•"'igi™'  )  Stability  of  Digitalis  Leaf  Extracts. 
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Fig.  III. 
Summary. 
1.  Alcoholic  extracts  of  digitalis  leaves,  as  well  as  the  leaves 
themselves,  gradually  lose  part  of  their  activity ;  the  losses  in  the 
extracts  from  young  drug  were  irregular  and  the  velocity  of  this 
reaction  in  alcoholic  solution  was  much  greater  than  in  the  drug 
itself. 
2.  An  equilibrium  of  somewhat  marked  stability  results,  indicat- 
ing that  the  leaf  contains  a  constituent  much  more  stable  than  a 
second  active  but  unstable  constituent  which  is  also  present. 
3.  In  the  leaf  studied  the  more  stable  component  represents  less 
than  half  the  total  activity  of  the  young  dried  leaf  (40  per  cent.). 
The  results  obtained  on  extracts  made  from  older  drug  indicate  (but 
not  conclusively)  that  the  drug,  having  lost  more  or  less  of  the  un- 
stable active  component,  yields  an  extract  which  naturally  comes  to 
equilibrium,  at  a  greater  activity,  owing  to  the  predominance  of  the 
more  stable  constituent.  This  is  conspicuously  shown  in  Fluid- 
extract  4,  where  a  rundown  drug  at  least  16-18  months  old  (76  per 
