3o8 
Hies,  and  it  should  be  noted  that  he  was  working  with  Gl.  falfaUs 
and  T.  brucei,  which  is  not  ordinarily  transmitted  by  this  species. 
He  thinks  that,  in  nature,  Gl.  fusca,  by  which  T.  gambiense  has 
been  transmitted  experimentally,  spreads  human  trypanosomiasis. 
The  principal  argument  that  Gl.  pal  falls  is  the  natural  carrier  of 
Sleeping  Sickness  is  that  the  geographical  distribution  of  the  two 
coincide  to  a  great  extent,  and  this  is  certainly  a  most  striking  fact. 
The  waterways  have  always  been  used  as  highways  in  preference  to 
land  routes,  and  also  as  sources  of  food,  so  that  the  spread  of  the 
disease  along  them  has  been  greatly  facilitated  by  the  abundant 
opportunities  afforded  the  very  local  Gl.  pal  falls  to  feed  on  both 
infected  and  uninfected  people.  Even  in  those  cases  in  which  other 
species  of  tsetse  flies  have  been  found  in  association  with  Gl.  fal falls, 
the  possible  share  they  may  have  had  in  the  spread  has  been  over¬ 
shadowed  by  that  of  this  particular  variety.  It  is  only  within  the  last 
three  or  four  years  that  the  disease  has  spread  far  enough  to  come  m 
contact  with  other  species  of  tsetse  flies,  Gl.  morsUans  more 
particularly,  in  territory  where  Gl.  falfalis  does  not  exist.  As  we 
said  above,  we  should  naturally  expect  that  transmission  by  this  fly 
would  go  on  very  much  more  slowly  than  by  Gl.  falfalis.  The 
question  can  only  be  settled  by  means  of  a  patient  and  thorough 
investigation ;  it  is  one  v/hich  should  be  carried  out  without  delay. 
If  it  can  be  shown  conclusively  that  Gl.  morsitans  will  not  transmit, 
except  mechanically,  the  saving  in  expense  to  the  various  adminis¬ 
trations  concerned  will  more  than  balance  many  times  the  cost  of  the 
work,  and  if,  on  the  other  hand,  it  should  be  shown  that  Gl.  morstians 
IS  a  natural  carrier,  there  will  yet  be  time  to  take  more  active  steps  to 
protect  the  threatened  countries  from  invasion.  Until  the  question  is 
answered  decisively,  the  possibility  must  never  be  forgotten,  and  must 
be  acted  upon  to  some  extent. 
In  conclusion,  we  may  refer  to  the  conditions  under  which  labour 
IS  allowed  to  leave  both  Rhodesia  and  Nyasaland.  Quite  recent  y 
arrangements  have  been  made  with  the  administration  of  Southern 
Rhodesia  that  no  labourers  from  the  British  colonies  to  the  north 
shall  be  accepted  unless  provided  with  Government  passes.  In  order 
that  the  natives  can  obtain  these  passes,  they  must  be  examined 
medically,  and  in  addition  are  examined  a  second  time  when  they 
have  reached  their  destination.  No  natives  from  a  Sleeping  Sickness 
