AFeJn;iP872RM'}    New  Method  for  Preparing  Pepsin.  53 
is  hardly  noticed,  but  after  some  time  the  small  globules  will  appear 
on  the  surface. 
The  watery  solution  of  pepsin  decomposes  readily;  after  a  few 
days  small  flakes  separate  from  the  clear  solution,  which  increase  in 
number  by  longer  standing,  and  on  the  fourth  day  already  it  emits  a 
foul  disagreeable  odor. 
The  watery  solution  of  pepsin  shows  very  little  action  on  coagula- 
ted albumen  ;  a  certain  quantity  of  albumen,  which  by  a  watery  so- 
lution was  hardly  acted  upon  in  twenty-four  hours,  was  readily  dis- 
solved, after  addition  of  a  few  drops  of  hydrochloric  acid.  A  watery 
extraction  of  the  mucous  membrane  was  also  experimented  with,  with 
the  same  result;  before  the  addition  of  hydrochloric  acid  it  did  not 
dissolve  albumen  ;  after  acidulating  it  the  albumen  dissolved  easily. 
Properties  of  Acidulated  Pepsin.  An  acidulated  solution  of 
pepsin  was  made  of  such  strength,  that  one  fluid-ounce  contained  one 
grain  of  purified  pepsin  and  two  drops  of  hydrochloric  acid,  and  ex- 
perimented with. 
By  boiling,  the  clear  liquid  becomes  turbid  and,  upon  cooling,  depos- 
its flakes. 
By  addition  of  alcohol  it  remains  clear  at  first,  but  upon  standing, 
flakes  of  pepsin  separate  from  it. 
Strong  hydrochloric  acid  produces  slight  turbidity,  which  disappears 
by  addition  of  more  acid  or  by  dilution  with  water. 
Chloride  of  sodium  gives  the  characteristic  precipitate. 
Bi-chloride  of  mercury  produces  opalescence. 
Tannin  forms  a  heavy  precipitate,  soluble  in  hydrochloric  acid. 
Gallic  acid  shows  no  action. 
Carbonate  and  bi-carbonate  of  soda  produce  a  precipitate  soluble 
in  excess. 
Modified  Pepsin. — A  solution  of  carbonate  of  soda  carefully 
added  to  a  solution  of  pepsin  produces  a  precipitate  which,  upon  being 
separated  from  the  liquid,  will  prove  to  be  pepsin  ;  but  a  little  more 
of  carbonate  of  soda  will  redissolve  it  again,  and  the  liquid  no  longer 
contains  pepsin  ;  that  is,  the  pepsin  is  destroyed  or  modified. 
This  circumstance  caused  me  to  say  in  my  essay  (Amer.  Journ.  of  Ph. 
1871,  page  6,)  "  dry  pepsin,  precipitated  with  alcohol  from  its  solution, 
did  not  act  at  all  on  albumen ,"  which  remark  I  herewith  revoke  as 
erroneous.  The  fact  was  that,  intending  to  make  pure  pepsin  and 
not  getting  a  precipitate  by  alcohol  in  the  sour  solution,  I  added  car- 
