56  New  Method  for  Preparing  Pepsin.  {AV^i',mtK' 
Pepton  precipitate. — An  equal  volume  of  saturated  salt  solution 
added  to  the  pepton  solution  produces  a  copious,  perfectly  white  pre- 
cipitate, which,  upon  being  collected  on  a  filter,  drained,  pressed  and 
dried,  yields  a  hard  white  substance  containing  pepsin,  peptons,  chloride 
of  sodium  and  a  little  acid.  Put  into  water  it  becomes  translucent,  like 
horn,  and  dissolves  after  some  time. 
Its  solution  has  an  acid  reaction ;  is  not  coagulated  by  heat ;  hy- 
drochloric acid  produces  a  heavy  precipitate  which,  by  dilution  with 
water  or  by  addition  of  more  acid,  will  redissolve ;  with  alcohol  it  be- 
comes opalescent  and  forms  after  some  time  a  precipitate. 
Bichloride  of  mercury  gives  a  heavy  white  precipitate. 
Coagulated  albumen  put  into  the  watery  solution  is  hardly  acted 
upon,  but  when  acidulated  with  hydrochloric  acid  it  is  dissolved. 
Digestive  power  of  the  Pepton  precipitate. — The  digestive 
power  of  the  precipitate,  obtained  by  addition  of  sodium  chloride  to 
the  pepton  solution  is  remarkable.  In  many  cases  a  solution  of  one 
grain  of  the  precipitate  in  one  oz.  of  acidulated  water  dissolved  100 
grains  of  coagulated  albumen. 
With  20  grains  of  saccharated  pepsin  in  2  oz.  of  acidulated  water 
I  dissolved  240  grs.  of  coagulated  albumen  ;  the  precipitate  obtained 
»  from  this  solution  by  chloride  of  sodium  weighed,  when  dry,  12  grains, 
of  which  1  grain  dissolved  100  grs.  of  coagulated  albumen  ;  from  this 
last  solution  again,  by  chloride  of  sodium,  10  grains  of  precipitate  were 
obtained,  of  which  1  grain  dissolved  between  20  and  30  grs.  of  coagu- 
lated albumen.  In  this  way  the  20  grs.  of  saccharated  pepsin,  for 
which  I  only  claim  the  power  to  dissolve  240  grs.  of  albumen  in  6 
hours,  dissolved  at  the  rate  of  between  4000  and  5000  grains. 
The  solution  of  1500  grs.  of  albumen,  obtained  by  fractional  addi- 
tion of  albumen  and  acidulated  water  to  an  acidulated  solution  of 
half  a  grain  of  purified  pepsin,  mentioned  above,  furnished  with 
chloride  of  sodium  a  precipitate,  which  also  had  considerable  digestive 
power. 
Relation  of  Chloride  of  Sodium  to  the  digestive  power  of 
Pepsin. — By  its  preparation  the  commercial,  saccharated  pepsin 
contains  always  a  small  quantity  of  chloride  of  sodium;  in  my  ex- 
periment, to  obtain  a  pure  pepsin  free  of  sodium  chloride,  I  succeeded 
by  using  alcohol,  but  the  resulting  product  had  less  digestive  power 
than  purified  pepsin,  which  still  contains  salt.    It  was,  therefore,  in- 
