352  Pharmacy  of  Tethelin.  {AnijtJn0eUr'i9ih9arm' 
The  belief  was  later  expressed  by  Robertson  and  Ray9  that  the 
direct  action  of  tethelin  appeared  to  consist  of  retardation  of  growth, 
and  that  the  later  acceleration  is  due  to  compensatory  factors  which 
develop  in  the  animal  itself  in  response  to  the  abnormal  dosage  of 
the  active  principle  of  the  anterior  lobe  of  the  pituitary  body. 
They  preferred  this  view  for  the  reason  that  the  compensatory 
acceleration  was  more  intense  when  the  retarding  factor,  tethelin, 
was  discontinued  after  the  twelfth  week  of  age  of  the  mice  and  the 
eighth  week  of  the  administration.  Finally  they  presented  two  pos- 
sibilities to  explain  the  effect  of  tethelin  upon  the  healing  of  super- 
ficial wounds  and  upon  the  growth  of  inoculated  carcinoma,  namely, 
that  tethelin  accelerates  the  growth  of  the  epithelial  tissues  and  di- 
rectly or  indirectly  retards  the  growth  of  the  other  and  collectively 
more  bulky  tissues,  or  that  tethelin  retards  the  growth  of  all  tissues, 
but  indirectly  accelerates  the  growth  of  epithelial  tissues  in  situ  by 
disproportionately  retarding  the  growth  of  other  tissues  and  thus 
favoring  the  epithelial  tissue  in  the  competition  for  nutritive  ma- 
terials. 
Physical  and  Chemical  Characteristics. 
Tethelin  is  a  white  or  pale  cream-colored  substance,  which  is 
readily  powdered.  It  rapidly  absorbs  aqueous  vapor  when  exposed 
to  damp  air  and  becomes  moist  and  darkens  in  color. 
A  combination  of  air  and  moisture  results  in  active  decomposi- 
tion of  tethelin,  the  tethelin  becoming  damp  and  dark  in  color  and 
suffering  a  lowering  of  its  iodine-absorption  power.10 
When  heated,  tethelin  begins  to  darken  at  a  temperature  lying 
between  100  and  no°  C,  and  when  heated  to  still  higher  tempera- 
tures, the  substance  progressively  darkens  and  softens  as  the  tem- 
perature rises. 
Heat  is  particularly  active  in  bringing  about  decomposition  of 
tethelin,  particularly  in  access  of  air  and  moisture.11 
Tethelin  is  soluble  in  water  to  the  extent  of  5  per  cent.,  forming 
at  that  concentration  a  brown,  turbid  solution.  More  dilute  solu- 
tions are  paler  in  color  and  1  per  cent,  solutions  are  but  slightly 
opalescent.  Aqueous  solutions  of  tethelin  have  a  greasy  odor, 
somewhat  resembling  brain  tissue. 
9  Robertson,  T.  B.,  and  L.  A.  Ray,  Journ.  Biolog.  Chemistry,  1919, 
XXXVII,  u.  456. 
10  Robertson,  T.  B.,  Jour.  Biolog.  Chem.,  1916.  XXIV,  p.  415. 
11  Robertson,  T.  B.,  Calif.  State  Jour.  Med.,  Dec,  1917. 
