137 



This comprises the country on the northern boundary of the Be1giai> 

 Congo along the Ubangi and Mbomu Rivers, and between their northern 

 tributaries, the Kotto and the Uara, between 4° and 8° N. Lat. and 

 19° and 23° E. Long., which is roughly about 350 miles square. The 

 three principal tribes are the Yakomas on the Ubajigi and the Mbomu 

 Rivers to the south-west, a large area in the centre inhabited by the 

 Nsakara, and the Sandes or Niam-niam to the east and north-east. 

 The Yakoma population is dense and largely employed by Europeans, 

 and sleeping sickness is rife amongst them. The Nsakara country is also 

 densely populated along certain lines at a distance from the Mbomu 

 River,' but the people are relatively healthy and sleeping sickness is 

 entirely absent, while to the east the Sande country has been decimated 

 by the disease. Long continued tribal fighting has caused the people 

 to live in a type of hut so constructed for defence that ventilation is 

 practically impossible. The epidemic began about 1900, arid has raged 

 more or less ever since, spreading into the Egyptian Sudan. Just 

 before the disease broke out in Sande, a very fatal epizootic occurred 

 among the local buffaloes and in some places spread to antelopes, 

 monkevs and domestic animals, and the natives firmly beheve in a 

 relationship between this outbreak and the sleeping sickness, which 

 immediately followed it. Attention is called to the importance of 

 preventing 'the spread of the disease to the Nsakara country, which 

 is thus placed between two serious centres of infection, and the danger 

 is greatlv increased by the fact that the natives of the infected area 

 provide a large portion of the labour employed by Europeans and 

 travel considerable distances. In the Yakoma country species of 

 Glossina are rare, though G. palpalis is to be found in the forest which 

 here and there lines the banks of some tributaries of the Ubangi. 

 With the exception of these very limited areas, Glossina is not found ; 

 none were seen in the villages "near the banks, and they were never 

 met with on the river itself. Sfomoxys was also comparatively scarce, 

 but Tabanidae and mosquitos swarmed. Mansonia sp. was specially 

 abundant in certain villages where the disease was prevalent and in 

 the marshv plains. Anophelines Were very much rarer and Stegomyvi 

 was never found. Along the Rivers Chinko and Vovodo and their 

 branches flowing southwards to the Mbomu as far north as the sixth 

 parallel, G. palpalis is everywhere to be found. In the Semongo 

 district, where sleeping sickness has raged since its importation from 

 Rafai, no G. palpalis are to be found, and the disease is probably 

 maintained by G. morsitans. Culex and Mansonia are by no means 

 rare, and further up the river Mansonia is so abundant that the 

 inhabitants are compelled to adopt a special form of hut. The popula- 

 tion thus hves under very crowded conditions and this, in the 

 author's opinion, greatly assists the spread of the disease. The 

 percentage of persons attacked by the disease is calculated at 40 for 

 the western centre (Yakoma) and 20 for the eastern. In the former 

 area the epidemic has existed for 6 or 7 years and 15 to 18 years in 

 the latter. The same biting insects are found in the central Nsakara 

 area, where the disease does not exist, as in the others, G. palpalis 

 occurring along the rivers in the centre and to the south, and 

 G. morsitans in the more northern parts. Mosquitos are not very 

 numerous and are represented by species of Mansonia and Anopheles. 

 Other biting insects are Slomoxys and Tabanids. SimuUum is very 



