TO THE LUANGWA VALLEY, NOUTn-EASTERN RHODESIA. 315 



Luangwa, since most of the inland villages in the neighbourhood remain to 

 be examined. 



Four or more cases, of which details are not yet to hand, have just been 

 discovered in the country to the north of Fort Jameson near Chinunda, on 

 or near the main road. 



There would thus seem to be definite centres of infection associated with 

 the main roads. This does not altogether exclude Glossina morsitans^ though 

 it is neither more nor less abundant in these localities than elsewhere in the 

 valley, since it might not yet have had time to become infected at a distance 

 from these main roads. On the other hand, apart from the evidence from 

 elsewhere in Africa, there is any amount of this species west of the Mchinga 

 Escarpment, and therefore between these areas and those where G. palpalis 

 occurs. We should, therefore, expect cases to have occurred between the 

 Mchingas and Kasama before the present ones between Fort Jameson and 

 the Mchingas. It is true^ however, that the climatic conditions west of the 

 Mchinga Escarpment are very different. 



The situation with regard to G.fusca is still more perplexing. It is true 

 that it occurs in the neiohbourhood of Haroreaves, but it has not been found 

 on the Nyamadzi nor to the north of Fort Jameson, an extremely waterless 

 area which would seem most unsuitable to it. On the other hand, we know 

 it to be locally not uncommon on the west shore of Lake Nyasa, from whence 

 fresh cases are recently reported. Nevertheless near Karonga, where, as 

 Dr. Sanderson informs me, G.fusca is common, no cases of Sleeping Sickness 

 have been discovered, in spite of the fact that there is, or has been, direct 

 connection between this [jlace and the shores of Lake Tanganyika. 



It has already been shown how scarce this insect is in the neighbourhood 

 of Hargreaves, and that there is evidence that it is, at least, not abundant at 

 other times of year. It becomes therefore extremely difficult to comprehend 

 how it has become the cause of so many infections ; and there are almost 

 certainly more to be discovered. There is no evidence that this species enters 

 native villages, rather the contrary. The only time that the local native 

 would be likely to be bitten would be when he is bathing or drawing water. 

 This he usually does during the day and not at dusk, when the fiy appears 

 to be most active. 



This being the case, it l)ecomes even more incomprehensible that the fiy 

 should have become infected, even were it certainly able to carry the parasite ; 

 e.specially as there is no evidence that anything but a very small number of 

 natives from palpalis areas could ever have travelled over these roads. If the 

 infection is a mechanical one^ the organism eft'ecting this must necessarily be 

 numerous and in the habit of frequently biting human beings. The only 

 other biting flies, excluding mosquitos, which, at the time of my visit, at all 

 answered to this description were three species of lahamis, viz. : — 



T, ta^niola and its varieties, a species allied to T. dita^niatus, and the species 



