544 
Method  for  Estimation  of  Pepsin. 
t  Am.  Jour.  Pharm. 
\   December,  1915. 
Goodman,4  working  with  the  Jacoby  method,  concluded  from 
a  limited  number  of  cases  that  a  uniform  acidity  was  not  necessary. 
Rose  takes  exception  to  this  and  demands  for  his  method  a  final  uni- 
form acidity.    He  states  : 
It  will  be  seen  that  the  enzyme  content  is  expressed  by  much  larger  num- 
bers when  the  total  acidity  is  0.05  per  cent,  of  hydrochloric  acid  than  when  it 
is  0.2  per  cent.  This  is  not  due  to  the  greater  activity  of  the  pepsin  under 
such  conditions,  but  to  the  decreased  turbidity  of  the  globulin  solution,  resulting 
from  the  decreased  acidity. 
In  part  I  can  agree  with  him.  but  I  do  not  see  that  this  justifies  the 
neutralization  of  the  stomach  contents  under  examination.  His 
statement  is  true  if  the  final  acidity  is  low,  but  if  i  Cc.  of  0.6  per  cent, 
hydrochloric  acid  be  added,  then  the  additional  acidity,  present  by 
virtue  of  that  contained  in  the  gastric  contents,  can  have  no  influence 
on  the  turbidity,  and  hence  is  not  misleading  as  to  enzymolysis.  The 
following  typical  experiment  illustrates  the  point : 
Tubes. 
I 
2 
3 
4 
5 
6 
7 
8 
9 
10 
II 
12 
13 
1  Cc.  of  per  cent. 
HC1  
1   Cc.  of  0.25% 
pea  globulin.  . 
0.6 
1 
0.3 
1 
O.15 
I 
0.075 
1 
0.0375 
I 
0.0187 
1 
0.0093 
I 
0.0046 
1 
O.OO23 
I 
0.0012 
I 
0.0006 
I 
0.0003 
H2O 
I 
Final  total  acid- 
ity, per  cent . . 
0.3 
0.15 
0.075 
0.0375 
0.0187 
0.0093 
O.OO46 
0.0023 
0.0012 
0.0006 
0.0003  0.0001 
0.0 
These  tubes  were  allowed  to  stand  15  minutes,  and  at  the  end  of 
that  time  tubes  1,  2,  3,  4,  and  5  showed  the  same  maximum  turbidity, 
so  far  as  perceptible  to  the  naked  eye.  Tubes  6,  7,  and  8  showed  no 
maximum  and  progressively  less  turbidity.  Tubes  9  to  13  were  all 
clear,  not  even  showing  an  opalescence.  The  same  result  was  ob- 
tained at  the  end  of  an  hour.  To  another  series,  with  the  above 
result  at  the  end  of  15  minutes,  was  added  1  Cc.  of  0.6  per  cent, 
hydrochloric  acid  ;  after  10  minutes,  all  the  tubes  showed  a  maximum 
turbidity,  with  no  perceptible  difference  between  them.  That  is  to 
say,  if  the  final  total  acidity  is  only  0.2  per  cent.,  or  increased  to  even 
0.4  per  cent.,  there  is  no  apparent  difference  in  the  turbidity  of  the 
tubes.  This  certainly  shows,  from  the  standpoint  of  turbidity,  that 
it  is  unnecessary  first  to  neutralize  the  gastric  contents.  Even  were 
the  total  acidity  of  a  gastric  juice  under  examination  100  to  120.  the 
