﻿ENTOMOLOGICAL 
  ASPECTS 
  OF 
  AN 
  OUTBREAK 
  OF 
  SLEEPING 
  SICKNESS. 
  343 
  

  

  Conditions 
  under 
  which 
  Tsetses 
  of 
  the 
  morsitans 
  Group 
  concentrate 
  on 
  Man. 
  

  

  Observations 
  here 
  and 
  elsewhere 
  in 
  the 
  territory 
  show 
  that 
  concentrations, 
  

   large 
  or 
  small, 
  of 
  tsetses 
  that 
  are 
  indicated 
  by 
  the 
  proportion 
  of 
  the 
  sexes 
  to 
  be 
  

   concentrating 
  their 
  attention 
  on 
  man 
  are 
  caused 
  by 
  the 
  relative 
  absence 
  of 
  game 
  

   and 
  by 
  nothing 
  else. 
  With 
  game 
  absent, 
  they 
  may 
  take 
  place 
  at 
  villages, 
  particularly 
  

   perhaps 
  near 
  primary 
  or 
  secondary 
  centres, 
  and 
  along 
  paths, 
  on 
  travelling 
  parties, 
  

   and 
  at 
  the 
  more 
  suitable 
  patches 
  of 
  bush 
  crossed 
  by 
  the 
  paths, 
  as 
  at 
  water- 
  

   holes, 
  streams, 
  and 
  particular 
  thickets 
  and 
  vleis 
  ; 
  for 
  at 
  such 
  places 
  (as 
  we 
  have 
  

   seen, 
  p. 
  332) 
  flies 
  are 
  apt 
  to 
  leave 
  their 
  carriers, 
  at 
  such 
  places 
  they 
  tend 
  to 
  persist 
  

   in 
  smaller 
  or 
  greater 
  numbers 
  throughout 
  the 
  year, 
  and 
  at 
  water-holes 
  and 
  streams 
  

   the 
  natives 
  themselves 
  (each 
  party 
  carrying 
  in 
  an 
  accession 
  of 
  flies) 
  break 
  their 
  

   journey 
  to 
  drink 
  or 
  cook 
  their 
  food 
  or 
  to 
  rest, 
  and 
  sit 
  with 
  other 
  natives 
  who 
  have 
  

   preceded 
  or 
  followed 
  or 
  met 
  them 
  there, 
  while 
  all 
  are 
  bitten 
  repeatedly 
  by 
  the 
  

   same 
  tsetses. 
  In 
  game 
  country 
  concentrations 
  of 
  the 
  particular 
  kind 
  referred 
  to 
  

   do 
  not 
  take 
  place, 
  except 
  very 
  temporarily 
  or 
  incompletely. 
  Thus 
  tsetses 
  may 
  

   attach 
  themselves 
  specially 
  to 
  passing 
  man 
  for 
  a 
  week 
  or 
  two 
  only, 
  after 
  a 
  grass 
  

   fire, 
  or 
  when, 
  near 
  the 
  end 
  of 
  the 
  long 
  grass 
  period, 
  game 
  is 
  attracted 
  away 
  to 
  early 
  

   "burns." 
  At 
  the 
  long 
  grass 
  season 
  natives 
  leave 
  the 
  paths 
  less 
  and 
  so 
  probably 
  

   come 
  into 
  contact 
  with 
  far 
  fewer 
  tsetses, 
  but 
  those 
  flies 
  that 
  once 
  come 
  to 
  them 
  

   may 
  tend 
  to 
  remain 
  on 
  the 
  paths 
  and 
  in 
  the 
  villages 
  owing 
  to 
  the 
  fact 
  that, 
  with 
  

   the 
  grass 
  long, 
  they 
  will 
  not 
  easily 
  detect 
  other 
  prey 
  by 
  sight. 
  That 
  they 
  may 
  

   detect 
  them 
  otherwise 
  was 
  suggested 
  by 
  the 
  waj' 
  a 
  succession 
  of 
  tsetses 
  would 
  some- 
  

   times 
  find 
  their 
  way 
  to 
  us 
  singly, 
  until 
  a 
  large 
  number 
  had 
  collected, 
  when 
  we 
  

   stood 
  still 
  for 
  long 
  in 
  one 
  place. 
  I 
  think 
  that 
  these 
  minor 
  types 
  of 
  concentration 
  

   may 
  be 
  disregarded, 
  except 
  where 
  actual 
  sleeping 
  sickness 
  or 
  conditions 
  specially 
  

   favourable 
  to 
  it 
  (such 
  as 
  famine 
  and 
  game 
  destruction) 
  are 
  present. 
  Here 
  they 
  

   might 
  act 
  as 
  accentuating 
  factors. 
  Most 
  of 
  the 
  cases 
  of 
  sleeping 
  sickness 
  enumerated 
  

   by 
  natives 
  were 
  described 
  as 
  having 
  taken 
  place 
  either 
  "at 
  hoeing 
  time" 
  (two 
  

   months 
  after 
  grass-burning), 
  or 
  when 
  the 
  crops 
  were 
  sprouting 
  (temperature 
  rising 
  

   and 
  flies 
  abundant), 
  or 
  at 
  " 
  Ramadhan 
  " 
  (the 
  date 
  of 
  which, 
  retrogressing 
  each 
  

   year, 
  has 
  probably 
  travelled 
  during 
  this 
  outbreak 
  from 
  September 
  to 
  May). 
  It 
  is 
  

   interesting 
  to 
  note 
  also 
  that 
  of 
  the 
  first 
  two 
  dates 
  referred 
  to, 
  the 
  first 
  coincides 
  

   with 
  and 
  the 
  second 
  shortly 
  follows 
  the 
  usual 
  climax 
  of 
  the 
  beer-drinking 
  season. 
  

  

  This 
  brings 
  me 
  to 
  the 
  point 
  that, 
  whatever 
  small 
  part 
  may 
  be 
  played 
  by 
  the 
  

   game, 
  no 
  one 
  who 
  has 
  observed 
  the 
  habits 
  of 
  the 
  natives 
  can 
  well 
  regard 
  man 
  as 
  

   other 
  than 
  the 
  chief 
  or 
  only 
  reservoir 
  in 
  any 
  human 
  trypanosome 
  infection. 
  Sick 
  

   natives 
  — 
  even 
  very 
  sick 
  natives 
  — 
  spend 
  much 
  of 
  their 
  time 
  outside 
  the 
  huts 
  with 
  

   children 
  playing 
  near 
  them, 
  women 
  stamping 
  grain 
  or 
  grinding 
  and 
  preparing 
  food 
  

   beside 
  them, 
  men 
  sitting 
  about 
  (sometimes 
  for 
  hours) 
  occupied 
  or 
  idling. 
  People 
  

   drop 
  in 
  from 
  neighbouring 
  villages 
  or 
  (particularly 
  on 
  a 
  main 
  road) 
  pass 
  through 
  in 
  

   travelling 
  and 
  — 
  an 
  important 
  habit 
  from 
  South 
  Africa 
  to 
  Tanganyika 
  Territory 
  

   — 
  they 
  stop, 
  sit 
  down 
  with 
  the 
  inhabitants, 
  and 
  give 
  their 
  news 
  and 
  receive 
  that 
  of 
  

   the 
  locality 
  over 
  a 
  platter 
  of 
  food 
  that 
  seems 
  always 
  ready 
  for 
  production 
  and 
  

   round 
  which 
  the 
  men 
  of 
  the 
  village 
  also 
  crowd, 
  each 
  person 
  dipping 
  in 
  his 
  hand 
  

   in 
  turn 
  while 
  the 
  same 
  tsetses 
  bite 
  all. 
  This 
  habit 
  of 
  stopping 
  to 
  exchange 
  news 
  

   — 
  indulged 
  in 
  always, 
  even 
  on 
  the 
  open 
  road 
  — 
  is 
  one 
  main 
  factor. 
  Another 
  is 
  the 
  

   beer-drink, 
  which, 
  in 
  great 
  part, 
  and 
  in 
  some 
  tribes 
  more 
  than 
  others, 
  takes 
  place 
  

   outside 
  the 
  huts 
  and 
  in 
  the 
  day-time. 
  Travellers 
  tend 
  to 
  stop 
  at 
  a 
  village 
  in 
  any 
  

   case, 
  but 
  if 
  a 
  beer-drink 
  should 
  be 
  taking 
  place 
  there 
  or 
  in 
  a 
  village 
  near 
  (and 
  it 
  

   can 
  always 
  be 
  heard 
  from 
  a 
  distance), 
  they 
  stop 
  often 
  for 
  hours 
  or 
  for 
  the 
  period 
  

   of 
  its 
  duration, 
  which 
  may 
  be 
  three 
  days, 
  and, 
  crowded 
  densely 
  round 
  the 
  beer-pots, 
  

   come 
  into 
  intimate 
  and 
  continuous 
  contact 
  with 
  the 
  population 
  of 
  all 
  the 
  villages 
  

   round 
  — 
  invited 
  wholesale 
  to 
  assist 
  in 
  the 
  hoeing 
  of 
  his 
  garden 
  that 
  has 
  constituted 
  

   the 
  owner's 
  object 
  in 
  brewing 
  the 
  beer. 
  The 
  same 
  thing 
  happens 
  at 
  the 
  next 
  village 
  

   and 
  the 
  next, 
  for 
  the 
  hoeing 
  season 
  (at 
  and 
  following 
  which, 
  according 
  to 
  the 
  

  

  