466  Relative  Value  of  Different  Pepsin  Tests.  {^"'sipt.alS^''"'' 
known  quantities  of  albumen,  and  weigh  the  undissolved  residues  in 
the  manner  above  indicated. 
An  objection  may  possibly  be  raised  to  this  modified  method,  viz., 
that  albumen  as  ingested  is  not  in  the  form  of  a  dry  powder,  and  that 
we  ought  to  copy  as  nearly  as  possible  the  conditions  existing  in  the 
stomach.  To  this  I  would  reply  that  it  does  not  matter  in  the  least, 
to  us,  as  analysts,  what  are  the  conditions  which  obtain  in  the  stomach ; 
since  there  is  no  absolute  test  for  pepsin,  we  can  only  compare  one 
sample  against  another,  and  that  which  dissolves  the  most  albumen  in 
the  shortest  time  is  taken  to  be  the  best. 
Another  imperfect  method  of  analysis  is  that  employed  in  the  ex- 
amination of  malt  extracts  for  diastase ;  in  which  a  certain  weight  of 
extract  ought  to  dissolve  a  certain  weight  of  starch  in  ten  minutes, 
when  if  it  does  so  dissolve  it,  the  extract  is  a  good  one,  if  not  it  is  to 
be  condemned.  The  more  correct  way  is  to  ascertain  the  reducing 
power  on  Fehling's  solution,  before  and  after  digestion  with  an  excess 
of  starch,  and  I  intend  to  say  a  few  words  upon  this  subject  on  a 
future  occasion,  when  I  have  ascertained  the  maximum  amount  of 
diastase  existing  in  the  best  samples  of  malt. — The  Analyst,  Aug.  1888. 
 *  
RELATIVE  VALUE  OF  DIFFERENT  PEPSIN  TESTS.^ 
By  James  H.  Stebbins,  Jr. 
The  methods  I  propose  to  discuss  in  this  paper  are  three,  viz. : 
the  U.  S.  P.  test,  the  Man  waring  test  and  the  Kremel  test. 
According  to  the  experiments  of  numerous  investigators,  the  peptic 
digestion  of  albuminoids  depends  upon  several  conditions. 
1.  The  temperature. 
The  pepsin  of  fish  acts  energetically  at  20°  C,  but  the  pepsin  of 
mammals  requires  a  higher  temperature,  and  it  has  been  found  that 
peptonization  is  most  active  between  35°  C.-50°  C.  Above  this,  di- 
gestion runs  much  slower  and  ceases  totally  towards  70-80°  C. 
2.  The  quantity  of  pepsin. 
There  being  no  such  thing  as  absolutely  pure  pepsin,  it  has  been 
impossible  to  determine,  with  accuracy,  the  amount  of  albumen  which 
can  be  converted  into  peptone  by  a  given  quantity  of  the  ferment. 
^  Abstract  from  a  paper  in  Journal  of  the  American  Chemical  Society,  March, 
1888. 
