A";nu°aVry,Pi5o2rm-}    Pharmacological  Assay  of  Drugs.  5 
is  0-05  —  01  c.c. ;  the  reaction  would  therefore  indicate  any  differ- 
ence amounting  to  4  per  cent,  of  the  minimal  dose,  or  2  per  cent,  of 
the  maximal,  which  is  sufficiently  accurate  for  all  practical  purposes, 
An  assay  made  a  month  later  by  my  assistant,  who  was  in  ignorance 
of  my  results,  indicated  0-013  c.c.  as  the  smallest  quantity  of  the 
original  extract  which  gave  the  reaction. 
One  of  the  chief  difficulties  in  this  method  of  assay  is  the  sensi- 
tiveness of  the  reagent — the  animal — to  external  conditions.  This 
is  especially  true  in  the  case  of  frogs,  which  vary  considerably  at 
different  seasons  in  their  reactions  unless  special  precautions  be 
taken.  My  experience  has  been,  however,  that  if  enough  care  be 
taken  in  the  selection  of  the  animals,  the  results  are  sufficiently 
constant.  Of  course,  the  size  of  the  animal  must  be  as  close  to  the 
standard  as  possible ;  all  abnormal  conditions,  such  as  occur  in  the 
spawning  season,  must  lead  to  the  elimination  of  individual  speci- 
mens, and  there  are  many  practical  details  which  can  be  learned 
only  by  actual  experience. 
When  it  is  possible,  it  is  desirable  to  assay  a  specimen  in  several 
species  of  animals  in  order  to  eliminate  as  far  as  possible  such  vari- 
ations ;  for  example,  digitalis  and  its  allies  may  be  assayed  on  the 
frog,  and  contral  experiments  may  then  be  performed  on  the  rabbit 
or  some  other  mammal.  In  many  cases,  however,  the  reaction  is 
much  more  sharply  defined  in  one  species  than  in  others ;  thus 
ergot  can  be  standardized  practically  only  on  fowls,  and  cannabis 
indica  is  best  assayed  in  dogs  in  my  experience.  The*  actual  mode 
of  procedure  in  making  a  pharmacological  assay  can  be  taught  only 
practically,  and  a  correct  use  of  the  method  requires  a  fair  knowl- 
edge of  physiology  and  experimental  pharmacology.  The  drugs 
which  I  have  tested  with  this  method  are  those  comprised  in  the 
digitalis  series  which  are  in  common  use  (digitalis,  squill  and  stro- 
phantus), cannabis  indica  and  ergot.  The  variations  in  the  strength 
of  the  preparations  of  the  digitalis  series  were  considerable,  amount- 
ing to  50  per  cent.,  but  were  positively  trifling  compared  with  those 
exhibited  by  the  fluid  extracts  of  cannabis  indica  and  of  ergot.  I 
have  repeatedly  found  that  those  preparations  bearing  the  labels  of 
reputable  houses  were  practically  inert  in  quantities  considerably 
larger  than  those  advised  in  therapeutics.  The  method  is  of  course 
available  for  other  preparations  whether  they  contain  alkaloids 
(gelsemium)  or  such  indifferent  substances  as  are  found  in  male 
