Am-feyr*^m'  }  U.  S.  P.  Standard  for  Pituitary  Extract.  2oi 
Comparative  Activity. 
During  the  past  three  years  I  have  made  over  500  kymographic 
tracings  of  the  isolated  uterus  in  testing  pituitary  glands,  solutions, 
and  finished  commercial  extracts  made  in  this  laboratory  and  also 
in  others,  and  during  this  experience  I  have  never  found  it  necessary 
to  apply  as  low  a  dilution  as  1:20,000  of  any  commercial  extract 
within  the  age  limit.  Indeed,  it  is  rare  that  I  ever  apply  a  1  :  100,000 
dilution.  The  uteri  on  the  average  have  required  dilutions  of  from 
1 :  160,000  to  1  : 600,000,  occasionally  1  : 800,000  to  1  :  1,000,000,  and 
rarely  1 : 2,000,000.  This  fact  by  itself  is  not  of  much  importance, 
since  some  uteri  are  extremely  sensitive,  but  it  is  significant  in  con- 
nection with  the  fact  that  my  dilutions  of  B-imid  effective  on  these 
same  uteri  have  been  about  that  directed  in  the  pharmacopoeia,  that 
is,  usually  from  1:16,000,000  to  1:40,000,000.  Occasionally  a 
greater  dilution  of  B-imid  has  been  necessary  but  rarely  a  lesser. 
My  experience  with  first-class  pituitary  extracts  has  led  me  to  adopt 
as  a  standard  requirement  that  a  1  : 250,000  dilution  should  equal 
1:20,000,000  B-imid.  (This  dilution  of  the  extract  has  no  refer- 
ence to  the  amount  of  gland  contained,  but  means  1  part  of  finished 
extract  as  drawn  from  the  ampoule  to  250,000  parts  of  Locke's 
solution.)  In  order  to  illustrate  this  relationship,  a  few  self- 
explanatory  tracings  are  reproduced  at  the  end.  As  evidence  that 
this  is  about  what  one  would  expect  of  a  carefully  prepared  pitui- 
tary extract,  let  us  consider  the  following : 
Fenger  (3),  in  testing  fresh  posterior  lobes  from  full  grown 
cattle  and  calves,  found  the  following  dilutions  of  a  5  per  cent,  solu- 
tion to  be  equivalent  to  1  : 20,000,000  B-imid  solution : 
Full-grown  cattle    1 :  38,000 
Calves   1 :  40.000 
Let  us  use  the  1  : 40,000  dilution  for  convenience.  Since  1  part  of 
a  5  per  cent,  solution  of  fresh  posterior  lobe  diluted  40,000  times  is 
equivalent  to  1 : 20,000,000  B-imid,  then  the  fresh  lobe  itself  would 
be  equivalent  to  this  standard  in  a  dilution  twenty  times  as  great,  or 
1 : 800,000.  Now  if  a  commercial  extract  were  made  from  such 
material,  without  loss  of  activity,  so  as  to  represent  .2  to  .3  grams 
of  fresh  lobe  per  1  Cc.  (which  is  about  what  commercial  prepara- 
tions represent),  then  we  should  expect  such  an  extract  to  be  equiva- 
lent to  the  standard  in  two  tenths  to  three  tenths  as  great  a  dilution, 
or  1  :  160,000  to  1 : 240,000. 
