PIGMENTAET  SYSTEM  OP  THE  FEOG. 
636 
thigh,  or  of  cutaneous  branches  in  the  dorsal  region,  did  not  prevent  the  parts  of  the 
skin  supplied  by  them  from  varying  -in  colour  along  -with  the  rest  of  the  body  under  the 
influence  of  light;  and,  supposing  that  in  such  operations  all  connexion  was  severed 
between  the  portions  of  integument  concerned  and  the  central  organs  of  the  nervous 
system,  he  inferred  that  the  pigmentary  changes  induced  by  light  were  effected  inde- 
pendently of  either  the  cerebro-spinal  axis  or  the  usually  recognised  sympathetic  gan- 
glia. He  nevertheless  regarded  such  variations  as  probably  reflex  in  their  nature,  and 
attributed  them  to  a peripheral  ganglionic  apparatus  in  the  skin  itself ; and  this  opinion 
appeared  confirmed  by  the  circumstance  that  direct  irritation  operated  in  the  same  man- 
ner upon  the  colour  of  a detached  piece  of  integument  as  upon  that  of  the  living  animal. 
At  the  same  time,  as  he  observed  paleness  of  tint  to  result  from  irritation  of  the  cord,  or 
of  the  nerves  distributed  to  a particular  part  of  the  surface,  he  concluded  that  the  spinal 
system  was  also  capable  of  acting  on  the  pigment-cells,  and  so  accounted  for  the  supposed 
influence  of  psychical  excitement  upon  the  tint  of  the  skin.  Thus,  according  to  his  view, 
the  cutaneous  pigmentary  system  was  circumstanced  like  the  heart  or  intestines,  which, 
though  possessing  the  faculty  of  independent  action  by  virtue  of  their  intrinsic  ganglia, 
may  also  have  their  movements  affected  by  mental  emotion*. 
In  the  course  of  some  experiments  performed  in  April  1857,  with  reference  to  the 
influence  exerted  by  the  cord  upon  the  cahbre  of  the  arteries,  I noticed  on  two  occa- 
sions that  partial  dmsion  of  the  roots  of  the  nerves  for  one  of  the  hind  legs  within  the 
spinal  canal  was  immediately  followed  by  increased  paleness  of  the  limb,  of  transient 
character,  after  which  the  leg  assumed  precisely  the  same  colour  as  the  other,  this 
result  being  in  accordance  with  vox  Wittich’s  description.  But  I further  observed  in 
two  cases  in  which  such  operations  had  been  performed,  that  when  a considerable  time 
had  elapsed,  \iz.  nine  hours  in  one  instance  and  two  days  in  the  other,  the  limb  whose 
nerves  had  been  cut  was  decidedly  darker  than  the  rest  of  the  body.  Similar  results 
were  once  obtained  from  the  division  of  the  sciatic  nerve  in  the  thigh.  When  the 
operation  was  performed,  \iz.  at  4^*  30“  p.m.  on  the  4th  of  April,  1857,  the  pigment  was 
in  the  stellate  condition  in  the  webs,  the  tint  of  the  skin  being  moderately  dark ; and 
this  state  of  things  continued  unchanged  in  both  limbs  for  the  next  six  hours.  On  the 
following  day,  however,  the  leg  operated  on  was  seen  to  be  very  dark,  and  the  pigment 
in  its  webs  was  reticular ; while  in  the  rest  of  the  body  the  colour  remained  as  before, 
and  the  pigment  was  still  stellate.  This  striking  contrast  continued  unaltered  for  two 
days,  when  it  was  destroyed  by  the  body  generally  assuming  the  darkest  possible  tint. 
The  diffusion  of  the  pigment  in  consequence  of  division  of  nerves  appeared  to  be  the 
counterpart  of  the  concentration  produced  by  their  irritation,  and  it  seemed  probable 
that  the  want  of  constancy  in  the  results  in  the  former  case  was  caused,  like  the  variable 
amount  and  duration  of  arterial  dilatation  after  such  operations  f,  by  the  place  of  the 
divided  trunks  being  supplied  by  other  branches ; and  that,  if  the  nerves  of  a limb  were 
all  completely  severed,  diffusion  would  necessarily  take  place.  With  the  view  of  testing 
* Vide  Muller’s  Archiv,  he.  cit.  p.  56.  t 610. 
