264 
DECOMPOSITION  OF  IODIDE  OF  STARCJS,  ETC. 
it  passed,  under  this  form,  through  the  circulation  and  into  the 
excretions.  Several  circumstances,  however,  are  opposed  to  this 
view.  First,  the  iodide  of  starch  is  decomposed,  not  only  by  the 
saliva,  serum  of  the  blood,  and  pancreatic  juice,  which  are  alka- 
line ;  but  also,  quite  as  promptly,  by  urine  and  gastric  juice, 
which  are  acid  in  reaction.  Secondly,  the  gastric  juice,  as  al- 
ready mentioned,  has  no  power  of  preventing  the  union  of  starch 
and  iodine,  when  taken  fresh  from  the  stomach  of  the  fasting 
animal,  but  yet  gains  this  power  in  a  high  degree  when  artifi- 
cially digested  with  meat  at  100°  F.  It  seems  nearly  certain, 
therefore,  that  the  iodine  combines,  in  this  instance,  with  some 
of  the  albuminoid  matters  dissolved  by  the  gastric  juice. 
This  reaction  of  iodine  with  the  animal  substances  is  further 
illustrated,  in  a  very  striking  manner,  by  the  following  experi- 
ments, performed  at  the  suggestion  and  with  the  assistance  of 
my  friend,  Dr.  Wm.  H.  Ellett 
I.  If  a  mixed  solution  of  boiled  starch  and  iodide  of  potas- 
sium be  spread  upon  the  surface  of  the  skin,  and  the  two  poles  of 
a  galvanic  battery  applied  to  the  moistened  surface  a  short  dis- 
tance from  each  other^no  perceptible  discoloration  appears,  pro- 
vided the  galvanic  current  be  not  very  powerful ;  while  if  the 
same  poles  be  applied  to  a  piece  of  bibulous  paper,  moistened 
with  the  same  solution,  the  blue  iodide  of  starch  appears  at  once 
at  the  positive  pole. 
II.  If  the  negative  pole  of  the  batfcery  be  placed  in  contact 
with  the  bibulous  paper,  moistened  as  above,  the  positive  pole 
taken  in  the  left  hand,  and  the  circuit  completed  by  touching 
the  bibulous  paper  with  the  right  forefinger,  the  shock  is  felt, 
but  no  discoloration  of  the  paper  is  produced  ;  but  if  the  circuit 
be  completed  by  a  steel  needle,  held  in  the  right  hand,  a  dark 
stain  immediately  appears  on  the  paper. 
III.  The  negative  pole  was  placed  in  contact  with  the  mois- 
tened paper,  and  a  fresh  piece  of  animal  membrane  (uterus  of 
the  cow)  attached  by  one  end  to  the  positive  pole.  The  other 
end  of  the  animal  membrane  was  then  cut  to  a  fine  point,  by 
which  the  circuit  was  completed  on  the  paper  ;  but  no  stain  oc- 
curred. A  steel  needle  was  then  thrust  through  the  animal- 
membrane,  and  the  circuit  completed  by  the  point  of  the  needle? 
when  the  discoloration  of  the  paper  immediately  appeared. 
