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44  ON  THE  SOLUBILITY  OF  MEDICINAL  PRINCIPLES. 
bie  and  capable  of  sustaining  animal  life,  are  insoluble  in  pure 
alcohol,  while  the  resins,  alkaloid  salts,  essential  oils  and  those 
fixed  oils  which  are  medicinal,  are  soluble  in  that  menstruum. 
It  is  at  once  objected  to  these  views,  that  there  are  many  vege- 
table substances  from  which  pure  alcohol  will  not  extract  the 
medicinal  virtues ;  that  for  this  purpose  water,  dilute  alcohol, 
acids,  ether  or  other  agents  are  requisite,  and  are  hence  prescrib- 
ed in  our  pharmaceutical  formulae.  It  is  true  that  to  eliminate 
these  principles  in  the  first  place  from  their  native  combinations 
in  the  plant,  such  agents  are  necessary,  not  because  such  medi- 
cinal principles  are  not  themselves  soluble  in  alcohol,  but  be- 
cause they  are  so  enveloped  in  and  shielded  by  other  principles 
which  are  not  soluble  in  that  menstruum  that  it  cannot  reach 
them. 
If  we  dissolve  a  mixture  of  gum  acacia  and  muriate  of  mor- 
phia, and  reduce  the  solution  to  dryness  and  a  coarse  powder, 
strong  alcohol  will  not  dissolve  out  the  morphia  from  that  pow- 
der ;  not  because  it  is  not  soluble  in  the  alcohol,  but  because  it 
is  protected  by  the  insoluble  gum.  But,  if  now  we  re-dissolve 
this  mass  and  pour  the  solution  into  a  proper  quantity  of  strong 
alcohol,  the  gum  will  be  precipitated,  and  the  morphia  remain  in 
solution,  and  may  thus  be  recovered  and  isolated. 
So  in  extracting  the  virtues  of  most  plants  it  is  necessary,  or 
at  least  expedient,  to  use  other  agents  besides  alcohol  to  bring 
into  solution  all  their  elements,  and  thus  disengage  the  principles 
we  seek.  In  most  cases  water  is  necessary  as  one  of  these 
agents,  for  the  purpose  of  dissolving  the  nutritive  principles  and 
expanding  the  vegetable  fibre.  In  some  cases  the  medicinal 
elements  are  found  enveloped  in  others  which  are  not  soluble 
either  in  water  or  alcohol,  as  wax,  caoutchouc,  and  the  fatty  oils. 
Then  we  require  ether,  benzole  or  camphene,  for  their  perfect 
and  speedy  elimination,  but  when  once  freed  from  such  shield- 
ing substances  the  medicinal  elements  are  all  found  to  be  solu- 
ble in  alcohol  alone.  When  the  principle  sought  is  a  fixed  medi- 
cinal oil,  we  find  ether  to  be  used  to  great  advantage,  because  it 
dissolves  that  principle  to  the  exclusion  of  most  others,  and  thus 
presents  the  medicine  in  a  very  pure  and  concentrated  form,  as 
in  the  ethereal  extract  of  ergot,  capsicum,  filix  mas,  &c,  but 
