142  The  Opsonins  and  Bacterial  Vaccines.  {^Varc^S)?!™' 
not  so  simple  as  it  at  first  appeared,  as  little  by  little  new  facts  are 
developed  which  amplify  our  knowledge  of  the  subject. 
It  was  shown  by  Denys  and  Leclef,  in  1895,  tnat  when  rabbits 
were  immunized  against  Streptococcus  pyogenes  the  serum  acquired 
but  slight  bactericidal  properties,  but  that  such  serum,  when  brought 
in  contact  with  the  leucocytes  of  normal  or  immunized  rabbits, 
greatly  enhanced  their  phagocytic  activity.  Conversely  no  accelera- 
tion of  phagocytosis  was  observed  when  the  corpuscles  were  brought 
in  contact  with  the  serum  of  a  normal  animal. 
Mennes  two  years  later  confirmed  this  by  showing  that  similar 
results  were  obtained  from  the  blood  serum  of  guinea-pigs  treated 
with  cultures  or  toxins  of  Pneumococci. 
A  method  of  measuring  the  phagocytic  activity  of  the  leucocytes 
was  developed  by  Leishman  in  1902.  In  1 903  Wright  and  Douglas 
made  an  extensive  study  of  the  phagocytes,  when  brought  in  con- 
tact with  suspensions  of  Staphylococcus  pyogenes,  and  were  able  to 
show  : 
(1)  Quoting  from  the  original  :  "  We  have  here  conclusive  proof 
that  the  blood  fluids  modify  the  bacteria  in  a  manner  which  renders 
them  a  ready  prey  to  the  phagocytes.  We  may  speak  of  this  as  an 
'  opsonic  '  effect  (opsono  [a  Latin  verb],  I  cater  for ;  I  prepare  victuals 
for),  and  we  may  employ  the  term  '  opsonins '  to  designate  the  ele- 
ments in  the  blood  fluids  which  produce  this  effect." 
(2)  Normal  blood  serum  and  plasma  possess  the  same  opsonic 
action  upon  bacteria. 
(3)  Serum  loses  its  opsonic  action  when  heated  to  6o°  C.  This 
is  spoken  of  as  inactivated  serum. 
(4)  Inactivated  serum  and  physiological  salt  solution  have  the 
same  influence  upon  phagocytosis. 
(5)  "  The  opsonic  power  of  the  blood  fluids  disappears  gradually 
on  standing,"  losing  about  50  per  cent,  of  its  activity  in  five  or  six 
days. 
(6)  An  anti-opsonic  effect  is  noted  when  blood  serum  is  digested 
with  typhoid  bacilli. 
(7)  When  a  condition  of  immunity  is  conferred  upon  patients  in- 
fected by  Staphylococci,  by  vaccination  with  heated  cultures  of 
Staphylococci,  the  opsonic  action  of  the  patient's  blood  serum  is 
greatly  augmented. 
Neufeld  and  Kimpau  (1904)  found  in  antistreptococcic  and  pneu- 
