Aji2!Srfi£m'}  E*P*rt  testimony.  7 
Opinions  may,  in  certain  cases  of  chemical  analysis,  differ  as  to 
the  scope  and  conclusiveness  of  special  tests.  In  all  such  cases  it  is 
a  simple  matter  for  the  expert  witnesses  on  both  sides  to  state  the 
issue,  first  in  technical  terms  for  the  record,  secondly  in  non-tech- 
nical terms  for  the  enlightenment  of  court  and  jury,  and  in  such  a 
way  as  to  make  clear  the  exact  point  in  dispute  and  its  bearing  on 
the  final  judgment  of  fact.  It  is  also  easy  to  take  the  opposite 
course  with  intent  to  becloud  the  issue.  Were  the  straightforward, 
scientific,  impartial  way  obligatory  in  every  instance,  many  issues 
which  have  been  allowed  to  occupy  much  of  the  time  and  attention 
of  courts  and  juries  would  at  once  be  shown  to  be  based  on  triviali- 
ties ot  no  possible  importance  in  the  cause  at  trial. 
Still  another  source  of  confusion  between  fact  and  opinion  arises 
from  the  questioning  of  expert  witnesses  as  to  what  may  be  termed 
facts  of  science,  and  the  -failure  of  courts  to  rule  uniformly  as  to 
just  what  testimony  of  this  kind  is  admissible.  One  court  will 
permit  the  widest  and  wildest  latitude  ;  another  will  exclude  as 
"  hearsay  "  all  matters  outside  the  personal  experience  of  the  expert 
witness.  I  do  not  purpose  to  discuss  these  conflicting  rulings  from 
a  legal  viewpoint.  Shall  doctors  decide  when  judges  disagree  ?  But 
I  may  be  permitted  to  point  out  the  logical  and  scientific  difficulties 
involved  in  both  positions. 
First  let  us  consider  the  position  of  an  expert  witness  called  upon 
to  differentiate  between  the  knowledge  he  has  obtained  from  read- 
ing and  that  which  he  has  acquired  by  personal  observation. 
How  far  a  chemist  or  pharmacist  may  be  able  to  do  this,  I  do  not 
know.  If  you  have  all  verified  by  balance-tests  and  other  appro- 
priate methods  the  atomic  weights,  the  valencies,  the  electric  posi- 
tions, and  other  properties  of  all  the  elements,  and  the  structures 
of  all  the  compounds,  perhaps  you  may  begin  to  think  of  qualifying 
under  the  "  no  hearsay  "  rule.  I  doubt,  however,  whether  any  phy- 
sician could  state  accurately  how  much  of  the  composite  pictures 
he  carries  in  his  mind  of  the  symptomatology  and  pathology  of 
diseases  and  of  the  effects  of  drugs — even  of  a  disease  so  common 
as  typhoid  fever  or  of  a  drug  so  much  used  as  opium  or  mercury — 
is  based  upon  cases  personally  observed,  to  the  exclusion  of  those 
read  about.  One  of  the  best  known  pathologists  in  America,  a  man 
of  enormous  experience,  told  me  that  he  had  never  personally  made 
a  post-mortem  examination  of  a  case  of  combined  sclerosis  of  the 
