236 F. W. DRY. 



searching especially for Simulium but finding none. Inquiries were made from a 

 large number of natives, who replied, either that they knew nothing at all about 

 the fly, or that they knew of it near the Chemosit River. 



Simulium was therefore not a factor in the presence or transmission of trypano- 

 somiasis on the farm where this outbreak had occurred. 



The evidence recorded above, combined with the fact that no other outbreak 

 of trypanosomiasis was recorded in the district, points to the probability that the 

 disease was transmitted on the farm to healthy animals from one or more animals 

 which were infected when they came on to the farm. If that be so, suspicion would 

 fall first on Stomoxys. 



II. Possible Connection of Simulium with a Disease of Human Beings. 



The Lumbwa name for this Simulium is " kekonjek." A place infested with 

 Simulium is spoken of as " kapkekonjek." The insect has been identified by 

 Mr. F. W. Edwards, of the British Museum, as Simulium neavei, Roubaud. 



The badly infested country, so far as I was able to ascertain from my own 

 observations and from inquiries from the Lumbwa, is covered with dense forest, 

 mostly of thorn trees, white and red, with occasional open spaces (see Plates vii 

 and viii). It is well watered, and it is unlikely that there is any point within that 

 area much more than two miles from some stream, large or small. About three 

 miles below the junction of the Chemosit and Kipsoni Rivers one fly was captured, 

 this being the lowest point reached on that river on the trip ; Simulium was present 

 there in only small numbers and it was evident that, lower down, neither the Lumbwa 

 on the right bank of the river, nor the Kisii on the left, paid any attention to the 

 fly. It was also taken in small numbers in a tributary valley of the Sondo River 

 on the left bank a mile from the Sondo ; in this valley there were scattered clumps 

 of trees but not continuous forest. 



The flies are appreciably less numerous in thin than in thick forest (see Plate viii), 

 and while present in the middle of open spaces — say a quarter of a mile in diameter — 

 are there distinctly less numerous than in the forest. This falling off in numbers as 

 one gets away from dense forest is quite a sudden one. 



The flies are active, the Lumbwa told me, and my own observations are consistent 

 with what they said, from about seven o'clock in the morning until five in the after- 

 noon, and especially so in the afternoon. Very little is seen of them when rain is 

 falling, and I was told, and from my own collecting believe it to be so, that the flies 

 are not so active in intense sunshine as when the sun is less bright. They pay little 

 attention to people on the march, but if one remains still in infested country they 

 appear immediately. They bite very readily and often raise half-inch wheals, a 

 drop of blood frequently exuding from the puncture. In badly-infested forest a 

 person sitting with a bare back and allowing the flies to do as they liked would 

 probably be bitten once a minute at the very least. 



It is the accepted belief of the Lumbwa and Kisii amongst whom I moved, that a 

 disease is caused by the bites of these flies, the chief symptom being that the skin is 

 in folds (Plate vii, fig. 1). It would seem that these folds appear first on the small 

 of the back, but sometimes the skin higher up the back, and more rarely that of the 

 front and sides of the body was seen to be affected in the same way, while occasionally, 

 though this was only so with elderly people, the condition would extend to the arms 

 and legs. Sometimes the skin was spotty, as shown in the photograph, and occasional 

 cases were shown to me as Simulium disease in which spots, but no folding, were 

 present. People with the affection scratch themselves a great deal. 



Many of the affected people that I saw were able to carry on their usual activities, 

 but some looked to be in quite a feeble condition. I asked one young man if he 



