64  Preparation  of  Thyroid  Extract.  {^^^bfSal^'y^rjT™' 
enters  the  blood  directly  and  not  through  the  stomach.  To  imitate 
the  physiological  conditions  I  am  convinced  that  we  should  adminis- 
ter the  same  biological  sort  of  thyroid  proteid  by  hypodermic  injec- 
tion. The  human  patient  should  receive  human  thyroid  proteid 
by  hypodermic  injection.  Of  course  such  a  conclusion  is  of  theoreti- 
cal interest  only,  but  during  the  last  three  years  I  have  had  many 
opportunities  to  compare  upon  human  subjects  the  effects  produced 
by  administration  of  various  forms  of  thyroid  preparations  and  from 
these  observations  the  only  possible  conclusion  is  that  the  human 
thyroid  is  by  far  the  best  for  the  human  subject.  When  we  give 
the  human  thyroid  extract  we  give  a  substance  ready  for  instant  use, 
and  a  comparatively  small  quantity  will  act  more  effectively  from 
the  qualitative  and  quantitative  stand-point  than  a  larger  quantity  of 
any  other  kind  of  thyroid  material.  These  other  forms  probably 
act  very  largely  by  stimulating  the  gland  of  the  individual  to  whom 
they  are  administered. 
In  its  effects  upon  simple  goitre,  myxoedema,  cretinism,  athyroid 
symptoms  found  occasionally  in  the  later  periods  of  exophthalmic 
goitre,  and  various  metabolic  disorders  associated  with  hypofunc- 
tion  of  the  thyroid,  there  is  no  other  substance  which  acts  so  eco- 
nomically and  efficiently  as  the  proteid  precipitated  from  extracts 
of  normal  human  thyroid  glands  by  acetic  acid  and  heat  to  44°  C. 
For  the  reasons  above  outlined  we  should  use  only  the  proteid 
obtained  by  a  similar  method  from  animal  glands.  Accordingly  the 
original  precipitate  is  washed  repeatedly  with  normal  saline  by  de- 
cantion  or  centrifugation  until  the  wash-water  is  free  from  biuret 
reacting  substances.  It  is  then  dissolved  by  the  addition  of  a  little 
sodium  hydroxide,  the  solution  filtered  through  a  thick  paper  mat  and 
again  precipitated  by  acidifying  with  acetic  acid.  Heat  is  rarely 
required  for  the  second  precipitation.  The  washing  process  is  re- 
peated and  more  proteid-like  material  removed  from  the  precipitated 
globuhn.  The  final  washed  precipitate  is  centrifugated  or  filtered 
out  and  dried  at  low  temperature,  or  it  may  be  kept  in  solution  and 
after  filtration  through  a  Berkefeld  kept  for  hypodermic  adminis- 
tration. 
Proteids  have  been  prepared  in  this  manner  from  glands  of  pigs, 
beeves,  sheep,  and  the  human  gland.  The  prepared  proteid  shows 
quite  as  wide  a  variation  in  its  iodine  content  as  do  the  fresh  glands. 
In  the  following  table  is  given  a  series  of  iodine  analyses  of  thyroid 
glands  obtained  from  healthy  animals. 
