Xirar>,mr-}      Preparation  of  Thyroid  Extract.  59 
improvement  which  Dr.  Rig'gs  has  introduced  is  the  addition  of  an 
active  reduction  by  Devarda's  alloy  of  the  solution  of  the  fusion 
mass,  thus  reducing  the  iodate  to  iodide  and  insuring  a  full  yield. 
The  figures  given  in  his  paper  show  that  it  is  with  the  glands  con- 
taining only  a  very  small  quantity  of  iodine  that  the  largest  errors 
are  made.  For  instance,  with  sheep  thyroids,  which  contained  only 
.03  mg.  iodine  per  gramme  of  fresh  gland,  77  per  cent,  of  the  iodine 
was  found  after  reduction.  Subsequent  experience  has  borne  out 
these  findings  and  we  have  repeatedly  had  glands  for  analysis  which 
were  found  to  be  iodine  free  by  the  older  method,  but  were  found  to 
contain  marked  quantities  of  iodine  after  reduction.  In  no  instance 
have  we  found  a  thyroid  gland  free  from  iodine,  and  we  have 
analyzed  a  wide  variety  of  thyroid  glands  during  the  last  two  years. 
In  view  of  these  facts  I  am  of  the  opinion  that  we  are  not  at  present 
justified  in  saying  that  iodine-free  thyroid  has  an  effect  similar  to 
that  obtained  by  the  normal  iodized  product,  and,  furthermore,  it 
seems  probable  that  many  of  the  results  ascribed  to  iodine-free  thy- 
roid are  really  caused  by  a  proteid  containing  only  an  exceedingly 
small  quantity  of  iodine.  The  recent  paper  of  Hunt  and  Seidell  ^ 
gives  the  most  striking  evidence  yet  published  that  iodine-free 
thyroid  does  have  the  characteristic  metabolic  effect  of  the  iodized 
gland,  but  I  believe  the  explanation  of  their  results  is  to  be 
found  in  the  fact  that  their  method  of  determining  iodine  was  faulty, 
and  the  cjuantity  of  material  used  for  iodine  analysis  too  small. 
These  authors  are  agreed,  however,  that  iodine-containing  thy- 
roid is  much  more  effective  than  iodine-free  thyroid,  and  give 
figures  to  show  that  the  physiological  effect  is  in  direct  proportion 
to  the  iodine  content.  Such  a  conclusion  is  in  harmony  with  the 
findings  of  most  students  of  this  subject  and  agrees  with  the  experi- 
ments made  in  my  laboratory.  I  regard  it,  therefore,  as  probable 
that  functional  activity  is  proportional  to  iodine  content,  other  fac- 
tors being  the  same. 
The  thyroid  gland  contains  a  variety  of  protein  substances  which 
contain  iodine  and  according  to  some  investigators  other  iodine- 
free  proteids.  The  methods  of  isolating  these  proteins  have  not 
been  uniform  and  as  a  result  it  seems  prol^able  that  authors  have 
given  different  names  to  the  same  substances.  The  most  conclusive 
work  upon  the  chemistry  of  the  thyroid  has  been  done  by  Oswald,' 
who  is  led  to  conclude  that  thyreoglobulin  is  the  characteristic  iodine- 
containing  proteid  found  in  the  gland.    He  describes  another  pro- 
