EXTRACTION  OF  CANTHARIDIN. 
117 
necessary  to  find  a  liquid  which,  whilst  exerting  no  action  upon 
the  cantharidin,  should  have  the  property  of  dissolving  the 
substances  which  have  been  simultaneously  extracted.  Bisul- 
phide of  carbon  possesses  this  property  ;  and,  by  taking  advan- 
tage of  this  circumstance,  it  becomes  an  easy  task  to  prepare 
cantharidin  in  a  state  of  purity. 
The  process  is  simply  as  follows : — The  crushed  flies  are  ex- 
hausted by  chloroform,  the  solution  is  distilled  to  dryness  at  a 
very  gentle  heat,  and  the  green  residue  heated  with  bisulphide 
of  carbon.  By  this  means  the  fatty,  resinous,  waxy,  and  other 
matters  are  dissolved,  and  the  cantharidin  remains ;  this  last  is 
thrown  upon  a  filter  washed  with  bisulphide  of  carbon,  and 
crystallized  from  chloroform. 
It  is  obvious  that,  omitting  the  crystallization,  this  is  at 
once  a  quantitative  process  for  the  estimation  of  the  blistering 
principle. 
Cantharidin  exists  in  good  samples  of  the  flies  to  the  amount 
of  from  4  to  5  parts  in  1000 ;  its  formula,  as  usually  given, 
C5H602,  demands  revision.  Chloroform  is  the  best  solvent  of 
this  principle,  but  it  dissolves  also  in  acetone,  the  oils  and  fats, 
and,  to  a  smaller  extent,  in  alcohol  and  ether. 
It  may  be  sublimed  without  change,  but  its  well-known 
serious  effects  upon  the  animal  economy  render  it  necessary  to 
use  all  caution  in  this  experiment.  Accompanying  this  crystal- 
line body,  upon  which  the  activity  of  cantharidin  depends,  is  a 
number  of  others,  the  most  notable  of  which  as  regards  quantity 
is  the  fat. 
The  following  are  the  substances  which  have  been  extracted 
from  the  blistering-beetle,  together  with  the  action  of  various 
solvents. 
1.  Cantharidin ;  soluble  in  chloroform,  insoluble  in  bisul- 
phide of  carbon. 
2.  Fat. 
3.  Resinous  matter  ;  soluble  in  chloroform  and  in  bisulphide 
of  carbon. 
4.  Waxy  matter ;  soluble  in  bisulphide  of  carbon  and  in 
boiling  alcohol,  less  soluble  in  chloroform. 
5.  Yellow  matter. 
