307 
by  the  observations  of  Martin.  Leboeuf  and  Roubaud  on  the 
occurrence  of  hut-infections,  which  they  are  inclined  to  attribute  to  the 
agency  of  such  domestic  mosquitoes  as  Stegomyia  and  Mansonia. 
That  Stegomyia  will  transmit  T.  gambiense  we  know.* 
With  Gl.  morsitans  the  probability  of  mechanical  trans¬ 
mission  happening  is  perhaps  slight,  but  the  danger  will  be  propor¬ 
tionate  to  the  number  of  cases  which  are  present.  This  fly  is  not 
nearly  so  local  in  its  habits  as  Gl.  palpalis,  and  consequently  is  not 
afforded  the  same  opportunities  of  acting  as  carrier.  It  is  very 
surprising  to  notice,  even  in  the  case  of  Gl.  palpalis,  the  slow  rate 
at  which  the  disease  spreads  under  the  most  favourable  circumstances. 
In  two  or  three  villages  on  Lake  Tanganyika  where  this  fly,  as  well 
as  Gl.  morsitans,  was  caught  in  the  gardens,  and  into  which  the 
disease,  in  all  probability,  was  introduced  four  or  five  years  ago,  only 
nine  or  ten  cases  of  the  disease  were  found,  and  if  this  is  so,  it  is  quite 
conceivable  that  the  rate  of  spread,  in  the  event  of  Gl.  morsitans 
being  an  active  transmitter,  as  opposed  to  a  mechanical  one,  would  be 
much  slower. 
Gl.  fal-pahs  is  restricted  to  the  immediate  vicinity  of  water,  so  that  it  has 
constant  opportunities  of  feeding  on  the  natives  when  they  come  to  wash,  fish,  and 
draw  water.  Gl.  morsitans  is  not  restricted  to  these  localities,  but  is  usually  found 
in  the  bush,  and,  m  general,  avoids  the  villages  and  the  gardens  which  surround 
them.  Consequently  the  natives  are  not  exposed  to  the  bites  of  this  fly  in  the 
same  way  as  they  are  to  those  of  Gl.  falfalis. 
On  the  other  hand,  it  cannot  be  regarded  as  settled  that 
Gl.  morsitans  transmits  merely  mechanically.  In  some  parts  of 
Africa,  Gl.  palpalis  transmits  various  cattle  trypanosomes  which  in 
other  localities  are  carried  by  Gl.  morsitans,  and  other  examples  of 
the  same  nature  might  be  cited.  If  we  institute  analogies  with  other 
protozoa,  we  see  that  malaria,  for  instance,  is  not  transmitted  merely 
by  one  particular  species  of  mosquitoes,  but  that  even  many  different 
genera  are  implicated.  The  same  thing  is  seen  in  the  case  of 
redwater  and  ticks.  Recently  Kleinef  has  made  experiments  which 
suggest  that  a  cycle  in  the  life  of  trypanosomes  does  occur  in  tsetse 
Heft  Mayer,  1907,  Archiv.  f.  Schiffs-  und  Tropenhygiene,  Bd.  XI, 
t  Kleine,  1909,  Deutsche  med.  Wochenschrift,  March  18. 
■t>al-b'^^  confirmation  of  this  work  by  Bruce,  who  used  in  his  experiments  Gl. 
n  p.  dimor-phon  and  T.  gambiense,  is  an  additional  argument  for  using 
morsitans  in  a  similar  set  of  experiments. 
