362 
Standardisation  of  Drugs.. 
f  Am.  Jour.  Pharm. 
\     August,  1910. 
We  would  prefer  this  definition  of  the  cat  unit  rather  than  that 
which  would  embrace  any  digitalis  body  required  to  produce  a  simi- 
lar effect  within  the  same  period  of  time  when  used  in  this  way. 
The  reasons  for  this  will  be  apparent  from  the  discussion  of  the 
method. 
When  crystalline  ouabain,  amorphous  strophanthin,  or  a  prepara- 
tion of  strophanthus  is  to  be  tested,  it  is  only  necessary  to  inject  the 
solution  from  a  syringe  or  burette  into  the  femoral  vein  until  the 
animal  begins  to  show  toxic  symptoms.  The  injection  is  then  inter- 
rupted, or  continued  more  slowly  until  the  unmistakable  signs  of 
approaching  death  are  seen.  These  signs  are  so  typical  that  one  is 
rarely  mistaken  concerning  them.  They  consist  in  irregularity  of 
the  heart,  difficult  respiration,  convulsions,  and  frequently  a  peculiar 
cry,  after  which  recovery  is  extremely  rare.  If  death  does  not  occur 
in  a  few  minutes  the  injection  is  continued  with  extreme  caution. 
Other  members  of  the  digitalis  group  may  be  tested  in  the  same 
way,  but  the  results  will  be  somewhat  too  high  as  a  rule,  and  in  that 
case  the  necessary  correction,  usually  amounting  to  about  20  per 
cent.,  may  be  made,  or  the  assay  may  be  made  more  accurately 
by  a  modification  of  the  technic.  Somewhat  more  uniform  results 
are  obtained  if  about  75  per  cent,  of  the  total  amount  of  the  digitalis 
bodv  is  injected  in  the  first  fifteen  minutes  and  the  remainder  in 
the  following  hour.  These  results  will  still  be  too  high,  and  we 
have  therefore  devised  a  modification  of  the  method  of  estimating 
some  of  the  other  digitalis  bodies  which  gives  results  which  we  be- 
lieve to  be  nearly  as  accurate  as  those  obtained  with  crystalline 
ouabain  itself. 
It  might  be  better  to  explain  the  reason  for  this  modification 
first,  but  for  convenience  the  discussion  will  be  given  later. 
lust  as  the  analytical  chemist  may  find  it  desirable  to  determine 
the  alkalinity  of  a  liquid  by  adding  an  excess  of  acid  and  titrating 
back  with  an  alkali,  so  we  have  been  able  to  obtain  more  accurate 
results  in  some  cases  when  we  inject  a  measured  amount  of  the  digi- 
talis body  (tincture  or  infusion  of  digitalis,  or  digitoxin)  in  the 
first  period  of  about  ten  minutes,  and  after  an  interval  of  twenty 
minutes  continue  the  injection,  substituting  a  solution  of  crystalline 
ouabain  for  that  of  the  digitalis  body  under  examination  until  the 
death  of  the  animal,  or  until  the  toxic  symptoms  appear-.  Naturally, 
we  assured  ourselves  that  ouabain  was  capable  of  replacing  the  other 
digitalis  bodies  before  we  adopted  this  method. 
