134 INSECTS AND MAN 



apparently unharmed by the trypanosomes, they form an 

 inexhaustible source, from which Glossina morsitans may 

 become infected. For when once a fly has bitten an ante- 

 lope whose blood harbours the parasite, it becomes, after 

 a developmental period, a source of infection to man. 



This, then, in brief, is the present state of our knowledge 

 of sleeping sickness. Either Glossina palpalis or Glossina 

 morsitans may carry the disease, the former in the shape 

 of Trypanosoma gambiense, the latter as Trypanosoma 

 rhodesiense. Whichever trypanosome is introduced into 

 the human system, the result is the same ; the clinical 

 manifestations of disease, caused by the two parasites, are 

 practically identical, though Trypanosoma gambiense is 

 probably more virulent. Some excellent results have been 

 obtained in the control of the disease, as transmitted by 

 Glossina palpalis, owing to its habit of never leaving the 

 neighbourhood of water. What can be done with Glossina 

 morsitans and its limitless living reservoir of Trypanosoma 

 rhodesiense ? This is a problem which has excited, and is 

 exciting, considerable controversy. Suggestions have been 

 made for wholesale slaughter of big game and for driving 

 them back far from the limits of human habitation, in the 

 hope that the flies, deprived of their source of infection, may 

 ultimately become non-infective. Into the ethics of the con- 

 troversy it would be out of place to enter, rather let us 

 turn to the flies themselves and learn something of their 

 life-histories. 



Glossina palpalis (fig. 34) is a bluish or olive-grey fly 

 with brown markings ; its abdomen is brown, and on the 

 first segment is a light-coloured triangular area with 

 the apex pointed posteriorly. The second segment has a 

 similar, though smaller, triangular mark, and it is continued 

 as a pale stripe down the abdomen to the end of the fifth 

 segment. Its geographical distribution is confined to the 

 areas drained by the Senegal, Congo, and Niger, and it fre- 

 quents districts where forest trees provide the shade it loves, 



