263 
It  was  observed  also  that  the  ratios  of  infection  amongst  batches 
of  flies  caught  in  various  sections  of  the  island  were  markedly 
different,  e.g. :  — 
Section 
Positive 
Negative 
Percentage 
A  . 
47 
40 
54 
B 
7 
22 
24- r 
c  . 
24 
45 
34-9 
No  apparent  reason  existed  for  these  discrepancies.  Section  A, 
the  most  heavily  infected,  was  directly  opposite  the  camp,  and  our 
natives  were  constantly  going  and  coming  from  the  water  along  this 
stretch,  so  that  it  was  avoided  by  all  the  birds.  No  crocodiles  were 
ever  seen  along  this  bit  of  the  shore. 
About  a  third  (33" i  per  cent.)  of  the  flies  which  were  examined 
showed  evidence  of  having  fed  on  blood  (61  out  of  185).  In  25,  oval, 
nucleated  cells  were  seen;  in  35,  the  pigment  and  detritus  left  from 
digested  blood ;  and  in  only  one,  fresh  mammalian  blood  was  found, 
evidently  from  one  of  the  boys  engaged  in  catching  the  flies. 
In  November,  401  flies  were  caught,  396  males  and  5  females. 
One  hundred  of  these  were  examined,  99  males  and  i  female,  and  41 
were  found  to  be  infected. 
Positive 
Negative 
Percentage 
Males .  41 
58 
41-4 
Females  . .  ...  o 
...  I 
0 
At  this  time  special  attention  was  devoted  to  the  proboscis,  but  in 
no  case  were  parasites  found  in  this  part  of  the  flies. 
B.  Glossina  morsiians. 
Of  365  flies,  313  were  males  and  52  females,  a  proportion  of  6  .-  i. 
One  hundred  and  thirteen  were  examined,  and  of  these  32' 8  per  cent, 
showed  signs  of  having  fed  on  blood  (in  3  mammalian  blood  corpuscles 
M'ere  observed,  and  in  34  blood  pigment),  practically  the  same  per¬ 
centage  as  noted  in  the  case  of  GL  falfalis.  All  traces  of  blood 
disappear  from  the  intestine  of  Gl.  morsiians  in  about  96  hours,  and 
it  is  altogether  probable  that,  if  the  flies  feed  on  blood  alone,  they  are 
capable  of  remaining  alive  without  it  for  some  considerable  period. 
The  condition  of  the  abdominal  organs  of  many  of  the  flies  which 
were  examined  was  such  as  to  render  it  perfectly  clear  that  much 
longer  than  four  days  had  elapsed  since  last  they  had  fed  on  blood. 
