468  Relative  Value  of  Different  Pepsin  Tests.  {'^"'siXilS^''"' 
1.  The  test  is  based  upon  the  amount  of  albumen  which  can  be 
dissolved  in  a  given  time  (including  peptone  and  intermediary 
products),  but  does  not  take  into  consideration  the  amount  of  pep- 
tone actually  formed,  and  this  I  claim  to  be  of  the  greatest  import- 
ance. 
2.  It  directs  that  a  given  pepsin  shall  digest  at  least  50  pts.  of 
coagulated  albumen.  Now,  in  order  to  determine  how  much  albumen 
has  actually  been  dissolved,  it  is  necessary  to  use  an  excess  of  albu- 
men, and  then  weigh  what  reniains  undissolved.  The  test  in  ques- 
tion does  not  specify  how  much  albumen  shall  be  used,  but  leaves  it 
entirely  to  the  option  of  tPie  experimenter.  I  consider  this  to  be  a 
weak  point,  as  it  makes  quite  a  difference  whether  only  a  small  or 
large  quantity  of  albumen  is  used. 
3.  It  is  difficult  to  see  how  accurate  results  are  to  be  obtained  by 
weighing  the  amount  of  undissolved  albumen  remaining  after  a  diges- 
tion, because  it  is  impossible  to  find  two  samples  of  coagulated  albu- 
men, which  contain  exactly  the  same  quantity  of  moisture ;  and 
besides  this,  the  quantity  of  moisture  is  very  liable  to  vary  during  the 
weighing,  owing  to  the  loss  of  moisture  by  evaporation. 
4.  It  is  not  stated  how  long  the  eggs  should  be  boiled.  This  is  a 
very  important  matter,  as  digestion  differs  greatly  according  to  whether 
the  eggs  are  boiled  for  a  short  or  a  longer  time. 
5.  No  provision  is  made  for  the  size  of  the  pieces  of  coagulated  al- 
bumen. This,  also,  is  very  important,  as  it  has  been  found  that  the 
greater  the  surface  of  the  albumen  exposed  to  the  peptic  ferment,  the 
greater  will  be  the  amount  of  albumen  digested. 
6.  This  test  applies  only  to  saccharated  pepsins,  and  no  provision  is 
made  for  other  brands  of  pepsin. 
It  will,  therefore,  be  seen  that  the  U.  S.  P.  pepsin  test  is  absolutely 
unreliable  and  misleading. 
Lately  my  attention  has  been  called  to  a  pepsin  test,  which  I  will 
designate  by  its  author's  name,  the  "  Manwaring  test.^^  In  this  test 
Manwaring  has  tried  to  avoid  as  much  as  possible  the  bad  points  of 
the  U.  S.  P.  test;  but  in  doing  this  he  has  stumbled  against  other 
sources  of  error  which  I  will  try  to  make  clear  further  on. 
The  test  can  best  be  described  in  the  words  of  its  author  : 
"  The  design  of  the  following  mode  of  testing  the  dissolving  power 
of  pepsin  is  to  conform  as  nearly  as  possible  to  the  U.  S.  P.  test,  which, 
contemplating  the  testing  of  the  saccharated  form,  makes  no  provi- 
