MOSQUITO CONTROL 



281 



quantity of sawdust and give off a constant film. Thus for each condi- 

 tion, with a slight modification of the application, they obtain an excel- 

 lent and lasting film not destroyed by rains. Dr. Metz modified this 

 method by putting the oil-soaked sawdust in bags which he fastened to 

 the bottom of streams. Probably no other system of oiling is as adaptable 

 or as satisfactory as this sawdust method. Geiger and Purdy (1919) 



•rioJUr 



Fig. 59. — Submersible automatic bubbler for distributing oil orer surface of water. 



(Ebert.) 



have just reported success in reduction of mosquito incidence in rice 

 fields by broadcasting oil-impregnated sawdust and without injury to 

 the rice. 



Dr. Ebert, early in 1918, developed an automatic oiler (fig, 59) con- 

 sisting of a cylinder sunk beneath the water which takes in water and 



Fig. 60. — Method o1 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 large 

 tidal bay amidst rank vegetation produces a constantly, evenly dis- 

 tributed film of oil which is very efl^ective. The size of the cylinder is 

 gauged by the size of the stream. The distance to be placed apart must 

 depend upon the film obtained. Lieut. Brigham (1918) of the Army 

 Medical Corps used the same principle when he filled a bottle with crude 

 oil, cut two. grooves in the cork and poured oil in one groove. When 

 dropped in the water this automatically bubbled. To reach inaccessible 



