MOLECULAR  DISSYMMETRY  OF  ORGANIC  PRODUCTS.  11 
time  of  its  publication.  I  was  then  a  pupil  at  the  Normal  School, 
leisurely  meditating  on  the  beautiful  studies  of  the  molecular 
constitution  of  bodies,  and  attained,  as  I  thought  at  least,  to  a 
clear  comprehension  of  the  principles  generally  admitted  by 
physicians  and  chemists.  The  preceding  note  disturbed  all  my 
ideas.  What  precision  in  all  the  details  !  Are  there  two  bodies 
whose  properties  have  been  better  studied,  better  compared? 
But  in  the  actual  state  of  science  can  we  conceive  two  sub- 
stances so  similar  without  being  identical?  M.  Mitscherlich 
himself  tells  us  what  was,  in  his  mind,  the  consequence  of  this 
similitude  : 
The  nature,  the  number,  the  arrangement,  and  the  distance  of 
atoms  are  the  same.  If  this  is  true,  what  then  becomes  of  this 
definition  of  chemical  species,  so  rigorous,  so  remarkable  for  the 
time  in  which  it  appeared,  given  in  1823,  by  M.  Chevreul  ? 
In  compound  bodies,  species  is  a  collection  of  beings  identical  in 
the  nature,  the  proportion  and  the  arrangement  of  their  elements. 
In  short,  the  note  of  M.  Mitscherlich  rested  in  my  mind  as 
an  obstacle  of  the  first  order  to  our  manner  of  considering  ma- 
terial bodies. 
Every  body  will  understand  now,  that,  being  prepossessed,  for 
reasons  stated,  with  a  notion  of  a  possible  correlation  between 
hemihedrity  of  the  tartrates  and  their  rotary  property,  the 
note  of  M.  Mitscherlich,  of  1844,  would  recur  to  my  memory. 
M.  Mitscherlich,  I  at  once  supposed,  was  deceived  upon  one 
point.  He  could  not  have  seen  that  his  double  tartrate  was 
hemihedrie,  that  his  paratartrate  was  not,  and  if  these  things  are 
so,  the  results  of  his  note  are  not  extraordinary ;  and  I  would 
have  in  it  besides  the  best  criterion  of  my  preconceived  idea 
about  the  correlation  of  hemihedrity  and  the  rotary  pheno- 
menon. 
I  then  hastened  to  resume  the  study  of  the  crystalline  form 
of  the  two  salts  of  M.  Mitscherlich.  I  found,  in  fact,  that 
the  tartrates  were  hemihedrie  like  all  the  tartrates  which  I 
had  previously  studied,  but,  strangely  enough,  the  paratartrate 
was  also  hemihedrie.  Only  the  hemihedrie  faces  which,  in  the 
tartrate,  had  all  the  same  direction,  were  inclined  in  the  para- 
tartrate sometimes  to  the  right,  sometimes  to  the  left.  In  spite 
of  all  that  was  unexpected  in  this  result,  I  did  not  the  less  pursue 
