Am.  Jour.  Pharm. 
Sept.,  1888. 
Pepsin. 
465 
pieces  of  albumen  were  placed  on  blotting-paper  to  remove  superfluous 
moisture,  and  weighed.  The  gain  in  weight  of  the  albumen  in  the 
check  experiment,  due  to  absorbed  water,  was  calculated  into  percen- 
tage, and  the  same  deducted  from  the  weights  of  the  other  portions 
which  had  been  subjected  to  the  action  of  various  pepsins.  This, 
although  an  improvement  upon  the  old  method,  proved  likewise  un- 
reliable, because  the  water  absorbed  was  not  equal  in  each  experiment. 
The  albumen  which  was  immersed  in  acidulated  water  only  quickly 
dried,  superficially,  when  placed  on  blotting-paper,  whereas  that  which 
had  been  acted  on  by  pepsin  was  rendered  glutinous  and  incapable  of 
being  dried  in  this  manner.  In  fact  one  sample  weighed  considerably 
more  than  it  did  at  starting,  even  after  deducting  the  allowance  for 
water  absorbed. 
I  next  tried  much  smaller  pieces  of  albumen,  about  1  cc,  in  hope 
that  complete  solution  might  ensue,  and  a  time  value  be  obtained.  I 
soon  found,  however,  that  the  solubility  does  not  depend  upon  the 
mass,  but  upon  the  surface  exposed. 
Finally  I  discarded  altogether  the  use  of  fresh  white  of  egg,  and 
had  recourse  to  dry  powdered  albumen,  prepared  by  drying  in  a  steam 
oven  and  levigation  in  a  mortar.  With  this  I  succeeded  in  getting 
accurate  comparisons  between  the  digestive  powers  of  various  pepsins. 
Albumen  in  this  form  dissolves  with  rapidity,  owing  to  its  state  of 
fine  division.  Any  remaining  undissolved  can  be  filtered  ofP  on  a 
counterpoised  filter  paper,  and  heated  in  a  water  oven  until  absolutely 
dry.  It  is,  however,  unnecessary  to  do  this  when  two  samples  only 
are  compared  against  each  other,  nor  is  it  essential  to  know  the  actual 
weight  of  albumen  employed,  provided  it  be  the  same  in  each  experi- 
ment. ,  This  is  ensured  by  placing  some  on  the  naked  pan  of  the 
balance  (there  is  no  objection  to  so  doing,  as  it  is  a  dry  gritty  powder, 
and  does  not  adhere  to  the  metal),  and  counterpoising  by  a  similar 
addition  to  the  other  pan. 
Let  the  albumen  fall  on  the  centre  of  the  filtered  liquid,  avoiding, 
if  possible,  contact  with  the  glass  of  the  beaker.  It  soon  sinks,  and 
after  the  lapse  of  some  time,  a  simple  inspection  will  show  which  is 
dissolving  with  the  greater  rapidity.  Agitation  assists  solution,  there- 
fore take  the  two  beakers,  one  in  each  hand,  and  rotate  the  contents 
equally.  When  one  sample  has  dissolved  all  the  albumen  it  is  mani- 
festly superior  to  the  other  which  has  failed  to  do  so  in  the  given  time. 
If  many  samples  have  to  be  compared  it  will  be  necessary  to  start  with 
