128 
The  Origin  of  Tragacanth. 
f  Am.  Jour.  Pharm. 
\       Mar.,  1878. 
and  finally  disorganized.  Thus  cavities  are  formed  filled  with  liquid 
containing  the  fragments  of  the  destroyed  tissues.  The  cavities  grad- 
ually increase  in  size  in  consequence  of  the  disintegration  of  the  neigh- 
boring cells,  and  whenever  they  occur  near  the  epidermal  layers  they 
may  force  an  opening  through  them,  and  thus  cause  larger  or  smaller 
fissures  ;  but  if  they  remain  enclosed  on  all  sides  they  become  recep- 
tacles of  gum.  This  gum  near  the  walls  of  the  cavity  appears  in  the 
shape  of  gelatinous  warts,  which  grow,  turn  yellow  or  brown,  and 
finally  fill  up  the  hollow  space.  When  near  fibres,  it  appears  first  to 
exude  from  them,  and  gradually  to  alter  them  together  with  their  con- 
tents. If  the  cavities  occur  near  the  bark,  or  near  soft  woody  tissue, 
their  contents  occur  in  the  well-known  shape  of  transparent  tears. 
This  is  the  origin  of  the  gums  in  the  Rosaceae  and  Acaciae,  which 
consist  mainly  of  gummic  or  metagummic  acid.  Tragacanth  differs 
from  these  gums  both  in  its  origin  and  properties.  Hugo  v.  Mohl 
considers  it  likewise  as  a  pathological  product,  having  some  similarity 
with  the  other  gums,  and  to  be  the  result  of  a  more  or  less  complete 
transformation  of  the  cells  of  the  pith  and  of  the  medullary  rays,  into 
a  gelatinous  substance,  which  swells  by  the  imbibition  of  water  to  sev- 
eral hundred  times  the  size  of  the  original  cells.  On  examining  the 
anatomical  structure  of  the  Astragali  furnishing  this  substance  we  find 
that  the  pith  and  medullary  rays  have  changed  more  or  less  and  all  the 
intermediate  stages  in  this  gradual  transformation  are  observable.  The 
cells,  which  originally  assumed  a  hard,  horny  consistence,  without  alter- 
ing their  shape,  ultimately  condense  into  a  homogeneous  mass,  in  which 
the  cell  walls  are  no  longer  perceptible.  This  seemed  to  confirm  the 
opinion  of  Guibourt,  that  the  soluble  portion  of  tragacanth  consists  of 
arabin  and  the  insoluble  portion  of  a  mixture  of  cellulose  and  starch, 
both  partly  altered.  But  this  view  is  as  little  exact  as  the  statement 
generally  met  with  in  the  books,  that  the  soluble  portion  differs  from 
arabin  in  not  being  thickened  by  ferric  salts,  and  that  after  precipitation 
by  alcohol  it  possesses  a  peculiar  mucilaginous  consistence.  The  por- 
tion insoluble  in  hot  water  was  called  bassorin,  and  stated  to  have  the 
general  constitution  of  amylaceous  substances,  to  differ  greatly  from  cel- 
lulose, and  to  be  characterized  by  swelling  greatly  in  water. 
Guibourt  mentions  starch  as  a  constituent  and  others  have  observed 
the  same,  and  that  vermiform  tragacanth  contains  more  than  the  flakes  > 
the  manner  in  which  tragacanth  forms,  according  to  Mohl,  would 
