^m^Ss™1'}    Standardisation  of  Digitalis  Bodies.  117 
standardized  by  biological  methods,  if  death  be  made  the  end 
reaction,  on  account  of  the  great  variability  in  the  reactivity  of  this 
central  nervous  mechanism,  at  least  quantitatively. 
The  factors  of  minor  importance  in  the  choice  of  the  method  for 
biological  standardization  of  the  digitalis  bodies  are  several.  The 
first,  and  the  one  which  has  been  invoked  against  the  cat  method 
most  often,  is  the  matter  of  difficulty.  The  frog  methods  are  very 
simple  in  so  far  as  the  mere  injection  is  concerned  but  it  requires 
the  exercise  of  considerable  judgment  and  experience,  not  to  say 
some  knowledge  of  physiology,  to  determine  exactly  when  the 
ventricles  may  be  said  to  have  just  come  to  systolic  standstill,  and 
such  accurate  determination  is  essential  in  the  one  hour  frog  method. 
Again,  the  quantities  of  the  solutions  which  are  used  for  frogs 
are  so  small,  and  the  dilutions  relatively  so>  great,  that  very  slight 
inaccuracy  in  measurements  or  in  the  calibration  of  instruments 
are  likely  to  lead  to  gross  variations  in  the  results,  which  are,  at  least, 
confusing  to  the  observer. 
The  guineapig  method  is  probably  the  simplest  of  all  of  the 
methods  advocated,  but  its  other  disadvantages  are  such  as  to  make 
it  unlikely  of  adoption. 
The  cat  method  is  less  simple  in  technique  than  the  others,  but 
it  is  not  so  difficult  as  its  critics  would  have  us  believe.  First,  it  is. 
said  to  be  very  difficult  to  insert  a  cannula  into  the  vein  of  an 
anaesthetized  cat.  Our  laboratory  boys  perform  this  operation 
readily,  and  we  find  that  our  students  experience  no  great  difficulty 
in  learning  this  simple  procedure  after  only  one  or  two>  trials. 
The  question  of  the  maintenance  of  anesthesia  has  already  been 
discussed. 
The  duration  of  the  rate  of  injection  is  another  stumbling  block 
for  our  critics.  They  tend  to  "make  a  mountain  out  of  a  mole 
hill"  in  this  matter,  for  it  is  really  quite  simple,  with  a  very  limited 
experience  or  by  reference  to  previous  results,  to  estimate  with 
reasonable  accuracy  how  rapidly  the  injection  of  any  given  digitalis 
preparation  should  be  given.  For  example,  if  the  operator  has  a 
tincture  of  digitalis  of  unknown  strength  to  test,  he  may  assume 
that  it  is  of  about  the  average  activity,  for  most  tinctures  ap- 
proximate the  average.  By  reference  to  previous  tests  he  can  find 
that  a  rough  average  to  be  expected  would  be  about  100  mg.  per  kg. 
of  animal.  By  diluting  the  tincture  with  nine  volumes  of  saline  solu- 
tion he  then  makes  each  ten  cubic  centimetres  contain  about  the 
expected  dose,  he  then  has  but  to  multiply  the  weight  of  the  cat  in 
