Attack by Drainage 125 



that open ditches are not always followed by 

 perfect "Anopheles drainage" need not in any way 

 discourage the sanitarian. He must overcome 

 many apparently difficult problems, or his work 

 will not be successful. Open ditches should be 

 made as straight as possible, and have narrow 

 bottoms. The side slopes should be clean cut. 



Drains with flat grades may often deteriorate 

 to conditions that actually produce Anopheles. 

 Sometimes it is difficult to prevent the formation of 

 "pot-holes" in ditches on heavy grades, and as 

 each foot of open ditch means an item of expense 

 for maintenance, the drainage scheme should be 

 planned to use the least total length of ditches. 

 To attain the best results, we must be sure the 

 drain is correctly located. There is often a choice 

 of locations for a drainage ditch. The character 

 of the surface soil may be such that the necessity 

 for certain branch ditches is doubtful. When 

 working in wet areas it is often best to locate and 

 install the main ditches before the laterals are 

 definitely located. This is especially true of 

 extensive areas covered with water and jungle 

 where the low places are not yet known, and their 

 drainage can be planned better after the deep 

 water has been removed. 



Additional advantages ensue in cases where 



