IX 

 TSETSE-FLIES AND COLONISATION 



DURING the last twenty years or so rapid strides have been 

 made in the science of Medical Entomology ; in fact, nearly 

 the whole of our knowledge of insect-borne diseases has been 

 acquired during this relatively brief period, and the results 

 have caused no little surprise both to the scientist and to the 

 layman. 



The principal vectors of disease are mosquitoes, sand-flies 

 of the genus Phlebotomus, tsetse-flies, house-flies, fleas and 

 lice, and the distantly related Acaridae such as mites and ticks. 

 These and hordes of other blood-sucking creatures tend to 

 make man's life intolerable, and the place in which he lives 

 sometimes untenable. 



The history of the movement in connection with the 

 transmission of disease in both man and his domesticated 

 animals by blood-sucking insects commences with the brilliant 

 discovery, made by Sir Patrick Manson in the year 1878, that 

 elephantiasis in man is transmitted by mosquitoes ; and it 

 is this discovery that has, in no small measure, been the 

 keynote to all subsequent discoveries. 



With regard to tsetse-flies and their effect on African 

 travel, adventure and colonisation, let me say at once that 

 this subject has not been singled out for exceptional treat- 

 ment because the diseases which these insects transmit are 

 either more general or responsible for a greater mortality 

 among men and the domestic animals than other tropical 

 diseases. So far as domestic stock is concerned, the mortality 

 from tsetse-fly disease in certain portions of Africa is con- 



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