82 
The  Starch  Grain. 
J  Am.  Jour.  Pharm. 
i    February,  1914. 
Ihis  is  the  product  with  which  we  are  specially  concerned  in 
the  present  article.  Hereto  t  ore,  the  minute  study  of  the  starch 
grain,  particularly  of  its  structure,  has  been  of  scientific  interest 
only,  but  with  the  application  of  scientific  methods  in  nearly  every 
department  of  industry,  it  is  coming  to  have  a  practical  application. 
The  commercial  reserve  starches  are  derived  from  various 
plants,  and  not  only  enter  largely  into  food  products  but  are  also 
used  for  a  variety  of  technical  purposes.  The  grains  of  the  re- 
serve starches  have  a  number  of  characteristic  features.  They 
vary  in  size,  in  shape,  in  internal  structure,  and  also  to  a  con- 
siderable extent  in  composition.  The  variation  in  composition  is 
shown  by  the  use  of  aniline  stain  and  also  by  the  use  of  iodine. 
By  the  treatment  of  starch  with  iodine  solution,  we  may  distinguish 
three  kinds  of  reserve  starch:  (i)  one  which  is  colored  deep  blue, 
as  potato  and  maranta;  (2)  one  which  is  colored  somewhat  purplish, 
changing  to  cinnamon-brown,  as  corn  and  wheat;  and  (3)  one 
which  is  colored  brownish-red,  as  in  the  amylo-dextrin  starches 
of  comfrey  and  a  few  other  plants. 
The  shape  of  the  grains  varies  from  polygonal  to  ellipsoidal, 
the  shape  being  influenced  by  the  number  of  grains  in  a  cell.  Under 
the  micro-polariscope  the  grains  are  seen  to  be  anisotropic,  the 
polarization  effects  differing  with  the  grains  of  the  different  classes. 
Polarizing  effects  are  usually  produced  by  crystals,  but  may  be 
produced  by  substances  in  a  condition  of  tension,  as  minute  globules 
of  glass.  It  should  also  be  stated  that  cell  walls  have  this  same 
property  of  double  refraction,  and  it  is  very  likely  that  the  sub- 
stances in  the  starch  grains,  as  well  as  in  the  cell  wall,  are 
crystalloidal  and  arranged  in  spherite  aggregates,  resembling  those 
of  inulin,  a  product  closely  resembling  starch. 
The  theories  which  have  been  advanced  regarding  the  struc- 
ture of  the  starch  grain,  have  been  largely  based  on  studies  of 
the  potato  starch  grain.  It  was  originally  thought  to  be  in  the 
nature  of  a  globule  filled  with  a  fluid.  Fritzche,  Schleiden  and 
others  considered  it  to  be  made  up  of  more  or  less  concentric 
layers  formed  around  a  central  or  excentral  point.  While  it  may 
be  true,  as  pointed  out  by  Naegeli,  that  many  of  the  reserve  and 
glucose  starch  grains  arise  free  in  the  cell,  the  view  of  Schimper 
that  starch  grains  always  develop  within  plastids,  is  generally 
accepted  at  the  present  time. 
The  internal  structure  of  the  starch  grain  is  shown  in  several 
