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ME.  J.  LISTEE  ON  THE  EAELY  STAGES  OF  INFLA^OIATION. 
that  the  vessels  are  abnormally  loaded  with  blood,  and  if  the  irritation  be  continued,  the 
cuticle  will  be  raised  in  the  form  of  a blister.  If,  now,  the  loosened  epidermis  be  artifi- 
cially removed  on  the  earliest  occurrence  of  effusion,  a scarlet  raw  surface  will  be 
exposed  ; and  on  pressing  the  tender  dermis  fiimly  with  the  finger,  and  suddenly  removing 
the  pressure,  it  will  be  found  that  while  the  redness  will  for  the  most  part  have  moment- 
arily disappeared,  there  will  be  many  minute  red  points  from  which  the  blood  cannot 
be  expelled.  This  shows  that,  whde  the  blood  is  in  part  still  free  to  move,  there  are 
some  minute  vessels  completely  clogged  with  it.  Again,  if  a portion  of  mustard  be 
placed  on  the  skin  covering  the  dorsal  aspect  of  one  of  the  fingers,  abnonnal  red- 
ness will  very  speedily  be  produced,  which  in  the  first  instance  disappears  completely 
on  pressure ; but,  if  the  mustard  has  been  kept  on  long  enough,  can  be  only  imperfectly 
dispelled ; and  if  the  application  be  still  longer  continued,  vesication  will  be  the 
result.  I had  lately  the  opportunity  of  examining  the  brain  of  a man  who  had  died  of 
tetanus,  complicated  with  incipient  meningitis ; the  post  mortem  appearance  of  the 
latter  being  maculiform  congestion  of  the  pia  mater.  Ha\ing  stripped  off  a portion  of 
the  affected  membrane,  and  carefully  washed  away  with  a camel’ s-haii’  brush  the  cerebral 
substance  adhering  to  it,  I applied  the  microscope  to  one  of  the  affected  spots,  and 
found  that  all  the  minute  vessels  were  filled  with  crimson  blood,  while  those  of  the 
surrounding  parts  were  comparatively  pale.  It  was  evident  that  the  red  coi'puscles 
were,  in  the  former,  so  closely  crammed  together  as  to  produce  the  appearance  of  a 
uniform  mass,  while  in  the  latter  they  were  present  only  in  their  usual  proportion  to 
the  liquor  sanguinis.  Thus  it  appears  that  in  the  human  subject,  inflammation,  whether 
induced  by  mechanical  irritation  or  by  an  acrid  application  such  as  mustard,  or  of 
spontaneous  origin,  is  characterized  at  an  early  period  by  a certain  amount  of  obsti'uction 
to  the  progress  of  the  blood  through  the  minute  vessels ; a phenomenon,  which  it  is 
therefore  of  great  importance  to  understand. 
It  fortunately  happens,  that  we  have,  in  the  transparent  web  of  the  frog’s  foot,  an 
opportunity  of  obserAdng  with  the  utmost  facility  the  circulation  of  the  blood  in  the 
living  animal,  and  of  watching  the  effects  produced  upon  it  by  irritating  causes.  It 
may  naturally  appear  very  doubtful  whether  observations  made  upon  creatui-es  so  low  in 
the  animal  kingdom  as  the  Amphibia,  can  with  propriety  be  brought  to  bear  upon  human 
pathology.  A few  facts  will,  however,  suffice  to  shoAv  that  no  such  doubts  need  be  enter- 
tamed.  If  a portion  of  moistened  mustard  be  placed  upon  the  web  of  a fi'og,  tied  out 
under  the  microscope,  the  blood-vessels  will  soon  be  found  abnormally  red ; and  if  the 
application  be  continued  long  enough,  all  the  capillaries  will  become  choked  ufith  cor- 
puscles so  closely  packed  as  to  present  the  appearance  of  a uniform  crimson  mass ; and 
by  and  by  the  epidermis  will  be  found  raised  in  the  form  of  a blister  over  the  part  on 
which  the  mustard  lay.  These  effects  are  precisely  similar  to  those  which  we  have  seen 
to  be  produced  by  it  upon  the  human  skin;  and  before  effusion  has  taken  place,  the 
vessels  of  the  affected  part  exactly  resemble  those  of  the  congested  spot  of  inflamed  pia 
mater  above  described.  Again,  if  dry  heat  be  made  to  act  upon  a part  of  the  frog’s  foot, 
