314 
Tannins  of  Some  EricacecE. 
Am.  Jour.  Pharru. 
June,  1896. 
defined  compounds  have  been  found ;  and  that,  for  substances 
so  difficult  to  isolate  and  purify,  the  percentage  compositions 
indicated  by  ultimate  analysis  are  sufficiently  near  to  one  or  the 
other  of  two  general  molecular  formulas  as  to  make  their  agreement 
with  one  of  these  almost  imperative. 
But  these  principles  have  been  classified  with  respect  to  other 
properties,  even  to  the  part  they  are  supposed  to  play  in  the 
economy  of  plants.  They  are,  therefore,  often  spoken  of  as  patho- 
logical and  physiological,  the  qualifying  names  which  Wagner1 
applied  in  1866  to  the  two  divisions  of  his  classification  of  the  then 
known  tannins  according  to  the  conditions  under  which  they  seemed 
to  be  present  in  the  plant.  The  former  term  was  intended  to 
designate  those  tannins  found  on  vegetable  tissues,  which  had  been 
injured  by  the  sting  of  an  insect,  while  to  the  latter  division  was 
assigned  the  great  number  of  tannins  present  in  normal  or  uninjured 
vegetable  tissues.  To  exemplify  these  classes,  the  well-known  gal- 
lotannic  acid  which  is  obtained  from  galls — the  excrescences  on  the 
twigs  and  leaves  of  Quercus  lusitanica,  caused  by  the  punctures  and 
deposited  ova  of  Cynips  Gallae  tinctorial — was  proposed  for  the  one, 
and  the  tannin  of  oak  bark,  whose  detection  as  a  definite  principle 
had  been  made  100  years  before,  offered  for  the  other.  But  although 
these  terms,  pathological  and  physiological,  have  been  used  to  dis- 
tinguish two  classes  of  tannins,  investigation  has  not  shown  that  the 
occurrence  of  gallotannic  acid  in  vegetable  tissue  is  in  all  cases 
under  a  pathological  condition,  for  in  some  plants  it  has  been  proven 
to  be  the  only  tannin  therein  existing,  and  for  this  indisputable  rea- 
son it  must  be  looked  upon  as  a  physiological  tannin.  So  it  is  now 
agreed  that  some  of  the  tannins  which  occur  in  uninjured  or  normal 
vegetable  tissue  are  identical  with  gallotannic  acid.  Notable  among 
those  which  have  been  found  to  possess  the  same  composition  as 
gallotannic  acid,  and  on  that  account  have  come  into  conflict  with 
the  proposed  definitions  of  Wagner,  are  the  tannins  of  sumac,  chest- 
nut wood  and  bark,  pomegranate  bark  and  cloves.  Some  observa- 
tions of  the  most  prominent  members  of  the  natural  order  Ericaceae, 
which  yield  tannin-bearing  medicinal  drugs,  led  the  author  to  believe 
this  order  to  be  a  promising  field  for  the  investigation  of  the  possible 
1  Beitrage  zur  Kenntniss  und  zur  quatititativen  Bestimmung  der  Gerbsaureu. 
Zeit.  anal.  Chem.,  5,  1. 
