Am.  Jour.  Pharm. ") 
December,  1915.  j" 
Method  for  Estimation  of  Pepsin. 
543 
necessary  first  to  neutralize,  and  in  so  doing  a  grave  error  is  made. 
The  effect  upon  pepsin  of  alkalis,  even  in  dilution,  is  a  question  about 
which  there  is  no  dissension.  Even  very  dilute  alkalis  will  inhibit, 
if  not  destroy,  the  action  of  pepsin.  The  following  experiment  brings 
out  the  point :  A  o.i  per  cent,  solution  of  scale  pepsin  was  made  con- 
taining 77.0  Cc.  N/14  hydrochloric  acid.  I  Cc.  of  this  solution  was 
exactly  neutralized  with  0.77  Cc.  N/14  sodium  hydroxide  and  diluted 
to  10.  Another  1  Cc.  portion,  without  neutralization,  was  diluted  to 
10.  Both  were  now  subjected  to  digestion  at  500  to  520  C.  for  15 
minutes,  as  follows : 
Pepsin  Solution. 
Neutralized  tubes.* 
'  Unneutralized  tubes. f 
1 
2 
3 
4 
5 
1 
3 
4  ! 
5 
0.25  per  cent  pea  globulin  . 
I 
I 
I 
I 
1 
1 
1  i 
1 
0.6  per  cent  HQ  
I 
I 
I 
1 
I 
; 
1 
1 
r 
Distilled  water  
0.9 
O.J 
0-5 
0.2 
0.0 
0.9 
0.7 
0.5 
0.2 
0.0 
10  x dilated  pepsin  
O.I 
0-3 
0-5 
0.8 
1.0 
0.1 
0.3 
0.5 
0.8 
1.0 
*  No' perceptible  digestion  in  any. 
t  Complete  digestion  in  3,  4,  and  5.    Pepsin  =  (1      0.5)  X  10  =  20. 
Controls:  Boiled  pepsin  4  globulin  +  acid  =  negative.    Water  +  globulin  +  acid  =  nega- 
tive. 
In  the  above  case  it  is  evident  that  the  greatest  part  of  the  pepsin 
has  been  destroyed  or  inhibited.  All  of  the  pepsin  has  not  necessarily 
been  destroyed,  but  evidently  enough  to  prevent  digestion  within  the 
limit  of  time  and  temperature.  If  more  pepsin  and  less  acid  were 
present,  then  after  neutralization  one  would  expect  to  find  some 
pepsin.  It  seems  that  an  enzyme  is  not  destroyed  immediately,  in  the 
way  an  acid  solution  can  be  neutralized.  In  neutralization  of  weak 
acid  solutions  with  alkali  as  dilute  as  N/14  sodium  hydroxide,  there  is 
no  question  but  that,  for  the  moment,  there  is  an  alkaline  reaction  at 
the  point  of  contact  with  the  alkali.  Since  this  is  true,  if  we  partially 
neutralize  a  weak  acid  solution  containing  pepsin,  there  ought  to  be 
a  reduction  of  pepsin.  About  the  effect  of  alkalis  on  pepsin  there  can 
be  no  question ;  hence  the  above  assumption  is  supported  by  the  fol- 
lowing experiment :  Gastric  contents  were  removed  from  two  normal 
individuals,  after  an  Ewald  test  meal,  and  these  determinations  made  : 
Total 
acidity. 
Free 
acidity. 
Rose 
exact. 
Proposed 
method. 
Jacoby 
exact. 
Jacoby 
neutral- 
ized. 
Neutral- 
ized one- 
half,  then 
Rose. 
R 
55 
60 
42 
45 
Trace. 
Trace. 
41 
41 
100 
100 
Trace. 
Trace. 
16 
16 
M  
