Am.  Jour.  Pliarm. 
May,  1892. 
Bark  of  Populus  Alba. 
227 
The  liquid  obtained  with  stronger  ether  had  a  lighter  yellow  color, 
a  bitter  taste  and  a  slightly  acid  reaction,  and  did  not  respond  to 
tests  for  gallic  acid  or  alkaloids.  The  bitter  principle  was  partly 
taken  up  by  water,  and  the  remainder  by  alcohol,  was  wholly 
soluble  in  amylic  alcohol,  could  not  be  obtained  crystallized,  and 
reduced  Fehling's  solution. 
Th.e  tincture  made  with  absolute  alcohol  was  dark  green,  very 
bitter  and  slightly  astringent.  Petroleum  ether  removed  from  the 
extract  a  somewhat  acrid  principle,  which  on  standing  acquired  a 
vanilla-like  odor.  Ether  removed  a  bitter  resinous  substance ; 
chloroform  a  granular  bitterish  and  sweet  substance ;  and  the 
residue  was  a  very  bitter  extract. 
Different  processes  were .  followed  with  the  view  of  isolating  the 
bitter  principle ;  but  it  could  not  be  crystallized.  However,  the 
bitter  extracts  treated  with  sulphuric  acid  and  potassium  bichromate 
developed  the  odor  of  salicylic  aldehyde.  This  reaction,  the  bitter 
taste  of  the  bark  and  the  sweet  taste  of  the  principle  dissolved  by 
chloroform  suggest  the  presence  of  salicin  and  populin. 
Calcium  oxalate  is  present  in  the  bark ;  also  a  compound 
resembling  tannin  in  its  behavior  to  ferric  chloride,  but  not  precipi- 
tated by  gelatin. 
The  bark  used  for  these  experiments  was  2  or  3  mm.  thick ;  the 
smooth,  greenish-white  outer  surface  is  marked  with  small  warts, 
usually  arranged  in  transverse  lines,  and  is  easily  scraped  off  from 
the  green  layer.  The  inner  surface  is  longitudinally  striate.  The 
bark  breaks,  transversely  and  longitudinally,  with  a  short  fracture. 
Viewed  under  the  microscope,  a  thin  suberous  layer  is  seen ;  the 
primary  bark  contains  raphides,  imbedded  in  the  parenchyma ;  the 
liber  has  the  fast  fibres  in  small  bundles  arranged  in  tangential  lines, 
accompanied  by  raphides,  and  separated  by  broad  layers  of  paren- 
chyma ;  the  medullary  rays  consist,  upon  transverse  section,  near 
the  inner  surface  of  one  row  of  cells,  but  become  much  broader 
towards  the  outer  layer.  The  leaf  has,  beneath  its  upper  surface,  a 
double  row  of  palisade  cells. 
Note  by  the  Editor. — When  Braconnot,  in  1830,  discovered  populin 
in  the  bark  of  Populus  tremula,  he  made  also  some  observations 
with  the  bark  of  P.  alba,  which  seemed  to  indicate  the  presence  of 
the  same  compound.  From  the  latter  bark  he  isolated  a  notable 
quantity"  of  salicin.    In  1835  J.  E.  Herberger  isolated  from  6  oz. 
