^ovfcTiSS"-}  Food  Preservatives.  505 
In  this  State  convictions  have  been  obtained  in  several  cases 
upon  the  principle  that  if  it  can  be  shown  that  the  preservative  is 
poisonous  in  any  dose,  it  is  to  be  considered  a  poison  absolutely, 
and  its  use  contravenes  the  law.  It  seems  to  me  that  this  sets  at 
nought  the  whole  science  of  pharmacodynamics.  The  question 
whether  or  not  a  substance  is  a  poison  is  one  of  dose.  No  sub- 
stance is  absolutely  a  poison.  If  we  adopt  the  interpretation  of  a 
term  that  is  advocated  by  some  authorities,  many  articles  of  food 
will  come  into  the  category  of  injurious  substances  and  their  use 
could  be  forbidden.  Vanillin,  caffeine,  citric  acid  are  all  capable  of 
producing  disturbances  of  function  when  taken  in  large  amount  or 
continuously,  yet  as  taken  in  common  beverages  they  are  generally 
regarded  as  wholesome.  Even  the  old-established  preservatives 
would  go  down  under  this  system.  Acetic  acid,  upon  which  the 
preservative  action  of  vinegar  depends,  is  one  of  the  most  corrosive 
substances  known ;  wood-smoke  owes  its  preservative  quality  to 
creosote  and  its  analogues,  also  highly  corrosive.  The  truth  is,  the 
definition  of  a  poison  must  involve  the  questions  of  dose  and  manner 
of  administration.  Hydrogen  sulphide,  for  instance,  is  actively 
toxic  in  one  form  of  administration  and  not  so  in  another. 
We  have  lately  had  in  this  city  an  interesting  instance  of  the 
peculiarities  of  expert  testimony,  when  it  depends  on  mere  opinions 
rather  than  inferences  for  actual  experiment.  The  food  authorities 
of  Pennsylvania  not  long  ago  forbade  the  sale  of  vegetable  articles 
colored  with  copper,  because  this  metal  was  regarded  as  dangerous. 
Dr.  H.  W.  Wiley,  in  a  public  lecture  last  winter,  deprecated  the 
sale  of  such  articles,  although  not  definitely  declaring  the  metal 
poisonous.  Since  that  time  experts  in  another  bureau  of  the 
Department  of  Agriculture  have  been  active  in  declaring  that  cop- 
per is  quite  harmless,  and  several  Philadelphia  physicians  have  been 
supporting  this  view.  One  set  of  experts  tells  us  that  copper  can- 
not be  allowed  in  appreciable  amounts  in  any  food  article ;  another 
set,  equally  eminent  and  equally  positive,  tells  us  that  it  is  entirely 
harmless  in  drinking  water.  Who  shall  decide  when  doctors  disa- 
gree ? 
What  data  are  there  to  show  that  salt  is  entirely  harmless  in 
food  ?  What  proof  have  we  that  sodium  benzoate  is  more  objec- 
tionable than  the  ingredients  of  wood-smoke  ? 
