I^IE.  J.  LISTEE  ON  THE  EAELT  STAGES  OF  INFLAMMATION. 
675 
has  been  observed  to  remain  fluid  but  coagulable  in  the  tunica  vaginalis,  seems  to  show 
that  serous  membranes  are  similarly  circumstanced ; and  it  appears  probable  that  the 
same  may  be  the  case  with  other  tissues. 
But  though  some  of  the  facts  above  mentioned  furnish  clear  evidence  that  ordinary  solid 
matter  induces  coagulation  by  an  attractive  agency,  it  by  no  means  follows  that  the  tissues 
are  necessarily  merely  neutral  in  their  conduct  towards  the  blood  in  this  matter.  It  is 
quite  possible  that  they  may  exert  an  active  influence  upon  it,  in  consequence  of  which 
the  particles  of  flbrine  may  experience  a mutual  repulsion,  in  the  same  way  as  would 
seem  to  be  the  case  with  the  pigment-granules  of  the  chromatophorous  cells  of  the  frog 
dining  the  process  of  diffusion*.  Indeed  some  such  hypothesis  seems  almost  necessary 
in  order  to  explain  the  remarkable  fact,  that  the  blood  coagulates  within  a few  hours  of 
death  in  the  cavities  of  the  heart  and  great  venous  trunks,  though  it  retains  its  fluidity 
for  days  in  the  smaller  vessels.  Thus  in  the  human  subject  twenty-four  hours  after  death 
I have  found  clots  in  the  heart  and  larger  veins,  including  the  upper  parts  of  the  axil- 
laiy  and  femoral  trunks,  but  fluid  blood  in  the  lower  parts  of  those  vessels  and  all  their 
branches  in  the  limbs.  It  seemed  possible  at  first  that  this  difference  might  depend  on 
the  position  of  the  great  vessels  in  the  thorax  and  abdomen,  where  decomposition  be- 
gins earlier  than  in  the  limbs.  But  this  proved  not  to  be  the  case ; for  in  a horse  twelve 
hours  after  it  had  been  killed,  I found  the  blood  fluid  in  the  intercostal  and  small 
cardiac  veins,  though  coagulated  in  the  vena  cava  and  the  coronary  vein  of  the  heart, 
which  is  in  that  animal  of  very  large  size.  There  being  no  reason  to  suppose  the  walls 
of  the  larger  vessels  differently  constituted  from  those  of  the  smaller  ones,  or  more 
liable  to  undergo  post  mortem  changes,  the  natural  interpretation  of  these  facts  seems 
to  be  that  the  blood  has,  even  within  the  body,  a certain  tendency  to  coagulation, 
coimteracted  by  an  influence  exerted  upon  it  by  the  containing  tissues,  which,  operating 
to  less  advantage  the  larger  the  mass  of  the  fluid  acted  on,  fail,  at  least  after  death,  to 
prevent  it  from  following  its  natural  course  in  vessels  of  a certain  magnitude.  Again, 
d'  we  suppose  that  the  tissues  are  merely  passive  with  regard  to  the  blood,  it  seems  dif- 
ficult to  understand  the  rapid  solidification  of  a large  quantity  shed  into  a cup.  For 
we  have  seen  that  mere  exposure  to  the  atmosphere  will  not  account  for  the  fact ; 
while  at  the  same  time  the  experiments  upon  the  sheep’s  foot  indicate  that  an  ordinary 
solid  has  but  a very  limited  range  of  operation  upon  the  surrounding  blood f,  and  that 
the  clot  which  it  induces  does  not  propagate  itself  to  more  distant  parts ; so  that  the 
central  portions  of  such  a mass  of  blood  should  remain  fluid,  unless  we  admit  that,  when 
* ISee  p.  6-34  of  this  volume. 
t I fiud  that  if  a needle  is  iuti-oduced  into  a vessel  aud  removed  after  the  expiration  of  about  two  minutes, 
before  any  deposit  of  fibrine  has  yet  occurred  upon  it,  a certain  amount  of  coagulation  nevertheless  takes 
place  afterwards  in  that  particular  part  of  the  vessel  in  which  the  needle  had  lain.  This  is  a curious  circum- 
stance, indicating  that  an  impression  leading  to  coagulation  is  produced  upon  the  blood  by  contact  with  an 
ordinary  solid  for  a shorter  time  than  causes,  during  its  presence,  any  visible  solidification.  The  clot,  how- 
ever, is  verj’  slow  in  forming  and  very  incomplete,  so  that  such  cases  cannot  be  compared  with  the  perfect 
and  rapid  coagulation  of  a large  mass  of  blood  ontside  the  body.  Indeed,  when  blood  is  drawn  into  a large 
cup,  a great  deal  of  it  never  touches  the  side  (the  ordinary  solid)  even  for  an  instant. 
