Take  two  samples  of  cod-liver  oil,  one  perfcrHy  neutral  (by  no  means  easily
procured),  and  an  ordinary  brown  o\\.—e.g.,  De  Jongh's.  The  latter  contains
much  free  fatty  acid.  Place  5  cc.  of  each  in  two  test-tubes,  and  pour  on  them
a  little  solution  of  sodic  carbonate  (i  per  cent.).  The  neutral  oil  is  not
emulsified,  while  the  rancid  one  is  at  once,  and  remains  so.  Many  oils  that
do  not  taste  rancid  contain  free  fatty  acids,  and  only  some  of  them  give  up
their  acid  to  water,  just  according  as  the  fatty  acid  is  soluble  or  not  in  water.
8.  (B.)  The  Fat-Splitting  Action  of  Pancreatic  Juice  (Steapsin
or  pialyn,  the  ferment).
(a.)  Prepare  a  Perfectly  Neutral  Oil. — A  perfectly  neutral  oil  is  required,
and  as  all  commercial  oils  contain  free  fatty  acids,  they  must  not  be  used.
Place  olive  or  almond  oil  in  a  porcelain  capsule,  mix  it  with  not  too  much
baryta  solution,  and  boil  for  some  time.  Allow  it  to  cool.  The  unsaponified
oil  is  extracted  with  ether,  the  ethereal  extract  separated  from  the  insoluble
portion,  and  the  ether  evaporated  over  warm  water.  The  oil  should  now  be
perfectly  neutral  {Krukcnhcrg).
{b.)  Mix  the  oil  with  finely  divided,  perfectly  fresh  pancreas  (not  a  watery
extract),  and  keep  it  at  40''  C.  After  a  time  its  reaction  becomes  acid,  owing
to  tlie  formation  of  a  fatty  acid.  This  experiment  is  by  no  means  easy  to  per-
form, and  some  observers  deny  altogether  the  existence  of  a  fat-splitting
fennent.  The  free  fatty  acids  thus  liberated  unite  with  the  alkaline  bases  of
bile,  and  form  soaps.
9.  IV.  Milk-Curdling  Ferment.
