102  Physiological  Standardization.  {%aJr°ch"'moann' 
weighing  the  advisability  of  introducing  such  tests  into  their  busi- 
ness and  who  wish  to  know  the  likelihood  of  the  innovation's  paying, 
and  are  wondering  where  they  can  find  some  one  qualified  to  under- 
take the  work.  To  such  I  shall  try  to  give  some  facts  that  may 
serve  as  an  aid  in  deciding  whether  the  biological  assay  is  of  suffi- 
cient value  to  justify  the  expense  involved,  by  an  unprejudiced 
summary  of  what  in  my  opinion  may  and  may  not  be  hoped  from  it. 
And  first  I  shall  speak  of  its  limitations.  We  sometimes  read  of 
the  physiological  test  being  used  as  a  control  of  the  chemical  assay. 
To  attempt  to  corroborate  the  findings  of  the  chemist  by  a  test 
on  the  living  animal  is  about  as  sensible  as  it  would  be  for  a  navi- 
gator to  regulate  his  chronometer  by  an  Ingersoll  watch ;  the  relative 
accuracy  of  the  chemical  and  physiological  assay  is  about  the  same 
as  that  of  the  $200  chronometer  and  the  dollar  watch.  The  latter 
is  in  its  place,  however,  a  very  useful  apparatus ;  a  cheap  watch  is 
better  than  none  at  all. 
The  experienced  chemist  can  obtain  accurate  results  because  he 
knows  the  common  sources  of  error  which  are  likely  to  vitiate  his 
conclusions  and  how  to  guard  against  them.  In  biological  assay  we 
know  only  of  a  few  of  the  possible  causes  of  inaccuracy  and  even 
some  of  these  we  cannot  exclude. 
Foremost  among  the  difficulties  that  destroy  the  accuracy  of  the 
biological  test  stands  that  mystery  of  which  we  know  nothing  but  to 
which  we  give  the  name  of  idiosyncrasy.  Every  physician  recog- 
nizes well  the  inexplicable  susceptibilities  of  certain  persons  to  cer- 
tain drugs,  but  many  scientists  forget  that  man  is  after  all  an  animal 
and  that  the  same  biological  facts  hold  for  the  humbler  as  for  the 
highest  type  of  mammal.  After  we  learn  to  appreciate  this  possibil- 
ity of  mistake  the  only  means  that  we  have  to  guard  against  it  lies 
in  the  repetition  of  experiment  sufficiently  often  that  by  the  laws  of 
chance  any  exceptional  result  will  not  greatly  modify  the  average. 
Think  of  a  chemist  who  would  make  routinely  nine  or  ten  assays 
of  the  same  specimen  and  then  expect  an  error  of  10  or  20  per  cent. 
Another  well-known  but  frequently  neglected  fact  is  that  disease 
has  a  potent  influence  on  the  reaction  of  the  economy  to  chemical 
agents.  Dogs  and  frogs  are  as  likely  to  be  sick  as  are  men,  indeed 
more  so.  It  is  often  quite  impossible  to  recognize  an  abnormal 
condition  in  an  animal  that  you  see  but  once  for  a  few  minutes  im- 
mediately before  the  experiment ;  against  this  fallacy  the  only  defense 
we  have  is  again  the  multiplicity  of  observation. 
