ANove<mberPhx9Ii9'  )  Standardization  of  Digitalis  Preparations.  723 
was  2  Cms.  above  the  level  of  the  canula  "  C,"  the  solution  thus 
being  delivered  at  a  slight  pressure.  The  technique  of  the  perfusion 
may  be  found  on  referring  to  my  first  paper.  Previous  to  the  ex- 
periment the  saline  content  of  the  glass  canula  and  tube  as  far  as  the 
tap  "  X "  was  accurately  measured  in  drops  for  each  canula,  and 
this  amount  allowed  for  in  the  tracings. 
It  seemed  feasible  if  the  same  conditions  were  maintained  as  re- 
gards (a)  rate  of  flow  of  the  perfusing  solutions — i.e.,  constancy  of 
pressure  from  the  supply  reservoir — and  (b)  the  use  of  solutions  of 
equal  percentage  strength,  that  the  quantity  of  liquid  perfused 
through  the  heart  should  be  directly  proportional  to  the  strength  of 
the  preparations  used. 
In  this  perfusion  test  only  a  certain  proportion  of  the  active  con- 
stituents are  used  up ;  but  we  may  reasonably  assume  that,  provided 
the  above  conditions  are  observed,  the  amount  absorbed  by  the 
tissues  will  be  proportional  to  the  weight  of  the  hearts  used;  or, 
carrying  this  hypothesis  still  further,  to  the  respective  body  weights 
of  the  frogs  used  (subject,  of  course,  to  slight  frog  variation).  The 
amounts  used,  therefore,  reduced  to  the  values  per  100  Gm.  frog, 
should  be  directly  proportional  to  the  strengths  of  the  solutions,  and 
thus  to  the  respective  M.L.D.'s. 
The  following  table  of  results,  calculated  per  100  Gm.  frog 
weight,  was  obtained  from  various  tinctures  by  this  method.  The 
M.L.D.  of  each  tincture  was  obtained  by  the  colorimetric  estimation, 
and  also  by  the  actual  Minimum  Lethal  Dose  method  by  injection, 
and  recorded  in  the  table. 
The  time  taken  to  kill  the  heart  in  these  experiments  showed  no 
striking  similarities.  This  discrepancy  is  probably  due  ito  (the 
variation  in  relative  quantities  of  the  several  glucosides  present. 
Summarizing  the  table,  the  quantity  of  solution  necessary  to  kill 
the  heart  (recorded  on  the  tracing  in  drops)  approximates  very 
nearly  in  tinctures  of  the  same  Minimum  Lethal  Dose,  and  is  di- 
rectly proportional  in  tinctures  of  different  strengths.  The  values 
obtained,  I  admit,  are  merely  measures  of  toxicity,  but  the  thera- 
peutic action  can  be  actually  seen  during  the  experiment,  and  excess 
of  any  one  glucoside  may  be  easily  detected  in  the  tracing.  Although 
these  results  approximate  fairly  well,  yet  I  do  not  consider  them 
sufficient  for  the  standardization  of  a  tincture  by  this  means  alone. 
Considering  the  subject  now  from  a  chemical  standpoint,  the 
solution  of  the  difficulty  seems  to  lie  in  estimating  the  relative  quan- 
