544  Standardisation  of  Commercial  Papain.  { December 'wu"' 
are  not  given.  North  does  not  state  whether  or  not  the  active 
samples  contained  any  starch,  although  this  adulterant  was  noted 
by  him  in  the  valueless  samples.  North  used  the  test  which  is  official 
for  pepsin.  A  residue  of  36  c.c.  is  obtained  from  ten  grammes  of 
coagulated  egg-albumin.  In  the  assay  0.05  gramme  of  papain  is 
allowed  to  act  on  ten  grammes  of  albumin.  After  digestion  with  a 
good  sample  of  papain  a  residue  of  only  6  c.c.  remains.  In  his 
calculations  North  allows  for  a  blank  of  1  c.c,  exactly  as  in  the  U. 
S.  P.  method  for  pepsin.  The  proteolytic  activity  then  was  cal- 
culated as  follows :  There  remained  6-1  or  5  c.c.  of  albumin  after 
the  digestion,  hence  30  c.c.  was  digested.  The  proteolytic  ratio, 
therefore,  was  ft  or  ?.  If  the  papain  had  digested  the  10  grammes 
completely,  the  proteolytic  ratio  would  have  been  1  :  200.  In  this 
case,  then,  the  ratio  was  1  :  171.  This  ratio,  like  the  one  given  by 
Graber,  is  for  digestion  in  an  acid  medium. 
Rippetoe4  assayed  papain  by  using  40  c.c.  of  a  0.1  per  cent, 
sodium  hydroxide  solution,  10  grammes  of  egg-albumin  (prepared 
as  directed  in  the  U.  S.  P.),  and  by  carrying  out  the  digestion  at 
520  C.  for  six  hours.  The  quantity  of  papain  used  was  0.1  or  0.2 
gramme.  The  residue  left  after  digestion  was  transferred  to  a 
graduated  cylinder  and  the  final  volume  made  up  to  70  c.c.  The 
proteolytic  activity  was  indicated  by  the  fact  that  digestion  with 
0.1  gramme  papain  left  a  residue  of  18  c.c,  while  a  blank  measured 
43  c.c  Other  experiments  described  by  Rippetoe  show  the  in- 
hibiting action  of  hydrochloric  acid  when  present  in  quantities  of 
0.2  per  cent,  or  0.3  per  cent. 
H.  M.  Adams  5  again  calls  attention  to  the  presence  of  starch, 
and  points  out  the  fact  that  pepsin  may  be  detected  by  making  a 
quantitative  digestion  of  beef  in  the  presence  of  0.2  per  cent,  hydro- 
chloric acid.  Adam's  method  of  assay  is  identical  with  that  de- 
scribed by  Graber,  except  that  the  medium  employed  is  neutral  in- 
stead of  acid.  Results  are  given  showing  the  inhibiting  action  of 
0.3  per  cent,  hydrochloric  acid. 
In  a  recent  paper  F.  F.  Shelley  6  has  applied  a  modification  of 
Sorensen's  method,  and  offers  a  standard  for  pawpaw  juice  on  the 
*Jour.  Ind.  and- Eng.  Chem.,  4,  517  (1912). 
6  Jour.  Ind.  and  Eng.  Chem.,  6,  669  (1914). 
8  Analyst,  39,  170. 
