46 
DETECTIVE  POWER  OF  THE  MICROSCOPE. 
siderable  doubt  as  to  the  accuracy  of  the  extraordinary  revela- 
tions that  he  gave,  confidently,  to  the  public  in  the  pages  of  the 
Lancet.  Every  person  conversant  with  chemistry  was  well 
aware  what  a  useful  adjunct  the  microscope  has  been  to  the 
chemical  analyst,  in  distinguishing  the  form  of  minute  crystals, 
and  thereby  determining  their  true  character,  when  mixed  with 
organic  or  inorganic  bodies ;  but  few  foresaw  that  it  might  be 
employed  as  a  means  of  analysis  itself,  in  mixtures  of  organised 
substances. 
In  fact,  in  physiological  chemistry,  the  microscope  is  preferred 
to  every  other  resource  as  a  means  to  detect  the  presence  of  mi- 
nute quantities  of  organic  crystalline  compounds  in  the  complex 
fluids  secreted  by  animals. 
Dr.  C.  G.  Lehmann,  a  very  high  authority,  observes,  when 
speaking  of  the  tests  for  the  detection  of  urea,  that  the  best 
method  to  ascertain  its  presence,  is  by  the  formation  of  its  salts 
with  nitric  and  oxalic  acids,  and  to  submit  the  salts  so  formed, 
when  crystallised  by  the  evaporation  of  their  menstruum,  to  mi- 
croscopic examination,  and  thus  to  ascertain  the  correct  shape 
of  the  crystals,  "which,  if  the  investigation  is  to  be  unquestion- 
able, the  acute  angles  must  be  always  measured;"  for,  as  he 
farther  remarks,  that  « a  good  crystallometric  determination 
yields  the  same  certainty  as  an  elementary  analysis,  which,  in 
these  cases,  would  never  or  extremely  seldom  be  possible."* 
These  evidences  of  the  value  of  the  microscope  as  a  means  of 
testing  by  the  ph}7sical  characteristics  of  a  crystalline  substance, 
might  be  multiplied  almost  innumerably  from  the  same  and  other 
authorities. 
However  extraordinary  the  statement  may  appear,  that  Dr. 
Lehmann  and  others  prefer  the  microscope  as  the  agent  by 
which  the  composition,  or  some  of  the  ingredients,  of  a  complex 
body  are  to  be  determined,  when  those  ingredients  are  crystal- 
line, the  results  of  the  investigations  of  Drs.  Hassal  and  Pereira, 
and  Mr.  Quekett,  are  yet  more  remarkable  and  worthy  of  atten- 
tion ;  for  they  prove  that  the  microscope  is  the  only,  or  at  least 
the  only  good  means  which  science  has  at  present  discovered  to 
detect  the  admixture  or  adulteration  of  non-crystalline  organic 
substances. 
*  Lehmann's  Physiological  Chemistry,  vol.  i.  pp.  150  and  160. 
