar  cause,  I felt  siu-e  that,  if  the  blood 
were  retained  within  the  vessels,  the  arrest  of  the  circulation  could  not  be  instantaneous 
in  its  effects  upon  the  pigment,  but  that  some  minutes  would  probably  be  requii-ed  to 
develope  them ; during  which  time  the  diffusion  resulting  fi-om  liberation  of  the  pigment- 
cells  from  the  influence  of  the  ganglia  in  the  trunk  would  proceed  unchecked.  Accord- 
ingly, on  the  3rd  of  September,  1858,  having  tied  a string  tightly  roimd  the  ankle  of  a 
pale  frog,  I immediately  amputated  above  the  ligature,  and,  avoiding  the  loss  of  time 
involved  in  tying  out  the  toes,  placed  the  foot  at  once  on  a plate  of  glass  mth  a drop 
of  water,  two  adjacent  toes  being  kept  apart  by  morsels  of  moistened  lint.  Within  a 
minute  and  a half  of  the  application  of  the  string,  the  pigment  in  the  web  was  obsen  ed 
to  be  in  the  angular  condition,  with  short  simple  projecting  processes,  e.  approaching 
