52  New  Method  for  Preparing  Pepsin, 
it  has  to  be  done  very  rapidly,  as  the  pepsin  swells  up  considerably 
and  looses  its  tenacity.  By  operating  in  this  manner  I  obtained  a 
pepsin  which  dissolves  in  acidulated  water  to  quite  a  clear  colorless 
liquid,  but  as  it  still  contains  traces  of  salt,  I  preferred  to  call  it  Pur- 
ified Pepsin. 
I  obtained  a  pepsin  quite  free  of  chloride  of  sodium — which  by 
combustion  did  not  leave  any  ashes — by  swelling  purified  pepsin  in 
water  to  a  thick  mucilaginous  liquid  and  mixing  it  with  alcohol  of  95  per 
cent.  A  gelatinous  almost  transparent  precipitate  is  formed,  which  is 
put  on  a  cloth,  washed  with  diluted  alcohol,  then  pressed  and  dried.  This 
preparation  did  not  leave  any  ashes  by  combustion,  but  I  was  greatly 
disappointed  in  my  expectation,  when  I  found  that  the  digestive 
strength  of  this  pure  pepsin  was  not  as  great  as  that  of  the  purified  pep- 
sin, which  still  contains  sodium  chloride.  No  doubt  the  use  of  alco- 
hol had  impaired  the  digestive  power  of  the  pepsin  to  some  extent. 
Properties  of  Pepsin.  The  pepsin  is,  as  already  mentioned, 
very  soluble  in  water,  when  recently  precipitated,  but  when  once  air 
dry  dissolves  but  slowly  and  only  in  very  small  quantities  in  water. 
The  dry  purified  pepsin,  when  put  into  water,  swells  up  considera- 
bly, becomes  perfectly  white  and,  when  vigorously  shaken,  disintegrates 
to  small  floccules,  which  swim  in  the  liquid  and  remain  suspended  for 
a  long  time,  while  a  very  small  quantity  will  dissolve. 
The  watery  solution  has  an  almost  neutral  reaction,  is  coagulated 
by  boiling,  and  gives  with  alcohol  a  transparent,  gelatinous  precipitate. 
With  sulphate  of  copper  it  remains  clear  at  first,  but  after  several 
hours  becomes  turbid. 
Bi-chloride  of  mercury  gives  immediately  a  white  precipitate. 
With  tannin  a  very  copious  white  precipitate  is  obtained. 
Nitrate  of  lead  forms  a  white  precipitate. 
The  precipitate,  formed  by  chloride  of  sodium,  is  very  characteris- 
tic and  at  the  same  time  very  interesting.  When  a  saturated  solution 
of  chloride  of  sodium  is  added  to  a  clear  solution  of  pepsin,  not  too 
concentrated,  at  first  a  jelly-like  transparent  coagulation  is  formed, 
which  disappears  upon  stirring,  and  the  liquid  acquires  a  slightly  opa- 
lescent appearance ;  after  a  short  time  it  becomes  more  turbid  and 
small  flakes  are  noticed  floating  in  it,  which  soon  will  form  into  small 
transparent  globules  and  as  such  rise  to  the  surface.  When  the  quan- 
tity of  pepsin  in  a  liquid  is  very  small,  the  opalescence  and  turbidity 
