THE HAEMOFLAGELLATES 



199 



or Tsetse-fly disease in South-East Africa, is conveyed by Glossina morsitans 1 

 (Fig. 3, A and B), while the other, T. gambiense, the cause of sleeping- 

 sickness, has for its carrier in Uganda another Tsetse-fly, G. palpalis. 



Working upon this knowledge, many investigators have at one tii 

 or another performed series of experiments with a view to finding out 

 whether any developmental cycle is undergone by the parasites while in 

 the fly, and whether definite periods of infectivity occur, on the analogy 

 of the malarial parasites in mosquitoes. The earlier results obtained 

 seemed to indicate that the role of the fly was purely mechanical the 

 insect acting merely like an artificial inoculating tube. Bruce, in the 

 course of his pioneer work in Zululand, found that the flies could, with 



D. 



Fio. 3. 



Various blood-sucking flies. A and 13, Glossinu morsitans (transmits Trypanosoma britcii, 

 of Nagana), x 2 ; C, Hippobosm rufipes (thought to transmit T. theileri, the cause of " bile-sick- 

 uess"), x H; D, TalKtnus lineola (probably conveys the Surra parasite, T. evansi), x 1 ; E, 

 Stomoxys calcitmns (suspected in connection with T. equinnm, of Itf al de Caderas), x 2J. (A and 

 B from Lav. and Mesn., after Bruce ; C after L. and M. ; D and E after Salmon and Stiles.) 



varying success, infect a healthy animal if allowed to bite it up to forty- 

 eight hours after being themselves fed on an infected one, but not after- 

 wards. Similarly, Bruce, Nabarro, and Greig (8) ascertained that G. 

 palpalis could give rise to an infection eight, twenty -four, or forty-eight 

 hours after feeding, but after two days they could no longer obtain a 

 successful inoculation. Moreover, some experiments extended over two 

 months gave no sign of any periodicity of infection. Nevertheless, these 

 workers found that the Trypanosomes could at all events live and retain 

 their mobility in the stomach of the fly up to seventy-one hours. 



Similar results were obtained by Minchin, Gray, and Tulloch. In 

 their interesting report (59) these authors state that they could find 

 no evidence of a fly becoming infectious at any particular period after 



1 This parasite is also conveyed, in different districts, by (,'. 

 G. fuscft. 



