AmNoTx878.rm*}    The  Microscope  in  Materia  Medica.  525 
the  root  in  question,  has  little  bark  relative  to  its  woody  and  inert 
centre.  No.  2,  a  section  from  a  fair  sample  of  the  senega  of  com- 
merce with  a  keel,  has  much  more  bark  in  proportion  to  its  woody  por- 
tion, and  No.  3,  a  section  of  a  rootlet,  is  nearly  all  bark.  Calculating 
now  the  superficial  area  of  parenchymatous  tissue  of  the  bark  which 
contains  the  senegin,  and  comparing  it  with  the  prosenchymatous  or 
woody  tissue,  which  is  inert,  the  relative  proportions  in  the  three  roots 
will,  approximately,  of  course,  stand  thus  : 
Rootlet,  8*5  to  i,  (or  relatively)  .  .  .17 
Middle-sized  senega,  3  to  1,  .  .  .  6 
The  senega  in  question,  1  to  2,  .  .  .2 
It  will  be  observed  how  closely  the  superficial  area  of  parenchy- 
matous tissue,  in  which  alone  the  active  principle  resides,  corresponds 
with  the  relative  proportions  of  senegin  in  the  roots  and  rootlets 
analyzed  by  Schneider. 
These  enlarged  drawings  are  to  scale  and  the  relative  proportions 
exactly  those  of  the  microscopic  sections  from  which  they  were 
drawn.  It  will  now  be  seen  why  the  rootlets  yield  so  much  more 
active  principle  than  either  of  these  roots,  and  it  will  at  the  same  time 
be  evident  why  the  sample  in  question  yields  a  decoction  so  deficient 
in  strength.  Schneider  remarks  that  it  would  be  impossible  to  obtain 
rootlets  in  sufficient  quantity  to  meet  the  demand  for  senega,  and  recom- 
mends the  use  of  roots  of  medium  thickness,  in  accordance  with  the 
results  of  his  analyses,  and  probably  if  these  are  well  furnished  with 
rootlets,  so  much  the  better. 
The  keel,  generally  considered  an  important  feature  of  good  senega 
root,  is  due  to  a  peculiar  development  of  bast  or  liber  tissue  on  one 
side,  and  the  same  root  may  be  quite  round  in  one  part,  and  have  a 
development  of  keel  in  another  ;  this  keel  is  shown  in  section  No.  2. 
Having  isolated  the  elementary  organs  of  a  section  across  this  particu- 
lar part  of  the  root,  separated  the  tabular  cells  of  the  epidermis,  the 
cells  of  the  parenchymatous  tissue,  and  also  the  liber  cells  represented 
by  these  waves  in  cellular  tissue,  and  examined  the  individual  cells  so 
separated,  I  have  always  found  that  those  of  the  parenchymatous  tissue 
contained  granular  and  oily  matter,  whilst  the  liber  cells  were  free  from 
it ;  and  reasoning  from  analogous  instances  I  am  led  to  conclude  that 
the  liber  tissue  does  not  equally  with  the  parenchymatous  contain  the 
active  principle,  and  this  may  probably  be  the  reason  why  middle- 
