674 
ME.  J.  LISTEE  OX  THE  EAELT  STAGES  OE  IXFLMNH.IATIOX'. 
to  the  vein,  except  at  the  lips  of  the  wound*.  This  shows  that  an  ordinaiT  solid  pos- 
sesses an  attraction  for  the  particles  of  the  fibiine,  such  as  is  not  exercised  by  the  walls 
of  the  vessels ; or,  in  other  words,  that  the  vascular  parietes  differ  from  all  ordinarv  sohd 
substances  in  being  destitute  of  attraction  for  that  element  of  the  liquor  sanguinis. 
The  blood-vessels  are  not  the  only  constituents  of  the  animal  body  which  have  these 
remarkable  relations  to  the  blood.  If  the  integument  of  a sheep’s  foot  be  partially 
reflected,  and  one  of  the  subcutaneous  veins  immediately  wounded,  so  as  to  let  some 
blood  run  into  the  angle  between  the  skin  and  the  rest  of  the  limb,  before  any  diyintr 
of  the  tissues  has  occurred,  care  being  taken  that  no  hairs  or  other  solid  matters  have 
been  introduced,  this  blood  will  remain  in  whole  or  in  part  fluid  for  half  an  hour  or 
more ; whereas,  if  blood  from  the  same  vessel  be  placed  in  contact  with  any  ordinary 
solid,  whether  on  the  foot  or  elsewhere,  it  will  coagulate  in  perhaps  five  minutest. 
This  is  sufficient  proof  that  the  subcutaneous  cellular  tissue  resembles  the  lining  mem- 
brane of  the  vessels  in  its  conduct  towards  the  blood.  The  long  time  dming  which  blood 
* From  what  has  been  stated  in  the  text,  it  is  evident  that  the  ammonia  theory  of  Dr.  B.  “W.  Eichabdsov 
does  not  account  for  the  fluidity  or  coagulation  of  the  blood  within  the  vessels.  But  the  facts  mentioned 
by  tliat  gentleman  in  the  valuable  essay  which  has  gained  the  last  Asxlet  Cooper  prize,  and  also  my  own 
experience  [see  the  paper  before  referred  to],  have  convinced  me  that  a certain  amount  of  the  volatile  alkali 
does  exist  in  freshly-drawn  blood,  and  that  it  has  the  effect  of  retarding  the  process  of  coagulation.  This 
principle  must  be  borne  in  mind  in  all  experiments  upon  this  subject,  in  order  to  understand  circumstances 
which  would  otherwise  be  inexplicable.  Thus,  if  the  foot  of  a sheep  be  obtained  with  the  blood  retained  in 
the  vessels  by  a bandage  applied  before  the  death  of  the  animal,  and,  after  reflection  of  the  skin,  a needle  be 
introduced  into  a vein  by  a free  opening  made  by  the  scissors,  a deposit  of  fibrine  will  be  found  upon  it  in 
perhaps  five  minutes ; but  if  the  needle  be  pushed  through  the  coats  of  such  a vein,  so  as  to  introduce  it 
without  previous  wound  of  the  vessel,  and  allow  little  opportimity  for  escape  of  ammonia,  the  deposit  will 
not  take  place  for  a quarter  of  an  hour  or  more.  Agaiu,  the  blood  obtained  by  wounding  a vein  imme- 
diately after  reflecting  the  skin,  within  the  first  few  homs  after  the  death  of  the  animal,  takes  a much 
longer  time  to  coagulate  the  blood  shed  from  the  same  vessel  after  the  lapse  of  half  an  honi'  or  so  ; doubtless 
in  consequence  of  escape  of  ammonia  having  occurred  in  the  interval.  This  circumstance  seems  to  prove 
that  the  ammonia  is  free  ia  the  blood  in  its  normal  condition  AGthin  the  vessels,  and  not  merely  liberated 
during  the  process  of  coagulation ; for  it  is  to  be  remembered  that  the  mere  woimdiug  of  a vein  in  no  way 
interferes  vdth  the  fluidity  of  the  blood  in  it,  except  at  the  woimd. 
t After  the  blood  has  lam  for  some  time  in  the  angle  between  the  skin  and  the  bmb,  it  coagulates,  if 
removed  from  it,  much  more  rapidly  than  blood  freshly  shed  from  a vessel.  Thns,  in  one  case,  blood  let 
out  from  a vein  was  part  of  it  placed  at  once  on  a glass  plate,  and  part  allowed  to  run  into  the  angle 
between  the  skin  and  limb.  That  on  the  glass  plate  was  not  completely  coagulated  for  ten  minutes : but 
that  in  the  other  situation,  having  been  left  for  twenty  minutes,  and  then  transferred  to  the  plate,  \\  as  a 
consistent  clot  within  six  seconds,  indeed  as  soon  as  I could  examine  it.  This  fact  seems  to  me  to  tlnmv 
great  light  upon  the  subject  of  coagulation.  The  sudden  transition  from  perfect  fluidity  to  a coagtdum 
can  only  be  explained,  I conceive,  on  the  hypothesis  that  the  ammonia  had  almost  aU  escaped  while  the 
blood  lay  in  the  angle ; yet  this  escape  had  not  caused  coagulation.  Hence  it  seems  to  follow,  that  am- 
monia is  in  no  way  essential  to  the  fluidity  of  the  blood  while  it  is  surrounded  by  healthy  tissues.  Another 
point,  which  the  simple  experiments  upon  the  sheep’s  foot  show  cleaidy,  is  that  a certain  amount  of  aui- 
monia  in  the  blood  Avill  retard  without  preventing  the  deposit  of  fibrine  upon  a needle  or  other  ordinarv 
soHd  introduced  into  the  vessels  ; and  it  appears  very  doubtful  whether  healthy  blood  ever  contains  sufficient 
ammonia  to  prevent  such  an  occurrence. 
