314  ^  Cant  har  ides,  {^^ne^^o"™' 
largely  in  excess  of  the  amount  of  cantharidin  found  by  DragendorfF 
m  good  samples  of  Spanish  flies,  viz.:  0*351  to  0*5  per  cent.,  and 
serves  to  illustrate  in  a  striking  manner  the  remarks  on  cantharides  by 
that  chemist,  published  in  the  "Pharmacist:"^ 
"Apothecaries  frequently  complain  that  some  canthaiides  do  not 
furnish  an  active  blistering  plaster;  that  the  same  furnish,  even  when 
treated  with  acetic  ether,  an  extract  so  poor  in  cantharidin  that  with  its 
aid  no  good  Drouott's  blistering  tissue  can  be  produced.  In  most 
case>  the  opinion  is  expressed  that  the  flies  contain  too  small  a  percent- 
age of  cantharidin.  My  experience  teaches  me  to  discredit  the  latter 
opinion.  It  is  possible  to  obtain  good  preparations  even  from  such 
apparently  poor  cantharides,  it  being  only  necessary  to  thoroughly 
extract  the  cantharidin  they  contain.  ...  I  would  say  that  by 
the  aid  of  soda  or  potassa  the  entire  amount  of  cantharidin  contained 
in  the  flies  may  be  rendered  active.  The  finely  powdered  flies  are 
mixed  to  a  paste  with  diluted  alkaline  lye  of  about  I'l  sp.  gr.,  heated 
in  the  water  bath  for  twenty-five  to  thirty  minutes,  when  sufficient 
muriatic  acid  is  added  to  have  a  trifling  surplus  of  the  same,  and  the 
whole  mass  is  dried  radidly  in  the  water  bath.  The  residue,  which  we 
may  call  prepared  cantharides,  is  powdered  anew,  and  employed  for 
the  preparation  of  the  plaster,  or  for  the  extract  with  acetic  ether  for 
use  upon  tissue." 
Had  the  Spanish  flies  examined  been  subjected  to  this  treatment  with 
solution  of  soda  and  hydrochloric  acid,  they  would  have  yielded  a  blis- 
tering plaster  of  the  activity  of  which  there  would  have  been  no  doubt. 
I  am  able  to  give  a  further  proof  of  the  very  imperfect  nature  of 
the  exhaustion  of  the  flics  by  ether  in  the  estimation  of  cantharidin  in 
the  residue  after  treatment  with  that  menstruum.  Forty  pounds  of 
such  residues  were  sent  to  Professor  DragendorfF  by  a  house  in  St. 
Petersburg  engaged  in  the  manufacture  of  large  quantities  of  Drouott's 
plaster.  The  treatment  of  a  kilogram  had  yielded  such  an  unex- 
pectedly large  quantity  of  cantharidin  as  to  offer  an  inducement  ta 
estimate  the  same  more  exactly. 
29*297  grams  of  the  exhausted  flies,  finely  powdered,  yielded  me 
0'22i8  gram  of  nearly  pure  cantharidin;  correction  for  alcohol  aud 
water  0*0192  (the  flies  having  been  previously  exhausted  with  ether 
no  correction  for  petroleum  ether  was  necessary);  total  amount  o*24iG 
gram,  equivalent  to  0*g22  per  cent,  of  cantharidin. 
^  Loc.  cit.,  p.  79. 
