182 
A  Study  of  Starch  Grains. 
( Am.  Jour.  Pharm. 
\      April,  1899. 
occurs  frequently  in  the  mounting  of  the  specimen,  and  is  especially 
noticeable  as  a  result  of  the  processes  to  which  the  plant  has  been 
subjected  in  the  manufacture  of  food  and  medicine.  The  single 
grains  thus  separated  are  more  or  less  angular.  It  sometimes  oc- 
curs that  a  single  starch  grain  possesses  apparently  2  points  of 
origin  of  growth,  when  it  is  spoken  of  as  being  half-compound. 
While  there  is  considerable  variation  in  the  shape  of  the  grains  iso- 
lated from  different  species  of  plants,  there  is  also  a  greater  variation 
in  the  grains  from  different,  or  even  the  same,  plants  of  the  same 
species.  This  variation  more  frequently  occurs  than  is  generally 
supposed,  so  that  the  greatest  care  must  be  exercised  in  utilizing 
the  shape  alone  in  determining  the  botanical  source  of  the  grains 
present  in  the  specimen  under  examination.  There  is  also  con- 
siderable variation  in  the  size  of  the  grains  not  only  from  the  same 
plant  but  even  in  the  same  cell. 
Some  foods  and  drug  products  are  variously  treated  in  preparing 
them  for  the  market,  and  there  is  necessarily  more  or  less  of  an 
alteration  of  the  typical  starch  grains.  For  instance,  they  may  be 
treated  over  the  naked  fire  as  jalap  root,  or  moistened  and  dried 
either  by  exposure  to  the  sun  or  near  a  fire  as  in  guarana,  or  in 
hot  water  as  aconite  tubers.  In  such  cases  the  starch  grains  are 
changed  to  swollen  masses  or  are  more  or  less  corroded. 
One  of  the  most  striking  properties  of  starch  grains  is  that  when 
viewed  by  polarized  light  they  show  a  neutral  cross  which  extends 
from  the  point  of  origin  of  growth  to  the  periphery  of  the  grain. 
This  neutral  cross  appears  to  turn  as  Nichol's  prism  is  revolved 
and  to  produce  the  various  colors  of  the  rainbow.  We  likewise 
find  that  starch  grains  from  different  sources  do  not  behave  alike 
towards  polarized  light.  The  distinctness  of  the  cross  as  well  as 
the  kind  of  colors  produced,  as  Nichol's  prism  is  revolved, 
varies  considerably,  and  we  are  inclined  to  the  opinion  that  this 
subject  is  well  worth  careful  study  from  a  practical,  as  well  as  scien- 
tific, standpoint. 
MICRO-CHEMICAL  EXAMINATION  OF  STARCH. 
It  has  already  been  shown  that  most  starch  grains  give  a  blue 
color  when  treated  with  iodine  solutions,  but  that  some  are  turned 
red  by  the  employment  of  this  reagent.  It  is  supposed  by  some 
investigators  that  there  is  an  actual  chemical  combination  which 
