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and the pools filled with gravel or rubble. It is seldom 

 necessary in such cases to make formal stone, brick, or 

 cement surface-drains, or to lay in subsoil pipes. We must 

 remember that puddles can be spoilt for larvae, even if they 

 are not entirely drained away ; either by running a current 

 of water through them, or by breaking up their surface with 

 stones and rubble. Pools formed in the soft earth at the 

 bottom of watercourses require filling in with large stones 

 and gravel. Pools in the hollows of rocks, as those found 

 in the bed of drying streams, require to be filled up by 

 concrete (one part of Portland cement to two of sand) 

 mixed with stones ; or they can be often released by cutting 

 the rims of rock. Water lying on flat fields or other 

 surfaces can generally be released by small crow's-foot 

 channels the smaller the better. Boggy ground on the 

 margin of ponds, tanks, and streams, can be dealt with 

 similarly. Made surface drains should be kept free of silt. 



Deeper Pools, Pits, and Ponds. These should be filled 

 up where possible by earth, or by rubbish collected from 

 the houses. Where they cannot be filled up they can often 

 be spoilt for larvae, by clearing away the vegetation on 

 their banks in which the larvae love to hide. Larvae do not 

 like open water of any depth, especially when it is free 

 from vegetation. It is astonishing how soon even large 

 pits and ponds can be filled up with rubbish collected from 

 houses by the Culex gang (paragraph 1 2). 



Disused Wells, Pits, and Tanks. These should be filled 

 up if possible ; or cleared of vegetation and oiled regularly. 

 Owners of premises often give great trouble about such 

 places ; in which case the municipal authorities ought to 

 be approached on the matter. Often, however, no larvae 

 exist in them. 



