Am.  Jour.  Pharm. 
Dec,  1876. 
The  Gums  of  Senegal. 
563 
As  the  result  of  the  study  of  the  mode  in  which  the  gum  is  produced 
from  the  verek,  the  author  is  of  opinion  that  the  starting  point  is  cer- 
tainly in  the  cambium.  When  a  transverse  incision  is  made  in  a  young 
branch,  there  is  observed  at  first  a  sort  of  exudation,  badly  defined, 
between  the  wood  and  the  bark*  As  the  exudation  becomes  more 
considerable  it  raises  the  bark,  and  makes  its  way  to  the  exterior  through 
any  cracks  or  fissures.  But  as  there  are  two  layers  in  this  zone-^a 
Jigneous  and  a  cellular  layer — the  question  arises,  In  which  layer  does 
the  gum  take  its  origin  ?  For  the  following  reasons  the  author  be- 
lieves it;  to  be  formed  in  the  lingneous  layer,  at  the  expense  of  the  crude 
sap  circulating  therein. 
(1)  Upon  different  specimens  of  verek  he  has  observed  that  at  the 
level  of  the  base  of,  the  gummy  exudations  the  exterior  woody  bundles 
become  deviated  in  the  form  of  a  capsule,  and  present  traces  of  an 
erosive  or  destructive  action.  In  , very  young  branches,  by  the  aid  of 
a  microscope,  these  bundles  may  be  distinguished,  dissociated  and 
jagged,  in  the  midst  of  the  gummy  matter. 
(2)  ,  The  balls  of  gum  are  frequently  marked  with  very  regular  cavi- 
ties, similar  to  those  produced  in  a  viscous  mass  by  blowing  air  into  it 
through  a  slender  tube.  These  cavities  cannot  be  due  to  the  penetra- 
tion of  a  gas  coming  directly  from  without,  for  they  face  inwards,  /. 
towards  the  base  of  the  exudations  ;  they  could  only  be  produced  by 
the  air  from  the  vessels  of  the  sap  wood,  ruptured  and  dissociated  at 
the  same  time  as  the  woody  fibres. 
(3)  The  mineral  elements  of  gum  (lime,  etc.)  belong  to  the  crude 
Sap.     •  •  •         ^^^■■•■■^■■■^  ~n<  .    ■     ,  z>:r'i  •:  :  ;;  •  .  ■  \- 
Gum,  however,  is  not  simply  water  charged  with  salts,  neither  is  it 
a  highly  concentrated  saline  solution.  It  is  a  product  that  presents 
great  analogy  of  chemical  composition  with  lignose.  The  author, 
therefore^  considers  gum  to  be  the  result  of  a  kind  of  liquefaction  of 
the  elements  of  the  sap  wood  by  the  crude  sap, 
It  is  incontestable  that  the  formation  of  gum  is  connected  with  an 
anomalous  state,  due  to  excess  of  nutrition.  It  is  observed  more  par- 
ticularly at  the  points  of  budding  and  at  the  bifurcation  of  the  branches, 
and  it  acquires  a  remarkable  development  upon  abnormal  nodosities — 
in  fact  wherever  the  nutritive  action  exists  in  the  greatest  intensity. 
Beyond  certain  limits,  this  energy  in  the  rising  of  the  sap  is  accom- 
panied by  a  slackening  of  the  circulation,  which  leads  to  a  stagnation 
