Attack by Oiling 157 



Breeding places for mosquitoes have been found 

 in catch basins of sewers, particularly during long 

 intervals between rains. This condition has been 

 remedied by small drips, but it would be better 

 to use a device making it impossible for mosquitoes 

 to enter catch basins except at the time water 

 flows into the basin. 



The measure of success in the operation of a drip 

 is that it shall work as nearly automatically as 

 possible. The ideal drip is one that, once adjusted, 

 requires no further attention except refilling. With 

 heavy oil, the ideal has not been attained in 

 Panama. We were compelled to use drips that 

 worked in a fairly satisfactory manner. Although 

 far from perfection, the drips were extremely 

 useful. 



The difficulties encountered in devising a satis- 

 factory drip are: 



That crude oil is too thick to permit of making 

 use of capillary attraction, as may be done with 

 kerosene and light oils. 



It contains a large quantity of suspended solids, 

 which in time block a small hole or wick, and the 

 flow either stops altogether, or is greatly impeded. 



The oil becomes more viscid in the cooler 

 temperature of the night, and may stop flowing 

 until it is warmed later in the morning. 



