172     Medium  for  Mounting  Starches  and  Pollens.  {AmApXimrE1' 
as  being  the  very  article  for  mounting  starches  in.  I  prepared  some 
and  found  it  to  answer  the  purpose  admirably ;  it  is  as  follows : 
Selected  Gum  Arabic   ^  ij. 
Glycerin  s.   
Distilled  Water,  of  each   f  25  iss. 
Thymol...  :   gr.  i 
These  are  all  placed  in  a  wide-mouth  bottle,  which  is  corked  care- 
fully to  exclude  dust,  and  placed  in  a  warm  situation.  It  takes  several 
days  to  effect  a  perfect  solution,  the  mixture  being  stirred  up  occa- 
sionally. When  all  is  dissolved  strain  through  linen,  and  set  aside  the 
liquid  about  a  week  longer  to  get  rid  of  air  bubbles  and  to  allow  any 
small  particles  that  may  have  passed  through  the  strainer  to  settle  to  the 
bottom  ;  or  it  can  be  filtered  through  absorbent  cotton  by  using  a  fun- 
nel for  hot  filtration,  which  consists  of  a  double  tin  case  holding  water, 
kept  at  the  required  temperature  by  a  spirit  lamp  placed  under  the 
projecting  arm.  A  glass  funnel  fits  inside  of  the  hot  water  bath,  a 
plug  of  absorbent  cotton  is  placed  in  the  funnel,  and  the  solution  is 
passed  through  it.  After  filtration  it  is  best  preserved  in  compres- 
sible tubes. 
To  mount  starches  or  pollens,  a  clean  slide  is  breathed  on  and  then 
dusted  over  with  the  starch  or  pollen  to  be  mounted ;  the  surplus  is 
removed  by  gently  tapping  the  slide  against  any  hard  substance — a 
table,  for  instance.  Enough  of  the  starch  will  adhere  to  the  slide, 
and  will  be  nicely  distributed  over  the  field.  A  drop  of  the  mounting 
medium  is  now  placed  on  the  slide  carefully  and  the  cover  placed  over 
it.  If  there  are  any  air  bubbles  in  the  mounting  medium  when  placed 
on  the  slide  they  should  be  carefully  picked  out  with  a  mounting 
needle.  If  the  medium  is  kept  in  a  compressible  tube  there  is  not 
much  danger  of  air  bubbles  on  squeezing  out  a  drop  ;  or  if  there  are 
any,  they  will  be  on  the  surface,  and  can  be  readily  removed  with  a 
mounting  needle.  The  slide  can  then  be  finished  immediately  by 
running  a  ring  of  any  kind  of  cement  around  the  edges  of  the  cover 
glass,  and  the  mount  is  permanent. 
The  medium  can  be  colored  blue  by  adding  a  small  quantity  of 
aniline  blue,  although  it  is  not  necessary,  as  the  structure  of  the 
starches  can  be  plainly  seen.  They  should  be  examined  by  central 
and  oblique  illumination,  and  with  the  polariscope,  to  give  the  student 
interested  in  this  subject  an  idea  of  the  beauty  of  starches  and 
pollens. 
