702 
ME.  J.  LISTEE  ON  THE  EAELT  STAGES  OE  TNFEAAnrATTON. 
of  the  body  of  the  cell,  the  more  circumferential  parts  of  which  contain  only 
colourless  fluid,  and  are  therefore  invisible. 
Fig.  7 is  an  outline  of  the  wall  of  a large  blood-vessel,  with  chromatophorous  cells  in  its 
external  coat.  The  pigment  is  almost  completely  concentrated,  but  the  form 
of  the  section  of  the  black  masses,  where  they  are  seen  edgewise,  shows  that 
they  are  not  spherical,  but  disc-shaped. 
Figs.  8,  9,  and  10  are  drawn,  with  a much  higher  power,  from  young  fi’ogs,  with  small 
pigment-cells : they  exhibit  especially  the  form  and  relations  of  the  nucleus. 
In  fig.  10  the  pigment  is  shown  in  an  unhealthy  state,  the  molecules  being  irregularly 
aggregated. 
PLATE  XLVIII. 
represents  the  efiects  produced  by  irritants  upon  the  pigmentary  tissue  and  the  blood- 
vessels of  the  frog’s  foot. 
Fig.  1 shows  the  results  of  the  application  of  mustard  to  the  web.  The  pigment  was  at 
first  in  the  stellate  condition  as  on  the  left-hand  side  of  the  sketch,  and  it 
remained  permanently  in  that  state  in  the  part  on  which  the  mustard  lay, 
while  at  the  same  time  intense  inflammatory  congestion  was  produced  there, 
indicated  by  the  deep  red  colour  of  the  vessels.  Just  beyond  the  edge  of  the 
mustard  the  imitating  vapour  of  the  volatile  oil  gave  rise  to  full  difiusion  of 
the  pigment  (an  effect  peculiar  to  mustard  and  a few  other  irritants  when 
acting  mildly),  but  without  material  inflammatory  disorder  of  the  blood ; as 
seen  in  the  stripe  down  the  middle  of  the  drawing.  Durmg  the  progress  of 
the  case  the  animal  changed  to  a pale  colour  in  the  body  generally,  assuming 
the  dotted  aspect  depicted  on  the  right-hand  side  of  the  sketch  in  all  parts 
which  had  not  been  acted  on  by  the  mustard,  and  thus  deprived  for  the  time 
being  of  the  power  of  concentration.  It  will  be  observed  that  the  blood-vessels 
of  the  healthy  part  are  not  materially  smaller  than  those  of  the  congested 
region;  the  deep  colour  of  the  latter  being  due  to  then  containing  closely- 
packed  red  corpuscles,  while  the  former  are  pale  in  consequence  of  the  blood 
"within  them  having  the  normal  proportion  of  colourless  liquor  sanguinis. 
Fig.  2 illustrates  the  efiects  of  mechanical  "violence.  The  lower  half  of  the  sketch  repre- 
sents part  of  an  area  in  one  of  the  Avebs  of  a dark  frog,  which  was  pinched 
with  a pair  of  padded  forceps  so  as  to  give  rise  to  inflammatory  congestion. 
The  animal  afterwards  grew  much  paler,  so  that  in  healthy  parts  the  pigment 
assumed  the  angular  or  slightly  stellate  appearance  shown  in  the  upper  pait 
of  the  drawing.  But  on  the  particular  spot  on  which  the  mechanical  Aioleuce 
had  operated,  the  chromatophorous  cells  being  incapable  of  dischai'gmg  their 
usual  functions,  the  pigment  remained  in  the  fully-difiused  state  in  wliich  it 
was  at  the  commencement  of  the  experiment. 
