488  Cat  Method  for  Tcstino-  Dioritalis,  lite.  JAm  jour.  Pharm. 
'  <;>         e5  ^  j     OitubtT,  lyil. 
tliis  work,  then  one  great  (Hfficuhv  woukl  be  removed.  This  point 
is  of  immense  importance  to  the  manufacturer  by  whom  nearly  all 
of  the  practical  physiological  assaying  will  always  be  done. 
Having  experienced  difficulty  in  buying  cats,  an  attempt  was 
made  at  this  laboratory  to  raise  them,  but  this  met  with  poor  success. 
It  has  seemed  that  only  under  the  very  best  conditions  can  cats  be 
kept  well  for  any  considerable  length  of  time.  It  has  been  our 
not  infrequent  experience  that  cats  will  refuse  sweet  milk  and  raw 
beef  for  some  time  after  having  been  received,  and  while  an  abun- 
dance of  food  has  been  supplied,  our  cats  have  usually  lost  in  weight. 
When  cats  are  needed  for  this  w^ork  they  should  be  made  to  fast 
for  at  least  twenty-four  hours,  as  otherwise  vomiting  will  frequently 
occur,  particularly  under  digitalis.  Greater  accuracy  can  also  be 
obtained  in  regard  to  the  weight. 
Lactating  animals  cannot  be  depended  upon  as  they  seem  to 
possess  a  greater  tolerance  for  the  drug,  the  degree  depending  on 
the  stage  of  lactation. 
The  Period  and  Rate  of  Injection.  The  lethal  dose  of  any  of 
the  digitalis  bodies  cannot,  of  course,  be  told  at  the  outset.  This  is 
indeed  the  figure  sought.  Therefore,  50  per  cent,  of  the  lethal 
dose  "  is  a  quantity  which  can  only  be  widely  approximated  by  one's 
experience  with  the  given  preparation.  Whether  this  point  in  itself 
is  a  matter  of  great  importance,  within  certain  wide  limits,  I  am 
unable  to  say.  It  would  seem  to  be  of  importance,  however,  that  the 
injection  of  all  of  these  drugs  be  proportioned  as  evenly  as  possible 
over  the  ninety  minutes.  After  one  has  injected  an  amount  of 
digitalis,  for  example,  and  has  waited  the  twenty  minutes,  he  is 
ready  to  proceed  with  the  ouabain  solution.  Since  he  does  not 
know  the  value  of  the  digitalis,  he  does  not  know,  consequently,  how 
much  ouabain  solution  it  will  be  necessary  to  inject  during  the  fol- 
lowing period  of  one  hour.  And  not  knowing  this  point,  he  is  unable 
to  judge  how  rapidly  to  inject.  If  he  calculates  on  5  c.c.  when  10  c.c. 
would  actually  be  required,  then  he  will  come  to  the  end  of  the 
ninety-minute  period  with  the  animal  still  alive,  and  he  must  cau- 
tiously proceed  with  the  probable  result  that  one  hundred  and  five 
minutes  or  so  will  be  covered  in  completing  the  experiment.  And 
having  injected  at  a  slower  rate  possibly  a  larger  amount  of  ouabain 
may  have  been  required.  On  the  other  hand,  if  he  calculates  on 
10  c.c.  when  only  5  c.c.  are  necessary,  he  may  kill  the  animal  before 
the  end  of  the  period — perhaps  in  seventy-five  minutes.   And  having 
