ME.  J.  LISTEE  ON  THE  EAELY  STAGES  OE  INFLAMMATION. 
683 
in  inverse  proportion  to  the  energy  with  which  the  mustard  acts,  was  well  illustrated 
by  the  experiment  which  furnished  the  drawing  given  in  Plate  XLVIII.  fig.  1 *. 
In  that  case,  a frog  having  been  prepared  in  the  manner  mentioned  in  the  note  to 
page  611,  a portion  of  very  strong  mustard  was  placed  upon  the  middle  of  one  of  the 
webs,  the  pigment  being  in  the  stellate  condition,  such  as  is  seen  on  the  left-hand  side 
of  the  sketch,  which  represents  a part  of  the  edge  of  the  spot  to  which  the  irritant 
was  applied,  together  with  an  adjoining  portion  of  the  web.  Shortly  after  this  had 
been  done,  I noticed  that  the  pigment  was  in  a state  of  full  diffusion  in  a ring  round 
about  the  opaque  mass,  producing  the  reticular  appearance  shown  in  the  stripe  down  the 
middle  of  the  sketch.  I had  in  a previous  case  seen  a similar  ring  become  affected  with 
congestion,  when  a portion  of  mustard  had  been  applied  for  a long  time,  in  conse- 
quence of  the  pungent  vapour  of  the  volatile  oil  playing  upon  the  neighbouring  parts 
of  the  web,  and  there  could  be  no  doubt  that  the  effect  on  the  pigment  in  the  present 
instance  was  due  to  the  same  cause ; but  in  the  latter  no  material  change  was  as  yet 
\isible  in  the  blood  except  close  to  the  edge  of  the  mustard,  where  the  corpuscles  were 
seen  to  be  abnormally  adhesive.  After  the  lapse  of  about  an  hour,  the  area  on  which 
the  irritant  had  lain  being  examined,  was  found  to  be  the  seat  of  the  most  intense  inflam- 
matory congestion,  indicated  in  the  drawing  by  the  crimson  colour  of  the  vessels,  but 
the  pigment  there  had  experienced  only  an  exceedingly  slight  degree  of  diffusion,  being, 
in  fact,  almost  exactly  in  the  same  state  as  at  the  commencement  of  the  experiment. 
Thus  the  vapour  of  the  volatile  oil,  though  operating  too  mildly  to  cause  inflammatory 
congestion,  nevertheless  induced  the  highest  possible  degree  of  pigmentary  diffusion ; 
but  the  mustard,  where  it  lay  actually  in  contact  with  the  web,  and  acted  energetically 
upon  it,  arrested  that  very  process  of  diffusion  to  which  its  gentler  operation  gives  rise. 
In  the  progress  of  the  case  it  happened  that  the  animal  changed  from  the  medium 
tint  which  it  had  at  first  to  a very  pale  colour,  the  pigment,  in  the  web  generally,  assu- 
ming the  dotted  condition  depicted  on  the  right-hand  side  of  the  drawing.  Yet  many 
hours  after  the  mustard  had  been  removed,  the  pigment  on  which  it  had  acted  retained 
its  stellate  disposition,  and  the  reticular  appearance  in  the  surrounding  ring  also 
remained  unchanged,  showing  that  the  power  of  concentration  had  been  permanently 
lost  in  those  parts,  and  affording  a favourable  opportunity  for  obtaining  by  means  of 
the  camera  lucida  a delineation  of  the  medium,  and  both  extreme  conditions  of  the 
pigment  in  the  same  web.  Next  day  the  experiment  was  rendered  still  more  instructive 
by  the  skin  becoming  excessively  dark,  the  pigment  undergoing  full  diffusion  in  the 
healthy  parts  of  the  web,  so  that  the  contrast  between  the  ring  about  the  congested  area 
and  the  surrounding  regions  no  longer  existed : yet  the  stellate  condition  was  still  main- 
tained where  the  mustard  had  lain,  showing  that  it  had  suspended  the  faculty  of  diffusion 
no  less  than  that  of  concentration. 
Croton  oil  now  no  longer  seemed  anomalous  in  its  operation.  Its  curiously  slow 
action  upon  the  frog  is  comparable  to  the  mild  influence  of  the  vapour  of  mustard,  and 
the  slight  amount  of  inflammatory  appearance  which  I had  sometimes  observed  in  a 
* This  experiment  was  performed  subsequently  to  the  reading  of  the  paper 
