50  New  Method  for  Preparing  Pepsin.  {^feJftSBT* 
time  trying  to  improve  it,  I  discovered  some  tests  which  I  considered 
useful  in  the  preparation  of  dry  pepsin.  Before  this  I  had  wished 
to  prepare  pepsin  in  the  dry  state,  but  was  not  inclined  to  follow  the 
tedious  and  in  some  way  uncertain  processes  usually  given. 
Following  up  the  hint  received  by  certain  tests  with  a  number  of 
experiments,  I  succeeded  at  last  to  obtain  a  very  satisfactory  product. 
The  action  of  saturated  solutions  of  some  of  the  neutral  salts  of 
the  alkalies  on  different  protein  substances  induced  me  to  try  their  ef- 
fect on  pepsin.  For  this  purpose  I  prepared  an  extraction  of  the  mu- 
cous membrane  of  fresh  hogs  stomachs  with  water,  acidulated  with 
muriatic  acid,  which  after  repeated  filtrations  formed  an  opalescent 
yellowish  liquid.  Equal  volumes  of  this  liquid  and  of  a  saturated 
solution  of  sulphate  of  soda,  when  well  mixed  together,  formed  a 
precipitate,  which  was  collected  on  a  filter,  pressed  and  dried ;  a  very 
small  quantity  of  it,  dissolved  in  water  with  the  aid  of  a  few  drops 
of  hydrochloric  acid,  dissolved  coagulated  albumen.  Other  satura- 
ted saline  solutions  were  now  experimented  with,  viz  :  of  sulphate  of 
magnesia  and  chloride  of  sodium,  and  also  a  solution  of  chloride  of 
calcium  of  1.27  spec.  grav. 
By  these  solutions  precipitates  were  likewise  found  to  form,  posses- 
sing properties  identical  with  that  obtained  by  sulphate  of  soda,  but 
I  finally  decided  to  employ  chloride  of  sodium  as  the  precipitant,  as 
by  a  comparative  test,  which  of  the  four  different  salts  would  produce 
the  most  precipitate,  the  proportion  was  :  chloride  of  sodium  4,  sul- 
phate of  magnesia  3 J,  sulphate  of  soda  2,  chloride  of  calcium  1, 
so  that  chloride  of  sodium  gave  twice  as  much  precipitate  as  sul- 
phate af  soda,  and  four  times  as  much  as  chloride  of  calcium.  But 
besides  the  larger  yield,  the  sodium  chloride  has  the  preference  for  its 
antiseptic^properties.  A  part  of  the  precipitate,  formed  by  sulphate 
of  magnesia  and  allowed  to  remain  in  the  liquid,  had  a  putrid  odor  after 
the  third  day,  while  a  moist  precipitate,  formed  by  chloride  of  sodium 
and  set  aside  purposely  for  experiments,  proved  to  be  good  after  six 
months. 
Preparation  of  Pepsin.  On  this  basis  I  now  began  to  prepare 
pepsin.  Of  the  well  cleaned  fresh  hog  stomach  the  mucous  membrane 
is  dissected  off,  chopped  finely  and  macerated  in  water,  acidulated 
with  muriatic  acid,  for  several  days,  daring  which  time  the  mass  is 
frequently  well  stirred.  The  resulting  liquid,  after  being  strained, 
is,  if  not  clear,  set  aside  for  at  least  twenty-four  hours  in  order  to 
