391 
THE  EFFECT  OF  MOSQUno  LARVAE 
UPON  DRINKING  WATER 
BV 
Rl^BER'r  BOYCE.  F.R.S.,  and  F.  C.  LEWIS 
[Received  for  publication  February  26,  igio.) 
In  all  yellow  fever  countries,  it  is  well  known  that  the  presence  of 
Stegomyia  larvae  in  any  collection  of  water  is  a  source  of  clanger,  so 
much  so,  that  in  very  many  British  Colonies  penalties  are  now 
enforced  against  stagnant  water,  and  the  presence  of  mosquito  larvae 
is  deemed  evidence  of  this. 
ff  the  water  cannot  be  thrown  away,  then  it  must  be  securel)- 
protected  by  netting  from  Mosquitos,  or  it  must  be  oiled  or  stocked 
with  larvae-destroying  fish. 
It  so  happens  that  the  larvae  of  the  Stegomyia  are  most  commonU' 
iound  in  clean  water,  the  Stegomyia  calopus  selecting  clean  water  to 
deposit  her  eggs  in.  Clean  water  is  of  course  the  water  usually  found 
in  and  around  all  houses,  being  required  for  domestic  use,  for  drinking 
and  cooking  purposes,  baths,  flowers  and  for  any  domestic  pets  or 
animals  kept  on  the  premises.  It,  therefore,  is  not  to  be  wondered  at 
that  111  the  yellow  fever  zone  the  presence  of  larvae  is  taken  as 
evidence  that  the  water  is  clean.  But  their  presence  is  onh  evidence 
that  the  clean  water  was  in  all  probability  the  only  a\ailable  water 
near  to  or  in  the  house  found  by  the  Stegomyia  in  which  to  deposit 
her  eggs.  From  the  fact  that  Stegomyia  larvae  were  usually  met  with 
m  clean  water,  they  became  in  time  to  be  regarded  in  a  beneficial 
light — to  possess  in  fact  a  clarifying  influence  upon  water.  fliey 
were  regarded  as  scavengers,  taking  into  their  interiors  any  bacteria 
or  other  minute  organisms  which  might  be  present,  'fhe  normal  food 
ol  mosquito-larvae  consists  of  minute  forms  of  vegetable  matter,  and 
therefore  they  no  doubt  do  consume  bacteria.  Hence  it  was  argued 
that  their  presence  in  water  barrels  supplied  from  the  roofs  of  houses 
would  be  distinctly  useful,  for  it  was  urged  that  the)'  might  consume 
pathogenic  bacteria  derived  from  the  dust  of  the  roofs  or  from  the 
