Am.  Jour.  Pharm. 
December,  1915. 
J     Method  for  Estimation  of  Pepsin.  541 
A  MODIFICATION  OF  ROSE'S  METHOD  FOR  THE 
ESTIMATION  OF  PEPSIN.* 
By  Maurice  H.  Giyexs,  Assistant  Biochemist,  United  States  Public  Health 
Service. 
In  spite  of  all  the  work  that  has  been  clone  to  isolate  pepsin  in  a 
pure  condition  the  results  have  been  negative ;  for  this  reason  it  is  as 
yet  impossible  to  offer  a  method  for  its  quantitative  determination. 
As  a  matter  of  fact,  while  a  number  of  so-called  quantitative  methods 
have  been  devised,  the  results  obtained  are  only  of  value  from  a 
comparative  standpoint.  Such  comparisons,  however,  are  of  decided 
importance  and  any  means  which  will  further  their  approach  to  a 
standard  basis  are  worthy  of  consideration.  It  is  with  this  view  that 
a  modification  of  Rose's  method  is  here  offered. 
It  is  not  necessary  to  review  all  of  the  many  methods  proposed 
for  the  estimation  of  pepsin.  Suffice  it  to  say  that  those  of  Mett,1 
Jacoby-Solms,2  and  Rose 3  are  most  used.  Each  has  certain 
advantages  at  once  apparent  to  a  worker,  but  the  rapidity  and  ease  of 
the  latter  method,  with  the  modification  here  offered,  would  seem  to 
warrant  its  use.  The  Mett  method  has  been  in  use  so  long  that  it  is 
not  necessary  to  describe  the  procedure.  That  of  Jacoby  depends 
on  the  digestion  of  a  0.5  per  cent,  solution  of  ricin  in  5  per  cent, 
sodium  chloride,  at  37 0  C.  for  three  hours,  with  varying  amounts 
of  a  V100  diluted  gastric  juice.  Rose's  method  demands  the  diges- 
tion of  a  0.25  per  cent,  solution  of  pea  globulin  in  10  per  cent,  sodium 
chloride,  at  370  C.  for  one  hour  or  at  500  to  520  C.  for  15  minutes, 
with  varying  amounts  of  a  previously  neutralized  gastric  juice  usually 
diluted  five  times. 
Against  the  use  of  both  the  Mett  and  the  Jacoby  methods  can  be 
offered  at  once  the  consumption  of  time,  not  to  mention  other  factors. 
It  is  not  always  possible- to  get  ricin  and  this  led  us  to  use  the  Rose 
method.  It  does  not  seem  justifiable,  however,  to  neutralize  the 
gastric  contents  as  Rose  does.  He  lays  much  stress  upon  this  point 
and  says  the  failure  to  neutralize  is  a  serious  objection  to  the  Jacoby 
method.  He  thinks  the  final  acidity  in  each  tube  should  be  the  same. 
In  so  neutralizing  the  method  is  rendered  unreliable.       Evidence  is 
*  Reprinted  from  Bulletin  No.  101,  Hygienic  Laboratory,  United  States 
Public  Health  Service. 
