Am.Jour,  Pharm.  £  TJlCOnCS  of  Blood-C 'oaguldtiotl  703 
essential  to  the  success  of  the  investigation  to  determine  how  the 
course  of  the  process  could  be  protracted  and,  moreover,  how  it  could 
be  stopped  at  the  first  period  of  its  evolution,  so  as  to  make  pos- 
sible the  separation  of  the  cells  from  the  still  liquid  plasma.  Several 
methods  have  been  devised;  I  shall  mention  them  very  briefly. 
Concentrated  salts,  magnesium  sulphate  for  instance,  hinder  the 
coagulation.  Common  salt  especially  answers  the  purpose,  being  a 
normal  constituent  of  the  organism.  Blood  from  the  artery  to  which 
from  three  to  five  per  cent,  of  salt  has  immediately  been  added  yields 
by  centrifugalization  a  clear  plasma  which  does  not  clot  so  long  as 
the  high  saline  concentration  is  maintained,  but  which,  when  diluted 
with  an  amount  of  distilled  water  sufficient  to  re-establish  the  normal 
saline  content,  clots  rather  quickly.  Decalcifying  salts,  the  type  of 
which  is  sodium  oxalate,  prevent  completely  the  coagulation,  calcium 
salts  being  necessary  to  this  phenomenon.  By  centrifugalization  a 
clear  plasma  is  obtained,  which  tends  to  clot  when  a  soluble  calcium 
salt,  such  as  calcium  chloride,  is  restored. 
Coagulation  is  also  prevented  if  to  the  active  contact  of  glass  a 
contact  is  substituted,  which  is  not,  if  we  may  so  express  it,  felt  by 
the  blood  or  the  plasma.  A  liquid  does  not  feel  a  wall,  I  mean  does 
not  react  physically  to  it,  unless  it  is  capable  of  adhering  to  it. 
Freund  was  the  first  to  show  that  blood  flowing  from  the  artery 
does  not  clot,  or  at  least  clots  very  slowly,  when  received  in  a  vessel 
the  inside  of  which  has  been  coated  with  oil  or  vaseline.  Since  it 
forms  a  solid  coating,  paraffin  is  very  suitable  to  such  experiments, 
and  frequently  permits  the  separation  of  the  cells  and  the  plasma 
by  centrifugalization.  In  conjunction  with  Gengou  I  observed  that 
by  these  means  a  clear  plasma  can  be  obtained  and  be  kept  fluid  for 
twenty-four  hours,  but  that  clotting  soon  occurs  when  the  plasma  is 
brought  into  contact  with  glass.  This  experiment  shows  that  the 
contact  of  glass  can  bring  about  its  effect  without  the  presence  of 
any  cells,  that  is,  without  any  vital  interference — we  have  to  do 
with  a  physico-chemical  phenomenon. 
The  blood  of  certain  animals,  namely,  birds  and  fishes,  as 
Delezenne  has  shown,  clots  very  slowly  by  itself,  coagulation  being 
greatly  hastened  by  the  addition  even  of  traces  of  tissue  extract. 
Without  the  help  of  decalcification  or  of  paraffin  coating  the  blood 
of  a  bird  will  remain  fluid  for  a  long  time  and  even  yield  by  centrif- 
ugalization a  permanently  liquid  plasma,  provided  that  the  tube  in- 
