As™ptembe? fffiB™ }     ^  Structure  of  the  Starch  Gram.  413 
however,  that  it  can  be  demonstrated  that  the  peripheral  layer  of 
the  starch  grain  is  a  distinct  membrane. 
It  is  well  known  that  upon  the  addition  of  an  iodin  solution  to 
unaltered  starch  grains  at  the  ordinary  temperature,  the  grains  are 
colored  blue  ;  while  the  solution  or  filtrate  remains  colorless  or  some 
shade  of  yellow,  depending  upon  the  amount  or  strength  of  iodine 
solution  that  has  been  used.    If  on  the  other  hand  the  grains  are 
triturated  with  sand  (one  part  of  starch  to  five  of  sand)  for  a  short 
time  previous  to  the  addition  of  the  water,  the  filtrate  will  be  col- 
ored a  deep  blue  upon  the  addition  of  an  iodin  solution.  Heretofore 
it  has  been  supposed  by  some  that  the  blue  coloration  was  due  to 
the  presence  of  fine  particles  which  went  through  the  filter  and  were 
suspended  in  the  filtrate,  while  in  reality  there  is  a  true  solution  of 
the  starch  ;  or  in  other  words  the  soluble  starch  has  been  liberated 
from  the  grain  by  the  rupture  of  the  peripheral  layer.     A  polari- 
scopic  examination  of  the  starch  solutions,  after  clarification  by  means 
of  talcum,  showed  that  they  have  marked  dextro-rotatory  proper- 
ties. '  The  angle  of  rotation  for  solutions  of  corn,  wheat,  maranta, 
and  potato  starch  ranged  from  0-3814  to  0-8770°.    Furthermore,  a 
microscopic  examination  of  the  triturated  starch  shows  the  grains 
to  be  in  various  stages  of  disintegration,  and  this,  taken  together 
with  the  behavior  of  starch  toward  iodin,  as  well  as  the  other 
observations  referred  to,  would  indicate  that  the  starch  grain  con- 
sists of  a  membrane  that  is  insoluble  in  water  at  ordinary  tempera- 
ture ;  and  an  interior  portion  which  is  at  least  in  part  soluble  in 
water  at  ordinary  temperature,  that  is,  consists  of  soluble  starch  or 
starch  that  is  colored  blue  with  iodin.     This  technique  enables  us 
to  differentiate  at  once  the  soluble  starch  present,  which  heretofore 
has  not  been  supposed  to  exist  in  the  unaltered  starch  grain.  As 
to  whether  this  substance  is  identical  with  the  granulose  of  Nageli 
(2)  is  a  problem  which  remains  to  be  determined.    It  may  be  added 
that  this  method  furnishes  a  means  of  separating  the  constituents  in 
the  unaltered  grain,  and  is  to  be  preferred  to  the  methods  which 
have  been  employed  heretofore,  of  using  solutions  of  ferments  or 
mineral  acids,  which  give  rise  to  altered  substances,  and  hence  do 
not  give  a  true  differentiation  of  the  substances  as  they  naturally 
occur  in  the  starch  grain. 
This  brings  us  then  to  consider  the  views  of  Raspail  (3),  in  con- 
nection with  those  of  others,  in  regard  to  the  nature  of  the  starch 
grain,  which  may  be  summarized  as  follows: 
