354 
ON  A  FALSE  CINCHONA  BARK  OP  INDIA. 
chestnut.  The  complete  identity  in  the  behaviour  of  the  two 
substances  leaves,  however,  no  room  for  doubt.  It  is  also  re- 
markable that  horse-chestnut  bark  has  obtained  a  reputation  on 
the  continent  of  Europe,  being  like  the  Hymenodictyon  in  India, 
a  good  substitute  for  cinchona  bark.  Lindley  and  other  authors 
mention  that  it  has  been  recommended  as  a  valuable  febrifuge 
in  intermittents. 
The  occurrence  of  the  same  principle  in  genera  so  widely  sep- 
arated (botanically)  as  Hymenodictyon  and  JEsculus  will  recall 
to  mind  the  more  famous  but  parallel  instance  of  the  common 
constituent  of  tea  and  coffee.  But  in  the  former  case  there  is  a 
further  interesting  link  of  connection.  In  an  exhaustive  chemi- 
cal examination  made  by  liochleder  of  the  cotyledons  and  bark 
of  the  horse-chestnut,  he  found  as  a  constituent  of  the  former  a 
substance  isomeric  with  quinovine,  the  bitter  constituent  of  cin- 
chona leaves,  and  also  occurring  in  the  bark.  The  full  signifi- 
cance of  these  coincidences  will  doubtless  one  day  be  made  ap- 
parent. 
The  fluorescence  of  a  slightly  alkaline  solution  of  the  eescule- 
tin  obtained  as  above  is  the  most  beautiful  instance  of  that 
phenomenon  that  has  ever  come  under  my  notice.  It  is  finely 
seen  when  the  solution  is  illuminated  by  the  light  of  sulphur 
burning  in  oxygen. 
The  cause  of  the  loss  of  bitterness  which  the  hymenodictyon 
bark  suffers  by  keeping  is  more  readily  explained.  iEsculin, 
by  contact  with  changing  organic  substancs,  becomes  slowly  con- 
verted into  assculetin,  and  glucose  by  the  same  decomposition 
that  can  be  more  immediately  produced  by  boiling  with  acids. 
When  a  solution  of  assculin  is  mixed  with  emulsion  of  sweet 
almonds,  the  change  takes  place  in  about  two  days.  The  soluble 
bitter  substance  of  the  fresh  bark  gradually  changes  into  the 
sparingly  soluble  sesculetin,  which  has  comparatively  little  taste, 
the  bark  becoming  less  bitter  from  day  to  day.  That  this  is 
really  the  case  can  be  experimentally  shown  by  boiling  a  few 
fragments  of  stale  bark  in  a  test-tube  with  some  water ;  on 
cooling,  an  abundance  of  glittering  crystals  will  be  deposited, 
which  can  readily  be  recognized  by  their  form  and  their  behavior 
towards   polarized   light.     They  form   beautiful  microscopic 
