302 CONVEYANCE OF PARASITE. 



mammal.* In this case the Tsetse would be a true host f of the 

 parasite, and not the mere " inoculating needle " which Colonel 

 Bruce's investigations would lead us to suppose. Colonel Bruce 

 found that the Tsetse is capable of conveying the disease forty- 

 eight hours after feeding on an animal suffering from Nagana,| 

 which would certainly allow plenty of time for the Trypanosome 

 to make its way back from the fly's stomach into the pi'oboscis, 

 assuming no process of reproduction to take place. If this is 

 what happens, there would seem to be no reason whatever why 

 one species of Glossina should not be capable of conveying the 

 parasite of Nagana as well as another, since Dr. Hansen's 

 investigations § tend to show that the proboscis of each species is 

 identical in structure. On the other hand, if the Tsetse is a 

 true host of the parasite, the latter may still be conveyed, if not 

 by all the species of Glossina, at any rate by more than one 

 species, just as the parasite of sestivo-autumnal fever in man is 

 stated to be conveyed by several species of mosquitoes of the 

 genus Anopheles. According to Laveran and Mesnil [171], who 

 quote from Blanchard, the deaths of the camels, mules, and 

 donkeys, of an expedition at Imi, on the Webi Shebeli, Somali- 

 land, as observed by Brumpt, did not appear to be due to 

 Glossina morsitans, but to a closely allied species. In view of 

 the locality, this was doubtless Gl. longipemiis, Corti. Never- 

 theless, it must be admitted that there is yet no definite 

 evidence of the occurrence of Tsetse-fly disease in a locality 

 where Glossina morsitans is not found, because our know- 

 ledge of the distribution of this species of Tsetse, as of that of 

 all the other species, is still far from complete; and the 

 unexpected discovery that Gl. morsitans occurs in Togoland,|l 

 whei-e Tsetse-fly disease is known to exist, is suflicient to show 

 that the species extends much further from the Limpopo and the 

 Zambesi than has hitherto been supposed. We must, therefore, 

 be careful not to assume too hastily that Gl. morsitans is absent 

 from a country where Nagana is known to occur, simply because 

 no specimens have yet been collected there. At the same time, 

 without attempting to draw deductions from it, it seems advis- 



* Colonel Bruce's observations, however, so far as they go, would seem 

 to negative this, since they show that the hsematozoa are still active and 

 apparently unaltered in what remains of the blood in the stomach cf the 

 fly nearly five days after its meal. Bruce writes : " Immediately after 

 feeding, the tube of the proboscis can be seen to be crammed full of red 

 blood corpuscles, among which the hsematozoa can be seen actively 

 wriggling. Up to 46 hours after feeding I have seen living hsematozoa 

 and red blood corpuscles in the proboscis. After 118 hours the hsematozoa 

 are still very numerous and vigorously active in what remains of the 

 blood in the stomach. After 140 hours the stomach is empty." {Cf. 

 Appendix A, p. 278.) 



■j- The definitive, not the intermediate host as stated by German writers. 

 Cf. p. 260, note *. 



X See p. 275. § Cf. Chapter V. || See Chapter IV., p. 85. 



