﻿ENTOMOLOGICAL 
  ASPECTS 
  OF 
  AN 
  OUTBREAK 
  OF 
  SLEEPING 
  SICKNESS. 
  335 
  

  

  experiment 
  with 
  numbers 
  of 
  natives 
  and 
  cattle. 
  It 
  proved 
  useful, 
  and 
  an 
  inspection 
  

   took 
  place 
  at 
  B 
  to 
  remove 
  all 
  remaining 
  tsetse 
  (I 
  think 
  one 
  only 
  was 
  present). 
  From 
  

   B 
  to 
  K, 
  the 
  actual 
  experiment, 
  was 
  600 
  yards 
  in 
  length, 
  a 
  stretch 
  of 
  road 
  on 
  

   which 
  tsetses 
  had 
  been 
  abundant. 
  The 
  width 
  of 
  complete 
  clearing 
  (D) 
  varied 
  from 
  

   53 
  to 
  80 
  yards. 
  E 
  and 
  H 
  were 
  solitary 
  large 
  acacias 
  left 
  uncut, 
  each 
  with 
  a 
  good 
  

   clear 
  stem. 
  G 
  was 
  a 
  large, 
  white, 
  conspicuous 
  mosquito 
  net 
  in 
  use 
  for 
  the 
  second 
  

   experiment 
  I 
  shall 
  describe. 
  

  

  From 
  two 
  to 
  three 
  natives 
  and 
  two 
  cattle 
  were 
  placed 
  at 
  each 
  station 
  shown 
  

   above 
  (E, 
  G, 
  H, 
  K, 
  and 
  X, 
  X, 
  X). 
  There 
  were 
  seven 
  pairs 
  in 
  all, 
  the 
  last 
  pair 
  working 
  

   X 
  5 
  , 
  H 
  and 
  afterwards 
  K. 
  E 
  and 
  G 
  cattle 
  stayed 
  where 
  they 
  were, 
  but 
  the 
  X's 
  

   occasionally 
  moved 
  to 
  each 
  other 
  up 
  and 
  down 
  the 
  road 
  or 
  took 
  up 
  intermediate 
  

   stations 
  on 
  it, 
  some 
  of 
  them 
  with 
  a 
  clear 
  view 
  to 
  the 
  bush 
  owing 
  to 
  the 
  grass 
  having 
  

   been 
  destroyed 
  by 
  the 
  dragging 
  away 
  of 
  trees 
  and 
  shrubs, 
  others 
  in 
  long 
  grass. 
  

  

  light 
  bush 
  with 
  scattered 
  fly. 
  

  

  •erna^*. 
  . 
  

  

  C/eare 
  d 
  ap 
  proach. 
  JOyards 
  wi 
  de. 
  

  

  Untouched 
  Acacia 
  Wood/and, 
  tsetses 
  abundant. 
  

  

  C. 
  JOyards 
  wide, 
  c/eared 
  but 
  bush 
  stiff 
  lying, 
  tsetses 
  abundant. 
  *- 
  

   O. 
  at/, 
  width 
  70yds.. 
  cleared 
  and 
  bush 
  dragged 
  away 
  to 
  ZX 
  ©/y 
  

  

  to_ 
  Sengererna^ 
  £%- 
  *' 
  ■**- 
  X- 
  J 
  X- 
  rr 
  Xr- 
  - 
  

  

  ^~^J(net 
  of 
  

   F 
  As 
  O, 
  above. 
  ^n^x. 
  £xpt.Z) 
  

  

  Light 
  bush 
  with 
  > 
  ^oQ 
  ^^S 
  

  

  few- 
  and 
  scattered 
  / 
  j? 
  J^ 
  / 
  As 
  C, 
  above. 
  

  

  tsetses. 
  / 
  ft 
  p 
  ?/ 
  ~M 
  

  

  Granite 
  ^ 
  p 
  e 
  / 
  Untouched 
  Acacia 
  Woodland, 
  tsetses 
  abundant. 
  

  

  Kopje. 
  ov 
  S 
  

  

  Result. 
  — 
  The 
  results 
  at 
  the 
  stations 
  varied 
  in 
  the 
  most 
  interesting 
  manner. 
  

   At 
  E, 
  a 
  conspicuous 
  mgongwa 
  acacia 
  just 
  80 
  yards 
  from 
  the 
  nearest 
  bushes 
  (of 
  the 
  

   granite 
  kopje 
  on 
  the 
  one 
  side 
  and 
  a 
  few 
  slightly 
  out-jutting 
  acacias 
  at 
  F 
  on 
  the 
  

   other), 
  flies 
  of 
  both 
  sexes 
  were 
  taken 
  steadily 
  all 
  day 
  to 
  the 
  total 
  number 
  of 
  77. 
  

   Yet 
  X 
  1 
  close 
  by, 
  and 
  sometimes 
  moved 
  closer, 
  saw 
  not 
  one. 
  

  

  The 
  catchers 
  stationed 
  at 
  G, 
  the 
  conspicuous 
  white 
  mosquito 
  net, 
  also 
  took 
  flies 
  

   steadily 
  all 
  day, 
  as 
  did 
  acacia 
  H 
  and 
  (in 
  much 
  greater 
  numbers) 
  post 
  K 
  on 
  the 
  road 
  

   where 
  it 
  left 
  the 
  clearing. 
  Yet 
  X 
  2 
  , 
  X 
  3 
  and 
  X 
  4 
  took 
  none 
  at 
  all 
  when 
  stationed 
  in 
  

   long 
  grass 
  and 
  only 
  half 
  a 
  dozen 
  in 
  all 
  when 
  in 
  view 
  of 
  the 
  bush. 
  

  

  The 
  fact 
  that 
  natives 
  were 
  working 
  in 
  the 
  bush 
  (though 
  in 
  two 
  compact 
  and 
  localised 
  

   parties) 
  complicated 
  the 
  experiment 
  by 
  rendering 
  it 
  possible 
  that 
  they 
  drew 
  off 
  or 
  

   fed 
  a 
  number 
  of 
  flies 
  that 
  might 
  otherwise 
  have 
  been 
  attracted 
  to 
  the 
  road, 
  and 
  the 
  

   line 
  of 
  dragged-off 
  trees 
  (X 
  to 
  Y), 
  while 
  containing 
  numerous 
  tsetse, 
  was 
  obstruc- 
  

   tive 
  to 
  vision 
  from 
  the 
  bush 
  behind, 
  but 
  it 
  seems 
  likely 
  even 
  from 
  this 
  incomplete 
  

   experiment 
  : 
  — 
  

  

  (1) 
  That 
  a 
  clearing 
  even 
  of 
  70 
  yards 
  on 
  each 
  side 
  of 
  a 
  road 
  would 
  afford 
  great 
  

   protection 
  when 
  the 
  grass 
  is 
  long, 
  but 
  is 
  likely 
  to 
  be 
  much 
  less 
  useful 
  when 
  it 
  is 
  short. 
  

  

  (2) 
  That 
  the 
  period 
  of 
  long 
  grass 
  is 
  probably 
  for 
  the 
  fly 
  a 
  period 
  of 
  relative 
  

   difficulty 
  in 
  finding 
  food-animals. 
  Here 
  we 
  have 
  some 
  slight 
  experimental 
  confirma- 
  

   tion 
  of 
  a 
  point 
  to 
  which 
  Fiske 
  and 
  Duke 
  have 
  drawn 
  attention. 
  

  

  (3) 
  That 
  both 
  sexes 
  of 
  this 
  tsetse 
  range 
  to 
  some 
  extent, 
  flying 
  to 
  conspicuous 
  

   objects 
  such 
  as 
  isolated 
  trees 
  and 
  (probablv) 
  rocks 
  at 
  a 
  distance 
  of 
  not 
  less 
  than 
  

   80 
  yards 
  in 
  cleared 
  country, 
  perhaps 
  much 
  more. 
  It 
  follows 
  from 
  this 
  that 
  no 
  trees, 
  

   however 
  clean-stemmed, 
  must 
  be 
  left 
  in 
  a 
  road-clearing. 
  Also 
  that 
  the 
  high, 
  black- 
  

   green 
  euphorbia 
  hedges 
  that 
  make 
  the 
  villages 
  so 
  conspicuous 
  may 
  be 
  a 
  disadvantage 
  

   when 
  the 
  village 
  is 
  within 
  one 
  or 
  two 
  hundred 
  yards 
  of 
  bush. 
  

  

  Experiment 
  II. 
  Range 
  of 
  Perception. 
  — 
  A 
  wide 
  mosquito 
  net 
  was 
  erected 
  at 
  E 
  and 
  

   more 
  than 
  300 
  flies 
  turned 
  into 
  it, 
  of 
  both 
  sexes. 
  The 
  idea 
  was 
  to 
  pass 
  a 
  large 
  number 
  

   of 
  men 
  and 
  cattle 
  to 
  windward 
  and 
  note 
  up 
  to 
  what 
  distance 
  the 
  tsetses 
  would 
  fly 
  

   to 
  that 
  side 
  of 
  the 
  net 
  on 
  receiving 
  their 
  scent. 
  

  

  (8053) 
  z 
  

  

  