﻿350 
  C. 
  F. 
  M. 
  SWYNNERTON. 
  

  

  (morsitans) 
  were, 
  day 
  after 
  da} 
  7 
  throughout 
  the 
  journey, 
  most 
  plentiful 
  and 
  most 
  

   vicious. 
  There 
  was 
  very 
  extensive 
  traffic 
  on 
  the 
  road, 
  and 
  Dr. 
  May 
  believed 
  that 
  

   the 
  fly 
  was 
  subsisting 
  on 
  man. 
  In 
  this 
  case 
  no 
  sleeping 
  sickness 
  had 
  resulted, 
  but 
  

   the 
  elevation 
  was 
  5,000 
  feet 
  and 
  over, 
  and 
  the 
  result 
  in 
  this 
  place 
  of 
  the 
  removal 
  

   of 
  the 
  game 
  would 
  appear 
  to 
  give 
  us 
  the 
  key 
  to 
  all 
  the 
  previously 
  quoted 
  observations. 
  

  

  Passing 
  to 
  T. 
  gambiense, 
  we 
  may 
  note 
  that 
  more 
  than 
  one 
  observer 
  mentions 
  the 
  

   relative 
  lack 
  of 
  game 
  in 
  the 
  sleeping 
  sickness 
  areas 
  of 
  the 
  Congo, 
  and 
  that 
  Roubaud 
  

   associates 
  the 
  most 
  intense 
  infection 
  with 
  the 
  greatest 
  lack 
  of 
  game 
  and 
  with 
  special 
  

   concentration 
  on 
  man 
  by 
  G. 
  palpalis 
  {op. 
  cit., 
  p. 
  226). 
  He 
  also 
  suggests 
  the 
  utilitv 
  

   of 
  enquiring 
  whether, 
  in 
  those 
  regions 
  in 
  which 
  Nyasaland 
  sleeping 
  sickness 
  is 
  present, 
  

   G. 
  morsitans 
  does 
  not 
  live 
  in 
  closer 
  intimacy 
  with 
  man 
  than 
  it 
  does 
  in 
  other 
  inhabited 
  

   areas. 
  I 
  would 
  substitute 
  " 
  localities," 
  " 
  roads 
  " 
  or 
  even 
  "villages," 
  for 
  " 
  regions 
  " 
  in 
  

   an 
  area 
  like 
  the 
  Luangwa 
  valley 
  in 
  which 
  the 
  disease 
  is 
  sporadic. 
  Roubaud 
  suggests 
  

   the 
  existence 
  of 
  -local 
  races 
  of 
  Glossina 
  that 
  have 
  become 
  specially 
  sensitive 
  to 
  

   infection 
  by 
  a 
  given 
  virus 
  — 
  a 
  point 
  to 
  consider 
  in 
  relation 
  to 
  our 
  Usukuma 
  outbreak. 
  

   Bouffard 
  mentions 
  small 
  endemic 
  centres 
  of 
  the 
  disease 
  in 
  the 
  French 
  Sudan 
  in 
  which 
  

   game 
  is 
  definitely 
  absent 
  while 
  tsetses 
  are 
  everywhere 
  present, 
  but 
  believes 
  that 
  in 
  

   the 
  vast 
  belts 
  of 
  the 
  Banifing 
  and 
  the 
  Black 
  Volta 
  some 
  wild 
  animal, 
  perhaps 
  hippo- 
  

   potamus, 
  supplies 
  the 
  infection 
  to 
  man. 
  Yet 
  his 
  observations 
  as 
  given, 
  to 
  the 
  effect 
  

   that 
  the 
  danger 
  of 
  infection, 
  amounting 
  almost 
  to 
  certainty, 
  is 
  confined 
  to 
  the 
  two 
  

   or 
  three 
  months 
  of 
  the 
  year 
  during 
  which 
  antelopes 
  are 
  precluded 
  from 
  coming 
  to 
  

   the 
  river 
  and 
  the 
  concentration 
  and 
  eagerness 
  of 
  the 
  fly 
  in 
  relation 
  to 
  man 
  become 
  

   extraordinary, 
  suggest 
  to 
  the 
  reader 
  that 
  the 
  infection 
  may 
  be 
  brought 
  about 
  by 
  

   intense 
  direct 
  transmission 
  as 
  between 
  the 
  members 
  of 
  the 
  boat-crews 
  should 
  any 
  

   one 
  amongst 
  them 
  be 
  a 
  carrier 
  of 
  the 
  trypanosome. 
  Dalziel 
  {op. 
  cit., 
  p. 
  251) 
  states 
  

   of 
  the 
  Munshi 
  tribe 
  in 
  Northern 
  Nigeria 
  that 
  they 
  " 
  have 
  not 
  exterminated, 
  indeed, 
  

   but 
  greatly 
  reduced 
  the 
  number 
  of 
  wild 
  animals. 
  Tsetse 
  flies 
  abound, 
  however, 
  and 
  

   in 
  certain 
  localiities 
  sleeping 
  sickness 
  is 
  endemic." 
  In 
  this 
  particular 
  case 
  partly 
  

   immune 
  dwarf 
  cattle 
  are 
  regarded 
  as 
  possibly 
  forming 
  a 
  reservoir, 
  but 
  it 
  may 
  be 
  

   that 
  without 
  them 
  matters 
  would 
  be 
  worse. 
  Finally 
  may 
  be 
  mentioned 
  the 
  records 
  

   as 
  to 
  the 
  scarcity 
  of 
  game 
  on 
  the 
  shores 
  of 
  Lake 
  Victoria 
  that 
  were 
  devastated 
  by 
  the 
  

   epidemic. 
  It 
  would 
  be 
  of 
  interest 
  to 
  know 
  whether 
  as 
  the 
  result 
  of 
  the 
  Busoga 
  

   famine 
  the 
  natives 
  had 
  greatly 
  reduced 
  any 
  important 
  food-animal 
  of 
  the 
  fly 
  and 
  so 
  

   intensified 
  its 
  concentration 
  on 
  themselves. 
  Mr. 
  Hobley 
  tells 
  me 
  that 
  the 
  dearth 
  of 
  

   mammals 
  in 
  Kavirondo 
  was 
  extraordinary. 
  

  

  These 
  latter 
  observations 
  refer 
  to 
  a 
  different 
  fly 
  and 
  a 
  trypanosome 
  that 
  is 
  now 
  

   more 
  resistant 
  to 
  human 
  serum 
  than 
  is 
  T. 
  rhodesiense 
  ; 
  but 
  the 
  knowledge 
  that 
  

   man 
  is 
  the 
  all-important 
  reservoir 
  in 
  the 
  west 
  renders 
  it 
  advisable 
  that 
  we 
  should 
  

   apply 
  the 
  logician's 
  " 
  razor 
  of 
  Occam 
  " 
  to 
  the 
  case 
  of 
  the 
  sister 
  disease 
  before 
  

   we 
  give 
  weight 
  to 
  alternative 
  hypotheses. 
  

  

  Probable 
  Utility 
  of 
  the 
  Game. 
  

  

  The 
  definitely 
  mentioned 
  failure 
  to 
  find 
  sleeping 
  sickness 
  away 
  from 
  the 
  

   much-used 
  labourers' 
  route 
  in 
  Taute's 
  foci, 
  the 
  absence 
  of 
  known 
  sleeping 
  sickness 
  

   on 
  certain 
  roads 
  much 
  crossed 
  by 
  game 
  in 
  Tanganyika 
  Territory 
  — 
  not 
  that 
  this 
  line 
  

   of 
  evidence 
  can 
  yet 
  be 
  regarded 
  as 
  secure 
  — 
  May's 
  evidence, 
  and 
  the 
  general 
  facts 
  

   of 
  the 
  Usukuma 
  outbreak, 
  suggest 
  that 
  the 
  trypanosome 
  does 
  not 
  gain 
  and 
  may 
  not 
  

   keep 
  up 
  its 
  full 
  infectivity 
  for 
  man 
  in 
  places 
  in 
  which 
  the 
  fly 
  does 
  not 
  depend, 
  or 
  ceases 
  

   to 
  depend, 
  on 
  man 
  for 
  its 
  food 
  ; 
  further, 
  that 
  man, 
  at 
  least 
  for 
  all 
  practical 
  purposes, 
  

   is 
  the 
  only 
  reservoir 
  ; 
  and 
  that 
  in 
  either 
  case 
  an 
  epidemic, 
  once 
  started, 
  is 
  likely 
  

   to 
  cease 
  to 
  spread 
  as 
  an 
  epidemic 
  when 
  it 
  comes 
  into 
  definite 
  contact 
  with 
  a 
  game 
  

   population 
  that 
  is 
  sufficient 
  to 
  break 
  freely 
  the 
  continuity 
  of 
  the 
  attendance 
  of 
  the 
  

   fly 
  on 
  man, 
  and 
  reduc? 
  its 
  avidity, 
  though 
  very 
  local 
  reductions 
  of 
  the 
  game 
  might 
  

  

  