PIGMENTAEY  SYSTEM  OE  THE  EEOG. 
643 
vided  my  view  were  correct.  Accordingly,  at  2*^  10"‘  p.m.  on  the  21st  of  December,  1857, 
I introduced  beneath  the  skin  of  the  back  of  a pale  frog  a portion  of  Urari  extract,  for 
which  I was  indebted  to  the  kindness  of  Dr.  Cheistison.  At  2*^  25“  reflex  action  was 
entirely  abolished,  the  creature  being  to  all  appearance  dead,  so  far  as  could  be  judged 
by  the  naked  eye,  although  the  microscope  showed  that  circulation  continued  in  the 
webs.  The  pigment  meanwhile  had  become  stellate,  but  did  not  continue  in  that  con- 
dition, being,  half  an  hour  later,  found  fully  concentrated.  Soon  after  this,  however, 
diffusion  again  commenced,  and  continued  to  advance  steadily  till  circulation  ceased 
early  the  following  morning,  at  which  time  the  integument  was  almost  black.  In  the 
course  of  a few  hours,  however,  it  Avas  brought  again  back  to  the  palest  possible  tint  by 
post  mortem  concentration. 
The  diflusion  which  ultimately  took  place  in  this  case  was  no  doubt  due  to  loss  of 
function  on  the  part  of  the  central  ganglia  or  the  nerves  connecting  them  with  the  pig- 
ment-cells. But  from  the  occurrence  of  concentration  half  an  hour  after  the  faculty  for 
reflex  action  had  ceased,  we  learn  that  these  nerves,  hke  the  intrinsic  motor  nerves  of  the 
heart  and  intestines,  remain  unafiected  by  the  Urari  poison  for  a considerably  longer 
time  than  those  which  excite  the  contractions  of  the  voluntary  muscles.  We  further 
learn  from  the  fact  that  post  mortem  concentration  came  on  as  usual,  that  the  pigment- 
ceUs  retain  their  powers,  and  also  their  capability  of  acting  in  mutual  harmony  after  the 
rhythmical  contractions  of  the  heart  have  been  abolished  by  this  poison. 
Such  experiments  are  so  readily  performed,  and  the  efiects  produced  upon  the  pig- 
ment-cells or  the  nerves  which  govern  them  are  so  obviously  indicated  by  the  changes 
of  colour  in  the  integument,  that  I venture  to  recommend  this  method  of  investigation 
to  those  who  are  occupied  in  studying  the  action  of  poisons. 
