112 SECTIONAL ADDRESSES 
of stream-bank arrangement, would seem to vary from, say, 5 to loper square 
mile in Districts of small population to 40 to 50 in the more populous. 
TSETSE FLY. 
No element of the human environment is more important than the 
distribution of the tsetse flies (Glossina). G. palpalis, the carrier of 
sleeping sickness, appears happily to be either absent or innocuous over 
nearly all the country, the only districts where the disease has been 
yoo miles 
Fic. 2.—Sketch-map of Northern Rhodesia, showing Distribution of (1) Tsetse 
Fly and (2) Native-owned Cattle. 
reported in recent years being the Luapula and Luangwa valleys, the 
shore of Lake Tanganyika, and a small part of the upper Kafue valley. 
But with the bearers of Nagana it is quite otherwise. The presence of 
these flies is a menace to cattle owners, European and native, and un- 
fortunately they infest the greater part of theterritory. Their distribution, 
as plotted from the reports and certain local maps, reveals three large 
tracts that are free of fly. The first includes the greater part of Barotseland. 
East of this lies a broad fly belt ; within this the flies seem to be spreading, 
and at the southern end the belt is extending both eastward and westward 
toward the native and European cattle land of the lower Kafue and the 
