296 SCIENCE IN AFRICA 



tributes towards the efficiency of control (Swellengrebel 1931). 

 Filling up and draining waste land containing breeding-places, 

 canalization, covering water-supplies, and improved sanitation 

 have greatly reduced malaria in many places, such as Nigeria, 

 where it was previously a serious danger. The work on Lagos 

 Island and adjoining parts of the mainland may be mentioned as 

 a good example. The expense involved in such operations is, how- 

 ever, heavy. Where water cannot be covered, it may sometimes 

 be made unsuitable for breeding by other means. Thus oiling, for 

 which Paris green has sometimes been found a satisfactory sub- 

 stitute, destroys larvae and prevents breeding in open water (Symes 

 1932). As a temporary measure the addition of cut grass or of 

 vegetable refuse to waters has proved effective in Uganda. The 

 effectiveness of such measures is increased when they are used in 

 conjunction with an attack on the malarial organisms in the 

 human host. This question is discussed in Chapter XVI. 



A valuable contribution to the study of mosquitoes is a mono- 

 graph on those of the Culicines of the Ethiopian region by Hopkins 

 (1936). Other publications on this subject are numerous, especi- 

 ally those by medical entomologists in the several territories; 

 among them the work of C. B. Symes of Kenya may be mentioned. 



Much of the research on Aedes aegypti L., the vector o^ yellow 

 fever, has naturally been of the same type as that on the vectors of 

 malaria. Investigations on breeding-places and the influence of 

 climate and local conditions, piped water-supplies and effective 

 sanitation have resembled those on Anopheles. The important work 

 on the endemicity of yellow fever, in relation to the distribution of 

 Aedes and the possible spread of the disease, is discussed in Chapter 

 XVI. 



Another serious disease transmitted by mosquitoes is Jilariasis, of 

 which the casual agents are Filaria spp., especially {Wuchereria) 

 bancrofti. Apparently the relation between insects and the disease 

 still calls for much research. Dissections of mosquitoes in search 

 of micro-filariae in them suggest that Anopheles gambiae and A. 

 funestus are probably the chief vectors in most places (Taylor 1930), 

 although positive results have also been obtained with A. pharoensis 

 Theo., A. theileri Edw., and, in Egypt, Culex pipiens L. (Khalil, 

 Halawani, and Hilmy 1932). 



