68  Biological  Standardisation.         { ^bruary, 
of  this  action,  the  blood  pressure  is  raised,  peristalsis  is  increased 
and  the  tone  of  an  inert  uterus  is  aroused. 
It  is  logical  to  assume  that  all  the  effects  are  due  to  a  constituent 
which  acts  on  unstriated  muscle  and  to  choose  one  of  these  as  a  test 
reaction — one  which  is  accurate  and  measurable.  If,  however,  the 
action  on  the  pregnant  uterus  is  due  to  a  constituent  other  than  that 
which  affects  the  blood  pressure,  then  it  is  essential  that  the  oxytocic 
test  be  applied  to  those  preparations  intended  for  obstetrical  work. 
But  for  the  assay  of  such  as  are  used  to  control  the  blood  pressure 
in  cases  of  shock  it  would  be  necessary  to  apply  the  blood  pressure 
test. 
While  some  investigators,  notably  Fuhner  (12),  claimed  to  have 
produced  evidence  that  two  or  more  constituents  are  present  in  an 
active  extract,  others  have  found  the  two  principal  effects  to  go 
hand  in  hand,  pointing  either  to  the  presence  of  only  one  active  con- 
stituent or  to  a  constant  ratio  in  the  content  of  the  two  constituents. 
Roth  (13)  whose  work  was  probably  the  basis  for  the  choice  both 
of  the  method  and  the  standard  test  dose,  submitted  little  conclusive 
evidence  for  his  choice  of  the  oxytocic  method.  He  made  his  selec- 
tion because  "  the  simplicity  of  the  isolated  uterus  method,  together 
with  the  fact  that  the  uterus  of  the  virgin  guinea  pig  shows  little 
variation  in  its  reaction  to  pituitary  extracts  even  after  hours,  places 
it  above  other  methods  in  point  of  desirability  as  a  method."  His 
objection  to  the  blood  pressure  method  is  "that  one  encounters  a 
degree  of  tolerance  when  a  second  or  succeeding  dose  is  given." 
On  the  latter  point  he  submits  as  evidence  of  toleration  a  series 
of  14  consecutive  injections  of  pituitrin,  only  9  of  which,  however, 
illustrate  his  point.  Each  of  the  first  five  were  followed  by  an  almost 
identical  rise  in  pressure,  while  the  others  were  made  in  a  manner 
contrary  to  his  own  suggestion,  namely,  "the  period  between  injec- 
tions to  be  at  least  30  minutes  long."  The  nine  injections  were 
made  with  an  average  interval  of  5  minutes  and  into  a  dog  which 
was  apparently  incompletely  anesthetized.  He  submits  no  evidence 
whatever  on  the  point  that  "  little  variation  is  shown  in  the  reaction 
of  the  isolated  uterus  to  pituitary  extracts  even  after  hours." 
While  the  method  is  apparently  simple  the  test  strips  of  uterus 
muscle  which  will  respond  differently  to  different  sized  doses  with 
any  degree  of  accuracy  are  so  few  that  a  dependable  test  can  rarely 
be  made.  On  the  other  hand  a  blood-pressure  test  can  be  made  on 
dogs  with  few  exceptions  and  the  "tolerance  "  referred  to  is  scarcely 
