ENTOMOLOGY

MOSQUITO CONTROL 281quantity of sawdust and give off a constant film. Thus for each condition,with a slight modification of the application, they obtain an excellentand lasting film not destroyed by rains. Dr. Metz modified thismethod by putting the oil-soaked sawdust in bags which he fastened tothe bottom of streams. Probably no other system of oiling is as adaptableor as satisfactory as this sawdust method. Geiger and Purdy (1919)0 _-.. oA0 r,--. -- .J... ,-FIG. 59.-Bubmersible automatic bubbler for distributing oil oyer surface of water.(Ebert.)have just reported success in reduction of mosquito incidence in ricefields by broadcasting oil-impregnated sawdust and without injury tothe rice.Dr. Ebert, early in 1918, developed an automatic oiler (fig. 59) consistingof a cylinder sunk beneath the water which takes in water andFIG. GO.-Method 01 petrolization with oil soaked sawdust.(Ebert.)displaces the oil, the amount of displacement being regulated by spigots.This oiler dropped under a bridge in a big river or placed in a largetidal bay amidst rank vegetation produces a constantly, evenly distributedfilm of oil which is very effective. The size of the cylinder isgauged by the size of the stream,. The distance to be placed apart mustdepend upon the film obtained. Lieut. Brigham (1918) of the ArmyMedical Corps used the same principle when he filled a bottle with crudeoil, cut two grooves in the cork and poured oil in one groove. Whendropped in the water this automatically bubbled. To reach inaccessible