Anopheles Propagation Areas 79 



accumulated. If not disturbed or frightened 

 they can be seen at rest on the water surface but 

 often they dive or hide before the observer is 

 sufficiently near to notice them. It is not usual 

 to find them where such natural protection or 

 source of food are absent. Grass and plants 

 growing in the water are favorable, but dead 

 vegetation appears to be more satisfactory. After 

 a little practice an observer becomes expert in 

 judging whether parts of a body of water contain 

 larvse. It is found convenient to use a small white 

 enamel- ware saucer to dip for larv^; this can be 

 carried in a coat pocket when not needed. For 

 continuous inspection work a white enamel-ware 

 dipper is used to advantage. Where vegetation is 

 present and larvae are hiding in it, the saucer or 

 dipper may be pushed up to the plant or grass 

 stalks rapidly, and the larvae drawn out of theif 

 hiding-places by suction as the water enters the 

 saucer, or dipper. This method will obtain larvae 

 that are not detected in the water by the eye alone. 

 When either of these methods fail, the larvae may 

 be detected by the application of larvacide. This 

 substance spreads quickly under the water surface, 

 and the larvae rise rapidly in their efforts to escape. 

 It is much used in the Canal Zone and manj?- places 

 can be rapidly examined by using a small quantity. 



