506 
Pepsin  Assay 
Am.  Jour.  Pliarm. 
Oct..  1892. 
weighed  as  quickly  as  is  consistent  with  accuracy  on  a  balanced 
watch-glass  or  evaporating  dish,  and  if  any  sticks  to  the  dish  it 
must  be  rinsed  out  with  some  of  the  acidulated  water  and  thus  all 
transferred  to  the  bottle  or  flask.  The  weighed  albumen  is  to  be 
triturated  in  a  small  mortar  with  some  of  the  acidulated  water,  and 
the  mixture  then  poured  into  the  bottle  containing  the  pepsin,  using 
the  remaining  acidulated  water  for  rinsing  purposes.  The  corked 
bottle  and  contents  are  now  to  be  subjected  to  the  heat  of  the  water- 
bath,  maintained  at  105  °  F.  as  nearly  as  possible,  for  6  hours,  being 
well  shaken  not  oftener  than  once  every  five  minutes  and  at  least 
every  ten  minutes,  always  restoring  the  bottle  to  the  bath  quickly. 
At  the  end  of  6  hours,  if  the  pepsin  tests  1  :  2,500,  not  more  than  a 
few  undissolved  flakes  should  remain,  consisting  mostly  of  the 
membraneous  portion  of  egg. 
If  the  means  of  weighing  are  sufficiently  accurate,  it  is  an 
advantage  as  regards  labor  and  time  to  use  gr.  of  pepsin  instead 
of  y2  gr.,  reducing  correspondingly  the  albumen  and  acidulated 
water,  or,  accuracy  may  be  attained  and  still  less  materials  used,  by 
thoroughly  triturating  in  a  small  Wedgewood  mortar  1  gr.  of  a 
pepsin  with  9  gr.  sugar  of  milk,  1  I+/  gr.  of  the  mixture  containing 
gr.  of  the  pepsin.  The  greatest  care  is  necessary  in  weighing 
the  pepsin,  for  part  of  a  grain  of  a  I  :  2,500  test  pepsin  dis- 
solves 25  gr.  of  albumen.  Prescription  weights  and  scales  are 
generally  far  too  inaccurate  for  operating  with  less  than  y2  gr.  ot 
pepsin.  It  is  certainly  advisable  to  provide  a  set  of  accurate  grain 
weights. 
The  foregoing  proportions  of  materials  are  given  for  the  purpose 
of  enabling  one  to  prove  whether  or  not  a  pepsin  test  1  :  2,500;  or, 
which  of  two  or  more  brands  most  closely  approximate  this  power, 
in  which  case  the  same  quantities  of  materials  are  always  to  be  used. 
If  testing  a  pepsin  claimed  to  be  of  higher  or  lower  power  than 
I  :  2,500,  it  is  necessary  to  observe  the  same  conditions  given,  and 
maintain  the  same  proportions  of  albumen  and  acidulated  water, 
varying  only  the  quantity  of  pepsin — for  instance,  in  testing  a 
I  :  2,000  pepsin,  use  one-fourth  more  pepsin,  thus,  albumen  1,250 
gr.  -f  acidulated  water  27  fl.  oz.  —  a  1  :  2,000  test  pepsin  5/g  gr.,  or 
of  a  I  :  2,500  test  pepsin  y2  gr. 
If  a  pepsin  is  of  unknown  strength,  its  proportion  must  vary  until 
the  quantity  is  found  which  will  practically  dispose  of  all  the  albu- 
