Dr Stephens, The Prevention of Malaria. 125 



search, or by making of pools if necessary. The same is true of 

 all native villages, at least all those we have ever visited, for it 

 is generally impossible to exclude local breeding grounds in the 

 rains, and possibly in the dry season. It is a peculiar condition 

 that in such native quarters mosquitoes may still be found even 

 after a drought of some months. 



We may sum up by saying that Anopheles occur very widely 

 distributed. Often it is difficult to detect them, but if a native 

 village or small collection of huts occurs here they congregate even 

 if breeding-places are absent or only exist during the rainy season. 

 It is worth noting that to the breeding- places of the genus, which 

 have been adequately described by many authors, we may add as 

 not infrequent spots, native canoes and deep wells 30 — 40 ft. 



Accra. 



In the country around Accra we were unable to find a single 

 natural breeding-place, but artificial ones — excavations made by 

 the natives around their huts for various purposes — exist in many 

 hundreds. With the advent of the dry season most of these pits 

 become dry and breeding-places are now only found where the 

 ground water is sufficiently near the surface to be reached by the 

 deeper excavations (6 — 10 ft.). On the higher parts of the district, 

 40 — 60 feet above sea level, in the dry season the ground water is 

 not reached in the numerous pits existing everywhere and in con- 

 sequence large areas are now free from breeding-places. 



Around the borders of the lagoons which are a feature of the 

 coast the conditions are different. Here the ground water is reached 

 within a few feet and in the driest season numerous pits dug by the 

 natives along the margin of the lagoon contain Anopheles larvae. 



This condition shews that the effect of salt lagoons and low- 

 l} T ing salt marshes is an indirect one, as in the lagoons themselves 

 larvae were not found. 



Lagos. 



Lagos is situated upon low-lying alluvium and is surrounded 

 by extensive lagoons. The highest point of the island is not 

 above 20 feet above sea level. A considerable tract in the centre 

 of the town lies about 10 feet above sea level. This central 

 area is approximately level but its margins sink rapidly towards 

 the lagoons. Between this sloping ground and the lagoons there 

 is a strip of land of varying width which lies almost at lagoon 

 level. This strip is bounded by the 5-foot contour line. The 

 heaviest rains are rapidly absorbed in the central elevated portion 

 of the island so that in a few days after continuous rain all surface 

 pools have disappeared. The subsiding water however emerges 

 again around the borders of this tract forming a line of oozing 

 water extending around nearly the whole island. It is here that 



VOL. XI. PT. II. 10 



