﻿342 
  C. 
  F. 
  M. 
  SWYNNERTON. 
  

  

  There 
  was 
  no 
  indication 
  of 
  new 
  and 
  independent 
  infections. 
  Every 
  case 
  appeared 
  

   traceable 
  to 
  contact 
  with 
  sick 
  persons 
  in 
  the 
  presence 
  of 
  tsetses. 
  Man 
  seemed 
  now 
  

   the 
  sole 
  reservoir, 
  however 
  the 
  first 
  infection 
  arose. 
  

  

  The 
  outbreak 
  seemed 
  already 
  to 
  have 
  halted 
  in 
  its 
  northward 
  course 
  at 
  the 
  time 
  

   of 
  our 
  visit. 
  Yet 
  the 
  northern 
  barrier 
  against 
  the 
  game, 
  with 
  which 
  the 
  check 
  

   coincided, 
  was, 
  unlike 
  the 
  eastern, 
  by 
  no 
  means 
  of 
  a 
  nature 
  to 
  check 
  the 
  disease. 
  

   Concealment 
  (of 
  which 
  we 
  obtained 
  no 
  evidence) 
  and 
  areas 
  of 
  more 
  open 
  woodland 
  

   with 
  fewer 
  tsetses 
  were 
  two 
  possible 
  explanations 
  of 
  the 
  fact 
  that 
  the 
  disease 
  had 
  

   not 
  appeared 
  in 
  villages 
  into 
  which, 
  on 
  the 
  analogy 
  of 
  its 
  previous 
  history, 
  it 
  might 
  

   already 
  have 
  been 
  carried 
  again 
  and 
  again 
  ; 
  but 
  it 
  was 
  strange 
  that 
  cases 
  should 
  be 
  

   concealed 
  more 
  here 
  than 
  elsewhere. 
  The 
  check 
  did, 
  however, 
  coincide 
  with 
  two 
  other 
  

   changes 
  : 
  game 
  was 
  present 
  in 
  fair 
  numbers 
  and 
  baboons 
  were 
  numerous, 
  and 
  (a 
  conse- 
  

   quence 
  of 
  this) 
  an 
  equality 
  in 
  the 
  sexes 
  of 
  the 
  tsetse, 
  with 
  local 
  excesses 
  of 
  females, 
  

   had 
  been 
  succeeded 
  by 
  a 
  general 
  great 
  excess 
  of 
  males. 
  In 
  any 
  case 
  (cf. 
  the 
  footnote 
  

   on 
  p. 
  351, 
  and 
  the 
  instance 
  of 
  the 
  Luangwa 
  valley) 
  there 
  is 
  no 
  reason 
  why 
  odd 
  

   cases 
  should 
  not 
  occur 
  in 
  game 
  country, 
  and 
  these 
  will 
  doubtless 
  yet 
  be 
  found. 
  

  

  XVIII. 
  — 
  The 
  Facilities 
  for 
  Direct 
  Transmission. 
  

  

  Comparison 
  with 
  the 
  Conditions 
  under 
  which 
  Direct 
  Transmission 
  spreads 
  Nagana. 
  

  

  For 
  the 
  spread 
  of 
  trypanosomiasis 
  in 
  a 
  herd 
  of 
  cattle 
  by 
  means 
  of 
  direct 
  transmission 
  

   a 
  heavy 
  infestation 
  by 
  the 
  flies 
  appears 
  necessary 
  (as 
  in 
  the 
  great 
  October-December 
  

   outburst 
  of 
  Tabanidae), 
  combined 
  with 
  close 
  contact 
  amongst 
  the 
  cattle 
  ; 
  and 
  the 
  

   result, 
  as 
  I 
  have 
  seen 
  myself, 
  varies 
  from 
  no 
  or 
  few 
  infections 
  to 
  heavy 
  infection. 
  

   Chambers 
  records 
  (Vet. 
  Review, 
  i, 
  1917, 
  p. 
  222) 
  an 
  instance 
  in 
  which 
  280 
  cattle 
  out 
  

   of 
  300 
  died 
  as 
  a 
  result 
  of 
  the 
  introduction 
  of 
  three 
  infected 
  beasts 
  in 
  tsetse-free 
  

   country. 
  

  

  With 
  the 
  flies 
  few 
  or 
  the 
  temperature 
  low 
  it 
  may 
  be 
  that 
  the 
  cattle 
  resist 
  the 
  

   occasional 
  trypanosomes 
  injected, 
  but 
  under 
  the 
  October-December 
  conditions, 
  

   with 
  hundreds 
  of 
  flies, 
  constantly 
  disturbed, 
  to 
  every 
  animal, 
  individual 
  beasts, 
  

   few 
  or 
  many, 
  may 
  even 
  through 
  dint 
  of 
  sheer 
  repeated 
  biting 
  receive 
  some 
  approach 
  

   to 
  the 
  number 
  of 
  trypanosomes 
  that, 
  after 
  cyclical 
  development, 
  fill 
  the 
  proboscis 
  

   of 
  a 
  tsetse. 
  

  

  In 
  view 
  of 
  Duke's 
  most 
  illuminating 
  suggestion 
  (Parasitology, 
  xi, 
  31st 
  Oct., 
  

   1919) 
  that 
  direct 
  transmission 
  by 
  G. 
  palpalis 
  may 
  play 
  a 
  very 
  important 
  role 
  in 
  

   human 
  epidemic 
  trypanosomiasis 
  of 
  the 
  gambiense 
  type, 
  it 
  is 
  interesting 
  to 
  enquire 
  

   whether 
  the 
  conditions 
  under 
  which 
  mechanical 
  transmission 
  produces 
  outbreaks 
  

   in 
  herds 
  of 
  cattle 
  ever 
  exist 
  for 
  man 
  in 
  relation 
  to 
  infection 
  that 
  is 
  carried 
  by 
  flies 
  

   of 
  the 
  morsitans 
  group. 
  

  

  The 
  Tabanidae 
  may, 
  I 
  think, 
  be 
  ruled 
  out 
  at 
  once 
  as 
  an 
  important 
  factor. 
  They 
  

   attack 
  man 
  but 
  seldom 
  in 
  anything 
  approaching 
  the 
  numbers 
  in 
  which 
  tsetses 
  very 
  

   ordinarily 
  come 
  to 
  him, 
  and 
  they 
  also 
  relatively 
  seldom 
  succeed 
  in 
  sucking 
  blood. 
  

   The 
  same, 
  in 
  somewhat 
  less 
  degree, 
  applies 
  to 
  Stomoxys. 
  

  

  On 
  the 
  other 
  hand, 
  the 
  tsetses 
  G. 
  morsitans 
  and 
  G. 
  swynnertoni 
  do 
  attack 
  man 
  — 
  

   seldom, 
  unless 
  he 
  is 
  on 
  a 
  bicycle 
  or 
  a 
  car, 
  quite 
  in 
  the 
  numbers 
  in 
  which 
  the 
  October 
  

   Tabanids 
  swarm 
  on 
  cattle, 
  yet 
  often 
  in 
  very 
  considerable 
  numbers 
  indeed. 
  They 
  

   have 
  fewer 
  individuals 
  among 
  whom 
  to 
  divide 
  their 
  attentions 
  than 
  have 
  the 
  Tabanids 
  

   in 
  the 
  cattle-kraal, 
  and 
  they 
  are 
  individually 
  exceedingly 
  persistent, 
  so 
  that 
  even 
  

   half 
  a 
  dozen 
  of 
  them, 
  not 
  feeding 
  seriously 
  or 
  often 
  driven 
  off, 
  might 
  transfer 
  many 
  

   trypanosomes 
  directly 
  in 
  the 
  course 
  of 
  half 
  an 
  hour 
  from 
  a 
  sick 
  person 
  to 
  a 
  friend 
  

   sitting 
  chatting 
  beside 
  him, 
  or 
  as 
  between 
  the 
  members 
  of 
  a 
  party 
  travelling. 
  Tsetses, 
  

   again, 
  tend 
  to 
  be 
  present 
  in 
  greater 
  or 
  less 
  numbers 
  for 
  many 
  more 
  months 
  than 
  the 
  

   Tabanidae, 
  and 
  the 
  fact 
  that 
  an 
  infected 
  person 
  takes 
  a 
  few 
  months 
  to 
  die 
  will 
  

   bridge 
  any 
  ordinary 
  gap. 
  

  

  