Attack by Drainage 127 



mosquitoes, and certain breeding grounds may be 

 harmful only at one short period of the year, or 

 only during the wettest part of an unusually rainy 

 year. The latter condition calls for attention 

 when Anopheles originate in water coming from 

 seepage outcrops. 



Many problems on the Isthmus differ from those 

 encountered in other parts of the tropics where 

 mosquito eradication or control measures will be 

 undertaken in the near future, and it may become 

 necessary to modify Isthmian sanitary practice to 

 attain results rapidly and economically in other 

 localities. However, it is thought that an outline 

 of difficulties encountered, and a brief account of 

 the methods used to overcome them, may be of 

 assistance to other communities suffering from 

 malarial fever. 



OPEN DRAINS OR DITCHES 



This type of drain may be divided into two 

 classes: First, those that are intended to carry off 

 storm water during rainy periods, and becoming 

 dry a day or two after the rain ceases, are known as 

 storm-water drains. Secondly, those that carry 

 off water for a period of more than a week, or 

 which hold more or less water continuously. 



Some storm-water ditches may fall under the 



