238 INHEEITED IMMUNITY TO FLY DISEASE. 



domestic dogs survive the bite many months. On the 

 other hand, native dogs whose ancestors have been bred 

 in the fly country for many generations do not succumb 

 to the poison. The same rule applies to goats reared 

 under similar conditions ; though it would seem it must 

 not be applied to sheep or cattle. Of all domestic animals 

 the lowly donkey alone makes a good fight of it. As high 

 a proportion as four donkeys out of five have spent a 

 whole season in the fly country without signs of the poison 

 taking efiect ; though donkeys will, it is believed, at times 

 die of fly bites in the second season after being bitten. As 

 a rule, animals bitten by flies in the diy season wUl live 

 till the first rains fall, when they die within a few days. 

 In the same way a horse if bitten will generally die within 

 twenty-four hours of being driven through a river. . . . 

 Like the ' horse sickness ' and malarial fever, this curse 

 to travel and transport undoubtedly recedes before the 

 ' advance of civilisation, so that the far future may yet see 

 the extinction of the Tsetse. 



" Oswell reported the existence of the fly some 600 

 miles south of the Zambezi, when he hunted there fifty 

 years ago. Now waggons can be taken from Bechuanaland 

 to the Zambezi without any danger of the oxen being 

 ' stuck.' Several flies are necessary to produce a fatal 

 effect, but in passing through a belt in the day-time 

 several are forthcoming. At night the danger is very 

 small, though it is a mistake to imagine that the Tsetse 

 keeps such early hours as other flies. I have at times 

 been worried by them an hour after the sun has gone 

 down, and have known flies to buzz into my tent as late 

 as 9 o'clock on a dark night and make a bold dash for 

 supper at my expense. At that time of night they are 

 easily caught, and almost invariably found their Avay into 

 spirits of wine. 



" With all their faults, these destructive little creatures 

 have the merit of being clean feeders. The natives, in 

 taking an animal through a fly-belt, plaster it with cow- 

 dung, which eflfectively keeps the fly at a safe distance. . . ." 

 (pp. 61-65). 



From the head-ioaters of the Sejlefula River to the 

 Nanyate : Latitude of evening camp, as given on author s 

 map, 16° 47' 9" S. ; approximate longitude, 25° 48' E. — 



