306  Alexandria  and  India  Senna.  '{Am'S'MOTarm" 
The  objection  that  fragments  may  be  counted  as  whole  hairs  is 
easily  overcome  by  choosing  some  readily  distinguishable  part  of 
the  hair,  such  as  the  tip,  and  using  only  it  as  the  unit  of  estimation. 
From  the  results  obtained  in  the  latest  series  of  experiments  the 
following  test  appears  sufficient  to  distinguish  either  senna  alone, 
or  a  mixture  of  the  two,  and  it  is  therefore  proposed  for  these  pur- 
poses :  Take  a  portion  of  the  No.  60  powder  and  place  it  in  a  small 
homoeopathic  vial,  and  add  to  it  twice  its  volume  of  a  mixture 
Fig.  7.  India  senna,  No.  60  powder  ;  b,  stomata  ;  c,  hair  ;  d,  hair  scar  ; 
e,  nebenzellen. 
of  water  and  glycerin  in  equal  parts.  Thoroughly  shake  this  mix- 
ture, and  while  still  turbid  with  the  suspended  powder,  place  a  drop 
on  each  of  several  glass  slips,  and  cover  with  cover  glasses.  If  air 
bubbles  or  too  great  opacity  exist,  heat  to  boiling  over  an  alcohol 
lamp.  Search  for  hairs  showing  the  tips  present,  and  if  they  appear 
abundant,  one  to  four  in  each  field  of  a  i^-inch  objective,  Alexandria 
senna  is  present.    To  further  confirm  this,  examine  several  frag- 
