524  The  Microscope  in  Materia  Medica.  {^i™^^ 
purpose  No.  2,  a  section  of  the  senega  of  commerce  may  be  taken. 
The  cortical  portion  or  bark  of  the  root  is  divided  into  three  parts,  an 
outer  layer  or  periderm,  composed  of  a  series  of  two  or  three  tabular 
cells  of  a  yellowish-brown  color  ;  next,  a  middle  layer  of  thin  walled 
parenchymatous  tissue,  the  outer  cells  stretched  for  the  most  part  in  a 
tangential  direction.  This  layer  is  very  unequally  developed  when 
there  is  a  keel  to  the  root,  as  is  the  case  in  this  section  \  on  that  side  it 
is  smallest,  from  there  it  increases  gradually  till  it  reaches  the  opposite 
side,  where  it  displaces  more  or  less  completely  the  inner  layer,  which 
is  the  most  fully  developed  on  the  keel  side,  where  also  may  be  seen 
the  bast  or  liber  cells,  and  passing  through  this  tissue  the  medullary 
rays. 
Although  the  histological  elements  of  these  three  sections  are  iden- 
tical, yet  in  their  relative  proportions  the  three  roots  differ  materially, 
and  to  the  result  of  these  differences,  bearing  immediately  on  the  greater 
or  less  activity  of  the  root,  attention  will  next  be  directed. 
Senega  has  probably  not  received  so  much  attention  as  other  sub- 
stances of  the  vegetable  Materia  Medica,  but  Schneider,  in  1875,1 
undertook  the  determination  of  the  following  points:  the  active  princi- 
ple of  the  senega  root,  and  what  part  of  the  root  contained  it  in  the 
greatest  quantity  ;  but  with  the  latter  part  only  we  shall  have  to  do  on 
the  present  occasion.  Trommsdorff  had,  in  1832,  stated  that  the  active 
principle  resided  in  the  bark  of  the  root  only,  and  not  at  all  in  the 
woody  tissue  of  the  centre,  and  Schneider  confirmed  the  correctness  of 
his  conclusions  by  analyses  of  different  roots  and  different  parts  of  the 
same  root.  The  conclusions  he  arrived  at  may  be  summed  up  as  fol- 
lows, giving  to  the  active  principle  of  the  root  the  name  of  senegin. 
Rootlets,  .  .  .    9-26  per  cent,  senegin. 
Middle-sized  roots,         .  .  328 
Thick  roots,  .  .  .  3*02 
Crown  of  the  root,         .  .  2*6 
The  central  woody  portion  being  inert,  I  shall  pass  over  that  part 
and  not  further  allude  to  it,  excepting  in  reference  to  the  space  it 
occupies  relative  to  the  parenchymatous  tissue,  the  seat  of  the  active 
principle.  From  the  conclusions  of  Trommsdorff  and  Schneider  that  the 
bark  only  yields  the  active  principle,  it  will  be  seen  that  these  sections 
shave  an  immediate  practical  bearing  on  the  value  of  senega  root.  No.  1, 
1  "Archiv  der  Pharmacie." 
