ADecimh4r!hi9OTm*}      Opsonu  Theory  and  Tuberculosis.  565 
reduces  to  a  minimum,  the  possibilities  of  air  bubbles.  The  tube  in 
question  is  simply  that  of  Wright's  with  a  small  central  bulbous 
swell*:g.  I  say  small  advisedly,  because  if  made  with  a  large  bulb, 
much  of  its  contents  are  lost  on  account  of  its  adherence  to  the 
sides.  To  mix  the  blood  cream  serum  and  the  emulsion  they  are 
passed  and  repassed  through  this  bulb  a  dozen  or  more  times, 
allowing  the  mixture  to  collect  in  the  bulb  in  which  it  is  incubated. 
It-is  important  that  the  contents  of  the  control  tube  and  those  in  the 
others  to  be  tested  should  each  be  passed  through  the  bulb  the 
same  number  of  times. 
PREPARING  THE  EMULSION. 
At  the  Phipps  Institute  we  prepare  our  emulsions  in  a  manner 
similar  to  that  adopted  by  Wright  and  others.  The  bacilli  from 
flasks  of  broth  culture  filtered  through  filter  paper  or  a  Pasteur 
filter  are  washed  in  water  and  subsequently  with  salt  solution  of  a 
strength  of  1-5  per  cent,  and  sterilized.  A  drop  or  two  of  this  same 
strength  salt  solution  is  placed  in  a  mortar  and  a  very  small  mass  of 
bacilli  added.  The  mixture  is  rubbed  up  now  for  ten  to  fifteen 
minutes  when  a  drop  or  two  more  of  the  solution  is  added  and  the 
grinding  process  continued  for  a  few  minutes,  and  so  on,  until  the 
total  amount  of  emulsion  equals  about  I  c.c.  This  is  transferred  to  a 
test  tube,  centrifugalized  a  few  minutes  and  the  supernatant  fluid* 
of  a  milky  opacity  free  from  clumps  of  the  organism,  is  drawn  off  and 
is  ready  for  use.  Nevertheless,  it  is  always  advisable  to  make  a  test 
of  the  emulsion  before  proceeding  to  employ  it  for  investigations 
Failure  to  do  this,  as  I  have  learned  from  bitter  experience,  often 
means  the  useless  sacrifice  of  time  and  labor,  to  say  nothing  of  the 
vexation  to  which  one  is  apt  to  give  vent,  in  a  way  that  is  more, 
forcible  than  elegant.  Too  thick  an  emulsion  renders  counting  of 
the  bacilli  impossible,  or  at  least  difficult  and  uncertain,  while,  if  too 
sparse  the  index  is  materially  affected.  Kinghorn,  Twitchel,  Carter 
and  'others,  in  a  series  of  experiments  have  shown  that  the  phagocytic 
index  is  in  proportion  to  the  dilution.  An  emulsion  which  gives 
from  one  to  four  bacilli  to  a  cell  is  suitable.  It  is  our  custom  to 
prepare  it  in  quantities,  a  good  deal  of  work  being  saved  thereby. 
With  proper  precaution  against  contamination  it  can  be  kept  for 
several  days.  At  Saranac  Lake  Sanatorium  emulsification  is  brought 
about  by  means  of  a  porcelain  ball  mill.    Von  Ruch,  however, 
