The method of application must be varied to suit the size and situation of the piece of water to be dealt with. Small puddles, such as those left in the course of roadside ditches, may most economically be dealt with by, as it were, lightly wiping over the surface with a wisp of rags dipped in the oil; filling in being in such cases out of the question, as to do so would be equivalent to obstructing the drainage; and it is quite impossible to maintain an exact and uniform gradient in an unrevetted channel. For larger collections of water, by far the best appliance is an ordinary gardener’s watering-pot. The oil should be applied mainly along the windward side of the pool by a coolie, who should, if possible, walk out some distance into the water, and should be trained to sprinkle the oil by rapid single sweeps of the rose of the can, a few steps being taken between each sweep, as there is no need to make the loop-shaped areas of water sprinkled in this way continuous, as the oil will spread laterally and join each of them together even if separated by several yards, and no advantage whatever appears to be gained by applying the oil thickly. In exceptional cases, such as the moats of fortifications, where the water is enclosed within high vertical walls, a garden syringe may be required in place of the watering can. In situations such as the pools in canal beds, ditches, &c., the oiling must obviously be done after each flow of water through the channel; but in most ordinary situations, the effects of a careful oiling may be trusted to last for at least three weeks, as, though larvæ may be beginning to reappear by the end of that period, none of them will have had time to complete their metamorphoses. For the destruction of wintering larvæ, two oilings, one at the commencement, and one towards the end of the cold season, amply suffice; and in Continental hot climates it is needless to repeat the process during the dry hot season, as at that time only artificial breeding places, such as garden tanks, require attention, and these are better dealt with by periodical emptying.