﻿I'IlOCEEDlI^JGS 
  OJ' 
  lllE 
  1''0UET1I 
  ENTOMOLOGICAL 
  jVIEETIJNG 
  i87 
  

  

  Tlie 
  small 
  solubility 
  of 
  HgCl, 
  together 
  with 
  the 
  fact 
  of 
  an 
  cxcecdingiy 
  

   minute 
  quantity 
  of 
  the 
  salt 
  being 
  necessaiy 
  to 
  kill 
  the 
  larvcO, 
  offers 
  iield 
  

   for 
  an 
  investigation 
  as 
  to 
  its 
  practical 
  value 
  as 
  a 
  larvicide. 
  The 
  advant- 
  

   age 
  of 
  HgCl 
  lies 
  especially 
  in 
  its 
  being 
  poisonous 
  to 
  the 
  larvte 
  in 
  doses 
  

   which 
  cannot 
  have 
  any 
  effect 
  on 
  the 
  human 
  system, 
  so 
  that 
  even 
  drmk- 
  

   ing 
  water 
  of 
  ponds, 
  etc., 
  can 
  be 
  safely 
  treated 
  with 
  it. 
  

  

  The 
  activities 
  of 
  the 
  larvse 
  being 
  almost 
  solely 
  connected 
  with 
  the 
  

   surface 
  of 
  water, 
  all 
  remedial 
  and 
  preventive 
  mvestigations 
  are 
  reduced 
  

   to 
  one 
  of 
  finding 
  out 
  a 
  toxic 
  substance 
  which 
  will 
  keep 
  to 
  the 
  surface 
  

   and 
  not 
  enter 
  into 
  solution, 
  so 
  as 
  to 
  prevent 
  unnecessary 
  expense 
  and 
  the 
  

   pollution 
  of 
  the 
  entire 
  quantity 
  of 
  water. 
  But 
  such 
  a 
  condition 
  is 
  hard 
  

   to 
  satisfy, 
  as 
  the 
  substance 
  must 
  at 
  the 
  same 
  time 
  be 
  non-poisonous 
  to 
  

   human 
  beings 
  and 
  cheaper 
  than 
  the 
  existing 
  larvicides 
  and 
  lasting 
  in 
  

   effect 
  — 
  a 
  property 
  which 
  should 
  probably 
  be 
  considered 
  its 
  crowning 
  

   merit. 
  

  

  A 
  large 
  number 
  of 
  experiments 
  was 
  carried 
  out 
  on 
  the 
  relative 
  value 
  

   of 
  kerosine 
  and 
  HgUl 
  as 
  larvicides. 
  It 
  has 
  been 
  calculated 
  that 
  the 
  

   cost 
  of 
  0-001 
  gm. 
  HgCl 
  would 
  be 
  aproximately 
  equivalent 
  to 
  that 
  of 
  

   half 
  a 
  minim 
  of 
  the 
  oil 
  ; 
  but 
  as 
  even 
  one 
  minim 
  of 
  the 
  oil 
  faded 
  to 
  kill 
  

   the 
  larvae, 
  two 
  minims 
  of 
  the 
  oil 
  (equivalent 
  to 
  about 
  four 
  times 
  the 
  cost 
  

   of 
  HgCl 
  necessary 
  to 
  attain 
  the 
  same 
  result) 
  were 
  used 
  and 
  the 
  results 
  

   are 
  shown 
  in 
  Graph 
  6. 
  It 
  will 
  be 
  seen 
  that 
  the 
  humediate 
  effect 
  of 
  the 
  

   application 
  of 
  the 
  oil 
  was 
  to 
  kill 
  the 
  larvas 
  almost 
  instantaneously 
  Out 
  

   that 
  it 
  quickly 
  lost 
  in 
  strength 
  through 
  voiatiiization, 
  whereas 
  tne 
  action 
  

   of 
  HgCl, 
  though 
  slow 
  and 
  unsteady, 
  was 
  generally 
  sare. 
  The 
  transitory 
  

   nature 
  of 
  the 
  effect 
  of 
  kerosine, 
  however 
  violent 
  its 
  immediate 
  action, 
  

   imposes 
  severe 
  limitations 
  on 
  its 
  practical 
  value 
  as 
  a 
  iarvicide, 
  as 
  it 
  

   would 
  involve 
  continuous 
  replenishment 
  if 
  any 
  cohection 
  of 
  water 
  were 
  

   to 
  be 
  kept 
  free 
  of 
  mosquitos.* 
  In 
  this 
  respect 
  the 
  superiority 
  of 
  HgCi 
  

   is 
  evident. 
  

  

  Calomel 
  has 
  two 
  serious 
  drawbacks 
  : 
  firstly, 
  it 
  generally 
  fails 
  to 
  kiii 
  

   the 
  larvsef 
  ; 
  secondly, 
  it 
  woidd 
  be 
  difficult 
  to 
  keep 
  the 
  salt 
  particles 
  

   lloatmg 
  for 
  any 
  considerable 
  period.^ 
  With 
  regard 
  to 
  the 
  first 
  point, 
  the 
  

  

  * 
  Various 
  workers 
  have 
  investigated 
  tlie 
  nature 
  of 
  the 
  action 
  of 
  kerosine 
  on 
  niostiuito 
  

   larvae, 
  in 
  the 
  course 
  of 
  which 
  it 
  has 
  been 
  brought 
  out 
  that 
  its 
  action 
  is 
  not 
  of 
  the 
  nature 
  

   of 
  a 
  simple 
  meclianical 
  interference 
  with 
  their 
  respiration, 
  but 
  that 
  it 
  is 
  ehiehy 
  the 
  volatile 
  

  

  i3q[aito 
  

  

  |- 
  From 
  a 
  large 
  number 
  of 
  experiments 
  with 
  various 
  kinds 
  of 
  oils 
  and 
  toxic 
  substances 
  

   it 
  appears 
  that 
  with 
  those 
  substances 
  which 
  operate 
  by 
  means 
  of 
  theii' 
  volatile 
  properties, 
  

   pupas 
  die 
  earlier 
  than 
  the 
  larvse, 
  whereas 
  with 
  those 
  which 
  operate 
  through 
  the 
  mouth,' 
  

   larvse 
  are 
  the 
  first, 
  and 
  in 
  most 
  cases 
  the 
  only 
  ones, 
  to 
  die. 
  

   $ 
  Harris 
  and 
  Meyer, 
  Berichte, 
  June 
  1894. 
  

  

  