Choice  of  a  System  of  Disposal. — The  system  of  disposal
that  is  needed  for  a  particular  locality  will  depend  largely  on
what  disposition  is  finally  made  of  the  effluent.  If  the  effluent  is
discharged  into  a  large  body  of  water,  an  ImhoflF  tank  with  chlorin
treatment  of  the  effluent  will  constitute  an  efficient  system.  If
the  effluent  from  a  disposal  plant  is  discharged  into  a  small
stream  which  is  used  as  a  source  of  water-supply,  it  may  be
necessary  that  the  disposal  plant  shall  consist  of  a  collecting  tank,
a  sprinkling  fflter,  a  sand  fflter,  and  a  chlorinating  apparatus.
The  disposal  plant  must  be  adapted  to  the  particular  locality
which  it  serves.
Sewer  System. — ^A  sewer  system  consists  of  collecting  pipes
or  sewers,  and  a  disposal  plant.  A  health  officer  has  little  to  do
with  the  sewers  directly,  except  when  they  are  broken  or  ob-
structed. The  construction  and  maintenance  of  sewers  are  en-
gineering problems  with  which  an  engineering  department  has
to  deal.
A  health  officer  has  very  little  power  over  a  private  sewer
system,  except  to  require  that  the  disposal  shall  be  done  in  a
sanitary  manner.  He  cannot  require  a  householder  or  the
managers  of  an  institution  to  install  any  particular  type  of  sewer
system.  But  a  health  officer  who  understands  sewer  systems  will
often  be  asked  to  give  advice  regarding  their  instaUation  and
management.  If  a  health  officer  condemns  a  sewer  system  at  a
private  residence,  or  an  institution,  he  shovld  be  able  to  advise
the  owners  or  managers  what  system  to  install  in  its  place,  where
to  locate  the  disposal  plant,  and  how  to  manage  the  system.
