IO 



the insects are old ones which have lived in the bush since 

 the last rainy season. Fortunately these conditions do not 

 obtain much in large towns, where the fight against mos- 

 quitoes must chiefly be waged. 



But, though Anopheles can scarcely be said to be "home- 

 bred mosquitoes" to the same extent as Culex are, they 

 are generally most numerous in houses nearest to the 

 breeding pools. They naturally select the nearest houses 

 for obtaining their human food. Freetown, Sierra Leone, 

 presents several examples of this. The unhealthiest and 

 most Anopheles-haunted parts of the town are just those 

 parts where the pools and puddles are most numerous. It 

 was shown by CHRISTOPHERS and STEPHENS that in the 

 dry season there the insects were most prevalent in houses 

 adjoining a drying water-course full of puddles. In Tower 

 Hill Barracks, situated on a small open eminence in the 

 middle of the town, Anopheles are very rare, though this 

 eminence is, or rather was, surrounded by numerous pools 

 at a distance of a few hundred yards the reason being 

 that the Anopheles bred in the pools preferred to obtain 

 their food in the houses of natives at the foot of the 

 eminence, to wandering up the hill in search of it. 



In short, Anopheles, like other mosquitoes, and indeed 

 most animals, are essentially local in their habits. They 

 are most numerous where they can breed and feed most 

 easily. They are not spread uniformly over the country 

 like the air we breathe. The idea that swarms of them 

 can be blown into towns by winds from distant marshes is 

 erroneous. If we remove the breeding pools at any one 

 spot we shall certainly largely reduce the Anopheles at that 

 spot, even though a few insects may occasionally wander 

 in from without. In other words, in most towns where 



