127 



RESULTS OBTAINED FROM A MONTHLY EXAMINATION OF 



THE NATIVE DOMESTIC WATER-RECEPTACLES AT LAGOS, 



SOUTHERN NIGERIA, IN 1910-1911. 



By Dk. W. M. Graham, 



Director of the Medical Research Institute, Lagos, 



Last year an attempt was made to collect the mosquito larva; breeding in the 

 vicinity of the Institute at Yaba, near Lagos, and to identify them with their 

 imagines. This year it was decided to conduct a similar investigation in the 

 township of Lagos itself. My attention had been directed to the importance of 

 the subject by the occurrence of an outbreak of Yellow Fever in Sierra Leone and 

 the Gold Coast ; and further, I had been requested to suggest a set of instruc- 

 tions such as would enable the native Sanitary Inspectors in Lagos to identify 

 the larva of Stegomyia fasciata. 



Inherent difficulties rendered it impracticable to draw up any instructions 

 which would enable the native Inspectors to make correct identifications, and 

 the matter seemed of sufficient importance to warrant a complete investigation of 

 the domestic mosquito fauna of the Lagos township. 



The investigation was conducted in the following manner. I arranged with 

 the Sanitary Department to have the native Sanitary Inspectors instructed to 

 empty the contents of each water-receptacle in native yards, found to contain 

 mosquito larvae, into suitable bottles, which, when labelled with the letters of the 

 Sanitary Division and District and the date of collection, were to be forwarded 

 daily to the Laboratory. 



On arrival there, the contents of each bottle were transferred to a shallow white 

 tray, and examined with a hand-lens, and the various species isolated for more 

 detailed examination, or for breeding experiments. As the relative importance 

 of separate facts is usually obscure at the beginning of such an investigation, I 

 determined to identify and tabulate as completely as possible all living creatures 

 found. 



The investigation was begun in August, 1910, by the examination of the 

 contents of 364 water-receptacles from native yards in the four Sanitaiy Divisions 

 of the township. I further asked to be supplied monthly with the contents of at 

 least 100 water-receptacles from these 4 divisions. The collection of these samples 

 was efficiently carried out, except during the months of November and December, 

 when the contents of only 43 and 61 receptacles respectively were received at the 

 Institute. 



In practice, this method of ascertaining the mosquito fauna of a native town 

 has proved relatively easy of execution ; the results have proved more accurate 

 and complete than those obtainable by other methods ; and any seasonal variation 

 in numbers or distribution can be very readily observed. The catching of 

 mosquitos in native yards and houses is difficult, and offers none of the 

 advantages gained by dealing with the larvaj, and even approximate finality is 



