April, 12] JENNINGS; MOSQUITO CONTROL IN TROPICS 139 



hollow, the effect is very lasting. Its bulk is a serious obstacle to its 

 use and tanks, filled from the tank cars in which it is received, are 

 placed at various points in each station which can be reached by rail. 

 Barrel carts are used to transport the oil where roads exist; but in 

 rough and broken country, pack-mules must be resorted to in distrib- 

 uting the supply to the oilers and in filling drip barrels. The oil is 

 applied by means of a knapsack spray-pump and by drip barrels pro- 

 vided with a specially devised spout from which the oil drips slowly. 

 These are placed at the head of ditches and small streams at a good 

 height above the water, upon striking which, the drop spreads immedi- 

 ately to a thin film and floats away. This automatic method is very 

 effective. 



The manufactured larvacide possesses the advantage of very much 

 less bulk, though this is partly offset by the fact that the entire body of 

 the water is permeated and a correspondingly larger amount of the 

 preparation must be used. It also is applied by spray pumps at a 

 strength of about 20 per cent, in water. It is quickly fatal to the larvae 

 of mosquitoes but unfortunately also to fishes and the predaceous larvae 

 of dragon and damsel flies and other aquatic insects. Its effect is 

 quite evanescent and it must be renewed at short intervals, but the 

 thoroughness and quickness with which it does its work renders it 

 exceedingly effective. It is not suited to use in bodies of water of 

 large volume, though when appHed to the edges of even large streams 

 the results are excellent. Though sometimes unavoidably interrupted, 

 the plan of oiling operation provides for the covering of all territory 

 every seven days, and this period is sometimes shortened in case of 

 necessity. This effectively anticipates any possible emergence of 

 adult mosquitoes, should breeding have recommenced. 



The catching by hand of mosquitoes in barracks to which they have 

 gained access is an important aid in preventing malarial infection. 

 Colored laborers, chosen from the oiling gangs for intelligence and relia- 

 bility, are selected for the purpose. These men are armed T\ath 

 killing bottles charged with chloroform wdth which they go through 

 the buildings, catching the resting mosquitoes, of which they secure 

 a large percentage. The visits are made daily or at longer intervals as 

 the degree of infestation demands. After once entering a well screened 

 building, few Anopheles escape and if the blood-filled female is over- 

 looked by the catcher upon his first round, she is almost certainly 

 captured before she has reached the infective period. An adjunct 

 to the killing bottle, in the shape of a wire gauze fly killer or "swatter," 

 in the language of the day, is also carried by the men and is useful in 

 securing such mosquitoes as are inaccessible to the killing bottle. 

 Small electric torches have been used by inspectors in examining 



