TSETSE-FLIES AND COLONISATION 219 



Our knowledge of the diseases and the causative agents has 

 been greatly increased, the way of preventing their spread has 

 been determined, and I have hopes that further research will 

 enable us to suppress them altogether ; thereby we may 

 extend our colonies into the vast tracts of country which at 

 the moment are clothed with forest and bush, forming the 

 deadly haunts of the tsetse-fly and for the most part a barrier 

 to the advancement of tropical agriculture and colonisation, 

 and to the occupation by science of new fields of research. 



