706  Theories  of  Blood-Coagulation  \Am'S™\m*rm' 
with  the  tissue  extract  so  as  to  generate  a  fresh  supply  of  throm- 
bin. 
But  the  question  immediately  arises  whether  such  an  assump- 
tion, deduced  from  experiments  in  which  tissue  extract  plays  an  im- 
portant role,  may  be  without  further  question  applied  to  the  auto- 
matic coagulation  of  pure  blood.  As  a  matter  of  fact,  it  must  be 
kept  in  mind  that  injected  into  the  circulation,  the  tissue  extracts 
are  highly  toxic,  causing  sudden  death  due  to  intravascular  coagula- 
tion. Undoubtedly  they  contain  some  coagulating  principle  foreign 
to  the  blood  itself.  This  substance  upon  which  I. shall  not  dwell  today, 
our  present  task  being  merely  the  study  of  the  coagulation  of 
pure  blood,  in  all  probability,  is  of  an  albuminoid  nature,  and  is 
markedly  thermolabile.  It  is  specifically  related  to  the  tissues,  does 
not  exist  in  the  blood,  and  could  not  be  considered  as  a  real  mother- 
substance  of  thrombin.  But  we  must  immediately  add  that,  besides 
this  peculiar  principle,  the  tissue  cells,  nevertheless,  contain  one  of 
the  two  mother-substances  of  thrombin.  This  exists  also  in  the 
blood  cells,  is  of  lipoid  nature  and  may  be  designated  cytozyme. 
The  other  mother-substance,  called  by  us  serozyme,  is  furnished 
by  the  blood  fluid  and  is  present  in  the  serum.  But  let  us  see  how 
these  determinations  have  been  arrived  at? 
The  assumption  that  the  blood  cells  furnish  one  of  the  mother- 
substances  of  thrombin  is  in  perfect  accordance  with  the  results  of 
experiments  dealing  with  the  part  played  by  those  cells,  and  chiefly 
by  platelets,  in  the  coagulation.  Platelets  can  be  easily  separated  by 
centrifugalizing  oxalated  blood  at  a  moderate  speed  for  a  short 
while ;  being  very  light,  they  remain  in  suspension,  whereas  red  and 
white  corpuscles  are  thrown  down,  the  turbid  supernatant  fluid 
pipetted  off  being  very  rich  in  platelets.  Now  if  such  a  platelet- 
plasma  is  centrifugalized  for  a  long  time  and  at  a  very  nigh  speed, 
the  platelets  finally  are  sedimented  and  a  clear  plasma  may  be  ob- 
tained from  which  the  platelets  have  not  been  thoroughly  eliminated, 
this  being  impossible,  but  in  which  they  are  present  only  in  small 
numbers.  Comparing  these  two  plasmas,  the  one  very  rich,  the  other 
very  poor  in  platelets,  Lesourd  and  Pagniez  found  that  after  recalci- 
fication  the  former  clots  rapidly,  the  latter  slowly.  Completing  these 
experiments,  with  Delange,  by  comparing  the  coagulating  influence, 
on  oxalated  plasma,  of  the  two  serums  yielded  respectively  by  the 
coagulation  of  plasma  rich  in  platelets  and  of  plasma  poor  in  plate- 
