ME.  J.  LISTEE  ON  THE  EAELY  STAG-ES  OE  INELAMMATION. 
677 
aggregated,  although,  if  the  skin  be  carefully  replaced  so  as  to  prevent  drying  of  the 
tissues,  the  blood  will  remain  fluid  in  that  part  of  the  vein  for  many  hours.  Whether 
the  adhesiveness  of  the  corpuscles  in  this  case  depend  on  a post  mortem  change  in  the 
vessels,  or  whether  it  is  merely  the  result  of  the  large  size  of  the  vein  preventing  the 
tissues  from  acting  effectually  on  the  blood,  remains  to  be  determined ; but  such  a fact 
seems  to  prove  that  a higher  grade  of  vital  activity,  so  to  speak,  is  required  to  prevent 
adhesiveness  of  corpuscles  than  to  maintain  the  fluidity  of  the  blood.  Hence  it  is  pro- 
bable that,  even  if  the  blood  were  at  rest  in  the  vessels  of  a part,  a stronger  degree  of 
irritation  would  be  required  in  order  to  determine  coagulation  than  would  suffice  to  induce 
adhesiveness  of  the  corpuscles,  which  seems  to  be  a more  sensitive  test  of  a deviation  of 
the  tissues  from  the  standard  of  health.  I have  however  ascertained,  by  experiments 
upon  the  amputated  sheep’s  foot,  that  if  caustic  ammonia  is  applied  freely  to  a part  of 
a vein  after  pressing  the  blood  out  of  it,  and  the  blood  allowed  to  return  when  the 
ammoniacal  odour  has  passed  off,  coagulation  takes  place  in  the  portion  of  the  vessel 
which  has  been  so  treated,  although  the  chemical  action  of  ammonia,  if  any  of  it  remained 
in  the  tissues,  would  tend  to  prevent  or  check  coagulation*.  I have  also  found  a similar 
local  clot  form,  though  more  slowly,  after  merely  pinching  a piece  of  a vein. 
The  principal  results  obtained  in  this  section  may  be  summed  up  as  follows : — 
The  effects  produced  upon  the  circulation  by  the  application  of  an  irritant  to  a vas- 
cular part  are  twofold,  consequent  upon  two  primary  changes  in  the  tissues,  which, 
though  often  concomitant,  are  entmely  mdependent  both  in  nature  and  mode  of  pro- 
duction. One  of  these  is  dilatation  of  the  arteries  (commonly  preceded  by  a brief  period 
of  contraction),  ghing  rise,  in  proportion  to  the  increase  of  calibre,  to  more  free  flow 
through  the  capillaries,  the  blood  remaining  unaffected,  except  in  the  rate  of  its  pro- 
gress. This  purely  functional  phenomenon  is  developed  indirectly  through  the  medium 
of  the  nervous  system,  being  not  limited  to  the  part  acted  on  by  the  irritant,  but  im- 
plicating a surrounding  area  of  greater  or  less  extent.  The  other  change  is  the  result 
of  the  du’ect  operation  of  the  mitating  agent  upon  the  tissues,  which  experience  some 
alteration,  in  consequence  of  which  the  blood  in  then’  vicinity  becomes  impaired,  losing 
the  properties  which  characterise  it  while  within  a healthy  part,  and  which  render  it 
fit  for  transmission  through  the  vessels,  and  assuming  those  which  it  exhibits  when 
removed  from  the  body  and  placed  in  contact  with  ordinary  solid  matter.  The  first 
indication  of  this  disorder  of  the  vital  fluid  is,  that  its  corpuscles,  both  red  and  white, 
acquh’e  some  degree  of  adhesiveness,  which  makes  them  prone  to  stick  to  one  another 
and  to  the  vascular  parietes,  and,  lagging  behind  the  liquor  sanguinis,  to  accumulate  in 
abnormal  numbers  in  the  minute  vessels.  This  adhesiveness  may  exist,  in  proportion 
to  the  severity  of  the  affection,  in  any  degree,  from  that  which  merely  gives  rise  to  a 
very  slight  preponderance  of  the  corpuscular  elements  of  the  blood  in  the  part,  up  to 
that  which  induces  complete  obstruction  of  the  capillaries ; and  when  the  irritation  has 
been  very  severe,  the  liquor  sanguinis  also  shows  signs  of  participation  in  the  lesion  by 
a tendency  to  solidification  of  the  fibrine. 
* See  the  paper  “ On  Spontaneous  Gangrene,”  &c.,  before  referred  to. 
