Am.  Jour.  Pharm.  "I 
October,  1903.  J 
Mydria tic  A  Ikaloids. 
455 
salt  of  racemic  acid  and  crystallizing  below  28°  C.  he  obtained  large 
rhombic  crystals,  part  of  which  possessed  right  hemihedral  faces  and 
part  left  hemihedral  faces.  In  other  words  one  crystalline  form  was 
an  exact  mirror  picture  of  the  other.  By  isolating  these  two  forms 
mechanically  and  decomposing  them  separately  he  obtained  two 
tartaric  acids  of  identical  composition,  of  which  the  one  with  right 
hemihedral  faces  turned  the  plane  of  polarized  light  the  same 
number  of  degrees  to  the  right  as  the  one  with  the  left  hemihedral 
faces  turned  it  to  the  left.  By  combining  solutions  of  equal  quantities 
of  these  two  optically  active  acids  he  regenerated  racemic  acid 
which  is  optically  inactive.  The  same  results  were  nicely  accom- 
plished by  means  of  the  alkaloids  cinchonine  and  quinicine.  When 
racemate  of  cinchonine  was  allowed  to  crystallize  from  its  solution 
Pasteur  noticed  that  the  cinchonine  salt  of  1-tartaric  acid  separated 
out  first,  while  the  salt  of  the  d-acid  remained  in  solution.  In  the 
case  of  quinicine  racemate  the  opposite  results  were  observed,  viz., 
the  salt  of  d-tartaric  acid  separated  first.  Further,  by  inoculating  a 
solution  of  the  acid  ammonium  salt  of  racemic  acid  with  the  fungus 
Penicillium  glaucum,  the  salt  of  d-tartaric  acid  was  selected  for 
destruction,  leaving  the  salt  of  1-acid  in  solution. 
Since  these  isomeric  substances  differ  from  each  other  principally 
in  their  physical  properties  they  first  received  the  name  physical 
isomers.  Later  this  term  was  supplanted  by  the  more  appropriate 
term  geometrical  or  stereo-isomers. 
Pasteur  and  others  attempted  to  explain  the  phenomena  of  stereo- 
isomerism by  a  difference  in  the  arrangement  of  the  atoms  of  a 
compound  in  space,  but  they  were  at  a  loss  to  know  just  how  these 
atoms  or  groups  were  to  be  placed.  In  1874  two  investigators, 
Le  Bel  and  van't  Hoff,  working  independently,  ascribed  optical 
activity  and  the  isomerism  of  optically  active  carbon  compounds  to 
the  presence  in  the  molecule  of  one  or  more  asymmetric  carbon 
atoms,  i.  e.y  carbon  atoms  that  are  linked  with  four  atoms  or  groups 
that  are  all  different,  from  each  other.  While  this  theory  was 
received  with  hesitation  and  much  opposition  at  first,  it  can  be  safely 
said  that  not  a  single  optically  active  carbon  compound  is  known 
which  does  not  bear  out  this  hypothesis.  Not  all  compounds, 
containing  asymmetric  carbon  atoms,  however,  are  optically  active. 
Among  the  stereo-isomeric  carbon  compounds  none  are  of 
greater  interest  or  importance  Jhan  some  of  the  plant  alkaloids. 
