The  removal  of  trees,  vines  and  shrubs  from  the  vicinity
of  dwellings  is  considered  by  Gorgas  an  important  measure,
as  these  serve  as  hiding  places  for  the  insects  by  day.1

A  certain  amount  of  protection  may  be  secured  by  the
application  to  the  skin  of  substances  annoying  to  the  mos-
quito, or  of  ointment  which  mechanically  interferes  with
biting.  Oil  of  citronella  or  eucalyptus,  and  petroleum  or
cocoanut  oil  or  vaseline,  are  used,  but  such  applications
are  not  by  most  writers  considered  of  much  value.
Fourth.  Mosquito  Prevention.  —  Theoretically  the  most
effectual  way  to  eradicate  malaria  is  to  prevent  the  growth  of
mosquitoes.  While  their  complete  destruction  is  not  usually
possible,  its  attempt  must  always  take  first  rank  in  preventive
measures.  The  fact  that  mosquitoes  are  a  great  nuisance,
as  well  as  carriers  of  disease,  makes  still  more  desirable  their
extermination  wherever  possible.  Large  sums,  in  certain
parts  of  the  United  States,  are  being  expended  in  fighting  the
1  Gorgas,  J.  Am.  M.  Ass.,  Chicago,  1909,  LII,  1967.
390       THE  SOURCES  AND  MODES  OF  INFECTION

salt-marsh  mosquito,  which  is  harmless  so  far  as  carrying
disease  is  concerned.
Fifth.  Draining.  —  When  mosquitoes  breed  in  pools  and
swamps,  as  they  so  often  do,  draining  and  filling  must  be
done.  If  water  cannot  be  entirely  gotten  rid  of,  the  banks  of
streams,  ponds  and  ditches  must  be  straightened  and  deepened,
and  freed  from  vegetation,  to  remove  hiding  places  for  the
larvae  and  permit  their  destruction.  Gorgas  insists  upon  the
importance  of  having  this  work  done  by  men  especially  trained
for  it,  and  supervised  by  experts.  Ordinary  contractors  and
laborers  are  sure  to  overlook  breeding  places  and  to  neglect  im-
portant details  of  the  work.  Many  species  of  Anopheles  breed
in  cisterns  or  accidental  receptacles  of  water  near  houses.
