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-MR.  J.  LISTEE  ON  THE  EAELT  STAGES  OF  INFLA3DIATION. 
SECTION  IT. 
On  the  Effects  of  Irritants  upon  the  Tissues. 
The  object  ox"  the  present  section  is  to  inquire  into  the  nature  of  that  primaiy  change 
which  we  have  seen  to  be  produced  in  the  tissues  by  the  direct  action  of  imtants  upon 
them. 
The  conclusion  akeady  arrived  at,  that  blood  flowing  through  an  irritated  part 
approaches  more  and  more  nearly,  in  proportion  to  the  intensity  of  the  affection,  the 
condition  which  it  assumes  when  separated  fi-om  the  h\ing  body,  naturally  leads  us  to 
infer  that  the  tissues  concerned  are  in  some  degree  approximated  to  the  state  of  ordi- 
nary matter,  or,  in  other  words,  have  suffered  a diminution  of  power  to  discharge  the 
offices  peculiar  to  them  as  components  of  the  healthy  animal  frame. 
This  inference  is  strongly  supported  by  considering  what  common  effect  is  likely  to 
be  produced  upon  the  tissues  of  the  fr’og’s  web  by  all  the  various  agents  known  to  cause 
inflammatory  congestion.  To  take  first  the  case  of  mechanical  Aiolence.  A forcible 
pinch  of  the  delicate  web  seems  likely,  a priori,  to  impair  its  powers ; for  if  the  lesion 
be  sufficiently  severe,  complete  death  of  the  part  will  result.  An  elevated  temperature 
proves  equally  destructive  if  carried  far  enough ; and  its  operation  to  a degree  just 
short  of  this,  while  it  produces  congestion,  can  hardly  fail  to  cause  diminished  vigoiu'  in 
the  tissues.  So  also  powerful  chemical  agents,  if  used  cautiously,  give  rise  to  inflam- 
mation ; but  if  otherwise,  kill  the  part  they  act  on.  Even  the  pimgent  irritants  which 
do  not  exert  much  chemical  action,  seem  to  benumb  the  energies  of  the  spot  to  which 
they  are  applied.  Thus  a morsel  of  capsicum  placed  on  the  tip  of  the  tongue  speedily 
produces  numbness  there,  and  a piece  of  mustard  lying  on  the  Anger  for  an  hour  or 
two  dulls  the  sensibility  of  the  skin.  Chloroform,  too,  while  it  very  readily  induces 
stagnation  followed  by  vesication  in  the  frog’s  web,  is  an  agent  which  appears  likely  to 
benumb  the  vital  energies.  If  a small  frog  be  put  into  a bottle  of  water  highly  charged 
mth  carbonic  acid,  and  removed  from  it  some  time  after  all  motion  of  the  limbs  has 
ceased,  it  will  be  found  that,  though  the  heart  is  still  beating,  the  blood-vessels  of  the 
webs  are  loaded  with  stagnant  corpuscles.  After  a while,  however,  resolution  will  take 
place,  and  some  time  later  the  animal  will  regain  its  consciousness.  Here  it  appears 
probable  that  the  carbonic  acid,  poisoning  the  web  as  well  as  the  brain,  paralyses  for  a 
time  the  functional  acti\dty  of  both ; and  that  the  return  of  the  cfrculation,  like  the 
recovery  of  the  cerebral  functions,  depends  on  a restoration  of  the  dormant  faculties  of 
the  affected  tissues. 
Perhaps  the  most  instructive  case  is  that  of  the  galvanic  shock,  which  the  following 
circumstances  first  showed  me  to  be  capable  of  causing  inflammatory  congestion.  Being 
desirous  of  ascertaining  the  effects  of  galvanism  upon  the  cutaneous  pigmentary  system, 
I applied  the  poles  of  a battery  in  rather  powerful  action  to  the  skin  of  the  head  of  a 
frog,  when,  the  shock  affecting  the  brain,  the  animal  Avas  stunned  and  lay  perfectly 
motionless.  This  state  of  things  being  favourable  for  pm’suing  my  inquiry  by  aid  of 
the  microscope,  I drew  down  one  of  the  passive  limbs,  and  having  placed  the  foot  under 
