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ME.  J.  LISTEE  OX  THE  EAELT  STAGES  OF  IXFLA3BIATI0X. 
shed  from  the  vessels,  it  is  liberated  from  an  influence  which  previously  kept  in  check 
a spontaneous  proneness  to  coagulation.  Hence  it  seems  likely  that  a foreign  solid 
introduced  into  a vein  acts  not  by  creating  a disposition  to  aggregate  on  the  part  of  the 
fibrine,  but  by  increasing  a pre-existing  tendency  to  it  (as  a thread  induces  the  crystal- 
lization of  sugar-candy),  exalting  the  mutual  attraction  of  its  particles  to  a degree  which 
overcomes  a counteracting  agency  on  the  part  of  the  tissues. 
Further  inquiry  will,  in  all  probability,  throw  clearer  light  upon  this  subject,  but  m 
the  meantime  the  facts  already  known  furnish  to  the  unaided  senses  indisputable  proof 
of  the  fundamental  principle  to  which  we  were  led  by  microscopical  obseiwation,  Hz. 
that  the  tissues  through  which  the  blood  flows  have,  when  healthy,  special  relations  to 
the  Htal  fluid,  by  virtue  of  which  it  is  maintamed  in  a fit  state  for  transmission 
through  the  vessels.  Further,  the  differences  of  adhesiveness  in  the  coi’puscles  accord- 
ing as  the  blood  is  surrounded  by  healthy  tissues  or  ordinary  matter,  can  now  be  no 
longer  matter  of  surprise,  kno-wing  as  we  do  the  alterations  which  take  place  in  the 
chemical  condition  of  the  liquor  sanguinis  in  consequence  of  such  changes  of  circum- 
stances, and  also  the  great  effect  produced  upon  the  adhesiveness  of  the  red  discs  in 
blood  outside  the  body  by  slight  variations  in  the  quality  of  the  plasma  ■*. 
The  freedom  from  attraction  for  the  fibrine,  if  not  the  actual  repulsion  of  it,  on  the  part 
of  the  walls  of  healthy  blood-vessels,  seems  to  explain  the  well-kno^vn  fact  in  pathology, 
that  when  healthy  capillaries  are  subjected  to  abnormal  pressure  in  consequence  of  venous 
obstruction,  the  fluid  squeezed  through  their  parietes  consists  almost  exclusively  of  semm ; 
the  fibrine  being  apparently  excluded  from  their  pores  as  hquid  mercury  is  from  those 
of  flannel,  or  any  other  texture  composed  of  a material  destitute  of  attraction  for  it. 
From  the  speedy  coagulation  of  lymph  effused  into  the  interstices  of  inflamed  organs 
or  upon  inflamed  serous  surfaces,  compared  with  the  length  of  time  that  blood  has  been 
known  to  remain  fluid  after  being  poured  out  into  such  situations  in  a state  of  health, 
and  also  from  the  deposition  of  fibrine  which  occurs  at  an  early  period  upon  the  lining 
membrane  of  the  vessels  in  arteritis  or  phlebitis,  whether  in  the  limited  inflammation 
which  results  from  the  application  of  a ligature,  or  in  the  more  extensive  afiection  which 
is  apt  to  occur  spontaneously,  it  would  appear  that  the  liquor  sanguinis,  like  the  corpus- 
cles, tends  to  comport  itself  near  inflamed  tissues  as  if  in  the  Hcinity  of  ordinary  solid 
substances.  It  is  true  that  coagulation  is  not  observed  to  occm*  in  the  vessels  of  the 
frog’s  web  after  the  application  of  irritants ; but  this  is  accounted  for  by  the  length  of 
time  required  for  the  occurrence  of  the  process  within  the  vessels,  the  liquor  sanguinis 
passing  on  into  healthy  regions,  leaving  the  adhesive  corpuscles  behind  it.  Adhesiveness 
of  corpuscles  may,  however,  come  on  in  ckcumstances  which  admit  of  permanent  fluidity 
of  the  blood.  Thus  if  a cat  be  killed  without  hemorrhage,  and  one  of  the  jugular  veins 
be  exposed  and  tied  in  two  places,  and  the  animal  be  then  suspended  by  the  head  so 
that  the  vein  may  be  vertical  in  position,  the  upper  part  of  the  venous  compartment 
included  between  the  ligatures  will  within  a very  few  minutes  become  colourless  in  con- 
sequence of  rapid  subsidence  of  the  red  corpuscles,  implying  that  they  are  already  closely 
* See  Section  I.  p.  650. 
