Attack by Filling 119 



tate the finding of newly formed breeding places 

 at the early part of the wet season when much 

 Anopheles production takes place. 



After the deep fills are made there is sometimes 

 a considerable flow of water under them, which 

 outcrops near the toe of the fill and has to be cared 

 for, either by an intercepting ditch, or by oiling. 



HYDRAULIC FILLS 



In digging the canal channel near the Pacific 

 and Atlantic terminals, pipe line dredges were 

 used. These dredges cut the material near the 

 suction end of the pumps and draw it in with 

 the water. This muddy liquid, containing from 

 ten to twenty per cent, of solid material, is then 

 forced through pipe lines for long distances. The 

 lowlands are surrounded by dykes and the liquid 

 mass fills the enclosure. When the stirface water 

 is at first drained off, the mass of silt and mud 

 dries very slowly. Its depth may be anywhere 

 from one to ten feet or more. 



In many places pools and depressions produce 

 mosquitoes before the fill has time to settle and 

 dry. As the mud dries numerous cracks are 

 formed which catch and hold rain-water. As the 

 drying proceeds the cracks widen from a fraction of 

 an inch to three inches and sometimes are more 



