INSECTS AND HUMAN DISEASE 131 



Medicine, to study the disease on the spot. These two 

 scientists, to whose discoveries much of our present know- 

 ledge of sleeping sickness is due, established themselves at 

 Nawalia, in the Luangwa Valley, which runs north to south 

 through the middle of North-East Rhodesia. The valley 

 has an evil reputation, and is closed to Europeans on 

 account of sleeping sickness, whilst natives may neither 

 enter nor leave it. In this lonely spot, cut off from all 

 civilisation, these two men, at imminent peril to themselves, 

 spent eighteen months, working to discover why sleeping 

 sickness was spreading in districts where Glossina palpalis 

 was unknown. Although Nawalia is the site of an old 

 government station, no palatial dwelling or well-equipped 

 laboratory was vouchsafed the scientists ; simply wattle and 

 daub structures sufficed : they were " glorified native huts." 

 Even their ordinary wants were at times in jeopardy, for, 

 as Dr Yorke said, in describing his work, " All our stores 

 had to be carried by natives from Fort Jackson (120 

 miles distant), a procedure which at times resulted in a 

 certain amount of exasperation. For example, on one 

 occasion we sent in an order for a hundred pounds of 

 flour and a six-gallon tin of paraffin oil. After about three 

 weeks the carriers returned with a note and an empty oil 

 tin. In the letter was written, ' Sorry no flour, herewith 

 the oil.' On the way back the natives had perforated the 

 paraffin tin, either accidentally by letting it down suddenly 

 on a sharp stone, or designedly to render the load lighter." 

 The domestic stock in the valley was decimated by try- 

 panosomiasis, and many of the natives employed by the 

 commission died of sleeping sickness. 



The headquarters had scarcely been established before 

 Drs Kinghorne and Yorke announced an epoch-making 

 discovery. Luangwa Valley was reeking with sleeping 

 sickness, yet not a single tsetse fly, of the species that was 

 believed to be the only carrier of human trypanosomes, 

 could be found. An allied species, Glossina morsitans, 



