Augnsl\%"^:  ]         Methods  for  Digitalis  Assay.  53 1 
easily,  the  guinea  pig  not  at  alL  The  frog  will  not  respond  to  the 
action  of  a  febrifuge  since  its  temperature  is  always  that  of  the 
surrounding  medium.  But  all,  including  man,  have  the  heart  and  the 
circulatory  system  which  either  directly  or  through  the  nerves  are  acted 
upon  by  external  influences  such  as  drugs.  Certain  features  of  these 
effects  may  differ,  but  fundamentally  the  fact  remains  unassailable. 
We  therefore  take  issue  with  Beal  to  this  extent,  that  while  there  are 
unquestionably  cases  in  which  the  action  of  a  drug  on  man  differs 
materially  from  that  on  certain  animals,  these  are  exceptional  cases. 
Practically  every  physiological  reaction  in  man  has  its  counter- 
part in  some  animal. 
It  is  on  this  basis  that  the  science  of  pharmacology  is  founded. 
Through  the  investigation  of  the  action  of  drugs  on  animals  many 
of  their  valuable  properties  have  been  discovered;  by  this  means 
most  of  these  actions  have  been  explained.  Digitalis  acts  as  a 
diuretic.  Is  it  a  direct  action  on  the  kidneys  or  is  it  only  an  in- 
direct effect  of  its  action  on  the  circulatory  system?  By  animal 
experiment  and  not  by  observation  of  humans  this  has  been  made 
clear.  Digitalis  has  a  strongly  tonic  action  on  the  heart  and  vessels. 
Is  its  action  directly  on  the  muscles  or  is  this  an  effect  of  its  action 
on  the  nerves?  Again  we  are  rewarded  by  the  answer  as  a  result 
of  animal  experiments. 
But  the  critic  is  perhaps  still  dissatisfied.  Granted  that  all  this 
is  true  he  yet  is  skeptical  on  one  or  two  points.  How  is  it  possible 
to  standardize  drugs  even  if  the  action  on  some  animal  is  apparently 
similar  to  its  action  on  man?  This  is  a  logical  question  and  de- 
serves an  answer. 
Digitalis  administered  to  animals  in  doses  comparable  to  the 
therapeutic  dose  for  man  does  not  show  a  measurable  effect  except 
when  such  doses  are  given  intravenously  to  an  anesthetized  animal, 
the  effect  being  measured  by  the  aid  of  a  myocardiograph  or  similar 
instrument — a  measurable  effect  sufficient  for  qualitative  purposes. 
For  a  quantitative  test  comparison  must  be  made  with  a  standard  just 
as  the  chemist  must  have  absolutely  pure  reagents  or  must  be  able  to 
discount  the  impurities  by  running  a  blank  or  some  similar  procedure. 
Digitalis  will  slow  the  beat  of  the  heart,  increase  the  amplitude 
of  the  beat,  raise  the  blood  pressure,  but  the  amount  necessary  to 
bring  about  a  definite  degree  of  change  in  these  measurable  reac- 
tions differs  with  different  dogs,  so  the  effect  of  the  sample  on  one 
dog  cannot  be  compared  with  the  effect  of  the  standard  on  another 
