98 



Catiin, they were freely attacked in sunlight by A. tarsimaciilatus and 

 A- alhimnnus. In the dark, the light of a lantern protected the 

 illuminated part of the body, and observers standing in the direct rays 

 of an acetylene lamp were not bitten, though the shadow even of a 

 finger permitted the attack of A. albimaniis at once. Anophelines 

 are most voracious at dusk and soon after dawn, and the exceptional 

 biting in daylight at Gatun may perhaps be explained by the urgent 

 need of blood. Though hundreds of Culicines are found dead in the 

 globes of electric lights, Anophelines are practically never thus 

 attracted. 



A. alhimanus usually flies against light breezes and this species 

 travels much further from its breeding grounds than A. pseudopundi- 

 pentiis or A. malefactor. Details are given of many interesting 

 observations on the flight of mosquitos and of the methods used for 

 staining individuals in order to determine the length of flight. Of 

 40 stained specimens recovered, 24 were found to have travelled from 

 1,300 to 1,600 yards from the point of liberation. 



In the filHng of depressions, which is a necessary part of anti- 

 mosquito work, the surface cracks which form must be carefully 

 filled up, and every precaution must be taken against subsoil 

 water collecting either under the made soil or in the borrow pits. 

 The use of drains, and the best mode of construction in order to 

 prevent them from becoming breeding places, is dealt with at length. 



The problem of oiling on a large scale is fully considered. The 

 oil kills either from specific toxicity or by clogging the breathing 

 tubes, or possibly by reducing the surface tension and making it 

 difficult for the larvae to remain long enough at the surface to rupture 

 the film and obtain air. The objection to kerosene is that the film is 

 so thin that it is easily broken by floating material and other causes ; 

 it is expensive and is apt to be wasted because it is difficult to see 

 where the film is satisfactory. It is also liable to take fire from 

 sparks, etc., especially near a railway. Crude oil of asphaltum is 

 extensively used in Panama, as it is cheap, though its poor spreading 

 qualities would make it unsuitable in any other climate. Various 

 methods of oiUng are described in detail, especially the drip 

 method ; for small streams, etc., small bundles of cotton waste soaked 

 in oil and kept in place by tying to a stone or some fixed object, are 

 said to be very effective, and to give a film of oil for a week or more ; 

 the waste can be used again and again. The oil used on the Canal 

 Zone for these purposes amounts to about half a milhon gallons 

 annually. An extensive plant has been laid dow^l at Ancon for the 

 production of a special larvicide, the formula of which is as follows : — 

 Resin 150-200 lb., soda 30 lb., crude carbolic acid, (gravity 0'97), 

 150 U.S. galls. These are boiled together in a special apparatus and 

 the product is a black, liquid, resin soap which emulsifies freely with 

 fresh water. The carbolic acid must contain at least 15 % of phenol, 

 and must not be of a higher gravity than that stated ; if the larvicide 

 is of standard strength and quality, an emulsion of 1 in 5,000 should 

 kill an Anopheline larva in ten minutes. This preparation is cheap; 

 the high concentration saves cost in transport ; its action is very 

 uniform and rapid ; it is easily made ; is harmless or nearly so to the 

 higher animals ; there is no risk from fire ; it kills larvae embedded in 



