﻿ENTOMOLOGICAL 
  ASPECTS 
  OF 
  AN 
  OUTBREAK 
  OF 
  SLEEPING 
  SICKNESS. 
  321 
  

  

  The 
  elevation 
  of 
  the 
  country 
  varies 
  from 
  3,726 
  feet 
  at 
  the 
  lake 
  level 
  to 
  4,500 
  feet 
  

   and 
  more 
  on 
  some 
  of 
  the 
  more 
  prominent 
  hills 
  and 
  plateaux, 
  and 
  as 
  much 
  as 
  6,600 
  feet 
  

   at 
  points 
  north-west 
  of 
  the 
  Isuria 
  Escarpment. 
  

  

  German 
  charts 
  show 
  the 
  main 
  area 
  with 
  which 
  we 
  are 
  here 
  concerned 
  as 
  possessing 
  

   a 
  break 
  in 
  the 
  rains, 
  a 
  very 
  strongly-marked 
  dry 
  season 
  and 
  a 
  rainfall 
  of 
  20-30 
  inches. 
  

   Passing 
  south-west 
  and 
  south 
  the 
  dry 
  season 
  remains 
  marked, 
  the 
  break 
  in 
  the 
  

   rains 
  gets 
  weak 
  and 
  disappears, 
  and 
  the 
  rainfall 
  rises 
  to 
  30^40 
  inches 
  ; 
  this 
  area 
  

   appears 
  to 
  coincide 
  approximately 
  with 
  that 
  which 
  is 
  covered 
  with 
  Brachystegia 
  

   wooding. 
  West 
  of 
  the 
  Lake, 
  in 
  the 
  Bukoba 
  area, 
  the 
  dry 
  season 
  is 
  shown 
  as 
  shortened, 
  

   the 
  break 
  as 
  weakened, 
  and 
  the 
  rainfall 
  at 
  a 
  figure 
  of 
  60-80 
  inches. 
  

  

  Ukerewe, 
  the 
  town 
  and 
  Sultanate 
  of 
  Mwanza 
  and 
  the 
  northern 
  portion 
  of 
  Uzinza 
  

   are 
  shown 
  in 
  a 
  category 
  intermediate 
  between 
  the 
  last 
  two 
  and 
  with 
  a 
  rainfall 
  of 
  

   40-60 
  inches. 
  That 
  is, 
  the 
  dry 
  season 
  is 
  more 
  marked 
  in 
  the 
  main 
  (Usukuma) 
  

   fly-area 
  investigated 
  than 
  at 
  Mwanza, 
  and 
  the 
  rainfall 
  just 
  half, 
  though 
  the 
  same 
  

   fly 
  occurs 
  on 
  the 
  Ukerewe 
  mainland, 
  where 
  the 
  rainfall 
  is 
  apparently 
  the 
  same 
  as 
  

   at 
  Mwanza. 
  The 
  point 
  is 
  of 
  importance 
  in 
  relation 
  to 
  the 
  possibility 
  of 
  effective 
  

   grass-burning. 
  

  

  The 
  dry 
  season 
  was 
  commencing 
  when 
  I 
  arrived 
  early 
  in 
  May, 
  and 
  the 
  climatic 
  

   conditions 
  contrasted 
  strongly 
  with 
  those 
  of 
  the 
  same 
  months 
  at 
  Entebbe. 
  This 
  

   difference 
  is 
  perhaps 
  reflected 
  in 
  the 
  persistence, 
  in 
  spite 
  of 
  probable 
  vicissitudes, 
  

   of 
  some 
  of 
  the 
  splendid 
  primary 
  forest 
  of 
  the 
  latter 
  region, 
  in 
  the 
  always 
  green 
  grass 
  

   of 
  Entebbe 
  and 
  the 
  northern 
  islands, 
  and 
  in 
  the 
  contrast 
  of 
  both 
  with 
  the 
  low, 
  dry, 
  

   savannah 
  woodland 
  and 
  xerophilous 
  shrub 
  formations 
  of 
  Usukuma 
  (PI. 
  xii, 
  fig. 
  2). 
  

  

  III. 
  — 
  The 
  Open 
  Country. 
  

  

  This 
  includes 
  (1) 
  rolling, 
  grassy, 
  undulating 
  country, 
  close-grazed 
  by 
  numerous 
  

   small 
  herds 
  of 
  cattle 
  and 
  dotted 
  over 
  with 
  millet 
  fields 
  and 
  village-enclosing 
  rings 
  

   of 
  black-green 
  Euphorbia 
  — 
  great 
  areas 
  that 
  are 
  one 
  cleared 
  field 
  and 
  owe 
  their 
  

   nearly 
  complete 
  freedom 
  from 
  bush 
  to 
  the 
  presence 
  of 
  a 
  long-concentrated 
  human 
  

   population 
  and 
  the 
  browsing 
  of 
  stock 
  (PI. 
  xii, 
  fig. 
  1) 
  ; 
  the 
  granite 
  kopjes 
  of 
  this 
  

   open 
  country 
  in 
  a 
  few 
  places 
  carry 
  bush 
  or 
  scrub, 
  but, 
  even 
  then, 
  owing 
  to 
  their 
  

   isolation, 
  harbour 
  no 
  fly 
  ; 
  and 
  (2) 
  great 
  mbugas 
  (PI. 
  xiii, 
  fig. 
  1), 
  kept 
  open 
  and, 
  in 
  

   parts, 
  fly- 
  free 
  by 
  excessive 
  seasonal 
  moisture 
  or 
  by 
  the 
  browsing 
  of 
  game. 
  The 
  

   outstanding 
  examples 
  are 
  (a) 
  the 
  extensive 
  mbugas 
  of 
  the 
  Rowana 
  and 
  Mbarangeti, 
  

   that 
  form 
  a 
  broad, 
  relatively 
  clean 
  and 
  useful 
  break 
  across 
  the 
  north 
  of 
  the 
  infected 
  

   thorn 
  area 
  from 
  the 
  Lake 
  in 
  the 
  direction 
  of 
  Ikoma, 
  and 
  (b) 
  the 
  Serengeti 
  Plain, 
  

   which 
  bounds 
  this 
  area 
  on 
  the 
  east. 
  

  

  Small 
  vleis 
  or 
  mbugas 
  (seasonally 
  swampy 
  glades) 
  are 
  scattered 
  very 
  freely 
  through 
  

   the 
  woodland 
  area 
  generally. 
  The 
  nearest 
  short 
  English 
  rendering 
  for 
  a 
  " 
  vlei 
  " 
  

   (South 
  Africa 
  and 
  Southern 
  Rhodesia), 
  " 
  dambo 
  " 
  (Nyasaland), 
  or 
  " 
  mbuga 
  " 
  (East 
  

   Africa) 
  would 
  be 
  "seasonal 
  swamp." 
  On 
  the 
  other 
  hand, 
  "mbuga" 
  includes 
  

   naturally 
  open 
  land 
  that 
  is 
  not 
  swampy, 
  and 
  all 
  three 
  words, 
  I 
  believe, 
  may 
  

   include 
  open 
  land 
  that 
  is 
  permanently 
  swampy. 
  

  

  IV. 
  — 
  The 
  Acacia 
  Thorn 
  Area. 
  

  

  The 
  general 
  acacia 
  area 
  includes 
  — 
  and 
  encloses 
  — 
  a 
  number 
  of 
  woodland 
  forma- 
  

   tions 
  : 
  — 
  

  

  (1) 
  Acacia 
  Savannah 
  Forest. 
  — 
  There 
  are 
  several 
  actual 
  acacia-dominated 
  

   formations. 
  Each 
  is 
  dominated 
  by 
  a 
  different 
  species 
  of 
  the 
  genus 
  and 
  is 
  confined 
  

   to 
  particular 
  conditions, 
  especially 
  as 
  regards 
  drainage. 
  These 
  formations 
  between 
  

   them 
  cover 
  the 
  uncleared 
  country 
  with 
  savannah 
  wooding 
  and 
  tree 
  savannah 
  and 
  the 
  

   cleared 
  country 
  with 
  their 
  live 
  roots. 
  The 
  five 
  most 
  important 
  formations 
  are 
  : 
  — 
  ■ 
  

  

  (a) 
  That 
  of 
  the 
  fine 
  tall 
  " 
  mgongwa 
  " 
  acacia 
  on 
  the 
  best-drained 
  deeper 
  soils. 
  

  

  (b) 
  That 
  of 
  the 
  dainty 
  yellow-flowered 
  " 
  sesa 
  " 
  acacia 
  (.4. 
  stenocarpa, 
  Hochst.). 
  

  

  (8053) 
  y 
  2 
  

  

  