52 THE ESTIMATE OF THE COST 



The best larvicide for mosquitos is the aboli- 

 tion and prevention of stagnant water collections ; 

 but the second best is the use of oil. Cesspools 

 should be replaced by a sewerage ; local marshes 

 ought to be drained, or filled up and reclaimed ; in- 

 filtration water collections levelled ; and house-tanks 

 and water-butts dispensed with by a better, or more 

 constant, pressure of water on the town mains. But 

 while such municipal reforms are being carried out 

 or discussed, the reduction of mosquitos may be con- 

 ducted by the use of oil as a larvicide. 



The oil most commonly used for this purpose is 

 petroleum. In Egypt equal parts of refined and 

 crude petroleum mixed together is generally used. 

 As a matter of fact, any oil may be employed, as 

 already pointed out, for it is the mechanical action 

 of the oil resting on the surface of the water in an 

 even layer that suffocates the mosquito larvae, and 

 not any poisonous effects. But petroleum is usually 

 the cheapest, and the oil commonly used for this 

 reason ; it is also obtainable everywhere. But even 

 petroleum is expensive when used in large quantities. 

 Its cost varies in different countries, and in different 

 localities of the same country. For example, at Cairo 

 the mixed oil costs sixpence per gallon, at Port Said 

 it is a trifle less. When the mosquito campaign was 

 first started in the latter town, the crude oil was more 

 expensive than the refined, because the latter was 

 imported " in bulk " in tank steamers, while the 

 crude petroleum was only brought from the East 

 Indies in small quantities at a time, and the freights 



