124 The Control of Mosquitoes 



If a competent civil engineer devotes his entire 

 attention to these matters, he not only makes a 

 study of details affecting the problem, but will 

 probably invent new methods of procedure and 

 new short cuts. It is not unusual for an engineer 

 to leave minor ditching work to the judgment of a 

 gang foreman, who makes the ditches too wide, 

 spoils the grades, and frequently the work is not 

 only unsuccessful, but expensive to maintain, and 

 ultimately becomes a dangerous source of Anoph- 

 eles. It is possible for an improperly drained 

 area to produce more mosquitoes after the ill- 

 planned work is concluded, than before the drain- 

 age was begun. 



- An ideal scheme of drainage would be a plan to 

 remove all standing water from the Anopheles- 

 producing area, and take care of all storm water 

 in such a manner that within a short period after 

 a storm the ground surface and ditches would 

 become dry. These conditions would eliminate 

 Anopheles and many other species of troublesome 

 mosquitoes. 



In many places in the tropics this ideal cannot 

 be attained, because of such factors as geological 

 formation, texture of surface soil and subsoil, 

 topography, vegetation, the extent and distribu- 

 tion of rainfall, and air movement. The mere fact 



