APPENDIX B 293 



where sleeping sickness is found, but crocodiles are 

 absent. 



In the present absence of complete knowledge 

 respecting the trypanosome and the tsetse-flies, the 

 best that can be done is, so far as is practicable, to 

 close infected districts, to prevent the passage of 

 infected individuals into uninfected areas, and, by 

 clearing the rank vegetation along the banks of rivers 

 and the shores of lakes in the vicinity of villages, to 

 destroy the breeding-grounds of tsetse-flies in the 

 places where they are most likely to have an oppor- 

 tunity of infecting human beings. If, however, Pro- 

 fessor Koch's suggestion of tnal de coit is proved b}?^ 

 subsequent investigations, and * transmission of the 

 disease between the sexes in the human subject is 

 possible and reciprocal, it is obvious that comparatively 

 little good is likely to be effected by measures directed 

 against what ma^^ prove to be only an occasional 

 alternative method of infection. Should such be the 

 case, the outlook is indeed dark, for it is difficult to 

 see what general measures can be suggested that offer 

 any hope of preventing the spread of the disease in 

 actual practice ' {Journal of Tropical Medicine). 



The tsetse-flies {Glossina:) comprise ten species, 

 which are confined to Africa. They are sombre- 

 coloured, narrow-bodied flies from about 8 to 12 

 millimetres long, with a thick proboscis projecting 

 horizontally in front of the head. When the fly is at 

 rest the wings overlap each other, crossing like the 

 blades of a pair of scissors. Glossina palpalis has been 

 found from Senegal to Angola on the west, through 

 the Congo and Lualaba to Tanganyika and the Victoria 

 Nyanza, and northwards along the Nile to the Uganda- 

 Sudan border. The flies are seldom, if ever, found 

 above 4,000 feet, and always near water. A swampy 

 shore is not much to their taste ; they are most com- 



