594  Microscopical  and  Urinary  Notes.  {AmDec.!''iSoarm' 
about  $85  to  #100,  according  to  quality  of  the  objectives,  and 
whether  the  stand  be  provided  with  sliding-tubes  or  with  a  rack  and 
pinion. 
For  a  beginning  a  magnifier,  one  eye-piece,  a  J^-inch  objective 
and  a  condenser  on  stand  will  be  all  that  is  necessary,  besides  the 
microscope  stand;  the  lowest  price  of  all  of  which  is  about  $25  to 
$30.  This  will  be  sufficient  for  the  first  six  or  twelve  months,  then 
the  remainder  can  be  gradually  added,  the  2-inch  objective  being 
the  least  necessary  objective.  Of  the  apparatus,  the  nose-piece  is 
of  such  a  convenience  that  it  rapidly  becomes  a  necessity.  A 
microtome  (section  cutter)  can  be  dispensed  with,  free-hand  cutting 
serving  all  useful  purposes,  though  the  sections  seldom  will  be  ele- 
gant. The  turn-table  is  rendered  necessary  by  the  use  of  circular 
cover-glasses.  Practically,  square  cover-glasses  serve  exactly  as 
well,  but  are  not  considered  as  elegant  as  the  circular  ones;  with 
these  a  turn-table  is,  of  course,  superfluous. 
Objectives. — These  are  generally  divided  into  three  classes  : 
student's,  professional  and  first-class,  which  now-a-day  means  only 
objectives  with  low  and  medium  angular  aperture;  wide  angled; 
and  with  the  widest  angle  obtainable.  At  present  the  objectives  of 
each  class  are  made  and  corrected  as  carefully  as  possible;  some 
twenty  years  back,  however,  the  lower  angled  ones  ("student's") 
were  generally  poorly  corrected,  and  entirely  unreliable  for  exact 
investigations.  The  practical  difference  between  low  and  medium 
angled  objectives  and  those  of  the  widest  angle  is  that  a  wide 
angled  objective  shows  more  of  the  very  minute  details  and  shows 
them  better  than  a  low  angled  one  of  the  same  focus,  which  often 
fails  to  show  them  at  all.  Happily  for  us  pharmacists  the  minute- 
ness of  the  details  in  question  is  far  greater  than  any  we  have  to 
investigate;  the  so-called  "  student's "  serve  all  our  purposes,  and 
are  very  much  cheaper.  It  is  an  entirely  different  thing  when  we 
want  to  study  the  layers  of  the  cell  wall,  for  instance,  or  bacteria, 
then  we  cannot  do  without  objectives  of  a  very  wide  angle. 
Cover-glasses. — The  attention  of  those  interested  in  the  influence 
of  the  thickness  of  the  cover-glass  on  the  definition  and  resolution 
of  the  object  examined,  and  how  to  counteract  this  influence  by 
either  shortening  or  lengthening  the  draw-tube — is  called  to  an 
instructive  article  of  Ed.  Bausch,  in  the  October  number  of  the 
"Microscope"  (Trenton,  N.  J.). 
