^°'sip?.?im'"'*}    Relative  Value  of  Different  Pepsin  Tests.  467 
We  know  only  that  the  amount  is  very  large,  provided  that  from 
time  to  time  a  little  acid  and  water  is  added  in  order  to  maintain  a 
certain  degree  of  dilution. 
The  quantity  of  albuminoid  which  can  be  digested  in  a  given  time 
increases  rapidly  with  the  quantity  of  pepsin  employed  till  it  reaches  a 
maximum,  and  then  decreases  slowly.  The  quantity  of  peptone  finally 
obtained  increases  with  the  proportion  of  pepsin. 
3.  The  quantity  of  water. 
As  the  products  of  digestion  accumulate,  the  rate  of  peptonization 
gradually  decreases.  The  addition  of  a  fresh  quantity  of  acidulated 
water  causes  the  peptic  action  to  recommence  until  it  has  reached  a 
certain  limit,  beyond  which  the  reaction  ceases  entirely. 
4.  The  nature  and  quantity  of  the  acid  used. 
A  large  number  of  acids  may  take  the  place  of  hydrochloric  acid  in 
peptic  digestions,  but  none  of  them  are  as  efficient  as  the  latter.  A. 
Mayer  found  that  with  the  use  of  hydrochloric  acid,  complete  peptoni- 
zation occurred  in  from  3  to  5  hours ;  with  nitric  acid  in  about  5 
hours,  with  oxalic  acid  in  13  hours,  and  with  sulphuric  acid  in  19 
hours. 
According  to  Briicke,  peptonization  is  already  very  active  in  a 
medium  containing  only  0.8  parts  of  hydrochloric  acid  per  1,000,  and 
attains  its  maximum,  with  a  concentration  of  1  pt.  of  acid  in  1,000  of 
water.  A  too  large  proportion  of  acid  hinders  peptonization,  7  pts. 
of  acid  per  1000  of  water  being  sufficient  to  make  the  action  very 
slow.  Mayer  thinks  that  the  most  favorable  proportion  of  acid  is  2 
pts.  per  1,000  water,  or  0.2  per  bent. 
5.  The  time  of  action. 
6.  The  variety  and  character  of  the  albumen. 
One  of  the  most  largely  used  tests  in  this  country  is  the  U.  S.  P. 
test,  which  reads  as  follows  : 
"  One  pt.  of  saccharated  pepsin  dissolved  in  500  pts.  of  water,  acid- 
ulated with  7.0  pts.  of  hydrochloric  acid,  should  digest  at  least  50  pts. 
of  hard  boiled  egg  albumen,  in  5  or  6  hours,  at  100-104°  F.  (37.5 
-40°  C.)'^ 
The  above  test  seems  simple,  but,  in  reality,  it  is  unreliable  and 
misleading,  as  no  two  persons  using  the  same  pepsin  can  obtain  the 
same  or  even  approximate  results ;  it  is,  therefore,  not  surprising  that 
we  meet  with  such  a  diversity  of  conclusions. 
The  weak  points  in  the  above  test  are  the  following  : 
