64  Standardisation  of  Heart  Tonics.  {A^u°^^a- 
not  reliable  for  digitalis  leaves.  Kraft  has  isolated  a  new  active 
glucoside  which  he  calls  Gitalin,  which  probably  has  the  chemical 
formula  C28H48O10.  This  glucoside  is  amorphous  but  forms  a 
crystalline  hydrate,  C28H48O104H2O.  Gitalin  readily  decomposes  in 
any  solvent  except  chloroform  into  anhydrogitalin  C23H4609  which  on 
hydrolysis,  with  a  dilute  acid  in  the  presence  of  alcohol,  changes  to 
anhydrogitaligenin  C22H3405  and  a  sugar  which  was  found  to  be 
identical  with  Kiliani's  digitoxose.  Another  new  glucoside  was  also 
isolated.  This  he  called  Gitin,  and  it  is  inactive  physiologically.  It 
is  crystalline  and  melts  at  265  °  C.  It  is  considered  similar  to,  but  not 
identical  with,  Kiliani's  digitonin. 
Digitoxin  is  often  considered  the  chief  active  glucoside  in  digitalis 
and  chemical  determinations  of  this  constituent  have  been  frequently 
made  in  the  hope  of  finding  a  relationship  between  the  digitoxin  con- 
tent and  the  therapeutic  activity,  but  the  results  in  almost  every  case 
have  proved  a  failure.12  If  the  digitoxin  from  a  given  amount  of 
drug  is  isolated  it  will  be  found  that  the  total  amount  of  digitoxin  is 
very  much  less  toxic  than  the  amount  of  drug  from  which  it  was 
obtained,  hence  it  seems  absolutely  necessary  to  resort  to  pharmaco- 
logical standardization  if  any  definite  idea  of  the  therapeutic  strength 
is  desired. 
Pharmacologic  Standardization  of  Digitalis. 
At  least  three  distinctly  different  pharmacologic  methods  have 
been  proposed  for  the  standardization  of  Digitalis — the  frog  method, 
the  guinea  pig  method,  and  the  cat  method. 
The  Frog  Method. 
The  frog  method  was  first  proposed  by  Houghton  in  1898. 13  He 
found  that  "  fairly  accurate  data  could  be  obtained  from  the  appli- 
cation of  a  solution  containing  Strophanthin,  Digitalin,  etc.,  to  the 
laid-bare  frog's  heart,  by  comparing  the  action  of  the  drug  thus 
tested  with  that  of  a  sample  of  known  strength."  After  much  ex- 
perimental work  this  method  was  replaced  by  the  use  of  a  simpler 
one — namely,  the  determination  of  the  minimum  lethal  dose  for  frogs 
under  definite  conditions.  Although  the  original  method  as  modified 
by  Houghton  gives  quite  satisfactory  results,  yet  various  workers 
have  proposed  certain  changes  in  the  conditions  under  which  the  test 
is  to  be  made.  For  example,  twelve  hours  was  specified  as  being  the 
length  of  time  that  observations  should  be  made  after  injection  of  the 
