446 
COMPOSITION  OF  THE  AQUA  LAURO-CERASI. 
dilute  hydrocyanic  acid,  a  proposition  to  substitute  the  latter 
for  the  former  would  be  unjustifiable  ;  but  as  it  is  the  opinion  of 
all  who  have  written  upon  the  subject  that  the  action  of  the  two 
remedies  is  in  every  respect  the  same,*  if  we  become  convinced 
that  we  gain  an  important  advantage  by  the  change  we  should 
certainly  adopt  it. 
The  aqua  lauro-cerasi  is  not  included  among  the  formulae  of 
the  London  Pharmacopoeia,  but  finds  a  place  among  those  of  the 
Pharmacopoeias  of  Dublin  and  Edinburgh.  The  process  for  its 
preparation  is  in  both  of  these  essentially  the  same.  One  pound 
of  fresh  laurel  leaves  are  digested  in  two  and  a  half  pints  of 
water,  and  a  pint  of  the  liquid  is  distilled  over  and  filtered. 
Laurel  water  as  thus  prepared  is  nothing  more  than  a  dilute  solu- 
tion of  hydrocyanic  acid,  to  which  the  presence  of  a  small 
quantity  of  volatile  oil  gives  its  peculiar  odor  and  taste.  The 
dose  is  by  no  means  well  fixed,  being  given  by  some  authorities 
at  from  ten  minims  to  twenty  minims,  and  according  to  others 
ranging  from  3ss.  to  3i. 
The  leaves  of  the  cherry  laurel  have  never  been  perfectly 
examined,  but  of  the  nature  of  two  of  their  constituents  there 
exists  no  doubt.  These  are — firstly,  a  volatile  oil,  resem- 
bling in  its  physical  properties  very  closely  that  obtained  from 
bitter  almonds,  and  in  chemical  constitution  agreeing  with  it  in 
every  particular ;  secondly,  hydrocyanic  acid.  Both  of  these 
substances  are,  as  has  been  already  stated,  held  in  solution  by 
the  distillate  from  the  leaves. 
The  chief  cause  of  the  uncertainty  of  this  preparation  lies  in 
the  fact  that  the  quantity  of  hydrocyanated  oil  obtained  from 
the  leaves  varies  with  their  age.  Thus  Christison  found  that 
1000  grains  of  the  buds  and  unexpanded  leaves  of  May  and  June 
gave  6.33  grains  of  oil,  but  when  they  had  in  July  attained  their 
full  size  the  same  quantity  yielded  but  3,1  grains,  while  in  the 
May  following  the  quantity  had  diminished  to  0.6  grains.  Not 
only  is  the  quantity  of  oil  liable  to  variation,  but  what  is  still 
more  important,  the  quantity  of  hydrocyanic  acid  which  it  con- 
*According  to  Goppert,  liowever,  the  poisonous  action  of  cherry  laurel 
water  does  not  depend  on  the  hydrocyanic  acid  which  it  contains,  but  upon 
some  property  peculiar  to  itseJf. 
