664 
ME.  J.  LISTEE  ON  THE  EAELT  STAGES  OE  INFLA^OIATION. 
without  stagnation,  as  a consequence  of  the  application  of  this  irritant  for  an  extremely 
brief  period*.  Long  after  all  the  blood  which  could  possibly  have  been  directly  acted 
on  by  the  chloroform  has  left  the  vessels,  successive  fresh  portions  continue  to  expe- 
rience precisely  similar  changes  in  passing  through  the  irritated  area. 
Heat  produces  similar  effects.  If  the  foot  of  a frog  which  is  under  the  influence  of 
chloroform  be  covered  entirely  with  wet  lint,  except  a small  area  of  one  of  the  webs, 
and  a red-hot  cautery  iron  be  held  for  a few  seconds  about  half  an  inch  above  the 
exposed  part,  inflammation  will  be  excited  in  the  area  in  proportion  to  the  time  of 
the  action  of  the  dry  heat  upon  it ; but  on  removal  of  the  lint,  the  circulation  will  be 
found  perfectly  healthy  in  the  surrounding  parts.  In  the  severer  cases  stagnation  is 
universal  in  the  exposed  area,  and  the  epidermis  becomes  eventually  raised  by  the 
exudation  of  serum  beneath  it ; but  in  milder  instances  nothing  more  than  accumula- 
tion of  slowly-moving  corpuscles  is  produced,  and  I have  observed  this  state  of  the  part 
to  continue  for  hours  after  the  heat  was  applied.  Here  again  the  effect  on  the  blood 
was  obviously  not  due  to  the  direct  action  of  the  heat  upon  it,  but  to  some  changes 
which  it  had  effected  in  the  tissues  of  the  part  on  which  it  had  acted. 
Evidence  of  the  same  kind,  but  still  more  conclusive,  is  derived  from  the  effects  of 
mechanical  irritation,  where  the  agency  is  free  from  all  objection  of  possible  chemical 
action  on  the  blood.  The  method  adopted  was  that  of  compressing  a small  part  of  the 
middle  of  the  web  between  little  pads  of  soft  material  attached  to  the  ends  of  the  blades 
of  a pair  of  surgical  dressing  forceps,  by  which  the  degree  of  pressure  could  be  regu- 
lated at  will.  The  results  of  this  treatment  were  identical  with  those  of  heat,  as  just 
described.  If  the  pressure  was  not  made  too  severe,  no  mechanical  obstruction  was  pro- 
duced in  the  vessels,  which  nevertheless  became  loaded  with  slowly-mo^ing  or  stagnant 
corpuscles ; and  on  one  occasion  I observed  the  capillaries  of  an  area  which  had  been 
pinched,  still  transmitting  languid  streams  of  blood  containing  great  excess  of  cor- 
puscles several  days  after  the  injury  had  been  inflicted,  while  in  the  surrounding  parts 
the  circulation  continued  perfectly  healthy.  Mechanical  riolence,  like  heat,  chloroform 
and  mustard,  had  effected  an  alteration  in  the  tissues  on  which  it  operated,  in  conse- 
quence of  which  the  blood  in  their  vicinity  assumed  abnormal  characters ; and  many 
other  facts  of  similar  nature  might  be  added,  if  necessary,  to  show  that  this  is  the 
course  always  followed  when  accumulation  of  corpuscles  irr  the  vessels  is  indrrced  by  the 
action  of  irritants. 
In  discussions  regarding  the  causes  of  the  phenomena  of  mflammatiorr  seerr  irr  the 
frog’s  web,  the  great  difficulty  has  hitherto  been  to  accourrt  for  the  puzzling  fact,  tliat 
while  the  arteries  still  retain  that  state  of  enlarged  calibre  which  is  best  adapted  for  easy 
transmission  of  the  blood,  its  accelerated  movement  comes  to  give  place  to  unnatrual 
* The  gradual  supervention  of  the  elFects  of  irritation  upon  the  hlood  may  be  watched  very  conveniently 
by  arranging  a piece  of  lint  soaked  in  chlorofoi’m,  so  that  the  vapour  may  play  upon  the  web  while  the  eye 
of  the  observer  is  over  the  microscope.  If  the  cliloroform  be  removed  when  the  tendency  to  accumulatiou 
of  corpuscles  exists  in  a very  slight  degree,  restoration  to  health  wiU  occur  within  a few  minutes. 
