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.
At that season indeed, the undried-up breeding places are so few and far between that people have only themselves to thank if mosquitoes are in evidence at all; and yet in many places there is no season of the year when they are so numerous and tormenting. There are no remaining natural breeding-places, and the pains of a weekly stroll round one’s premises to ensure the emptying and cleaning out of all garden tanks, water-vessels, &c., are all that is required to secure complete immunity at that season of the year, but it is most difficult to induce people to take even this trifling trouble; and the mosquitoes are likely to flourish undisturbed until the existence of breeding places within the premises of any person is treated by the authorities in the same way as other dangerous nuisances; and yet these very people are the loudest in their condemnation of the inertia of the native in sanitary matters, and while they maintain malaria breweries on a scale in which the modest extent of his premises forbids him to compete, inveigh against him for starting a cholera factory on the most modest lines. The native who refuses to avail himself of the protection against plague of a health camp is, they admit, an impracticable fool for his pains; but the _sahibs_ of the civil lines, whose gardens supply a large share of the harmful mosquitoes to the neighbouring city, are merely “common-sense” people who attach no importance to doctor’s fads and “scientific rot” of all sorts. The native, however, has at least usually the excuse that he is unable to read or write; and for the rest, does not pretend to be a very highly civilised person.