41 6  Active  Prmciple  oj  Thyroid  Gland.     { ^"^  ^Tnniy9To: 
tillation,  and  after  standing  for  a  time  the  mono-sodium  salt  of 
thyroxin  separates  out.  The  latter  is  purified  by  dissolving  it  in  an 
alkaline  alcoholic  solution,  then  saturating  with  carbonic  acid  gas 
and  distilling  off  the  alcohol;  the  same  operation  may  be  repeated 
five  or  six  times,  using  acetic  acid  in  the  place  of  carbonic  acid,  until 
the  thyroxin  as  ''4-5-6-hydro-4-5-6-iodo-2-oxy-/3-indolpropionic  acid," 
of  the  empiric  formula  C11H10NO3I3. 
It  occurs  in  three  different  forms:  (i)  A  ketonic  form: 
CIH 
Hic/\c  =  C  —  CH2  —  CHo  —  COOH 
HIC 
CH  NH 
(2)  A  tautomeric  enolic  form : 
CIH 
HICf    >C  =  C  —  CH2  —  CH2  —  COOH 
m6^Jc^^c  —  OH 
CH  N 
(3)  With  an  open  pyrrolic  nucleus,  due  to  fixation  of  H2O,  so  that 
this  body  possesses  both  the  characters  of  a  di-acid  and  of  a  primary 
amine : 
CIH 
Hic/Nc  =  C  —  CH2  —  CH2  —  COOH 
CH  NH2 
HIC'v^^Cs^  COOH 
The  author  states  that  the  first  form  is  the  anhydride  of  the  third, 
and  these  bear  the  same  relationship  to  each  other  as  creatinin  to 
creatin.  The  third  form  is,  therefore,  "thyroxin,"  and  occurs  as 
such  in  the  thyroid  gland;  it  cannot  be  obtained  in  crystalline  form, 
but  crystallizes  only  on  being  converted  into  its  anhydride.  Kendall 
found  that  during  the  months  of  January,  February  and  March  the 
glands  contain  only  a  slight  percentage  of  thyroxin,  whereas  during 
the  summer  months  there  is  an  increase  amounting  to  400  per  cent., 
and  this  is  the  time  when  the  glands  should  be  used  for  the  extraction 
of  their  thyroxin. 
