534         Preparations  of  the  Suprarenal  Glands.  {A^vembex%u' 
again  exercised  to  prevent  the  entrance  of  air  into  the  vessel. 
Within  a  few  moments  after  the  injection  the  blood-pressure  is 
enormously  increased,  but  it  quickly  falls  again  to  the  normal.  As 
soon  as  the  blood-pressure  has  become  normal  a  second  injection  is 
made  in  precisely  the  same  manner,  of  a  known  quantity  of  the 
standard  solution  of  the  suprarenal  gland.  Again  increased  blood- 
pressure  results.  A  comparison  of  first  and  second  tracings  will 
show  whether  more  or  less  of  the  solution  being  assayed  should  be 
injected  to  produce  the  same  rise  in  blood  pressure  as  is  produced 
by  a  given  amount  of  the  standard  preparation.  Ultimately,  by 
repeating  the  injections,  the  requisite  amount  of  the  preparation 
being  assayed  will  be  found  which  will  produce  a  rise  in  blood-pres- 
sure equal  to  that  produced  by  a  given  quantity  of  the  standard. 
The  extent  of  the  rise  in  blood-pressure  varies  in  proportion  to  the 
amount  of  the  active  constituent  of  the  suprarenal  gland  injected. 
Several  dogs  are  usually  required  for  making  an  assay.  Two  kinds 
of  tracings  may  be  made.  Complete  when  the  drum  of  the  kymo- 
graph is  allowed  to  run  continuously,  and  abbreviated  when  the 
drum  remains  stationary,  while  the  reaction  takes  place.  In  the 
latter  the  rise  in  blood-pressure  is  recorded  as  a  short,  perpendicular 
line.  These  abbreviated  tracings  answer  admirably  for  most  work, 
as  only  variations  in  blood-pressure  are  taken  into  account.  The 
smoked  paper  tracings  are  fixed  by  dipping  them  into  shellac,  and 
allowing  them  to  dry.  A  great  many  precautions  must  be  observed 
in  carrying  out  the  experiments,  such  as  the  amount  of  material 
injected  at  one  time,  since  the  extent  of  the  increase  in  blood-pres- 
sure must  be  sub-maximal,  the  volume  of  fluid  injected  at  one 
time,  the  length  of  time  required  in  making  the  injections,  etc.,  but 
in  keeping  with  all  other  methods  of  pharmacologic  assay  the  con- 
ditions obtaining  in  the  experiments  must  be  kept  constant  and  the 
reaction  of  the  preparation  being  assayed  must  be  compared  with 
a  known  standard. 
Naturally  the  question  will  arise  as  to  what  should  be  the  standard. 
At  first  a  freshly  prepared  fluid  extract  of  fresh  bovine  suprarenal 
glands  was  employed  as  a  standard,  but  after  the  isolation  of  the 
active  constituent,  adrenalin,  I  adopted  it  as  a  standard,  because  its 
activity  remains  constant  while  other  preparations  of  the  suprarenal 
glands  are  prone  to  undergo  decomposition,  and  consequent  altera- 
tion in  strength.    The  animals,  after  the  experiments  are  concluded, 
