524     NOMENCLATUKE,  ETC.,  IN  THE  MATERIA  MEDICA,  U.  S.  P. 
The  term  kernel  as  employed  by  the  Pharmacopoeia  for  almonds 
and  nutmegs  is  good  as  far  as  it  goes.  Nutmeg  consists  simply 
of  the  albumen  enclosing  the  small  embryo  of  Myristica  mos- 
chata.  But  almonds,  as  our  Pharmacopoeia  orders  (but  not  de- 
fines) them,  evidently  mean  the  seeds  ;  for  in  Mistura  and 
Syrupus  amygdalae  it  is  expressly  directed  to  blanch  them,  (this 
direction  is  not  contained  in  the  formula  for  extr.  pruni  virg. 
fluid),  and  the  object  of  blanching  is  merely  to  remove  the  seed 
coverings  ;  hence  it  is  either  unnecessary  to  direct  the  blanching 
of  almonds,  or  by  the  term  amygdalus  the  Pharmacopoeia  means 
the  seed  and  not  the  kernel,  which  latter  is  exalbuminous  and 
consists  of  the  embryo  only. 
The  term  juice  as  used  by  our  Pharmacopoeia  is  a  very  con- 
venient one,  but  does  not  convey  any  definite  idea ;  if  we  place 
a  few  of  these  so-called  juices  side  by  side,  as  for  instance 
limonis  succus,  aloe,  manna,  acacia,  copaiba,  ammoniacum, 
opium  and  guaiaci  resina,  their  properties  make  it  very  apparent 
that  we  have  before  us  a  heterogenous  collection.  The  juice 
proper  of  a  plant  is  an  aqueous  liquid,  holding  inorganic  salts 
and  various  organic  compounds  in  solution,  and  will,  perhaps  in 
all  cases,  when  evaporated  spontaneously  or  by  means  of  arti- 
ficial heat,  produce  a  mass,  aloe  and  kino  for  instance,  in  appear- 
ance resembling  and  in  point  of  fact  identical  with  the  extracts. 
Opium,  scammonium,  lactucarium  and  probably  some  of  the  gum 
resins  are  not  obtained  from  what  is  understood  by  the  juice  of 
the  respective  plants,  but  from  the  liquid  contained  in  peculiar 
vessels,  the  milk  vessels  ;  this  milk -juice,  the  physiological  func- 
tion of  which  is  not  at  all  understood,  is  of  a  different  composi- 
tion from  the  true  juice,  and  usually  congeals  very  readily  on 
exposure  to  the  air. 
Guaiac  resin  is  a  secretion  of  the  tree,  stored  away  in  the 
heartwood,  and  has  no  connection  with  the  juice.  Recent  in- 
vestigations have  shown  that  the  gums,  some  gum  resins,  and 
probably  manna,  some  volatile  oils  and  resins  are  generated  by 
the  metamorphosis,  the  deorganization  of  the  vegetable  cells, 
and  therefore  constitute  a  retroformation  of  the  insoluble  tissues 
into  soluble  compounds. 
It  is  plainly  wrong  to  define  by  the  same  name  substances 
