68  Standardisation  of  Heart  Tonics.  {^Zy^oit 
The  tests  are  repeated  until  the  amount  of  the  drug  is  found 
which  will  produce  the  characteristic  symptoms  of  Digitalis  poisoning 
and  kill  a  250  gm.  guinea  pig  in  two  hours. 
Post-mortem  examinations  are  always  made  to  note  the  con- 
dition of  the  heart  and  dilation  of  the  blood-vessels. 
In  testing  solid  preparations  of  Digitalis  a  weighed  quantity  of 
the  preparation  is  shaken  with  a  definite  amount  of  physiological 
salt  solution  so  that  two>  cubic  centimetres  of  the  liquid  will  represent 
one-tenth  gramme  of  the  drug.  This  method  has  been  found  quite 
satisfactory,  but  Pittinger  23  has  found  that  more  concordant  results 
are  obtained  if  the  time  of  observation  is  extended  from  two  hours 
to  twenty-four  hours.  One  disadvantage  to  the  method  is  that  the 
cost  of  the  required  pigs  is  usually  greater  than  the  frogs  necessary 
for  Houghton's  method.  This  objection  is  largely  overcome  by  manu- 
facturers of  antitoxin  who  can  use  the  pigs  that  have  survived  the 
antitoxin  tests  for  digitalis  tests.  These  pigs  cannot  again  be  used 
for  testing  serum  on  account  of  anaphylaxis,  and  by  the  time  they 
have  completely  recovered  from  the  antitoxin  tests  they  may  weigh 
much  more  than  250  gm.,  which  is  the  weight  specified.  No  pro- 
vision is  made  for  the  varying  susceptibility  of  the  pigs  and  it  is 
doubtful  if  the  pig  test,  as  it  is  usually  carried  out,  will  give  any  more 
reliable  results  than  a  larger  number  of  frogs  that  have  been  "  stand- 
ardized "  with  crystalline  strophanthin. 
The  Cat  Method  of  Hatcher  and  Brodie.24 
This  method  is  based  upon  the  determination  of  the  minimum 
lethal  dose  for  cats.  The  cat  is  anaesthetized  with  ether  and  about 
one-half  of  the  amount  of  the  preparation  being  tested  necessary  to 
kill  the  animal  is  injected  directly  into  the  venous  circulation.  The 
originators  of  this  test  have  found  that  if  preparations  of  digitalis  or 
other  members  of  this  series  are  injected  until  the  cat  dies,  the  results 
will  usually  be  too  high,  hence,  after  twenty  minutes  a  1  to  100,000 
solution  of  Merck's  Ouabain  is  cautiously  injected  until  the  cat  shows 
signs  of  dying,  namely,  rapid  respiration,  which  soon  becomes  irregu- 
lar and  is  accompanied  by  convulsive  movements.  The  Ouabain 
should  be  injected  in  such  amounts  that  the  cat  should  die  ninety 
minutes  after  the  beginning  of  the  test. 
The  "  cat  unit "  is  the  amount  of  crystalline  Merck's  Ouabain 
which  is  fatal  within  about  ninety  minutes  to  each  kilogram  body 
