^?;birarV,79i™'}      Preparation  of  Thyroid  Extract.  6i 
times  their  volume  of  normal  saline  solution  made  very  faintly  alka- 
line by  sodium  hydroxide.  Three  or  four  drops  of  a  ten  per  cent, 
solution  of  sodium  hydroxide  are  added  to  every  litre  of  salt  solu- 
tion. The  extract  is  shaken  vigorously  at  room  temperature  for  one 
or  two  hours  and  is  then  transferred  to  the  refrigerator,  where  it 
is  allowed  to  remain  for  twelve  to  eighteen  hours.  At  the  end  of 
this  time  a  large  portion  of  the  proteid  has  been  dissolved  by  the 
saline.  The  clear  extract  is  obtained  by  filtering  first  through  gauze 
to  remove  the  larger  fragments  and  then  through  paper  pulp  by  the 
help  of  a  Buchner  funnel,  after  the  method  of  Osborne.  As  stated 
before,  this  extract  contains  a  variety  of  proteids  and  proteid  frag- 
ments and  our  object  is  to  separate  the  pure  iodine  containing  glob- 
ulin from  the  other  constituents  by  as  brief  and  simple  a  method 
as  possible.  This  may  be  accomplished  by  salting  out  the  proteid, 
filtering  and  finally  dialyzing  the  precipitate,  a  procedure  which  re- 
quires a  great  deal  of  time  and  which  exposes  the  product  to  abun- 
dant opportunities  for  infection  and  decomposition.  The  plan  we 
have  finally  adopted  is  to  acidify  with  acetic  acid  and  heat  to  44°  C. 
for  10  minutes.  Extracts  of  the  different  species  of  glands  behave 
in  characteristic  fashion.  The  addition  of  acetic  acid  to  extract  of 
sheep  glands  gives  a  scanty  precipitate  or  none  at  all ;  such  as  does 
form  may  be  filtered  out  and  is  found  to  be  richer  in  iodine  than  any 
fraction  obtained  subsequently.  On  heating  an  abundant  flocculent 
precipitate  is  obtained  at  44°  C.  This  precipitate  is  rich  in  iodine,  it 
dissolves  readily  in  a  weak  alkaline  solution,  and  is  precipitated  again 
by  acetic  acid.  Its  behavior  with  regard  to  dialysis  and  salt  pre- 
cipitation is  that  of  a  globulin  ;  it  contains  more  iodine  than  any 
proteid  obtained  from  the  filtrate  heating  to  a  higher  temperature, 
and  is  by  far  the  most  abundant  proteid  in  the  gland.  If  this  pro- 
teid is  removed  by  filtration  and  the  filtrate  heated  to  a  higher  tem- 
perature, a  further  precipitate  is  obtained  at  65 ^-70°,  a  third  at 
82°-86°,  and  a  fourth  after  boiling  for  some  time.  All  of  these  pro- 
teids contain  iodine  but  in  relatively  much  less  amount  than  in  the 
precipitate  at  44°,  they  form  only  a  small  part  of  the  entire  proteid 
content,  and  they  do  not  redissolve  in  a  weak  alkaline  solution. 
After  all  coagulable  proteids  are  removed  the  filtrate  contains 
substances  giving  the  proteid  color  reactions  and  containing  a  by 
no  means  negligible  quantity  of  iodine.  If  the  whole  gland  extract 
is  used  for  therapeutic  purposes  it  follows  that  all  of  the  various 
iodized  fractions  are  administered.    I  believe  that  some  of  these  sub- 
