230  How  to  D'stinguish  Viburnum  Barks,  {^'i^mt^' 
were  rendered  partly  invisible  by  the  presence  of  their  contents.  It 
is  essential,  when  examining  the  fluid  mixture  of  the  powder  (in, 
say,  a  homoeopathic  vial),  to  take  samples  from  the  bottom,  middle 
and  top  of  the  fluid,  in  order  to  obtain  all  of  the  elements.  In  the 
case  of  Viburnum  prunifolium,  doubtless  the  stone-cells  will  be 
found  in  the  bottom  of  the  bottle  after  it  has  stood  for  a  time. 
Fig.  6. — Viburnum  prunifolium.  Powdered  trunk-bark,  X  400  :  a,  stone- 
cells;  b,  inner  bark  cells;  c,  middle  bark  cells;  d,  outer  cells  of  middle  bark  ; 
<?,  inner  cells  of  inner  bark;  f,  cells  from  outer  layer. 
A  word  in  regard  to  drawings  and  the  meaning  of  illustrations. 
In  order  to  present  an  intelligible  representation  of  the  microscopi- 
cal elements  of  a  powder,  or  to  understand  these  representations,  it 
should  be  understood  that  it  is  necessary,  in  some  cases,  to  eliminate 
certain  features,  and  to  accent  others.  The  true  picture,  in  order  to 
be  descriptive,  may  be  obtained  by  selecting  from  many  different 
views;  so  -that  any  drawing,  such  as  I  have  presented  here,  is  un- 
derstood as  what  could  be  seen  under  most  favorable  circumstances. 
