SIGNIFICANCE OF STEGOMYIA FASCIATA IN WEST AFRICA. 259 



Measure IV. 



Another measure of great economic importance to the welfare of the 

 community is the filling in of swamp land and general drainage. Not only 

 does a measure of this kind affect the general liealth, and the breeding of 

 mosquitos, but it is a work of great commercial advantage, for it reclaims 

 land. Already in Southern Nigeria a great step in this direction has been 

 made by the employment of the sand-pump to fill in swamps. 



The drainage of the town should be early planned out, and then carried 

 out from time to time as funds will allow. 



Culicides for the destruction of Larvae. 



The most economical, least dangerous, and most readily procured of all 

 culicides, are the various preparations of petroleum. This oil can be used 

 on a large or small scale_, and it can be either sprayed or poured on the 

 water. For all stagnant collections of water in pools or lagoons it is 

 excellent_, and its culicide action remains long after such collections of 

 water have been treated. It must be recollected that under a powerful 

 tropical sun the oil evaporates in a comparatively short period, and that 

 therefore the treatment must be renewed every few days. I made some 

 experiments this year in order to determine how soon the effect of the 

 oil passed off. My experiments consisted in placing in a large tub of 

 water, of one square yard superficial measurement, a number of the larvse 

 of the Stegomyia. Then I poured on to the surface one ounce of kerosene oil, 

 and exposed the tub either in the bright sunshine, or kept it under shade. 

 I timed the starting of the experiment, and the time when the larvae ceased 

 to move. 



Ed'periment I. 



Surface covered with one ounce of oil and exposed to powerful sun. 



Stegomyia larvae placed in water at 12 noon ; at 3 P.M. all larvae dead^ and 

 most of the oil evaporated. 



E.rperiment II. 



To determine rate of evaporation. At the end of 3 hours the oil had 

 evaporated, leaving but a faint smell and producing only a slight oil stain 

 on blotting-paper. 



Experiment III. 



Half an ounce of oil poured on the water. Larvae placed in the water 

 at 12.30 P.M., and all dead at 1.30 p.m. ; at 5.25 p.m. the oil had evaporated 

 with the exception of a faint odour and very slight iridescence. I then 

 placed fresh Stegomyia larvae in the tub without adding any additional 

 oil, and at G.30 the larvae were dead. It appears that the small quantity of 

 dissolved oil has a culicide action. 



